veterinary ectoparasites - biology, pathology and control

Veterinary Ectoparasites:Biology, Pathology and Control

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Veterinary Ectoparasites:Biology, Pathology and Control

Second Edition

Richard WallBSc, MBA, PhD

David ShearerBvetMed, CertSAD, PhD, CBiol, MIBiol, MRCVS

bBlackwellScience

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# 1997, 2001 byBlackwell Science LtdEditorial Offices:Osney Mead, Oxford OX2 0EL25 John Street, London WC1N 2BS23 Ainslie Place, Edinburgh EH3 6AJ350 Main Street, MaldenMA 02148 5018, USA

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Contents

Preface to Second Edition ixAcknowledgements x

Chapter 1 The Importance and Diversity ofArthropod Ectoparasites 1

1.1 Introduction 11.2 Ectoparasite±host relationships 11.3 Ectoparasite damage 21.4 The evolution of ectoparasite±host

relationships 31.5 A modern and growing problem? 51.6 An introduction to arthropod

structure and function 61.6.1 Arthropod segmentation 61.6.2 The arthropod exoskeleton 61.6.3 Jointed legs 81.6.4 Spiracles and gas exchange 81.6.5 The arthropod circulatory

system 91.6.6 The arthropod nervous system 101.6.7 Digestion and absorption 111.6.8 Arthropod sense organs 121.6.9 Arthropod reproduction 131.6.10 Arthropod size 13

1.7 Patterns of arthropod development 141.7.1 Moulting 141.7.2 Simple and complex life-cycles 14

1.8 The classification of diversity 161.9 The origins of arthropods 161.10 Living arthropod groups 17

1.10.1 Arachnids 181.10.2 Insects 191.10.3 Other living arthropod classes 20

1.11 Arthropod distributions 21Further reading and references 22

Chapter 2 Mites (Acari) 232.1 Introduction 232.2 Morphology 23

2.3 Life history 252.4 Pathology 262.5 Classification 26

2.5.1 Astigmata 262.5.2 Prostigmata 272.5.3 Mesostigmata 27

2.6 Recognition of mites of veterinaryimportance 27

2.7 Astigmata (Sacroptiformes) 272.7.1 Sarcoptidae 27Guide to the suborders of Acari 28Guide to species and families ofveterinary importance 282.7.2 Psoroptidae 34Guide to the identification of life-cyclestages of Psoroptes mites 362.7.3 Knemidocoptidae 402.7.4 Listrophoridae 412.7.5 Astigmatid mites of minor

veterinary interest 432.8 Prostigmata (Trombidiformes) 44

2.8.1 Demodicidae 442.8.2 Cheyletiellidae 452.8.3 Trombiculidae 472.8.4 Psorergatidae 482.8.5 Prostigmatid mites of minor

veterinary interest 492.9 Mesostigmata (Gamesid mites) 50

2.9.1 Macronyssidae 502.9.2 Dermanyssidae 522.9.3 Mesostigmatid mites of minor

veterinary interest 53Further reading and references 54

Chapter 3 Ticks (Acari) 553.1 Introduction 553.2 Morphology 55

3.2.1 Ixodidae 553.2.2 Argasidae 57

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3.3 Life history 583.3.1 Ixodidae 583.3.2 Argasidae 60

3.4 Pathology 613.4.1 Cutaneous effects of tick feeding 613.4.2 Systemic effect: vectors of disease 613.4.3 Systemic effects: tick paralysis 643.4.4 Other systemic effects 65

3.5 Classification 653.6 Recognition of ticks of veterinary

importance 65Guide to tick identification 66

3.7 Ixodidae 673.7.1 Ixodes 673.7.2 Dermacentor 713.7.3 Haemaphysalis 743.7.4 Rhipicephalus 753.7.5 Boophilus 763.7.6 Amblyomma 773.7.7 Hyalomma 78

3.8 Argasidae 783.8.1 Argas 783.8.2 Otobius 803.8.3 Ornithodoros 80

Further reading and references 81

Chapter 4 Adult Flies (Diptera) 834.1 Introduction 834.2 Morphology 834.3 Life history 854.4 Pathology 864.5 Classification 87

4.5.1 Cyclorrhapha 874.5.2 Brachycera 884.5.3 Nematocera 88

4.6 Recognition of flies of veterinaryimportance 88

4.7 Cyclorrhapha 88Guide to families of adult Diptera ofveterinary importance 89

4.7.1 Muscidae 924.7.2 Fanniidae 974.7.3 Hippoboscidae (keds and forest

flies) 984.7.4 Glossinidae (tsetse flies) 994.7.5 Cyclorrhaphous flies of minor

veterinary interest 1004.8 Brachycera 101

4.8.1 Tabanidae (horse flies, deerflies and clegs) 101

4.9 Nematocera 1044.9.1 Simuliidae (black flies) 1044.9.2 Ceratopogonidae (biting midges) 1074.9.3 Culicidae (mosquitoes) 1084.9.4 Psychodidae (sand flies) 110

4.10 Other Diptera of veterinary interest 1114.10.1 Eye gnats 111


Chapter 5 Myiasis 1145.1 Introduction 1145.2 Morphology 1145.3 Life history 1155.4 Pathology 1165.5 Classification 1165.6 Recognition of dipterous agents of

myiasis 117Guide to third-stage larvae causingmyiasis in domestic animals 117Guide to genera of adult Dipteracausing myiasis in domestic animals 119

5.7 Oestridae 1215.7.1 Oestrinae 1215.7.2 Gasterophilinae 123

Guide to the third-stage larvaeof the most importantGasterophilus species 124

5.7.3 Hypodermatinae 1265.7.4 Cuterebrinae 129

5.8 Calliphoridae 1305.8.1 Cochliomyia 1305.8.2 Chrysomya 1325.8.3 Lucilia 1345.8.4 Phormia and Protophormia 1375.8.5 Calliphora 1385.8.6 Cordylobia 139

5.9 Sarcophagidae 1405.9.1 Wohlfahrtia 140


Chapter 6 Fleas (Siphonaptera) 1436.1 Introduction 1436.2 Morphology 1446.3 Life history 1466.4 Pathology 1486.5 Classification 149

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6.6 Recognition of fleas of veterinaryimportance 149

6.7 Pulicidae 1496.7.1 Ctenocephalides 149Guide to the flea species of veterinaryimportance 1506.7.2 Spilopsyllus 1546.7.3 Echidnophaga 1556.7.4 Pulex 1566.7.5 Xenopsylla 156

6.8 Ceratophyllidae 1576.8.1 Ceratophyllus 1576.8.2 Nosopsyllus 158

6.9 Flea species of minor veterinaryinterest 160Further reading and references 160

Chapter 7 Lice (Phthiraptera) 1627.1 Introduction 1627.2 Morphology 1627.3 Life history 1647.4 Pathology 1647.5 Classification 1657.6 Recognition of lice of veterinary

importance 166Guide to the genera of lice ofveterinary interest 166

7.7 Amblycera 1687.7.1 Menoponidae 1687.7.2 Boopidae 1697.7.3 Gyropidae 169

7.8 Ischnocera 1707.8.1 Philopteridae 1707.8.2 Trichodectidae 172

7.9 Anoplura 1747.9.1 Haematopinindae 1747.9.2 Linognathidae 1767.9.3 Polyplacidae 177


Chapter 8 The Diagnosis and Control ofEctoparasite Infestation 179

8.1 Introduction 1798.2 Diagnosis of ectoparasite infestation 179

8.2.1 Hair examination 1808.2.2 Acetate strip examination 1808.2.3 Superficial skin scraping

(epidermal surface examination) 180

8.2.4 Deep skin scraping (deepepidermal examination) 181

8.2.5 Collection of free-livingectoparasites 181

8.2.6 Biopsy and histopathology 1818.3 The chemical control of ectoparasites ±

ectoparasiticides 1818.3.1 Ectoparasiticides: early

compounds 1818.3.2 Ectoparasiticides: neurotoxins 1828.3.3 Ectoparasiticides: insect growth

regulators 1848.3.4 Repellents 1858.3.5 Desiccants 185

8.4 Mode of ectoparasiticideapplication 185

8.4.1 Topical preparations 1858.4.2 Systemic preparations 1858.4.3 Environmental preparations 186

8.5 Problems with chemical control 1868.5.1 Poisoning and environmental

contamination 1868.5.2 Resistance 187

8.6 Non-chemical control ofectoparasites 187

8.6.1 Physical control 1878.6.2 Barriers 1888.6.3 Biological control 1888.6.4 Vaccination 1888.6.5 Trapping 1898.6.6 Sterile insect technique 1898.6.7 Modelling and forecasting 189

8.7 Cattle 1908.7.1 Mites 1908.7.2 Ticks 1928.7.3 Flies 1938.7.4 Myiasis 1948.7.5 Fleas 1958.7.6 Lice 195

8.8 Sheep 1968.8.1 Mites 1968.8.2 Ticks 1998.8.3 Flies 1998.8.4 Myiasis 2008.8.5 Fleas 2028.8.6 Lice 202

8.9 Horses 2028.9.1 Mites 202

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8.9.2 Ticks 2048.9.3 Flies 2058.9.4 Myiasis 2078.9.5 Fleas 2088.9.6 Lice 208

8.10 Pigs 2088.10.1 Mites 2088.10.2 Ticks 2108.10.3 Flies 2108.10.4 Myiasis 2108.10.5 Fleas 2118.10.6 Lice 211

8.11 Goats 2118.11.1 Mites 2118.11.2 Ticks 2138.11.3 Flies 2148.11.4 Myiasis 2148.11.5 Fleas 2158.11.6 Lice 215

8.12 Dogs 2158.12.1 Mites 2158.12.2 Ticks 2198.12.3 Flies 2198.12.4 Myiasis 2208.12.5 Fleas 2218.12.6 Lice 221

8.13 Cats 2228.13.1 Mites 2228.13.2 Ticks 2258.13.3 Flies 2258.13.4 Myiasis 2268.13.5 Fleas 2268.13.6 Lice 227

8.14 Rabbits 2278.14.1 Mites 2278.14.2 Flies 2298.14.3 Myiasis 2298.14.4 Fleas 2308.14.5 Lice 230

8.15 Guinea-pigs 2308.15.1 Mites 2308.15.2 Flies 2318.15.3 Myiasis 2318.15.4 Fleas 2318.15.5 Lice 232

8.16 Mice and rats 2328.16.1 Mites 2328.16.2 Flies 2338.16.3 Myiasis 2338.16.4 Fleas 2338.16.5 Lice 233

8.17 Hamsters and gerbils 2348.17.1 Mites 2348.17.2 Flies 2358.17.3 Myiasis 2358.17.4 Fleas 235

8.18 Ferrets 2358.18.1 Mites 2358.18.2 Ticks 2368.18.3 Myiasis 2368.18.4 Fleas 236

8.19 Birds 2368.19.1 Mites 2368.19.2 Ticks 2388.19.3 Flies 2388.19.4 Myiasis 2398.19.5 Fleas 2398.19.6 Lice 240

8.20 Reptiles 2408.20.1 Mites 2408.20.2 Ticks 2408.20.3 Flies 2408.20.4 Treatment of reptile

ectoparasites 241Further reading and references 241

Glossary 243Index 253

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Preface to Second Edition

There are many textbooks on medical and veter-inary entomology. But, although usually treatedas a unified subject, the importance of arthropodparasites in the medical and veterinary fields isclearly different. In medical entomology blood-feeding flies are of paramount importance, pri-marily as vectors of pathogenic disease. Mostexisting textbooks reflect this bias. However, inveterinary parasitology, ectoparasites such as thelice, mites, ticks, fleas or dipteran agents ofmyiasis assume far greater prominence and themost important effects of their parasitic activitymay be mechanical damage, pruritus, blood loss,myiasis, hypersensitivity and dermatitis. Ecto-parasite infestation of domestic and companionanimals, therefore, has clinical consequencesrequiring a distinct approach to diagnosis andcontrol. Hence, this book has been written withthis in mind, specifically for practitioners andstudents of veterinary medicine, animal husban-dry and applied animal sciences. As is usual, theterm entomology is used here loosely, to coverboth insects and arachnids.

This book focuses primarily on the arthropodectoparasites of temperate habitats. To someextent this distinction has been blurred slightly,since so many ectoparasite species have beentransported worldwide with humans and domes-

tic animals. But, for the most part, importantectoparasites from tropical and sub-tropicalhabitats have been described only briefly andwould require their own volume to do themjustice.

Since the book is directed primarily at the non-entomologist, to improve the book's logicalstructure and comprehensibility it has beendeemed appropriate to abridge some of the moreinvolved entomological debates, particularly inrelation to arthropod classification and phyloge-netics. A reading list is presented at the end ofeach chapter to act as a stepping-stone into thespecialist literature, where this is required. Inparticular, the recognition guides in each chapterneed to be used with a degree of caution since theyare not comprehensive and, where more detailedidentification is required, specialist keys should beconsulted. Similarly, in the discussion of thecontrol of ectoparasites, the principles of controland ectoparasiticide use have been emphasised;any attempt to provide a detailed recipe for con-trol might be inappropriate in different parts ofthe world and would go out of date rapidly. Itshould be stressed that all insecticides should beused in strict accordance with the manufacturer'slocal instructions.

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Acknowledgements

I first would like to thank my wife Shelagh for herpatient support and encouragement throughoutthe preparation of this work. I also would like toexpress my gratitude to my parents, Shirley andDouglas, for their considerable help and gui-dance.

Richard Wall

I would like to thank my wife Alison for hersupport and advice during the writing of thisbook. I would also like to thank many of mycolleagues, in particular Mr L.R. Thomsett andMr A.I. Wright, who encouraged me to pursue aninterest in veterinary dermatology and veterinaryectoparasites.

David Shearer

We would like to thank Shelagh Wall and AlisonShearer and Drs Les Strong and Roger Averywho read all, or parts of, the manuscript of thisbook and helped to eliminate many factual andtextual errors. We are grateful to Dr Sheila Cris-pin for allowing us to use two of her photographson the front cover and to Alison Shearer for theuse of some of her clinical photographs. We aregrateful to Jenny Howard who provided invalu-able assistance with preparation of the secondedition.

Richard Wall and David Shearer

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Chapter 1

The Importance and Diversity ofArthropod Ectoparasites

1.1 INTRODUCTION

The arthropods are a bewilderingly diverseassemblage of invertebrates, containing over 80%of all known animal species and occupying almostevery known habitat. They include such familiaranimals as flies, crabs, centipedes and spiders aswell as a plethora of small and little knowngroups.

There are more species of arthropod than allother animals on earth combined; over a millionspecies have been described and millions moremay be awaiting description or discovery.Dazzlingly beautiful, behaviourally complex andecologically essential, they play fundamental rolesin almost all biological communities and ecosys-tems.

Among the great variety of species of arthro-pod and lifestyles that they display, a relativelysmall number have developed the ability to livedirectly at the expense of other animals, known ashosts. This relationship is to the detriment of thehost but does not usually kill the host immedi-ately. This is described as parasitism. The degreeof harm caused by the parasite may vary con-siderably, and may only be evident at certaintimes, such as when the host is in poor conditionor the parasite density is high. It is important tostress that the parasite lives at the expense of thehost and to distinguish parasitic from commensalrelationships, in which the host neither benefitsnor is harmed. Harm may be defined in practical,proximate terms, as a reduction in factors such ascondition, mobility or growth of the host, or inultimate, evolutionary terms as a reduction in theability of the host to pass on its genes to the nextgeneration.

Arthropods parasitise a wide range of hosts,including other arthropods. This book isconcerned specifically with the economicallyimportant arthropods which spend all or someportion of their lives parasitising livestock, poul-try or companion animals. These parasites, with afew exceptions, live on or burrow into the surfaceof their host's epidermis and are generallydescribed as ectoparasites.

1.2 ECTOPARASITE±HOSTRELATIONSHIPS

Within the broad definition of parasitism givenabove, the association between arthropod ecto-parasite and vertebrate host may take a variety offorms. In some cases the parasite may be totallydependent on the host, in which case the para-sitism is described as obligatory. Alternatively, theparasite may feed or live only occasionally on thehost, without being dependent on it, in which casethe parasitism is described as facultative.

The host provides a number of importantresources for the ectoparasite. Most vitally, thehost supplies a source of food, which may beblood, lymph, tears or sweat or the debris of skin,hair or feathers. The host's body also provides theenvironment in which many ectoparasites live,generating warmth, moisture and, within the skinor hair, a degree of protection from the externalenvironment. The host may also provide trans-portation from place to place for the parasite, asite at which to mate and, in many cases, themeans of transmission from host to host.

Despite the benefits of a close association withthe host, there is considerable variation in the

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amount of time spent on the host by variousspecies of ectoparasite. Some ectoparasites, suchas many of the species of lice for example, live incontinuous association with their host through-out their life-cycle and are therefore highlydependent on the host. The majority of ectopar-asites, however, have only intermittent contactwith their host, and are free-living for the majorportion of their life-cycles. In some cases ecto-parasites, such as many of the species of mite, arehighly host-specific; only one host species isexploited and, in some instances, the parasite canexist only on one defined area of the host's body.Other species are able to exploit a wider range ofhosts.

Whether a pest is an obligatory or facultativeectoparasite, lives in continuous or intermittentassociation with its host, or is host specific or ageneralist, is of interest from a biological per-spective and has major implications for both thecontrol of ectoparasites and the treatment ofectoparasite-associated disease.

1.3 ECTOPARASITE DAMAGE

As a result of their activity, arthropod ectopar-asites may have a variety of direct and indirecteffects on their hosts. Direct harm caused may bedue to:

. Blood loss: although each individual ectopar-asite only removes a small volume of bloodfrom a host, in large numbers the bloodremoved by feeding may be directly debilitat-ing and anaemia is common in heavily infestedhosts. In one study in the USA it was estimatedthat over 90 kg of blood was removed by ticksfrom a cow over a single season. Similarly, thefeeding of horse flies may be responsible forthe loss of up to 0.5 litres of blood per day fromcattle. Two hundred fleas feeding on a kittenmay be capable of removing up to 10% of theanimal's blood over a period of several days.

. Myiasis: the infestation of the living tissueswith fly larvae causes direct damage tocarcasses or skin.

. Skin inflammation and pruritus: various skin

infestations caused by arthropod activity causepruritus (itching), often accompanied by hairand wool loss (alopecia) and occasionally byskin thickening (lichenification). The presenceof ectoparasites on or burrowing into the skincan stimulate keratinocytes to release cyto-kines (e.g. IL-1) which leads to epidermalhyperplasia and cutaneous inflammation. Theantigens produced by ectoparasites (e.g.salivary and faecal) can in some individualsstimulate an immune response leading tohypersensitivity. Sarcoptes scabiei infestationin the dog, for example, leads to an IgE-mediated type I hypersensitivity which ismanifested in severe cutaneous inflammationand pruritus.

. Toxic and allergic responses: caused by anti-gens and anticoagulants in the saliva of blood-feeding arthropods.

The behaviour of ectoparasites also may causeharm indirectly, again particularly when they arepresent at high density, causing:

. Disturbance: the irritation caused, particularlyby flies as they attempt to feed or oviposit,commonly results in a variety of behaviourssuch as head shaking, stamping, skin twitch-ing, tail switching or scratching. Cattle underpersistent attack from flies may congregate in agroup with their heads facing the centre. Sheepunder attack from nasal bot flies may be seenpressing their nostrils to the ground beforerunning short distances and repeating theaction. These activities may result in reducedgrowth and loss of condition because the timespent in avoidance behaviour is lost fromgrazing or resting. Different individuals of ahost population usually vary considerably inthe level of parasitism and this may be asso-ciated with their behavioural responses. Forexample, in cattle the more passive individualsand tolerant individuals tend to be mostheavily attacked by blood-feeding flies.

. Self-wounding: the activity of particular ecto-parasites, such as warble flies, may causedramatic avoidance responses in the intendedhost, known as gadding. The stampeding

2 Veterinary Ectoparasites: Biology, Pathology and Control

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animal may inflict serious self-injury followingcollision with fences and other objects.

. Social nuisance: large populations of flies maybreed in animal dung, particularly in andaround intensive husbandry units. The activityof flies may result in considerable social andlegal problems, especially where suburbandevelopments have encroached on previouslyrural areas. Adult flies and their faeces mayalso decrease the aesthetic appearance andvalue of farm facilities and produce, such ashens' eggs, and cause irritation and annoyanceto employees.

In addition to direct effects, one of the mostimportant roles of ectoparasites is in their actionas vectors of pathogens. These pathogens includeprotozoa, bacteria, viruses, cestodes (tapeworms)and nematodes (round worms). Pathogens suchas bacteria and viruses may be transmitteddirectly to new hosts, the ectoparasite acting as amechanical vector. These pathogens may bepicked up on the body, feet or mouthparts whenthe ectoparasites feed. Mechanical transmissionusually has to occur within a few hours of theoriginal contact with the infected host, becausethe survival of most pathogens is relatively limitedwhen exposed outside their host.

Alternatively, for many protozoa, tapewormsand nematodes, the pathogens need to go throughspecific stages of their life-cycle in the body of thearthropod ectoparasite. In these cases thearthropod serves as an intermediate host and isknown as a biological vector. Again the vectoracquires the pathogen from an infected animalwhen it feeds. After development of the pathogenin the vector, the vector becomes infective and cantransmit the pathogen when it next feeds. Incontrast to mechanical transmission, biologicaltransmission requires a period of time betweenacquisition of the pathogen and the maturation ofinfection. The vector may then remain infectivefor the remainder of its life. The effects ofpathogens on the vector are largely unknown andthis may be a fruitful area for future research;those studies which have been possible suggestthat there may be measurable costs to the vectorfor carrying a heavy infection.

A pathogen may reside and multiply in alter-native vertebrate hosts which are immune or onlymildly infected by it. For example, the bacteriumYersinia pestis, which causes bubonic plagueknown as `the black death', is endemic in wildrodent populations. However, in domestic ratsand humans, to which it is transmitted by fleas, itis highly pathogenic. Such alternate hosts areknown as reservoirs of disease.

The direct damage caused by most ectopar-asites is directly proportional to their abundance.This is not the case, however, for disease vectors,where even very low numbers of infected vectorsmay cause considerable economic and welfareproblems.

Although relatively few in number, throughtheir direct and indirect effects on their hosts, thevarious species of arthropod ectoparasite havehad, and continue to exert, a major impact on thehistory of humans and their domesticatedanimals.

1.4 THE EVOLUTION OFECTOPARASITEÐHOSTRELATIONSHIPS

Insects and related arthropods probably arose atleast 500 million years ago, 300 million yearsbefore warm-blooded vertebrates. Unfortunately,the poor geological record for insects gives uslittle direct evidence of how parasitism evolved.Nevertheless, it would appear likely that, overtime, as the terrestrial vertebrates appeared onearth several species of arthropod were able toexploit the new resource and opportunitiescreated.

Parasitism probably evolved at least twice, andpossibly several times, independently in differentarthropod groups, depending on the relationshipbetween the ectoparasite and its host. One routemay have involved arthropods which were pre-adapted to living with vertebrates. These arthro-pods initially may have fed on general organicmatter, and then moved to scavenging detritus,such as skin or hair, present in a vertebrate lair ornest. From here, coupled with the generalised

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feeding habits, it is only a short evolutionary stepfor the ectoparasite to move on to the host to feedon skin and hair and, in some cases, to facultativeand obligate blood-feeding.

The second route to ectoparasitism may haveinvolved arthropods which had existing adapta-tions which allowed them to feed on vertebrates.These arthropods may have had mouthpartsalready adapted for biting, rasping or sucking.They were perhaps liquid feeders, which occa-sionally opportunistically fed on blood inwounds, or they may have been active predators,in the adult or pre-adult stages, perhaps of otherarthropods. Again, from taking the occasionalmeal from a vertebrate some subsequently mayhave switched to depending on blood as a foodsource.

These two evolutionary pathways involvesimilar adaptations, but they have led to verydifferent relationships with the host. The gen-erally accepted viewpoint throughout most of thetwentieth century has been that commensalism orvery mild parasitism is the inevitable eventualevolutionary end product of host±parasite co-evolution. It was thought that parasites would beselected to minimise the damage that they did tothe host and that virulent (damaging) parasiteswere more recently evolved and were poorlyadapted. This was because more virulent parasitesmight quickly weaken and damage the host and, ifthe host were to die, either as a direct result of theparasitism or perhaps because the weakened hostmight succumb to disease or predation, the ecto-parasite would lose the benefits of a predictablefood supply, protection from the external envir-onment and its means of dispersal. However,more recent work has shown that there may begood evolutionary reasons to expect a wide rangeof levels of pathogenicity and damage caused bydifferent parasites, depending on the particularbehaviour and ecology of both the parasite andhost, and the way in which these two animalsinteract.

Ectoparasites, such as many of the lice or mites,which live in relatively permanent associationwith their hosts, are usually small, with relativelylow mobility. The risks and uncertaintiesassociated with living without their host and

having to find another meal are sufficiently highthat for these animals excessive virulence, leadingto the death or debilitation of the host, mightresult in their own death and failure to reproduce.Hence, these ectoparasites have become obligate,host-specific specialists, in normal circumstances,doing minimal damage and, in some cases, exist-ing almost as commensals, e.g. species of Demo-dex mites. In many cases these arthropods maywell have followed the first evolutionary route toectoparasitism; even before becoming ectopar-asites they were pre-adapted to living in closeassociation with vertebrates and their survivaland dispersal depended on the continued exis-tence and health of the vertebrate with which theywere associated.

In contrast, an ectoparasite that (a) wasrelatively mobile, so that it could find a new hostquickly and efficiently, (b) was relatively resistantto the adverse effects of climate, so that it couldsurvive without its host and (c) had a broad rangeof relatively abundant hosts on which it couldfeed, might be expected to evolve higher levels ofvirulence to maximise the amount that could be`extracted' from a host as quickly as possible. Forsuch an ectoparasite, the death of the host wouldbe of little importance since it could survive wellindependently and find a new host quickly whenneeded. Arthropods with these characteristics,which inflict relatively high levels of damage, suchas many of the blood-feeding flies and ticks, mayhave followed the second evolutionary route toparasitism, starting off as free-living scavengersor predators which subsequently becameopportunistic feeders on vertebrates.

Of course, varying degrees of virulence betweenthe extremes described will have evolved,depending on the precise interactions between theectoparasite and host. The associations seentoday between ectoparasites and hosts are alsothe outcome of the response of the host to theectoparasite. From the perspective of the host, theattention of any parasites is, by definition,unwelcome. As arthropods evolved new ways ofexploiting their hosts more effectively, the hostsalso evolved strategies to combat the activities ofthe ectoparasites. These range from immuneresponses to behaviours such as grooming,


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periodic changing of nest sites or bedding, or evenseasonal mass migrations to avoid areas of highparasite density. Hosts that were better able totolerate their ectoparasites, minimised thedamage caused or developed ways of riddingthemselves of ectoparasites, survived longer andproduced more offspring than other hosts.However, over time ectoparasites have also beenselected to try to get round or exploit these hostresponses. Hence, over the millions of years, aconstant evolutionary battle has been waged, inwhich arthropods have been evolving to exploitvertebrate hosts and in which hosts have been co-evolving to mitigate the effects of parasites ontheir fitness.

However, in relatively recent history, theassociations between ectoparasites and their hostshave been subjected to a number of dramaticchanges, mediated by human activity, which haveresulted in a substantial shift in the nature ofmany parasite±host relationships.

1.5 A MODERN AND GROWINGPROBLEM?

During the late mesolithic and early neolithicperiods, 10 000±20 000 years ago, livestock andcompanion animals were first domesticated andfarmed by humans (Fig. 1.1). This developmenthas continued to the present day and has beencombined with rapidly growing human popula-tions, expansion and settlement in new areas,increased rates of human movement worldwideand increasing urbanisation.

. The massive increase in human populationshas necessitated a growing intensification ofanimal husbandry, not only to meet theimmediate demands for food and animal pro-ducts such as wool and leather, but also toprovide draught animals and fulfil the multi-tude of roles that animals play in humansociety. More and more animals have beenreared using more intensive husbandry prac-tices. This presents ectoparasites with a super-abundance of hosts. The higher host densityincreases the potential for ectoparasitetransmission and allows ectoparasites, adaptedto experience huge mortalities associated withfinding a new host, to build up massive popu-lation densities in very short periods of time.

. The artificial selection of livestock, poultry andcompanion animals for domestication andhigh productivity has been associated in manycases with a reduction in resistance to ecto-parasite damage and the exaggeration offeatures which confer greater susceptibility toectoparasite infestation. For example, theouter coat of primitive sheep is stiff and hairyand covers a woolly undercoat which onlygrows in winter. The outer hairs are known askemps. In highly domesticated sheep, thesekemps are absent and the fleece consistsentirely of the woolly undercoat which growsall year round. Selection for a longer, thickfleece has increased the susceptibility of sheepto various types of disease and ectoparasite,particularly blowfly myiasis.

. With the increasing global movement ofhuman populations, domestic animals havebeen transported into new areas of the worldwhere they are attacked by endemic ectopar-asites to which they have little or no resistance.This has been the case particularly with theintroduction of domestic cattle, Bos taurus,into areas where they are attacked by a widevariety of ectoparasites and ectoparasite-bornediseases, which previously existed only onindigenous Bovidae or other Artiodactyla. Themovement of humans and domestic animalshas also allowed the introduction of ectopar-asites into areas in which they were previouslyabsent, such as sucking lice (Anoplura)

Fig. 1.1 Detail from Tomb 3, Beni Hasan, Egypt (fromNewberry, 1893).


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introduced into Australia with sheep. In thenear future, the majority of the world popu-lation will live in urban areas. This growingurbanisation of humans and their associatedcompanion animals provides arthropods andarthropod-borne diseases with a large, con-centrated pool of potential hosts and enablesectoparasites to transfer between individualhosts more readily. In addition, in houses,which they frequently share with their com-panion animals, humans have created condi-tions in which many species of arthropod pestsurvive and flourish, often in areas of the worldwhere they would otherwise perish. This isespecially the case for fleas and mites, wheremodern houses can provide them with care-fully controlled temperature, humidity andlighting, a protective microhabitat and aregular supply of hosts.

1.6 AN INTRODUCTION TOARTHROPOD STRUCTURE ANDFUNCTION

To those unfamiliar with invertebrate morphol-ogy and physiology, arthropods can seemdauntingly complex. They have many anatomicalfeatures which are often analogous to those ofvertebrates but which are totally dissimilar instructure and function. In the following sections,a brief overview of a range of key arthropodfeatures is presented, with specific reference to theectoparasites of veterinary interest. This is by nomeans a comprehensive examination of the sub-ject. A huge range of variation exists in the mor-phology and physiology of this diverse phylumand for a more detailed treatment the reader isreferred to more specialist texts at the end of thechapter.

1.6.1 Arthropod segmentation

Arthropods are metameric, that is they aredivided into segments. However, within a numberof arthropod classes, particularly the arachnids

and the insects, there has been a tendency forsegmentation to become reduced and, in many ofthe mites for example, it has almost disappeared.Reduction in segmentation has occurred throughloss, fusion or the tendency for segments tobecome dramatically changed in structure to fulfilspecific functions, often associated with feeding,oviposition or mating. However, even in thosearthropods that have almost lost their segmenta-tion, it can usually still be seen in the embryo.

A characteristic feature of many arthropodgroups is the division of the body into clusters ofsegments, such as the head, thorax and abdomen(Fig. 1.2). This is known as tagmatisation. Eachtagma contains a specific set of segments and isspecialised for functions different from those ofthe other tagmata.

1.6.2 The arthropod exoskeleton

The exoskeleton is the outer covering which pro-vides support and protection to the living tissuesof arthropods. In many respects it is one of thekeys to the success of the phylum, but it alsoimposes many limitations.

The exoskeleton is non-cellular. Instead it iscomposed of a number of layers of cuticle whichare secreted by a single outer cell layer of the bodyknown as the epidermis (Fig. 1.3). The outer layerof cuticle, the epicuticle, is composed largely ofproteins and, in many arthropods, is covered by awaxy layer. The next two layers are the outerexocuticle and the inner endocuticle. Both arecomposed of a protein and a polysaccharidecalled chitin, which has long, fibrous moleculescontaining nitrogen. The chitin molecules arebundled into microfibrils which are aligned par-allel to each other. The parallel microfibrils areonly loosely bound side by side to each other insheets, so they are flexible across their axis but arevery resistant to stretching ± like a rope. Proteinchains run between the microfibril bundles, toform a stable, complex glycoprotein. In this state,therefore, cuticle is naturally pale-coloured andflexible. For extra strength the exocuticle may betanned, or sclerotised. This is where the proteins,interwoven between the chitin bundles, become


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tightly cross-linked with quinones, providingextra strength from the additional cross-linkagesformed with the cuticular proteins. The sclero-tised cuticle is hard and dark in colour.

The cuticle is often penetrated by fine porecanals which allow the passage of secretions fromthe epidermis to the surface. The cuticle has manyoutgrowths in the form of scales, spines, hairs andbristles. These outgrowths fall into two cate-gories: those which are simply fine foldings of theouter layer of the cuticle (microtrichiae) and thosewhich are articulated, such as setae (macro-trichiae). Microtrichiae can be very fine and givethe arthropod distinctive, often irridescent, col-our patterns. The articulated setae are attached tothe cuticle by a thin membrane in a pit knows asthe alveolus. Setae are hollow outgrowths of the

Fig. 1.2 A winged damselfly (a) and primitively flightless silverfish (b), showing division of the body into head,thoracic and abdominal segments (reproduced from Gullan & Cranston, 1994).

Fig. 1.3 Diagrammatic section through the arthropodintegument.


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epicuticle and exocuticle, secreted by a trichogencell (Fig. 1.3). The socket is secreted by a tormo-gen cell.

Movement is made possible by the division ofthe cuticle into separate plates, called sclerites.Primitively these plates are confined to segmentsand the cuticle of each segment is divided intofour primary plates: a dorsal tergum, two lateralpleura and a ventral sternum (Fig. 1.4). However,this pattern has frequently disappeared eitherbecause of fusion or subdivision of the segments.

Plates are connected by flexible intersegmentalor articular membranes, where the cuticle is notsclerotised and is flexible. These joints allow thebody to move. In most arthropods the interseg-mental membrane is folded beneath the segmentin front (Fig. 1.5). The muscles attach on theinside of the exoskeleton, the opposite of thevertebrate body plan. Muscles are often attachedto rod-like invaginations of the cuticle calledapodemes (Fig. 1.5). The soft, flexible, unsclero-tised cuticle present at the joints of the adultarthropod exoskeleton also occurs in the integu-ment of larval arthropods.

Colour is very important in many groups ofarthropds, providing warning colouration, sexualrecognition signals or camouflage, for example.The colours of most arthropods are produced bythe deposition of yellow, orange and red car-otenoid or brown melanin pigments within thecuticle. However, iridescent greens and purplesmay result from structural features of the cuticle

itself, such as microtrichia, which selectivelyscatter or reflect light of specific wavelengths.

1.6.3 Jointed legs

The name arthropod is derived from the ancientgreek arthron, meaning joint, and pous, meaningfoot. Primitively each arthropod segment bears apair of leg-like appendages. However, the numberof appendages has frequently been modifiedthrough loss or structural differentiation. Ininsects there are always three pairs of legs. Inmites and ticks there are three pairs of legs in thelarval life-cycle stage and four pairs in the nym-phal and adult stages. The cuticular skeleton ofthe legs is divided into tube-like segments con-nected to one another by articular membranes,creating joints at each junction (Fig. 1.5). The legsare usually six-segmented.

1.6.4 Spiracles and gas exchange

The process of getting oxygen to the tissues hasbeen solved in many different ways by the var-ious groups of arthropods. For some of thesmallest arthropods we will meet in this text, theexoskeleton is thin and lacks a waxy epicuticle.For these animals oxygen and carbon dioxidesimply diffuse directly across the cuticle. How-

Fig. 1.4 Cross-section through the exoskeleton of ageneralised arthropod, showing the tergum, pleuronand sternum of a single segment.

Fig. 1.5 (a) Articulation of a generalised arthorpod legjoint. (b) A multicellular apodeme. (c) Intersegmentalarticulation, showing the intersegmental membrane

folded beneath the segmental exoskeleton (afterSnodgrass, 1935).


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ever, this method of gas exchange is only func-tional over very short distances and for verysmall animals. In most of the terrestrial groupsof arthropod ectoparasite to be considered in thisbook, the protective cuticle is punctured by anumber of openings. In the insects these open-ings are called spiracles; in the mites and ticksthey are called stigmata. Spiracles or stigmatamay be set in a sclerotised cuticular plate called aperitreme. Insects, at most, have two pairs ofthoracic and eight pairs of abdominal spiracles.This number is frequently reduced. Mites andticks may have anything from none up to fourpairs of stigmata, when present, usually locatedon the anterior half of the body.

Typically spiracles or stigmata open into achamber or atrium with a mechanism for openingor closing, called a valve. The openings lead tocuticle-lined air-conducting tubes called tracheae,formed by invagination of the epidermis duringdevelopment. The tracheae form longitudinal andtransverse tracheal trunks that interconnectamong the segments. The tracheae branchrepeatedly as they extend to all parts of the body(Fig. 1.6). In some, particularly fast flying insects,part of the tracheal system is expanded to form airsacs. The branches of the tracheae end within thecells of muscles and other tissues in extremely finetracheoles which are the principal sites of gasexchange. The ends of the tracheoles contain fluidand are usually less than 1 mm in diameter.

Tracheoles are particularly numerous in tissueswith high oxygen requirements.

Other types of arthropod, not considered here,show completely different adaptations for gasexchange; the terrestrial scorpions and spiders forexample have book lungs, while the aquaticcrustaceans have gills.

Ventilation

Oxygen enters through the respiratory openingsand passes down the trachea, usually by diffusionalong a concentration gradient. Carbon dioxideand (in terrestrial insects) water vapour move inthe opposite direction. Water loss is a majorproblem for most terrestrial arthropods and forthem gas exchange is often a compromise betweengetting enough oxygen into the body while mak-ing sure that they do not desiccate. Hence inperiods of inactivity the respiratory openings areoften kept closed, only opening periodically.

Diffusion is only effective over small distances.Hence, in large and active insects active pumpingmovements of the thorax and/or abdomen may beused to help to ventilate the outer parts of thetracheal system. Rhythmic thoracic movementsor compression/telescoping of the abdomen helpto expel air from the outer trachea or the air sacs.Co-ordinated opening and closing of the spiraclesusually accompanies ventilation movements andserves to effect a unidirectional flow of air.Anterior spiracles open during inspiration andposterior ones during expiration.

1.6.5 The arthropod circulatorysystem

The arthropod circulatory system is relativelysimple, consisting of a series of central cavities orsinuses, called a haemocoel, separated by mus-cular septa. The haemocoel contains blood, calledhaemolymph. In contrast to vertebrates, thehaemolymph is not involved in gas exchange. Thevolume of the haemolymph may be substantial:20±40% of body weight. Haemolymph is a wateryfluid composed of an aqueous solution of

Fig. 1.6 A spiracle, trachea and tacheoles (afterSnodgrass, 1935).


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inorganic ions, lipids, sugars, amino acids,proteins, organic acids and other compounds andcells. It is often clear and colourless but in somespecies may be pigmented ± green, blue (or rarelyred). All chemical exchanges between organs aremediated by the haemolymph: hormones aretransported, nutrients are distributed from thegut, wastes are removed from the excretoryorgans. However, haemolymph does not comeinto contact directly with the cells because theinternal organs and the epidermis are covered bya basement membrane.

In most mites the circulatory system consistsonly of a network of sinuses. Circulation prob-ably results from contraction of body muscles.Insects, on the other hand have a functionalequivalent of the heart, the dorsal vessel (Fig. 1.7).This vessel varies in position and length in dif-ferent arthropod groups, but in all of them thedorsal vessel consists essentially of a wide tubewith one or more chambers, running along thelength of the body and perforated by pairs oflateral openings called ostia. The ostia onlypermit a one-way flow of haemolymph into the

dorsal vessel. The dorsal vessel lies in acompartment of the haemocoel called the peri-cardial sinus.

The dorsal vessel pumps haemolymph forwardtowards the head and eventually into sinuses ofthe haemocoel in the head. Haemolymph thenpercolates back through the haemocoel to thepericardial sinus, until it is again picked up by thedorsal vessel. The pericardial sinus is separatedfrom the main compartment of the haemocoel bya septum known as the dorsal diaphragm (com-posed of musles and connective tissue). Thedorsal diaphragm supports the dorsal vesssel andis punctured by a series of segmental openings.There is also a ventral diaphragm, associated withthe ventral nerve cord. Circulation is aided byperistaltic contractions of the ventral diaphragm,which direct the haemolymph backwards andlaterally. Haemolymph is generally circulated toappendages unidirectionally by various tubes,septa, valves and pumps. Muscular pumps arecalled accessory pulsatile organs and occur at thebase of the antennae and legs.

1.6.6 The arthropod nervous system

Arthropods have a complex nervous systemassociated with the well-developed sense organs,such as eyes and antennae, and behaviour that isoften highly elaborate.

The central nervous system consists of a dorsalbrain in the head which is connected by a pair ofnerves which run around the foregut to a series of

Fig. 1.7 Generalised arthropod circulatory system. (a)

Longitudinal section through the body. (b) Transversesection through the abdomen (reproduced from Gullan& Cranston, 1994, after Wigglesworth, 1972).

Fig. 1.8 Generalised digestive tract of an arthropod,showing the fore-, mid- and hindgut. The cuticularlinings of the foregut and hindgut are indicated by thicklines.


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ventral nerve cord ganglia (Fig. 1.7). In theembryo each segment gives rise to a pair ofganglia which then fuse to form a single ganglion,and this pattern can still be seen in primitivearthropods. The ganglia are connected betweensegments by pairs of connective nerves. In moreadvanced arthropods ganglia may be fused. Inblowflies, for example, there is only a singlethoracic ganglion and no abdominal ganglia, and

in the mites and ticks there is only a singlecephalothoracic ganglion.

1.6.7 Digestion and absorption

The gut of an arthropod is essentially a simpletube that runs from mouth to anus (Fig. 1.8).Nutrients are absorbed across the gut wall

Fig. 1.9 (a) Head of a dragon fly, showing two large compound eyes and, between them, three ocelli. (b)Longitudinal section through an ommatidium with an enlargement of a transverse section. (c) Longitudinal sectionthrough an ocellus (from Gullan & Cranston, 1994).


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directly into the haemolymph. The precise shapeof the gut varies between arthropods, variousoutpockets or large digestive glands being pre-sent, depending on the precise nature of their diet.

In insects, the gut is divided into three sections:the foregut, midgut and hindgut (Fig. 1.8). Theforegut and hindgut consist of invaginations ofthe exoskeleton at the mouth and anus, respec-tively; therefore they are lined with cuticle. Influid-feeding arthropods there are prominentdilator muscles which attach to the walls of thepharynx, to form a pump. The foregut is con-cerned primarily with the ingestion and storage offood, the latter usually taking place in the crop.Between the foregut and the midgut is a valvecalled the proventriculus. In some arthropods, theproventriculus may be armed with teeth andfunctions in the crushing and grinding of food.The midgut is the principal site of digestion andabsorption. It has a cellular lining which secretesdigestive enzymes. Absorption takes place largelyin the anterior of the midgut, in large outpocketscalled gastric caecae. The hindgut terminates inan expanded region, the rectum, which functionsin the absorption of water and the formation offaeces. Nitrogenous wastes are eliminated fromthe haemocoel by long, thin projections called theMalpighian tubules, which open into the gut at thejunction of the mid- and the hindgut. In mites andticks the gut follows a broadly similar plan, butmay be simplified, often with only one pair ofMalpighian tubules.

1.6.8 Arthropod sense organs

The sensory receptors of arthropods are usuallyassociated with modifications of the chitinousexoskeleton. One common type of receptor isconnected with hairs, bristles and setae. Thebristle may be designed so that it acts as amechanoreceptor, movement triggering thereceptor at its base. Alternatively, the bristle maycarry chemoreceptors. Other common modifica-tions for receptors are slits or pits in the exoske-leton. These may house chemoreceptors or theopening may be covered by a membrane with anerve ending attached to its underside, to detect

vibrations. Such receptors may be scattered overthe body or concentrated on appendages such asthe legs or antennae.

Most arthropods have eyes, but these can varygreatly in complexity. Some contain only a fewphotoreceptors. For example, in the stemmata oflarval holometabolous insects and the ocelli oflarval and adult hemimetabolous insects, a cor-neal lens overlies from 1 to 1000 sensory cells(Fig. 1.9). These simple eyes do not form imagesbut are very sensitive at low light intensities andto changes in light intensity. Other types ofarthropod eye, known as compound eyes, arelarge and complex with thousands of retinal cells(Fig. 1.9).

The compound eyes of insects and manycrustaceans are composed of many long, cylind-rical units. Each unit, called an ommatidium iscovered at its outer end by a translucent cornea,called a facet, derived from the cuticle. The facet,which is often hexagonal, functions as a lens.Internal to the cornea, the ommatidium containsa long, cylindrical element called the crystallinecone which functions as a second lens. Behindthis, elongated retinula nerve cells, usually eight innumber, are packed together in a tall, translucentcylinder. Each retinula cell is wedge-shaped andthe inner part of each, known as a rhabdomere, isfolded to form microtubules running perpendi-cular to the axis of the ommatidium. The junctionof these microtubules running down the centre ofthe retinula cells is known collectively as therhabdom. The retinula cells contain black orbrown photosensitive molecules of a protein±retinene complex called rhodopsin.

The retinula nerve cells are also surrounded bya ring of light-absorbing pigment cells whichscreen the light entering each ommatidium fromits neighbour.

The rhabdomeres of an ommatidium functionas a single photoreceptor unit and transmit asignal that represents a single point of light.Individual ommatidia cannot form a detailedimage and only overall light intensity is registered.Each ommatidium points in a slightly differentdirection. The image formed by a compound eye,therefore, represents a series of apposed points oflight of different intensities, termed an apposition


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image. The detail available depends on the num-ber of ommatidia present. There is no mechanismfor accommodation and the principal function ofa compound eye is in detecting movement as animage passes from one ommatidium to the next.This is assisted in many arthropods by the factthat the total corneal surface is highly convex,resulting in a wide visual field. In addition, manyarthropods have colour vision, mediated by var-iations in the visual pigment in the retinula cells.

However, an apposition image does not workwell at low light intensity. Therefore, in arthro-pods adapted for living in conditions of low lightintensity, the screening pigment is retracted sothat light can pass from one ommatidium to thenext, forming a superposition image. While thisimage is less sharp, this maximises light gathering,making it more likely that a rhabdom will bestimulated than if it was dependent only on lightentering its own facet. In addition, a mirror-likelayer at the back of the eye, known as the tape-tum, serves to reflect light a second time throughthe rhabdom.

1.6.9 Arthropod reproduction

In arthropods the sexes are separate and mating isusually required for the production of fertile eggs.However, in some species males may be absentand females reproduce by parthenogenesis, pro-ducing identical genetic copies of themselves.Most arthropods lay eggs. However, some spe-cies, such as the flesh flies, are ovoviviparous andretain their eggs internally until they hatch. Theythen larviposit live first-stage maggots. Otherspecies, such as the sheep ked or tsetse fly, areviviparous, retaining the larvae and nourishingthem until they are fully developed.

The female reproductive system is composed ofa pair of ovaries (Fig. 1.10). Each ovary is dividedinto egg tubes, or ovarioles. The ovarioles join thelateral oviduct which in turn meets a medianoviduct. This often ends in an ovipositor. Aportion of the median oviduct may be expandedto receive the aedeagus during copulation.

The male reproductive system is usuallycomposed of a pair of testes, each subdivided into

a set of sperm tubes or follicles in which theformation of sperm takes place (Fig. 1.10). Thefollicles join the vas deferens, which is oftenexpanded into the seminal vesicle which stores thesperm. The vas deferens join a common ejacula-tory duct which ends in the external genitalia,with an intromittent organ, the penis, or aedea-gus. Accessory glands produce secretions whichmay form a packet, called a spermatophore, whichencloses the sperm and protects it duringinsemination.

Sperm may be delivered directly to the femaleduring copulation or, as in some species of mite,the spermatophore is deposited on the groundand the female is induced to walk over and pickup the spermatophore with her genital opening.Sperm are usually stored by the female in simpleseminal receptacles or more complex organscalled spermathecae. As an ovulated egg passesdown the median oviduct it is fertilised by spermreleased from the spermathecae. Accessory glandsjoin the median or lateral oviducts and in manyspecies produce secretions that coat and protectthe eggs.

1.6.10 Arthropod size

The patterns of arthropod anatomy andphysiology are intimately related to their size. The

Fig. 1.10 Generalised (a) female and (b) malereproductive systems (from Gullan & Cranston, 1994,after Snodgrass, 1935).


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largest terrestrial insects and spiders weigh nomore than about 100 g and the smallest are lessthan 0.25 mm in length. Only marine forms havemanaged to attain relatively large sizes; theJapanese spider crab, Macrocheira, may have aleg-span of over 3.5 m. The respiratory and cir-culatory systems described above, for example,are both efficient for arthropods but would notwork for larger animals. The exoskeleton canprovide remarkable rigidity but, because massincreases by the cube while surface area increasesby the square, an exoskeleton for a mammal-sizedarthropod would be too heavy to allow it tomove. Small size also gives arthropods theappearance of great strength because the power ofa muscle is proportional to the area of its cross-section, while the mass it moves is proportional tovolume. Hence, small animals have muscles witha low cross-sectional area-to-volume ratio, rela-tive to larger animals. Thus, a cat flea can jumpabout 30 cm, which would correspond to a jumpof about 300 m for a human.

1.7 PATTERNS OF ARTHROPODDEVELOPMENT

1.7.1 Moulting

An external skeleton results in problems for agrowing animal, since it essentially encases it in aframe of fixed size. The solution evolved byarthropods is the periodic shedding of the exo-skeleton, called moulting or, more properly,ecdysis.

Before the old skeleton is shed the epidermisdetaches itself from the old cuticle (apolysis) andsecretes a new epicuticle. The new epicuticle is softand wrinkled at this stage. Enzymes (chitinasesand proteinases) are then produced which passthrough the new epicuticle and begin to erode theold endocuticle; the exocuticle is not affected.Muscle attachments and nerve connections areunaffected and the animal can continue to behavenormally. Following digestion of the endocuticlenew undifferentiated tissue, known as procuticle,is also produced. Exocuticle is absent along spe-cific paths known as moulting lines. The old

skeleton splits along these predetermined linesand the animal pulls out of the old encasement.

The soft, whitish exoskeleton of the newlymoulted animal is stretched, often by the inges-tion of air or water. Once expanded, quinonescross-link cuticular proteins of the new procuticle,particularly in its outer layers, forming exocuticle.This cross-linking results in hardening and dar-kening of the cuticle. Endocuticle continues to bedeposited, on a daily cycle, for some time aftermoulting, producing daily growth lines that canbe used to estimate age in some species of insect.The internal tissues of the animal may then beexpanded to fill the new frame.

The stages between moults are known as stages,or stadia, and the form of the stadium as theinstar. This terminology is confusing and is oftenconfused in the scientific literature. But, in itssimplest form, moults that give rise to new char-acters produce new instars. Hence, for example, afly larva moults twice, but the larva remainsmorphologically very similar; these are thereforecorrectly termed the first, second and third stagesof the larval instar.

The duration of each stadium becomes longeras the animal becomes progressively older. Inmany insects the growth which is achieved at eachmoult is predictable and dependent on the size ofthe previous stadium or instar. For example,according to Dyer's law, when the number of thestadium is plotted against the logarithm of somemeasurement on the insect's exoskeleton, astraight line is obtained.

1.7.2 Simple and complexlife-cycles

In arthropods, growth and maturation from eggto adult may be accomplished via a number ofdifferent developmental paths. In most, thejuvenile stadia broadly resemble the adult, exceptthat the genitalia and, where appropriate, wingsare not developed. The juveniles, usually callednymphs, are similar to the adults in appearance,feeding habits and habitat. The animal makes anew cuticle and sheds the old one at intervalsthroughout development, typically four or five


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times, increasing in size before the emergence ofthe adult. This is often described as a simple life-cycle with incomplete or partial metamorphosis,known as hemimetabolous metamorphosis (Fig.1.11). In general, the same cells or tissues thatmake larval structures go on to make the samestructures in the adults after the final moult.

In other arthropods, however, particularlysome higher insects, there has been a trendtowards increasing functional and structuraldivergence in juvenile and adult stages (Fig. 1.12).The juvenile instar, which may be referred to as a

larva, maggot, grub or caterpillar, has becomeconcerned primarily with feeding and growth andmay bear no physical resemblance to the adult. Incontrast, the adult, or imago, has become thespecialised reproductive and dispersal instar. Inthe juvenile stages the cuticle is usually soft andpliable and is not differentiated into hardenedplates. These stages depend on a hydrostaticskeleton, provided by fluid pressure in the hae-mocoel, for support and movement. To reach theadult form, the larva must undergo completemetamorphosis, during which the entire body isreorganised and reconstructed. The transforma-tion between the juvenile and the adult is madepossible by the incorporation of a pupal stage,which acts as a bridge between juvenile and adult.The juvenile feeds, moults and grows until it hasreached its final juvenile stadium. In many speciesof fly (Chapter 4), the cuticle of the final larvalstage contracts and tans to form a protective shell,the puparium. In other insects, such as the fleas(Chapter 6), the larva may spin a protectivecocoon of silk produced by the salivary glands,prior to a final moult within the cocoon. The pupalies within the puparium or cocoon. The pupadoes not feed and is generally (but not always)immobile. However, it is metabolically very activeas old larval tissues and organs are lost orremoulded and replaced by adult organs. Duringthe process of pupation, tissues undergo histolysisand are reassembled in the adult form. The pupais probably a highly modified final juvenile stage,which has become specialised for the breakdownof larval structures and reconstruction of adultfeatures.

When pupal development is complete, thecocoon or puparial case contains a fully devel-oped, pharate adult. The adult bursts out of thecocoon using body spines and a projection on thehead or, in the case of the higher (cyclor-rhaphous) flies, from the puparium using aninflatable membranous sac on its head, called aptilinum. Once free of the cocoon or pupariumthe newly emerged teneral adult begins to stretchits still soft cuticle, prior to hardening and dar-kening. This pattern of development is describedas a complex life-cycle with holometabolousmetamorphosis.

Fig. 1.11 Life-cycle of the louse, Menopon gallinae,displaying hemimetabolous metamorphosis and

passing through three nymphal stages prior toemergence as a reproductive adult (modified fromHerms & James, 1961).

Fig. 1.12 Life-cycle of a fly (Diptera) displaying a

holometabolous life-cycle, with the egg giving rise tomaggot-like larva, pupa and finally reproductive adult(from Gullan & Cranston, 1994).


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1.8 THE CLASSIFICATION OFDIVERSITY

To make sense of the diversity of animal species,they are classified into biological units. Theseunits are usually based on similarities in mor-phological characters, but may increasingly bebased on isoenzyme electrophoresis and DNAanalysis. The structure of the classification aimsto describe biologically meaningful groups,usually attempting to represent evolutionarypathways. There are six basic categories intowhich organisms are classified:

. Phylum

. Class

. Order

. Family

. Genus

. Species

The species is the basic operational biologicalunit, from which all other levels of classificationascend. A species is generally considered to be agroup of interbreeding natural populations thatare reproductively isolated from other suchgroups. Hence, even if able or induced to inter-breed, matings between species usually result ininfertility or reduced fertility of the hybrid off-spring. Groups of species are assembled into thenext rank of classification, the genus.

All animals and plants are named according toa binomial system, devised by the Swedish nat-uralist Carl Linnaeus in the eighteenth century.The first word of an organism's name is the gen-eric name and is identical for all members of eachgenus. The second word is the specific name,unique to each species. Once the generic name hasbeen given in full in a text, it may be shortened toits initial letter. Many specific names describesome characteristic feature of the species, forexample the name of the tsetse fly, Glossinapallidipes, means the Glossina with pale feet.

Even within a species not all populations areexactly the same and often there may be con-siderable variation associated with geographical,environmental, seasonal and genetic factors.Within a species, geographically isolated

populations may be classified as subspecies, witheach subspecies showing slight morphologicaldifferences but still being capable of interbreedingnormally where populations overlap.

At the other end of the spectrum, the com-plexities of animal taxonomy have brought aboutthe need to introduce numerous intermediateranks in the classification, such as the subgenus,subfamily, suborder and also, for particularlycomplicated groups, a range of other terms suchas species complex, tribe and super-family. Thereis no fixed limit to the number of categories thatcan be used. It is important to remember, how-ever, that these groups are artificial creations ofthe taxonomist who is attempting to give order tothe confusing diversity of arthropod forms. Thereis, therefore, no single `correct' classification and,indeed, arthropod systematics is often the subjectof heated debate!

It is helpful to note that the names of super-families usually end in `-oidea', families in `-idae'and subfamilies in `-inae'.

1.9 THE ORIGINS OF ARTHROPODS

As described previously in this chapter, thephylum Arthropoda can be well defined by thepresence of seven features:

. Segmented bodies

. Exoskeleton

. Jointed limbs

. Tagmatisation

. Dorsal blood vessel

. Haemocoel

. Ventral nerve cord

However, within the phylum there is considerablevariation in morphology and the evolutionaryorigins of the different groups are far from clear.

There is general agreement that the arthropodsprobably evolved from some primitive polychaetestock or an ancestor common to both. Poly-chaetes are a class of metameric annelid worms,with a pair of paddle-like appendages on eachsegment. However, there has been considerabledebate about whether the arthropods arose from


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a single common ancestor (monophyletic origin)or arose from a number of more or less relatedancestors (polyphyletic origin).

The initial monophyletic view was based onanalysis of morphological similarities andsuggested that all arthropods arose from a basictrilobite or pre-trilobite stem (Fig 1.13). Thetrilobites were believed to be the most primitive ofall known arthropods. Once abundant in theoceans 500 million years ago, they are nowextinct. Trilobites had oval, flattened bodies,usually about 3±10 cm in length, with a thickeneddorsal cuticle and ventral appendages. Themajority of trilobites appear to have been bottomdwellers and crawled over mud and sand usingtheir walking legs. It was proposed that, from theprimitive trilobites, one line may have led to asubphylum known as the Mandibulata, contain-ing the crustaceans (for example crabs, shrimpsand barnacles), myriapods (millipedes andcentipedes) and insects (for example flies, locustsand ants). A second line may have led to a sub-phylum known as the Chelicerata, containing anaquatic group, the merestomes (for examplehorseshoe crabs) and a terrestrial group, thearachnids (for example spiders, scorpions, mitesand ticks).

However, while there was general agreementthat the chelicerates constitute a natural group,as do the insects and the myriapods, the crusta-ceans did not appear to fit easily within theinsect±myriapod assemblage. There was grow-ing acceptance that insect±myriapod mandiblesare structurally different to crustacean mand-ibles and that the superficial similarities reflectconvergent evolution, that is these featureshave arisen independently in each group,rather than reflecting any close phylogeneticancestry.

The monophylectic view, therefore, was lar-gely replaced by a polyphylectic scheme, duelargely to the work of Manton. This suggestedthat, given the diversity of the arthropod groups,they must have arisen as a number of indepen-dent branches from the basic polychaete stock.From marine polychaete ancestors, severalgroups may have invaded land independently,giving rise to ancestral forms from which themyriapod±insect assemblage arose. Indepen-dently marine, perhaps bottom-dwelling, groupsmay have given rise to the crustaceans, the trilo-bites and chelicerates.

However, more recently the use of DNA ana-lysis and cladistic techniques have given renewedsupport for a monophyletic origin of arthropodsfrom annelid worms. Nevertheless, there is stillconsiderable debate about the precise relation-ships of the various arthropod groups within thephylum. For example, analysis of ribosomalDNA places the Myriapoda closer to the Cheli-cerata than the Insects (Hexapoda) and Crusta-cea. In contrast, studies of mitochondrial DNAsupport the view, outlined above, that the Crus-tacea, Myriapoda and Insecta may be consideredtogether in one subphylumMandibulata, with theChelicerata as a second subphylum; which is therelationship between the various groups pre-sented here (Fig. 1.14).

1.10 LIVING ARTHROPOD GROUPS

Only two classes, the Arachnida and the Insecta,contain species of major veterinary importance(Fig. 1.15).

Fig. 1.13 A trilobite (ventral view) (reproduced fromFox & Fox, 1964).


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1.10.1 Arachnids

Members of the class Arachnida are a highlydiverse group of largely carnivorous, terrestrial,chelicerate arthropods. They are characterised byhaving the body divided into two parts, thecephalothorax and the abdomen. The unseg-mented cephalothorax is usually covered dorsallyby a solid carapace. In primitive forms theabdomen is divided into two; however, in mostforms this segmentation has been lost.

On the cephalothorax the first pair of appen-dages, which are positioned in front of the mouth

and which are used in feeding, are called cheli-cerae. The name Chelicerata comes from theancient Greek chele, meaning claw, and keras,meaning horn. The mouthparts do not have truejaws. The second pair of appendages appearbehind the mouth and are called pedipalps. Theirprecise structure and function varies from orderto order. The arachnids do not possess antennaeor wings and they only have simple eyes.

In the class Arachnida there is only one groupof major veterinary importance, the sub-classAcari (sometimes also called Acarina), containingthe mites and ticks. Other major sub-classes ororders of arachnid include the scorpions (Scor-piones), spiders (Araneae) and pseudoscorpions(Pseudoscorpiones) (Fig. 1.16).

The subclass Acari is an extremely diverseassembly, grouped together more from taxo-nomic convenience than true phylogenetichomogeneity. They are the most abundant of thearachnids; over 25 000 species have been descri-bed to date. They are usually small, averagingabout 1 mm in length. However, some ticks maybe over 3 cm in length. The cephalothorax andabdomen are broadly fused and abdominal seg-mentation is inconspicuous or absent, so that thebody appears sack-like. The pedipalps are usuallyshort, sensory structures associated with thechelicerae in a discrete structure called a gnatho-soma. The body posterior to the gnathosoma isknown as the idiosoma. There are four basic life-cycle stages: the egg, a six-legged larva, eight-

Insecta Non-insecthexapods

Myriapoda Crustacea Arachnida

Trilobites

Hexapoda

Mandubulata

Fig. 1.14 Relationships of the major classes ofarthropod.

Order

Diptera (flies)

Phthiraptera (lice)

Siphonaptera (fleas)

Astigmata (mites)

Prostigmata (mites)

Mesostigmata (mites)

Metastigmata (ticks)

Insecta

Arachnida Acari

ClassPhylum

Arthropoda

Fig. 1.15 The arthropod orders of verinaryimportance.

Fig. 1.16 Common orders of the class Arachnida. (a) Aspider (Xysticus cristatus), (b) a scorpion (Buthusoccitanus) and (c) a pseudoscorpion (Chelifer

cancroides) (reproduced from Savory, 1935).


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legged nymph and eight-legged adult. However,these may be further divided into pre-larva, larva,protonymph, deutonymph, tritonympha andadult. There may also be more than one moult ineach of these instars. In many Acari, pre-larvaland larval instars take place within the egg orhave been lost. In others, one or more of thenymphal instars may be omittted.

In the adult, the idiosoma is subdivided into theregion that carries the legs, the podosoma, andthe area behind the last pair of legs, the opistho-soma. The legs are six-segmented and areattached to the podosoma at the coxa, alsoknown as the epimere. This is then followed bythe trochanter, femur, genu, tibia and tarsus.

There are three main lineages of extant mites:the Opiloacariformes, the Parasitiformes and theAcariformes. The Opiloacariformes are thoughtto be the most primitive of the living mites and arenot parasitic. The Parasitiformes possess one tofour pairs of lateral stigmata posterior to thecoxae of the second pairs of legs and the coxae areusually free. The Parasitiformes include the ticks,described as the Ixodida or Metastigmata, andthe gamesid mites or Mesostigmata. The Acar-iformes do not have visible stigmata posterior tothe coxae of the second pair of legs and the coxaeare often fused to the ventral body wall. TheAcariformes includes the mite-like-mites, theSarcoptiformes and Trombidiformes, oftendescribed as the Astigmata and Prostigmata,respectively. The terms Metastigmata, Mesos-tigmata, Astigmata and Prostigmata relate to theposition of the respiratory openings on the bodyand provide a convenient way of distinguishingthe four orders of parasitic importance. Hence,this is the classification system that will be fol-lowed here (Fig. 1.15). The mites and ticks andthe veterinary problems they cause will be con-sidered in detail in Chapters 2 and 3, respectively.

1.10.2 Insects

The insects are a very large and successful class,constituting about 90% of all known arthropods.Members of the class Insecta can be distinguishedfrom the other arthropods by the presence of only

three pairs of legs in adults, and the broaddivision of the tagmata into three sections: head,thorax and abdomen (Fig. 1.17).

The head carries the main sensory organs: thesingle pair of antennae, a pair of compound eyesand, often, three simple eyes, or ocelli. The mouthis surrounded by mouthparts composed of threepairs of appendages: the mandibles or jaws, fol-lowed by a pair of maxillae, then by the labium.These appendages are serially homologous withthe legs. However, the mouthparts of differentinsects show a remarkable variety of specialisa-tion which is related to their various diets, andwhich will be considered in detail in the appro-priate chapters of the text.

The thorax, which forms the middle region ofthe body, is composed of three fused segments:the prothorax, the mesothorax and the meta-thorax. On each of these segments there is a singlepair of legs. Each leg is composed of six segments.The basal section of the leg articulating with thebody is the coxa, which is followed by a short,triangular trochanter. There then follows thefemur, the tibia, one to five segments of the tarsusand, finally, the pretarsus composed of a pair ofclaws. The legs of insects are generally adaptedfor walking or running but, as we will see, someare modified for specialised functions such asjumping (fleas) or clinging to the hairs of theirhost's body (lice).

Many groups of insect have two pairs of wingsarticulating with the mesothorax and metathorax.Some groups of primitive insects have neverdeveloped wings while others, such as the fleasand lice, which once had wings, have now lost

Fig. 1.17 Common orders of the class Insecta: (a) abutterfly (Lepidoptera), (b) a beetle (Coleoptera) and

(c) a parasitic wasp (Hymenoptera) (reproduced fromGullan & Cranston, 1994).


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them completely. Others, such as some of thehippoboscids, which we will meet in Chapter 4,have wings for only a short time as adults, afterwhich they are shed. The wing consists of a net-work of sclerotised veins which enclose regions ofthin, transparent cuticle called cells. The veins actas a framework to brace and stabilise the wingand may carry haemolymph and nerves. Thearrangement of the veins tends to be character-istic of various groups of insect species and so isimportant in identification and taxonomy. Wingsare a key reason for the success of the class,allowing insects to migrate, locate distant foodsources, escape predators, find mates and colonisenew habitats. In several groups of insect, such asgrasshoppers, true bugs and beetles, the frontwings have been modified to various degrees asprotective coverings for the hind wings andabdomen. In the true flies (the Diptera) the hindwings have been reduced to form a pair of club-like halteres, which are used as stabilising organsto assist in flight.

The abdomen is composed of 9 to 11 segments,although the tenth and eleventh segments areusually small and not externally visible and theeleventh segment has been lost in most advancedgroups. The genital ducts open ventrally on seg-ment 8 or 9 of the abdomen and these segmentsoften bear external organs that assist in repro-duction. The genitalia are composed of structureswhich probably originated from simple abdom-inal appendages. In the male, the basic externalgenitalia consist of one or two pairs of claspers,which grasp the female in copulation, and thepenis (aedeagus). However, there is considerablevariation in the precise shape of the male genitaliain various groups of insect and these differencesmay be important in the identification of species.In the female the tip of the abdomen is usuallyelongated to form an ovipositor.

Within the class Insecta there are generallyconsidered to be 29 orders, of which only three,the flies (Diptera), fleas (Siphonaptera) and lice(Phthiraptera), are of veterinary importance.Adult flies and their veterinary importance will bediscussed in Chapter 4 and the problems causedby fly larvae in Chapter 5. Fleas and lice will beconsidered in Chapters 6 and 7, respectively.

1.10.3 Other living arthropodclasses

Crustacea

There are probably more than 26 000 species ofCrustacea. Almost all are aquatic and themajority are marine. The class includes suchfamiliar animals as the crabs, lobsters, shrimps,crayfish and woodlice, as well as many thousandsof tiny planktonic species that play an essentialrole in marine food webs (Fig. 1.18).

Their bodies are organised into a head andsegmented thorax, often combined in a cepha-lothorax, and posterior abdomen. Anteriorly thehead bears five pairs of appendages, the first twoof which are the antennae. The third pair ofappendages is the mandibles which flank themouth and behind these are two pairs of feedingappendages. Behind the head, the thorax is oftencovered by a carapace which arises as a fold of thehead and which may overhang the sides of thebody.

Primitively, each of the many segments of thethrorax and abdomen carries a pair of modifiedappendages. Crustacean appendages are descri-bed as biramous, since typically they are com-posed of an inner and an outer branch. However,the structure is very variable since the segments

Fig. 1.18 The crustacean, Carcinus maenas (from Bell,1853).


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have undergone various degrees of fusion andreduction and the thoracic and abdominalappendages are often modified to performspecific specialised functions, such as swimming,crawling, sperm transmission or egg brooding.

The Crustacea are of little or no veterinaryimportance, with the exception perhaps of cope-pod crustaceans, known as `fish lice'. Copepodcrustaceans are specialised ectoparasites whichattach to the gill filaments or fins and feed bypiercing and sucking.

Myriapoda

The Myriapoda contains the familiar millipedes(Diplopoda) and centipedes (Chilopoda) as wellas two groups of small, soil-dwelling arthropodsthe Pauropoda and the Symphyla.

The centipedes and millipedes are relativelylong, narrow-bodied and multi-legged. All have asegmented head with a pair of antennae (Fig.1.18). The remainder of the body is composed ofmany similar leg-bearing segments. The numberof segments and the number of legs increase ateach moult throughout life ± this is described asanamorphic. There is no metamorphosis (ameta-boly). Millipedes have two pairs of legs per seg-ment while centipedes have one pair. Millipedesare predominantly herbivorous or saprophagous(feeding on decaying vegetation). In contrast, thecentipedes are mainly nocturnal predators, feed-ing on other arthropods or small vertebrateswhich they kill using poison injected from themodified first pair of legs, which resemble pincers.

1.11 ARTHROPOD DISTRIBUTIONS

The general distribution of animals is stronglydetermined by geography and climate. Inreflecting geographical divisions, the world isoften divided into six zoogeographical regions,each region containing its characteristic animaland plant species (Fig 1.19). Each region isusually isolated by physical boundaries such asdeserts, mountains and oceans. Each regioncontains many species of animal and plant which

are endemic (native to the region) or which areindigenous (have dispersed or migrated therenaturally). Superimposed on these regions, dif-ferences in temperature and rainfall caused bydifferences in latitude, altitude and `con-tinentality', create further divisions into climaticbiomes: tropical, sub-tropical, temperate andpolar (Fig. 1.19). The distribution of many speciesof animal may be strongly limited to specificbiomes, either directly by climate or indirectlythrough the effects of climate on the habitat andresources that the animal requires.

This book focuses on the ectoparasites oftemperate habitats in theNearctic and Palaearcticregions, which together form one large realmknown as the Holarctic. Nevertheless, whendealing with arthropod pests of veterinaryimportance, it is notable that they have been ableto spread worldwide, carried with livestock andhumans. In many cases they are also largelyprotected from the effects of climate by the warmmicroclimate of their host's body and the houses

Fig. 1.19 (a) World zoogeographic zones. (b) Worldclimatic biomes.


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and other buildings that humans construct.Hence the zoogeographic regions and climaticbiomes freqently prove to be an inadequatedescription of the distribution of ectoparsiticarthropods and, where appropriate, ectoparasitesof various regions of the temperate southernhemisphere will also be discussed.

FURTHER READING AND REFERENCES

Anderson, R.M. & May, R.M. (1982) Coevolution of

hosts and parasites. Parasitology, 85, 411±26.Barnes, R.D. (1974) Invertebrate Zoology. W.B. Saun-ders, London.

Bell, T. (1853) A History of the British Stalk-eyedCrustacea. John Van Voust, London.

Boore, J.L., Collins, T.M., Stanton, D., et al. (1995)

Deducing the pattern of arthropod phylogeny frommitochondrial DNA rearrangements. Nature, 376,163±5.

Chapman, R.F. (1971) The Insects: Structure and

Function. English Universities Press, London.Clutton-Brock, J. (1987) A Natural History of Domes-ticated Mammals, Cambridge University Press,

Cambridge.Davies, R.G. (1988) Outlines of Entomology. Chapman& Hall, London.

Evans, H.E. (1984) Insect Biology. A Textbook ofEntomology. Adison Wesley, Massachusetts.

Ewald, P.W. (1983) Host±parasite relations, vectors

and the evolution of disease severity. Annual Reviewof Ecology and Systematics, 14, 465±85.

Ewald, P.W. (1993) The evolution of virulence.Scientific American, 268, 56±62.

Ewald, P.W. (1995) The evolution of virulence: aunifying link between parasitology and ecology.Journal of Parasitology, 81, 659±69.

Fallis, A.M. (1980) Arthropods as pests and vectors ofdisease. Veterinary Parasitology, 6, 47±73.

Fox, R.M. & Fox, J.W. (1964) Comparative Entomol-

ogy. Reinhold Publishing Corporation, New York.Freidrich, M. & Tautz, D. (1995) Ribosomal DNAphylogeny of the major extant arthropod classesand the evolution of myriapods. Nature, 376,

165±7.

Gullan, P.J. & Cranston, P.S. (1994) The Insects. AnOutline of Entomology. Chapman & Hall, London.

Harwood, R.F. & James, M.T. (1979) Entomology in

Human and Animal Health. Macmillan, New York.Herms, W.B. & James, M.T. (1961) Medical Entomol-ogy. MacMillan, New York.

Kettle, D.S. (1984) Medical and Veterinary Entomol-ogy. Croom Helm, London.

Kim, K.C. (1985) Coevolution of Parasitic Arthropodsand Mammals. John Wiley and Sons, Chichester.

Lane, R.P. & Crosskey, R.W. (1993) Medical Insectsand Arachnids. Chapman & Hall, London.

Lenski, R. & May, R.M. (1994) The evolution of

virulence in parasites and pathogens: a reconciliationbetween two conflicting hypotheses. Journal ofTheoretical Biology, 169, 253±65.

Manton, S.M. (1973) Arthropod phylogeny ± a modernsynthesis. Journal of Zoology, 171, 111±30.

Marshall, A.G. (1985) The Ecology of EctoparasiticInsects. Academic Press, London.

May, R.M. & Anderson, R.M. (1990) Parasite±hostcoevolution. Parasitology, 100, 89±101.

Neaberry, P.E. (1893) Beni Hasan, Part 1. In: Arche-

ological Survey of Egypt. Egypt Exploration Fund,Kegan Paul, Trench, Trabner, London.

Poulin, R. (1996) The evolution of life history strategies

in parasitic animals. Advances in Parasitology, 37,107±34.

Roberts, M.J. (1995) Spiders of Britain and Northern

Europe. Harper Collins, London.Savory, T.H. (1935) The Arachnida. Edward Arnold,London.

Snodgrass, R.E. (1935)Principles of InsectMorphology.

McGraw-Hill, New York.Waage, J.E. (1979) The evolution of insect/vertebrateassociations. Biological Journal of the Linnean

Society, 12, 187±224.Walker, A. (1994) Arthropods of Humans and DomesticAnimals. A Guide to Preliminary Identification.

Chapman & Hall, London.Walter, D.E. & Proctor, H.C. (1999) Mites. Ecology,Evolution and Behaviour. CABI Publishing, Wall-ingford.

Wigglesworth, V.B. (1972) The Principles of InsectPhysiology. Chapman & Hall, London.

Zinser, H. (1934) Rats, Lice and History. Little &

Brown, Boston.


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Chapter 3

Ticks (Acari)

3.1 INTRODUCTION

The ticks are obligate, blood-feeding ectopar-asites of vertebrates, particularly mammals andbirds. Ticks are arachnids, in the sub-class Acari,closely related to the mites. They are usuallyrelatively large and long-lived compared to mites,surviving for up to several years. During this timethey feed periodically taking large blood meals,often with long intervals, spent off the host,between each meal. Since a large proportion ofthe life-cycle of most tick species occurs off thehost, the habitat in which they live is of particularimportance. The tick habitat must satisfy twomain requirements: there must be a large enoughconcentration of host species for each of thedevelopmental instars to locate a new host and asufficiently high humidity for the ticks to main-tain their water balance. In areas where thehumidity is low, ticks resist desiccation byspending shorter periods questing for hosts. Theyalso enter diapause at unfavourable times of theyear. Dormancy is initiated by changes in daylength and temperature.

Tick bites can be directly debilitating todomestic animals, causing mechanical damage,irritation, inflammation and hypersensitivity and,when present in large numbers, feeding may causeanaemia and reduced productivity (see section3.4). The salivary secretions of some tick speciesmay cause toxicosis and paralysis. Ticks may alsotransmit a range of pathogenic viral, rickettsialand bacterial diseases to livestock. Hence,although the ticks are a relatively small order ofonly about 800 species, they are one of the mostimportant groups of arthropod pests of veterinaryinterest.

A single family, the Ixodidae, known as thehard ticks, contains almost all the species of tick

of veterinary importance. A second family, theArgasidae, known as the soft ticks, contains arelatively small number of species of veterinaryimportance. A third family of tick, the Nuttal-liellidae, contains only a single, little-known spe-cies which is found in the nests of swallows insouthern Africa.

3.2 MORPHOLOGY

3.2.1 Ixodidae

Ixodid ticks are relatively large, ranging between2 and 20mm in length. The body of the unfed tickis flattened dorsoventrally and is similar instructure to that of mites, being divided into onlytwo sections, the anterior gnathosoma (or capi-tulum) and posterior idiosoma, which bears thelegs. The terminal gnathosoma is always visiblewhen an ixodid tick is viewed from above.

The mouthparts of ticks are structurally similarto those of mites (Fig. 3.1). The gnathosomacarries a pair of four-segmented palps, which aresimple sensory organs, which help the mite tolocate its host. The fourth segment of each palp isreduced and may articulate from the ventral sideof the third, forming a pincer-like structure.Between the palps lies a pair of heavily sclero-tised, two-segmented appendages called cheli-cerae, housed in cheliceral sheaths. At the end ofeach chelicera is a rigid, somewhat triangular,plate bearing a number of sclerotised tooth-likedigits. The chelicerae are capable of moving backand forth and the tooth-like digits are used to cutand pierce the skin of the host animal duringfeeding. The enlarged, fused coxae of the palpsare known as the basis capituli. The basis capitulivaries in shape in the different genera, being

55

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rectangular, hexagonal or triangular. The lowerwall of the basis capituli is extended anteriorlyand ventrally to form an unpaired medianhypostome, like an underlip, which lies below thechelicerae. The hypostome does not move, but inlarvae, nymphs and adult females is armed withrows of backwardly directed ventral teeth.

The hypostome is thrust into the hole cut by thechelicerae and the teeth are used to attach the ticksecurely to its host. As the hypostome is insertedthe palps are spread flat on to the surface of thehost's skin. Salivary secretions contain antic-oagulants and other active compounds whichpromote lesion development. The large quantityof salivary fluid produced is the principal avenuefor disease transmission in the hard ticks. Asfeeding commences the tick tilts its body to anangle of at least 458 to the skin, and this angle maybecome steeper as feeding proceeds.

Hard ticks remain attached for several daysduring feeding. For ticks with long mouthparts,attachment by the chelicerae and hypostome issufficient to anchor the tick in place. However,for ticks with short mouthparts, attachment ismaintained during feeding by secretions from the

salivary glands which harden around the mouth-parts and effectively cement the tick in place.Female ticks can show substantial increases insize when they engorge during feeding; some ofthe larger species of Amblyomma can increasefrom just under 10mm to over 25mm in lengthand increase from about 0.04 g to over 4 g inweight. However, these impresive figures under-estimate the amount of blood imbibed, becausealmost as soon as they start to feed ticks begin todigest the blood meal and excrete waste materials.

The immature stages of ticks are very similarmorphologically to the adults. The larvae, some-times known as seed ticks, are six-legged. Adultand nymphal ticks have four pairs of legs (seesection 3.3). The region of the idiosoma whichcarries the legs is called the podosoma and theregion behind the legs is the opisthosoma. Eachleg is attached to the body at the coxa. The coxamay be armed with internal and external ventralspurs, and their number, size and shape may beimportant in species identification (Fig. 3.2). Thecoxa is then followed by the trochanter, femur,genu, tibia and tarsus. The legs of ticks, like thoseof mites, usually end in a pair of claws and a well-developed, pad-like pulvillus. Located on the tarsiof the first pair of legs is a pit known as Haller'sorgan, which is packed with chemoreceptor setaeand used in host location. Chemoreceptors arealso present on the palps, chelicerae and scutum.

Male ixodid ticks are usually smaller thanfemales. Males imbibe relatively little blood whenthey feed and show little increase in size. Ixodidticks possess a sclerotised dorsal shield or plate onthe idiosoma known as a scutum (Fig. 3.3). In

Fig. 3.1 Tick mouthparts: (a) ventral view, showingtoothed hypostome; (b) dorsal view, showing the

chelicerae behind the cheliceral sheaths.

Fig. 3.2 (a) Ventral view of the coxae and (b) segmentsof the leg of a generalised ixodid tick.


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males, the scutum covers the entire dorsal surface,whereas in females the scutum is relatively smallto facilitate the size increase which occurs duringfeeding. The scutum is difficult to see in a fullyengorged female. If the scutum has a pattern ofgrey and white on a dark background, it isdescribed as ornate, if not it is described asinornate.

Ticks do not possess antennae, and when eyesare present they are simple and are located dor-sally at the sides of the scutum. There are anumber of grooves, largely on the ventral side ofticks. The number and presence of these groovesmay be important in identification. Uniformrectangular regions on the posterior margins ofthe body are known as festoons and are alsoseparated by grooves (Fig. 3.3).

The larvae lack stigmata and a tracheal system,and water loss and respiration take place directlythrough the integument. Adult and nymphal tickshave a pair of respiratory openings, the stigmata.The stigmata lead to a complex branching systemof tracheae (see section 1.6.4). The stigmata arelarge and positioned posterior to the coxae of thefourth pair of legs. Each is often surrounded by astigmatal plate which is circular or oval (Fig. 3.4).

Sexual differentiation is usually not obvious inthe larva and nymph, and immature ixodidsgenerally look like small females but without thegenital opening. In adults the genital opening, thegonopore, is situated ventrally behind the

gnathosoma, usually at the level of the secondpair of legs (Fig. 3.4). The genital apron is alightly sclerotised flap originating in front of andcovering the genital opening. A pair of genitalgrooves starts at the gonopore and extendsbackwards to the anal groove. The anus is alsolocated ventrally, usually being posterior to thefourth pair of legs. The anal groove surrounds theanus. Adult males possess a pair of testes, and avas deferens extends from each testis to openthrough the gonopore. Males and females arebrought together, usually on the host, by aggre-gation and sex-recognition pheromones. Themale has no external genitalia so, after ejecting amass of sperm in a spherical spermatophore, thespermatophore is grasped by the chelicerae of themale and implanted into the female gonoporebefore being pushed into the female genital tract.

3.2.2 Argasidae

In the Argasidae, the body is leathery andunsclerotised, with a textured surface. The cuticlein unfed ticks may be characteristically markedwith grooves or folds (Fig. 3.5). The fourth seg-ment of the palp is the same size as the third andthe palps may appear somewhat leg-like. Innymphs and adults the gnathosoma is not visiblefrom the dorsal view, being located ventrally in arecess called the camerostome. When present theeyes are positioned in lateral folds above the legs.The stigmata of Argasidae are small and placed

Fig. 3.3 Dorsal view of a generalised female, ixodidtick.

Fig. 3.4 Ventral view of a generalised male, ixodid tick.

Ticks (Acari) 57

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anterior to the coxae of the fourth pair of legs.The integument is inornate. There is little sexualdimorphism. Pulvilli are usually absent or rudi-mentary in adults and nymphs, but may be welldeveloped in larvae.

3.3 LIFE HISTORY

3.3.1 Ixodidae

The life cycles of ixodid ticks involve four instars:egg, six-legged larva, eight-legged nymph andeight-legged adult (Fig. 3.6). During the passagethrough these stages ixodid ticks take a number oflarge blood meals, interspersed by lengthy free-living periods. The time spent on the host mayoccupy as little as 10% of the life of the tick. Theyare relatively long-lived and each female mayproduce several thousand eggs.

Most hard ticks are relatively immobile and,rather than actively hunting for their hosts, themajority adopt a `sit and wait' strategy. However,a few, including some species of Hyalomma,

Fig. 3.5 An argasid tick, Argas vespertilonis: (a) dorsal view of female and (b) ventral view of female (reproduced

from Arthur, 1963).

Fig. 3.6 Life-cycle of an ixodid tick (reproduced fromUrquhart et al., 1987).


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actively approach their host. To obtain a bloodmeal, field-inhabiting ticks show a behaviourknown as questing. They climb to the tips ofvegetation, such as grass, usually at a heightappropriate to their host. Questing heights of upto 2m have been recorded for larval stages ofIxodes scapularis in the USA. At the approach ofa potential host the tick begins to wave the firstpair of legs in the direction of the stimulus. Theticks detect the approach of the host using cuessuch as carbon dioxide and other semiochemicalsemitted by the host, which they sense using thechemoreceptors, particularly those packed intoHaller's organ on the tarsi of the first pair of legs.Vibrations, moisture, heat and passing shadowsmay also be important cues in host recognition.Once contact is made, as the host animal brushespast, the ticks transfer to the host, and then moveover the surface to find their preferred attachmentsites, such as the ears. Preferred sites for attach-ment may be highly specific to the particularspecies of tick. Although all stages are capable ofsurvival on a variety of hosts, the larvae andnymphs are usually most successful on smalleranimals. As a result, where both larger andsmaller potential host species are present and inclose proximity, the higher survival of theimmature stages may result in particularly largetick populations and severe infestations.

The host-location behaviour of ticks representsan intrinsically risky way of finding a host animal

and many probably die without ever feeding. Tocompensate for the risks involved, ticks havedeveloped a variety of complex life-cycles andfeeding strategies which reflect the nature of thehabitat which the various species of tick inhabitand the probability of contact with an appro-priate host.

For ixodid ticks, which inhabit forests andpastures where there is a relatively plentifulsupply of host animals and in habitats whereconditions are suitable for good survival duringthe off-host phase, a three-host life-cycle has beenadopted (Fig. 3.7). Larvae begin to quest severaldays to several weeks after hatching, the precisetime depending on temperature and humidity. Onfinding a suitable host, usually a small mammalor bird, the larvae begin to feed. Blood feedingtypically takes between 4 and 6 days. On com-pletion of feeding the larvae drop to the groundwhere, 2 to 3 weeks later, they moult to becomenymphs. After another interval, again which mayvary between several days and several monthsdepending on environmental conditions, nymphsalso begin to quest for a second host. The secondhost need not necessarily be of the same species asthe first. After feeding, the nymphs drop to theground and then moult to become adults. Finally,after a further interval, adults begin to quest. Thethird host is usually a large mammal. On theirfinal host females mate and then engorge.Following the final blood meal adult females drop

Fig. 3.7 A three-host feeding strategy of an ixodid tick.

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to the ground where they lay large batches ofseveral thousand eggs over a period of days orweeks. Oviposition can be delayed for severalweeks until conditions are suitable for survival ofthe eggs. Adult males may remain unattached onthe host animal and attempt to mate with as manyfemales as possible. Most ixodid ticks have athree-host feeding strategy.

For a relatively small number of ixodid ticks,about 50 species, which inhabit areas where hostsare scarce and in which lengthy seasonal periodsof unfavourable climate occur, two- and one-host feeding strategies have evolved (Fig. 3.8). Intwo-host ticks, such as Rhipicephalus bursa, lar-vae locate the host, then feed, moult to nymphalstages, feed again and then drop to the groundand moult to become adults. The adults thenseek a second and usually larger host on which to

feed. Adults then drop to the ground, lay theireggs and die. Where the environment and con-tact with the host are highly unpredictable, one-host species such as Boophilus annulatus andDermacentor albipictus occur. After hatchingfrom the egg, the larvae of these species locate asuitable host, which is usually a large herbivor-ous mammal. They then feed and moult tobecome a nymph. There is a single nymphalstage, during which they again feed, prior tomoulting to become an adult. Finally they feedas adults, drop off their host and females laytheir eggs.

In temperate habitats, feeding and generationcycles of hard ticks are closely synchronised withperiods of suitable temperature and humidityconditions. Ticks, particularly in the immaturestages, are very susceptible to desiccation. Thecuticle is covered by a waxy layer which is largelyimpermeable to water, but when ticks are activewater loss through the stigmata is more pro-nounced. To minimise drying out they startquesting when saturated with water and return tothe humid ground level when dehydrated. Watermay also be imbibed by drinking.

3.3.2 Argasidae

Argasid, soft ticks are more common in deserts ordry conditions. In contrast to the hard ticks,argasid soft ticks tend to live in close proximity totheir hosts: in chicken coops, pigsties, pigeonlofts, birds' nests, animal burrows or dens. Inthese restricted and sheltered habitats the hazardsassociated with host finding are reduced andmore frequent feeding becomes possible. As aresult, argasids typically have a multi-hostdevelopmental cycle. The single larval instar feedsonce, before moulting to become a first-stagenymph. There are between two and seven nym-phal stages, each of which feeds and then leavesthe host, before moulting to the next stage. Adultsmate away from the host and feed several times.The adult female lays small batches of 400 to 500eggs after each feed. In contrast to the slow-feeding ixodids, argasid ticks feed for only a fewminutes.

Fig. 3.8 (a) One-host and (b) two-host feedingstrategies of ixodid ticks.


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3.4 PATHOLOGY

Ticks are primarily parasites of wild animals andonly about 10% of species feed on domestic ani-mals, primarily sheep and cattle. The effect ofticks on host species can be divided into:

. Cutaneous effects:inflammationinfection

. Systemic effects:transmission of micro-organisms from

another hostparalysis of the hostbacteriaemia resulting from introduction of

micro-organisms

3.4.1 Cutaneous effects of tickfeeding

At the site of a tick bite focal dermal necrosis andhaemorrhage occur, followed by an inflammatoryresponse, often involving eosinophils. Although ahypersensitivity reaction may be involved in thelocal response, the innate inflammatory responseand dermal necrosis is sufficient to damage thehide. Tick-bite wounds can become infected withStaphylococcus bacteria, causing local cutaneousabscesses or pyaemia. Heavy tick infestation canresult in significant blood loss, reduced pro-ductivity, reduced weight gain and can causerestlessness. Tick-bite lesions may also predisposeanimals to myiasis (see Chapter 5).

3.4.2 Systemic effects: vectors ofdisease

Through their blood-feeding habits, ticks areimportant as vectors of animal disease, trans-mitting a wide range of pathogenic viruses, rick-ettsia, bacteria and protozoa. In addition, manyof the major diseases transmitted by ticks, such asthe tick-borne encephalitides, Lyme borreliosis,relapsing fevers or Rocky Mountain spottedfever, are pathogenic to humans. Wild and

domestic animals are particularly important asreservoirs of the organisms causing these diseasesthrough an animal/tick/human cycle of contact.

Ticks are effective vectors because:

. They attach securely to their hosts, allowingthem to be transferred to new habitats while onthe host.

. The lengthy feeding period allows large num-bers of pathogens to be ingested.

. While feeding the ticks often regurgitate,introducing pathogens to the host.

. Feeding on a number of different hosts allowsthe transfer of pathogens from host to host.

. Many species of tick are long lived.

. Females lay large numbers of eggs and there-fore tick populations have rapid potential forincrease.

. If they fail to find a host they can survive forlengthy periods without feeding.

. Ingested pathogens may be passed from larvato nymph and nymph to adult (trans-stadial)and may also be transferred from adult femalesto the next generation via the ovaries (transo-varial).

. Non-viraemic transmission may occur betweenco-feeding ticks.

Louping ill

This is a tick-borne disease, caused by a flavivirus(LI), which affects the central nervous system ofthe host, leading to encephalomyelitis. LI is thewestern variant of a more extensive tick-bornefever (TBE) antigenic complex of viruses. LI isconfined to the UK, Ireland and parts of Norwayand France. It leads to rapid death in some casesor incoordination, ataxia, torticollis and paralysisfollowed by coma and death in others. Althoughit is primarily a problem associated with sheep inthe UK and Ireland, where the primary vector isthe sheep tick Ixodes ricinus, it may also affectcattle, dogs and humans. It is maintainedprimarily in a sheep/tick cycle, although ground-nesting birds, such as grouse, and hares may alsobe important reservoirs of the pathogen. How-ever, less than 1 in 1000 ticks usually carry the

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virus. The LI virus can easily be transmittedbetween co-feeding ticks. The morbidity rateamongst lambs can be greater than 50%; how-ever, most are protected against infection for thefirst 3 months of life by antibodies in colostrum.Lifelong immunity occurs following infection.The disease can be a problem in adult non-immune sheep introduced into affected areas;however, vaccination with an inactivated vaccineis possible. In continental Europe, small mam-mals have been shown to be important hosts ofother TBE viruses, which may also affect humans,and non-viraemic transmission occurs betweenco-feeding I. ricinus.

African swine fever

This is an acute, contagious disease caused by anunclassified DNA virus. Originally confined toAfrica, the disease spread to Portugal, Spain,Italy and France in the 1960s, causing substantialmortality. It may be transmitted by variousspecies of the argasid genus Ornithodoros, inparticular Ornithodorus moubata porcinus, andmay cause high mortality in domestic pigs. Pigsinitially have an asymptomatic pyrexia followedby cutaneous blue blotches, depression, anorexia,weakness and death. Vomiting and diarrhoea arevariable signs.

Ehrlichiosis (tick-borne fever)

The agent of tick-borne fever in sheep and cattlein western Europe is the rickettsia-like parasiteEhrlichia (Cytocetes) phagocytophila. The infec-tion is characterised by recurrent pyrexia, anor-exia and lethargy. Infection in cattle can lead torespiratory distress, reduced milk yield andabortion in the later stages of pregnancy. Expo-sure of naive pregnant ewes to tick-borne fevercan also result in outbreaks of abortion, followedby septic metritis. Infection of lambs leads to anincreased susceptibility to staphylococcal infec-tions and louping ill. Most ticks carry the para-sites, hence infection may be supported by verysmall tick populations.

A closely related rickettsia-like organism isEhrlichia canis, a parasite of wild and domesticCanidae, which may cause disease in domesticdogs. The organism is spread by Rhipicephalussanguineus and causes anaemia with thrombocy-topenia and leucopenia in association withpyrexia.

In humans, Ehrlichia chaffeensis is the causa-tive agent of granulocytic ehrlichiosis, often calledrashless Rocky Mountain spotted fever. It istransmitted by both dog ticks (Dermacentor var-iabilis) and lone star ticks (Amblyomma amer-icanum). Symptoms include fever, headache,muscle pain, vomiting and anaemia.

Rocky Mountain spotted fever

This is an acute febrile disease caused by Rick-ettsia rickettsii which has been recorded fromalmost every state in the USA, particularly east-ern states, as well as parts of South America. It istransmitted primarily by the Rocky Mountainwood tick, Dermacentor andersoni, in westernstates and the American dog tick, D. variabilis, ineastern states. Vectors in the southern states(Texas and Oklahoma), Mexico and SouthAmerica are Amblyomma americanum, Rhipice-phalus sanguineus and Amblyomma cajennense,respectively. It is particularly important as adisease of humans but may have pathogenic sig-nificance for dogs, where it may cause fever andlethargy.

Other spotted fevers caused by members of therickettsia are present in other parts of the world.In South Africa and southern Europe R. conoriicauses spotted fevers with various local names.The vectors in South Africa responsible forspeading this rickettsia are Rhipicephalus sangui-neus and Haemaphysalis leachi and the dog isconsidered an important reservoir species insouthern Europe. The tick-borne R. australiscauses tick typhus in Queensland, Australiawhere the ixodid tick Ixodes holocyclus is thelikely vector. All stages of infected ticks cantransmit the disease.

In humans, Rocky Mountain spotted fever ischaracterised by headache, fever and aching


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muscles lasting up to 2 weeks after the initialcontact with the tick. Two to three days after thefever begins, a rash appears on the wrists andankles, spreading to the palms, soles, and torso.As the infective organism spreads through thecirculation it may cause haemorrhage, leading tocollapse of the vascular system and death.

Q fever

The causative agent of Q fever is the rickettsialparasite Coxiella burnetii, which is enzootic incattle, sheep and goats in many parts of the world.It is transmitted by ixodid ticks. The organism isrelatively non-pathogenic in domestic animals buthas been associated with anorexia and abortion.

Lyme borreliosis

Lyme disease or borreliosis is a disease caused bya tick-borne infection with the spirochaete, Bor-relia burgdorferi. It is widespread in the USA and,in recent years, has become increasingly recog-nised in Europe, the former USSR and China.The geographical spread of the disease is partlyattributed to migratory birds, which harbour theimmature stages of many vector tick species. Thedisease is transmitted by various species of Ixodes;I. ricinus in north-western Europe, I. scapular-is(dammini) in north-eastern USA, I. pacificus inwestern USA, Amblyomma americanum in easternUSA (New Jersey) and I. persulcatus in easternEurasia, China and Japan. The nymphal stage ofI. ricinus is thought to be reponsible for the mosttransmission of the spirochaete; in some parts ofits range, up to 30% of I. ricinus nymphs arethought to be infected.

Ixodid ticks found in pastures grazed by live-stock are often not infective, suggesting thatlivestock are not significant reservoirs of thespirochaete. However, ticks collected from theedges of fields and on grass verges, where smallwild mammals are more abundant, more com-monly carry the spirochaete. Since ixodid ticksfeed just once in each stage, trans-stadial trans-mission, where the spirochaete is acquired at one

stage and passed on by the following stage, isthought to be responsible for maintaining theinfection through the tick life-cycle.

The infection has been detected in numerousanimals, including dogs, cats and cattle. In thedog clinical signs include pyrexia, lethargy,anorexia, lymphadenopathy and lameness due toarthritis. The clinical signs of Lyme borreliosis inhorses are lameness, laminitis, chronic weightloss, low grade fever, swollen joints and anterioruvetitis. Cattle affected with acute Lyme borre-liosis show signs of swollen joints, stiffness, feverand decreased milk production, and in some casesweight loss, laminitis and abortion. In chroniccases these clinical signs are accompanied byneurological signs such as depression, beha-vioural changes and dysphagia. In humans, Lymedisease is multi-systemic and characterised by alocal reaction (skin rash), commonly many inchesin diameter, with flu-like symptoms and sub-sequent development of polyradiculoneuritis,impaired hearing and vision and meningitis.These symptoms develop within 3 to 32 days.

Theileria

Protozoa of the genus Theileria, especially T.parva, are economically important parasites ofdomestic livestock, largely cattle, primarily inAfrotropical regions. They cause a range ofdiseases, including East Coast fever ± a highlypathogenic disease of cattle in eastern Central andSouthern Africa, causing high mortality ininfected stock.

Tularemia

Rabbit fever is caused by infection with thebacterium Franciscella tularensis. It is a flu-likeillness causing repeated bouts of severe fever,enlarged lymph nodes, conjunctivitis or pneu-monia. Many tick species transmit the diseaseincluding the lone star tick, RockyMountain tick,Pacific coast tick, American dog tick and westernblack-legged tick. All stages of tick vectors arecapable of transmitting the infection. This illness

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primarily infects rabbits, but can be transmittedto humans if in close contact with infectedanimals.

Relapsing fever

The causative agents of relapsing fever are spir-ochaetes called Borrelia, including B. hermsii, B.turicatae and B. parkeri. It occurs worldwide.Infection is typified by repeated bouts of feverlasting approximately one week, alternating withafebrile periods. This is accompanied by chills,headache, muscle aches and joint pain. Soft ticksbelonging to the genus Ornithodoros are respon-sible for its transmission, most notably O. hermsi.

Babesiosis

Protozoan babesias cause pyrexia, severe hae-molytic anaemia, haemoglobinuria and death ofinfected animals, particularly cattle. These dis-eases may be known commonly as Redwater feverand Texas fever. Many species of Babesia havebeen described, the most important of which are:

. Babesia bovis, in Central and South America,Asia, Europe and Australia which is spread insouthern Europe by species of Rhipicephalusand in other areas by various species ofBoophilus.

. Babesia divergens, which occurs in northernEurope and is spread by Ixodes ricinus. Itcauses anaemia and death in cattle.

. Babesia bigemina, which occurs in southernparts of the former USSR and southern Eur-ope, an important vector of which is Boophilusmicroplus. It was also introduced into southernUSA, from which it has since been eradicated.

. In southern Europe, Asia, South Africa andthe USA, Babesia canis causes a disease knownas malignant jaundice in dogs. In Europe it iscarried by Dermacentor marginatus and Rhi-picephalus sanguineus.

. Babesia cabali and B. equi are parasites ofhorses. Babesia equi is generally more patho-genic than B. cabali. In the peracute course of

the disease death may occur within 2 days ofteronset. In the acute form, the disease lasts for 8to 10 days, after which the animal recovers andbecomes a carrier. These parasites are spreadby Rhiphicephalus bursa in the Mediterraneanbasin and Rhiphicephalus evertsi in tropicoe-quatorial Africa.

Adult female ticks acquire infections duringfeeding which they transfer transovarially to theirprogeny. Hosts are then infected by feeding ticklarvae. Calves may be protected in their first yearby antibodies received in colostrum. Variousother species of Babesia parasitise sheep (B. ovis)and humans (B. microti).

Bovine anaplasmosis

This is an important infection of cattle caused bythe rickettsia-like parasites Anaplasma marginaleand A. centrale, which infect the host's ery-throcytes. Although originally tropical and sub-tropical in distribution, they now may be foundworldwide. Anaplasmosis is an acute or chronicfebrile infectious disease producing anaemia andjaundice, which may result in high (30±50%)mortality in infected animals. However, theseverity of the disease depends on the age of thehost; the probability of death increasing with age.Species of Boophilus, Rhipicephalus, Ixodes andDermacentor have all been implicated as vectors.

3.4.3 Systemic effects: tickparalysis

The presence of a neurotoxin in the saliva offeeding female ticks can cause a disease known astick paralysis. The toxin disrupts motor nervesynapses in the spinal cord and blocks neuro-muscular junctions, by preventing the liberationof acetylcholine and causing damage to receptorsites. About 40 or so species may cause tickparalysis, each of which may possess a uniquetoxin. Tick paralysis is caused primarily by Der-macentor andersoni in western North America,Dermacentor variabilis in eastern North America,


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Ixodes holocyclus in Australia and Ixodes ribi-cundus and Rhipicephalus evertsi in South Africa.

The first signs of tick paralysis begin approxi-mately 5 days after attachment and feeding by thefemale tick. Symptoms include peripheral nervedysfunction, respiratory difficulty, cardiovasculareffects, vomiting and changes in body tempera-ture. In humans, paralysis of the lower limbsspreads to the rest of the body within a few hours.Fatal cases have occurred. Most cases of tickparalysis seen by veterinarians are in dogs andcats, but other species can be affected. Tickparalysis is an important cause of death amongstsheep, cattle and goats in various parts of theworld, including the USA, South Africa andAustralia. In these larger species, it is the youngerand smaller animals which are likely to be worstaffected, particularly if a number of femaleparalysis ticks are attached. Tick paralysis alsooccurs in poultry associated with larval feeding ofsome Argas spp. Paralysis in both humans andanimals has been diagnosed after attachment by asingle female tick.

3.4.4 Other systemic effects

Tick-bite wounds may allow the entry of bacteria,especially staphylococci, into the circulation,leading to the development of bacteriaemia andsepticaemia. This is particularly important inlambs, where tick infestation resulting in staphy-lococcal bacteraemia can cause heavy losses. Theorganism spreads to affect many organ systems,including joints and the meninges of the brain andspinal cord, producing arthritis and meningitis,respectively.

3.5 CLASSIFICATION

In general, mites and ticks are considered tobelong to the subclass Acari, in the classArachnida. The Acari is divided into three mainlineages of extant mites: the Opiloacariformes, theParasitiformes and the Acariformes. The Para-sitiformes possess one to four pairs of lateralstigmata posterior to the coxae of the second pairs

of legs and the coxae are usually free. The Para-sitiformes include the ticks, described as the orderIxodida or Metastigmata, and the gamesid mitesor Mesostigmata, which were discussed inChapter 2.

There are about 800 species of Metastigmata,divided into two major families of importance:the Ixodidae, known as the hard ticks, of whichthere are about 650 species, and the Argasidae,known as the soft ticks, of which there are about150 species. Thirteen genera of Ixodidae arerecognised, two of which are of major veterinaryinterest in temperate habitats: Ixodes and Der-macentor. Ixodes is the largest genus of hard tick,containing 217 species, which are widely dis-tributed, particularly in the OldWorld. The genusDermacentor is relatively small with about 30species, most of which are found in the NewWorld. A further four genera, Rhipicephalus,Haemaphysalis, Boophilus and Amblyomma con-tain one or more species of veterinary importance,and the genus Hyalomma is of minor interest intemperate habitats.

The family Argasidae contains four genera ofwhich two contain species of veterinary impor-tance: Argas and Otobius. The genus Ornitho-doros is of minor interest in temperate habitatsand the fourth genus, Antricola, infests cave-dwelling bats in Central and North America.

3.6 RECOGNITION OF TICKS OFVETERINARY IMPORTANCE

Tick identification beyond family and genus isextremely difficult. This difficulty is exacerbatedby the considerable variation that may existwithin species and the problems of identifyingimmature stages. The guide presented below(modified from Varma, 1993) and the speciesdescriptions given in the following pages areintended as a general guide to the ticks of veter-inary interest in temperate habitats. For moredetailed descriptions of species, their immaturestages and the diseases they transmit, readers aredirected to more specialist texts at the end of thischapter.

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Guide to tick identification

1 Hypostome with backwardly directedbarbs; stigmatal shields present behindcoxae of the fourth pair of legs or laterallyabove the coxae of legs 2 or 3; stigmatawithout peritremes; tarsi of the first pairof legs with a sensory pit . . . . . . . . . . . . .

. . . . . . . . . . . . METASTIGMATA (IXODIDA)

Gnathosoma projecting anteriorly andvisible when specimen seen from above;scutum present, covering the dorsal sur-face completely (male) or the anteriorportion only (female); stigmatal plateslarge, situated posteriorly to the coxae ofthe fourth pair of legs . . . . . . IXODIDAE 2

Gnathosoma ventral and not visible whenadult is viewed from above; scutumabsent; dorsal integument leathery; stig-matal plates small, situated anteriorly tothe coxae of the fourth pair of legs; eyes,if present, in lateral folds ARGASIDAE 11

2 Anal groove surrounding the anus distinct,both anteriorly and posteriorly (Figs 3.10±3.12) . . . . . . . . . . . . . . . . . . . . . . . . Ixodes

Anal groove entirely posterior to the anus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

3 Eyes absent . . . . . . . . . . . . . . . . . . . . . . 4

Eyes present . . . . . . . . . . . . . . . . . . . . . . 5

4 Palps short and broad, about twice as wideas segment 2 with obvious outer angula-tion at the base (Fig. 3.9) . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . Haemaphysalis

5 Palps wider than long or, at most, onlyslightly longer than their width . . . . . . 6

Palps much longer than wide . . . . . . . 10

6 Basis capituli usually hexagonal dorsally(Fig. 3.9); medium- sized or small ticks,usually without colour patterns . . . . . . 7

Basis capituli rectangular dorsally (Fig.3.9); large ticks with definite colour pat-terns (Figs 3.13±3.15) . . . . Dermacentor

7 Festoons absent; stigmatal plates round oroval; anal groove faint or obsolete . . . 8

Festoons present; stigmatal plate with atail-like protrusion; anal groove distinct 9

8 Palps with dorsal and lateral ridges; malewith normal legs . . . . . . . . . . . Boophilus

9 Basis capituli without pronounced lateralangles (Fig. 3.9); males with ventralplates; males with coxae of fourth pair oflegs normal (Fig. 3.17) . . Rhipicephalus

10 Palps with second segment less than twiceas long as third segment (Fig. 3.9); scutumwithout pattern . . . . . . . . . . . Hyalomma

Palps with second segment more thantwice as long as third segment (Fig. 3.9);scutum with pattern; male without ven-tral plates (Fig. 3.18) . . . . . Amblyomma

11 Body periphery undifferentiated, withouta definite suture distinguishing the dorsalfrom ventral surface . . . . . . . . . . . . . . 12

Body surface flattened and usually struc-turally different from the dorsal surface,with a definite suture distinguishing dorsaland ventral surface (Fig. 3.19) . . . . Argas

12 Adult integument is granular; hypostomevestigial; nymphal integument spiny;hypostome well developed (Fig. 3.20) . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . Otobius

Adult and nymph integument leathery;hypostome well developed Ornithodoros


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3.7 IXODIDAE

3.7.1 Ixodes

Ixodes is the largest genus in the family Ixodidae,with about 250 species. The second segment of thepalps may be restricted at the base, creating a gapbetween the palp and chelicerae (Fig. 3.9). Themouthparts are long and are longer in the femalethan male. The fourth segment of the palps isgreatly reduced and bears chemoreceptor sensilla.They are small, inornate ticks which do not haveeyes or festoons (Fig. 3.10). Males have severalventral plates which almost cover the ventralsurface. Ixodes can be distinguished from otherixodid ticks by the anterior position of the analgroove (Fig. 3.11). In other genera of the Ixodidaethe anal groove is either absent or is posterior tothe anus.

Ixodes ricinus

The European sheep tick or castor bean tick,Ixodes ricinus, is the commonest tick species innorthern and central Europe, making it an ecto-parasite of major concern to farmers and veter-inarians. It is frequently found in agricultural andforest areas.

Morphology: adults are red-brown but femalesappear light grey when engorged.Males are about2.5±3mm in length and all four pairs of legs arevisible. Unfed females are about 3±4mm in lengthand up to 10mm in length when engorged. Theposterior internal angle of the coxa of the firstpair of legs bears a spur which overlaps the coxaof the second pair of legs (Fig. 3.11). The tarsi areof moderate length (0.8mm in the female and0.5mm in the male) and tapering (Fig. 3.12).

Life-cycle: Ixodes ricinus is a three-host tick andits life-cycle from egg to adult takes 3 years, witheach stage lasting one year. Blood feeding occursat each stage for a period of only a few days.Adult females lay 1000 to 2000 eggs in the soil.These hatch in the summer and larvae feed for thefirst time the following summer. Larvae are about

Fig. 3.9 Diagrammatic dorsal view of the gnathosomaof seven genera of ixodid ticks (from Smart, 1943). (a)

Ixodes, (b) Hyalomma, (c) Dermacentor, (d)Amblyomma, (e) Boophilus, (f) Rhipicephalus and (g)Haemaphysalis.

Fig. 3.10 Adult Ixodes ricinus in dorsal view: (a) maleand (b) female (reproduced from Arthur, 1963).

Fig. 3.11 Ventral view of the coxae of adult male. (a)

Ixodes ricinus, (b) Ixodes hexagonus and (c) Ixodescanisuga (reproduced from Arthur, 1963).

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1mm long, are yellowish in colour and have onlythree pairs of legs. Once hatched, they climb on tovegetation ready to attach to a passing host.Larvae feed for 3 to 5 days, increasing their bodyweight by 10 to 20 times, then drop back on to thevegetation where they digest their blood meal andmoult to become nymphs. Nymphs are about 2mm long, resemble the adults and have four pairsof legs. The nymphs begin to seek a new host afterabout 12 months, again feeding for 3 to 5 days,before dropping off the host and moulting intothe adult stage. The nymphal host is usually largerthan that of the larvae, typically a bird, rabbit orsquirrel. Twelve months later adults begin toquest. Once they have located a host they feed forabout 2 weeks, during which time they also mate.The adult female consumes up to 5ml of hostblood and swells to the size of a broad bean.Males take smaller, intermittent meals andremain on the host for longer periods. Afterdropping to the ground females lay their eggs.Hence, during their 3-year life, I. ricinus are onlyparasitic for about 3 weeks.

Immature stages will feed on any vertebrates,but are most commonly found on rodents orbirds, which move amongst the vegetation.Adults will only feed on large mammals, such assheep, cattle or deer and so climb higher in thevegetation. The availability of livestock, andparticularly sheep, strongly determines theabundance of ticks in most areas.

Ixodes ricinus is essentially a tick of temperateEurope. It requires high humidity to survive,generally above 80%, and the patterns of feedingactivity reflect this requirement. In general, feed-

ing activity is most pronounced in April andMay.Ticks begin to quest when temperatures riseabove a critical threshold of about 78C. This isfollowed by a short period of questing activity,lasting up to 8 weeks. Adults and nymphs startquesting earlier than larvae. However, the dura-tion of the active questing phase can be con-siderably shorter or longer, depending on thenature of the habitat. The high humidityrequirement prevents them being active in sum-mer, and ticks that fail to feed in spring desiccateand do not survive over summer. However, theprecise pattern of seasonal activity is highlyvariable and is strongly influenced by life-cyclestage, habitat, climate and host availability. Inmany parts of its range, a proportion of the tickpopulation feeds in August or September, over-winters as fed ticks and moults the followingsummer. This is seen particularly in the west ofBritain.

As a result of its requirement for high humidity,in general, I. ricinus is associated with areas ofdeciduous woodland containing small mammalsand deer. However, in areas with sufficient rain-fall large populations may occur in moorland andmeadows with rough grazing, where the majorityfeed on livestock.

Pathology: feeding I. ricinus are often foundaround the ears, eyelids and lips of dogs, cats,sheep and cows. In sheep, all stages prefer thehair covered areas to fleeced areas. Larvae con-gregate around rostral areas of the head and thelimbs, while adults attach to the neck and ears.In cattle I. ricinus are most often found in theaxilla and around the udder and populations areusually greater on heifers than on dairy cows andcalves.

Average infestation levels are usually low, witharound 50±80% of a host population carryingjust one or no ticks. However, the distribution ofticks between hosts is usually strongly aggregatedwith a small proportion of hosts carrying themajority of parasites. Infestation levels on indi-vidual hosts of up to 451 on rodents, 2374 onhares and 2072 on individual roe deer have beenrecorded. These high tick densities representpotential blood losses of up to 65%, 13% and

Fig. 3.12 The tarsi of adult male (a) Ixodes ricinus, (b)Ixodes hexagonus and (c) Ixodes canisuga (reproduced

from Arthur, 1963).


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9%, respectively. Hence, anaemia may occur as adirect effect of blood feeding.

Tick feeding sites may become inflamed andinfected with Staphylococcus bacteria causingpyaemia. Ixodes ricinus is a vector of louping-illvirus of sheep, Lyme borreliosis and ehrlichiosis(tick-borne fever) of cattle. It also transmits theprotozoan Babesia divergens which causes Red-water fever in cattle and sheep in western Europe.Since unfed ticks are capable of surviving for longperiods at suitable humidities, disease transmis-sion can occur at any time during the warmermonths. All three developmental stages areknown to bite humans.

Ixodes hexagonus

The hedgehog tick, Ixodes hexagonus, is widelydistributed throughout Europe and north-westAfrica. In Europe to date, I. hexagonus has beenthe most commonly found tick on cats, and thesecond most common tick on dogs.

Morphology: adults are red-brown, with legs thatappear somewhat banded in colour. The scutumis broadly hexagonal (hence the name hexagonus)and, like I. ricinus, the coxae of the first pair oflegs also bears a spur. However, the spur issmaller and does not overlap the coxa of thesecond pair of legs (Fig. 3.11). When engorged thefemale may be up to 8mm in length. Males areabout 3.5±4mm in length. The tarsi are long (0.8mm in the female and 0.5 mm in the male) andsharply humped apically (Fig. 3.12).

Life history: this species is a three-host tickadapted to live with hosts which use burrows ornests. It is primarily a parasite of hedgehogs, butmay also be found on dogs and other smallmammals. The life-cycle is similar to that of I.ricinus: egg, hexapod larva, octopod nymph andadult, occurring over 3 years. All life-cycle stagesfeed on the same host for periods of about 8 days.After dropping to the ground adult females pro-duce 1000 to 1500 eggs over a period of 19 to 25days before death. The ticks may be active fromearly spring to late autumn, but are probablymost active during April and May.

Pathology: on dogs and cats, adult femalesusually attach themselves behind the ears, on thejaws, neck and groin. This species inhabits shel-tered habitats such as burrows and kennels andmay infest pets in large numbers when they areexposed. These ticks are often found to beresponsible when dogs become repeatedly infes-ted with ticks, particularly around the head area.The main host is the European hedgehog, and themovement of this host to urbanised areas mayincrease the risk of both people and their animalsbeing exposed to infectious diseases carried by I.hexagonus. It may also become a more significantpest in places where I. ricinus is absent. Apartfrom localised dermatitis and the risk of woundinfection, further adverse effects are unrecorded.Ixodes hexagonus is a biological vector of Borreliasp. and tick-borne encephalitis.

Ixodes canisuga

The dog tick or Ixodes canisuga is foundthroughout Europe, possibly as far east as Russia.

Morphology: the adults are small and paler incolour than I. ricinus, usually being yellowishbrown. Females are about 2mm in length whenunfed and up to 8mm in length when fullyengorged. Females have no coxal spur and inmales the spur is extremely small (Fig. 3.11). Thetarsi are of moderate length (0.6mm in the femaleand 0.35mm in the male) and are broad withprominent subapical humps (Fig. 3.12).

Life-cycle: this tick is adapted to life in a lair or aden. It may feed on a variety of hosts, includingfoxes and dogs. The life-cycle is similar to that ofI. ricinus: egg, hexapod lava, octopod, nymph andadult, and takes 3 years. Mating takes place in theden and adult males are only rarely found on thehost. Adult females lay relatively small numbersof eggs, probably about 400.

Pathology: infestation may cause dermatitis,pruritus, alopecia and anaemia but it is not animportant vector of disease. It may be a particularproblem in packs of dogs in kennels.

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Ixodes holocyclus

The Australian paralysis tick, Ixodes holocyclus,occurs in parts of New South Wales and coastalQueensland in Australia and can be found on awide host range, including wild rodents, dogs,domestic animals and man. It is most commonlyfound amongst low, leafy vegetation since thisprotects it against sun and wind exposure andmaintains the high humidity required for devel-opment.

Morphology: the unengorged female I. holocyclushas a yellow colouration that becomes grey after ablood meal. Their length is typically less than1 cm, but ticks measuring 1.8 cm have beenrecorded. In the male the body is smaller, flat,yellow-brown and the scutum covers the entiredorsal surface. There are four pairs of legs whichextend from the elongated capitulum in straightlines. The first and last pair are considerablydarker than the middle two. The body is oval, andthe scutum widens at the rear. The anal groove isV-shaped and festoons are absent.

Life-cycle: the life-cycle takes an average of oneyear to complete, depending on climatic condi-tions. Oviposition begins 11 to 20 days afterdetachment at a rate of 20 to 200 eggs per day.The adult female dies a few days after ovipositionceases. After an incubation period of 50 to 110days the eggs hatch. The larvae harden then climbonto vegetation to find the first host. After 4 to 6days of feeding the larva drops to the ground andmoults to become a nymph. The duration of thelarval stage is temperature dependent. Nymphsare very active 5 to 6 days after moulting andreadily attach to another host. Over the next 4 to7 days the nymph feeds and after a further 3 to 11weeks the nymph moults to become an adult. Dryconditions prolong this period and may be fatal.The adult attaches to another host within 7 to 77days. Feeding can last for between 6 and 30 days,the period being longest in cool weather. In warmweather the female engorges rapidly. After about3 days of feeding the female begins to producetoxin, causing paralysis if the host is not immune.Males do not engorge, instead they attach for

short periods as they search for a potential mate.Humid conditions are essential for survival of allstages of this tick. An ambient temperature of278C is thought to be optimal for rapid develop-ment. Temperatures above 328C or below 78C arefatal after a few days.

Pathology: despite their low numbers on a host, I.holocyclus infestations can kill cattle, particularlycalves, and small domestic animals. Just 50 larvaeor five nymphs will kill a 40 g rat, and largernumbers of either can cause paralysis in dogs andcats. Ixodes holocyclus is the main cause of tickparalysis in Australia. Its paralysing toxin hasbeen reported to affect at least 20 000 domesticanimals annually. Generally only the adult stageinfests cattle, with the worst outbreaks in latewinter, spring and summer. Ixodes holocyclus isalso a vector for Coxiella burnetii (Q fever) andRickettsia australis (Queensland tick typhus).

Ixodes scapularis (dammini)

The `shoulder tick' or `black-legged ticked' para-sitises cattle, sheep, horses, dogs, cats, birds andreptiles. It is commonly found in and nearwooded areas throughout north America.

Morphology: females are typically 3±3.5mm inlength, while males are slightly smaller. Bothsexes have a dark brown colouration, though thefemale is slightly redder on its posterior half.Adults can be identified by their large mouth-parts, which are longer than the basis capituli,and an anal grove in the ventral side that forms anarch over the anus. All developmental stages canenlarge to two to three times their normal sizeafter a blood meal.

Life-cycle: it is a three-host tick with a 2-year life-cycle. Eggs deposited in the spring hatch into six-legged larval ticks in summer months, whichattach to small mammals or birds to obtain theirfirst blood meal. The larvae overwinter beforemoulting to become a nymph. Nymphs moult tothe adult stage that same summer, then attach to alarger mammalian host where they remain


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throughout the winter. Mating can occur on oroff the host.

Pathology: Ixodes scapularis(dammini) inflicts avery painful bite. Nymphal and adult stages ofthis tick are the most common vector for Lymedisease in North America. They are also impli-cated in the transmission of Francisella tularensis.

Other Ixodes species of veterinaryinterest

. Ixodes rubicundus is found in South Africa,particularly in hill and mountain areas, and isthe primary cause of tick paralysis here.

. The taiga tick, Ixodes persulcatus, is morpho-logically very similar to I. ricinus, but thefemale adult has a straight or wavy genitalopening rather than arched as in I. ricinus. Ithas a similar life history to I. ricinus, althoughadults are rarely active during autumn. It has amore easterly distribution, being widespreadthroughout eastern Europe, Russia and as fareast as Japan. Ixodes persulcatus is a majorvector of the human diseases Russian spring±summer encephalitis virus and Lyme borre-liosis.

. Ixodes pacificus, the western black-legged tick,is commonly found in the western US andBritish Columbia. This three-host tick affectsrodents, lizards and large mammals such ashorses, deer and dogs. It is known to be avector of Lyme disease and the rickettsiaresponsible for equine granulocytic ehrliciosis.

3.7.2 Dermacentor

Ticks of the genusDermacentor are medium-sizedto large ticks, usually with ornate patterning. Thepalps and mouthparts are short and the basiscapituli is rectangular (Fig. 3.9). Festoons andeyes are present. The coxa of the first pair of legsis divided into two sections in both sexes. Coxaeprogressively increase in size from I to IV. Themales lack ventral plates and, in the adult male,the coxa of the fourth pair of legs is greatly

enlarged. Most species of Dermacentor are three-host ticks, but a few are one-host ticks. The genusis small with about 30 species, most of which arefound in the New World. Several of the speciesare directly associated with Rocky Mountainspotted fever, Q fever, tularaemia and Coloradotick fever. The salivary secretions of some speciesmay produce tick paralysis.

Dermacentor variabilis

The American dog tick, Dermacentor variabilis, isparticularly abundant in central and easternstates of the United States of America, althoughits range may extend as far north as Canada. Theyare most commonly found in open areas with tallgrass or brush.

Morphology: Dermacentor variabilis is an ornatetick, with a base colour of pale brown and a greycolour pattern (Fig. 3.13). Males are about 3±4mm in length and females about 4mm in lengthwhen unfed, and 15mm in length when engorged.The mouthparts are short. The basis capituli isshort and broad (Fig. 3.9). The coxae of the firstpair of legs have well-developed external spurs.

Life-cycle: Dermacentor variabilis is a three-hosttick. It feeds on rodents and lagomorphs duringits larval and nymphal life stages. Adults areimportant parasites of wild and domestic carni-vores. Adult females feed for 1 to 2 weeks, during

Fig. 3.13 Adult Dermacentor variabilis: (a) dorsal viewof female, (b) dorsal view of male (reproduced fromArthur, 1962).

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which time mating occurs on the host. Femalesthen drop to the ground where they lay approxi-mately 4000±6000 eggs. After about 4 weeks theeggs hatch and larvae begin to quest. Larvae feedfor about 4 to 5 days, before dropping to theground and moulting. Nymphs feed for about 5to 6 days, before leaving the host. Underfavourable conditions, the life-cycle from egg toadult may take only 3 months.

Pathology: Dermacentor variabilis is a commonparasite of dogs and may cause tick paralysis. Itoccasionally parasitises cattle and may transmitbovine anaplasmosis. It is also an importantvector of Rickettsia rickettsii (Rocky Mountainspotted fever) in the USA and is able to transmitthe bacteria which causes tularemia (hunter'sdisease). Adults first are abundant from late Aprilthrough to June, though they will continue to bepresent in small numbers throughout summer.These ticks tend to congregate around the headand neck.

Dermacentor andersoni

The Rocky Mountain wood tick, Dermacentorandersoni, is widely distributed throughout thewestern and central parts of North America fromMexico as far north as British Columbia. It isparticularly common amongst damp, grassy,brush-covered areas.

Morphology: Dermacentor andersoni is an ornatetick, with a base colour of brown and a greypattern (Fig. 3.14). Males are about 2±6mm inlength and females about 3±5mm in length whenunfed, and 10±11mm in length when engorged.The mouthparts are short. The basis capituli isshort and broad (Fig. 3.9). The legs are patternedin the same manner as the body. The coxae of thefirst pair of legs have well-developed external andinternal spurs.

Life-cycle: it is a three-host tick. Immature stagesprimarily feed on small rodents, while adults feedlargely on wild and domestic herbivores. Matingtakes place on the host, following which femaleslay up to 6500 eggs over about 3 weeks. The eggs

hatch in about 1 month, and the larvae begin toquest. Larvae feed for about 5 days, beforedropping to the ground and moulting to theoctopod nymphal stage. One- and two-yearpopulation cycles may occur. Eggs hatch in earlyspring and individuals that are successful infinding hosts pass through their larval stages inspring, their nymphal stages in late summer andthen overwinter as adults in a one-year cycle.Nymphs that fail to feed, overwinter and form aspring-feeding generation of nymphs the follow-ing year. Unfed nymphs may survive for up to ayear. Dermacentor andersoni is most common inareas of scrubby vegetation, since these attractboth the small mammals required by the imma-ture stages and the large herbivorous mammalsrequired by the adults.

Pathology: in cattle, D. andersoni may cause tickparalysis, particularly in calves, and may beresponsible for the transmission of bovine ana-plasmosis, caused by Anaplasma marginale. Italso transmits the Colorado tick fever virus andthe bacteria that cause tularemia. Dermacentorandersoni is the chief vector of Rickettsia rickettsii(Rocky Mountain spotted fever) in western USA.Each female ingests about 0.5±2.0ml of bloodand high infestation levels may therefore causeanaemia. Secondary infections and/or myiasismay occur in the bite wounds. Adult numberspeak in May, declining by July. Larvae andnymphs appear later and have usually dis-appeared by late summer.

Fig. 3.14 Adult Dermacentor andersoni: (a) dorsal viewof female, (b) dorsal view of male (reproduced fromArthur, 1962).


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Dermacentor albipictus

Known as the winter tick or elk, moose or horsetick, Dermacentor albipictus is found widely dis-tributed across much of North America fromnorthern Mexico to Canada. It is particularlycommon in most areas that experience freezingwinter weather and affects large mammals such aselk, moose, horses, cattle, antelopes and deer.

Morphology: similar to D. variabilis and D.andersoni, D. albipictus is an ornately patternedspecies with short mouthparts and a rectangularbasis capituli. In the adults of both sexes the coxaof the first pair of legs has an enlarged spur(bidentate) and in the male, coxae increase in sizefrom 1 to 4.

Life-cycle: Dermacentor albipictus is a one-hosttick. It feeds only in winter, usually betweenOctober and March/April, on horses, deer andrelated large mammals. Eggs hatch in 3 to 6 weeksand the larvae remain inactive until autumn, fol-lowing which they begin to quest. Feeding andmoulting occur on the same host animal and adultfemales mature about 6 weeks after initial larvalattachment. Adult females drop off the host andlay their eggs the following spring.

Pathology: heavy infestations with D. albipictusmay cause death from anaemia and it may be avector of Rickettsia rickettsii (Rocky Mountainspotted fever), tick paralysis and `winter' ana-plasmosis in domestic cattle. Heavy infestationscause hair loss and a condition known as `ghostmoose' in northern parts of the USA.

Dermacentor reticulatus

This species occurs in many parts of westernEurope, extending eastwards to Kazakhstan,particularly in wooded areas.

Morphology: both sexes are ornate, white withvariegated brown splashes (Fig. 3.15). In the adultfemale the ornate scutum is about 1.6mm inlength. In the adults of both sexes the coxa of the

first pair of legs has an enlarged spur (bidentate).The other coxae have short internal spurs thatbecome progressively smaller in legs 2 to 4. Thecoxae of the fourth pair of legs are large with anarrow, tapering external spur.

Life-cycle: Dermacentor reticulatus is a three-hostspecies. Adults parasitise larger domestic and wildmammals, cattle, horses, sheep, goats and pigs.Copulation takes place on the host. Females feedfor 9 to 15 days. Oviposition may last 6 to 40days, depending on temperature and humidity,with oviposition rate peaking on about the fifthday. A female may produce 3000 to 4500 eggs,though the total number of eggs produced isproportional to the size of the tick. Larvae hatchfrom the egg after about a month and withinabout 2 weeks begin questing. The feeding activ-ity of nymphs can last from midsummer to lateautumn. Immature stages feed on a variety ofsmall mammals, such as small rodents andcarnivores, and occasionally birds.

Pathology: it is particularly important as anectoparasite of cattle and may be found alongtheir backs in early spring. It transmits Babesiainfections to cattle, horses, sheep and dogs.

Fig. 3.15 Dorsal view of the gnathosoma and scutumof adult female (a) andmale (b)Dermacentor reticulatus(reproduced from Arthur, 1962).

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Other Dermacentor species ofveterinary interest

. The distribution of Dermacentor marginatus inwestern Europe is similar to that of D. reticu-latus. It is found in lowland mixed and decid-uous forest areas. It is a vector of the Russianspring±summer encephalitis virus and ofSiberian tick typhus.

. Dermacentor silvarum and Dermacentor nut-talli may be important ectoparasites in Eur-asia, with D. silvarum being more common inthe west and D. nuttalli in the east. Both tickscommonly parasitise lagomorphs, wildrodents, dogs, domestic animals and man.

. Dermacentor occidentalis, the Pacific Coasttick, is a three-host tick found in the south-western states of the USA. Immature stagescommonly feed on rodents, especially squir-rels, whereas adults may be found on largerdomestic animals. It may be a vector of bovineanaplasmosis.

3.7.3 Haemaphysalis

Ticks of the genus Haemaphysalis inhabit humid,well-vegetated habitats in Eurasia and tropicalAfrica. They are three-host ticks, with the larvaeand nymphs feeding on small mammals and birdsand adults infesting larger mammals and,importantly, livestock. Most species of the genusare small, with short mouthparts and a rectan-gular basis capituli (Fig. 3.9). Ventral plates arenot present in the male. Spiracular plates arerounded or oval in females and rounded orcomma-shaped in males. Like Ixodes spp., theseticks lack eyes, but they differ in having festoonsand a posterior anal groove. There are about 150species, found largely in the Old World, with onlytwo species found in the New World.

Haemaphysalis punctata

This species is widely distributed throughoutEurope, Scandinavia, North Africa and centralAsia.

Morphology: Haemaphysalis punctata is a small,inornate tick, with festoons, no eyes and shortmouthparts (Fig. 3.16). Sexual dimorphism is notpronounced. The adults of both sexes are about3 mm in length, the female reaching about 12mmin length when engorged. The basis capituli isrectangular, about twice as broad as long. Thesensory palps are short and broad, with the sec-ond segment extending beyond the basis capituli.The males have no ventral shields. The analgroove is posterior to the anus. The coxae of thefirst pair of legs have a short, blunt internal spur,which is also present on the coxae of the secondand third pair of legs and which is enlarged andtapering on the coxae of the fourth pair of legs.In the male the spur may be as long as the coxa(Fig. 3.16).

Life-cycle: Haemaphysalis punctata is a three-hosttick, feeding once in each of the larval, nymphaland adult life-cycle stages. After each feed it dropsfrom the host. Engorgement on the host may take6 to 30 days to complete and each female lays3000 to 5000 eggs. Large mammals, particularlycattle and sheep, are the preferred hosts foradults. Larvae and nymphs are more commonlyfound on small mammals and birds.

Pathology: in southern England and Wales H.punctata may be responsible for the transmissionof Babesia major in cattle and B. motasi in sheep;in other areas of Europe it transmits B. bigeminain cattle, B. motasi in sheep and Anaplasma

Fig. 3.16 Dorsal view of the gnathosoma and scutumof adult female (a) and male (b) Haemaphysalis

punctata. (c) Ventral view of the coxae of an adult male(reproduced from Arthur, 1963).


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marginale and A. centrale in cattle. It may alsocause tick paralysis.

Other Haemaphysalis species ofveterinary interest

. The rabbit tick, Haemaphysalis leporispalus-tris, is widely distributed throughout Southand North America, as far north as Alaska. Allstages primarily parasitise wild rabbits andhares and are only occasionally found ondomestic animals. They are often found inlarge numbers, up to 5000 per host, causingweakness, emaciation and sometimes death.They are thought to be a vector of Francisellatularensis.

. The bird tick,Haemaphysalis chordeilis, occurson game birds and poultry in North America,and may occasionally be found on cattle.

. The yellow dog tick, Haemaphysalis leachi, iscommon in Africa and parts of Asia and is avector of Babesia canis.

. Haemaphysalis bispinosa may cause proble-matic infestation of cattle and other domesticanimals in New Zealand.

. Haemaphysalis longicornis mainly affects cat-tle, horses, deer, donkeys and dogs, but alsoinfests sheep, pigs, goats and humans. Themain result of infestation is tick worry. Thislowers production in cattle and tick bitesdamage hides.

3.7.4 Rhipicephalus

The genus is composed of about 60 species, all ofwhich were originally endemic to the Old Worldand, for the most part, distributed throughoutsubSaharan Africa. However, many species havenow been introduced into a range of new habitatsworldwide. They are of veterinary importancesince they act as reservoirs and vectors of anumber of disease pathogens. The basis capituli ishexagonal (Fig. 3.9) and, in the male, pairedplates are found on each side of the anus. Theyare not ornate. Palps are short and eyes andfestoons are usually present. Spiracular plates are

comma-shaped. They infest a variety of mammalsbut seldom birds or reptiles. Most species arethree-host ticks but some species of the genus aretwo-host ticks. The only species of veterinaryinterest in temperate habitats is Rhipicephalussanguineus.

Rhipicephalus sanguineus

The brown dog tick, Rhipicephalus sanguineus, isthought to be the most widely distributed tickspecies in the world.

Morphology: it is a yellow, reddish or blackishbrown tick with hexagonal basis capituli andshort mouthparts. It is usually inornate with eyesand festoons present (Fig. 3.17). Unfed adultsmay be 3±4.5mm in length, but size is highlyvariable. Engorged females may reach a length of12mm. The coxa of the first pair of legs has alarge external spur (bifurcate). The legs maybecome successively larger from the anterior tothe posterior pair. The tarsi of the fourth pair oflegs possess a marked ventral tarsal hook (Fig.3.17). The anal groove encircles only the posteriorhalf of the anus and then extends into a mediangroove.

Life-cycle: Rhipicephalus sanguineus is a three-host tick with a very wide host range, which isunusual for an ixodid tick. However, it is parti-cularly associated with dogs, especially those

Fig. 3.17 Dorsal view of the gnathosoma and scutumof adult female (a) and male (b) Rhipicephalussanguineus. (c) Ventral view of the coxae and

trochanters of an adult male. Tarsi and metatarsi of thefourth pair of legs of an adult male (d) and female (e)(reproduced from Arthur, 1962).

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housed in kennels. It feeds on dogs during allthree life stages, but drops off and reattachesduring each stage. Eggs are deposited in thecracks of kennel walls or other areas used fre-quently by dogs, in batches of up to 5000. Larvaehatch from the egg within 20 to 30 days and beginto quest shortly after. Adult females are usuallyattached to the host for just one week. Males mayremain on the host for months. Larvae, nymphsand adults may infest the same host. Underfavourable conditions the life-cycle may requirejust 63 days, hence several generations may beexpected each year. It survives protected withinthe domestic environment. Without such protec-tion it would not be able to survive in temperatehabitats. Adults have been known to survive forup to 568 days without feeding.

Pathology: it is a very common parasite of dogsworldwide and is a vector of Babesia canis,causing haemolytic anaemia and jaundice indogs, and also Ehrlichia canis. On dogs Rhipice-phalus sanguineus is often found in the ears andbetween the toes. Immature stages prefer thepelage of the neck. It has the potential to buildup high numbers in kennels, hence very highinfestation levels can occur. Dogs may harbourall stages of the tick simultaneously. Rhipice-phalus sanguineus transmits East Coast feveramong cattle and the virus of Nairobi sheep dis-ease in East Africa. It is also a vector of RockyMountain spotted fever in some areas of theUSA and Mexico. Rhipicephalus spp. are vectorsof Babesia perroncitoi and Babesia trautmanni inpigs. Most animals, with the exception of guineapigs, appear unable to demonstrate resistance tothis tick species.

3.7.5 Boophilus

This small genus contains only five species whichare often known as `blue ticks'. They are one-hostticks and are found predominantly in tropical andsubtropical habitats. The only species of veter-inary interest in temperate habitats is Boophilusannulatus.

Boophilus annulatus

The cattle tick or cattle fever tick, Boophilusannulatus, is thought to have originated in centraland southern Europe and been introduced intoNorth America, where it is now confined tosouthern states.

Morphology: Boophilus annulatus is a small,brown, inornate tick with simple eyes but nofestoons. Unfed adults may be only 2 or 3mmlong, reaching lengths of up to 12mm whenengorged. The basis capituli is hexagonal dorsally(Fig. 3.9). The mouthparts are short and thecompressed palps are ridged dorsally and lat-erally. Adanal and accessory shields are present inthe male.

Life-cycle: it is a one-host tick which feeds pri-marily on cattle, though horses, sheep, goats anddeer may also act as hosts. From larva to adulttakes approximately 18 to 20 days. Mating takesplace on the host. The engorged female thendrops to the ground to oviposit 2000 to 3000 eggs.The entire life-cycle may be completed in as littleas 6 weeks and between two and four generationsmay occur per year, depending on climate.

Pathology: it is an important vector of Texascattle fever caused by Babesia bigemina and B.bovis. Skin irritation induces scratching and lick-ing, sometimes leading to secondary infections.Severe infestations may cause anaemia.

Other Boophilus species of veterinaryinterest

Boophilus microplus, the tropical or southerncattle tick, is widely distributed in the southernhemisphere and the southern states of the USAand is considered one of the most serious externalparasites of Australian cattle.

Morphology: Boophilus microplus is an unorna-mented tick. It has a hexagonal basis capitulumand no anal groove. Mouthparts are short andfestoons and eyes are absent.


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Life-cycle: Boophilus microplus is a one-host tick.Engorged females detach from the host and laybetween 2000 and 4500 eggs. Oviposition occursover a period of 12 to 14 days. The eggs hatch in 2to 6 weeks if conditions are suitable and may takeup to 145 days in unfavourable conditions. Fromthe attachment of the larva to engorgement of theadult female requires 3 weeks. After a blood mealthe engorged female will weigh up to 250 timesher unfed weight. The entire life-cycle can becompleted within 2 months, with the period spenton the host ranging from 17 to 52 days.

Pathology: this tick species most commonlyparasitises cattle, but also infests horses, donkeys,sheep, goats, dogs and pigs. It is an importantvector of bovine babesiosis. In horses, B. micro-plus causes tick worry and irritation. Other ani-mals show few symptoms. Although present allyear round, populations reach their peak insummer.

3.7.6 Amblyomma

Members of this genus are large, often highlyornate, ticks with long, often banded, legs. Unfedfemales may be up to 8mm in length and whenengorged may reach 20mm in length. Eyes andfestoons are present. Males lack ventral plates.They have long mouthparts with which they caninflict a deep, painful bite which may becomesecondarily infected. There are about 100 speciesofAmblyomma, largely distributed in tropical andsubtropical areas of Africa. However, oneimportant species is found in temperate NorthAmerica.

Amblyomma americanum

The lone star tick, Amblyomma americanum, socalled because of a single white spot on thescutum of the female, is widely distributedthroughout central and eastern USA. All stagesmay be found on wild and domestic animals andbirds, though larval populations are mostfrequently found on wild small mammals.

Morphology: the female is reddish brown in col-our. On the scutum are two deep parallel cervicalgrooves and a large pale spot at its posteriormargin (Fig. 3.18). This spot is iridescent, and soits colour depends on the light. The male is smallwith two pale symmetrical spots near the hindmargin of the body, a pale stripe at each side anda short oblique pale stripe behind each eye. Inboth sexes, coxa I has a long external spur and ashort internal spur and the mouthparts are muchlonger than the basis capituli.

Life-cycle: it is a three-host tick. Females ovipositbatches of 2000 to 10 000 eggs which hatch within3 or 4 weeks. The larvae cluster on vegetationand, on finding a suitable host, attach and feedfor up to a week. Female adults are fully engorgedafter 3 to 4 weeks of feeding, each taking 0.5±2.0ml of blood. During this period mating occurs.Larvae and nymphs feed on rodents, rabbits andground-inhabiting birds. Adults feed on largermammals such as deer, cattle, horses and sheep.Feeding larvae, nymphs and adults are activebetween early spring and late summer in distinctperiods corresponding with the feeding activity ofeach stage. There is usually a single generation peryear. It is particularly common in wooded areas.

Pathology: this tick is most commonly found onthe ears, flanks, head and belly. Each femaleingests 0.5±2.0ml of host blood, so large numberscan cause anaemia.Amblyomma americanum is an

Fig. 3.18 Dorsal view of the gnathosoma and scutumof adult female (a) and male (b) Amblyomma

americanum (reproduced from Arthur, 1962).

Ticks (Acari) 77

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important vector of Rickettsia rickettsii (RockyMountain spotted fever) and Francisella tular-ensis (tularaemia). It has also been implicated as avector of Borrelia burgdorferi (Lyme disease), Qfever, canine ehrlichiosis and human monocyticehrlichiosis. Bites may cause tick paralysis and insome areas wounds may be invaded by thescrewworm fly, Cochliomyia hominivorax. Infes-tation has been shown to reduce weight gain incattle, particularly Hereford steers.

Other Amblyomma species of veterinaryinterest

The Gulf Coast tick, Amblyomma maculatum, isfound in southern and central states of the USA,Mexico and South America. Larvae and nymphsfeed on small mammals and ground-nesting birds.Adults feed on cattle, horses, sheep and carni-vores. It is a three-host species with long mouth-parts which causes major problems in livestockbecause of its painful bite and the large quantityof blood removed. Its feeding can cause deformityof the ear in cattle, known as `gotch ear'. Adultsappear in late spring and throughout the summer.

3.7.7 Hyalomma

This is a genus of minor veterinary importance intemperate habitats. Species of this genus aremedium-sized or large ticks, with eyes and longmouthparts. The males have ventral plates oneach side of the anus. Hyalomma spp. are usuallytwo-host ticks, though some species may use threehosts. They are most commonly found on thelegs, udder, tail or perianal region. About 20species are found, usually in semi-desert lowlandsof central Asia, southern Europe and NorthAfrica. They can survive exceptionally cold anddry conditions. Adults of a number of speciesparasitise domestic mammals. Hyalomma aegyp-tium may be introduced on tortoises. Hyalommatruncatum causes sweating sickness.

3.8 ARGASIDAE

3.8.1 Argas

Species of the genus are usually dorsoventrallyflattened, with definite margins which can be seeneven when the tick is engorged. The cuticle iswrinkled and leathery. Most species are nocturnaland are parasites of birds, bats, reptiles or, occa-sionally, small insectivorous mammals. Mostspecies seldom attack humans. Species of thisgenus are usually found in dry, arid habitats.

Argas persicus

The fowl tick, Argas persicus, is of considerableveterinary importance as a parasite of poultry andwild birds. It originated in the Palaearctic but hasbeen introduced with chickens into most parts ofthe world and is now found throughout Europe,Asia and North America. However, in NorthAmerica a number of very closely related speciesArgas sanches, Argas radiatus and Argas miniatusmay also be present. It is also known as `chickentick', `adobe tick', `tampan' and `blue bug'.

Morphology: the unfed adult is reddish brown,turning slate blue when fed. The female is about8mm in length and the male about 5mm. Themargin of the body appears to be composed ofirregular quadrangular plates or cells and noscutum is present. Unlike hard ticks, the foursegments of the pedipalps are equal in length. Thestigmata are situated on the sides of the bodyabove the third and fourth pairs of legs. Theintegument is granulated, leathery and wrinkled.The hypostome is notched at the tip and themouthparts are not visible when the tick is viewedfrom above (Fig. 3.19).

Life-cycle: it is nocturnal and breeds and sheltersin cracks and crevices in poultry houses. Femalesdeposit batches of 25 to 100 eggs in cracks andcrevices in the structure of a poultry house. Up to700 eggs may be produced by a single female atintervals, each oviposition preceded by a bloodmeal. After hatching, larvae locate a host andremain attached and feed for several days. After


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feeding they detach, leave the host and shelter inthe poultry house structure. Several days laterthey moult to become first-stage nymphs. Theythen proceed through two or three nymphalstages, interspersed with frequent nightly feeds,before moulting to the adult stage. Adult malesand females feed about once a month, but cansurvive for 5 years or more without a blood meal.Females can become completely engorged within30 to 45 minutes. Under favourable conditionsthe life-cycle can be completed in about 30 days.All stages of these ticks remain around theroosting area of poultry, quiescent in the day andactively feeding at night. Argas persicus can sur-vive in empty poultry housing for years and maytravel long distances to find their hosts.

Pathology: this tick can undergo rapid increasesin abundance, passing through one to tengenerations per year, particularly where birds arepresent all year round. General symptoms includeirritation, decreased egg production and in severecases anaemia and tick paralysis. Each tickrequires a considerable quantity of blood forengorgement, and therefore heavy infestations

can take enough blood to bring about the death oftheir host. It is a vector of Borrelia anserina andAegyptianella pullorum among poultry, as well asavian spirochaetosis. The spirochaetes may bepassed from one generation of ticks to the nextthrough the egg, and transmitted to the host bybiting or by faecal contamination. Though com-mon pests of chickens and turkeys, they are notusually a significant veterinary problem, except insmall housed flocks. It will bite humans, parti-cularly if living in proximity to an infested flock.

Argas reflexus

This species is known as the pigeon tick becauseof its close association with this host, Columbalivia. It is abundant in the Middle and Near East,whence it has spread into Europe and most ofAsia.

Morphology: the adult Argas reflexus is between 6and 11mm in length and may be distinguishedfrom the fowl tick, Argas persicus, by its bodymargin, which is composed of irregular grooves,and the hypostome, which is not notched apically(Fig. 3.19). It is reddish brown in colour withpaler legs.

Life-cycle: the life-cycle is similar to that of A.persicus. The number of nymphal stadia rangesfrom two to four, with the fewest occurring incooler temperatures. The egg to adult life-cyclecan take up to 11 years to complete. It is noc-turnal and during the day lives in crevices in thepigeon house or nest material. It can withstandprolonged periods of starvation. Engorgedfemales diapause between July and August. Ifoviposition has already commenced, egg layingstops and resumes the following year without theneed for another blood meal.

Pathology: heavy infestations may cause deathfrom anaemia. It may also transmit fowl spir-ochaetosis. This tick occasionally bites humans,causing allergy. Its northern distribution throughEurope is limited by the temperature requirementof its eggs and oviposition in summer months,since A. reflexus eggs show low levels of cold

Fig. 3.19 Female Argas reflexus: (a) dorsal and (b)

ventral view (reproduced from Arthur, 1962). MarginofArgas reflexus (c) andArgas persicus (d). Hypostomeof female Argas reflexus (e) and Argas persicus (f)(reproduced from Arthur, 1963).

Ticks (Acari) 79

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tolerance. Typical winter temperatures of 38Ccause approximately 50% mortality in A. reflexuseggs.

3.8.2 Otobius

This small genus contains only two species: Oto-bius megnini and Otobius lagophilus.

Otobius megnini

The spinose ear tick is found through western andsouth-western North America and Canada, whereit originated. It has subsequently been introducedto southern Africa and India. It most commonlyinfests wild and domestic animals, includingsheep, cattle, dogs and horses. It has been foundin humans.

Morphology: the adult body is rounded poster-iorly and slightly attenuated anteriorly. Adultfemales range in size from 5 to 8mm in length;males are slightly smaller. They have no lateralsutural line and no distinct margin to the body.Nymphs have spines (Fig. 3.20). In adults thehypostome is much reduced and the integument isgranular. The body has a blue-grey colourationwith pale yellow legs and mouthparts.

Life-cycle: Otobius megnini uses a single host,primarily cattle or horses, but it may also attack

sheep or domestic cats and dogs as well as wildherbivores and canines. It is often associated withstables and animal shelters. Females lay their eggsin cracks and crevices in the walls of animalshelters, under stones or the bark of trees. Larvaeattach to a passing host and crawl deep into theouter ear. Here they feed for 5 to 10 days and thenmoult to first- and second-stage nymphs. From 5weeks to several months may be spent on the hostduring the larval and nymphal stages. The sec-ond-stage nymphs leave the ear and seek theshelter of a suitably protected site where theymoult to become adult. Adults do not feed.

Pathology: the larvae and nymphs feed in theexternal ear canal of the host, producing a severeotitis externa. Affected animals present palpationaround the ears and may even develop convul-sions. Feeding is disrupted and animals rapidlylose condition. Waxy exudate and debris arefound in the ear, impeding hearing. Hosts willshake their heads or hold it to one side. Byscratching their ears animals can cause local skintrauma and occasionally perforate the ear drum.This can lead to infection of the ear canal(including myiasis), ulceration and in some casesdeath from meningitis. In horses, clinical signs areoften mistaken for signs of colic.

Otobius lagophilus

Otobius lagophilus is an ectoparasite of rabbits inwestern USA and Canada.

3.8.3 Ornithodoros

This genus includes about 90 species, almost all ofwhich are found in tropical and subtropicalhabitats in both the Old and New World and areof only minor importance as parasites of domesticanimals in temperate habitats. MostOrnithodorosspecies are found in Africa, commonly in theburrows of warthogs and bush pigs, though otherspecies may be found in Central and SouthAmerica and the Rocky Mountain states of theUS. They are nocturnal and the mouthparts arewell developed. The integument has a wrinkled

Fig. 3.20 Dorsal view of nymphal Otobius megnini andpart of the integument showing hairs and spines(reproduced from Arthur, 1962).


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pattern which runs continuously over the dorsaland ventral surfaces. There is no distinct lateralmargin to the body, which appears sac-like.Species of this genus are found largely in habitatssuch as dens, caves, nests and burrows, and so arenot normally a problem for most domestic ani-mals. Several species of Ornithodoros inflictpainful bites and may be major vectors of relap-sing fever.

Ornithodoros hermsi

Morphology: the adult female O. hermsi is typi-cally 5 to 6mm in length and 3 to 4mm wide. Themale is morphologically similar, though slightlysmaller. When engorged their light sandycolouration takes on a greyish-blue hue.

Life-cycle: Ornithodoros hermsi is a three-hosttick. It is able to survive for long periods withouta blood meal, extending the duration of its lifecycle. Immature stages may live as long as 95 dayswithout food and the adults more than 7 months.

Pathology: it is thought to transmit African swinefever, leading in most cases to death. This speciesprimarily attacks wild animals, though it will bitehumans and it is an important vector of humanrelapsing fever.

Ornithodorus coriaceus

The Pajahuello tick of south-western NorthAmerica is associated with coastal and sierrafoothill habitats. It most commonly feeds oncattle and deer.

Morphology: it has a rounded body with no sharplateral margins. The body is generally flatteneduntil engorgement, when the dorsal surfacebecomes domed. The mouthparts cannot be seenwhen viewed from above. The integument has awrinkled texture.

Life-cycle: it is found in and around the restingplaces of its mammalian host. Eggs are depositedin cracks and crevices of buildings. The larvae

hatch, feed and moult to the nymphal instar.Adults will feed repeatedly for periods of about 10minutes and may remain on the host for up to 4years. They are capable of surviving for 3 years inbetween blood meals.

Pathology: it inflicts a painful bite, resulting inlocalised inflammation and reddening. They aremost commonly found on posterior areas of theirhosts such as the hind legs and lower back. Theywill readily feed from almost any warm-bloodedmammal, though they are particularly proble-matic in cattle and deer. They may bite humans ifthey come in contact with host bedding sites,possibly transmitting Q fever. They are known tobe vectors of the pathogens causing relapsingfever and African swine fever and to cause tickparalysis.

Other Ornithodoros species ofveterinary interest

. Ornithodoros parkeri and O. turicata (inwestern states of the USA), along with O.hermsi (of the Rocky Mountains and PacificCoast of North America), attack rodents andare vectors of various species of Borrelia.

. In parts of Africa O. savignyi and the O.moubata species complex are important ecto-parasites of cattle and humans.

. Ornithodoros turicata and O. talaje transmitrelapsing fever in southern areas of the USA,between Florida and California and northwardto Colorado, and Utah, and O. parkeri trans-mits the disease in the north-western area.


Arthur, D.R. (1962) Ticks and Disease. InternationalSeries of Monographs on Pure and Applied Biology,Vol. 9. Pergamon Press, London.

Arthur, D. R. (1963) British Ticks. Butterworths,

London.Baker, E.W., Camin, J.H., Cunliffe, F., et al. (1958)Guide to the Families of Mites. Institute of Acarol-

ogy, Contribution No 3. University of Maryland,Maryland.

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Bennett, C.E. (1995) Ticks and Lyme disease. Advancesin Parasitology, 36, 343±405.

Herms, W.B. & James, M.T. (1961) Medical Entomol-

ogy. MacMillan, New York.Hoogstraal, H. (1966) Ticks in relation to human dis-eases caused by viruses. Annual Review of Entomol-

ogy, 11, 261±308.Hoogstraal, H. (1967) Ticks in relation to humandiseases caused by Rickettsia species. Annual Reviewof Entomology, 12, 377±420.

Klomper, J.S.H., Black, W.C., Keirans, J.E. & Oliver,J.H. Jr (1996) Evolution of ticks. Annual Review ofEntomology, 41, 141±62.

Lane, R.S., Piesman, J. & Burgdorfer, W. (1991) Lymeborreliosis: relation of its causative agent to its vec-tors and hosts in North America and Europe. Annual

Review of Entomology, 36, 587±609.Muller, G.H., Kirk, R.W. & Scott, D.W. (1989) SmallAnimal Dermatology, W.B. Sauders, Philadelphia.

Murnaghan, M.F. & O'Rourke, F.J. (1978) Tick

paralysis. In: Arthropod Venoms (ed. S. Bettini), pp.419±64. Springer-Verlag, New York.

Needham, G.R. & Teal, P.D. (1991) Off-host physio-

logical ecology of ixodid ticks. Annual Review ofEntomology, 36, 659±81.

Ogden, N.H, Cripps, P., Davidson, C.C., et al. (2000)Ixodid tick species attaching to domestic dogs andcats in Great Britain and Ireland. Medical & Veter-

inary Entomology, 14, 332±8.Oliver, J.H. Jr (1989) Biology and systematics of ticks(Acari: Ixodidae). Annual Review of Ecology and

Systematics, 20, 397±430.Radostits, O.M., Blood, D.C. & Gay, C.C. (1994)Veterinary Medicine ± a Textbook of the Diseases ofCattle, Sheep, Pigs and Horses. BallieÁ re Tindall,

London.Sonenshine, D.E. (1986) Tick pheromones. CurrentTopics in Vector Research, 2, 225±63.

Urquhart, G.M., Armour, J., Duncan, J.L., et al.(1987) Veterinary Parasitology. Blackwell Science,Oxford.

Varma, M.G.R. (1993) Ticks and Mites (Acari). In:Medical Insects and Arachnids (eds R.P. Lane &R.W. Crosskey), pp. 597±658. Chapman & Hall,London.

Waladde, S.M. & Rice, M.J. (1982) The sensory basisof tick feeding behaviour.Current Themes in TropicalScience, 1, 71±118.

Wikel, S.K. (1996) Host immunity to ticks. AnnualReview of Entomology, 41, 1±22.


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Chapter 6

Fleas (Siphonaptera)

6.1 INTRODUCTION

The fleas (order Siphonaptera) are small, wing-less, obligate, blood-feeding insects. Over 95% offlea species are ectoparasites of mammals, whilethe others are ectoparasites of birds. The order isrelatively small with about 2500 described species,almost all of which are morphologically extremelysimilar.

Adult fleas usually live in temporary associa-tion with their host; flea morphology, physiologyand behaviour are intimately associated withhosts that are only intermittently available, tem-porary episodes of feeding and the microhabitatof the nest, burrow or dwelling of the host animal.Mammals and birds which do not build nests, orreturn regularly to specific bedding, lairs or bur-rows, generally do not have fleas. Hence, fleas arecommon on rodents, bats, carnivores and rabbitsand virtually absent on ungulates. Through theirclose association with the habitations of humansand their companion and domestic animals, anumber of species of flea have become distributedworldwide and now proliferate in previouslyinhospitable habitats.

Many species of flea are able to parasitise arange of hosts. This, combined with theirmobility, which allows them to move easilybetween hosts, makes them parasites of con-siderable medical and veterinary importanceand makes them difficult to control. Once ontheir host, fleas feed daily or every other day.Females require significantly more blood thanmales. Blood feeding may have a range ofdamaging effects on the host animal, causinginflammation, pruritus or anaemia. Fleas mayalso act as vectors of bacteria, protozoa, viru-ses and tapeworms. However, in veterinaryentomology fleas are probably of most impor-

tance as a cause of cutaneous hypersensitivityreactions.

The distinctiveness of fleas and the existence ofsmall isolated families suggest that they are a veryancient order, and fleas probably became para-sites of mammals relatively early in the history oftheir hosts. The first flea fossils are known fromthe Cretaceous (135±65 million years ago) andfleas almost identical to living species have beenfound embedded in amber, more than 50 millionyears old.

Fleas have no close relatives and their evolu-tion is the subject of some debate. It is thoughtthat they may have evolved from a commonancestor of the scorpion flies (Mecoptera). Thescorpion flies are medium-sized, usually wingedinsects, with long, narrow legs adapted for walk-ing and with the head elongated into a broadrostrum incorporating the mouthparts (Fig. 6.1).The ancestors of fleas may have resembled themecopteran family Boreidae which, like fleas, arewingless and capable of jumping. They feed ondetritus and other arthropods. We can speculatethat the mecopteroid ancestors of fleas may haveaccumulated in the burrows of mammals, whereexcrement and other arthropods were abundant,and subsequently switched to using their piercing

Fig. 6.1 Adult scorpion fly (Mecoptera) (reproducedfrom Gullan & Cranston, 1994).

143

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mouthparts, adapted for preying on other insects,for feeding on the blood of the mammalian ownerof the burrow. After evolving initially as parasitesof mammals, a small number of species appear tohave become secondarily adapted to parasitisebirds.

6.2 MORPHOLOGY

The adults are highly modified for an ectopar-asitic life and are structurally very different frommost other insects. In contrast to lice or ticks, theflea body is laterally compressed (Fig. 6.2). Adultsare wingless and usually between 1 and 6mm inlength, with females being larger than males. Thebody colour may vary from light brown to black.The body is armed with spines, which are directedbackward.

The function of the spines is a question ofsome debate. They may serve simply to protectthe articular membranes at joints between ter-gites. Alternatively, as is more commonly sug-gested, they may allow movement through thehair or feathers of the host while preventing dis-lodgement during grooming. This idea is sup-ported by the relationships that exist betweennumber and size of spines and the nature of thefur, feathers and habits of the host. Indeed, it haseven been suggested that the distance betweenpronotal spines may be directly related to the

diameter of individual hairs and the density ofthe host's hair.

As with all insects, the body is divided intohead, thorax and abdomen. The head is high,narrow and cuneate. The propleurosternum cov-ers the head from underneath to the peristomalaperture, rendering the head immobile. Headshape is highly variable and may be useful inspecies identification. Some caution is neededhowever, since head shape may also vary betweenthe sexes and individuals of a species. In somespecies, approximately midway along the anteriormargin of the frons is a small bump known as thefrontal tubercle, which is variable in shape andstructure. The ventral portion of the anterior partof the head is known as the gena. It may extendbackwards forming a distinct genal lobe, belowwhich is found the small, three-segmented, back-wardly directed antenna, in a groove known asthe antennal fossa. A conspicuous comb of spinesis often present on the gena, known as the genalctenidium. The spines of the ctenidium are heavilysclerotised outgrowths of cuticle rather thansetae. Eyes are absent in some species of nest flea.If present, however, the eyes are usually simpleand found on the head in front of the antennae.These eyes are probably reduced compound eyes,not displaced ocelli (simple eyes).

Ventrally there is a pair of broad maxillarylobes, known as stipes, bearing long maxillarypalps (Fig. 6.3). Below these structures are themouthparts, known as the fascicle, consisting of apair of fine grooved laciniae, sometimes bearingcoarse teeth. The grooved laciniae are closelyFig. 6.2 Morphological features on an adult flea

(reproduced from Gullan & Cranston, 1994).

Fig. 6.3 Head and mouthparts on an adult flea.


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opposed, forming a groove, in which lies thelabrum±epipharynx. The laciniae are supportedon each side by a pair of five-segmented labialpalps. The laciniae are used to puncture the host'sskin and the tip of the labrum±epipharynx entersthe capillary, allowing blood to flow up the foodcanal. Blood feeding may take 2 to 10 minutes tocomplete, with females taking almost twice asmuch blood as males.

The dorsal sclerites of the three thoracic seg-ments are distinct (pronotum, mesonotum andmetanotum). A pronotal ctenidium is present insome genera. In some genera, a characteristic,vertical, cuticular rod, known as the pleural rodor pleural ridge, is visible in the mesopleuron (Fig.6.2).

The posterior pair of legs of most species of fleais highly adapted for jumping. The energy forjumping is stored in the pleural arches, which arepads of a rubbery protein called resilin. Resilin isfound in the wing hinges of a number of species offlying insect, including the mecopteran ancestorsof fleas. Because of the lateral flattening whichhas occurred to the flea body, the resilin winghinges have moved from a dorsal to a lateralposition and form an inverted `U'-shaped masscapping the pleural ridge.

To jump, the femur of the third pair of legs isfirst rotated to a vertical position, bringing thetrochanter and tibia of the third pair of legs intocontact with the ground (Fig. 6.4). This move-ment results in a clamping of the three thoracicsegments in position, engaging the cuticular cat-ches. The resilin in the pleural arch is then com-pressed by the contraction of muscles and held inplace by the thoracic catches. In this `cocked'position the flea appears to be crouched with itsback arched.

On jumping, the femur rotates downwards,simultaneously the muscles holding the catches inplace relax, releasing the energy stored in theresilin. Because the tendon of the trochanteraldepressor becomes wedged in its socket and formsan inextensible anchor, force is transmitted downthe vertical ridges of the notum, pleuron and coxato the trochanter. The leverage for this movementis supplied by the point of attachment of thetendon of the trochanteral depressor acting

against the coxa±trochanteral hinge located at thebase of the line of force. After the trochanterleaves the ground the thrust is continued as the legstraightens and the descending femur exerts forcethrough the tibia (Fig. 6.5).

The peak acceleration of the rat flea, X. cheopisis 1350m/s2, producing forces acting on the flea ofapproximately 140 g. Astronauts in a space rocketexperience forces of up to 8 g. Resilin overcomestwo disadvantages of muscle: first is the slowenergy release of muscle and second is the factthat muscle acts slowly at low temperatures.Resilin is much less affected by temperature,which is why flea jumping ability is not stronglyimpaired by low temperature. The amount ofresilin is linked to jumping ability and this in turnis linked to the size of the host and the host-finding behaviour of the flea. The fleas of burrow-dwelling animals or nest-dwelling birds tend tohave limited jumping ability and may lack pleuralarches altogether. For example, the semi-sessilerabbit flea, Spilopsyllus cuniculi, can only jumpabout 4 cm. In contrast, the fleas of deer, whichhave no well-defined nest, have relatively largeamounts of resilin in their pleural arches and canmake correspondingly large jumps. Similarly, therat flea, X. cheopis, which weighs about 0.2±0.4mg, has an average jump of about 18 cm, witha maximum jump of about 30 cm.

The flea abdomen is clearly divided intosegments (Fig. 6.2). There are ten segments, butthe last three are highly modified in the terminalportion of the abdomen. Each of the eight visiblesegments bears a pair of spiracles. The shape ofthe abdomen may be used to distinguish the sexes.In female fleas both the ventral and dorsal sur-faces are rounded. In the male flea the dorsalsurface is relatively flatter and the ventral surfacegreatly curved. In both sexes, there is an organcalled the sensilium found on the dorsal surface ofthe terminal portion of the abdomen. The sensi-lium consists of a flat plate bearing a number ofdome-shaped structures from which bristles pro-ject. This organ probably serves some sensoryfunction, but its role has yet to be established.Behind the sensilium is a pair of anal stylets,bearing apical setae and a number of shorterbristles.

Fleas (Siphonaptera) 145

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In the male the penis, known as the aedeagus, isa complex, coiled structure consisting of one ormore penis rods. Claspers and modified tergitesand sternites of the 8th and 9th segments of theabdomen also make up the male genital appara-tus.

The larvae are white and maggot-like with adistinct, brownish head (Fig. 6.6). The head iswell developed, though eyeless, with well devel-oped chewing mouthparts. There are 13 bodysegments, each with a circle of backwardlydirected bristles. There are no appendages. Whenthey emerge, the larvae are about 1.5mm inlength. Fully grown larvae may be 4±10mm in

length. Larvae move forward by articulating theirbackward-projecting bristles and a pair of chit-inous hooks at the end of the terminal segment. Ifdisturbed, they may `flip' in circles, trying toescape. The pupa has the general shape andcharacteristics of the adult.

6.3 LIFE HISTORY

Two broad trends in the life-cycles of fleas areevident. A simple association with the nest habitatis preserved in many groups of the familyCeratophyllidae, characterised by infrequent and

Fig. 6.4 (Left) Metathorax and third leg in the relaxed position. The letters indicate the sequence of movements inpreparation for a jump. (a) The raising of the femur pulling the tendon of the trochanteral depressor downwards. (b)Rotation of link plate raising the third segment which brings it into line with the second segment. (c) Compression of

the resilin. (d) Engagement of thoracic catch in the metasternum and coxal/abdominal catch. (Right) Metathoraxand third leg showing the different sclerites in position when the flea is ready to jump. (a) Femur raised and thetendon of the trochanteral depressor held in the funnel-shaped socket. (b) Link plate fully elevated. (c) Resilin

compressed. (d) Thoracic and coxal/abdominal catches engaged. (Reproduced from Rothschild et al., 1972.)


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brief associations with the host and often con-siderable adult movement between hosts andnests. In contrast, many groups of the familyPulicidae show prolonged adult associations withthe host. However, within these broad categories,a high degree of co-evolution between individualflea species and their hosts may exist and thevariation in flea life-cycles may be considerable.

Fleas are holometabolous and go through fourstages: egg, larva, pupa and adult. Under idealconditions, the entire cycle may take only 18 daysto complete, although it can range from 6 to 12months. The rate of life-cycle completion isdependent on ambient conditions, particularlytemperature and humidity, since the adult andlarval stages are not resistant to extremes of cli-mate. Host availability also affects the timerequired to complete the life-cycle.

Under ideal conditions, a female flea can pro-duce up to several hundred eggs in its lifetime,

with batches of between 2 and 25 oviposited atintervals of 1 to 2 days. The eggs are usually largeand may supply many of the vitamins and sterolsrequired for subsequent larval development. Eggsmay be laid on the ground, in the host's nest orbedding or on the host itself. In some fleas, suchas the Oriental rat flea, the eggs are sticky; inothers, such as the sticktight flea, they are dry.Incubation time is variable, depending upon thetemperature and humidity, but eggs generallyhatch within a few days of oviposition. Underideal conditions, larvae will emerge after 2 to 6days.

The flea embryo is equipped with a sharp spineon the head to help it to burst through the egg-shell. Flea larvae are active and feed on protei-naceous organic debris, such as hair, feathers oradult flea faeces. Flea larvae usually live in thehost nest or bedding, but may occasionally befound on the host itself. The larvae of Hoplop-syllus live as ectoparasites in the fur of the arctichare, for example. Larvae are particularly sus-ceptible to desiccation. The larvae usually moulttwice until, when fully grown, the third-stagelarva spins a thin cocoon of silk. Particles ofdebris stick to the freshly spun silk, serving tocamouflage it. After a number of days of quies-cence, the cocooned larva transforms into a pupa.The duration of the pupal stage is highly depen-dent on ambient temperature, though lessdependent on high humidity than previous stages.After emerging from the pupal cuticle, the adultflea may remain within the cocoon until stimu-lated by a rise in temperature or other stimuluscaused by a host returning to the nest.

Both males and females are obligate bloodfeeders. Females require a blood meal before theycan begin to mature their eggs and in males ablood meal is needed before the epithethelial plugis opened in the testes. A female flea may ingestaround 15 times her body weight in blood daily.Most species of flea are host-preferential ratherthan host-specific and will try to feed on anyavailable animal. It is probably adaptation tolocal microclimate within a nest or habitat whichmakes fleas more or less common on particularhosts. However, while many species will attemptto feed on any available animal, and such a meal

Fig. 6.5 Sequence of events in the jump of a rat flea (ato e) (from Rothschild et al., 1972).

Fig. 6.6 Life-cycle of a typical flea (a) adult, (b) egg, (c)larva and (d) pupa (after SeÂ guy, 1944).


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may be advantageous in helping to keep the adultalive, in many cases full fertility is only achieved(or is only achieved rapidly) after feeding on aspecific host.

Generally, adult fleas do not actively search forhosts, rather awaiting the approach of a host.They may remain motionless until vibrations or asudden rise in temperature or humidity signal theproximity of a host animal and trigger jumping.Adults of the European chicken flea, Cer-atophyllus gallinae, will leave the nest and ascendvegetation, jumping in response to the passage ofshadows. The cat flea, Ctenocephalides felis felis,is attracted by warm objects, though only ifmoving and so creating an air current. Theresponse of this flea is greatest towards objectswith a temperature of about 408C.

During feeding adults excrete faeces which arerich in partially digested blood and which form animportant food source for the larvae. Adult fleascan also survive for long periods (up to 6 months)between feeds, allowing them to locate new hostsor to await the return of a host to its nest site.

Most fleas feed before mating. However, oth-ers, particularly bird fleas, copulate before takingan initial blood meal. Egg production may beginwithin a few days of adult emergence, provided ahost has been located. In most flea species ovi-position takes place as soon as appropriate con-ditions of temperature and humidity occur. Inothers, such as the rabbit fleas, S. cuniculi, andCediopsylla simplex in North America, oviposi-tion is intimately synchronised with the repro-ductive cycle of wild and domestic rabbits, as willbe described later. Adult fleas are often describedas long lived, and may survive for several monthsin the laboratory. However, in the wild theyprobably only continue to reproduce actively fora few days.

After contact has been made between the maleand female, in mobile species such as the chickenflea, C. gallinae, the male grasps the femaleabdomen from beneath using adhesive organs onthe inner surfaces of the erected antennae.Copulation may last for an average of 3 hours. Inmany species of flea a single penis rod is insertedinto the spermathecal duct. However, in the rab-bit flea, S. cuniculi, the two penis rods operate

together. The two penis rods enter the female andthe shorter, thicker rod lodges in the bursacopulatrix of the female and serves to guide thelonger rod, which has sperm wound around itsnotched tip, into the spemathecal duct. In otherflea species, such as S. cuniculi, the male antennaelack the adhesive discs and mating takes place asthe female is feeding.

6.4 PATHOLOGY

The feeding behaviour of fleas causes significantveterinary problems worldwide. In 1995 themarket for flea control products was worth overUS$1 billion in the USA.

. Flea bites vary in their effects depending on thesensitivity of the victim. The insects inject ahemorrhagic saliva that can cause severe irri-tation and a rash to those they bite. The typicalreaction to flea bites is the formation of asmall, central red spot surrounded by a redhalo, usually without much swelling. Bleedingmay occur.

. Although the size of each blood meal is small,repeated feedings and high infestation cancause significant blood loss, and heavy infes-tations may cause fatal iron-deficiency anae-mia in very young animals. For instance, afemale C. f. felis takes an average blood mealof 13.6 ml per day. Hence a population of 72fleas on a host could remove around 1ml ofblood every day.

. Inflammation and pruritus may occur at thesite of a flea bite, leading to self-woundingfrom scratching or biting by the host animal.

. Fleas are of primary veterinary importance asthe agents responsible for provoking flea-biteallergic dermatitis, particularly in dogs andcats. The first flea bite may cause no obser-vable skin reaction, but the host may develop ahypersensitivity, probably to antigens in theflea saliva. Subsequent bites over an extendedperiod may trigger an allergic dermatitis.Clinical signs differ between individuals. Indogs, primary lesions are discrete crustedpapules which cause intense pruritus and


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scratching, which produce areas of alopecia orpyotraumatic dermatitis. In cats, two distinctclinical manifestations are associated with fleaallergy: miliary dermatitis and feline symme-trical alopecia. So-called feline hormonal alo-pecia is now known to be due to self-trauma,usually as the result of fleas, and is termedfeline symmetrical alopecia. In feline symme-trical alopecia the skin appears normal, butmicroscopic examination of the distal hair tipsshows that they have been fractured by exces-sive grooming. However, in miliary dermatitis,the skin, especially across the dorsum andtrunk, is covered in crusted papules with vari-able degrees of hair loss. Experimental testshave shown that flea-allergic cats will groom-out significantly more fleas than those whichare flea-naive. Female fleas also producedfewer eggs on allergic cats.

. Cat fleas (C. f. felis), dog fleas (Ctenocephalidescanis) and human fleas (Pulex irritans) can actas intermediate hosts of Dipylidium caninum,the double-pored dog tapeworm. Tapewormeggs are passed out in the faeces of the verte-brate host, following which they are eaten byflea larvae along with general organic debris.The tapeworm eggs hatch in the midgut of theflea larva and the worm larvae penetrate thegut wall, passing into the haemocoel. Thetapeworm larvae develop within the flea bodycavity throughout larval, pupal and adult fleadevelopment, eventually encapsulating as aninfective larva, known as a cysticercoid. Dur-ing grooming, adult fleas are often eaten by thevertebrate host. The cysticercoids are thenliberated and develop into tapeworms in thedigestive tract.

. Fleas are also vectors of viral and bacterialinfections, particularly of diseases such asplague and tularaemia. This ability to transmitdisease pathogens is enhanced by their pro-miscuous feeding habits. The cat flea, C. f.felis, for example, has been found on over 50different hosts worldwide and so has greatpotential for spreading disease between bothindividuals and species. In animals, the rabbitflea, S. cuniculi, is the primary vector of myx-omatosis in some parts of the world.

6.5 CLASSIFICATION

The Siphonaptera is a small and very distinctorder. More than 2500 species have been descri-bed and the order may eventually be shown tocontain as many as 3000 species. There are gen-erally considered to be 15 or 16 families and 239genera. Only two families contain species ofveterinary importance: the Ceratophyllidae andthe Pulicidae. The Ceratophyllidae is a largefamily, at present thought to contain over 500species, of which about 80 species are parasites ofbirds and the remainder of which are parasites ofsmall rodents. Most species of the family areHolarctic in distribution. The Pulicidae areparasites of a range of mammals. They are dis-tributed worldwide.

6.6 RECOGNITION OF FLEAS OFVETERINARY IMPORTANCE

The physical differences between flea species andeven between families tend to be small and theremay be considerable variation between indivi-duals within a species. Identification, therefore, isoften difficult. The following is a general diag-nostic guide to the adults of the most commonspecies of veterinary importance found as para-sites on domestic and companion animals intemperate habitats (modified from Lewis, 1993).

6.7 PULICIDAE

6.7.1 Ctenocephalides

The 11 species of this genus are found largely inAfrica and Eurasia. Their hosts are primarilycarnivores, though they may also be found onsome lagomorphs and goats in the Mediterraneanregion.

Ctenocephalides felis felis

The cat flea, C. felis, is widely distributed world-wide. There are four recognised subspecies, all of


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which are primarily parasites of carnivores: Cte-nocephalides felis felis is now found worldwide,Ctenocephalides felis strongylus and Ctenocepha-lides felis damarensis are found in Africa andCtenocephalides felis orientis is found from Indiato Australia.

Morphology: a sloping, elongated font of the headis the hallmark of the cat flea. In the female C. f.felis the head is twice as long as high and pointedanteriorly. In the male C. f. felis the head is aslong as wide but is also slightly elongate

anteriorly. The adults are quite small, the femaleis typically 2.5mm long, while the male is slightlysmaller, sometimes less than 1mm. They have abrown/black colouration which lightens afterfeeding and expansion.

Ctenocephalides felis felis has both genal andpronotal ctenidia. The genal ctenidium consists of7 to 8 spines and the pronotal ctenidium about 16spines (Fig. 6.7). The teeth of the genal ctenidiumare all about the same length. On the dorsalborder of the hind (metathoracic) tibia in bothsexes of C. f. felis there are only six notches

Guide to the flea species of veterinary importance

1 Ctenidia absent . . . . . . . . . . . . . . . . . . . . 2

Ctenidium present, at least on the prono-tum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2 Pleural ridge absent . . . . . . . . . . . . . . . . 3

Pleural ridge present Xenopsylla cheopis

3 Frons sharply angled (Fig. 6.10); headbehind the antenna with two setae and, inthe female, usually with a well-developedoccipital lobe; the maxillary laciniae arebroad and coarsely serrated; adult femalesembedded in the skin in aggregations onbare areas; found on birds, especiallypoultry, also on cats, dogs, rabbits andhumans . . . . . . . Echidnophaga gallinacea

Frons smoothly rounded; head behindantennae with only one strong seta; con-spicuous ocular seta below the eye; a sin-gle, much reduced spine on the genalmargin (Fig. 6.11); on pigs, badgers,humans . . . . . . . . . . . . . . . . Pulex irritans

4 Genal ctenidium present . . . . . . . . . . . . 5

Genal ctenidium absent; pronotal cteni-dium with 18 to 20 spines; head with a rowof three strong setae below the eye (Fig.6.14); frontal tubercle on head of bothsexes conspicuous; 3 to 4 conspicuous

bristles on the inner surface of the hindfemur; on rodents Nosopsyllus fasciatus

Genal ctenidium absent; pronotal cteni-dium with more than 24 spines; head with arow of three strong setae below the eye(Fig. 6.13); on poultry Ceratophyllus spp.

5 Genal ctenidium formed of eight or ninespines oriented vertically . . . . . . . . . . . . 6

Genal ctenidium with 4 to 6 oblique spines;frontal tubercle conspicuous on head ofboth sexes (Fig. 6.9); on rabbits . . . . . . . .

. . . . . . . . . . . . . . . . . Spilopsyllus cuniculi

Genal ctenidium with 3 very short obliquespines; single vestigial spine on the genallobe; single short pronotal spine (Fig. 6.15);on hedgehogs, dogs and cats . . . . . . . . . . .

. . . . . . . . . . . . . . Archaeopsylla erinacei

6 Head strongly convex anteriorly in bothsexes and not noticeably elongate; hindtibia with 8 seta-bearing notches along thedorsal margin (Fig. 6.8); on cats and dogs

. . . . . . . . . . . . . . . Ctenocephalides canis

Head not strongly convex anteriorly anddistinctly elongate, especially in thefemale; hind tibia with six seta-bearingnotches along the dorsal margin (Fig. 6.7);on cats and dogs . . Ctenocephalides felis


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bearing setae (Fig. 6.7). Between the postmedianand apical long setae there is a short, subapicalspine.

The hairy, worm-like white larvae are nearlytwice as long as the adults. There is a distinct headregion which is brown and sclerotised, and 13body segments, each of which bears bristles. Analstruts are present. The pupal cocoon measuresabout 4mm in length and 2mm in width.

Life-cycle: adult cat fleas are positively photo-tactic and negatively geotactic, which causes themto move to the top of carpets, grass or othersubstrate. Here they await a passing host. Visualand thermal cues trigger jumping, and the pre-sence of carbon dioxide increases the orientationof fleas towards the host animal. The jumpingresponse is greatly enhanced when the light sourceto which they are orienting is suddenly andintermittently interrupted, as would be caused bya passing host. After locating a host, adult femalesmate and feed. Newly emerged female C. f. felisincrease in weight by up to 75% after feeding on acat for 12 hours. Within 10 minutes of feedingadults begin to produce faeces. Partially digestedhost blood forms a large component of the fleafaeces. The faeces quickly dries into reddish-blackfaecal pellets, known as `flea dirt'.

Once on its host C. f. felis tends to become apermanent resident. Within 24 to 48 hours of thefirst blood meal females begin to oviposit. The

eggs are pearly white and oval and about 0.5mmin length. In the laboratory, an adult female C. f.felis can produce an average of about 30 eggs perday and a maximum of 50 eggs per day, over a lifeof about 50 to 100 days. However, on a cat, theaverage life span is probably substantially lowerthan this, possibly less than 1 week. Eggs areusually deposited on the host, but fall to theground within a few hours. The rate of oviposi-tion is highest at times of day when cats normallyrest, early morning and late afternoon. As aresult, flea eggs are concentrated at resting sitesrather than over the large areas they roam. Theeggs cannot withstand major climatic variations,particularly in temperature and humidity. Onlythose eggs that fall into an appropriate environ-ment will ultimately develop into adults. At 70%relative humidity and 358C, 50% of eggs hatchwithin 1.5 days. At 70% relative humidity and158C it takes 6 days for 50% of eggs to hatch.Eggs cannot survive below 50% relative humid-ity.

Within the host's bedding, den or lair the larvaeof C. f. felis exist in a protected environment, withrelatively high humidity, buffered from theextreme fluctuations of ambient temperatures andprovided with detritus and a source of adult fleafaecal blood. The larvae have limited powers ofmovement (probably less than 20 cm beforepupation) and crawl about their environmentlargely at random, but are negatively phototacticand positively geotactic. In the domestic envir-onment this behaviour often takes them to thebase of carpets where they can encounter foodand are sheltered from light and mechanicaldamage. The faeces of the adult flea are the pri-mary food source for the larvae of all three larvalstages. At 248C and 75% relative humidity theduration of the three larval instars is about 1week, but in unfavourable conditions larvae maydevelop more slowly. At 138C and 75% relativehumidity larval development takes about 5 weeks,though the larval cycle can take up to 200 days.Larvae will only survive at temperatures between138C and 358C. The larvae are extremely sus-ceptible to desiccation and mortality is high below50% relative humidity. The areas within a build-ing with the necessary humidity for egg and larval

Fig. 6.7 The cat flea, Ctenocephalides felis felis: (a)

male head, (b) female head and pronotum and (c) hindtibia.


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development are limited. Sites outdoors are evenless common and flea larvae cannot develop inarid areas exposed to the hot sun. If found outsidethey typically inhabit the top few millimetres ofsoil.

When fully developed, the mature third-stagelarva empties its gut and spins a thin, silk cocoon.This process requires a vertical surface againstwhich it can align itself. Fragments of detritus andstones adhere to the cocoon giving it some degreeof camouflage. Within the cocoon the larvapupates. At 248C and 78% relative humidity theduration of the pupal stage is about 8 to 9 days. Ifthe pupal stage is disturbed the larvae will eitherspin another cocoon or develop into nakedpupae, showing that the cocoon is not essentialfor development into an adult. When fullydeveloped, adults emerge from the pupal cuticlebut may remain within the cocoon. Adults mayremain in this state for up to 140 days at 118C and75% relative humidity. At cooler temperatures,fully formed fleas may remain in their cocoons forup to 12 months.

Emergence of the adult from the cocoon istriggered by stimuli such as mechanical pressure,vibrations or heat. Adult emergence may beextremely rapid, when provided with appropriateconditions. The ability to remain within thecocoon for extended periods is essential for aspecies such as C. f. felis, since its mobile hostsmay only return to the lair or bedding at infre-quent intervals.

The fully formed adults begin to feed almost assoon as they are on their host, though they cansurvive for several days without feeding, providedthe relative humidity is above about 60%. Within36 hours of adult emergence most females willhave mated. Females will mate with several malesand egg laying begins 24 to 48 hours after the firstblood meal.

At 248C and 78% relative humidity, with aplentiful food supply, the total developmentalcycle of C. f. felis may be completed in as little as17 to 22 days for females and 20 to 26 days formales. Under most household conditions C. f.felis will complete the developmental cycle in 3 to5 weeks. However, under adverse conditions thiscan be extended to as long as 190 days.

Pathology: the cat flea, C. f. felis, is the mostcommon species of flea found on domestic catsand dogs throughout North America and north-ern Europe. Significantly more cats are infestedwith fleas than dogs, however, perhaps because oftheir tendency to roam, increasing their contactwith other cats. Fleas may be found on petsthroughout the year but, in the northern hemi-sphere, numbers tend to increase around latespring and early autumn, when ambient condi-tions are favourable for larval development.

Since each female C. f. felis can ingest as muchas 13.6 ml of blood per day, severe infestationsmay lead to iron-deficiency anaemia. Anaemiacaused by C. f. felis is particularly prevalent inyoung animals and has been reported in cats anddogs and, very rarely, goats, cattle and sheep.

Flea allergy dermatitis is one of the mostcommon causes of dermatological disease of dogsand cats. In cats, there are two distinct clinicalmanifestations associated with flea allergy: mili-ary dermatitis and feline symmetrical alopecia. Indogs, primary lesions are discrete crusted papulesfound usually on the lumbar-sacral area, theabdomen, the neck and inside the hind legs.Dermatitis associated with allergy to flea bites ischaracterised by intense pruritus and reddeningof the skin, with itching persisting up to 5 daysafter the bite. The resultant licking, chewing andscratching can lead to hair loss, self-inducedtrauma and secondary infection. Other symptomsinclude restlessness, irritability and weight loss,though the intensity of irritation varies greatlywith the individual attacked.

All dogs can become allergic to fleas, thoughatopic dogs are predisposed to developing reac-tivity. One bite may be sufficient to cause anallergic reaction. Intermittent flea exposureencourages development of a flea allergy, whilecontinual exposure appears to protect against it,as does contact with fleas at an early age. Thoughlittle is known about the allergens responsible forevoking the allergic response, recent findingssuggest that multiple proteins are important inflea bite hypersensitivity. In studies which haveattempted to determine how flea antigens reactwith canine IgG or IgE, at least 15 different fleacomponents have been found to bind IgE. No


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pattern of reactivity or differences in antibodystructure have been observed which distinguishdogs with flea allergy from dogs without, sug-gesting that there is little association betweenparticular antibody responses and allergic reac-tivity of dogs to fleas. Both immediate anddelayed hypersensitivity can be observed, andindividuals will vary in the strength and propor-tion of each type of sensitivity they express. Dogschronically infested with C. f. felis rarely developa state of natural tolerance resulting in loss ofclinical signs.

Cats kept in a flea-infested environment groomat twice the rate of cats in a flea-free environment.In normal grooming a cat may ingest almost 50%of its resident flea population within a few daysand cats fitted with Elizabethan collars, whichprevent grooming, harbour much greater popu-lations of fleas than cats free to groom. Theremoval of fleas during grooming reduces thechance of finding them during a skin and coatexamination. This is a particular diagnostic pro-blem in cats with a low flea burden but markedflea-bite hypersensitivity. In such cases, sincemany of the groomed fleas are ingested, exam-ination of the mouth may reveal fleas caught inthe spines of the cats tongue.

As a result of ingestion of fleas during groom-ing, C. f. felis is an important intermediate host ofthe tapeworm Dipylidium caninum. Tapewormeggs are passed out in faeces of the vertebratehost, following which they are eaten by flea larvaealong with general organic debris. The tapewormeggs hatch in the midgut of the flea larva and theworm larvae penetrate the gut wall, passing intothe haemocoel. The tapeworm larvae developwithin the flea body cavity throughout larval,pupal and adult flea development, eventuallyencapsulating as an infective larva, known as acysticercoid. After ingestion of the adult flea bythe host, cysticercoids are liberated and developinto tapeworms in the digestive tract.

Ctenocephalides felis felis also acts as an inter-mediate host of the non-pathogenic, sub-cutaneous filaroid nematode of dogs,Dipetalonema reconditum, which adults mayingest during blood feeding. It is also suspected oftransmitting murine typhus to humans and has

recently been implicated in the transmissionbetween cats of the bacterium Bartonella henselae,responsible for cat scratch disease in humans.

Ctenocephalides canis

Morphology: the dog flea, C. canis, is closelyrelated and is morphologically very similar to thecat flea, C. f. felis, although they cannot inter-breed and, therefore, are truly distinct species.The head of the female dog flea is more roundedon its upper and anterior surface than that of thecat flea, and less than twice as long as high. LikeC. f. felis, the dog flea has both genal and pro-notal ctenidia. The genal ctenidium consists of 7to 8 spines and the pronotal ctenidium about 16spines (Fig. 6.8). However, in both female andmale C. canis the first spine of the genal ctenidiumis shorter than the rest. On the dorsal border ofthe hind (metathoracic) tibia in both sexes of C.canis there are eight notches bearing stout setae(Fig. 6.8).

Life-cycle: the life-cycle of C. canis is very similarto that of C. f. felis. Egg production commences 2days after the male and female arrive on the dog.Eggs and larvae do not survive at temperatures ofover 358C, preferring a temperature rangebetween 13 and 328C and relative humiditybetween 50 and 90%. In these conditions evenunfed adults can survive for many weeks. Pupaemay remain dormant for a year or more, yet areable to hatch in 30 seconds when cues such asvibration indicate the presence of a suitable host.

Fig. 6.8 The dog flea, Ctenocephalides canis: (a) malehead, (b) female head and pronotum and (c) hind tibia.


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In an appropriate environment the total life-cyclemay take as little as 3 weeks.

The behavioural differences between dog andcat fleas seem largely to involve the range ofenvironmental conditions which their larvae arecapable of tolerating. While household dogs innorthern Europe and North America are morelikely to be infested by the cat flea, working dogsin kennels and dogs in rural areas or at higheraltitudes are more likely to be infested byC. canis.Dogs, cats, rats, rabbits, foxes and humans haveall been recorded as hosts of C. canis.

Pathology: as in the case of C. f. felis, the dog fleaC. canis is responsible for the production ofhypersensitivity and flea allergy dermatitis.Severe irritation causes scratching, leading to hairloss, inflammation and secondary infections, withskin thickening and pigmentation in severe cases.Dog fleas are more likely to be picked up from theenvironment than from contact with other dogs.Ctenocephalides canis may also act as an impor-tant intermediate host of the tapeworm D. cani-num.

6.7.2 Spilopsyllus

Spilopsyllus cuniculi

Morphology: the rabbit flea, S. cuniculi, has bothpronotal and genal ctenidia, the latter beingcomposed of four to six oblique spines (Fig. 6.9).Adults are dark brown and females are, onaverage, 1mm in length; males are slightly smal-ler. Eyes are present and the frons at the front ofthe head is rounded with the frontal tubercleconspicuous. There are two stout spines beneaththe eye.

Life-cycle: the rabbit flea, S. cuniculi, occurs onrabbit ears. It is more sedentary than most otherspecies of flea and remains for long periods withits mouthparts embedded in the host. Reproduc-tion is under the control of hormones in the bloodof the mammalian host. The presence of proges-terones inhibits or delays flea maturation. Fol-lowing mating, the adult female rabbit ovulates

and, about 10 days before parturition, the levelsof oestrogens and corticosteroids in the bloodincrease. These hormones cause the fleas to attachtightly to their host and stimulate development ofthe eggs of the female flea. When the young rab-bits are born, the fleas move down the face where80% are likely to be transferred to the youngrabbits, on which they feed, mate and lay theireggs. Copulation of S. cuniculi only takes place inthe presence of young rabbits (1 to 10 days old).An airborne kairomone emanating from thenewborn rabbits and their urine boosts copula-tion and reproduction. The hormones of the hostalso cause adult fleas to increase the rate offeeding and defecation by about five times. Thisprovides an abundance of food in the burrow forthe newly hatched larvae. Populations of S.cuniculi may increase dramatically during therabbit breeding season.

Adult female fleas on bucks or non-pregnantdoes are more mobile and will move to pregnantdoes if able. The rise in ear temperature duringrabbit mating will also stimulate movement offleas from one rabbit to another.

Pathology: when rabbits are not breeding, thedistribution of S. cuniculi is related to skin tem-perature, with fleas usually congregating on theears. Because they assemble here in large num-bers, the intensity of bites may cause considerableirritation and tissue damage. The rabbit flea, S.cuniculi, is the main vector of myxomatosis in

Fig. 6.9 Head and pronotum of a male rabbit flea,Spilopsyllus cuniculi (after Smart et al., 1943).


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rabbits and may transmit a nonpathogenticprotozoan, Trypanosoma nabiasi.

The rabbit flea may also be found on cats anddogs which hunt or frequent rabbit habitats. Onthese hosts they are commonly found on the faceand attached to the pinneal margin.

6.7.3 Echidnophaga

This genus contains 20 species distributedthrough Eurasia, Africa and Australia. The hostsare usually rodents, marsupials, carnivores andwarthogs. The genus contains one cosmopolitanspecies of veterinary importance, Echidnophagagallinacea.

Echidnophaga gallinacea

The sticktight flea, E. gallinacea, is a burrowingflea important mainly in domestic poultry.However, it may also attack cats, dogs, rabbitsand humans. It is most common in tropical areasthroughout the world, but may also be found inmany subtropical and temperate habitats.

Morphology: the adult sticktight flea is small;females are commonly about 2mm in length andthe males are less than 1 mm in length. The head issharply angled at the front (frons). There are nogenal or pronotal ctenidia (Fig. 6.10). On the headbehind the antenna there are two setae and, in thefemale, usually a well-developed occipital lobe.The thoracic segments are narrowed dorsally.Spiracles are present on the 2nd and 3rdabdominal segments. The mouthparts appearlarge, extending the length of the forecoxae, andproject from the head conspicuously. The max-illary laciniae are broad and coarsely serrated(Fig. 6.10). On the anteroventral surface of eachhind coxa there are three rows of minute, spini-form bristles.

Life-cycle: after host location, females aggregateon bare areas, often the head, comb or wattles.Newly emerged adults are active and movetowards sunlight, which helps them accumulateon the wattles of cocks or hens. After feeding,

females burrow into the skin where they attachfirmly with their mouthparts. Each female mayremain attached for between 2 and 6 weeks.Copulation then takes place. The skin around thepoint of attachment may become ulcerated. Thefemale begins oviposition an average of 6 to 10days after attachment, at a rate of about one tofour eggs per day. Eggs are laid in the ulcerationor dropped to the ground. If laid in the ulceration,larvae hatch, emerge from the skin and drop tothe ground to complete their development. Theincubation period may last from 4 to 14 days,though typically it takes 6 to 8 days. Eggs fail tosurvive temperatures of 438C and above. Thelarvae feed on chicken manure and developthrough three larval stages over a period of 14 to31 days. The pupal period generally requiresaround 9 to 19 days and the entire life-cycle maybe completed in 30 to 60 days. Adults generallylocate a new host and attach within about 5 to 8days after emergence.

Pathology: primarily important as a parasite ofbirds, the adult sticktight flea is an especiallyserious pest of chickens. However, it may also befound on humans, rats, cats, dogs, horses andlarger insectivores. Infestations on dogs may bepersistent if continually exposed to a source ofinfestation, and fleas are found on the poorlyhaired areas of the ventrum, scrotum, interdigital

Fig. 6.10 The sticktight flea, Echidnophaga gallinacea,female head and thorax (arrow marking angulation of

the frons) (after Smart et al., 1943).


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and periorbital skin and around the pinnae of theears.

The burrowing into and subsequent emergenceof larvae through the skin tissue can result inareas of ulceration, leading to secondary bacterialinfection. Sticktight fleas can occur at densities ofover 100 individuals per bird, all concentrated onthe head. As a result, infestation of poultry mayreduce growth and egg production. Severe infes-tation can lead to anaemia. Ocular ulceration,caused by self-trauma, may result in blindnessand starvation. Heavy flea burdens can result indeath, particularly in young birds.

Sticktight fleas may become abundant inpoultry yards and adjacent buildings. They arepotentially able to transmit the plague and mur-ine typhus but, since the females spend most oftheir lives attached to a single host, they are notconsidered to be significant vectors of disease.

6.7.4 Pulex

This genus contains six species and is distributedlargely throughout the Nearctic and Neotropicalregions. The most important species of veterinaryimportance, Pulex irritans, is cosmopolitan,although now rare.

Pulex irritans

Morphology: it has neither genal nor pronotalctenidia (Fig. 6.11). The outer margin of the headis smoothly rounded and there is a pair of eyes.This species can be distinguished from X. cheopisby the presence of the single ocular bristle belowthe eye and the absence of a row of bristles alongthe rear margin of the head. The metacoxae havea patch of short spines on the inner side. Themaxillary laciniae extend about halfway down theforecoxae, which distinguishes this species fromthe closely related Pulex simulans found onHawaii (where the laciniae extend for at leastthree-quarters the length of the forecoxae).

Life-cycle: the life-cycle is typical: egg, threelarval stages, pupa and adult. It is thought thatoriginally the principal hosts of this species were

pigs. Each adult female P. irritans lays around400 eggs.

Pathology: although described as the human flea,P. irritans can infest cats, dogs and many otherdomestic animals, although it is probably mostcommon on pigs. It breeds profusely in pigstiesand is usually the most important species in farmareas. People working with infested pigs can alsoeasily become infested and start infestations intheir homes. The bites of the human flea may begenerally distributed over the entire body. Pulexirritans can be found worldwide, but is nowuncommon in the United States and most ofnorthern Europe.

6.7.5 Xenopsylla

This genus of 77 species is distributed throughoutthe tropical and subtropical regions of the OldWorld. Its hosts are rats. There is a single speciesof veterinary importance in temperate habitats,the Oriental rat flea, X. cheopis.

Xenopsylla cheopis

The distribution of the Oriental rat flea, X.cheopis, largely follows that of its primary hostthe black rat, Rattus rattus.

Fig. 6.11 The human flea, Pulex irritans, female head

and pronotum (after Smart et al., 1943.


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Morphology: X. cheopis resembles P. irritans inthat both genal and pronotal ctenidia are absent(Fig. 6.12). The head is smoothly rounded ante-riorly. The flea has a light amber colouration. Themaxillary laciniae reach nearly to the end of theforecoxae. Eyes are present, yet it can only seevery bright light. Immediately behind the eyes aretwo short antennae. The segments of the thoraxappear relatively large and the pleural ridge ispresent in the mesopleuron of the thorax. There isa conspicuous row of bristles along the rearmargin of the head and a stout ocular bristle infront of the eye.

Life-cycle: the life-cycle of X. cheopis is typical:egg, three larval stages, pupa and adult. Humid-ities above 60±70% and temperatures above 128Care required for life-cycle development in thisspecies. The larval period may last 12 to 84 days,and the pupal and pharate adult period in thecocoon, from 7 to 182 days. Adults may survivefor up to 100 days if a host is available, and up to38 days without food, if humidity is high. Thereproductive effort of the flea has been shown todepend on the age of its host. Those fed solely onjuvenile mice produce a significantly lower num-ber of eggs than those infesting adult mice. This

may be due to differences in nutritional compo-nents of the blood, such as the ratio of variousamino acids.

Pathology: as well as its favoured host, the rat fleaX. cheopis also infests mice, cottontail rabbits andground squirrels. It has a worldwide distributionand is one of the most abundant fleas in thesouthern states of the USA. It is particularlycommon in urban areas.

The oriental rat flea is the chief vector of thepathogen Yersinia pestis, causing plague andmurine typhus in humans. Yersinia pestis inter-feres with the feeding of this flea by blocking thealimentary canal, leading to regurgitation of theblood meal and transferral of the bacillus into thewound. The starving flea then goes from host tohost trying to gain nutrition until it starves todeath. Xenopsylla cheopis is also an intermediatehost of helminths such as Hymenolepis diminutaand H. nana.

6.8 CERATOPHYLLIDAE

6.8.1 Ceratophyllus

This genus is largely Holarctic in distribution andcontains 62 species. The hosts are primarilysquirrels and other rodents. There are two speciesof veterinary importance because they feed onbirds, particularly poultry.

Ceratophyllus niger

The western chicken flea, Ceratophyllus niger, iscommon throughout the western USA, Canadaand Alaska.

Morphology: a genal ctenidium is absent and thepronotal ctenidium has more than 24 spines (Fig.6.13). Eyes are present and the head bears a rowof three strong setae below the eye. The pleuralridge is present in the mesopluron of the thorax.The body is elongated and about 4mm in length,considerably larger than the sticktight flea ofpoultry, E. gallinacea.

Fig. 6.12 The oriental rat flea, Xenopsylla cheopis,female head (after Smart et al., 1943).


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Life-cycle: the life-cycle is typical: egg, three lar-val stages, pupa and adult. Unlike the sticktightflea, E. gallinacea, the adult does not attach per-manently to its host. Adults and larvae are foundprimarily in chicken droppings.

Pathology: the western chicken flea is importantprimarily as a parasite of poultry, but also may befound on rats, cats, dogs and humans.

Ceratophyllus gallinae

The European chicken flea, Ceratophyllus galli-nae, is a very common flea of poultry and alsoinfests more than 75 species of wild birds andsome mammals. In Europe, the vast majority ofits hosts are hole-nesting tits, particularly greattits and blue tits. It is found predominantly in theOld World but has been introduced into south-east Canada and north-east USA.

Morphology: this flea may be identified by a lat-eral row of four to six bristles on the inner surfaceof the hind femur. Adults are typically 2±2.5mmlong with no antennal fossae. Eyes are present.Like C. niger, the pronotal comb bears more than24 teeth and the genal comb is absent (Fig. 6.13).There are no spines on the basal section of the legs.

Life-cycle: the life-cycle is typical: egg, three lar-val stages, pupa and adult. Before the female canbegin ovipositing she needs to feed on the hostseveral times. Unlike most other fleas, whichoften remain on the host and feed for long peri-ods, chicken fleas spend most of their time in thenest of the host, and only move on to the birds tofeed for short periods.

The larvae feed on detritus amongst the nestmaterial and on undigested blood from the adultfaeces. The larval stages are completed in a fewweeks, before the pupal cocoon is spun. The fleaoverwinters in the cocoon and emerges in an oldnest in spring as temperatures rise. Large num-bers may occur in the nests of passerine birdsand they may complete their life-cycle during theperiod of nest occupation by these birds. Workhas shown a negative correlation between fleaabundance and mean body mass of the broodbeing parasitised.

If the nest is reused by birds the followingyear, the newly emerged adults will attach to thenew hosts and continue the cycle. If the nest isnot reused, the newly emerged adults will maketheir way to the nest entrance, where they may beable attach to a bird that is examining the oldnest as a potential nest site. Alternatively theymay climb up trees and bushes; here they stopperiodically and face the brightest source oflight, jumping in response to a shadow passing infront of the light.

Pathology: feeding activity may cause irritation,restlessness and, with heavy infestations, anae-mia. In wild birds, flea reproduction and feedingactivity are synchronised with the breeding sea-son of the birds; in domestic chickens, flea activ-ity may continue all year round. Adult C.gallinae may also feed on humans and domesticpets.

6.8.2 Nosopsyllus

This genus is largely Palaearctic in distribution.There are four subgenera and about 50 species.The one cosmopolitan species of veterinarysignificance is Nosopsyllus fasciatus.

Fig. 6.13 Head and pronotum of a female chicken flea,Ceratophyllus (after Smart et al., 1943).


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Nosopsyllus fasciatus

Although originally European in distribution, thenorthern rat flea, Nosopsyllus fasciatus, has nowbeen transported to temperate habitats world-wide.

Morphology: the northern rat flea has a pronotalctenidium with 18 to 20 spines (Fig. 6.14). A genalctenidium is absent. Eyes are present and the headcarries a row of three setae below the eye. Thefrontal tubercle on the head of both sexes isconspicuous. There are three to four bristles onthe inner surface of the hind femur. The body iselongated and about 3±4mm in length.

Life-cycle: the life-cycle is typical: egg, three lar-val stages, pupa and adult. Life-cycle develop-ment may be completed at temperatures as lowas 58C. Larval stages are found only in the nestor burrow. The larvae of this species may pursueand solicit faecal blood meals from adult fleas.The larvae grasp the adult in the region of thesensilium using their large mandibles. Adultsrespond by defecating stored semi-liquid blood,which is then imbibed by the larvae directly fromthe anus. It is thought that both the adults andlarvae may possess gut symbionts to supplementtheir diet.

Pathology: its main hosts are rodents, particularlythe Norway rat Rattus norvegicus. However, ithas also been found on house mice, gophers andmany other hosts. The northern rat flea willattack and feed on humans. It is not thought to bean important vector of plague. It is known to be avector of Hymenolepis diminuta in parts of Eur-ope, Australia and South America.

Tunga penetrans

The sand flea, jigger or chigoe, is an importantparasite of humans in the Neotropical and Afro-tropical regions.

Morphology: Tunga penetrans has no ctenidia andno spiniform bristles on the metathoracic coxae.The head is angular and has an acute frontalangle. The thorax is short and reddish-brown.The female is about 1mm long before a bloodmeal, but may increase to a length of up to 7mmwhen gravid. The male flea is smaller, about0.5mm long, and never embeds in the host. Tungapenetrans exhibits neosomy, the ability to producenew cuticle without moulting.

Life-cycle: the fertilised female slashes the skin ofthe host with her mouthparts, then burrows intothe wound, inserting her head and body until onlythe last two abdominal segments are exposed.Host skin proliferates and covers the flea, all barthe last abdominal segments. A free-living mobileadult male mates with the embedded female. Thefemale remains attached, feeding and greatlyexpanding the size of the abdomen. The embed-ded female produces a nodular swelling, leavingonly a small opening to the outside through whichup to 200 eggs are passed and drop to the ground.The eggs hatch in 3 or 4 days, and the entire lifecycle requires about 17 days.

Pathology: once T. penetrans becomes engorgedwith blood, its presence causes great pain, andmay produce inflammation and localised ulcers.Tetanus and gangrene may result from secondaryinfections. Intense local irritation and pruritus arealso symptomatic of more minor infestations.

Fig. 6.14 The northern rat flea, Nosopsyllus fasciatus,male head (after Smart et al., 1943).


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This species originated as a parasite of pigs inSouth America and may cause death in piglets.

6.9 FLEA SPECIES OF MINORVETERINARY INTEREST

. Archeopsylla erinacei occurs on hedgehogs inEurope and North America and may betransferred to dogs and cats following contact.Adults are 2±3.5mm long and have a genalcomb of one to three short spines and a pro-notal comb of one short spine (Fig 6.15). LikeC. canis and C. f. felis, it can cause flea bitesensitivity when abundant on canine hosts.

. Leptopsylla segnis, the European mouse flea,occurs on the house mouse,Mus musculus, andrats. The adult is 1±2mm in length and can bedistinguished from other common fleas by itsgenal comb, which has only four blunt spines.A pair of spiniform bristles is present on eachside of the frons. This flea is common in Eur-ope, and is most abundant in the United Statesof America along the east and west coasts. Itthrives in cool weather and so is scarce duringthe summer. It may be involved as a weakvector of plague. It may also transfer to catsand dogs and occasionally bite humans.

. Diamanus montanus is a common flea ofground squirrels, throughout much of westernNorth America. It is similar in appearance to

the northern rat flea N. fasciatus. It is darkbrown, medium sized and has very long labialpalpi. It has a pronotal comb with 18 to 20spines, but lacks a genal comb.

. Xenopsylla brasiliensis is the predominantspecies of rat flea in rural parts of subSaharanAfrica and has been spread to India and SouthAmerica. It is a potential vector of Yersiniapestis.


Bibikora, V.A. (1977) Contemporary views on theinterrelationships of fleas and the pathogens ofhuman and animal diseases. Annual Review ofEntomology, 22, 23±32.

Dryden, M.W. (1989) Biology of the cat flea, Cteno-cephalides felis felis. Companion Animal Practice ±Parasitology/Pathobiology, 19, 23±7.

Dryden, M.W. & Rust, M.K. (1994) The cat flea:biology, ecology and control. Veterinary Para-sitology, 52, 1±19.

Gullan, P.J. & Cranston, P.S. (1994) The Insects. AnOutline of Entomology. Chapman & Hall, London.

Holland, G.P. (1964) Evolution, classification and hostrelationships of Siphonaptera. Annual Review of

Entomology, 9, 123±46.Humphries, D.A. (1967) The mating behaviour of thehen flea, Ceratophilus gallinae (Schrank) (Sipho-

naptera: Insecta). Animal Behaviour, 15, 82±90.Humphries, D.A. (1968) The host finding behaviour ofthe hen flea Ceratophilus gallinae (Schrank) (Sipho-

naptera). Parasitology, 58, 403±14.Lewis, R.E. (1972) Notes on the geographic distribu-tion and host preferences in the order Siphonaptera.

Part 1. Pulicidae. Journal of Medical Entomology, 9,511±20.

Lewis, R.E. (1993) Fleas (Siphonaptera). In: MedicalInsects and Arachnids (eds R.P. Lane & R.W.

Crosskey), pp. 529±75. Chapman & Hall, London.Rothschild, M. (1965) Fleas. Scientific American,213(6), 44±53.

Rothschild, M. (1975) Recent advances in our knowl-edge of the order Siphonaptera. Annual Review ofEntomology, 20, 241±59.

Rothschild, M., Schlein, Y., Parker, K. & Sternberg, S.(1972) The jump of the oriental rat flea Xenopsyllacheopis (Roths.). Nature, 239, 45±8.

SeÂ guy, E. (1944) Insectes Ectoparasites: Mallophages,Anopioures, Siphonapteres. Lechevalier, Paris.

Fig. 6.15 The hedgehog flea, Archaeopsylla erinacei,female head (after Smart et al., 1943).


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Smart, J.A. (1943) Handbook for the Identification ofInsects of Medical Importance. British Museum(Natural History), London.

Soulsby, E.J.L. (1982) Helminths, Arthropods andProtozoa of Domesticated Animals. BaillieÁ re Tindall,London.

Traub, R. (1972) The relationships between the spines,combs and other skeletal features of fleas (Sipho-

naptera) and the vestiture, affinities and habits oftheir hosts. Journal of Medical Entomology, 9, 601.

Traub, R. & Starcke, H. (1980) Fleas. A.A. Balkema,

Rotterdam.Urquhart, G.M., Armour, J., Duncan, J.L., Dunn,A.M. & Jennings, F.W. (1987) Veterinary Para-

sitology. Longman Scientific & Technical, London.


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Chapter 7

Lice (Phthiraptera)

7.1 INTRODUCTION

The lice (order Phthiraptera) are superbly adap-ted and highly successful insect ectoparasites ofbirds and mammals. Most species of mammalsand birds are infested by at least one species oflouse, excluding monotremes (the duck-billedplatypus and spiny ant-eater) and bats.

In complete contrast to most fleas or ticks, licespend their entire lives on the host and are highlyhost-specific, many species even preferring spe-cific anatomical areas. They usually only leavetheir host to transfer to a new one. To allow themto survive as permanent ectoparasites, lice show alarge number of adaptations which enable themto maintain a life of intimate contact with theirhost. They are small insects, about 0.5±8mm inlength, dorsoventrally flattened and possess stoutlegs and claws for clinging tightly to fur, hair andfeathers. All lice are wingless, but this is a sec-ondary adaptation to the parasitic lifestyle, andlice are thought to be derived originally fromwinged ancestors. They feed on epidermal tissuedebris, parts of feathers, sebaceous secretions andblood. They usually vary in colour from palebeige to dark grey, but they may darken con-siderably on feeding.

The Phthiraptera is a small order with about3500 described species, of which only about 20 to30 are of major economic importance. The orderis divided into four suborders: Anoplura, Ambly-cera, Ischnocera and Rhynchophthirina. However,the Rhynchophthirina is a very small suborder,including just two African species, one of which isa parasite of elephants and the other a parasite ofwarthogs. In the veterinary literature, theAmblycera and Ischnocera are usually discussedtogether and described as the Mallophaga which,in older textbooks, is accorded status as a sub-

order in its own right. Mallophaga literally means`wool eating' and the Amblycera and Ischnoceraare known as chewing lice. The Anoplura aredescribed as sucking lice. The description `bitinglice', sometimes used to describe the Anoplura, isa misnomer, because all lice bite.

7.2 MORPHOLOGY

Lice are clearly recognisable as insects since theyhave a segmented body divided into a head,thorax and abdomen (Fig. 7.1). They have threepairs of jointed legs and a pair of short antennae.All lice are dorsoventrally flattened and wingless.The sensory organs are poorly developed; the eyesare vestigial or absent.

Adult Mallophaga (Amblycera and Ischno-cera) are usually about 2±3mm in length. Theyhave large, rounded heads on which the eyes are

Fig. 7.1 Dorsal view of adult female of (a) sucking

louse, Haematopinus (reproduced from Smart, 1943)and (b) chewing louse, Bovicola (reproduced fromGullan & Cranston, 1994).

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reduced or absent (Fig. 7.1b). In the Amblycerathe four segmented antennae are protected inantennal grooves, so that only the last segment isvisible. In the Ischnocera the antennae are three-to-five-segmented and are not hidden in grooves.At least the first two segments of the thorax areusually visible (Fig. 7.1b). The single pair ofthoracic spiracles are on the ventral side of themesothorax. Typically there are six pairs ofabdominal spiracles, but the number may bereduced. The three pairs of legs are weak andslender and end in either one or two claws,depending on the species. The lice of birds usuallyhave two tarsal claws on each leg while only onetarsal claw is present on the lice of mammals.

Both suborders have distinct, mandibulatemouthparts which are typical of chewing insects,composed of a labrum, a pair of mandibles and apair of maxillae attached laterally to the labium,which is reduced to a simple broad plate. In theAmblycera the mandibles lie parallel to the ven-tral surface of the head and cut in a horizontalplane. There is a pair of maxillary palps, whichare two- to four-segmented. In the Ischnocera, themandibles lie at right angles to the head and cutvertically and there are no maxillary palps.Species from both these suborders usually feed onfragments of keratin in skin, hair or feathers andpossess gut symbionts or specific enzymes to aidits digestion. However, they will take bloodexuding from scratches in the skin and some areable to pierce the skin.

The sucking lice (Anoplura) are usually smallinsects; adults are about 2 mm long on average,but some species of Anoplura may be as small as0.5 mm in length or as large as 8mm in length.Characteristically the head is small in relation tobody size, but narrow and elongated (Fig. 7.1a).The antennae have five segments. The eyes arereduced or absent. The Anoplura have highlymodified mouthparts, quite different to those ofother insects, which are highly adapted for pier-cing the skin of their hosts (Fig. 7.2). They arecomposed of three stylets in a ventral pouchwhich form a set of fine cutting structures. Thetrue mouth, known as the prestomum, opens atthe anterior extremity of the ventral pouch. Theprestomum is usually lined with fine teeth. During

feeding the prestomum is inverted and the teethhelp to secure the louse to the host's skin. Thestylets are then used to puncture the skin andblood is sucked into the prestomum by a mus-cular cibarial pump. The mouthparts are usuallyretracted into the head when not in use, so that allthat can be seen of them is their outline in thehead or their tips protruding. There are no palps.

The thoracic segments of Anoplura are usuallyfused together and are difficult to distinguish.There is one pair of spiracles on the mesothoraxand six pairs on segments 3 to 8 of the abdomen.The abdomen has nine visible segments. Theabdomen may have sclerotised paratergal platesalong the sides. The Anoplura have what appearto be `crab-like' claws on each leg (Fig. 7.3). Theseare composed of a single claw projecting from thetarsus. This closes on to a projection from thetibia called a tibial spur. This structure enables thelice to cling to hairs.

Fig. 7.2 Longitudinal section through the mouthpartsand head of an anopluran louse.

Fig. 7.3 Detail of (a) the tarsus and claw and (b) an eggattached to a hair, of an anopluran louse,Haematopinus (reproduced from Smart, 1943).

Lice (Phthiraptera) 163

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The female has two pairs of lateral gonopods,giving the abdomen a blunt-ended shape, whereasthe sclerotised genitalia of the male give a morepointed posterior tip.

7.3 LIFE HISTORY

The nymph, which closely resembles a smallerversion of the adult, hatches from the egg within 1to 2 weeks of oviposition. Over the course ofbetween 1 and 3 weeks the nymphs feed andmoult through three to five stages, eventuallymoulting to become a sexually mature adult. Theentire egg to adult life-cycle can be completed inas little as 4 to 6 weeks. Mature female lice gen-erally deposit one to two eggs per day whensexually mature. Adults probably live for up to amonth, during which they lay about 50 to 100eggs on the host. This is not an exceptionally highreproductive rate when compared to other insectsbut, since eggs are cemented firmly to individualhairs or feathers (Fig. 7.3b) when present in aprotected, favourable microclimate, mortality ofimmature lice may be very low, allowing a rapidincrease in louse populations. Some species of licemay be facultatively parthenogenic, which greatlyincreases their potential rate of populationgrowth.

The Amblycera are thought to be more primi-tive than the Ischnocera. They exist as body lice ofbirds and mammals and show adaptations whichenable them to cling to smooth surfaces. In con-trast the Ischnocera are adapted for clinging tohair or feathers. They are more diverse and,generally, more host-specific than the Amblycera.The Anoplura are considered to be the mostadvanced suborder of lice and are, usually, highlyhost-specific and are found exclusively oneutherian (placental) mammals; there are nonative anopluran lice of marsupials or mono-tremes.

Lice usually are unable to survive for more than1 to 2 days off their host and tend to remain with asingle host animal throughout their lives. Mostspecies of louse are highly host-specific and manyspecies specialise in infesting only one part oftheir host's body. Transfer between hosts is most

commonly brought about by close physical con-tact between individuals.

Lice respond to warmth, humidity and chemi-cal odours. Many receptors are located on theantennae, but heat and humidity receptors arelocated over the entire body. Lice have a tightlydefined band of humidity and temperature pre-ferences and respond to humidity or temperaturegradients by showing increased rates of turning infavourable microclimates which tends to keepthem in favourable areas. In addition, theyusually move away from direct light and towardsdark objects.

7.4 PATHOLOGY

Heavy louse infestation is known as pediculosis.In medical entomology, lice are most well knownas vectors of important human diseases such astyphus and louse-borne relapsing fever. Blood-sucking lice associated with domestic animalshave also been implicated in the transmission ofdisease. For example, the pig louse, Haematopi-nus suis, may spread pox virus and cattle lice maytransmit rickettsial anaplasmosis. Some species oflice may act as intermediate hosts to the tape-worm, Dipylidium caninum. However, despitethis, lice are predominantly of veterinary interestbecause of the direct damage they can cause totheir hosts, rather than as vectors.

The effect of lice is usually a function of theirdensity. A small number of lice may present noproblem and in fact may be a normal part of theskin fauna. However, louse populations canincrease dramatically, reaching high densities.For example, the number of the louse Bovicolaovis on a sheep has been recorded as increasingfrom about 4000 in autumn to more than 400 000in spring. Such heavy louse infestations maycause pruritus, alopecia, excoriation and self-wounding. The disturbance caused may result inlethargy and loss of weight gain or reduced eggproduction. Severe infestation with sucking licemay cause anaemia. Heavy infestations areusually associated with young animals or olderanimals in poor health, or those kept in unhy-gienic conditions.


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Transfer of lice from animal to animal or fromherd to herd is usually by direct physical contact.Because lice do not survive for long off their host,the potential for animals to pick up infestationsfrom dirty housing is limited, although it cannotbe ignored. Occasionally, lice also may be trans-ferred between animals by attachment to flies(phoresy).

In temperate habitats, louse populations aredynamic and exhibit pronounced seasonal fluc-tuations. In cattle and sheep, population numbersincrease in late autumn and throughout the win-ter months, and then decrease during the warmweather of spring and early summer. Thisdecrease may be attributed to rising skin surfacetemperatures and, more significantly, to sheddingof the winter coat and self-grooming. As thethicker winter coat is shed adult lice, nymphs andeggs attached to the hairs are lost directly whilethose remaining experience reduced regulation ofthe microclimate and increased exposure toatmospheric conditions. The seasonal increase inlouse populations may be exacerbated by winterhousing, if the animals are in poor condition andparticularly if animals are deprived of theopportunity to groom themselves properly bybeing housed in stanchions. Louse infestationmay also be indicative of some other underlyingproblem, such as malnutrition or chronic disease.

Louse infestation is more common in cattlethan other domestic animals. Cattle which areheavily infested with lice develop an unthriftyappearance and can show reduced vigour orweight loss. The hair coat of louse-infested ani-mals becomes discoloured and will appear greasy.Dairy animals produce less milk when infested.Calves that become infested with lice in autumnmay not achieve normal weight gain rates duringthe winter and may remain stunted until spring. Ifpopulations of sucking lice are high, infestedanimals may become anaemic and may be pre-disposed to respiratory diseases, abortion anddeath. In sheep, transmission occurs throughdirect contact between ewe and lamb, ram andewe during mating, and during aggregation. Licemay be a problem in housed flocks and in heavilyfleeced breeds where there are increased trans-mission opportunities. After initial infestation of

a sheep, it takes several months before the lousepopulation has increased to the numbers thatcause rubbing and fleece loss. If the burden isheavy the fleece develops a characteristic tattyappearance, with snags of loose wool, and itdevelops a yellow stain. Shearing can remove ahigh proportion (up to 50%) of the louse popu-lation of a sheep.

Louse infestation in pigs is very common. Itoccurs most often in the folds of the neck and jowland around the ears. Light infestation causes onlymild irritation. Pediculosis in pigs leads toscratching and skin damage. In horses, lightinfestations are most commonly found in themane, base of the tail and submaxillary space. Asthe population of lice increases, the infestationmay spread over the body. As with other animals,the lice spread by contact and their presence leadsto irritation, restlessness and rubbing. Long-earedand long-haired breeds of dog and cat are espe-cially prone to infestation, although heavy infes-tations are most usually seen in neglected,underfed animals.

More than 40 species of chewing lice occur onbirds. Birds attempt to remove lice when groom-ing, scratching the head with the feet and preeningthe body with the bill. Infestation can cause severeirritation, leading to feather damage, restlessness,cessation of feeding and birds may pluck theirfeathers. Loss of weight and possibly death mayresult. Infestation is especially common on youngbirds and in barn or free-range flocks.

7.5 CLASSIFICATION

The classification of the Phthiraptera is complexand uncertain and remains the subject of revision,different authorities grouping or splitting thevarious families and genera to varying degrees.Traditionally the Phthiaptera has usually beendivided into two main orders or suborders, theAnoplura and the Mallophaga. However, theMallophaga is not a monophyletic group andmore recent taxonomic studies suggest that theorder Phthiraptera should properly be dividedinto four suborders: Amblycera, Ischnocera,Anoplura and Rhynchophthirina.


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The Amblycera includes six families, of whichspecies of the family Menoponidae, containingthe genera Menacanthus and Menopon, are ofmajor veterinary importance on birds. Theamblyceran family Boopidae contains species thatoccur on marsupials and a species of the genusHeterodoxus that may be of importance on dogs.Species of the genera Gyropus and Gliricola in thefamily Gyropidae may be important parasites ofguinea-pigs.

The Ischnocera includes three families, two ofwhich, Philopteridae and Trichodectidae are ofmajor veterinary importance. The Philopteridaecontains the genera Cuclotogaster, Lipeurus,Goniodes and Goniocotes, which are importantectoparasites of domestic birds. The Tricho-dectidae contains the genera Bovicola (referred toin some literature as Damalinia), Felicola andTrichodectes, which are ectoparasites of mam-mals.

There are about 490 species in the suborderAnoplura. Two families the Haematopinidae andLinognathidae, contain species of major veter-inary importance. The family Haematopinidaecontains a single genus of veterinary importance,Haematopinus. The family Linognathidae con-tains two genera of veterinary importance,

Linognathus and Solenoptes. The anopluranfamilies Polyplacidae (genus Polyplax) andHoplopleuridae contain species that are parasitesof rodents, and the family Echinophthiridaecontains species which are parasites of marinemammals. The Anoplura also contains the twofamilies of greatest medical interest, the Pedicu-lidae and Pthiridae, which will not be discussed inthis text.

As described previously, the Rhynchophthirinais a very small suborder including just two species,one of which is a parasite of elephants and theother of warthogs.

7.6 RECOGNITION OF LICE OFVETERINARY IMPORTANCE

The identification of lice is complex and the fea-tures used to describe many genera are obscure.However, because lice in general are highly host-specific, in many cases information relating to thespecies of host and the site of infestation willprovide a reliable initial guide to identification.The various species of lice are usually found in allgeographical regions of the world in which theirhost occurs.

Guide to the genera of lice of veterinary interest

1 Head broad, equal or almost equal inwidth to abdomen . . . . . . . . . . . . . . . . . 2

Head elongated, much narrower thanabdomen . . . . . . . . . . . . . . . . . . . . . . . . 12

2 Antennae hidden in antennal grooves;antennae four-segmented; maxillarypalps present . . . . . . . . . . . . Amblycera 3

Antennae not hidden in grooves; antennaethree- to five-segmented; maxillary palpsabsent . . . . . . . . . . . . . . . . . . Ischnocera 6

3 On birds . . . . . . . . . . . . . . . . . . . . . . . . . 4

On mammals . . . . . . . . . . . . . . . . . . . . . 5

4 Small lice, adults about 2 mm in length;abdomen with sparse covering of medium-length setae (Fig. 7.4b); found on thigh orbreast feathers; on birds, especiallypoultry . . Menopon spp. (Menoponidae)

Large lice, adults about 3.5 mm in length;abdomen with dense covering of medium-length setae (Fig. 7.4a); found on thebreast, thighs and around vent; on birds,especially poultry . . . . . . . . . . . . . . . . . . .

. . . . . Menacanthus spp. (Menoponidae)

5 On guinea-pigs; oval abdomen, broad inmiddle; six pairs of abdominal spiracles


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are located ventrolaterally within poorlydefined spiraclar plates (Fig. 7.6a) . . . . .

. . . . . . . . . . . . Gyropus spp. (Gyropidae)

On guinea-pigs; slender body, with sides ofthe abdomen parallel; five pairs ofabdominal spiracles located ventrallywithin distinct sclerotised spiraclar plates(Fig. 7.6b) . . Gliricola spp. (Gyropidae)

On dogs; relatively large, adults about3 mm in length; abdomen with a densecovering of thick, medium and long setae(Fig. 7.5) Heterodoxus spp. (Boopidae)

6 On birds; antennae five-segmented; tarsiwith paired claws . . . . . Philopteridae 7

On mammals; antennae three-segmented;tarsi with single claws Trichodectidae 10

7 Hind legs similar in length to first two pairs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Hind legs at least twice as long as first twopairs; body long and narrow; head withsmall narrow projections in front ofantennae; first segment of antennae con-siderably longer than following four seg-ments (Fig. 7.7b); on poultry; distribution,worldwide . . . . Lipeurus (Philopteridae)

8 Three long bristles projecting from eachside of the dorsal surface of the head;rounded body; adult about 2 mm in length(Fig. 7.7a); on poultry . . . . . . . . . . . . . . . .

. . . . . . . . . Cuclotogaster (Philopteridae)

Two long bristles projecting from eachside of the dorsal surface of the head . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

9 Head with prominent angles and a distincthollow margin posterior to the antennae;adult about 5 mm in length (Fig. 7.8b); onpoultry . . Goniodes spp. (Philopteridae)

Head lacking prominent angles; adult

about 2 mm in length (Fig. 7.8a); onpoultry . . . . Goniocotes (Philopteridae)

10 Head rounded anteriorly . . . . . . . . . . . 11

Head sharply angled anteriorly; legs small;abdomen smooth, with only three pairs ofspiracles (Fig. 7.9b); on cats . . . . . . . . . .

. . . . . . . . Felicola spp. (Trichodectidae)

11 Setae of abdomen large and thick (Fig.7.10); on dogs . . . . . . . . . . . . . . . . . . . . . .

. . . . Trichodectes spp. (Trichodectidae)

Setae of abdomen small or of mediumlength (Fig. 7.9a); on mammals . . . . . . . .

. . . . . . . . Bovicola spp. (Trichodectidae)

12 Distinct ocular points present behind theantennae; all legs of similar size; adult upto 5 mm in length; distinct paratergalplates visible on abdominal segments;ventral surface of the thorax with a dark-coloured plate (Fig. 7.11) . . . . . . . . . . . . .

. . Haematopinus spp. (Haematopinidae)

No ocular points behind the antennae;forelegs small . . . . . . . . . . . . . . . . . . . . 13

13 Two rows of ventral setae on eachabdominal segment . . . . . . . . . . . . . . . 14

One row of ventral setae on each abdom-inal segment; paratergal plates absent;spiracles on tubercles which protrudefrom the abdomen; distinct five-sidedsternal plate on the ventral surface of thethorax (Fig. 7.12b); on cattle . . . . . . . . . .

. . . . . . Solenoptes spp. (Linognathidae)

14 Paratergal plates absent; ventral sternalplate of thorax is narrow or absent (Fig.7.12a); on cattle, sheep, goats and dogs. . . . . Linognathus spp. (Linognathidae)

Paratergal plates present; ovoid sternalplate on the ventral surface of the thorax(Fig. 7.13); on rodents . . . . . . . . . . . . . . .

. . . . . . . . . . Polyplax spp. (Polyplacidae)


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7.7 AMBLYCERA

Amblycera are ectoparasites of birds, marsupialsor New World mammals. They have large,rounded heads on which the eyes are reduced orabsent. They are chewing lice with mouthpartsconsisting of distinct mandibles on the ventralsurface of the head and a pair of two±four seg-mented maxillary palps. Adults are medium-sizedor large lice, usually about 2±3mm in length. Thefour-segmented antennae are protected in anten-nal grooves, so that only the last segment isvisible.

7.7.1 Menoponidae

The family Menoponidae contains several spe-cies, of which two are of major veterinaryimportance:Menacanthus stramineus, the chickenbody louse, and Menopon gallinae, the shaftlouse. These species are ectoparasites of birds,particularly poultry.

Menacanthus stramineus

Morphology: the chicken body louse or yellowbody louse, M. stramineus, is relatively large, andadults are about 3.5mm in length (Fig. 7.4a). Thehead is almost triangular in shape and the ventral

portion of the front of the head is armed with apair of spine-like process. The palps and four-segmented antennae are distinct. The antennaeare club-shaped and mostly concealed beneaththe head. The flattened abdomen is elongated andbroadly rounded posteriorly with two rows ofsetae on each abdominal segment. There are threepairs of short, two-clawed legs.

Life-cycle: the entire life-cycle occurs on the host.Because the lice develop on their hosts and remainwarm, no overwintering occurs and infestationscan develop at any time during the year. Egglaying begins 2 to 3 days after the lice mature. Theeggs are glued to the base of the feathers in denseclusters, particularly around the vent. Eggs arecharacterised by filaments on the operculum andon the anterior part of the shell. The eggs hatch in4 to 7 days into nymphs, which resemble the adultin shape, but are smaller and almost transparent.Nymphs develop through three stages, each ofwhich lasts approximately 3 days. Adult femalesdeposit one to four eggs per day over their lifetimeof 12 to 14 days. On average, each female laysabout 20 eggs. The egg to adult life-cycle requiresa total of 2 to 3 weeks.

Pathology: M. stramineus is the most commonand destructive louse found on poultry. It attackschicken, turkey, guinea fowl, pea fowl, pheasantand quail. Large populations are particularlycommon on caged layers. The lice eat the barbsand barbules of the feathers. They are mostcommon on the breast, thighs and around thevent. In heavy infestations, the lice may be foundunder the wings and on other parts of the body,including the head. After introduction into a flockthe lice spread from bird to bird by contact. It isan extremely active species and infestation canresult in severe irritation, causing skin inflam-mation and localised scabs and blood clots. Birdsbecome restless and do not digest their foodproperly. Ultimately infestation may result indecreased hen weight, decreased clutch size anddeath in young birds and chicks. Populations mayreach as many as 35 000 lice per bird. Although ithas chewing mouthparts, the louse can cause

Fig. 7.4 Adult female of (a) Menacanthus stramineusand (b) Menopon gallinae, ventral view.


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anaemia by puncturing feather quills and feedingon the blood that oozes out.

Menopon gallinae

Morphology: the shaft louse, M. gallinae, is paleyellow in colour. It is a small louse; adults areabout 2 mm in length. It has small palps and apair of four-segmented antennae, folded intogrooves in the head (Fig. 7.4b). The abdomen istapered posteriorly in the female and rounded inthe male and has a sparse covering of small tomedium-length setae on its dorsal surface.

Life-cycle: adult females lay their eggs in clustersat the base of a feather. Eggs hatch into nymphs,which pass through three stages before moultingto become sexually mature adults. Individuals arehighly mobile and move rapidly.

Pathology: M. gallinae rests on the body feathershafts of chickens and feeds on parts of thefeathers. It occurs largely on the thigh and breast.Although common, it is rarely a severe pathogen.It may also infest turkeys and ducks, particularlyif kept in close association with chickens. Theshaft louse does not usually infest young birdsuntil they are well feathered.

7.7.2 Boopidae

The amblyceran family Boopidae contains specieswhich occur on marsupials and a single species,Heterodoxus spinigera, which may be of impor-tance on dogs and other Canidae.

Heterodoxus spinigera

Morphology: H. spinigera is a large yellowish-coloured louse; adults are about 5mm in length,with a dense covering of thick, medium and longsetae (Fig. 7.5). It can easily be distinguished fromother lice infesting domestic mammals, since thetarsi end in two claws, as opposed to one in theAnoplura and Trichodectidae.

Life-cycle: the life-cycle is typical, with eggsgiving rise to three nymphal stages and thereproductive adult. However, little detail isknown.

Pathology: largely confined to warmer parts ofAfrica, Australasia and the Neotropical andNearctic regions. The symptoms of infestation arevariable. Light infestation may have no obviouseffects, with pruritus and dermatitis evident atheavier parasite loads.

7.7.3 Gyropidae

The family Gyropidae contains two species whichmay be common ectoparasites of guinea-pigs:Gyropus ovalis and Gliricola porcelli. Species ofthis family may be distinguished from otherfamilies of chewing lice because the tarsi of themid and hind legs have either one or no claws.

Gyropus ovalis and Gliricola porcelli

Morphology: G. porcelli is a slender, yellow louse,typically measuring 1±2mm in length and0.3±0.4mm inwidth (Fig. 7.6b). The head is longer

Fig. 7.5 Adult female Heterodoxus, dorsal view

(reproduced from SeÂ guy, 1944).


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than it is wide and is rounded posteriorly. Themaxillary palps have two segments. Antennae arefour-segmented with pedicellate terminal seg-ments and are almost concealed by the antennalfossae. The five pairs of abdominal spiracles arelocated ventrally within distinct, sclerotisedspiracular plates. The stout legs are modified forgrasping hair but have no tarsal claws. A ventralfurrow on the abdomen aids attachment to hair.Gyropus ovalis is less elongate in shape thanGliricola porcelli; it is also about 1±2mm in lengthbut 0.5mm in width (Fig. 7.6a). Its head is widewith projecting posterior margins. The maxillarypalps have four segments and the club-likeantennae are four-segmented, with deep antennalfossae. The abdomen is broadest at themiddle andbears a fine covering of short dorsal hairs.The sixpairs of abdominal spiracles are located ven-trolaterally within poorly defined spiracularplates. Each legs bears a single tarsal claw.

Life-cycle: the life-cycles are typical: egg, threenymphal stages and reproductive adult. The whiteeggs are oval-shaped. Young nymphs resemblethe adults in shape but are lighter in colour. Theegg to adult cycle takes approximately 2 to 3weeks.

Pathology: these two species are commonly foundon guinea-pigs. Originally endemic to the Nearc-tic, they have now been transported worldwidewith the spread of their host. Gliricola porcelli istypically widespread on body fur, whilst Gyropusovalis tends to congregate around the back of thehead and throat. Both species eat skin debris andsebaceous secretions from the base of the hair.Light infestations may cause few problems. Irri-tation will cause the host to scratch, particularlybehind the ears. Heavier infestations may result inpruritus, a harsh coat and alopecia.

7.8 ISCHNOCERA

The Ischnocera includes the three families, two ofwhich are of major veterinary importance: Phi-lopteridae, on domestic birds, and Trichodecti-dae, on mammals. The Philopteridae have five-segmented antennae and paired claws on the tarsi.The Trichodectidae have three-segmented anten-nae and single claws on the tarsi.

7.8.1 Philopteridae

The Philopteridae contains four genera and fivespecies which are important ectoparasites ofdomestic birds, Cuclotogaster heterographus,Lipeurus caponis, Goniodes dissimilis, Goniodesgigas and Goniocotes gallinae.

Cuclotogaster heterographus

Morphology: the chicken head louse, C. hetero-graphus, has a rounded body with a large, slenderhead, which is rounded at the front (Fig. 7.7a).The adult is about 2.5mm in length. Three longbristles project from each side of the dorsal sur-face of the head and the five-segmented antennaeare fully exposed. Each leg has two tarsal claws.The abdomen is barrel-shaped in the female andmore elongate in the male. It bears a row of dorsalhairs on each segment.

Life-cycle: the pearly-white eggs are attachedsingly to the downy feathers close to the skin and

Fig. 7.6 Adult female (a) Gyropus ovalis and (b)Gliricola porcelli, in dorsal view (reproduced fromSeÂ guy, 1944).


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hatch within 5 to 7 days into minute, pale,translucent nymphs which resemble the adults inshape. The nymphs pass through three stages in25 to 40 days.

Pathology: as the common name suggests,chicken head louse C. heterographus occursmainly on the skin and feathers of the head,although it occurs occasionally on the neck andelsewhere. The lice feed on tissue debris. Infesta-tion with C. heterographus is particularly impor-tant in young birds. Infestations of young birdsand chicks may be pathogenic and sometimesfatal; the birds become weak and droopy andmay die within a month. When birds becomefairly well feathered, head lice infestationdecreases, but can increase again when the birdsreach maturity.

Lipeurus caponis

Morphology: the wing louse, L. caponis, is anelongated, narrow species, about 2.2mm in lengthand 0.3 mm in width (Fig 7.7b). The head is longand rounded at the front, and the antennae arefive-segmented and fully exposed. The legs arenarrow and bear two tarsal claws. Character-istically the hind legs are about twice as long asfirst two pairs. There are characteristic smallangular projections on the head in front of the

antennae. There are relatively few dorsal hairs onthe abdomen.

Life-cycle: eggs are attached to the feathers andhatch in 4 to 7 days. The nymphs pass throughthree stages in 20 to 40 days. Adults are relativelyinactive and may live for up to 35 days.

Pathology: common on chicken and other fowlthroughout the world, L. caponis occurs on theunderside of the wing and tail feathers. Patho-genic effects are usually slight in healthy animalsand include restlessness, irritation and generalunthriftiness. Young birds may be susceptible toheavy infestation, especially where underlyingdisease or malnutrition is debilitating.

Goniodes dissimilis and Goniodes gigas

Morphology: Goniodes are large lice, about 3mmin length. They are brown in colour. The broadhead is concave posteriorly, producing markedangular corners at the posterior margins (Fig.7.8b). The head carries two large bristles pro-jecting from each side of its dorsal surface. Theantennae have five segments and are fullyexposed. Each leg has two tarsal claws.

Fig. 7.7 Adult female of (a) Cuclotogasterheterographus and (b) Lipeurus caponis, dorsal view.

Fig. 7.8 Adult female of (a) Goniocotes gallinae and (b)Goniodes dissimilis, dorsal view.


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Life-cycle: the eggs are attached to the feathersand have an incubation period of 7 days. Thenymphs pass through three stages, followed bythe reproductive adult. Once they have reachedmaturity, males live for a maximum of up to 20days, females for up to 25 days. Females lay up to15 eggs in their lifetime and the entire life-cyclerequires about 1 month.

Pathology: these lice generally occur in smallnumbers and so they have little effect on the host.They can be found anywhere on the body andfeathers. Goniodes dissimilis is more abundant intemperate habitats and G. gigas in tropical areas.

Goniocotes gallinae

Morphology: the fluff louse, G. gallinae, is one ofthe smallest lice found on poultry, at about0.7±1.3mm in length. It has a pale yellow, almostcircular body. The head is rounded and carriestwo large bristles projecting from each side of itsdorsal surface (Fig. 7.8a). The antennae are five-segmented, fully exposed, and the same in bothsexes. There are two tarsal claws on each leg andfew hairs on the dorsal abdomen.

Life-cycle: the life-cycle is typical. Eggs areattached to the downy feathers close to the skin.The nymphs pass through three stages, followedby the reproductive adult.

Pathology: G. gallinae is a small louse of poultrythat occurs on the down feathers anywhere on thebody. It is generally of little pathogenic sig-nificance but high infestation can cause rest-lessness, damaged plumage and weight loss.

7.8.2 Trichodectidae

The Trichodectidae contains the three generaBovicola, Felicola and Trichodectes, which areectoparasites of mammals.

Bovicola

There are a number of morphologically similarhost-specific species, the most important of whichare Bovicola ovis on sheep and Bovicola bovis oncattle. Also of interest are Bovicola equi on horsesand Bovicola caprae on goats.

Morphology: B. bovis is a small, species,1.5±1.75mm in length and 0.35±0.55mm inwidth. Adults have a large broad head which isred in colour, and a reddish-brown body withdark transverse bands on the abdomen. The legsare slender and are adapted for moving amongstthe hair. The sheep body louse, B. ovis, is one ofthe smallest of mammalian lice; adults are only1.6mm long. It is pale-coloured with several darklateral bands across its abdomen. Bovicola equi istypically 1±2mm long. The head is broad and flatand the pale brown body is dorsoventrally flat-tened. In all three-species the head is roundedwith a pair of three-segmented antennae. Thetarsi carry a single claw (Fig. 7.9a).

Life-cycle: the egg to adult life-cycle of Bovicolaspp. typically requires 3 to 4 weeks. Bovicola bovismay be facultatively parthenogenic, allowing it tobuild up populations rapidly. Hence, sex ratios of1:20 females are typical in a population, but may

Fig. 7.9 Adult female of (a) Bovicola and (b) Felicola,

in dorsal view (reproduced from SeÂ guy, 1944).


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be higher. Females lay approximately one eggevery 35 hours, each of which is glued singly ontoa hair shaft. The emerging nymphs resemble adultlice in body shape but are smaller with lightersclerotisation and less distinct banding. Adultfemale B. ovis lay two or three eggs every 5 days.It is estimated to take about 20 weeks for apopulation of B. ovis on a sheep to increase from5000 to half a million, under favourableconditions.

Pathology: in general, light infestations by Bovi-cola may result in little damage or a chronicdermatitis. However, heavy infestations mayresult in intense irritation, pruritus, excoriationand alopecia.

In cattle B. bovis favours the top of the head,neck, shoulders, back and rump of both dairy andbeef cattle. As infestations increase, the lice mayspread down the sides and may cover the rest ofthe body. This louse feeds by scraping away scurfand skin debris from the base of the hairs, causingconsiderable irritation to the host animal. Theskin reaction can cause the hair to loosen and thecattle react to the irritation by rubbing orscratching, which will result in patches of hairbeing pulled or rubbed off. Scratching may pro-duce wounds or bruises and a roughness to theskin. This may lead to secondary skin infectionsand skin trauma such as spot and fleck grain lossin the hide, reducing its value. Bovicola bovis isone of the commonest cattle parasites in Europeand it is the only chewing louse found on cattle inthe USA. Although it causes less individualdamage than sucking lice, it is present in largernumbers and so can be extremely damaging.Infested cattle may cease feeding and showdisrupted feeding patterns.

On sheep, B. ovis favour areas close to the skin,especially on the shoulder, neck and back area.However, this species is highly mobile and canspread over the entire body, causing considerableirritation, restlessness, interrupted feeding andloss of condition. The pediculosis caused ischaracterised by rubbing, scratching and biting ofthe affected areas. Initially this causes a pulledeffect on the wool. Eventually, exuded serumfrom bite wounds causes wool matting and

discolouration, and large areas on the sides maybecome bare due to rubbing. Wounds may attractblowflies. Lice reduce the manufacturing qualityof wool and can reduce wool production by up to0.8 kg per head if left uncontrolled. Lice arespread within a flock by direct contact, especiallywhen sheep are crowded together in yards, trucksand saleyards. Adult lice positioned near to thetip of the wool fibre are passed on to the new hostas it brushes past an infected sheep. It takes asingle infested sheep just 4 months to infest thewhole flock.

Bovicola equi is probably the most common ofexternal parasites of horses, especially in tempe-rate climates. It is most prevalent on the head,mane, base of the tail and shoulder. The lice feedon the most superficial layers of skin and theexudates resulting from their irritant effects,causing the horses to scratch, rub and bitethemselves. Skin irritation and itching result in arough coat, skin infections and loss of hair. Heavyinfestations can cause weight loss and B. equi isthought to be a vector of equine infectiousanaemia.

Felicola

Felicola subrostrata

There is a single species of importance in thisgenus, Felicola subrostrata, which is an ectopar-asite of domestic cats.

Morphology: this louse is beige or yellow incolour, with transverse brown bands. Adults arean average of 1±1.5mm in length. The shape ofthe head is very characteristic, being triangularand pointed anteriorly (Fig. 7.9b). Ventrally thereis a median longitudinal groove on the head,which fits around the individual hairs of the host.The antennae have three segments, are fullyexposed and are similar in both sexes. The legs aresmall and slender and end in single claws. Theabdomen has only three pairs of spiracles and issmooth with few setae.

Life-cycle: eggs are laid on the cat fur and hatchin 10 to 20 days. The adult stage is reached within


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2 to 3 weeks and the egg to adult life-cyclerequires about 30 to 40 days.

Pathology: this is the only louse that commonlyoccurs on cats. Pediculosis is now rare in cats andis generally seen only in elderly or chronically-illanimals. It is more problematic in long-hairedbreeds and pathogenic populations may developunder thickly matted or neglected fur. Infesta-tions most commonly occur on the face, back andpinnae, causing a dull, ruffled coat, scaling, crustsand alopecia.

Trichodectes

Trichodectes canis

There is a single species of veterinary importancein this genus, Trichodectes canis, which is anectoparasite of domestic dogs. Other species ofthis genus infest other Canidae.

Morphology: T. canis is a small yellow louse, 1±2mm in length, with dark markings. The head isbroader than long and the antennae are three-segmented, short and exposed (Fig. 7.10). Thelegs are stout and their tarsi bear single claws,with which they tightly grasp the hair of theirhost. The abdomen has six pairs of spiracles onsegments 2 to 6 and many rows of large, thicksetae.

Life-cycle: the female lays several eggs per day forapproximately 30 days. Eggs hatch in 1 to 2 weeksand give rise to three nymphal stages. Thenymphs mature into reproductive adults withinabout 2 weeks. The egg to adult life-cycle requiresabout 30 to 40 days.

Pathology: T. canis can be a harmful ectoparasiteof dogs, particularly in puppies and old ordebilitated dogs. It is most commonly found onthe head, neck and tail attached to the base ofhairs. It feeds on tissue debris. It is a highly activespecies and infestation produces intense irritationaround predilection sites. Lice often congregatearound body openings or wounds, seekingmoisture. Intense pruritus, scratching, biting,sleeplessness, nervousness and a matted coat areall typical of T. canis infestation. Damage to theskin from scratching results in inflammation,excoriation, alopecia and secondary bacterialinvolvement. Trichodectes canis can also act as anintermediate host of the tapeworm Dipylidiumcaninum. The lice can live for 3 to 7 days ifremoved from the host and, therefore, can betransferred via shared combs and brushes as wellas by direct contact.

7.9 ANOPLURA

There are six families of sucking lice of mam-mals, two of which are of veterinary importance.These are Haematopinidae, species of which areparasites of ungulates, and Linognathidae, spe-cies of which are parasites of dogs and rumi-nants. The Pediculidae are parasites of primates;the Hoplopleuridae are largely parasites ofrodents. The Echinophthiridae are parasites ofmarine mammals and the Neolinagnathidae, inwhich there are only two species, are parasites ofelephant shrews. There are no sucking lice ofbirds.

7.9.1 Haematopinindae

There is a single genus of interest, Haematopinus.Fig. 7.10 Adult female of Trichodectes, dorsal view.


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Haematopinus

Twenty-six species have been described in thegenus Haematopinus of which three are of veter-inary importance in temperate habitats: the piglouse,Haematopinus suis, the horse sucking louse,Haematopinus asini, and the short-nosed cattlelouse, Haematopinus eurysternus. The tail louse,Haematopinus quadripertusus, and the buffalolouse, Haematopinus tuberculatus, may infestcattle and buffalo in tropical and subtropicalhabitats, but only the former species is of patho-genic significance.

Morphology: all the species of Haematopinus arelarge lice, about 4±5mm in length. They possessprominent angular processes, known as ocularpoints or temporal angles, behind the antennae(Fig. 7.11). Eyes are absent. The thoracic sternalplate is dark and well developed. The legs are ofsimilar sizes, each terminating in a single largeclaw which opposes the tibial spur. Distinctsclerotised paratergal plates are visible onabdominal segments 2 or 3 to 8.

The short-nosed cattle louse, H. eurysternus, ison average 2.5mm in length and can be dis-tinguished by its short, pointed head and broadbody. The head and thorax are yellow-brown andthe abdomen is blue-grey. Its opaque white eggs

are pointed at their base and hard-shelled. Theadult pig or hog louse,H. suis, is 4±6mm long andgreyish-brown in colour with brown and blackmarkings. It is the largest blood-sucking lousefound on domestic animals and is characterisedby a long, narrow head and long mouthparts. Thelegs bear large claws for clasping hairs. The horselouse, H. asini, is generally 3±3.5mm in length,yellow-brown and has a longer, more robust headthan H. suis.

Life-cycle: typically, Haematopinus spp. produceone to six eggs per day. These are glued to thehairs or bristles of the host and hatch in 1 to 2weeks. The emerging nymphs resemble the adultlouse except in size. In about 12 days, the nymphsmature into adults and within 4 days, after feed-ing and mating, the female lice may begin to layeggs. Adults die after about 10 to 15 days ofoviposition and an average of about 24 eggs arelaid per female. Haematopinus suis, however, hasa slightly higher rate of reproduction; eachH. suisfemale lays three to six eggs per day, producing upto 90 eggs over 25 to 30 days.

Pathology: Haematopinus spp. irritate their hostsby taking small but frequent blood meals. Eachtime they feed, they puncture the skin at adifferent place.

Haematopinus suis is the only species of lousefound on pigs and is very common. It usuallyoccurs in the folds of the neck and jowl, aroundthe ears and on the flanks and back. The majorityof nymphs occur on the head region. Lightinfestation causes only mild irritation. Pediculosisin pigs leads to self-inflicted injuries to their skinand hair such as excoriation, sores and thicken-ing, from scratching and rubbing. In severestcases, pigs may rub most of the hair off theirbodies and, if acquired by piglets, H. suis infes-tation may delay growth. Transfer is usually bycontact, but H. suis may survive for up to 3 daysoff its host. Hence, transfer also can occur whenanimals are put into recently vacated dirtyaccommodation.

On horses,H. asini is most commonly found onthe head, neck, back and inner surface of theupper legs. Symptoms include heavy dandruff

Fig. 7.11 Adult female of Haematopinus, dorsal view(reproduced from SeÂ guy, 1944).


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and greasy skin and eventually bald spots withraw, red centres. Light infestations may beasymptomatic but, if present in sufficient num-bers, they have been known to cause anaemia,weight loss and loss of vitality and appetite.Outbreaks of equine lice tend to be more frequentin the early spring, since the accumulated dirt inthe barn and tack room, plus dander from theshedding of winter coats, provide an ideal envir-onment for them. In horses, lice are oftenassociated with poor grooming and management.Thin, aged, stressed or physically compromisedhorses seem to be more susceptible. Horses canalso contract lice by picking them up frompoultry.

On cattle, infestations of the short-nosed cattlelouse, H. eurysternus, are most frequently repor-ted on mature animals, reaching their peak inwinter, and may cause anaemia and loss of con-dition. The short-nosed cattle louse occurs ondomestic cattle worldwide and is generally con-sidered to be the most important louse infestingcattle. It is primarily found in and around theears, tail, horns and top of neck, although it canoccur anywhere on the body of the host. Thecattle tail louse, H. quadripertusus, ispredominantly tropical or subtropical indistribution and is found largely in the long hairaround the tail. The normal hosts of H. quad-ripertusus are zebu cattle, Bos indicus.

7.9.2 Linognathidae

There are two genera of interest in the familyLinognathidae: Linognathus and Solenoptes.

Linognathus

More than 50 species of Linognathus have beendescribed, six of which occur on domesticanimals. The face louse, Linognathus ovillus, andthe foot louse, Linognathus pedalis, are importantectoparasites of sheep. The long-nosed cattlelouse, Linognathus vituli, is a parasite of cattle andLinognathus setosus parasitises dogs. Linognathusstenopsis is found on goats. The African blue

louse, Linognathus africanus, is a parasite of cattlein Africa, India to USA and parts of CentralAmerica.

Morphology: members of this family do not haveeyes or ocular points. The second and third pairsof legs are larger than the first pair and end instout claws. In species of the genus Linognathusthe thoracic sternal plate is absent or is weaklydeveloped (Fig. 7.12a). Paratergal plates areabsent from the abdomen. The foot louse, L.pedalis, is bluish-grey and up to 2mm long whenfully engorged. Its short pointed head is buried inthe skin when the louse is feeding. The long-nosedcattle louse, L. vituli, is blue/black, approximately2.5mm in length. The long, narrow, pointed headand slender body of these lice makes them easy toidentify. While feeding they extend their bodies inan upright position.

Life-cycle: adult females lay a single egg per day.Eggs hatch in 10 to 15 days, giving rise to nymphswhich require about 2 weeks to pass through threenymphal stages. The egg to adult life-cyclerequires about 20 to 40 days.

Pathology: two species of Linognathus are com-monly found on sheep, the face louse, L. ovillus,

Fig. 7.12 Adult female of (a) Linognathus and (b)

Solenoptes, in dorsal view (reproduced from SeÂ guy,1944).


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and the foot louse, L. pedalis. Linognathus ovillusis usually found on the ears and face of sheep. Thepreferred sites for L. pedalis are the feet, legs andscrotum. On the host L. pedalis is more sedentarythan L. ovillus and tends to occur in aggregationson the lower, less woolly parts of the leg, belly andfeet. At high densities, however, both species mayspread over the entire body. Infested animals willstamp their feet or bite the infested areas The licecause sheep to rub and scratch, sometimes to thepoint of denuding areas of skin. Infestation byLinognathous spp. results in a chronic dermatitis,characterised by constant irritation, rubbing andbiting of the fleece. Because they are blood fee-ders, anaemia is common where high populationsof lice exist. Anaemia may predispose animals torespiratory or other diseases.

Populations peak in spring and lambs may beparticularly susceptible to infestation. Transfer isusually through contact with infested animals,particularly when sheep are closely herded andpenned together. However, L. pedalis can survivefor several days off the host so infestations may bepicked up off contaminated pasture. Linognathusovillus occurs worldwide and L. pedalis is com-mon in the USA, South America, South Africaand Australasia.

On cattle, the long-nosed cattle louse, L. vituli,is most abundant on the dewlap, sides of the neck,shoulders and rump, though in high infestations itcan be found anywhere in the hair. It is morecommon on dairy cattle and can be particularlyproblematic in young animals.

Linognathus setosus is a common and wide-spread parasite of dogs, particularly the long earsof breeds such as the spaniel, basset and Afghanhounds. It may cause anaemia and is usually ofgreater pathogenic significance in youngeranimals.

Solenoptes

Only one species in the genus Solenoptes is ofveterinary importance: the little blue cattle louse,Solenoptes capillatus.

Morphology: S. capillatus is the smallest of the

anopluran lice found on cattle at about1.2±1.5mm in length. Eyes and ocular points areabsent. It has a short rostrum. Prominentabdominal tubercles bearing the spiracles projectfrom the sides of each abdominal segment. Thereare no paratergal plates on the abdomen. Thesecond and third pairs of legs are larger than thefirst pair and end in stout claws. In contrast tospecies of Linognathus, the thoracic sternal plateis distinct (Fig. 7.12b). The eggs of this lousespecies are small, short and dark blue and causehairs to bend at the point of attachment.

Life-cycle: eggs hatch in approximately 11 days togive rise to three nymphal stages, followed by thereproductive adult. The mature female lays one ortwo eggs per day. The egg to adult life-cyclerequires about 5 weeks.

Pathology: S. capillatus is an important ecto-parasite of cattle in the southern states of theUSA and Australia. It usually occurs in aggre-gations on the muzzle, neck, shoulders, back andtail, and in the cheek and neck in winter.

7.9.3 Polyplacidae

Lice of the genus Polyplax infest rodents. Twocommon species are Polyplax serrata and Poly-plax spinulosa (the spined rat louse)

Morphology: these lice are slender, 0.6±1.5mm inlength, and yellow-brown in colour. The headbears prominent, five-segmented antennae, noeyes and no ocular points (Fig. 7.13). There is adistinct sternal plate on the ventral surface of thethorax. The forelegs are small and the hind legsare large with large claws and tibial spurs. Theabdomen has seven to 13 dorsal plates, andapproximately seven lateral plates on each side.The egg is elongated, with a cone-like operculum.

Life-cycle: the eggs hatch in about 5 to 6 days togive rise to three nymphal stages, followed by thereproductive adult. The first nymphal stage isfound on the entire body, while older stages arefound predominantly on the front of the body.


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The entire life-cycle is completed in about 2weeks.

Pathology: widespread in body fur, these ecto-parasites may cause problems in laboratoryrodents. Polyplax spp. cause irritation, and rest-lessness and constant scratching, particularlybehind the ears. Anaemia, unthrifty appearanceand debilitation occur in heavy infestations. Thespined rat louse, P. serrata, may transmit variouspathogens. For example, it is thought to be avector of the agent of murine eperythrozoonosis.


Barker, S.C. (1994) Phylogeny and classification, ori-gins and evolution of host associations of lice.International Journal for Parasitology, 24, 1285±91.

Clay, T. (1970) The Amblycera (Phthiraptera: Insecta).Bulletin of the British Museum of Natural History(Entomology), 25, 73±98.

Cleland, P.C., Dobson, K.J. &Meade, R.J. (1989) Rateof spread of sheep lice (Bovicola ovis) and their effectson wool quality. Australian Veterinary Journal, 66,289±99.

Craufurd-Benson, H.J. (1941) The cattle lice of GreatBritain. Part I. Biology, with special reference toHaematopinus eurysternus. Parasitology, 33, 331±42.

Craufurd-Benson, H.J. (1941) The cattle lice of GreatBritain. Part II. Lice populations. Parasitology, 33,343±58.

Emerson, K.C. (1956) Mallophaga (chewing lice)occurring on the domestic chicken. Journal of theKansas Entomological Society, 29, 63±79.

Gullan, P.J. & Cranston, P.S. (1994) The Insects. An

Outline of Entomology. Chapman & Hall, London.Hopkins, G.H.E. (1949) The host associations of thelice of mammals. Proceedings of the Zoological

Society of London, 119, 387±604.Kim, K.C., Pratt, H.D. & Stojanovich, C.J. (1986) TheSucking Lice of North America, an Illustrated Manual

for Identification. Pennsylvania State UniversityPress, Pennsylvania.

Lyal, C.H.C. (1985) A cladistic analysis and classifi-cation of trichodectid mammal lice (Phthiraptera:

Ischnocera). Bulletin of the British Museum of Nat-ural History (Entomology), 51, 187±346.

Lyal, C.H.C. (1987) Co-evolution of trichodectid lice

and their mammalian hosts. Journal of Natural His-tory, 21, 1±28.

Matthysse, J.G. (1946) Cattle lice, their biology and

control. Cornell University Experimental StationBulletin, 832, 3±67.

Meleney, W.P. & Kim, K.C. (1974) A comparative

study of cattle-infesting Haematopinus with redis-cription of H. quadripertusus Fahrenholz, 1919(Anoplura: Haematopinidae). Journal of Para-sitology, 60, 507±22.

Nelson, B.C. & Murray, M.D. (1971) The distributionof the Mallophaga on the domestic pigeon (Columbalivia). International Journal for Parasitology, 1, 21±9.

Ronald, N.C. & Wagner, J.E. (1979) The arthropodparasites of the genus Cavia. In: The Biology of theGuinea Pig (eds J.E. Wagner & P.J. Manning), pp.

201±9. Academic Press, New York.SeÂ guy, E. (1944) Insectes Ectoparasites: Mallophages,Anopioures, Siphonapteres. Lechevalier, Paris.

Smart, J.A. (1943) Handbook for the Identification of

Insects of Medical Importance. British Museum(Natural History), London.

Walker, A. (1994) The Arthropods of Humans and

Domestic Animals. Chapman & Hall, London.

Fig. 7.13 Adult female Polyplax, dorsal view.


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Chapter 8

The Diagnosis and Control ofEctoparasite Infestation

8.1 INTRODUCTION

This chapter covers the diagnosis and treatmentof ectoparasite infestation and associated der-matoses of domestic animals. It includes discus-sion of ectoparasite control and the more widelyused types of ectoparasiticides, but not a com-prehensive list of all ectoparasiticides availableworldwide. The principles of ectoparasite controland ectoparasiticide use have been emphasised sothat the reader can apply these techniques usinglocally available ectoparasiticides. It should benoted that there is considerable variation in theavailability and licensing of ectoparasites acrossthe globe and it is impossible to document thedetails in a single text, and this should be borne inmind when using this book. It should be empha-sised that all insecticides should be used in strictaccordance with the manufacturer's instructionsand disposed of in an appropriate manner.

8.2 DIAGNOSIS OF ECTOPARASITEINFESTATION (Table 8.1)

In making a diagnosis of ectoparasitic infestationor an ectoparasite-associated dermatosis it isimportant to have an idea of the parasite involvedand its life-cycle. This can be achieved in manycases by direct collection of the parasite or itsfaeces. Some parasites, for example lice, live inintimate relationship with the host's skin and caneasily be found there. However, visiting parasites,such as biting flies, may be on the skin for only ashort period of time each day and a diagnosis isoften made by implication. Hence, a workingknowledge of the clinical signs of skin disease isusually also required.

When deciding which test or tests to perform todiagnose ectoparasite infestation, the questions tobe answered are:

Table 8.1 Diagnosis and isolation of parasites.

Anatomical site Techniques

Parasite type

Mites . . . . . . . . . .Lice . . . . .Fleas . . . . . .Ticks . . .Flies . . . .

Hair

Hairfollicle

Surface

Epidermis

Environment

Skin

scrape

Hairplucks

Hairbrushings

Acetate

strip

Serology

Biopsy

Visualexamination

Observationwhilst

feeding

179

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. Is the ectoparasite likely to be on the skin?

. If it is, then where on the skin is it living: on thehair, on the skin surface, in the epidermis ordermis or in the hair follicles?

. If not on the skin, but an intermittent visitor,can the parasite be identified while it is feedingor in areas of the immediate environment suchas the host's nest or bedding material?

. Are there any characteristic clinical or patho-logical features that indicate whether a specificparasite or a narrow range of parasites couldbe involved?

The diagnostic tests performed to collect a parti-cular parasite or find evidence of its presence willdepend on the answers to these questions.

8.2.1 Hair examination

Many of the larger ectoparasites, such as blowflylarvae or ticks, may be collected directly off a hostusing appropriately sized forceps. Small speci-mens may be picked up with the end of a mois-tened paintbrush. Unattached mites and ticks canbe removed by combing or brushing the hostanimal over a white enamel tray or sheet of paper.Brushing over moistened, white blotting paper orpaper towel may help to identify a flea infestation,since the dislodged flea faeces will stain red asthey dissolve on the paper.

Hairs, collected by coat brushing and plucking,should be mounted in mineral oil, such as liquidparaffin, and examined microscopically for evi-dence of ectoparasites. Eggs of some parasites,such as lice and Cheyletiella spp., may be foundattached to the hair shaft. Adult ectoparasitessuch as lice and various mites may also be foundby this method. The hair bulb and lower third ofthe plucked hair shaft should be examined forevidence of the follicular mite Demodex. This is auseful technique for the diagnosis of demodicosis,particularly when lesions occur on the feet. Incases of alopecia it may be useful to examine theupper portion of the hair for evidence of fracture,which occurs with self-induced alopecia due topruritus.

To ensure that the mouthparts are not left

behind, embedded living ticks may be removedmost effectively by dabbing the tick and the sur-rounding skin with alcohol. This relaxes the tick,allowing it to be pulled out intact. Alternatively,the tick can be covered with a layer of petroleumjelly, which prevents breathing and, after about30 minutes, the tick will drop off.

8.2.2 Acetate strip examination

Short strips of acetate tape (e.g. Sellotape orScotch 3M tape) can be applied repeatedly toeither the hair coat or clipped skin surface.Material and parasites in the coat or on the sur-face of the skin become attached to the tape,which is then mounted on to glass slides andexamined microscopically. This is a useful tech-nique for identifying surface mites.

8.2.3 Superficial skin scraping(epidermal surfaceexamination)

This is a routine technique. It is important toremove coat hair by gentle clipping (the hair canbe mounted and examined separately). The sur-face of the skin can then be scraped using a bluntscalpel blade and the material mounted in 10%potassium hydroxide (KOH) or liquid paraffin ona microscope slide. Alternatively, a few drops ofliquid paraffin can be applied and spread over theskin-scraping site and then scraped with a bluntscalpel blade. The emulsion of superficial epi-dermis and liquid paraffin is then spread over amicroscope slide, covered with a glass cover slipand examined under the microscope. It isimportant to note that 10% KOH should not beapplied to the skin directly. This technique can beused to identify surface mites and multiplescrapings should be taken to increase the like-lihood of ectoparasite detection. The materialcollected by dry skin scraping can also be digestedin 10% KOH for 20 minutes and centrifuged toconcentrate mites, which can be collected fromthe surface.


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8.2.4 Deep skin scraping (deepepidermal examination)

This is an extension of the superficial skin scrap-ing technique and should be performed followingor during squeezing of the skin between thethumb and forefinger. After the superficial layershave been removed for examination as describedabove, the procedure is repeated until capillaryooze occurs. This technique is useful in the diag-nosis of burrowing and deep follicular mites suchas Sarcoptes scabiei and Demodex spp. Multiplesites should be scraped to maximise detection ofectoparasites.

8.2.5 Collection of free-livingectoparasites

Mobile free-living mites, ticks and fleas can befound in bedding, nests and faecal material by acareful search or by shaking thematerial through atier of sieves of decreasing mesh size. They mayalso be swept from vegetation using a hand net.Most commonly used for collecting ticks, how-ever, is a blanket drag. This is a woollen blanket orcotton towel, about 1m square, attached to a barat one side. The drag is pulled across low-lyingvegetation and questing ticks attach to the cloth.

Adult flies can be collected using hand nets,usually consisting of a deep bag of fine meshnetting with a circular, wire-stiffened opening ona pole. Flies may be picked off as they visit theirhosts or baits of rotting carrion or faeces, usingeither a hand net or, more simply, by inverting aglass tube over them as they feed or rest. A widevariety of baited traps are also used to attract andcatch adult flies.

8.2.6 Biopsy and histopathology

Although this is not always as useful as directidentification of the parasite for diagnosis, it maybe of use in some circumstances, such as insectand arthropod bite lesions. Mites such as Demo-dex spp. are frequently seen in biopsy sections,

however Sarcoptes scabiei are infrequently seen inbiopsies from cases of sarcoptic mange (Plates 1,2). Histological changes associated with ectopar-asites include:

. An eosinophil-rich dermal infiltrate.

. Collagen degeneration, usually associated withdermal eosinophil infiltration.

. Focal dermal necrosis, which occurs in tick-bite lesions.

. Eosinophilic folliculitis and furunculosis,which may be associated with mosquito-bitelesions in cats and are now thought to occur inthe dog associated with arthropod-bite lesions.

. Eosinophilic pustule formation, which mayoccur in cases of flea-bite dermatitis, Sarcoptesscabiei infestation and cheyletiellosis in the dog.

. Lymphocytic mural folliculitis, which has beenassociated with demodicosis in the dog.

. Eosinophilic granulomas, which commonlyoccur in nodular skin disease in the horseassociated with flying insect bites (Plate 3).

8.3 THE CHEMICAL CONTROL OFECTOPARASITES ±ECTOPARASITICIDES

The drugs and chemicals used against ectopar-asites, known generally as ectoparasiticides(Table 8.2), contain a very restricted range ofelements: carbon, hydrogen, oxygen and nitrogenare almost universal, sulphur occurs in some,while fluorine, chlorine, iodine and phosphorousoccur occasionally. Ring structures are verycommon. All drugs have at least three names: asystemic chemical name (e.g. 2-cyclopropyla-mino-4, 6-diamino-s-triazine), a simpler genericname (e.g. cyromazine) and a trade name (e.g.Vetrazin1). In this chapter all chemicals arereferred to by their generic name.

8.3.1 Ectoparasiticides: earlycompounds

Early substances used against ectoparasites werefound largely by trial and error or were derived

The Diagnosis and Control of Ectoparasite Infestation 181

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from those developed for horticulture. The latterwere often highly toxic, being based on arsenicand mercury, as well as tar, petroleum and nico-tine. Carbon disulphide and rotenone (extract ofderris) were widely used against ectoparasites.The poisoning of livestock and dairy productswas not uncommon and consequently such che-micals have largely been replaced by pesticidesthat are inherently less toxic.

Sulphur, either as sublimed sulphur (lime sul-phur, flowers of sulphur) or precipitated sulphur(monosulfiram), is a traditional topical ectopar-asiticide. Sulphur has been incorporated in oint-ments, powders and shampoos. Sulphurshampoos are still used in veterinary dermatologyfor their keratolytic and keratoplastic propertiesin dry scaling dermatoses, rather than for anantiparasitic effect.

8.3.2 Ectoparasiticides: neurotoxins

Most ectoparasiticides act as neurotoxins atcentral nervous system synapses, axons or neu-romuscular junctions, leading to spastic or flaccidparalysis.

Organochlorines

Chlorinated hydrocarbons have been used inarthropod pest control since the early 1920s;hexachloroethane and hexachlorophene werelargely replaced by the salicylanilides. These werefollowed, in the 1940s, by DDT and the cyclo-dienes. However, these chemicals are persistentwithin the environment and the use of com-pounds such as DDT, g-BHC and dieldrin is nowtightly controlled or prohibited. Nevertheless, theless persistent methoxychlor, toxaphene and lin-dane still find appreciable use against biting fliesand lice in some parts of the world, where long-term persistence is considered important.

Organophosphates

These compounds replaced the chlorinatedhydrocarbons as insecticides and have been amajor class of pesticide since the 1950s. Organo-phosphates are potent cholinesterase inhibitors.The more commonly encountered organopho-sphates include diazinon, bromocyclen, cythioate,dioxathion, fenthion, malathion, chlorphenvin-phos, chlorpyrifos, dichlorvos and phosmet. They

Table 8.2 Ectoparasiticides grouped according to their mechanism of action.

Group/mode of action Examples

Early compounds Carbon disulphideRotenoneSulphur (lime sulphur/flowers of sulphur/monosulfiram)

Neurotoxins Organochlorines

OrganophosphatesCarbamatesTriazepentadienes

PhenylpyrrazolesPyrethrinsPyrethroidsMacrocyclic lactones

Insect growth regulators Juvenile growth hormones/analogues

Chitin synthesis inhibitorsTriazine derivatives

Repellents Pyrethrins

Desiccants Sodium polyborate


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can be used against a variety of ectoparasites,including fleas, lice, mites, ticks, keds and flies.Products for use on the animal and in the envir-onment are available and include formulationsfor use in dips, sprays, spot-ons and collars.Those most often incorporated in environmentalpreparations are chlorpyrifos, dichlorvos, iodo-fenphos, diazinon and malathion. These com-pounds are readily broken down and do nothave the residual problems associated with theorganochlorines. However, recent concern overneurotoxic side-effects associated with organo-phosphates has led to greater regulation of dip-ping procedures which, in addition to the disposalcosts, has led to a reduction in their use in farmanimals. Generally the use of organophosphatesis likely to diminish over the coming years as aresult of these concerns.

Carbamates

These also have anticholinesterase activity but areconsidered to be less toxic than the organopho-sphates and include carbaryl, bendiocarb andpropoxur.

Triazepentadienes (formamidines)

The only member of this group used in veterinarymedicine is amitraz. It is used as a dip for thecontrol of ticks on cattle and sheep, lice on cattleand pigs and sarcoptic mange on pigs and dogs. Itis also used for the treatment of demodecticmange on dogs. In some countries an impreg-nated collar is also available for flea control.

Phenylpyrrazoles

These are a relatively new group of ectopar-asiticides, currently represented only by fipronil,which acts by inhibiting the neurotransmitter g-aminobutyric acid (GABA). The effect is highlyspecific to the invertebrate GABA receptor,making it very safe to the mammalian host andallowing its use on young and pregnant animals.Fipronil has activity against fleas, ticks, lice,Trombicula spp. and Cheyletiella spp. Thechemical is lipophilic and diffuses into the

sebaceous glands of the hair follicle which thenact as a reservoir, giving fipronil a long residualactivity. There is evidence that it has an extremelyrapid knockdown effect, which occurs beforefleas have the opportunity to feed. Hence, it maybe especially useful in cases of flea allergic der-matitis. It is available as a spray and spot-onpreparations. There have been problems with theuse of Fipronil in small mammals and it is onlylicensed for use in the dog and cat.

Pyrethrins

These are synthetic compounds based on thenatural compound pyrethrum. This is extractedfrom the dried and powdered heads of Chry-santhemum cinereanaefolium. It is probably theoldest pesticide known and was first discoveredand used in China in the fifth century AD. Theplant was first introduced into Europe in the latenineteenth century. The active components ofpyrethrum are pyrethrins. Pyrethrins act on thecentral nervous system to give a rapid knock-down. However, they have poor residual activityand are quickly degraded by sunlight. Pyrethrin isused in insecticidal powders and shampoos whichoften contain other ingredients, such as piperonylbutoxide, with synergistic effects. Pyrethrins areused against lice and fleas, although for control ofthe latter frequent application and environmentalcontrol are also required.

Pyrethoids

These are synthetic chemicals based on pyrethrinwhich have a similar mode of action, but greaterstability. Degradation by UV light occurs, butmicroencapsulation has prolonged their activityto weeks. The microcapsules adhere to the insectectoskeleton and the pyrethroid is absorbedthrough the chitin to produce its toxic effect.Photostable pyrethroids used include permethrin,cypermethrin, deltamethrin and fenvalerate.Their activity is enhanced when combined withpiperonyl butoxide which acts as a synergist.Pyrethroids are used against fleas, flies, keds, liceand ticks. They are available in shampoos, sprays,powders and flea collars. Permethrin and


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fenvalerate are both available in environmentalproducts in the USA.

Macrocyclic lactones

The past decade has seen the introduction of anew group of natural products, the macrolideantibiotics, which have a 16-membered macro-cyclic lactone ring. These include the avermectinsand the milbemycins. The major avermectins areivermectin, abamectin, doramectin and sela-mectin. The major milbemycins are milbemycin,nemadectin and moxidectin. The avermectins,ivermectin and abamectin are fermentationmetabolities of the actinomycete Streptomycesavermitilis.Doramectin is a genetically engineeredavermectin. Selamectin is a novel semi-syntheticavermectin produced by fermentation of a novelstrain of Streptomyces avermitilis. Selemectin iseffective against fleas, Sarcoptes scabiei andOtodectes cynotis as well as nematodes. Themilbemycins are synthetically derived fromnemadectin, a natural fermentation product ofthe actinomycete Streptomyces cyanogriseus.These chemicals have a broad spectrum of activ-ity against arthropods and nematodes and lowvertebrate toxicity. They are highly effectiveagainst parasitic nematodes and blood-feedingectoparasites. Macrocyclic lactones are alsoeffective against non-blood-feeding ectoparasitessuch as bots, biting lice and chorioptes mites.

8.3.3 Ectoparasiticides: insectgrowth regulators

Insect growth regulators (IGRs) interfere withvarious aspects of arthropod growth and devel-opment, acting principally on embryonic, larvaland nymphal development and disrupting meta-morphosis and reproduction. As a result, IGRsdo not usually kill the target pests directly and,therefore, require more time to reduce ectopar-asite populations than conventional insecticides.The fact that they act on insect-specific phenom-ena provides IGRs with a high degree of selec-tivity between insects and vertebrates. IGRs can

be divided into three categories: juvenile hor-mones, chitin synthesis inhibitors and `others'.

Juvenile hormones and juvenile hormoneanalogues

Species-specific juvenile hormones are producedby most insects at some stage in their lives. Theyprevent metamorphosis until the larva is fullygrown. At certain stages juvenile hormone mustbe present, at others it must be absent, to permitnormal development. Removal of juvenile hor-mone from young larvae induces early puparia-tion and the emergence of dwarfed adults,whereas implants in mature ones may postponeor suppress metamorphosis altogether. The pre-sence of juvenile hormone may also prevent egghatch. A number of juvenile hormones have beenidentified, their structures established and, fromthese, derivatives known as the juvenile hormoneanalogues (JHA) or juvenile hormone mimicshave been developed. One of the oldest but stillthe most widely used of these is methoprene. Thenewer IGR, fenoxycarb, has been formulatedwith pyrethroids or organophosphates in spraysand washes for use on-animal and in the envir-onment. Pyriproxifen, which is active againstfleas at very small doses, has been released in theUSA and is available in spray, collar and washformulations.

Chitin synthesis inhibitors

An alternative target for IGRs is the arthropodcuticle, in particular the amino-sugar poly-saccharide chitin, which is an important elementin the structure of the arthropod exoskeleton.Chitin is relatively uncommon in other animalsand therefore any interaction with the synthesisor deposition of chitin offers a potential means tocontrol the development of arthropods selec-tively. Several chemical substances are knowninhibitors of chitin synthesis, including the ben-zoylphenylureas (BPUs). The primary effect ofBPU treatment is the disruption of chitin synth-esis, by prevention of the production of chitinmicrofibrils. In general, the insect dies during orimmediately following the time when chitin


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synthesis is critical to survival, usually at egghatch or at moult. This class of chemicals includescompounds such as diflubenzuron and tri-flumuron. Lufenuron is an orally administeredbenzoylphenylurea derivative used for flea con-trol, which enters the female flea from the bloodwhile feeding and leads to the production ofsterile eggs by interference with chitin production.

Other insect growth regulators

The third group of IGRs, the triazine derivatives,currently contains only one representative, cyro-mazine. Like the BPUs, cyromazine interfereswith moulting and pupation, but without actingdirectly on chitin synthesis. Another differenceconcerns the spectrum of activity. While BPUsusually act against a wide range of insects, cyro-mazine shows considerable specificity for thelarvae of higher Diptera and is reported to havelittle effect on the larvae of most other types ofinsect.

8.3.4 Repellents

Several compounds appear to have insect repel-lent activities and are incorporated in commercialrepellents. These include:

. Pyrethrin

. Diethyltoluamide (DEET)

. Ethanhexadiol

. Dimethyl phtholate

. Butopyronoxyl

These chemicals may be of use when treatingdermatoses associated with flying insects such asCulicoides spp. in horses.

8.3.5 Desiccants

Desiccants have been used to alter the environ-mental microclimate and thereby control fleasand free-living mites present in the environment,such as house-dust mites. In particular, the che-mical sodium polyborate applied annually to

carpets and furnishings in entire houses may givecomplete flea control. It is claimed that theproduct is of low toxicity, without odour and alsoreduces the number of house-dust mites withinthe environment, which is an importantconsideration when treating dogs with atopicdermatitis and concurrent flea allergy.

8.4 MODE OF ECTOPARASITICIDEAPPLICATION

Ectoparasiticides can be delivered to the parasiteby topical preparations applied to the host's coat,systemic preparations and environmental pre-parations. The choice of ectoparasite treatment orcontrol technique is influenced by the pathogen-esis of the dermatosis produced, the mode ofaction and efficacy of drugs available and, criti-cally, the life-cycle and habits of the parasite inquestion.

8.4.1 Topical preparations

Topical preparations available include dips,sponge-ons, sprays, powders, mousses, collarsand ear tags. They contain many of the chemicalsdescribed above. Topical preparations can beclassified as parasiticides, repellents andmechanical agents. Topical formulations of neu-rotoxic insecticides usually give rapid knockdownbut, with intermittently available parasites,lengthy residual activity is critical to ensure thatthe host is protected at periods when the parasiteis available.

8.4.2 Systemic preparations

Systemic preparations can be divided into inject-able, oral and topically applied products, all ofwhich are delivered to the ectoparasite during itsfeeding activity on the skin. However, there are anumber of drawbacks to the use of systemictreatments, particularly with slow-acting IGRs.First, if the ectoparasiticide takes some time to beeffective, treatment needs to be given before


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parasite populations reach a critical density.Second, free-ranging animals, such as cats, maycontinually reacquire infestations of parasitessuch as fleas from feral cats, wild animals andneighbours' untreated cats, maintaining theenvironmental supply of eggs, larvae and newlyemerged fleas. Finally, if the clinical signs are theresult of a hypersensitivity reaction to antigensinjected by the parasite during feeding, then anectoparasiticide delivered via the host's bloodmay not be effective in controlling the dermatitis.In cases of hypersensitivity, an ideal parasiticideprevents feeding and thereby the development ofclinical disease.

Systemic ectoparasiticides are of particularvalue in the control of ectoparasites that spendall, or a considerable portion, of their life-cycle onthe host, where rates of reinfestation are relativelylow and where the parasite load is an importantcause of disease or loss of production. In manycases, systemic ectoparasiticides are best used asone component of an ongoing, integrated controlprogramme.

8.4.3 Environmental preparations

For ectoparasites that are free-living in one ormore life-cycle stages, or are present on the hostfor only short periods, such as the ticks, fleas andflies, parasiticides may be directed at the free-living stages in the environment. However,parasites may escape chemical treatment of theenvironment, either by living in difficult to reachsites, such as the base of a carpet, or in aresistant life-cycle stage, such as the pupa or egg.Hence, the residual activity of any insecticide oracaricide is critical so that the ectoparasite willbe affected as it changes location or moves fromone life-cycle stage to another. Treatment of theenvironment is most effective for localisedectoparasite species, when the insecticide oracaricide can be focused at selected sites. Anideal environmental ectoparasiticide shouldtarget the parasite specifically and have lowtoxicity for all other species. Examples of moreenvironmentally discriminating products includethe IGRs.

8.5 PROBLEMS WITH CHEMICALCONTROL

The use of ectoparasiticides is associated withrisks of side-effects or poisoning resulting fromoverdose, species sensitivity, breed sensitivity oran interaction between administered medicines.In addition, the treatment of the wider environ-ment with insecticides almost inevitably leads tounwanted effects on non-target organisms.

8.5.1 Poisoning and environmentalcontamination

Many of the organochlorines and organopho-sphates are highly toxic to vertebrates andaccidental poisonings, resulting from careless use,overdosing or inappropriate treatment, are com-mon. Cats are particularly highly sensitive tolindane. Small or young dogs and cats can beeasily overdosed with organophosphate insecti-cides used for flea treatment, particularly whereflea collars are ingested, or used inappropriatelyor simultaneously with other organophosphatetreatments. The pyrethroids are generallybelieved to have a wide margin of safety withmammals, but are toxic to crustaceans and fish.Nevertheless, in cats and small dogs neurotoxiceffects have been recorded, particularly withpermethrin, fenvalerate, tetramethrin, chry-santhemate and deltamethrin, although in mostcases these have been associated with overdosing.

Environmental contamination and effects onnon-target animals have been well documented inthe case of the organochlorine insecticides;growing concern is associated with the organo-phosphates. The disposal of pesticides may createproblems, particularly when large volumes ofliquids, such as organophosphate sheep dips, areinvolved. As more is learnt of the long-term riskfrom disposal sites, proper and legal disposal hasbecome more difficult and of greater publicconcern.

The faeces of cattle provide a rich and uniquehabitat for over 200 species of invertebrate intemperate climates. Many of these species, parti-


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cularly the coprophagous beetles, perform a vitalrole in the nutrient cycle of pastures, assistingwith the conversion of the cattle dung into humus.In recent years it has been shown that a number ofdrugs given to livestock may be eliminated infaeces or urine in a largely undegraded and stilltoxic form. For example, dichlorvos, coumaphosand cruformate administered in normal doseshave deleterious effects on insects in the faeces ofcattle and horses for several days after treatment.This phenomenon may be considered advanta-geous in some cases and in-feed organopho-sphates have been used to eradicate the pestspecies of fly that breed in livestock dung. How-ever, insecticidal material in animal dung mayalso have a range of undesirable effects on non-target organisms.

Insecticidal material in dung may kill non-target insects and the loss of these insects mayprevent normal dung decomposition. Such effectshave been shown to be particularly pronouncedfor the avermectins, although not the milbemy-cins. Avermectins in cattle and horse dung areparticularly toxic at low doses to beetle andcyclorrhaphous fly larvae and the mortality ofthese insects may delay dung-pat decomposition.Nevertheless, the long-term impact of theseeffects is the subject of considerable dispute.There is no evidence that avermectins affectearthworms, and earthworms are also importantagents in dung-pat decomposition. It is widelyargued that the presence of earthworms and theabrasive effects of winter weather, in combinationwith uneven patterns of avermectin use betweenfarms and herds, will result in minimal environ-mental contamination from the widespread use ofavermectins. This debate has yet to be resolvedeither way.

8.5.2 Resistance

At the recommended doses modern anti-helminthics and insecticides are highly effective atremoving susceptible individuals, but they canimpose strong selection pressure for the develop-ment of resistance. Often selection by one type ofchemical hastens the development of resistance

against other previously effective compounds;cross- and multiple-resistance in ectoparasites isnow a growing problem, necessitating drugswitching and the use of alternative chemicals.The use of slow-release technology might wellplay a significant part in increasing the rate ofdevelopment of resistance. There can be littledoubt that resistance to existing chemicals isunlikely to be reversed and, indeed, will becomemore widespread, and that new compoundsdeveloped in the future will also select for resis-tance. Probably the most optimistic prognosis isthat appropriate management will allow the ratedevelopment of resistance to be reduced.

8.6 NON-CHEMICAL CONTROL OFECTOPARASITES

In addition to the use of ectoparasiticidal chemi-cals, increasing attention is being given to thedevelopment and application of simple andinexpensive, non-chemical control technologies.These usually work by modifying some aspect ofthe parasite's environment, on or off the host,either to increase ectoparasite mortality or toreduce its fecundity. These non-chemical techni-ques, in general, serve to reduce or suppressparasite populations, rather than bring abouttheir total elimination. As such, they should beseen as valuable components of a general ecto-parasite management programme. The range oftechniques that are currently the subject ofdevelopment is vast and will only be covered herebriefly.

8.6.1 Physical control

Modification of the parasite's off-host environ-ment may significantly reduce ectoparasiteabundance. For example, many of the dipteranpests of cattle and horses have larval stages whichdevelop in animal dung. Management of dung,therefore, is of prime importance in their controland considerable success can be achieved simplyby removing dung regularly from pastures or feed


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lots and dispersing it in such a way that it nolonger attracts ovipositing flies. Biting and non-biting flies also can be effectively controlledthrough simple procedures such as the removal ofmoist bedding and straw, food wastes, heaps ofgrass cuttings and vegetable refuse in which theybreed.

Similarly, changing the suitability of the on-host environment may help reduce the suscept-ibility of the host to ectoparasite attack. Forexample, in sheep, minimising pasture wormburdens to reduce diarrhoea, tail docking(amputation of the tails), crutching or dagging(the regular shearing of soiled wool from aroundthe breech) all help to minimise the incidence ofsheep blowfly strike by Lucilia sericata or L.cuprina by reducing wool soilage, thereby redu-cing the availability of oviposition sites and suit-ability of the fleece for larval survival.

Tick- and mite-infested pasture can be avoidedin some circumstances; grazing practices whichreduce contact with ticks, such as pasture spelling,which removes all major hosts for over a year,may cause the tick population to collapse. Har-vest mites, Trombicula spp., are commonly foundassociated with fruit trees and chalky soils; dogsaffected by this mite can be exercised away fromsuch areas. Forage mites may cause a dermatitisin various species including horses, and reducedexposure to infested hay may be an effectivecontrol measure; hay stored in lofts above stablescould be moved elsewhere or animals can beprevented access to hay barns. Dogs, cats andother species having access to poultry houses maydevelop dermatitis caused by the poultry miteDermanyssus gallinae and simply excluding thepet may solve the problem. Midges such as Culi-coides spp. feed on horses (causing `sweet itch') atparticular times of day and simply stabling duringmorning and evening may prevent or reduce theopportunities for feeding and thereby reduce theseverity of the clinical disease.

8.6.2 Barriers

There are various types of physical barrier thatcan be employed to protect the host from

ectoparasites. These may be fine mesh screens onwindows, plastic strips on milking parlour doorsor brow tassles for protection from flying insects.Such techniques may often be used in conjunctionwith an insecticide; one traditional treatment forthe control of sweet itch in horses is to apply amixture of liquid paraffin and benzoyl benzoateto the mane and tail base.

8.6.3 Biological control

Organisms which are predators, parasites, com-petitors and pathogens of the ectoparasite can beused as biological controls. For example, thenematode Steinernema carpocapsae has beenshown experimentally to parasitise and kill thepupal stage of Ctenocephalides felis and may be ofuse as part of a flea control programme whereoutdoor environmental treatment is important.House flies have been controlled in poultryfacilities by the release of pupal parasites. The useof imported dung-burying beetles to increase therate of removal of cattle pats has been attemptedin Australia, Canada and the USA, to prevent theemergence of dung-breeding flies. Considerableinterest is currently being given to the use of thebacteria Bacillus thuringiensis as a biologicalcontrol agent, particularly for lice. Nevertheless,the use of these techniques can be a complex andcostly operation and, as yet, cannot be attemptedroutinely.

8.6.4 Vaccination

Various types of vaccines are being developed foruse against ectoparasites. In particular, vaccinescomprising parasite gut wall antigens show thegreatest promise, particularly for ticks. The vac-cinated host develops antibodies directed againstthe parasite's gut wall. The parasite ingests theseantibodies in the blood feed and dies as a result ofthe antibody binding to the intestinal epithelium.

Discovery of a host humoral response to anti-gens of L. cuprina has stimulated considerableinterest in the production of a vaccine. Vaccina-tion of sheep with partially purified extract of L.


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cuprina larvae can result in a marked reduction ingrowth when larvae are fed on sheep. Experi-mental vaccines have been produced based onserine proteases secreted by larvae and larvalmembrane proteins. However, to date, no effec-tive commercially available vaccine has beendeveloped.

8.6.5 Trapping

Arthropods use a complex interaction of olfac-tory, visual and tactile cues to locate their hosts. Ifthese cues can be identified and isolated, they canbe selectively incorporated into trapping devicesat levels that produce exaggerated responses fromthe targets. Walk-through traps have beendeveloped for the control of Haematobia irritans,stable flies and face flies. The development oftraps for tsetse flies in Africa has been highlysuccessful, identifying and exploiting appropriatevisual shapes and colours in combination withhost-mimicking chemical odours to attract andcatch flies.

A screwworm adult suppression system(SWASS) has been used to attract C. hominivoraxin North America. This combines an insecticide(2% dichlorvos) with a synthetic odour cocktailknown as `Swormlure' to attract and kill adultflies. Field trials with the SWASS gave a 65±85%reduction in an isolated wild C. hominivoraxpopulation within 3 months. However, environ-mental concern about the release of large quan-tities of dichlorvos has resulted in the SWASSbeing largely abandoned as a control technique.

Traps baited with synthetic chemicals or car-rion have been developed to attract and kill thesheep blowflies L. sericata and L. cuprina. Atpresent, however, traps are generally of morevalue for sampling than control. Nevertheless,such techniques hold considerable promise forfuture development.

8.6.6 Sterile insect technique

By obtaining a high proportion of matings withfertile wild females, male insects, sterilised with

radiation and released into a wild population, caneventually drive the population of wild flies toextinction, provided that:

(1) Males are released in sufficiently high num-bers so that they outnumber the wild fertileflies;

(2) The released males are fully competitive withwild males; and

(3) The release area is isolated, to protectagainst immigration.

Probably the most successful example of the useof this technique has been the eradication of theNew World screwworm fly, C. hominivorax, fromthe south-western USA, Mexico and NorthAfrica. Management schemes based on sterile-insect work have also been tried in the control ofhaematophagous flies like Haematobia irritansand Stomoxys calcitrans. However, there aresevere constraints to the use of this technique. Theextensive rearing facilities required to breed andrelease large numbers of insects make applicationexpensive, and the additional aggravation causedby the release of billions of blood-feeding, dis-ease-carrying adult insects into the field makeseffective control problematic.

8.6.7 Modelling and forecasting

Models may be of particular value in helping topredict the seasonal patterns of abundance ofparticular ectoparasites and their economic con-sequences. The development of such predictivemodels may allow veterinarians, farmers andentomologists to use ectoparaciticides prophy-lactically. They may also allow ectoparasiticidetreatment to be integrated with non-chemicalcontrol techniques, to build effective parasitesuppression programmes.


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8.7 CATTLE (Table 8.3).

8.7.1 Mites

Sarcoptic mange

Clinical features

Sarcoptic mange is caused by the mite Sarcoptesscabiei and occurs in cattle worldwide. It causes apruritic dermatosis with papules, crusts, excoria-tion, secondary alopecia and lichenification. Thefemale mite burrows in the stratum corneum ofthe epidermis parallel to the surface and depositseggs and faeces within the burrows. The patho-genesis of the cutaneous lesions is thought to

involve the innate cutaneous reaction and ahypersensitivity reaction, most likely to faecalantigens. The lesions tend to occur on the face,neck, shoulders and across the rump.

Diagnosis

Diagnosis is confirmed by identification of mites,eggs and faecal pellets in skin scrapings.

Treatment

Topical treatment with organophosphates (forexample coumaphos, phosmet, diazinon ormalathion), usually with two applications cover-ing a period equal to two life-cycles, is effective.

Table 8.3 A guide to ectoparasites affecting cattle.

Clinical signs Diagnostic techniques

Parasite

type

Species

Mites Sarcoptes scabiei . . . . . .Psoroptes ovis . . . . . .Psoroptes natelensis . . . . . .Chorioptes bovis . . . . . .Demodex bovis . . +/± . . . . ?Demodex ghanesis . . +/± . . . . ?Unnamed demodex spp. . . +/± . . . . ?

Psoragetes bos . . . . .D. gallinae . . . . . . .

Lice Damalinia bovis . . . . . .Haematopinus eurysternus . . . . . .Linognathus vituli . . . . . .

Fleas C. felis . . . . .

Ticks Various . . . . . .

Flies Blood-feeding flies . . . . . ?Nuisance flies . . .Primary myiasis . . .Secondary myiasis . . .

Pruritus

Papules/erythem

a

Pustules

Crusts

Scaling

Alopecia

Erosion/ulceration

ClinicalSigns

Visualidentificationof

parasite

Skin

scrapings

Hairbrushings

Hairplucks

Acetate

stripexam

Parasite

foundin

the

surroundingenvironment

Biopsy

andhistology


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The organochloride g-BHC is also very effective,but environmental and toxicity concerns havelimited its use. Traditional treatments includesulphur preparations such as lime sulphur (2%)applied every 10 days on three occasions; thesecan be used on lactating cattle. The use of otherproducts on lactating and beef cattle varies withregard to milk and carcass withdrawal times andall should be used as directed by the manu-facturers. Systemic treatment with injectable for-mulations of ivermectin, abamectin, doramectin,eprinomectin or moxidectin, all at a dose of200 mg/kg, has become popular in recent years. Asingle injection is effective. It should be noted thata fatal idiosyncratic reaction to abamectin hasbeen reported in an inbred herd of Murray greycattle; however, this is not thought to be a generalbreed sensitivity to avermectins. Topical dor-amectin, epinomectin, ivermectin or moxidectinat 500 mg/kg can be used in the treatment ofbovine sarcoptic mange.

Psoroptic mange

Clinical features

Psoroptic mange is caused by Psoroptes ovis andleads to a pruritic dermatosis with papules, crusts,excoriation, secondary alopecia and lichenifica-tion. The lesions occur in skin folds, on thewithers, shoulders, neck, rump, base of tail andperineum. In severe cases the lesions may becomegeneralised with haematological and blood bio-chemical changes (mild anaemia, lymphopenia,neutrophilia, eosinophilia, elevated fibrinogenand globulins). The disease occurs worldwide.The species Psoroptes natalensis affects cattle inSouth Africa and South America and has beenintroduced into Europe.

Diagnosis

Diagnosis is confirmed by observation and iden-tification of mites, eggs and faecal pellets in skin.

Treatment

Topical organophosphates (e.g. coumaphos,phosmet or toxaphene in beef cattle) applied twice

to cover two mite life-cycles, are effective. Thehighly effective organochloride g-BHC is now nolonger used due to environmental concerns. Thetriazapentadiene, amitraz, has also been usedsuccessfully in the treatment of psoroptic mangein cattle. Systemic treatment with a singleinjection of ivermectin at a dose of 200 mg/kg iseffective. Doramectin and moxidectin are alsoeffective.

Chorioptic mange

Clinical features

This is caused by the mite Chorioptes bovis, whichcan live off the host for up to 2 months and maybe considered a commensal since it is found onnormal cattle. Numbers of mites increase duringthe winter and dermatological disease may occuras the result of a hypersensitivity. The clinicalsigns are pruritus, erythema, non-follicularpapules, crusts, excoriation and secondary alo-pecia. The lesions are found on the feet, hindlegs,udder, perineum, scrotum and tail. The neck andhead may also be affected in some cases. Chor-ioptic mange leads to reduced milk yield and lossof condition.

Diagnosis


Treatment

Topical organophosphates (for example couma-phos, phosmet, crotoxyphos), applied at intervalsof approximately 2 weeks, are effective in thetreatment of bovine chorioptic mange. Lime sul-phur (2%) applied weekly for 4 weeks has alsobeen used effectively.

Demodectic mange

Clinical features

Demodectic mange is caused by Demodex spp. ofmites, D. bovis (eyelids and body), D. ghanesis


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(eyelids) and an unnamed species (eyelids andbody), all of which are thought to be normal skincommensals. Clinical signs include follicularpapules and pustules, usually over the withers,lateral neck, back and flanks. These may becomegeneralised in severe cases. Concurrent pyodermamay occur, leading to furunculosis with ulcera-tion and crust formation. The disease is of eco-nomic significance due to hide damage.

Diagnosis

Diagnosis is confirmed by identifying mites onskin scrapings or hair pluckings. Examination ofthe hair bulb and shaft mounted in liquid paraffinreveals numerous mites. Histopathology of skinbiopsy will also reveal large numbers of miteswithin the hair follicles or free within the dermis ifa furunculosis is present. Other histological fea-tures include a perifolliculitis, mural folliculitis orfolliculitis involving mixed inflammatory cells butwith numerous mononuclear cells.

Treatment

In many cases demodicosis spontaneouslyresolves and treatment is unnecessary. The orga-nophosphate trichlorfon, used on three occasions2 days apart, has been advocated.

Psorergatic mange

Clinical features

Psorergatic mange occurs in the USA, Canada,Australia, New Zealand and South Africa, and iscaused by the itch mite Psorergates bos. It hasbeen suggested that the mite may be a normalcommensal since it has been isolated from normalskin. It usually produces a mildly pruritic der-matosis in cattle with patchy alopecia and scaling.

Diagnosis

Diagnosis is confirmed by finding mites, eggs andfaecal pellets in skin scrapings.

Treatment

If treatment is required, systemic ivermectin canbe used although topical lime sulphur (2%) hasalso been reported to be effective.

Poultry mite infestation

Clinical features

Occasionally the poultry mite Dermanyssus galli-nae may cause dermatitis in cattle. The mite,which is free-living in the environment, causes apruritus with papule and crust formation, espe-cially on the ventrum, limbs and muzzle.

Diagnosis

Diagnosis is confirmed by detection of mites inskin scrapings, acetate strips or within theimmediate environment.

Treatment

The most effective treatment is avoidance of theinfested environment which, alternatively, can betreated with a pesticide; several pesticides havebeen suggested, including malathion, coumaphos,methoxychlor, diazinon and lime sulphur.

8.7.2 Ticks

Clinical features

Various types of tick worldwide feed on cattle andcan cause dermatitis. Apart from species of thegenera Argas and Otobius, only the hard ticks areof veterinary importance. These tend to feed inparticular sites, but they can be found anywhereon the body. The ears, face, neck, axillae, groin,distal limbs and tail of cattle are favoured sites.The cutaneous signs associated with tick feedingin cattle include papules, pustules, ulceration andalopecia. The tick mouthparts penetrate the epi-dermis and become lodged in the dermis wherehaemorrhage, collagen degeneration and a


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wedge-shaped area of necrosis occur. Tick feedingcan introduce cutaneous bacteria into the skin,causing abscesses, or into the circulation, leadingto bacteraemia and septicaemia. The otherpotential systemic effects of ticks are tickparalysis caused by neurotoxins or the transmis-sion of micro-organisms such as Rickettsia rick-ettsii, the cause of Rocky Mountain fever in theUSA.

Diagnosis

Diagnosis is based on clinical examination andthe collection and identification of ticks from theskin.

Treatment

Ideally the cattle should be removed from theinfested pasture, although this is not alwayspractical and topical therapy is then used toreduce the tick population. The life-cycle of theparticular ticks involved will influence the appli-cation regime, with multiple-host ticks requiringprolonged insecticidal programmes, whereascontrol of one-host ticks may only require treat-ment for a few weeks of the year. Organopho-sphates and pyrethroids have been used to controltick populations but, with increasing concernover environmental contamination, there hasbeen a decline in the use of the former. Resistanceto various topical insecticides is also an increasingproblem. The following compounds have beenused in the control of ticks on cattle: amitraz,chlorpyrifos, chlorfenvinphos, coumaphos, cro-toxyphos, cypermethrin, cyprothrin, deltame-thrin, diazinon, dichlorvos, dioxathion, g-BHC,flumethrin, malathion, permethrin, phosmet,propetamphos and trichlorfon. These are avail-able in various formulations including sprays,dips and slow-release ear tags. Systemic treatmentwith 200 mg/kg ivermectin every 2 to 4 weeks hasalso been shown to prevent tick engorgement andreproduction. Management measures includeseparation of cattle from infested pasture andcultivation of the infested land.

8.7.3 Flies

Blood-feeding flies

Clinical features

Blood-feeding flies, particularly stable flies, hornflies and tabanids, can cause severe disturbanceand annoyance to cattle, leading to reducedweight gain, reduced milk production and hidedamage. Fly bites may cause pruritic papules andwheals. Blood-feeding flies may also be importantvectors of viral, bacterial and protozoal diseasesand filaroid nematodes.

Diagnosis

Diagnosis is based on clinical signs and observa-tion of adult flies feeding.

Treatment

Minimising the effects of blood-feeding flies isdifficult and involves the use of fly avoidancestrategies, repellents, topical insecticides and, insevere cases, treatment involves the use ofsystemic glucocorticoids. Control of breedingsites (animal dung, vegetable matter, still-waterpools) will help to reduce biting fly numbers.Topical treatment of animals with organopho-sphates (coumaphos, chlorfenvinphos, diazinon,dioxathion, fenchlorvos, malathion, phosmet,stirofos, trichlorfon) and pyrethrins (permethrin,cyfluthrin, cypermethrin) may give temporaryprotection. However, maintaining residual activ-ity on the host is difficult. Self-treatment systems,such as insecticidal dust bags and pyrethroid eartags, may be an effective way of maintaininginsecticide levels on an animal. Regular applica-tion of repellents will also help to prevent fly bites.Residual insecticide preparations can be usedwithin housing and on fly breeding sites. Housingin accommodation secured from fly entry willhelp to minimise fly activity around stock.


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Nuisance flies

Clinical features

The activity nuisance flies, such as the face fly,house flies and other muscids, cause disturbanceand irritation. These flies may also be mechanicalvectors of disease.

Diagnosis

Diagnosis is based on observation and identifi-cation of feeding flies.

Treatment

Topical organophosphates (malathion, couma-phos, crotoxyphos, trichlorfon) and pyrethroids(permethrin, cypermethrin) are effective in redu-cing fly numbers. Ear tags impregnated withcypermethrin or permethrin are also useful in thecontrol of these flies.

8.7.4 Myiasis

Hypodermiasis

Clinical features

Third-stage larvae of warble flies, Hypodermaspp., produce painful nodular lesions approxi-mately 3 cm in diameter with a central hole in theskin of the back. Infestation is seen most usuallyin young animals. If accidentally ruptured, or thelarva dies within the skin, anaphylaxis and deathmay occur. Hide damage is the main economiceffect of warbles. If larvae become lodged withinthe spinal cord, acute posterior paralysis withoutsystemic signs may occur. Flying adults ofHypoderma bovis cause annoyance and fright withrunning (gadding) to avoid the flies, resulting inloss of production.

Diagnosis

Diagnosis is based on the appearance of thecharacteristic cutaneous swellings along the back.

Treatment

Warble fly larvae in cattle can be effectivelycontrolled using systemic organophosphate pre-parations, applied as sprays, pour-ons or spot-ons. However, while systemic organophosphatescan kill migrating larvae, they are relatively inef-fective once larvae are inside their warbles. War-ble flies are sensitive to all formulations ofavermectins. Topical therapy using ivermectin ina 0.5% solution applied at a dosage of 500 mg/kg,and systemic therapy with ivermectin at a dosageof 200 mg/kg, have been reported to be effective.Similarly, moxidectin and doramectin are effec-tive against warble fly larvae.

Dermatobia

Clinical features

Dermatobia hominis, also known as the torsalo,berne or human bot fly, is a serious pest of cattlein Central America. The larvae create boil-likeswellings where they enter the skin. The cuta-neous swellings can be pruritic and the exit holesmay attract other myiasis flies. Infestation mayresult in damage to the hide and reduction in meatand milk production.

Diagnosis

Diagnosis is made on the identification of warblesin the skin and identification of larvae withinwounds.

Treatment

Historically, control of D. hominis has beenachieved by the application of various insecti-cides, at 2 to 4 week intervals, to livestock to killlarvae in warbles and to prevent reinfestation.Suitable insecticides include toxaphene (camphe-chlor), DDT/g-BHC mixtures, crufomate, fen-thion and trichlorophon. Intramuscular injectionof closantel (10±12.5mg/kg) has also been foundto give effective control. However, ivermectin,abamectin and doramectin, applied topically orby injection, are now commonly used.


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Cutaneous myiasis

Clinical features

Cutaneous myiasis of cattle is most commonlycaused by the obligate screwworms: Cochliomyiahominivorax (Nearctic and Neotropical regions),Chrysomya bezziana (Oriental and Afrotropicalregions) and Wohlfahrtia magnifica (easternPalaearctic). Myiasis occurs largely as a con-sequence of skin damage due to trauma; castra-tion or dehorning wounds are commonoviposition sites, as is the umbilicus of newly borncalves. Eggs may also be deposited in body ori-fices, such as the nostrils, eyes, mouth, ears, anusand vagina. Larvae-filled lesions may be ulcer-ated, cavernous and painful. Secondary bacterialinfection, toxaemia and dehydration lead todeath. Other Calliphoridae, including species ofLucilia, Chrysomya, Cochliomyia and Calliphora,may be secondary invaders of screwwormwounds, but only rarely initiate myiasis of cattle.

Diagnosis

Diagnosis is made on the basis of clinical signsand identification of larvae within wounds.

Treatment

The current recommended treatment for woundsinfested by C. hominivorax is a mixture of theorganophosphates coumaphos (5%) and chlor-fenvinphos (2%) powder in a vegetable oil base.For C. bezziana a range of insecticides has beenshown to be effective. Ivermectin, doramectin andorally administered closantel have also provedhighly effective in the treatment of C. bezzianaand C. hominivorax infestations.

8.7.5 Fleas

Clinical features

Fleas rarely affect cattle; however, infestationwith the cat flea, Ctenocephalides felis felis, hasbeen reported. Pruritic papular lesions occur atthe sites of feeding.

Diagnosis

Diagnosis is based on the clinical signs, collectionby coat brushing and identification of fleas.

Treatment

Topical treatment using organophosphates orpyrethroids along with environmental sprayingwill control fleas.

8.7.6 Lice

Clinical features

Lice cause a pruritic scaling dermatosis with focalsecondary alopecia and excoriations. The suckinglice, Haematopinus eurysternus, Linognathus vituliand Solenoptes capillatus, are found especially onthe head, neck, withers, tail, groin, axillae andventrum. The chewing louse, Damalinia bovis(Plate 4), is usually found on the neck, withersand tail. Heavy infestations of sucking lice maycause anaemia.

Diagnosis

Diagnosis is based on clinical signs and identifi-cation of lice in coat brushings. Characteristic liceeggs may also be found attached to hairs.

Treatment

Lice spend their entire life on the host, whichmakes treatment easy and effective. Topicalorganophosphates (for example chlorfenvinphos,coumaphos, chlorpyrifos, dichlorvos, diaxathion,diazinon, malathion, crotoxyphos, trichlorfon,phosmet and propetamphos), in spray and pour-on formulations, are effective. The pyrethoids,permethrin and cypermethrin, are also effective.Topical avermectins are effective against suckingand biting lice. A single injection of ivermectin ata dose of 200 mg/kg has been shown to be effectivein the treatment of sucking lice.


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8.8 SHEEP (Table 8.4)

8.8.1 Mites

Sarcoptic mange

Clinical features

Infestation by Sarcoptes scabiei is a rare conditionin sheep, but may occur occasionally, leading topruritus, excoriation, crusts, lichenification andsecondary alopecia. Lesions are found on theface, ears and legs.

Diagnosis

Diagnosis is confirmed by identification of mites,eggs and faecal pellets on skin scrapings.

Treatment

Topical treatment with organophosphates (forexample coumaphos, phosmet or diazinon)should be repeated at an interval of 10 to 14 days.Topical preparations are most effective if usedafter shearing. Systemic treatment with ivermec-tin, at a dose rate of 200 mg/kg given sub-cutaneously, should also be effective.

Table 8.4 A guide to ectoparasites affecting sheep.


Parasitetype

Species

Mites Sarcoptes scabei (rare) . . . . . .Psoroptes ovis . . . . . +/± . . .Chorioptes bovis . . . . . .Demodex ovis . . . . . .Trombicula spp. . . . . . . .Psoragetes ovis . . . .Forage mites . . . . .

Lice Linognathus ovillus . . . . . .Linognathus africanus . . . . . .Linognathus stenopsis . . . . . .Linognathus pedalis . . . . . .Damalinia ovis . . . . . .

Fleas Ctenocephalides felis(rare)

. . . . .

Ticks Various . . . . . . .

Flies Blood-feeding flies . . . .Melophagus ovinus . . .Nuisance flies . . . .Nasopharyngeal myiasis . .Primary myiasis . . .Secondary myiasis . . .

Pruritus

Papules

Pustules

Crusts

Scaling

Alopecia/w

ooldamage

Erosion/ulceration

Clinicalsigns


parasite

Skin

scrapings

Hairbrushings/acetate

stripexamination

Hairplucks

Serology

Parasite

foundin

the


Biopsy

andhistology


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Psoroptic mange (sheep scab)

Clinical features

This is one of the most common dermatologicaldiseases of sheep and is caused by Psoroptes ovis.Mite populations differing in virulence arebelieved to exist and debate continues about theirspecific or sub-specific status; Psoroptes cuniculi,which occurs in the ear, is considered by some tobe a strain of P. ovis rather than a separatespecies.

Sheep scab is thought to involve a type Ihypersensitivity to faecal antigens deposited onthe host's skin, leading to severe pruritus, excor-iation, pustules, wool matting and wool loss.Severely affected animals show hyperaesthesiawith lip smacking, seizures and eventually death.The disease is usually most severe during thewinter months, becoming latent or mild in thesummer, during which time mites are mostabundant in the body folds of the axilla, peri-orbital skin and ears.

Diagnosis

Diagnosis is based on history and clinical exam-ination and confirmed by identification of mites,eggs and faecal pellets on skin scrapings. Immu-notechnology for diagnosis of sheep scab bymeasurement of circulating antibodies is cur-rently being investigated and may lead to thedevelopment of an accurate commercial assay.

Treatment

Topical treatment with a variety of acaracidalcompounds is effective in treating psoropticmange. In the past g-BHC was commonly used asa dip formulation but environmental concernshave curtailed its use. Organophosphates havealso been used, although resistant strains ofPsoroptes ovis have been reported. Effective che-micals include coumaphos, phosmet, diazinon,propetamphos, flumethrin and lime sulphur.Dipping is required to soak animals sufficiently in

the acaricide. Systemic therapy with two injec-tions of ivermectin at 200 mg/kg 7 days apart iseffective. Doramectin (300 mg/kg) requires only asingle subcutaneous injection. In the future,alternative forms of treatment, such as vaccines,may become available.

Chorioptic mange

Clinical features

Chorioptic mange is caused by Chorioptes bovisand occurs in Europe, Australia and New Zeal-and, but has been eradicated from the USA.Clinical disease occurs in the winter and presentsas a pruritic dermatosis with papules, crusts,excoriation, secondary alopecia and lichenifica-tion. The lesions usually occur on the lower hindlimbs, ventral abdomen and scrotum. Scrotaldermatitis in rams can lead to testicular atrophyand infertility.

Diagnosis


Treatment

Topical organophosphates (coumaphos andphosmet) used in dips and repeated after 14 daysare effective in the treatment of ovine choriopticmange. Lime sulphur has also been reported to beeffective.

Demodectic mange

Clinical features

Ovine demodectic mange is an uncommon der-matosis caused by the follicular mite Demodexovis. The clinical signs are alopecia and scaling,especially on the face, neck and across theshoulders, with occasional involvement of thepinnae, lower limbs and around the coronarybands.


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Diagnosis

Diagnosis is confirmed by identification of mites,eggs and faecal pellets on skin scrapings or hairpluckings.

Treatment

Ovine demodicosis has been successfully treatedwith trichlorfon as a 2% whole-body dip every 2days on three occasions.

Trombiculidiasis

Clinical features

Mites of the genus Trombicula occasionally affectsheep, leading to papular lesions, usually on thelower limbs, ventrum, face and muzzle, withvariable degrees of pruritus and wool loss. In theinitial stages small clusters of orange larval mitescan be seen on the skin, although the lesions maypersist after the larval mites have vacated the skin.

Diagnosis

Diagnosis is by observation with the naked eyeand microscopic identification of the larval mitescollected from the skin by surface scraping oracetate strips.

Treatment

In most cases treatment is not necessary since thedermatosis resolves once the exposure to larvalmites ceases. In severe infestations, topical orga-nophosphates (for example coumaphos, chlor-pyriphos, malathion or diazinon) or lime sulphurcan be used to control the mites. If severe excor-iation occurs due to self-trauma, then gluco-corticoids can be used to alleviate the signs.

Psorergatic mange (Australian itch)

Clinical features

This is a pruritic dermatosis caused by the mitePsorergates ovis, which occurs in Australia, New

Zealand, Africa and South America. It has beeneradicated from the USA and has never beenreported in Europe. The fleece is chewed, mattedand discoloured, especially along the flanks andover the thighs.

Diagnosis

Diagnosis is confirmed by identification of mites,eggs and faecal pellets in skin scrapings. Multipleskin scrapings may be required since the mites aredifficult to find.

Treatment

Topical therapy by dip or spray applied twice, 14days apart, during the summer using an organo-phosphate (coumaphos, diazinon and malathion)is effective in controlling this mange mite. Topical2% lime sulphur is also effective. Systemic treat-ment with ivermectin given by subcutaneousinjection has also been used in the treatment ofovine psorergatic mange. Oral ivermectin is alsoeffective against Australian itch mite.

Forage mites

Clinical features

The free-living forage mites such as Caloglyphusberlesei andAcarus farinae can cause dermatitis inareas of contact with contaminated food, espe-cially the face, limbs and ventrum.

Diagnosis

Diagnosis is based on the history, clinical exam-ination and demonstration of forage mites in skinscrapings and forage.

Treatment

This dermatosis will resolve without therapy oncethe contaminated forage has been removed.


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8.8.2 Ticks

Clinical features

A range of species of tick feed on sheep and causedermatitis or systemic disease around the world.Ticks tend to feed at specific sites on the body,particularly around the ears, face, neck, axillae,groin and distal limbs, but they can be foundanywhere on the body.

The cutaneous signs associated with tick feed-ing in sheep include papules, pustules, ulcerationand alopecia. Tick feeding can introduce cuta-neous bacteria into the skin, causing abscesses, orsystemically, leading to bacteraemia and septi-caemia. The other potential systemic effects ofticks are tick paralysis caused by neurotoxins orthe transmission of micro-organisms such asRickettsia rickettsii, the cause of Rocky Moun-tain fever in the USA.

Diagnosis

Diagnosis is based on history, clinical examina-tion and the collection and identification of ticksfrom the skin.

Treatment

As with other farm animal species, sheep shouldbe removed from the infested pasture. This is notalways practical and topical therapy is then usedto reduce the tick population. The life-cycle of theparticular ticks involved will influence the appli-cation regime, with multiple-host ticks requiringprolonged insecticidal programmes, whereascontrol of one-host ticks may only require treat-ment for a few weeks of the year.

The following compounds have been used inthe control of ticks on sheep: amitraz, chlorpyr-ifos, chlorfenvinphos, coumaphos, crotoxyphos,cypermethrin, cyprothrin, deltamethrin, diazi-non, dichlorvos, dioxathion, g-BHC, flumethrin,malathion, permethrin, phosmet, propetamphos,stirofos and trichlorfon. These are available invarious formulations, including sprays, dips andslow-release ear tags.

Control of the spinose ear tick may be achievedby application of an insecticide dust or oil solu-tion directly into the ear. Environmental mea-sures include separation of sheep from infestedpasture and cultivation of the infested land.

8.8.3 Flies

Blood-feeding flies

Clinical features

Blood-feeding flies, particularly horse flies, blackflies, biting midges, stable flies and mosquitoes,can cause severe disturbance and annoyance tosheep. Fly bites may cause pruritic papules andwheals. Blood-feeding flies are also importantvectors of viral, bacterial and protozoal diseasesand filaroid nematodes.

Diagnosis


Treatment

Involves fly avoidance, repellents, topical insec-ticides and the use of systemic glucocorticoids insevere cases. For housed animals, control of flybreeding sites by the removal of animal dung,rotting vegetable matter or spilled feed will helpto reduce fly numbers. Similarly, elimination ofwater pools, manure-contaminated puddles orsewage outflows may help to reduce the abun-dance of mosquitoes and biting midges.

Topical treatment of animals with organo-phosphates (for example coumaphos, chlorfen-vinphos, diazinon, dioxathion, fenchlorvos,malathion, phosmet, stirofos or trichlorfon) andpyrethrins (for example permethrin, cyfluthrin orcypermethrin) may give some temporary protec-tion. Residual preparations can be used withinhousing and on fly breeding sites. Regular appli-cation of repellents will also help to prevent bites.


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Keds

Clinical features

Keds are wingless, tick-like, blood-feeding flies.They cause pruritus especially around the neck,flanks, rump and abdomen, resulting in rubbing,chewing and scratching. The wool becomes bro-ken and stained with ked faeces. Heavy infesta-tions cause anaemia and keds can transmit blue-tongue virus.

Diagnosis

Diagnosis is made on the basis of collection andidentification of keds from the fleece.

Treatment

Keds are easily controlled because they spendtheir entire life-cycle on the host. Many adultsand pupae are removed by shearing. Topicalinsecticides, such as organophosphates (forexample coumaphos or malathion), given in threeapplications, 14 days apart, are effective treat-ments.

Nuisance flies

Clinical features

The activity of nuisance flies, particularly thehead fly, Hydrotaea irritans, may cause severeirritation and disturbance to sheep. The feedingactivity of H. irritans may lead sheep to developself-inflicted wounds during head shaking andrubbing. These flies are also attracted to woundsin fighting rams, especially between the horn andskin. Secondary bacterial infection and myiasis byLucilia sericata may also occur at wound sites.

Diagnosis

Diagnosis is made on the basis of clinical signsalong with observation and identification of fliesfeeding on sheep.

Treatment

Topical organophosphates (for example crotox-yphos and dichlorvos) and pyrethroids (forexample permethrin or cypermethrin) may beeffective in reducing fly numbers.

8.8.4 Myiasis

Nasopharyngeal myiasis

Clinical features

Nasopharyngeal myiasis may be caused by larvaeof Oestrinae, the most common of which in sheepis the nasal bot fly, Oestrus ovis. Infestation maycause rhinitis, characterised by a sticky, mucoidnasal discharge which at times may be haemor-rhagic. Histopathological changes in the nasalmucosa of infected sheep include catarrhalinflammation and squamous metaplasia, char-acterised by conversion of secretory epithelium tostratified squamous type. Clinical symptoms ofinfestation may range from mild discomfort,nasal discharge, sneezing, nose rubbing or headshaking. Dead larvae in the sinuses can causeallergic and inflammatory responses, followed bybacterial infection and sometimes death. Larvaemay occasionally penetrate the olfactory mucosaand enter the brain, causing ataxia, circling andhead pressing.

Diagnosis

Diagnosis is made on the basis of clinical signsand identification of larvae.

Treatment

A single oral treatment of ivermectin at 200 mg/kgis systemically active against all three larval stagesof O. ovis. Rafoxanide administered orally at adose rate of 10mg/kg is effective.


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Cutaneous myiasis

Clinical features

Myiasis of sheep may be caused by the threespecies of obligate screwworm flies: Cochliomyia.hominivorax (Nearctic and Neotropical regions),Chrysomya bezziana (Afrotropical, Orientalregions) and Wohlfahrtia magnifica (easternPalaearctic). Myiasis is also caused by the facul-tative species belonging to the genera Lucilia,Calliphora, Phormia and Protophormia. Of these,myiases caused by Lucilia sericata and Luciliacuprina are of the greatest worldwide economicimportance.

Screwworm myiasis occurs largely as a con-sequence of skin damage due to trauma; shearing,tail-docking or castration wounds are commonoviposition sites. Eggs may also be deposited inbody orifices, such as the nostrils, eyes, mouth,ears, anus and vagina.

The main predisposing host factors for sheepmyiasis by species of Lucilia are faecal and urinesoiling, bacterial dermatitis (especially Dermato-philosis) and foot rot. The first two of these aremore likely to occur in breeds with marked skinfolds and long, fine wool. Skin damage aroundthe poll of fighting rams may precede the devel-opment of poll strike and bacterial infection ofcontinually wet fleece predisposes to body strike.

Affected animals become depressed, anorexicand usually rub, chew or scratch the affectedareas, which may be wet and the wool dis-coloured. Screwworm infestation may result incavernous lesions, with progressive necrosis andhaemorrhage; Lucilia infestation is generallymore superficial. Severe secondary bacterialinfection of wounds occurs with subsequenttoxaemia, septicaemia and death.

Diagnosis


Treatment

The wounds should be cleaned with an antiseptic

wash and an insecticidal, preferably larvicidalcompound, should be instilled into the lesions.Insecticides such as coumaphos, chlorfenvinphos,diazinon, dichlorvos, fenthion, fenchlorphos,malathion and stirofos are effective. Severelyaffected animals may need systemic antibiotic andsupportive therapy such as rehydration fluids.

Routine spraying or dipping with organopho-sphates (chlorpyrifos, chlorfenvinphos, couma-phos and diazinon) and pyrethroids (permethrin,cypermethrin) gives some protection againstmyiasis. More recently, topical use of the chitinsynthesis inhibitor, cyromazine, has been shownto protect sheep against blowfly strike for up to 8weeks. Topical ivermectin preparations have alsobeen reported to be effective in the control ofmyiasis caused by Lucilia spp. when used by ahand-jetting technique. Future developmentsinclude the possibility of vaccination againstLucilia spp.

Genetic variation in fleece rot and body strikesusceptibility has been identified between Merinosheep strains and bloodlines, and between indi-vidual sheep within flocks. There is therefore thepotential for selection for resistance to reduce theincidence of blowfly myiasis.

The reduction of conformational susceptibilityto strike by Lucilia spp., through removal of wooland skin folds, may also be brought about bymechanical means. Dagging, the removal of fae-cally soiled wool, and crutching, the regularshearing of wool from around the breech, mayboth reduce susceptibility to strike by eliminatingsuitable oviposition sites. Similarly, susceptibilityis reduced in ewes following annual shearing.Surgical removal of skin folds around the breech,the `Mules' operation, is also used for Merinosheep in Australia. The scar tissue formed fol-lowing this procedure results in a smooth, denu-ded area of skin, reducing faecal soiling and thedevelopment of potential oviposition sites. Taildocking (amputation) may also reduce theincidence of strike in sheep.


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8.8.5 Fleas

Clinical features

Fleas are a rare cause of dermatitis in sheep;however, infestation with Ctenocephalides felisfelis has been reported. A papular rash withpruritus and self-excoriation occurs.

Diagnosis

Diagnosis is made by collection and identificationof fleas from the coat.

Treatment

Topical treatment using organophosphates orpyrethroids along with environmental sprayingwill control fleas.

8.8.6 Lice

Clinical features

Sheep may become infested with both suckingand chewing lice which cause pruritus, self-excoriation and wool damage. Infestation withthe foot louse Linognathus pedalis causes footstamping and biting of the limbs. Apart fromfleece damage, lice also cause loss of production.The following species of lice affect sheep: Linog-nathus ovillus (face louse), L. africanus, L. ste-nopsis (goat louse), L. pedalis (foot louse) andDamalinia ovis.

Diagnosis

Diagnosis is made on the basis of clinical signsand identification of lice in the fleece.

Treatment

Lice spend their entire life-cycle on the host andare readily killed by most traditional organo-phosphates and organochlorine topical insecti-cides applied as a dip or spray. Topicalivermectin, the pyrethroid cypermethrin and theIGR triflumuron have also been shown to be

effective against D. ovis. Efficacy is improved ifused shortly after shearing.

8.9 HORSES (Table 8.5)

8.9.1 Mites

Sarcoptic mange

Clinical features

Infestation by Sarcoptes scabiei is a rare conditionin horses, but may occur occasionally, producinga pruritic dermatosis with crust formation, alo-pecia, excoriation and lichenification, especiallyon the head and neck.

Diagnosis

Diagnosis is confirmed by identification of mites,eggs and faecal pellets on skin scrapings.

Treatment

Topical treatments using organophosphates(coumaphos, malathion, methoxychlor), theorganochlorine g-BHC or lime sulphur appliedtwice, 2 weeks apart, are effective. Ivermectinapplied topically at 200 mg/kg is also effectiveagainst sarcoptic mange in horses.

Psoroptic mange

Clinical features

The mite Psoroptes ovis (=P. equi) can cause apruritic dermatosis with papules, thick crusts,excoriation and secondary alopecia. The diseasehas been reported in North America, Australiaand Europe. The lesions usually occur on thehead, ears, mane, udder, prepuce, axilla and tail.Psoroptes cuniculi can be found in normal ears buthas been associated with ear pruritus and headshaking.

Diagnosis



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Treatment

In generalised cases of psoroptic mange topicaltreatment using organophosphates (for examplecoumaphos, malathion or methoxychlor), or g-BHC applied by spray or dip twice, 14 days apart,is effective. In cases of otitis externa the externalear canal should be cleaned if possible with aceruminolytic agent and a topical otic acaricidalproduct used.

Chorioptic mange

Clinical features

Infestation with the mite Chorioptes bovis pro-duces pruritus, crusts, excoriation and secondaryalopecia. The lower limbs, caudal pastern and tailare usually affected, although generalised diseasehas been reported. The mite population increaseswith a fall in temperature and chorioptic mangeusually occurs in winter.

Table 8.5 A guide to ectoparasites affecting horses.


Parasitetype

Species

Mites Sarcoptes scabiei (rare) . . . . . .Psoroptes ovis . . . . . .Chorioptes bovis . . . . . .Demodex equi . +/± . . .Demodex caballi . +/± . . .Dermanyssus gallinae . . . . . .Forage mites . . . . . .

Lice Haematopinus asini . . . . . . . . . .Damalinia equi . . . . . . . . . .

Fleas E. galinacea/T. penetrans

(rare)

. . . . . . . .

Ticks Various . . . . . . . .

Flies Culicoides spp. . . . . . . . .Horse flies/deer flies/clegs

. . . . . . .

Forest flies(Hippobosca equina)

. . .

Other blood-feeding flies . . . . .Myiasis (primary or

secondary)

. . .

Pruritus

Papules

Pustules

Crusts

Scaling

Alopecia

Erosion/ulceration

Clinicalsigns


parasite

Skin

scrapings

Hairbrushings

Hairplucks/acetate

stripexamination

Serology

Parasite

foundin

the


Biopsy

andhistology


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Diagnosis


Treatment

Topical treatment using organophosphates (cou-maphos, malathion, methoxychlor) applied twice,14 days apart, is effective in the treatment ofchorioptic mange. Topical lime sulphur (2%) isalso effective. The use of oral ivermectin astreatment for chorioptic mange has been reportedwith varying degrees of success.

Demodectic mange

Clinical features

Two species of follicular mite affect horses:Demodex equi, affecting the body, and the longermite, D. caballi, affecting the eyelids and muzzle.Clinical signs of scaling and alopecia with orwithout papules and pustules occur on the face,shoulders, neck and limbs. Equine demodicosis israre.

Diagnosis

Diagnosis is confirmed by identification of mitesand eggs in skin scrapings and hair pluckings.

Treatment

There is little information regarding the mosteffective treatment for equine demodicosis.Investigation and treatment of underlying sys-temic disease should be performed.

Forage mites

Clinical features

Contact with free-living forage mites especiallyPyemotes tritici and Acarus farinae leads to apruritic dermatosis. The lesions are papules andcrusts which occur in areas of contact, especially

the head, muzzle, limbs and ventrum. If forage isstored overhead, then mites falling on to the horsebeneath can produce a dorsal distribution oflesions.

Diagnosis

Diagnosis is based on the history, clinical exam-ination and demonstration of forage mites in skinscrapings and forage samples.

Treatment

The dermatitis will resolve once the contaminatedforage is removed from the environment.


Clinical features

Occasionally the poultry mite Dermanyssus galli-nae may cause dermatitis in horses. The mite,which lives in the environment, causes a prurituswith papule and crust formation in areas of con-tact such as the ventrum, limbs and muzzle.

Diagnosis

Diagnosis is confirmed by detection of mites inskin scrapings or within the immediate environ-ment.

Treatment

The dermatitis will resolve once the horse isremoved from the infested housing or treatedwith an acaricidal compound. Spraying thehousing with organophosphates (malathion,coumaphos, methoxychlor, diazinon) or limesulphur is effective, if thorough.

8.9.2 Ticks

Clinical features

Various species of tick feed on horses, causingdermatitis or systemic disease. They tend to feed


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in specific sites, especially the ears, face, neck,axillae, groin, distal limbs and tail, but may alsobe found anywhere on the body. The cutaneoussigns associated with tick feeding in horsesinclude papules, pustules, ulceration and alope-cia. The larval form of Boophilus microplus causesa local hypersensitivity reaction with papule andwheal formation at the site of feeding.

Tick feeding can cause abscesses by theintroduction of surface bacteria into the skin orbacteraemia and septicaemia if the bacteria enterthe circulation. The other potential systemiceffects of ticks are tick paralysis caused by neu-rotoxins or the transmission of micro-organismssuch as Rickettsia rickettsii, the cause of RockyMountain fever in the USA.

Diagnosis


Treatment

Horses should be moved to uninfested pasture ifpractical, but acaricides may be required. Topicalorganophosphates (for example coumaphos,chlorfenvinphos, dioxathion, malathion or stir-ofos) and pyrethroids (for example decamethrinor flumethrin) can be used to reduce tick numbersand prevent complete engorgement. Cultivationof the infested land will also reduce tick numbers.

8.9.3 Flies

Biting midges

Clinical features

Biting midges, Culicoides spp., are importantectoparasites of horses, causing a cutaneoushypersensitivity reaction manifested as either aventral papular dermatitis or a dorsal dermatitisknown as `sweet itch' in the UK and `Queenslanditch' in Australia. Cases of sweet itch have apapular dermatosis, with crusting, ulceration and

scaling at the base of the tail and along the manewith severe pruritus. The horses rub the base oftail and mane against any suitable object, result-ing in skin thickening (lichenification), excoria-tion and loss of hair. The disease affects youngadults and usually shows a seasonal incidenceinitially. Large numbers of biting midges willcause annoyance and disturbance to horses.Culicoides spp. also act as vectors for the filaroidnematodes Onchocera spp. and the arboviruswhich causes African horse sickness.

Diagnosis

Diagnosis is based on clinical signs and observa-tion of Culicoides spp. feeding in the morning andevening. Differential diagnosis of the ventraldermatitis includes other biting flies such asStomoxys calcitrans and Haematobia irritans,chorioptic mange and dermatophilosis. Skinbiopsy reveals an eosinophilic perivascular der-matitis. Blood count may reveal a circulatingeosinophilia suggesting a parasitic or allergicdisease and intradermal skin testing, using aCulicoides antigen, may support the diagnosis.

Treatment

Treatment involves midge avoidance, repellents,topical insecticides and the use of systemic glu-cocorticoids in severe cases. Stabling during themorning and evening in accommodation securefrom midges reduces lesions, but their small sizemakes this difficult to achieve. Barriers applied tothe mane and tail such as liquid paraffin mixedwith an insecticide are traditional treatments inthe UK. Topical insecticides such as pyrethrins(for example cyfluthrin or cypermethrin), espe-cially in pour-on formulations, may be useful.The use of medicated bovine ear tags attached tohalters has been recommended in an attempt tocontrol these insects.


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Horse flies, deer flies and clegs

Clinical features

These flies produce deep, painful papules andwheals with haemorrhagic crust formation. Thelesions tend to occur on the ventral abdomen, legsand neck. Horse flies cause considerable dis-turbance to horses and large numbers can lead toanaemia. They are mechanical vectors for infec-tious equine anaemia, anthrax, trypanosomiasisand anaplasmosis.

Diagnosis

Diagnosis is made on the basis of history andclinical signs supported by observation andidentification of feeding flies.

Treatment

Control of these flies is extremely difficult.Housing during the day will reduce biting. Eartags attached to head collars or necklacesimpregnated with cypermethrin or cyfluthrinhave been reported to be effective in the control ofthese biting flies.

Forest flies

Clinical features

Hippobosca equina (New Forest fly, horse lousefly) is a common biting fly found worldwide thataffects horses, and sometimes cattle. The adultsmay be particularly abundant in warm, sunnyweather and feed on blood, especially around theperineum and between the hind legs. The fliesremain on the skin for long periods of time,causing annoyance and disturbance.

Diagnosis

Diagnosis is made on the basis observation andidentification of the feeding flies.

Treatment

Topical treatment with topical organophosphates(for example malathion, coumaphos, methoxy-chlor or diazinon) or pyrethroids (for exampledeltamethrin or cypermethrin) may be effective.

Other blood-feeding flies

Clinical features

Blood-feeding flies, particularly stable flies, hornflies, black flies and mosquitoes, can cause severedisturbance and annoyance in horses. Fly bitesmay cause pruritic papules and wheals. Thelesions may become haemorrhagic and necrotic.Hypersensitivity reaction to bites can occur.Blood-feeding flies may also be important vectorsof viral, bacterial and protozoal diseases andfilaroid nematodes.

Diagnosis


Treatment

Treatment involves fly avoidance, repellents,topical insecticides and systemic glucocorticoidsin severe cases. Control of breeding sites (forexample animal dung, vegetable matter, still-water pools) will help to reduce biting fly num-bers. Topical treatment of animals with organo-phosphates (for example coumaphos,chlorfenvinphos, diazinon, dioxathion, fen-chlorvos, malathion, phosmet, stirofos or tri-chlorfon) and pyrethroids (for examplepermethrin, cyfluthrin or cypermethrin) may givesome protection. Residual preparations can beused within housing and on breeding places.Necklaces impregnated with the pyrethoidcypermethrin are effective in reducing S. calci-trans numbers. Horses with severe dermatitis canbe given glucocorticoids or antihistamines toreduce the cutaneous inflammation and pruritus.Regular application of repellents will also help toprevent bites. Stabling at times of peak fly


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activity, in accommodation secured from flyentry, will help to prevent disturbance.

Nuisance flies

Clinical features

The activity nuisance flies, such as the face fly andhouse flies, lead to disturbance and irritation andmay be mechanical vectors of disease.

Diagnosis


Treatment

Control of nuisance flies may be assisted con-siderably by appropriate hygiene and removal ofdung, in which they breed. Topical organopho-sphates (for example crotoxyphos and dichlor-vos) and pyrethroids (for example permethrin andcypermethrin) may be effective in reducing flynumbers. However, topical or environmentalinsecticidal treatment usually brings only tem-porary relief from these fly species. Ear tagsattached to head collars or necklaces impregnatedwith cypermethrin or permethrin are also usefulin the control of flies.

8.9.4 Myiasis

Intestinal myiasis

Clinical features

First-stage larvae of horse bots, Gasterophilusspp., burrowing into the skin may cause severeirritation. Light infestations of bots in the sto-mach or intestine are believed to have littlepathogenic effect and are tolerated well. How-ever, bots may cause obstruction to the foodpassing from the stomach to the intestine, parti-cularly when the larvae are in or near the pylorus.The penetration of the mouth-hooks at the site ofattachment may result in erosions, ulcers, nodular

mucosal proliferation, stomach perforation, gas-tric abscesses, peritonitis and, in heavy infections,colic, general debilitation and even rectal pro-lapse. In particular, infestation with Gasterophiluspecorum has been associated with swallowingdifficulties associated with oesophageal constric-tion and hypertrophy of the musculature. Theoviposition behaviour of gasterophilids may alsocause disturbance, panic and self-wounding.

Diagnosis

Diagnosis is made on the identification of larvaein the mouth, oesophagus, stomach or faeces.

Treatment

Both trichlorphon and ivermectin paste have beenreported to be effective against Gasterophiluslarvae. Ivermectin has been used as a 1.87% oralpaste or a 1% injectable solution.

Cutaneous myiasis

Clinical features

Myiasis may be caused by the obligate screw-worms Cochliomyia hominivorax (Nearctic andNeotropical regions), Chrysomya bezziana(Oriental and Afrotropical regions), Wohlfahrtiamagnifica (eastern Palaearctic) or, more rarely,flies of the genera Lucilia, Calliphora, Proto-phormia or Phormia (worldwide). Similar predis-posing factors to those discussed for sheep andcattle exist. However, cutaneous myiasis is lesscommon in horses than sheep or cattle. Theshorter coat and regular grooming that manyhorses receive are likely to play a part inpreventing myiasis.

Diagnosis



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Treatment

Routine spraying with organophosphates (chlor-pyrifos, chlorfenvinphos, coumaphos and diazi-non) and pyrethroids (permethrin, cypermethrin)gives some protection against myiasis. Routinegrooming and prompt treatment of cutaneouswounds will help prevent myiasis.

8.9.5 Fleas

Clinical features

Fleas only occasionally infest horses. The speciesEchidnophaga gallinacea and Tunga penetranshave been reported to affect horses. Clinical signsinclude papules, crusts, pruritus, excoriations andsecondary alopecia.

Diagnosis

Diagnosis is based on history, clinical signs andidentification of fleas on the horse.

Treatment

Topical organophosphates, pyrethroids andfipronil are effective in the treatment of fleas. Thesource of the infestation and the environmentshould also be treated.

8.9.6 Lice

Clinical features

Horses can be infested by both chewing (Dama-linia equi) and sucking (Haematopinus asini; Plate5) lice. The clinical signs associated with liceinfestation are pruritus, scale, crusts, excoriationand secondary alopecia. Severe infestation withHaematopinus asini produces anaemia. Lice aremore common during the winter months when thecoat is long.

Diagnosis

Diagnosis is made on the basis of clinical signsand identification of lice in the coat.

Treatment

Lice spend their entire life-cycle on the host andare readily killed by most traditional organo-phosphates and organochlorine topical insecti-cides applied as a dip or spray. A spot-onpreparation containing cyhalothrin has beenreported effective in the treatment of equine lice.A single topical application of fipronil in sprayformulation has been used to treat pediculosiscaused by Damalinia equi andHaematopinus asiniin the horse.

8.10 PIGS (Table 8.6)

8.10.1 Mites

Sarcoptic mange

Clinical features

Sarcoptic mange is a common dermatosis of pigswith a worldwide distribution. Clinical signs aremarked pruritus, erythema, papules, crusts,excoriation and lichenification, particularly onthe ears, flanks, abdomen and rump.

Diagnosis

Diagnosis is based on history, clinical examina-tion and identification of mites, eggs and faeces inskin scrapings.

Treatment

Systemic ivermectin at a dose of 300 mg/kg is thetreatment of choice for porcine sarcoptic mange.Other effective topical treatments are organo-phosphates (for example malathion, coumaphos,diazinon, fenchlorvos, chlorfenvinphos, phosmetor trichlorfon), g-BHC, amitraz and avermectins.It is important to apply the topical acaricide tothe entire body and all in-contact animals shouldalso be treated. In feed ivermectin is also effective.


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Demodectic mange

Clinical features

Dermatitis may occur in pigs due to the miteDemodex phylloides. The lesions produced areerythema and papules and, if there is secondarybacterial infection or follicular rupture, pustulesand nodules. The lesions usually occur on thesnout, eyelids, ventral neck, ventrum and thighs.

Diagnosis

Diagnosis is confirmed by identification of mitesand eggs in skin scrapings and hair pluckings.

Treatment

The topical organophosphate trichlorfon hasbeen reported as effective in the treatment ofporcine demodicosis.

Forage mites

Clinical features

Contact with species of forage mite, in particularAcarus farinae, from contaminated foodstuffsmay cause a papular dermatitis. The lesionsusually occur in areas of contact, especiallyaround the face, muzzle and ventrum.

Diagnosis

Diagnosis is based on the history, clinical exam-ination and demonstration of forage mites in skinscrapings and forage samples.

Treatment

The dermatitis will resolve once the contaminatedforage is removed from the environment.

Table 8.6 A guide to ectoparasites affecting pigs.


Parasitetype

Species

Mites Sarcoptes scabiei . . . . . .Demodex phylloides . . . . . .

Lice Haematopinus suis . . . . . . .

Fleas Ctenocephalides felis . . . . . .Ctenocephalides canis . . . . . .Pulex irritans . . . . . .Echidnophaga gallinacea . . . . . .Tunga penetrans . . . . . .

Flies Primary myiasis . . .Secondary myiasis (rare) . . .

Pruritus

Papules

Pustules

Crusts

Scaling

Alopecia

Erosion/ulceration

Clinicalsigns


parasite

Skin

scrapings

Hairbrushings

Hairplucks/acetate

stripexamination

Serology

Parasite

foundin

the


Biopsy

andhistology


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8.10.2 Ticks

Clinical features

Tick-related diseases in pigs within the developedcountries have, until recently, been rare. Modernhousing methods prevent exposure to ticks but,with the return to traditional extensive pig farm-ing, to cater for the consumer demand, ticks andtheir related diseases may become more impor-tant. Ticks tend to feed at particular sites, espe-cially the ears, face, neck, axillae, groin, distallimbs and tail of pigs, although they can be foundanywhere on the body. The cutaneous signsassociated with tick feeding in pigs includepapules, pustules, ulceration and alopecia. Tickfeeding can introduce surface bacteria either intothe skin, causing abscesses, or systemically, lead-ing to bacteraemia and septicaemia. The otherpotential systemic effects of ticks are tickparalysis caused by neurotoxins or the transmis-sion of micro-organisms such as the virusresponsible for African swine fever.

Diagnosis


Treatment

Pigs should be moved to uninfested pasture ifpractical. However, acaricides may be required.Topical organophosphates (for example couma-phos, chlorfenvinphos, diazinon, dioxathion,fenchlorvos, malathion, phosmet, stirofos or tri-chlorfon), pyrethroids (for example decamethrin,flumethrin or cypermethrin) and amitraz can beused to reduce tick numbers and prevent completeengorgement. Systemic ivermectin may also pre-vent complete tick engorgement, thereby reducingtick numbers. Cultivation of the infested land willalso reduce tick numbers.

8.10.3 Flies

Blood-feeding flies

Clinical features

Blood-feeding flies cause disturbance, dermatitisand, especially in young pigs, anaemia. Fly bitesmay produce painful papules and weals withvariable pruritus.

Diagnosis

Diagnosis is based on the history and clinicalsigns.

Treatment

Control of fly breeding sites will help to reducebiting fly numbers; manure, wet straw, spilledfeed and rotting vegetable matter should beremoved regularly. The drainage of areas ofstanding water may help to reduce mosquitonumbers. The use of insecticides should only beconsidered as a supplement to appropriatehygiene.

Topical treatment of animals with organo-phosphates (coumaphos, chlorfenvinphos, diazi-non, dioxathion, fenchlorvos, malathion,phosmet, stirofos, trichlorfon) and pyrethrins(permethrin, cyfluthrin, cypermethrin) may givesome protection. Residual preparations can beused within housing and on fly breeding sites. Theuse of screens on windows and fly traps may be ofvalue.

8.10.4 Myiasis

Cutaneous myiasis

Clinical features

Myiasis may be caused by the obligate screw-worms Cochliomyia hominivorax (Nearctic andNeotropical regions), Chrysomya bezziana(Oriental and Afrotropical regions) and Wohl-fahrtia magnifica (eastern Palaearctic). Morerarely, flies of the genera Lucilia, Calliphora,


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Protophormia or Phormia (worldwide) may causemyiasis of pigs. Similar predisposing factors tothose discussed for sheep and cattle exist. How-ever, the lack of hair or wool makes myiasis muchrarer in pigs than sheep.

Diagnosis


Treatment

Routine spraying with organophosphates (cou-maphos, chlorfenvinphos, diazinon, dioxathion,fenchlorvos, malathion, phosmet, stirofos, tri-chlorfon) and pyrethroids (permethrin, cyflu-thrin, cypermethrin) gives some protectionagainst myiasis. Prompt treatment of cutaneouswounds will help to prevent myiasis.

8.10.5 Fleas

Clinical features

Fleas occasionally infest pigs. The species Cte-nocephalides felis, Ctenocephalides canis, Pulexirritans, Echidnophaga gallinacea and Tungapenetrans have been reported to infest pigs.Clinical signs include papules, crusts, pruritus andexcoriations. Fleas may act as a vector of swinepoxvirus.

Diagnosis

Diagnosis is based on history, clinical signs andidentification of fleas on the pig.

Treatment

Topical organophosphates (coumaphos, chlor-fenvinphos, diazinon, dioxathion, fenchlorvos,malathion, phosmet, stirofos, trichlorfon) andpyrethroids (permethrin, cyfluthrin, cyperme-thrin) are effective in the treatment of fleas. Thesource of the infestation and environment shouldalso be treated.

8.10.6 Lice

Clinical features

Pigs may be infested by the sucking louse, Hae-matopinus suis, which lives especially around theears, axillae and groin. The clinical signs asso-ciated with lice infestation are pruritus, scalecrusts, and excoriation. Severe infestation withH.suis produces anaemia. Haematopinus suis is alsoa vector for swine poxvirus.

Diagnosis

Diagnosis is made on the basis of clinical signsand identification of lice on the skin.

Treatment

Haematopinus suis spends its entire life-cycle onthe host and is readily killed by most traditionalorganophosphates (coumaphos, chlorfenvinphos,diazinon, dioxathion, fenchlorvos, malathion,phosmet, stirofos, trichlorfon) or g-BHC appliedas a dip or spray. Systemic ivermectin and mox-idectin are also effective in the treatment of swinepediculosis and have become the standard formof treatment in many countries.

8.11 GOATS (Table 8.7)

8.11.1 Mites

Sarcoptic mange

Clinical features

Sarcoptic mange is a pruritic dermatosis of goatscased by Sarcoptes scabiei, seen worldwide. Theclinical signs produced are pruritus, papules,crusts, excoriations, secondary alopecia andlichenification, affecting the face, ears, legs andneck.

Diagnosis



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Treatment

Effective topical treatments are organopho-sphates (for example malathion, coumaphos,crotoxyphos or trichlorfon) or lime sulphur. It isimportant to apply the topical acaricide to theentire body and in-contact animals should also betreated. Systemic ivermectin at a dose of 200mg/kg is also effective in the treatment of caprinesarcoptic mange.

Psoroptic mange

Clinical features

Psoroptes cuniculi can be found in normal caprineears and may be a commensal. However, in somecircumstances it may produce a pruritic otitis

externa, which may progress to otitis media andinterna. Crusts, alopecia and excroriation of thepinnae and external ear canal occur, with a headtilt if the middle or inner ear have become affec-ted. In some cases more generalised dermatitisoccurs with lesions on the face, poll, legs andinterdigital skin.

Diagnosis

Diagnosis is based on history, clinical examina-tion and identification of mites and eggs in skinscrapings.

Treatment

Psoroptic otitis externa can be treated with auralacaracidal preparations. Cleaning the ear with a

Table 8.7 A guide to ectoparasites affecting goats.


Parasitetype

Species

Mites Sarcoptes scabiei . . . . . . .Psoroptes cuniculi . . . . . .Chorioptes bovis(=caprae)

. . . . . . .

Demodex caprae . . . . . . . .

Lice Damalinia caprae . . . . . . . . .Damalinia limbata . . . . . . . . .Damalinia crassiceps . . . . . . . . .Linognathus stenopsis . . . . . . . . .Linognathus africanus . . . . . . . . .

Fleas Ctenocephalides spp. . . . . . . .

Ticks Various . . . . . .

Flies Blood-feeding flies . . . .Nuisance flies . . .Primary myiasis . . .Secondary myiasis . . .

Pruritus

Papules

Pustules

Crusts

Scaling

Alopecia

Erosion/ulceration

Clinicalsigns


parasite

Skin

scrapings

Hairbrushings

Hairplucks/acetate

stripexamination

Serology

Parasite

foundin

the


Biopsy

andhistology


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ceruminolytic ear cleaner to remove crust andcerumen before instilling the acaricide willincrease its efficacy. Topical organophosphates(for example malathion, coumaphos, crotox-yphos or trichlorfon) applied twice, 14 days apart,or weekly lime sulphur dips for 1 month are alsoeffective. Systemic ivermectin at a dose of 200 mg/kg is also effective in the treatment of caprinepsoroptic mange.

Chorioptic mange

Clinical features

This is caused by the mite Chorioptes bovis (=C.caprae) which produces a pruritic dermatosisusually in housed animals during the winter. Theclinical signs are papules, crusts, excoriation andsecondary alopecia on the feet, hind legs, peri-neum, udder and scrotum. In some cases lesionsalso occur on the neck and flanks.

Diagnosis

Diagnosis is based on history, clinical examina-tion and identification of mites and eggs in skinscrapings.

Treatment

Topical organophosphates (for example mala-thion, coumaphos, crotoxyphos or trichlorfon)applied twice, 14 days apart, or a weekly limesulphur dip for 1 month are effective in thetreatment of caprine chorioptic mange.

Demodectic mange

Clinical features

Caprine demodicosis is a relatively common der-matosis caused by the commensal follicular miteDemodex caprae which produces follicularpapules and nodules on the head, neck, shouldersand flanks. In some cases secondary infection andfollicular rupture occurs, producing ulcerationand sinus tract formation (furunculosis).

Diagnosis

Diagnosis is confirmed by identification of mitesand eggs on skin scrapings and hair pluckings.

Treatment

Weekly topical washes with malathion, tri-chlorfon or amitraz have been reported to beeffective in the treatment of caprine demodicosis.Any milk must be discarded during treatment. Ingoats with a few nodules, lancing and cleaningwith lugol's iodine or rotenone in alcohol hasbeen advocated.

Mites of minor importance

The mites Raillietia caprae and Raillietia manfediare commensals in some caprine ears. Raillietacaprae occurs in the USA, Mexico and Brazilwhile R. manfredi occurs in Australia.

8.11.2 Ticks

Clinical features

Various species of tick feed on goats and causedermatitis or systemic disease around the world.They feed particularly on the skin of the ears,face, neck, axillae, groin, distal limbs and tail, butthey can also be found in other areas of the body.The cutaneous signs associated with tick feedingin goats include papules, pustules, ulceration andalopecia. Tick feeding can introduce surfacebacteria into the skin, causing abscesses, or sys-temically, leading to bacteraemia and septicae-mia. The other potential systemic effects of ticksare tick paralysis caused by neurotoxins or thetransmission of micro-organisms such as Rick-ettsia rickettsii, the cause of Rocky Mountainfever in the USA.

Diagnosis



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Treatment

Goats should be moved to uninfested pasture ifpractical, although acaricides may be required.Topical organophosphates (for example mala-thion, coumaphos, crotoxyphos or trichlorfon)and pyrethroids (for example decamethrin, flu-methrin or cypermethrin) can be used to reducetick numbers and prevent complete engorgement.Systemic ivermectin may also prevent completetick engorgement, thereby reducing tick numbers.Cultivation of the infested land will also reducetick numbers.

8.11.3 Flies

Blood-feeding flies

Clinical features

Blood-feeding flies can cause disturbance andannoyance in goats. Fly bites may cause pruriticpapules and weals.

Diagnosis

Diagnosis is based on clinical signs and observa-tion of Cullicoides spp. feeding in the morningand evening.

Treatment

Treatment involves fly avoidance, repellents,topical insecticides and systemic glucocorticoidsin severe cases. Control of breeding sites (forexample animal dung, vegetable matter, waterpools) may help to reduce biting fly numbers.Topical treatment of animals with organopho-sphates (for example coumaphos, chlorfenvin-phos, diazinon, dioxathion, fenchlorvos,malathion, phosmet, stirofos or trichlorfon) andpyrethroids (for example permethrin, cyfluthrinor cypermethrin) may give some protection.Residual preparations can be used within housingand on breeding places. Regular application ofrepellents will also help to prevent bites. Stablingat times of peak fly activity, in fly-secure accom-modation, may help to prevent disturbance.

Nuisance flies

Clinical features

The activity nuisance flies, such as the face fly andhouse flies, cause disturbance and irritation andmay be mechanical vectors of disease.

Diagnosis


Treatment

Topical organophosphates (for example mala-thion, coumaphos, crotoxyphos or trichlorfon)and pyrethroids (for example permethrin orcypermethrin) are effective in reducing fly num-bers. Ear tags impregnated with cypermethrin orpermethrin also may be useful in the control ofnuisance flies.

8.11.4 Myiasis

Cutaneous myiasis

Clinical features

Myiasis in goats may be caused by the obligatescrewworms Cochliomyia hominivorax (Nearcticand Neotropical regions), Chrysomya bezziana(Oriental and Afrotropical regions) and Wohl-fahrtia magnifica (eastern Palaearctic). Cutaneousmyiasis of goats by species of Lucilia, or othercalliphorid blowflies, is less common than insheep, probably because of the more open hair ofgoats.

Diagnosis


Treatment

Routine spraying with organophosphates (forexample coumaphos, chlorfenvinphos, diazinon,


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dioxathion, fenchlorvos, malathion, phosmet,stirofos or trichlorfon) and pyrethroids (forexample permethrin, cyfluthrin or cypermethrin)gives some protection against myiasis. Prompttreatment of cutaneous wounds will help to pre-vent myiasis.

8.11.5 Fleas

Clinical features

Fleas occasionally infest goats. Ctenocephalidesspp. have been reported to infest goats. Clinicalsigns include papules, crusts, pruritus and excor-iations.

Diagnosis

Diagnosis is based on history, clinical signs andidentification of fleas on the goat.

Treatment

Topical organophosphates (for example mala-thion, coumaphos, crotoxyphos or trichlorfon)and pyrethroids (for example permethrin, cyflu-thrin or cypermethrin) are effective in the treat-ment of fleas. The source of the infestation andenvironment should also be treated.

8.11.6 Lice

Clinical features

Goats can be infested by both chewing (Damali-nia caprae, D. limbata and D. crassiceps) andsucking (Linognathus stenopsis and L. africanus)lice. The clinical signs associated with lice infes-tation are pruritus, scale, crusts, excoriation andsecondary alopecia. Severe infestation withLinognathus spp. produces anaemia. Lice aremore common during the winter months when thecoat is long.

Diagnosis

Diagnosis is made on the basis of clinical signsand identification of lice in the coat.

Treatment

Lice spend their entire life-cycle on the host andare readily killed by most traditional organo-phosphates (for example malathion, coumaphos,crotoxyphos or trichlorfon), pyrethroids (forexample permethrin, cyfluthrin or cypermethrin)and g-BHC. Topical insecticides applied as a dipor spray are usually applied twice, 14 days apart.

8.12 DOGS (Table 8.8)

8.12.1 Mites

Sarcoptic mange

Clinical features

Canine sarcoptic mange is an intensely pruriticdermatosis caused by the mite Sarcoptes scabiei.Typical lesions are papules, crusts, excoriationand secondary alopecia. The skin often has amousy odour and dogs become lethargic withweight loss as the disease progresses. The lesionsoccur on the ears (Plate 6), elbows, hocks andventral abdomen, but may become generalised(Plates 7 and 8). Gentle palpation of the pinnalmargins often elicits a marked scratch reflex. Thepathogenesis of the skin lesions is thought toinvolve a type I hypersensitivity to faecal anti-gens, while some dogs are thought to be asymp-tomatic carriers. In most cases the number ofmites present on the skin is small, but in otherslarge numbers of mites are present. The latteroften occurs in immunosuppressed dogs or thoseon chronic glucocorticoid therapy and has beentermed `Norwegian scabies' by some veterinarydermatologists.

Diagnosis

Diagnosis is based on history, clinical examina-tion and identification of mites, eggs and faeces inskin scrapings. In approximately 50% of cases,mites are not found and the diagnosis is based onclinical features and response to therapy.Although mites are occasionally found on histo-logical examination this is unusual and is not a


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useful diagnostic test. Faecal examination mayalso reveal mites and a blood count may reveal aneosinophilia. Serological measurement of serumantibodies (IgE) directed against faecal antigens isuseful in the diagnosis of sarcoptic mange whenno mites are found on skin scraping.

Treatment

The coat should be clipped, especially around thelesions, and keratolytic shampoo used to removethe crusts and scale. A topical acaracidal sham-

poo or wash should be used every 7 to 14 daysfor 4 to 6 weeks. Suitable scabicidal chemicalsare organophosphates (for example phosmet ormalathion), g-BHC or amitraz. Systemic iver-mectin at 200±400 mg/kg given twice, 14 daysapart, is effective, but should not be used incollies or collie crossbreds. It is important totreat all in-contact dogs and identify the source ifpossible. Re-exposure is sometimes a problem.Grooming equipment should also be cleanedthoroughly.

Table 8.8 A guide to ectoparasites affecting dogs.


Parasitetype

Species

Mites Sarcoptes scabiei . . . . . . . .Otodectes cynotis . . . . .Demodex canis +/± . +/± +/± +/± . +/± . . . .Unnamed short

demodex species

+/± . +/± +/± +/± . +/± . . . .

Cheyletiella yasguri . . . . . . .Trombicula spp. . . . . .Dermanyssus gallinae . . . . . . . . .

Lice Trichodectes canis . . . . . +/± . . . .Linognathus setosus . . . . . +/± . . . .

Fleas Ctenocephalides felis . . . . . . .Ctenocephalides canis . . . . . . .Archeopsyllus erinacei . . . . . . .Leptopsylla segnis . . . . . . .Pulex irritans . . . . . . .Ceratophyllus spp. . . . . . . .Echidnophaga gallinacea . . . . . . .

Ticks Various . . . . . . ?

Flies Blood-feeling flies . . . . ?

Primary myiasis . . .Secondary myiasis . . .

Pruritus

Papules

Pustules

Crusts

Scaling

Alopecia

Erosion/ulceration

Clinicalsigns


parasite

Skin

scrapings

Hairbrushings

Hairplucks/acetate

stripexamination

Serology

Parasite

foundin

the


Biopsy

andhistology


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Otodectic mange

Clinical features

The ear mite Otodectes cynotis causes otitisexterna with intense aural irritation, pruritus andhead shaking. Examination of the external earcanal reveals a thick reddish brown exudate withsome crust formation. Otodectes cynotis is verycontagious and is a particularly prevalent injuveniles. Although the pathogenesis of thelesions has not been elucidated, a hypersensitivitymay be involved and asymptomatic carriers exist.Occasionally ectopic infestation occurs where themite causes localised dermatitis on the skinespecially on the neck, rump and tail.

Diagnosis

Examination of the external ear canal using anauroscope reveals small, fast-moving mites (Plate9). Microscopic examination of aural exudate orsuperficial skin scrapings in ectopic cases revealsmites and eggs.

Treatment

Topical ceruminolytic ear preparations should beused to remove crust and cerumen from theexternal ear canal. An otic acaracidal product (forexample thiabendazole or permethrin) shouldthen be used for 2 weeks beyond a clinical cure.Amitraz (1ml diluted in 33ml mineral oil) can beused as an otic acaricide. Systemic ivermectin at200±400 mg/kg given twice, 14 days apart, iseffective but should not be used in collies or colliecrossbreds. Selamectin, as a topical spot-on pre-paration is also effective in the treatment ofOtodectes cynotis infestation in dogs.

Demodectic mange

Clinical features

Canine demodicosis is caused by the long folli-cular mite D. canis, although some workers claimto have identified a second, shorter species insome cases. Demodicosis is thought to occur as

the result of reduced cell-mediated immunity(juvenile form) or immunosuppression secondaryto other diseases (adult form). The suggestedpredisposing factors are genetic, age, short hair,poor nutrition, hormonal, stress, endoparasitesand debilitating diseases such as neoplasia.

There appear to be breed predispositions tocanine demodicosis which vary across the world.These include the West Highland white terrier,English bull terrier, Staffordshire bull terrier,boxer, pugs, Shar Pei, doberman and Germanshepherd dog. The disease occurs in a juvenile oradult onset form, either localised or generalisedand, if concurrent staphylococcal infectionoccurs, a pustular form. The juvenile form isusually localised without concurrent secondaryinfection with areas of alopecia, erythema andscaling, especially on head and legs (Plate 10).This form usually resolves without treatment.

The disease tends to become chronic if con-current staphylococcal infections occur (whichmay reduce cutaneous cell-mediated immunity);this form is called `pustular demodicosis'. Thesigns associated with pustular demodicosisinclude alopecia, erythema, pustules, crusts,variable pruritus and, in some cases, lymphade-nopathy.

Adult-onset demodicosis usually occurs in dogsolder than 5 years and may reflect underlyingdiseases causing immunosuppression, such ashyperadrenocorticism. Lesions include alopecia,scale and crust formation anywhere on the body,but most often on the head and legs (Plates 11 and12). Elderly dogs with spontaneous demodicosismay have underlying systemic neoplasia. A clin-ical syndrome seen particularly in young adultdogs is pododemodicosis, which is usually apustular form affecting all four feet (Plate 13).This disease is often chronic with concurrentpyoderma, and long-term control of both thebacterial infection and ectoparasite is required.Some cases of pododemodicosis can progress tothe generalised form.

Diagnosis

Diagnosis of demodicosis is made on the basis ofclinical features and the identification of numer-


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ous demodectic mange mites on superficial ordeep skin scrapings, hair pluckings or biopsy. Asignificant number of dogs with generaliseddemodicosis have anaemia. The histopathologicalfindings include perifolliculitis, folliculitis andfurunculosis, but if a mural folliculitis is present insections without intraluminal mites further sec-tions should be cut and examined.

Treatment

Juvenile demodicosis usually resolves sponta-neously if left untreated. Cases given glucocorti-coids may develop pyoderma and becomegeneralised. If a pyoderma is present then sys-temic antibiotics (cephalosporins are the mosteffective) and topical antibacterial washes shouldbe used until 7 to 10 days after resolution. Thecoat should be clipped and topical acaracidalagents should be used to control the demodicosis.Amitraz is currently the topical chemical ofchoice, usually used at 0.05% every 7 to 14 daysuntil two consecutive negative skin scrapings andhair plucks are obtained. Systemic ivermectingiven orally at between 400 and 800 mg/kg dailyhas been reported to be effective. The avermectin,milbemycin oxime, is available in many countriesand is effective in the treatment of canine demo-dicosis. In a small number of cases the demodi-cosis recurs several weeks or months afterapparently successful treatment. In these cases anunderlying disease should be sought andcontinual long-term therapy may be required.

Trombiculidiasis

Clinical features

Larvae ofTrombicula spp. occasionally affect dogsin the summer and autumn, leading to papularlesions usually on the lower limbs, ventrum, faceand muzzle, with variable degrees of pruritus(Plate 14). In the initial stages small clusters oforange larval mites can be seen on the skin,although the lesions may persist after the larvalmites have vacated the skin. The mites are mostoften seen in fruit-growing areas on chalky soil.

Diagnosis

Diagnosis is made by observation with the nakedeye and microscopic identification of the larvalmites collected from the skin (Plate 15).

Treatment

The dermatitis should resolve shortly after thelarvae have left the skin but acaricidal treatmentmay be necessary. In severe infestations topicalorganophosphates (for example coumaphos,chlorpyriphos, malathion or diazinon) or limesulphur can be used to control the mites. If severe,excoriation occurs due to self-trauma and gluco-corticoids can be used to alleviate the signs.

Cheyletiellosis

Clinical features

Cheyletiellosis is a contagious, variably pruriticinfestation caused by Cheyletiella yasguri andseen in dogs of any age, but particularly theyoung. Scaling, dry or greasy, occurs on the backand head along with a papular rash in some cases(Plates 16, 17 and 18). Asymptomatic carriersoccur and any in-contact animal should beexamined for mites and treated if necessary.

Diagnosis

Diagnosis is based on history, clinical examina-tion and identification of mites or eggs (Plates 19and 20). Microscopic examination of hairs col-lected by coat brushing or plucking may revealeggs attached to the hair or mites. Superficial skinscrapings and acetate-tape impressions may alsoreveal mites or eggs. Examination of a faecalsample by the faecal floatation technique mayalso be of use in diagnosis.

Treatment

Cheyletiellosis is easily treated with topical acar-icidal compounds such as the carbamates (forexample carbaryl), organophosphates (forexample phosmet, chlorpyriphos, malathion or


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diazinon) and fipronil. All in-contact animalsshould also be treated and an environmentalacaricidal spray used around the home.


Clinical features

The poultry mite Dermanyssus gallinae is anunusual cause of dermatitis in the dog. The mitemay come into houses from bird nests in the roofor eaves, but the disease is most often associatedwith dogs that have access to chicken houses. Theclinical signs include variable pruritus, papules,crusting and scaling, usually on the back andlimbs.

Diagnosis

The diagnosis is made on the basis of the clinicalfeatures and finding mites on skin scrapings,acetate-tape strips and coat brushings.

Treatment

Treatment is by topical insecticidal products andremoval of the source of infestation.

8.12.2 Ticks

Clinical features

Various species of ticks can be found on dogs indifferent parts of the world. They cause focalnecrosis and local inflammation within thedermis, can act as vectors for various micro-organisms, produce paralysis and, in severeinfestations, anaemia. The spinose ear tick, Oto-bius megnini, found in southern USA causes otitisexterna with head shaking and scratching and, insevere cases, convulsions. In Europe, the dog tick,Ixodes canisuga, castor bean tick, Ixodes ricinus,and hedgehog tick, Ixodes hexagonus, are parti-cularly important causes of localised dermatitisand potential vectors of disease in dogs.

Diagnosis


Treatment

Dogs should be kept away from tick-infestedpasture if possible. Topical insecticidal com-pounds such as carbamates (for example car-baryl), organophosphates (for examplechlorpyriphos, malathion or diazinon) andfipronil canbeused to kill ticks ondogs. Individualticks can be removed manually; however, careshould be taken to remove all the mouthparts.

8.12.3 Flies

Many flies can cause nuisance or annoyance todogs but they are not as great a problem as theyare in large, domestic species. There is growinginterest in the aetiology and pathogenesis ofulcerative lesions on the bridge of the nose pre-viously thought to be a form of pyoderma, socalled `nasal pyoderma'. The histological changesseen in these cases is of an eosinophilic fur-unculosis similar to that seen in mosquito-bitedermatitis of the cat. This raises the possibilitythese nasal lesions in the dog are due to a flyinginsect or other arthropod, such as spiders.

Sandflies

Clinical features

Flies of the genus Phlebotomus in the Old Worldand Lutomyia in the New World are of primaryimportance as vectors of the protozoan Leish-mania spp. Although these flies feed on dogs, theirbite is not usually associated with significant skindisease. However, during blood feeding, theintroduction of the protozoan Leishmania canlead to the development of a chronic exfoliativenon-pruritic dermatosis with scaling, especiallyon the face, pinnae and feet. The organism canalso produce a severe systemic disease.


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Diagnosis

Leishmaniasis is diagnosed on the basis of his-tory, clinical signs and serology. The diagnosis isconfirmed by histological identification of theorganism in the skin or internal organs.

Treatment

Topical treatment with organophosphates orpyrethroids may help reduce sandfly activity.Regular application of repellents such as DEETmay also help prevent bites.

Other blood-feeding flies

Clinical features

Blood-feeding flies may cause painful papules andweals, especially on the hairless areas of the head,ears, neck, ventrum and legs.

Diagnosis

Diagnosis is made on the basis of history, clinicalsigns and, ideally, observation and identificationof flies while feeding.

Treatment

Topical treatment with organophosphates orpyrethroids may help effect temporary relief frombiting flies. Regular application of repellents suchas DEET may also help to reduce fly feedingactivity. In severe cases of fly-bite dermatitissystemic or topical glucocorticoids can be used totreat the dermatitis.

8.12.4 Myiasis

Cutaneous myiasis

Clinical features

Myiasis of dogs may be caused by the obligatescrewworms Cochliomyia hominivorax (Nearcticand Neotropical regions), Chrysomya bezziana

(Oriental and Afrotropical regions) and Wohl-fahrtia magnifica (eastern Palaearctic). Cutaneousmyiasis may also be caused by species of Lucilia,Calliphora, Protophormia or Phormia, in variousparts of the world. Myiasis may occur in old ordebilitated dogs, particularly when wounds areleft untreated. Stray dogs injured in road trafficaccidents may develop myiasis if left unnoticed,paralysed and with severe cutaneous wounds.Long-coated dogs with untreated chronic diar-rhoea and faecal coat contamination may developmyiasis, especially in warm, humid weather.

Diagnosis


Treatment

Affected wounds are surgically debrided andsprayed or washed with organophosphates (forexample malathion) or pyrethroids (for examplepermethrin). Prompt treatment of cutaneouswounds will prevent myiasis.

Furuncular myiasis

Clinical features

Species of the genus Cuterebra are dermal para-sites largely affecting rodents and rabbits,although dogs may also be affected. They arefound exclusively in the New World. The larvaeproduce large, subdermal nodules and parasitismby more than one larva is common.

Diagnosis

Diagnosis is made on the basis of clinical signsand identification of larvae within or exitingwarbles.

Treatment

Little information is available relating to thetreatment of Cuterebra, but ivermectin, mox-idectin or doramectin are likely to be effective.


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8.12.5 Fleas

Clinical features

The most common flea seen on dogs is the cat fleaCtenocephalides felis felis. Several other specieshave been reported to cause dermatitis, includingCtenocephalides canis (Plate 21), Echidnophagagallinacea, Leptopsylla segnis, Pulex irritans andCeratophyllus spp. Flea-bite dermatitis is one ofthe most common canine dermatoses. Clinicalsigns include papules, crusts, pruritus, excoria-tions and secondary alopecia. The lesions mostlyoccur on the dorsum, around the tail base, theventral abdomen and the neck (Plates 22 and 23).

Diagnosis

Diagnosis is based on history, clinical signs andidentification of fleas or flea faeces on the dog.Intradermal skin testing using a flea extract mayalso be of some value in the diagnosis of flea-bitedermatitis.

Treatment

The treatment of dogs for flea infestation or flea-bite dermatitis involves:

. Application of an adulticide on to the affectedanimal's coat. Effective products may containorganophosphates, pyrethroids, carbamates orfipronil. Flea products for on-animal use comein spray, shampoo, wash and powder for-mulations.

. Application of an adulticide to all in-contactanimals (dogs and cats).

. Treatment of the environment using productsable to kill the egg, larval and pupal stages ofthe life-cycle. Products available include thosecontaining organophosphates, pyrethroids andIGRs. These are available in spray formula-tions. The IGR lufenuron may be given orallyto the dog and transferred to the flea in bloodat feeding, leading to the production of infer-tile eggs; this is a useful product if there is nosignificant reservoir host nearby (for example aneighbour's untreated dog or cat).

. Regular vacuuming to remove flea eggs andlarva will also help in a flea control pro-gramme.

. Control of small mammals in and around thehouse that may act as a reservoir host for fleas.

. Treatment of the affected animal with gluco-corticoids to alleviate the dermatitis andpruritus.

8.12.6 Lice

Clinical features

Dogs can be infested by both the chewing louse,Trichodectes canis (Plate 24), and the suckinglouse, Linognathus setosus. The clinical signsassociated with louse infestation are pruritus,scaling, crusts, coat matting, excoriation andsecondary alopecia. Severe infestation with L.setosus produces anaemia, especially in puppies.Lice are more common in kennels where asymp-tomatic carriers may act as reservoirs.

Diagnosis

Diagnosis is made on the basis of clinical signsand identification of lice in the coat. These can becollected by acetate-tape strips or coat brushingsfor examination under the microscope.

Treatment

Lice spend their entire life-cycle on the host andare readily killed by most organophosphates (forexample chlorpyriphos, malathion or diazinon),pyrethroids (for example permethrin), carba-mates (for example cabaryl), fipronil and g-BHC.Topical insecticides applied as a dip or spray areusually applied twice, 14 days apart. Severelyanaemic animals may require supportivetherapy.


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8.13 CATS (Table 8.9)

8.13.1 Mites

Sarcoptic mange

Clinical features

This is a very rare pruritic dermatosis of cats. Asmall number of cases have been reported inassociation with feline immunodeficiency virus,but the pathogenesis in these cases is unclear.

Diagnosis

Diagnosis is based on clinical features and iden-tification of mites in skin scrapings.

Treatment

Cats are highly susceptible to organophosphatetoxicity. However, malathion dips are effectiveand relatively safe. A lime sulphur dip every 10days until remission may also be effective.

Table 8.9 A guide to ectoparasites affecting cats.


Parasitetype

Species

Mites Sarcoptes scabiei(very rare)

. . . . . . . .

Notoedres cati . . . . . . .Otodectes cynotis . . . . .Demodex cati +/± +/± +/± +/± +/± . +/± . . . .Unnamed short

demodex species

. . . . . . . . . .

Cheyletiella blackei +/± +/± +/± . . . . .Trombicula spp. . . . . .Dermanyssus gallinae . . . . . . . . .

Lice Felicola subrostrata . . . . . +/± . . . .

Fleas Ctenocphalides felis . . . . . . .Spilopsyllus cuniculi . . . . . .Ctenocephalides canis . . . . . . .Leptopsylla segnis . . . . . . .Pulex irritans . . . . . . .Ceratophyllus spp. . . . . . . .Echidnophaga gallinacea . . . . . . .

Ticks Various . . . . . . ?

Flies Mosquito +/± . . . . . . ?

Primary myiasis . . .Secondary myiasis . . .

Pruritus

Papules

Pustules

Crusts

Scaling

Alopecia

Erosion/ulceration

Clinicalsigns


parasite

Skin

scrapings

Hairbrushings

Hairplucks/acetate

stripexamination

Serology

Parasite

foundin

the


Biopsy

andhistology


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Systemic ivermectin at 200±300 mg/kg repeatedafter 14 days may also be used.

Notoedric mange

Clinical features

This is a contagious pruritic dermatosis of the catcaused by the mite Notoedres cati which has alsobeen reported to affect foxes, dogs and rabbits.Notoedric mange is rare in the UK but endemic insome parts of the world. Characteristic lesionsinclude papules, yellow crusts, alopecia andlichenification occurring on the pinnae, face,eyelids, neck, elbows, perineum and feet. There isintense pruritus and in many cases peripherallymphadenopathy.

Diagnosis

Diagnosis is based on clinical features and theidentification of mites and eggs in skin scrapings.

Treatment

Treatment is similar to that described for sar-coptic mange. Malathion or lime sulphur dipsmay be used until remission occurs. Injections ofivermectin, at 300±400 mg/kg, are reported to beeffective in feline notoedric mange.

Otodectic mange

Clinical features

As in the dog, the ear mite Otodectes cynotis(Plate 9) causes otitis externa with intense auralirritation, pruritus and head shaking. Examina-tion of the external ear canal reveals a thick,reddish-brown exudate with some crust forma-tion. The infestation is very contagious and isparticularly prevalent in feral and young cats.Although the pathogenesis of the lesions has notbeen elucidated, a hypersensitivity may beinvolved and asymptomatic carriers exist. Occa-sionally ectopic infestation occurs where the mite

causes localised dermatitis on the skin, especiallyon the neck, rump and tail.

Diagnosis

Examination of the external ear canal using anauroscope reveals small, fast-moving mites.Microscopic examination of aural exudatemounted in liquid paraffin or superficial skinscrapings in ectopic cases reveals mites and eggs.

Treatment

Topical ceruminolytic ear preparations should beused to remove crust and cerumen from theexternal ear canal. An otic acaricidal product(thiabendazole, permethrin) should then be usedfor 2 weeks beyond a clinical cure. Selamectin as aspot-on is effective in the treatment of Otodectescynotis. Systemic ivermectin, at 200±400 mg/kg,given twice, 14 days apart, is effective and theadult cat appears to be relatively free of side-effects.

Demodectic mange

Clinical features

Demodicosis is a rare feline dermatosis caused bythe long follicular mite Demodex cati or the shortform, Demodex gatoi. Demodicosis due to D. catiis usually localised, affecting the periocular skin,eyelids, head and neck with erythema, scaling,crusts and alopecia. Ceruminous otitis externahas also been reported. Generalised demodicosisis very rare, but has been reported with variablepruritus, alopecia, scaling, crusting and hyper-pigmentation on the head, neck, legs and trunk.Feline demodicosis is usually associated withunderlying debilitating diseases such as diabetesmellitus, feline leukaemia virus infection (FeLV)and systemic lupus erythematosus (SLE). Thegeneralised disease has been seen in associationwith inflammatory bowel disease and concurrentlong-term corticosteroid administration. Theauthor has seen one case of feline demodicosiswith concurrent dermatophytosis.


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Demodicosis due to the short form ofDemodexoccurs in the absence of underlying disease, withsevere pruritus, alopecia, scaling, excoriation andcrusts. The lesions are usually on the head, neckand elbows. Symmetrical alopecia with or with-out scaling has also been reported with this typeof demodicosis.

Diagnosis

Demodicosis is diagnosed on the basis of clinicalfeatures and identification of mites in skinscrapings and hair pluckings. The short form isfound by superficial skin scraping, acetate stripsand within the stratum corneum on biopsy sec-tions.

Treatment

Some cases spontaneously recover but locallesions can be treated with lime sulphur dip, car-baryl, malathion or amitraz. Sedation, anorexiaand depression can be a problem especially withamitraz, particularly in kittens. Fenchlorphos andphosmet dips have also been reported to beeffective.

Trombiculidiasis

Clinical features

Larvae of Trombicula spp. occasionally affect catsin the summer and autumn, leading to papularlesions usually on the lower limbs, ventrum, faceand Henry's pocket at the base of the pinnae,producing variable degrees of pruritus. In theinitial stages small clusters of orange larval mitescan be seen on the skin, although the lesions maypersist after the larval mites have vacated the skin.The mites are most often seen in fruit-growingareas on chalky soil.

Diagnosis

Diagnosis is by observation with the naked eyeand microscopic identification of the larval mitescollected from the skin.

Treatment

The dermatitis should resolve shortly after thelarvae have left the skin; however, acaricidaltreatment may be necessary. In severe infestationstopical fipronil can be used to control the mites. Ifsevere excoriation occurs due to self-trauma thenglucocorticoids can be used to alleviate thepruritus and inflammation.

Cheyletiellosis

Clinical features

Cheyletiellosis is a contagious, variably pruriticinfestation caused by Cheyletiella blakei and isseen in cats of any age, but particularly the young.The disease is often mild with dry or greasyscaling on the back. In some cases there is apapulocrustous dermatitis affecting the dorsum,often described as miliary dermatitis. Asympto-matic carriers occur and any in-contact animalshould be examined for mites and treated ifnecessary.

Diagnosis

Diagnosis is based on history, clinical examina-tion and identification of mites or eggs. Micro-scopic examination of hairs collected by coatbrushing or plucking may reveal eggs attached tothe hair or mites. Superficial skin scrapings andacetate-tape impressions may also reveal mites oreggs. Examination of a faecal sample by the faecalfloatation technique may also be of use indiagnosis.

Treatment

Cheyletiellosis is easily treated with topical acar-icidal compounds such as the carbamates (forexample carbaryl) and fipronil. Systemic iver-mectin at 200±400 mg/kg is effective and the adultcat appears to be relatively free of side-effects. Allin-contact animals should also be treated and anenvironmental acaricidal spray used around thehome.


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Clinical features

The poultry mite Dermanyssus gallinae can causedermatitis in the cat. The mite may come intohouses from bird nests in the roof or eaves, butthe disease is most often associated with cats thathave access to chicken houses or those that reg-ularly raid birds' nests. The clinical signs arevariable and include pruritus, papules, crusts andscales, usually on the back and limbs.

Diagnosis

The diagnosis is made on the basis of the clinicalfeatures and finding mites on skin scrapings andcoat brushings.

Treatment

Topical treatment with insecticidal productslicensed for flea treatment (dichlorvos, perme-thrin) is effective. Removal of the source ofinfestation is required to prevent recurrence.

8.13.2 Ticks

Clinical features

Ticks cause local inflammation within the dermis,are potential vectors of various micro-organismsand produce paralysis and, in severe infestations,anaemia. The spinose ear tick, found in thesouthern USA, causes otitis externa with headshaking and scratching and, in severe cases, con-vulsions. In Europe the dog tick, Ixodes canisuga,castor bean tick, Ixodes ricinus, and hedgehogtick, Ixodes hexagonus, are important causes oflocalised dermatitis in cats.

Diagnosis


Treatment

Unlike other domestic species, cats are usuallyfree-ranging and control of their exposure toinfested pasture is impractical. Topical insectici-dal compounds such as pyrethroids and fipronilcan be used to kill ticks on cats.

8.13.3 Flies

Cats are normally free-ranging and are able toavoid flies more easily than other domestic spe-cies. Although they may, in theory, be bitten byflying insects, flies are not usually consideredclinically important, except for the notableexception of feline mosquito-bite hypersensitivity.

Feline mosquito-bite hypersensitivity

Clinical features

Mosquitoes have been shown to feed during thenight on the faces of cats, leading to a papulardermatitis with cutaneous oedema, epidermalulceration crusting and alopecia.

Diagnosis

Diagnosis is usually based on circumstantial evi-dence in history and clinical features. Observationof the mosquito feeding confirms the diagnosis.Histological examination of the lesional skinreveals an eosinophilic folliculitis andfurunculosis.

Treatment

Topical and systemic glucocorticoids are used totreat the lesions, but prevention requires confin-ing the affected cat indoors at night and coveringany windows with mosquito netting.


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8.13.4 Myiasis

Cutaneous myiasis

Clinical features

Myiasis may be caused by the obligate screw-worms Cochliomyia hominivorax (Nearctic andNeotropical regions), Chrysomya bezziana(Oriental and Afrotropical regions) and Wohl-fahrtia magnifica (eastern Palaearctic). Cutaneousmyiasis may also be caused by species of Lucilia,Calliphora, Protophormia or Phormia, in variousparts of the world. Myiasis may occur in old ordebilitated cats, particularly when wounds are leftuntreated. During warm humid weather catsparalysed and/or involved in road traffic acci-dents often develop myiasis. Long-coated catswith untreated chronic diarrhoea and faecal coatcontamination may develop myiasis, especially inwarm, humid weather.

Diagnosis


Treatment

Affected wounds are surgically debrided andsprayed or washed with organophosphates (forexample malathion) and pyrethroids (for examplepermethrin). Prompt treatment of cutaneouswounds will prevent myiasis. Clipping the hairaround the perineum, especially in long-coatedcats with a tendency toward diarrhoea, will alsohelp to prevent the development of myiasis.

Furuncular myiasis

Clinical features

Species of the genus Cuterebra are dermal para-sites largely affecting rodents and rabbits,although cats may also be affected. They arefound exclusively in the New World. The larvaeproduce large, subdermal nodules and parasitismby more than one larva is common.

Diagnosis


Treatment

Little information is available relating to thetreatment of Cuterebra, but ivermectin, mox-idectin or doramectin are likely to be effective.

8.13.5 Fleas

Clinical features

The most common flea seen on cats is Ctenoce-phalides felis felis. The rabbit flea, Spilopsylluscuniculi, may be found on the pinnal margin incats that hunt rabbits or enter burrows, causing amild papular dermatitis. Several other specieshave been reported to cause dermatitis in cats,including Ctenocephalides canis, Echidnophagagallinacea, Spilopsyllus cuniculi, Leptopsylla seg-nis, Pulex irritans and Ceratophyllus spp. Flea-bite dermatitis is one of the most common felinedermatoses. The clinical signs include:

. Symmetrical alopecia; this is due to excessivegrooming stimulated by pruritus (Plate 25).There are no lesions on the skin itself but thecat has broken hairs, usually on the ventrumand hind legs but occasionally also on theback.

. Miliary dermatitis; signs include papules,crusts, pruritus, excoriations and secondaryalopecia (Plate 26). The lesions mostly occuron the dorsum, around the tail base and theneck.

. `Eosinophilic granuloma complex' includingeosinophilic plaques (Plate 27).

Diagnosis

The diagnosis is based on history, clinical signsand identification of fleas or flea faeces on the cat.Intradermal skin testing using a flea extract mayalso be of some value in the diagnosis of flea-bite


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dermatitis. In cases of symmetrical alopecia dueto excessive grooming, microscopic examinationof the hair tips reveals fractured ends. Eosino-philic granuloma complex is diagnosed by biopsyand histopathology.

Treatment

Treatment for flea-bite dermatitis is as describedin the dog and involves:

. Application of an adulticide on to the affectedanimal's coat. Examples are products con-taining organophosphates, pyrethroids, car-bamates or fipronil. Flea products for on-animal use come in spray, shampoo, washesand powder formulations.

. Application of an adulticide to all in-contactanimals (dogs and cats).

. Treatment of the environment using productsable to kill the egg, larval and pupal stages ofthe life-cycle. Products available include thosecontaining organophosphates, pyrethroids andIGRs. The IGR, lufenuron, may be givenorally to the cat and transferred to the flea inblood at feeding, leading to the production ofinfertile eggs; this is a useful product if there isno significant reservoir host nearby (forexample a neighbour's untreated cat). A rela-tively recent environmental treatment is thedesiccant sodium polyborate, which is nowavailable in the USA and Europe for use in thehouse.

. Regular vacuuming to remove flea eggs andlarva will also help in a flea control pro-gramme.

. Control of small mammals in and around thehouse that may act as a reservoir host for fleas.

. Treatment of the affected animal with gluco-corticoids to alleviate the dermatitis andpruritus.

8.13.6 Lice

Clinical features

Cats are affected by only one species of louse,Felicola subrostrata. The clinical signs associated

with lice infestation are pruritus, scaling, crusting,coat matting, excoriation and secondary alopecia.Lice are more common in catteries whereasymptomatic carriers may act as reservoirs.Kittens are most often affected by lice.

Diagnosis

The diagnosis is made on the basis of clinical signsand identification of lice in the coat (Plate 28).

Treatment

Lice spend their entire life-cycle on the host andare readily killed by most organophosphates (forexample malathion or diazinon), pyrethroids (forexample permethrin), carbamates (for examplecabaryl) and fipronil (two applications of 0.25%spray or spot-on, 28 days apart). Topical insec-ticides applied as a dip or spray are usuallyapplied twice, 14 days apart.

8.14 RABBITS

8.14.1 Mites

Sarcoptic mange

Clinical features

Although rare, rabbits may develop a severepruritic, crusting dermatitis with excoriation andsecondary alopecia due to Sarcoptes scabieiinfestation.

Diagnosis

Diagnosis is on the basis of history, clinical signsand identification of mites in skin scrapings.

Treatment

Systemic treatment, using ivermectin orally or bysubcutaneous injection at 200±400 mg/kg on threeoccasions, 7 days apart, is effective. All in-contactanimals should also be treated. The cage orhousing should be cleaned.


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Notoedric mange

Clinical features

Although rare, Notoedres cati may also affectrabbits, also causing a pruritic, crusting derma-titis.

Diagnosis

Diagnosis is made on the basis of history, clinicalsigns and identification of mites in skin scrapings.

Treatment

Systemic treatment using ivermectin orally or bysubcutaneous injection at 200±400 mg/kg, on threeoccasions, 7 days apart, is effective. All in-contactanimals should also be treated. The cage orhousing should be cleaned.

Psoroptic mange

Clinical features

Psoroptes cuniculi is a common cause of otitisexterna and, occasionally, dermatitis in rabbits.The ear canal becomes full of a crusting, cer-uminous exudate and the pinnae become excori-ated by scratching. If the mite spreads to the bodya pruritic, crusting dermatitis occurs with lesionsespecially on the ventral abdomen and urogenitalregion.

Diagnosis

Diagnosis is made on the basis of history, clinicalsigns and identification of mites in the cer-uminous exudate of the external ear canal or skinscrapings. Otoscopic examination of the externalear canal may also reveal mites.

Treatment

Cleaning the external ear canal with a cer-uminolytic agent to remove the exudate should beperformed before giving acaricidal treatment. Forotitis externa alone, topical ivermectin applied

into the ear canal can be used. Systemic treatmentusing ivermectin orally or by subcutaneousinjection at 200±400 mg/kg, on three occasions, 7days apart, is effective. All in-contact animalsshould also be treated. The cage or housingshould be cleaned.

Leporacarus gibbus

Clinical features

This is a fur mite of rabbits which is thought to bea normal coat commensal. If present in largenumbers, it produces a pruritic, scaling dermati-tis. Underlying debilitating disease such as dentaldisease may be involved in the development of thefur mite dermatitis.

Diagnosis

Diagnosis is made on the basis of history, clinicalsigns and identification of mites in coat brushings,acetate strips and skin scrapings (Plates 29±31).

Treatment

Any underlying or concurrent disease should betreated. Systemic treatment using ivermectinorally or subcutaneously at 200±400 mg/kg, onthree occasions, 7 days apart, is effective. All in-contact animals should also be treated. The cageor housing should also be cleaned.

Cheyletiellosis

Clinical features

Cheyletiella parasitivorax is a common fur mite ofrabbits, which is likely to be a normal commensal,and asymptomatic carriers occur. If present insufficient numbers or if the affected animal has ahypersensitivity reaction to the mite, a variablypruritic, scaling dermatitis occurs. Secondaryalopecia occurs in pruritic cases. It is common forin-contact humans to develop a papular rash,especially on the forearms.


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Diagnosis

Diagnosis is made on the basis of history, clinicalsigns and identification of mites in coat brushingsand skin scrapings.

Treatment

Topical acaricides, such as pyrethrin powders anddichlorvos-containing sprays are effective againstCheyletiella spp. Systemic treatment using iver-mectin, orally or subcutaneously at 200±400 mg/kg, on three occasions, 7 days apart, iseffective.

8.14.2 Flies

Adult flies are not usually a problem in domesticsmall mammals, although rabbits and guinea-pigskept outdoors may be attacked by biting midges,mosquitoes, black flies and other blood-feedingflies. Diagnosis may be difficult, but fly-asso-ciated dermatitis should be considered in caseswith papular and urticaria lesions without evi-dence of resident ectoparasites. In such casestopical repellents, insecticides and mechanicalbarriers should be employed. Mosquito or fly netsmay be used and dichlorvos-impregnated flystrips hung near to the cages in an attempt tocontrol flying insects. Mosquitoes and black fliesare vectors of myxomatosis and other viral dis-eases in rabbits, especially in Australia.

8.14.3 Myiasis

Furuncular myiasis

Clinical features

Species of the genus Cuterebra are dermal para-sites of rodents and rabbits. The larvae producelarge subdermal nodules and parasitism by morethan one larva is common. They are foundexclusively in the New World.

Diagnosis


Treatment

Little information relating to the treatment ofinfestation by Cuterebra spp. is available, buttreatment with ivermectin, moxidectin ordoramectin is likely to be effective.

Cutaneous myiasis

Clinical features

Myiasis may be caused by the obligate screw-worms Cochliomyia hominivorax (Nearctic andNeotropical regions), Chrysomya bezziana(Oriental and Afrotropical regions) and Wohl-fahrtia magnifica (eastern Palaearctic). Cutaneousmyiasis may also be caused by species of Lucilia,Calliphora, Protophormia or Phormia, in variousparts of the world.Myiasis is a particular problemwith guinea-pigs and rabbits kept outdoors. Pre-disposing factors are long hair and urinary orfaecal contamination of the coat. Animals withdiarrhoea and perineal contamination duringwarm, sunny weather are particularly at risk ofdeveloping myiasis.

Diagnosis


Treatment

Affected wounds are surgically debrided andsprayed or washed with organophosphates(malathion) or pyrethroids (permethrin). Theperineum should be clipped in animals withdiarrhoea and washed once or twice daily toprevent myiasis. Prompt treatment of cutaneouswounds and good hygiene will prevent myiasis.


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8.14.4 Fleas

Clinical features

Ctenocephalides felis felis may affect rabbits,causing a pruritic papular dermatitis. The Eur-opean rabbit flea, Spilopsyllus cuniculi, whichlives on wild rabbits and within their burrows, israrely seen on domestic rabbits. The viral infec-tion myxomatosis is spread by Spilopsyllus cuni-culi in Europe. A wide variety of other species offlea can affect rabbits, including Pulex irritans,Echidnophaga gallinacea and Nosopsyllus fascia-tus.

Diagnosis

Diagnosis is based on history, clinical signs andidentification of fleas or flea faeces on the animal.

Treatment

Topical insecticides, including pyrethroids andorganophosphates, can be used on the animal,and efforts to control environmental sources offleas as described under flea treatment in cats anddogs should also be instigated.

8.14.5 Lice

Clinical features

The lice that affect rabbits are Haemodipsus ven-tricosus and H. setoni.

Diagnosis

Diagnosis is made on the basis of clinical signsand identification of lice and their eggs in the coatand on the hairs.

Treatment

Lice spend their entire life-cycle on the host andare readily killed by most organophosphates (forexample diazinon, malathion, methoxychlor) andpyrethroids (for example permethrin). Topicalinsecticides, applied as a dip or spray, are usually

applied twice, 14 days apart. The entire colonymust be treated. Systemic ivermectin, at 200±400 mg/kg, can be used effectively to control liceon rabbits.

8.15 GUINEA-PIGS

8.15.1 Mites

Trixicarus caviae

Clinical features

This sarcoptid mite causes a severely pruriticcrusting dermatitis with excoriation and second-ary alopecia in guinea-pigs (Plates 32±34). Themost severely affected animals may have convul-sions when handled or while scratching.Untreated animals die from anorexia andexhaustion. Asymptomatic carriers may act as asource of infestation or develop clinical diseasewhen under stress.

Diagnosis

Diagnosis is made on the basis of history, clinicalsigns and identification of mites in skin scrapings(Plate 35).

Treatment


Chirodiscoides caviae

Clinical features

This is a common fur mite of guinea-pigs whichmay be asymptomatic or, if present in largenumbers, causes a scaling, pruritic dermatitis withsecondary alopecia. Concurrent infestation withTrixicarus caviae can occur.


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Diagnosis

Diagnosis is on the basis of history, clinical signsand identification of mites in coat brushings andskin scrapings (Plate 36).

Treatment

Any underlying or concurrent disease should betreated. Systemic treatment using ivermectinorally at 200±400 mg/kg, on three occasions, 7days apart, is effective. All in-contact animalsshould also be treated. The cage or housingshould also be cleaned.

8.15.2 Flies

Adult flies are not usually a problem in domesticsmall mammals, although guinea-pigs kept out-doors may be attacked by biting midges, mos-quitoes, black flies and other blood-feeding flies.Diagnosis may be difficult but fly-associateddermatitis should be considered in cases withpapular and urticaria lesions without evidence ofresident ectoparasites. See comments on fliesaffecting pet rabbbits.

8.15.3 Myiasis

Furuncular myiasis

Clinical features

Species of the genus Cuterebra are dermal para-sites of rodents. The larvae produce large sub-dermal nodules and parasitism by more than onelarva is common. They are found exclusively inthe New World.

Diagnosis


Treatment

Little information relating to the treatment ofinfestation by Cuterebra spp. is available, buttreatment with ivermectin, moxidectin or dor-amectin is likely to be effective.

Cutaneous myiasis

Clinical features

Myiasis may be caused by the obligate screw-worms Cochliomyia hominivorax (Nearctic andNeotropical regions), Chrysomya bezziana(Oriental and Afrotropical regions) and Wohl-fahrtia magnifica (eastern Palaearctic). Cutaneousmyiasis may also be caused by species of Lucilia,Calliphora, Protophormia or Phormia, in variousparts of the world.Myiasis is a particular problemwith guinea-pigs kept outdoors. Predisposingfactors are long hair and urinary or faecal con-tamination of the coat. Animals with diarrhoeaand perineal contamination during warm, sunnyweather are particularly at risk of developingmyiasis.

Diagnosis


Treatment

Affected wounds are surgically debrided andsprayed or washed with organophosphates(malathion) or pyrethroids (permethrin). Theperineum should be clipped in animals withdiarrhoea and washed once or twice daily toprevent myiasis. Prompt treatment of cutaneouswounds and good hygiene will prevent myiasis.

8.15.4 Fleas

Clinical features

Ctenocephalides felis felis may affect guinea-pigsif juvenile forms are present in their environment.


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Diagnosis

Diagnosis is based on history, clinical signs andidentification of fleas or flea faeces on the animal.

Treatment

Topical insecticides, including pyrethroids andorganophosphates, can be used on the animal,and efforts to control environmental sources offleas as described under flea treatment in cats anddogs should also be instigated.

8.15.5 Lice

Clinical features

The lice which affect guinea-pigs are Gliricolaporcelli (Plate 37) and Gyropus ovalis. Guinea-piglice are common in colonies and usually asymp-tomatic, although heavy infestations produce apruritic, scaling dermatosis with secondaryalopecia.

Diagnosis


Treatment

Lice spend their entire life-cycle on the host andare readily killed by most organophosphates (forexample diazinon, malathion, methoxychlor),and pyrethroids (for example permethrin). Topi-cal insecticides, applied as a dip or spray, areusually applied twice, 14 days apart. The entirecolony must be treated. Systemic ivermectin, at200±400 mg/kg, can be used effectively to controllice on guinea-pigs.

8.16 MICE AND RATS

8.16.1 Mites

Notoedric mange

Clinical features

The rat ear mite, Notoedres muris, causes apruritic papular and crusting dermatitis usuallyaround the pinnae, head and neck.

Diagnosis


Treatment


Myocoptes musculinus

Clinical features

This is a common fur mite of mice but has alsobeen reported to cause a suppurative dermatitis inguinea-pigs. Infestation is often asymptomaticbut the mite may cause a scaling, crusting, pruriticdermatitis with secondary alopecia in mice.

Diagnosis

Diagnosis is on the basis of history, clinical signsand identification of mites in coat brushings andskin scrapings (Plate 38).

Treatment

Systemic treatment using ivermectin orally orsubcutaneous injection at 200±400 mg/kg, on threeoccasions, 7 days apart, is effective. All in-contactanimals should also be treated. The cage orhousing should also be cleaned.


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Psorergates simplex

Clinical features

This is a follicular mite that causes small, whiteintradermal nodules in mice.

Diagnosis

Diagnosis can be made by excision of a mass andmicroscopic examination of the dermal pouchcontaining mites.

Treatment

The use of topical malathion powder or methox-ychlor dip has been reported. Systemic treatmentusing ivermectin, orally at 200±400 mg/kg, may beeffective.

Myobia musculi/Radfordia affinis/Radfordia ensifera

Clinical features

Myobia musculi (Plate 39) and Radfordia affinisare common fur mites of mice. Radfordia ensiferaaffects rats. They are normally asymptomatic, butif present in large numbers they cause a scaling,pruritic dermatitis with excoriation and second-ary alopecia. Underlying debilitating disease,overcrowding and poor housing contribute to thepathogenesis of the disease.

Diagnosis

Diagnosis is made on the basis of history, clinicalsigns and identification of mites in coat brushings,acetate-tape strips and skin scrapings.

Treatment

Any underlying or concurrent disease should betreated and management problems corrected.Systemic treatment using ivermectin, orally at200±400 mg/kg, on three occasions, 7 days apart,is effective. All in-contact animals should also be

treated. The cage or housing should also becleaned.

Ornithonyssus bacoti

Clinical features

This is the tropical rat mite which causes derma-titis and pruritus in rats, mice and hamstersworldwide. In severe infestations hosts maybecome anaemic and die.

Diagnosis


Treatment

Topical acaricides or systemic ivermectin, orallyat 200±400 mg/kg, may be effective in the treat-ment of this parasite.

8.16.2 Flies

Adult flies are not usually a problem in domesticmice and rats.

8.16.3 Myiasis

This is a rare problem in domestic mice and rats.See comments on rabbits and guinea pigs.

8.16.4 Fleas

This is a rare problem in domestic mice and rats.

8.16.5 Lice

Clinical features

The lice which affect mice and rats are Polyplaxserrata (mice; Plate 40) and Polyplax spinulosa


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(rats). Polyplax spp. produce a pruritic, scalingdermatosis with anaemia and death if untreated.

Diagnosis


Treatment

Lice spend their entire life-cycle on the host andare readily killed by most organophosphates (forexample diazinon, malathion, methoxychlor),and pyrethroids (for example permethrin). Topi-cal insecticides, applied as a dip or spray, areusually applied twice, 14 days apart. Fipronilapplied to the entire body repeated after 10 days iseffective for the control of lice in mice and rats.The entire colony must be treated. Systemicivermectin, at 200±400 mg/kg, can be used effec-tively to control lice on mice and rats.

8.17 HAMSTERS AND GERBILS

8.17.1 Mites

Sarcoptic mange

Clinical features

Although rare, hamsters may develop a severepruritic dermatitis with excoriation and second-ary alopecia due to Sarcoptes scabiei infestation.

Diagnosis

Diagnosis is on the basis of history, clinical signsand identification of mites in skin scrapings.

Treatment

Systemic treatment, using ivermectin orally or bysubcutaneous injection at 200±400 mg/kg on threeoccasions, 7 days apart, is effective. All in-contactanimals should also be treated. The cage orhousing should be cleaned.

Demodectic mange

Clinical features

Demodicosis is a relatively common disease ofhamsters (Demodex criceti and Demodex aurati)and gerbils (Demodex meriones). These follicularmites produce folliculitis and subsequent hairloss. The clinical signs are a scaling dermatosisand alopecia. Demodicosis usually occurs as theresult of an underlying debilitating disease.

Diagnosis


Treatment

Topical treatment with a mixture of ronnel andpropylene glycol applied to one-third of the bodydaily. Topical amitraz treatment has also beenreported. Treatment is continued until skinscrapings are negative. Underlying debilitatingdiseases should be investigated and treated.

Ornithonyssus bacoti

Clinical features

This is the tropical rat mite which causes derma-titis in hamsters worldwide. In severe infestationshosts may become anaemic and die.

Diagnosis


Treatment

Topical acaricides or systemic ivermectin, orallyat 200±400 mg/kg, may be effective in the treat-ment of this parasite.


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8.17.2 Flies

Adult flies are not usually a problem in domestichamsters and guinea-pigs.

8.17.3 Myiasis

This is a rare problem in domestic hamsters andguinea pigs. See comments on rabbits and guineapigs.

8.17.4 Fleas

This is a rare problem in domestic hamsters andguinea-pigs.

8.18 FERRETS

8.18.1 Mites

Sarcoptic mange

Clinical features

Sarcoptic mange has been seen in pet, laboratoryand feral ferrets and is an intensely pruritic der-matosis caused by the mite Sarcoptes scabiei.Typical lesions are papules, crusts, excoriationand secondary alopecia. The lesions occur on thepinnae, face and ventral abdomen. Sarcopticmange only affecting the feet has been reported inferrets.

Diagnosis


Treatment

A keratolytic shampoo should be used to removethe crusts and scale. A topical acaricidal shampooor wash should be used every 7 to 14 days for 3 to6 weeks. Organophosphates and carbamates may

be toxic. Systemic ivermectin at 200±400 mg/kggiven twice, 14 days apart, is effective. Re-exposure is a potential problem. Groomingequipment should also be cleaned thoroughly.

Otodectic mange

Clinical features

The mite Otodectes cynotis causes otitis externawith intense aural irritation. Examination of theexternal ear canal reveals a thick reddish-brownexudate with some crust formation.

Diagnosis

Examination of the external ear canal using anauroscope reveals small, fast-moving mites.Microscopic examination of aural exudate orsuperficial skin scrapings in ectopic cases revealsmites and eggs.

Treatment

Topical ceruminolytic ear preparations should beused to remove crust and cerumen from theexternal ear canal. Systemic ivermectin at500 mg/kg given twice, 14 days apart, is effective,but congenital defects can occur if used in jills.

Demodectic mange

Clinical features

Demodex spp. have been reported to cause a non-pruritic localised dermatitis in ferrets. Excessiveuse of topical preparations containing gluco-corticoids has been reported to cause demodicosisin ferrets.

Diagnosis

Diagnosis of demodicosis is made on the basis ofclinical features and the identification of numer-ous demodectic mange mites on superficial ordeep skin scrapings, hair pluckings or biopsy.


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Treatment

Dipping in 0.0125±0.037% amitaz has beenreported as useful in the treatment of demodicosisin ferrets.

8.18.2 Ticks

Clinical features

Ixodes ricinus has been found on working ferretsin the UK. Other species of tick may affect ferretsin different parts of the world.

Diagnosis


Treatment

Individual ticks can be removed manually; how-ever, care should be taken to remove all themouthparts.

8.18.3 Myiasis

Cutaneous myiasis

Clinical features

Species of the genus Cuterebra and Hypodermabovis have been reported in mustelids.

Diagnosis


Treatment

The larvae should be manually removed andaffected wounds surgically debrided. Prompttreatment of cutaneous wounds will help to pre-vent myiasis.

8.18.4 Fleas

Clinical features

The cat flea Ctenocephalides felis can affectferrets. Clinical signs include papules, crusts,pruritus, excoriations and secondary alopecia.The lesions mostly occur on and around the tailbase, the ventral abdomen and thighs.

Diagnosis

Diagnosis is based on history, clinical signs andidentification of fleas or flea faeces on the ferret.

Treatment

The fleas on the ferret and in the environmentshould be treated. The approach to the latter is asdescribed for the dog and cat. Although notlicensed for ferrets, the author is aware of oneowner who has used fipronil spray for successfulcontrol of Ctenocephalides felis in her ferrets.

8.19 BIRDS

This section covers the diagnosis and treatment ofthe most important cutaneous ectoparasitesaffecting birds.

8.19.1 Mites

Knemidocoptic mange

Clinical features

In domestic poultry Knemidocoptes mutans causesscaling and crusting, which becomes honey-combed in appearance, around the legs, leading insome cases to foot deformation. The condition isknown as `scaly leg'. In parrots, budgerigars andparakeets, Knemidocoptes pilae infests the skinaround the beak and sometimes legs, causingproliferative scaling which may be honeycombedin appearance and leads to deformation of thebeak, anorexia and death if untreated. Thecondition is known as `scaly face' or `scaly beak'.


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The mite Knemidocoptes laevis gallinae burrows inthe skin around the feathers, causing pruritus andfeather loss on the back, neck, wings and aroundthe vent. Poultry, pheasants and geese are affec-ted and the condition is known as `deplumingitch'.

Diagnosis


Treatment

Topical treatment with ivermectin, g-BHC,organophosphates (for example coumaphos,malathion) or carbaryl is effective against Kne-modicoptes spp. Because of its potential toxicity,g-BHC should be used with care and applied tothe lesions on the head and legs, taking care toavoid oral ingestion. Systemic treatment of birdswith ivermectin, at 200 mg/kg intramuscularly, iseffective. Topical ivermectin applied as a spot-onis also effective.

Trombiculosis

Clinical features

The larval forms of Trombicula spp. can infestbirds during the summer and autumn, causingpruritus and cutaneous vesicles at the site ofbiting.

Diagnosis

Diagnosis is made on the basis of history, clinicalexamination and identification of mites feedingon the skin.

Treatment

The dermatitis will resolve once the mites haveleft the skin, although topical preparations con-taining acaricides such as coumaphos, pyrethrinand malathion can be used to kill the mites.

Ornithonyssus spp.

Clinical features

The northern fowl mite and tropical fowl mite,Ornithonyssus spp., spend their entire life-cycle onthe host, causing pruritus, plumage damage,weakness, anaemia and death. They affect poultryand wild birds.

Diagnosis

Mites can be collected and identified by micro-scopic examination. The presence of northernfowl mites is most easily determined by exam-ination of the base of the feathers around the ventarea on hens. The mites produce a rough andscaly condition on the skin and a darkening of thefeathers due to the dried blood and excreta.

Treatment

To minimise the risk of mite infestation all newbirds brought into a poultry house should beconfirmed as mite-free and, since the mites cansurvive for several days off-host, care must betaken to minimise the introduction of mites fromother houses on clothing or equipment. Infestedbirds should be treated topically with an acar-icidal compound such as pyrethroids, carbaryl,malathion or rotenone. Insecticidal sprays used totreat birds should be able to penetrate to the baseof feathers. The environment may also be treatedwith an insecticidal preparation.

Dermanyssus gallinae

Clinical features

The red mite Dermanyssus gallinae can causesevere dermatitis in poultry. The clinical signs arepruritus, plumage damage, weakness, reduced eggproduction, anaemia and death. As with Orni-thonyssus spp., this mite can also affect wild birds.

Diagnosis

The diagnosis is made on the basis of the clinicalfeatures and finding mites on the skin at night.


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Examination of the bird during the day will notreveal the mites, which feed only at night andspend the day in crevices in the walls.

Treatment

Hygiene procedures, as described for Ornitho-nyssus spp., should be adopted to prevent infes-tation. Topical treatment of the affected birdswith insecticidal products such as permethrin,carbaryl, malathion, cypermethrin or rotenonemay be effective. However, because this mite livesin cracks and crevices in the environment, thor-ough cleaning and insecticidal treatment ofinfested poultry houses is essential.

8.19.2 Ticks

Clinical features

There are numerous ticks which may affect birds,including larvae of Ixodes ricinus, Dermacentorreticulatus,Haemaphysalis spp. andRhipicephalusspp., and adult Argas spp. Avian ticks are usuallyonly a problem in outdoor aviary birds, free-range chickens or recently caught birds. Argaspersicus affects poultry and wild birds leading toanaemia, debilitation and loss of production andit transmits micro-organisms such as Borreliaanserina, Aegyptianella pullorum and spir-ochaetes.

Diagnosis

Diagnosis is based on the history, clinical signsand observation of feeding ticks. It should beremembered that Argas spp. are nocturnal feedersand examination of birds at night is necessary fordiagnosis.

Treatment

Topical treatment of the affected birds withinsecticidal products such as permethrin, car-baryl, malathion or rotenone is effective. Insecti-cidal treatment of the environment is essential.Reinfestation from wild bird sources may need tobe controlled by separation of captive birds.

8.19.3 Flies

Hippoboscids

Clinical features

These flat, tick-like flies feed on blood, causinganaemia and death in severe infestations. Theyalso transmit Haemoproteus spp.

Diagnosis

Diagnosis is made by capture and identificationof the flies in the plumage.

Treatment

Topical insecticides such as permethrin, carbaryl,malathion or rotenone are effective. It is impor-tant to keep domestic birds separated from wildbirds, which are a source of reinfestation.

Blood-feeding and nuisance flies

Clinical features

Nuisance flies, such as house flies, lesser houseflies and Ophyra spp., and blood-feeding flies,such as biting midges, mosquitoes and black flies,can cause disturbance, dermatitis and anaemia,particularly in poultry units. They can also act asvectors for protozoal, bacterial and viral infec-tions.

Diagnosis

The diagnosis is based on history, clinical signsand identification of feeding flies, especially atnight. Traps can be used to collect and identifyflying insects.

Treatment

The most direct and practical means of control-ling most nuisance flies in poultry houses is theappropriate management of the accumulatedmanure, since this forms the primary breeding sitefor many species, particularly when wet. This may


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be accomplished by a building design whichmaximises the ventilation of the manure, byprovision for drainage of water away from thehouse and by careful maintenance of the animalwatering system to minimise leaks.

Manure within a poultry house may be treatedwith insecticides; pyrethroids appear to be themost widely acceptable chemicals available forthis purpose. However, insecticidal treatment isoften not sufficiently persistent and cannotpenetrate the manure adequately to kill fly larvae.In addition, naturally occurring predator, para-sitoid and parasite populations are often sub-stantial and can contribute significantly to flycontrol. Insecticidal treatment of manure mayeliminate these beneficial arthropods. Hence,where possible, fly control should be promoted bymeasures which maintain populations of bene-ficial arthropods; during cleaning, the accumu-lated manure should not be removedsimultaneously and, where possible, portions ofthe manure should be removed in a staggeredschedule. Predator, parasitoid and parasitepopulations may also be augmented by periodicreleases in the animal production system.

Fly resting sites in the structure of a poultryhouse may be treated with a residual insecticide.Fly baits (containing an attractant and an insec-ticide or IGR) may be used to attract and killadults.

8.19.4 Myiasis

Cutaneous myiasis

Clinical features

Myiasis may be caused by the obligate screw-worms Cochliomyia hominivorax (Nearctic andNeotropical regions), Chrysomya bezziana(Oriental and Afrotropical regions) and Wohl-fahrtia magnifica (eastern Palaearctic). Cutaneousmyiasis may also be caused by species of Lucilia,Calliphora, Protophormia or Phormia, in variousparts of the world. Myiasis usually occurs becauseof plumage contamination, especially around thevent, or infestation of untreated wounds. Popu-

lations of facultative blowflies may be maintainedin and around poultry houses by the carcasses ofdead birds and broken eggs, which should beremoved and buried or incinerated.

Diagnosis


Treatment

Affected wounds are surgically debrided andsprayed or washed with organophosphates(malathion) and pyrethroids (permethrin).Prompt treatment of cutaneous wounds will pre-vent myiasis.

8.19.5 Fleas

Clinical features

Although not often seen, fleas probably affect allbirds, especially while in the nest. Fleas that affectpoultry are Ceratophyllus niger, C. gallinae andEchidnophaga gallinacea. Ceratophyllus spp.cause irritation, disturbance and anaemia insevere infestations. The sticktight flea Echidno-phaga gallinacea burrows into the skin andremains on the host, causing irritation and, inheavy infestations, anaemia.

Diagnosis

Diagnosis is made on the basis of history, clinicalsigns and identification of fleas on the bird.

Treatment

Topical insecticidal compounds such as perme-thrin, carbaryl, malathion or rotenone can beused to kill adult fleas on the bird. Larvae withinthe environment must be removed by physicallycleaning the aviary or chicken house and applyinga residual environmental insecticide.


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8.19.6 Lice

Clinical features

Lice are important ectoparasites of domesticbirds, causing irritation, pruritus, scratching andsecondary feather damage. Laying hens affectedwill have reduced egg production and viability.Although there are many important species ofavian lice, Cuclotogaster heterographus, Mena-canthus stramineus, Lipeurus caponis, Goniodesdissimilis, Goniodes gigas and Goniocotes gallinaeare the most important in domestic birds.

Diagnosis

Diagnosis is made on the basis of clinical signsand identification of lice in the plumage and theireggs attached to feathers.

Treatment

Lice spend their entire life-cycle on the host andare readily killed by most insecticides. Topicalinsecticidal compounds such as permethrin, car-baryl, malathion, cypermethrin or rotenone canbe used to kill lice on the bird.

8.20 REPTILES

8.20.1 Mites

Species belonging to the Mesostigmata andProstigmata paratasitise the skin of reptiles.

Mesostigmata

The most common mite affecting snakes isOphionyssus natricis; however other species canbe found, including Ophionyssus lacertinus,Ophionyssus mabuyae, Neoliponyssus saurarumand Ophidilaelaps spp.

Prostigmata

Two families of Prostigmata within the familyCheyletiellidae are ectoparasites of reptiles. These

are Ophioptidae, which live beneath the scales ofsnakes, and Cloacaidae, which live on the cloacalmucosa of turtles. Examples of cloacal mites areCloacarus faini (affects the snapping turtle), andChelydra serpentini and Chelydra beeri, both ofwhich affect the painted turtle, Chelydra picta.These cloacal mites cause mild irritation.

Trombiculidae

Some larval forms of members of the familyTrombiculidae parasitise reptiles. These includeTrombicula batatus, Vatacarus spp.,Herpetacarusleprochaeta, Herpetacarus cadignani and Micro-trombicula chamlongi. These parasites feed onlymph and skin tissue, but not on blood.

Pterygosamidae

The family Pterygosamidae contains specialistmites which tend to parasitise specific types oflizard. Geckobiella spp. affect iguanas whilstHirstiella spp. affect gekonid lizards. Zonuridlizards can be infested by Ixodiderma spp. Sca-phothrix spp. and Zonurobia spp. Geckobia spp.preferentially affect geckos. Generally speaking,these parasites occur in small numbers and bloodloss is not usually significant.

8.20.2 Ticks

Soft and hard ticks can affect reptiles. Argus spp.,Ornithodorus spp., Amblyomma spp., Aponommassp., Hyalomma spp., Haemaphysalis spp. andIxodes spp. all affect reptiles.

8.20.3 Flies

Some sand flies can feed on reptiles. These includemembers of the genera Phlebotomus, Sergento-myia, Lutzomyia and Warileya. Sand flies havebeen shown to transfer Leishmania spp. toreptiles. Mosquitos may feed on reptiles. Aedesaegypti can feed on turtles, lizards and geckos


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under laboratory conditions. Other genera whichfeed on reptiles and can be involved in the spreadof protozoan and viral infections include Culexand Anopheles. Culicoides spp. (midges) feed onreptiles and may play a role in the transfer ofprotozoa and viruses. Glossinia spp. (tsetse flies)feed on reptiles including snakes, lizards, tortoisesand crocodiles. Tabanidae (horse flies) may feedon reptiles. Myiasis can occur in reptiles, parti-cularly chelonia. The genera involved includeChrysomyia, Sarcophaga, Lucilia and Hemi-pyrella. It is important to remember that iver-mectins are contraindicated in chelonia.

8.20.4 Treatment of reptileectoparasites

See Table 8.10.


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Baron, R.W. & Colwell, D.D. (1991) Mammalian

immune responses to myiasis. Parasitology Today, 7,353±5.

Beck, T., Moir, B. & Meppen, T. (1985) The cost of

parasites to the Australian sheep industry. QuarterlyReview of Rural Economics, 7, 336±43.

Brander, G.C., Pugh, D.M., Bywater, R.J. & Jenkins,W.L. (1991) Veterinary Applied Pharmacology andTherapeutics, pp. 497±512. BaillieÁ re Tindall, London.

Cleland, P.C., Dobson, K.J. &Meade, R.J. (1989) Rateof spread of sheep lice (Damalinia ovis) and theireffects on wool quality. Australian Veterinary Jour-

nal, 66, 289±99.Coles, G. (1994) Parasite control in sheep. In Practice,16, 309±18.

Drummond, R.O., George, J.E. & Kunz, S.E. (1988)Control of Arthropod Pests of Livestock: A Review ofTechnology. CRC Press, Boca Raton, Florida.

Dryden, M.W. & Rust, M.K. (1994) The cat flea:biology, ecology and control. Veterinary Para-sitology, 52, 1±19.

Emerson, K.C. (1956) Mallophaga (chewing lice)

occurring on the domestic chicken. Journal of theKansas Entomological Society, 29, 63±79.

Fadok, V.A. (1984) Parasitic skin diseases of large

animals. Veterinary Clinics of North America, LargeAnimal Practice, 6, 3±26.

Fallis, A.M. (1980) Arthropods as pests and vectors of

disease. Veterinary Parasitology, 6, 47±73.Fox, J.G. (1998) Biology and Diseases of the Ferret, 2ndedn. Williams and Wilkins, Baltimore.

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51±6.Hall, M.J.R. & Wall, R. (1994) Myiasis of humans anddomestic animals. In Advances in Parasitology, Vol.

35, (eds J.R. Baker, R. Muller & D. Rollinson), pp.258±334. Academic Press, London.

Table 8.10 Ectoparasites in reptiles.

Drug Dose and route of administration Comments

Ivermectin 200 mg/kg Not with 10 days of diazepamadministrationNot in chelonia

Ivermectin* Mix 1ml ivermectin (1% w/v) with 2ml

propylene glycol, disperse in500±1000ml distilled water then use asa spray on the reptile and its

environment

The mixture has a shelf-life of 1±3

months at room temperature.Clean all the housing and its furniturefirst.

Not in chelonia

Dichlorvos impregnated strip

± Vapona16mm of strip/0.28m2 for up to 4 days Hang so that animals cannot touch the

strip

*Dr Fredric Frye, personal communication.


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Holmes, D.H. (1984) Clinical Laboratory AnimalMedicine. The Iowa State University Press.

Jacobs, D.E. (ed.) (2000) Selemectin ± a novel endec-

tocide for dogs and cats. Veterinary Parasitology, 91,161±405.

Keck, G. (1995) Poisoning and side-effects from ecto-

parasiticide treatment of small animals. VeterinaryInternational, 7, 20±31.

Kwochka, K.W. (1987) Fleas and related disease.Veterinary Clinics of North America, Small Animal

Practice, 17, 1235±62.Kwochka, K.W. (1987) Mites and related disease.Veterinary Clinics of North America, Small Animal

Practice, 17, 1262±84.Lofstedt, J. (1983) Dermatologic diseases of sheep.Veterinary Clinics of North America, Large Animal

Practice, 5, 427±48.Loomis, E.C. (1986) Ectoparasites of cattle. VeterinaryClinics of North America, Food Animal Practice, 2,299±321.

Loomis, E.C. (1986) Insecticides and acaricides forcattle. Veterinary Clinics of North America, FoodAnimal Practice, 2, 323±8.

Loomis, E.C. (1986) Epidemiology and control ofectoparasites of small ruminants. Veterinary Clinicsof North America, Food Animal Practice, 2, 397±426.

Medleau, L. & Rakich, P.M. (1992) Dermatologicdiseases. In Small Animal Medical Therapeutics (edsM.D. Lorenz, L.M. Cornelius & D.C. Ferguson), pp.

31±84. J. B. Lippincott, Philadelphia.Messinger, L.M. (1995) Therapy for feline dermatoses.Veterinary Clinics of North America, Small AnimalPractice, 25, 981±1005.

Moriello, K. & Mason, I.S. (1995) Handbook of SmallAnimal Dermatology. Permagon Press, London.

Muller, G.H., Kirk, R.W. & Scott, D.W. (1989) Small

Animal Dermatology. W.B. Saunders, Philadelphia.Mundell, A.C. (1990) New therapeutic advances inveterinary dermatology. Veterinary Clinics of North

America, Small Animal Practice, 20, 1541±56.Murnaghan, M.F. & O'Rourke, F.J. (1978) Tickparalysis. In Arthropod Venoms (ed. S. Bettini), pp.419±64. Springer-Verlag, New York.

Paradis, M. & Villeneve, A. (1988) Efficacy of iver-mectin against Cheyletiella yasguri infestation indogs. Canadian Veterinary Journal, 29, 633±5.

Radostits, O.M., Blood, D.C. & Gay, C.C. (1994)Veterinary Medicine ± a Textbook of the Diseases ofCattle, Sheep, Pigs and Horses. BallieÁ re Tindall,

London.Roberson, E.L. (1988) Chemotherapy of parasitic dis-eases. In Veterinary Pharmacology and Therapeutics(eds N.H. Booth & L.E. MacDonald), pp. 877±81.

Iowa State University Press, Ames, Iowa.Sargison, N. (1995) Differential diagnosis and treat-ment of sheep scab. In Practice, 17, 3±10.

Scott, D.W. (1988) Large Animal Dermatology. W.B.Saunders, Philadelphia.

Smith, M.C. (1983) Dermatologic diseases of goats.

Veterinary Clinics of North America, Large AnimalPractice, 5, 449±55.

Steelman, C.D. (1976) Effects of external and internalarthropod parasites on domestic livestock produc-

tion. Annual Review of Entomology, 21, 155±78.Tarry, D. (1985) The control of sheep headfly disease.Proceedings of the Sheep Veterinary Society, 2, 51±6.

Tarry, D.W. (1986) Progress in warbly fly eradication.Parasitology Today, 2, 111±16.

Tarry, D.W., Sinclair, I.J. & Wassall, D.A. (1992)

Progress in the British hypodermosis eradicationprogramme: the role of serological surveillance.Veterinary Record, 131, 310±12.

Tenquist, J.D. & Wright, D.F. (1976) The distribution,prevalence and economic importance of blowflystrike in sheep. New Zealand Journal of ExperimentalAgriculture, 4, 291±5.

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109±28. CRC Press, Cambridge.Wharton, R.H. & Norris, K.R. (1980) Control ofparasitic arthropods. Veterinary Parasitology, 6,

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Glossary

Abdomen The third major division of an insectbody.

Abscess Localised accummulation of pus orpurulent matter within a cavity oftensurrounded by a fibrous connective tissuecapsule.

Acalypterae Flies with small or no squamae orcalypters and no groove in the second antennalsegment.

Acari A sub-class of the class Arachnida, con-taining the mites and ticks.

Accessory gland A gland opening into the geni-tal chamber.

Accidental Fly species which act only as rare,accidental or chance agents of myiasis.

Adenotrophic viviparity The production of liveoffspring, where eggs are retained within thefemale oviduct until the larvae are mature, atwhich stage they are laid and immediatelypupate.

Aedeagus The male copulatory organ (penis).Afrotropical region The biogeographic region

which includes all of subSaharan Africa.Alate Possessing wings.Allergic Suffering from an allergy.Allergy An altered immunological reactivity on

the second or subsequent contact with anantigen; now used to when referring to hyper-sensitivity reactions.

Alopecia Loss of hair.Amblycera A suborder of chewing lice, includ-

ing the parasitic genera of birds Menopon andMecanthus.

Ambulacrum Terminal structures of the miteleg, usually composed of paired claws and anempodium.

Ametabolous Lacking metamorphosis; imma-ture stages lacking only genitalia.

Anaemia Literally means `no blood'. Now used

to indicate an reduction or deficiency of redblood cell count.

Anal fold A distinctive fold in the anal area ofthe wing.

Anal groove A shallow, semicircular groove,posterior or anterior to the anus in ticks.

Anautogenous Requiring an initial protein mealto initiate vitellogenesis and mature eggs.

Annelida A phylum containing the segmentedworms (bristleworms, earthworms, leeches).

Anopheline A mosquito belonging to the sub-family Anophelinae.

Anoplura A suborder of Phthiraptera, known assucking lice.

Anorexia Complete loss of appetite and noteating.

Antenna A paired segmented sensory organwhich protrudes antero-dorsally from the headnear the eyes.

Anterior Located towards the front (head end)of an animal.

Anthropophilic Associated with humans.Antibody A modified serum globulin.Antigen A molecule which induces the forma-tion of antibody.

Anus The posterior opening of the digestivetract, at the opposite end to the mouth, fromwhich waste products are expelled from thebody.

Apical At or towards the apex.Apodeme An ingrowth of the exoskeleton towhich muscles are attached.

Apolysis The separation of the old from the newcuticle during moulting.

Apterous Without wings, used to describe pri-mitive, wingless insects.

Argasid A tick of the family Argasidae, knownas the soft ticks.

Argasidae A family of ticks known as soft ticks

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because of the soft leathery cuticle and absenceof a scutum.

Arista Part of the antenna of cyclorrhaphousflies which protrudes from the third antennalsegment.

Arthropod An animal in the phylum Arthro-poda, characterised by the presence of a seg-mented body, an exoskeleton, jointed limbs,tagmatisation, a dorsal blood vessel, a haemo-coel and a ventral nerve cord.

Artilodactyla Even-toed ungulates; an order ofmammals containing the ruminants (deer, gir-affes, sheep, goats, antelopes and oxen) andpigs, hippopotami and camels.

Astigmata A suborder of mites, lacking stig-mata.

Autogenous Able to mature eggs as an adultwithout an initial protein meal.

Axilla The armpit area of birds and mammalsunderneath the forelegs, arms or wings.

Bacteria Single-celled micro-organisms with asimple nucleus intermediate in size betweenprotozoa and rickettsia.

Bacteriaema The presence of bacteria in theblood stream.

Basimere Part of the external reproductiveapparatus of male fleas.

Basis capituli The anterior part of the body ofmites and ticks formed from the expandedcoxae of the first pair of legs, from which themouthparts project.

Blowfly Name commonly given to flies of thefamily Calliphoridae, particularly thoseresponsible for cutaneous myiasis.

Boil An inflamed swelling in the skin.Bovidae Family of mammals containing the

sheep, goats, cattle, buffalo and antelope.Brachycera A suborder of stout-bodied dipter-

ous flies, with short antennae.Bristle A large seta.

Calliphoridae A family of dipterous flies,including screwworm flies and blowflies.

Calypter A membranous flap at the base of thewings of Diptera (also commonly known assquamae).

Calypterae Flies with large squamae or calyp-ters and a groove in the second antennalsegment.

Canidae A family of mammals, including thedogs, jackals, wolves and foxes.

Capitulum Anterior body of mites and ticksincluding the mouthparts (also commonlyknown as the gnathosoma).

Carbamate A synthetic insecticide.Caudal At or towards the anal end of an animal.Cell An area of the wing membrane of an insectpartially or completely surrounded by veins.

Ceratopogonidae A family of nematocerousDiptera, including the biting midges Culicoides.

Cerci A pair of appendages originating fromabdominal segment 11.

Chelicerae The paired piercing component ofthe mouthparts of mites and ticks.

Cheyleti Uidae A family of largely predatoryprostigmatid mites.

Chitin The major component of arthropodcuticle, a polysaccharide composed of acet-ylglucosamine and glucosamine subunits.

Chitin synthesis inhibitor An insecticide thatprevents chitin formation.

Class The taxonomic ranking between phylumand order, e.g. Insecta.

Claw A hooked structure at the distal end of thepretarsus, usually paired.

Clypeus Part of the insect head below the fronsto which the labrum is attached anteriorly.

Cockle Ridging of the skin of domestic animalscaused by the feeding of hippoboscid flies andlice.

Colostrum The milk secreted for 3 to 4 daysafter parturition which is rich in immunoglo-bulins.

Comb A row of spines, usually describing therow of projections on the head or thorax offleas; more properly known as the ctenidium.

Compound eye An aggregation of ommatidiaeach acting as a single facet of the eye.

Coprophagous Feeding on dung or excrement.Copulatory protuberance In some species of mitethe final nymphal female stage has a pair ofthese organs at the posterior end of the idio-soma; used for attachment to an adult male.

Copulatory suckers In some species of mite the

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adult male has a pair of these organs at theposterior end of the idiosoma; used forattachment to the copulatory protuberances ofnymphal females.

Cornea Cuticle covering the eye or ocellus.Cosmopolitan Distributed worldwide.Costa The most anterior longitudinal wing vein.Coxa The basal (first) leg segment.Crepuscular Active at low light intensities at

dawn or dusk.Crop The food storage area of the digestive

system, posterior to the oesophagus.Cross-veins Transverse wing veins that link the

longitudinal veins.Ctenidium A row of spines on the head or

thorax of fleas (pleural ctenidia).Culicidae A diverse family of blood-feeding

nematocerous Diptera, known as mosquitoes,of veterinary importance as vectors of variousprotozoan and viral pathogens and nematodeparasites.

Culicine A mosquito of the subfamily Culicinaewhich includes the majority of mosquitospecies, including the important genera Aedesand Culex.

Cuticle The external skeletal structure secretedby the epidermis, composed of chitin andprotein.

Cyclodines A class of organochlorine insecti-cides.

Cyclorrhapha A suborder of dipterous flies,characterised by the larva forming a pupariumfrom the last larval skin inside which pupationoccurs. They also have an antenna composed ofthree segments, the third of which bears aprotruding arista.

Cytokines Soluble molecules which act assignals between cells.

Demodicidae A family of prostigmatoid mite,containing the genus of veterinary importanceDemodex.

Demodicosis Infestation of the skin withDemodex mites.

Dermatitis Any inflammatory condition of theskin.

Detritivorous Feeding on organic detritus ofplant or animal origin.

Diapause Delayed development controlled byenvironmental conditions.

Dichoptic The condition in which there is a widegap between the eyes; typical of female Diptera.

Diptera An order of insects possessing only asingle pair of functional wings and a pair ofhalteres.

Distal At or near the furthest end from theattachment of an appendage.

Diurnal Active during daylight.Dorsal Upper surface. The side of the bodyopposite from where the legs project.

Dorsal vessel A longitudinal tube which acts asthe main pump for haemolymph.

Ecdysis The process of casting off the cuticle inthe final stage of moulting.

Eclosion Hatching from the egg.Ectoparasite A parasite that lives externally onits host.

Empodium A pad or seta on the pretarsus.Encephalitis Inflammation of the brain.Endemic Native or restricted to a particulargeographic area.

Endocuticle The flexible, unsclerotised innerlayer of the procuticle.

Endoparasite A parasite that lives internallywithin its host (see parasite).

Endopterygota Winged insects which havecomplete metamorphosis, the wings developingonly within the pupa.

Engorge To feed fully, usually with blood.Enzootic A disease present in a natural hostwithin its natural range.

Eosinophil A leucocyte with a multilobularnucleus and eosinophilic intracytoplasmicgranules. A member of the granulocyte series ofblood leucocytes.

Epicuticle The inextensible outermost layer ofcuticle.

Epidemic The spread of disease from its ende-mic area and/or from its normal host.

Epidermis In vertebrate animals this is the outerlayer of skin. In arthropods the epidermis is theinner living layer of the integument whichproduces the cuticle.

Epipharynx The ventral surface of the labrum ofinsect mouthparts.

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Epiphora Tear overflow.Epizootic An unusually high number of cases of

disease in an epidemic.Equidae A family of mammals, including the

horses and donkeys.Erythema Redness of the skin due to inflam-

mation.Excoriation Erosions and ulcerations caused by

mechanical damage especially scratching orbiting.

Exocuticle The rigid, sclerotised outer layer ofthe procuticle.

Exopterygota Winged insects which have anincomplete metamorphosis, the wings devel-oping externally in the immature stages andbecoming fully functional in the adults.

Exoskeleton The outer body layer, also knownas the integument or cuticle.

Facet Outer layer of the ommatidia that com-pose the compound eyes of arthropods.

Facultative Not obligatory.Family The taxonomic ranking between order

and genus.Fannidae A family of cyclorrhaphous Diptera,

including the lesser house fly; of importance asnuisance pests.

Femur In Diptera: the segment of the legbetween the trochanter and tibia or, if the tro-chanter is fused with the femur, between thecoxa and tibia. In Acari: the segment betweenthe trochanter and genu.

Festoon Rounded pattern or crenellations in theposterior body of some genera of ticks.

Flagellum The third part of the insect antenna,distal to the scape and pedicel.

Fore Anterior, towards the head.Foregut The part of the gut lying between the

mouth and the midgut.Frons The front (medio-anterior) part of the

insect head.Furuncular myiasis Myiasis where individual fly

larvae form boil-like infestations below theskin.

Furunculosis Rupture of hair follicle due tosevere inflammation.

Gadding Panic in livestock, usually cattle,

caused by the oviposition behaviour of adultflies, most usually warble flies, Hypoderma.

Gena An area at the side of the head of insects.Genal ctenidium A row of sclerotised spineslocated on the gena of some genera of flea.

Genital pore Opening in the body wall of thegenital duct of male or female arthropods (alsoknown as the gonopore).

Genitalia Ectodermally derived structures ofboth sexes associated with reproduction.

Genu In mites and ticks, the fourth leg segmentdistal to the femur.

Genus Taxonomic ranking between family andspecies.

Glossinidae A family of Diptera, containing asingle genus, Glossina, the tsetse flies.

Gnathosoma The anterior section of the body ofmites and ticks, incorporating the mouthparts(also known as the hypostome).

Grub See maggot.

Haematoma A blood-filled swelling.Haemocoel The main body cavity of arthro-pods.

Haemoglobin An iron-containg protein presentwithin red blood cells which carries oxygenaround the body.

Haemolymph The fluid filling the haemocoel.Haemolytic anaemia Anaemia due to lysis of redblood cells.

Haller's organ A pit in the tarsi of the forelegs ofticks which contain sensory chaemoreceptors.

Haltere Club-shaped, reduced hindwings ofDiptera, used as a sensory aid for balanceduring flight.

Hard tick A tick of the family Ixodidae.Described as hard because of the hard scutumon the dorsal surface.

Haustellum Sucking mouthparts.Head The anterior of the three major divisionsof an insect body.

Hermaphrodite Possessing both testes andovaries.

Hind At or towards the posterior.Hindgut The posterior section of the gut,extending from the midgut to the anus.

Hippoboscidae A family of dorsoventrally flat-tened Diptera, including the keds and forest

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flies, which live in close association with theirhosts.

Hippoboscoidea A small super-family of blood-feeding parasitic calypterate Diptera.

Holarctic Both Nearctic and Palaearcticregions.

Holometabolous Development in which there iscomplete metamorphosis, the body formchanging abruptly at the pupal moult.

Holoptic The condition in which there is a nar-row gap between the eyes; typical of maleDiptera.

Hormone A chemical messenger that regulatessome activity at a distance from the organ thatproduced it.

Host The organism on which a parasite feeds.Hyperplasia An excessive proliferation of tissue.Hypersensitivity An exaggerated or inappropri-

ate immune response to antigens, such as salivafrom arthropods; a type of allergy causing tis-sue damage.

Hypopharynx A median lobe of the preoralcavity of insect mouth parts.

Hypopygium A part of the external genitalapparatus of male flies, known as the penis.

Hypostome A part of the mouthparts of ticksand mites, situated between the palps.

Idiosoma The main body region of ticks andmites.

IgE A particular type of immunoglobulininvolved in immediate type I hypersensitivityreactions when bound to mast cells.

IL-1 A type of cytokine which is produced byvarious cells including macrophages, B lym-phocytes and keratinocytes.

Imago Adult insect.Inflammation The vascular and cellular tissue

response to injury characterised by pain, heat,redness, swelling and loss of function.

Insect Arthropod of the class Insecta.Instar A stage in the life-cycle of an arthropod,

such as egg, larva, pupa, adult.Integument The epidermis plus cuticle.Interleukins A group of soluble molecules

(cytokines) which act as signals between cells.These were originally identified whenproduced by leucocytes as signals for other

leucocytes; hence interleukins or between leu-cocytes.

Ischnocera A suborder of chewing lice, includ-ing the genera Damalinia on mammals andGoniodes on birds.

Ixodidae A family of ticks, known as hard ticksbecause of the hard scutum on the dorsalsurface.

Juvenile hormone A hormone released by thecorpora allata into the haemolymph, involvedin many aspects of insect physiology, includingmoulting.

Juvenile hormone mimics Synthetic chemicalsthat mimic the effects of juvenile hormone ondevelopment.

Kairomone A chemical used in communication,to the benefit of the receiver and which may beto the disadvantage of the producer.

Keratinocytes The epithelial cells which makeup most of the epidermis.

Keratitis Inflammation of the cornea.

Labella A paired organ (singular labellum),forming lobes at the apex of the proboscis,derived from the labial palps.

Labial palp A segmented appendage of thelabium.

Labium Forming the floor of the mouthparts (a`lower lip'), often with a pair of palps and twopairs of median lobes.

Labrum Forming the roof of the preoral cavity(an `upper lip').

Lacina The mesal lobe of the maxillary stipes.Larva An immature insect life-cycle stage whichfollows eclosion from the egg. Usually appliedto insects with complete metamorphosis.

Larviparous Reproduction in which the egghatches within the female and the larva isdeposited.

Lateral At, or close to, the sides.Lateral suture A line or ridge in the integumentof Argas ticks which divides the dorsal andventral surfaces.

Leg The walking limb of arthropods.Lesion Any pathological or traumatic deviationfrom normal tissue.

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Leucopenia A reduced number of circulatingwhite blood cells.

Lichenification A thickening and hardening ofthe skin with exaggeration of the surfacewrinkles.

Lymphadonopathy Disease of lymph nodesusually characterised by enlargement.

Macrotrichiae A trichoid sensillum, seta or hair,on the wings of insects, particularly cer-atopogonid midges.

Maggot A legless, larval insect; usually appliedto immature stages of clorrhaphous Diptera.

Malpighian tubules Thin, blind-ending tubule,originating near the junction of the mid- andhindgut, involved in nitrogenous waste excre-tion and water regulation.

Mamillae Small bumps in the integument of softticks such as Argas and Ornithodoros.

Mandible The jaws in biting and chewinginsects. May be a needle-like piercing organ, asin mosquitoes or tooth-like as in chewing lice.

Mange A skin disease cause by infestation withmites.

Mastitis Inflammation of the udder, usually dueto bacterial infection.

Maxilla The second pair of jaws in chewinginsects.

Maxillary palp A segmented sensory appendageborne on the stipes of the maxilla.

Mechanical transfer The movement of patho-gens by passive transfer, with no biologicalvector.

Medial Towards the middle (also median).Mesostigmata A suborder of mites, with stig-

mata located above the coxae of the 2nd, 3rd or4th pair of legs; also known as Gamesid mites.

Mesothorax The second segment of the thorax.Metamorphosis The relatively abrupt change in

body form between the immature and sexuallymature, adult stage.

Metastigmata A suborder of the Acari, knownas ticks, with stigmata located above the coxaeof the 2nd, 3rd or 4th pair of legs and a toothedhyperstome; also known as Ixodida.

Metathorax The third segment of the thorax.Microtrichiae Small extensions of the cuticle on

the wings of some insects.

Midge Common name for blood-feedingceratopogonid flies.

Midgut The middle section of the gut.Miliary Like millet seed.Moulting The formation of new cuticle followedby ecdysis.

Mouth-hooks The skeletal mouthparts of higherflies.

Muscidae A family of cyclorrhaphous Diptera,including the house fly and similar species.

Muscoidea A super-family of calypterate Dip-tera, containing the houseflies, horn flies andstable flies, of importance as nuisance and bit-ing pests.

Myiasis Infestation of the tissues of a living hostby fly larvae.

Nearctic region A biogeographic region whichincludes North America, from northern Mex-ico to Alaska, and Greenland.

Necrophagous Eating dead and/or decayinganimal matter.

Necrosis Tissue or cell death in the livingorganism.

Nematocera A suborder of slender dipterousflies, with antennae composed of six or moreelongated, articulating segments.

Neotropical region A biogeographic regionincluding southern Mexico, central and SouthAmerica.

Neurotoxin A toxic material which has its effecton nervous tissue.

New World North and South America.Nocturnal Active at night.Nomenclature The naming of plants and ani-mals.

Nulliparous A female that has not yet ovi-posited.

Nutelliellidae A small family of ticks containingonly a single species, found in the nests ofswallows.

Nymph In mites and ticks the second, and sub-sequent, immature stages. In insects, usuallythose with incomplete metamorphosis, allimmature stages.

Obligate Compulsory; a parasite which cannotsurvive without its living host.

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Obligatory See obligate.Ocelli The simple eyes of some adult and nym-

phal arthropods (singular ocellus).Oesophagus The foregut that lies anterior to the

pharynx and anterior to the crop.Oestridae A family of Diptera, containing the

obligate myiasis species the bots and warbles.Oestroidoa A super-family of calypterate Dip-

tera, of importance largely because larvae areagents of myiasis.

Old World Europe, Asia and Africa.Ommatidium A single element of the compound

eye.Ophthalmomyiasis Infestation of the eye with

dipterous larvae.Order The taxonomic ranking between class

and family, e.g. Diptera.Organochlorine A group of organic chemicals

containing chlorine, including several insecti-cides.

Organophosphate A group of organic chemicalscontaining phosphorus, including severalinsecticides.

Oriental The biogeographic region whichincludes Pakistan, India, South East Asia,southern China, Malaysia, Philippines andwestern Indonesia.

Ostium A slit-like opening in the dorsal vesselallowing the one-way movement of haemo-lymph from the pericardial sinus into the dorsalvessel.

Otitis An inflammatory condition of the ear.Ovariole Ovarian tubes that form the ovary and

in which the egg follicles develop prior toovulation.

Ovary One of the paired gonads of femalearthropods, usually composed of a number ofovarioles.

Ovigerous An egg-producing female mite.Oviparous Reproduction in which eggs are laid.Ovipositor The organ used for laying eggs.Ovoviviparity Retention of the developing fer-

tilised egg within the female arthropod; similarto viviparity but with no nutrition of the hat-ched young.

Palaearctic The biogeographic region whichincludes Europe, Iceland, North Africa,

Russia, central Asia, the Middle East, centraland northern China, Japan and Korea.

Palps Paired segmented organs associated withthe maxilla (maxillary palps) and labium (labialpalps); singular palp.

Papules A small, solid, red, elevated, circum-scribed cutaneous lesion up to 1 cm indiameter.

Parasite An organism that lives at the expenseof another (host) which it does not kill.

Parasitism The relationship between a parasiteand its host.

Parasitoid A parasite that kills its host.Paratergal plates Hardened, sclerotised plateson the lateral surface of the abdomen of someinsects, particularly lice.

Parous A female that has laid at least one egg.Parthenogenesis Development from an unferti-lised egg.

Pathogen A parasite which causes disease.Pedicel Stalked pretarsi of mites, particularlyastigmata.

Pediculosis Infestation with lice.Perianal The area around the anus of mammals.Pericardial sinus The body compartment thatcontains the dorsal vessel.

Perineum The area between the anus and thegenital opening of mammals.

Peritreme A paired, sclerotised process asso-ciated with the stigmata, seen especially in themesostigmatid mites.

Pharynx The anterior part of the foregut,anterior to the oesophagus.

Pheromone A chemical used in communicationbetween individuals of the same species.

Phlebotominea A subfamily of dipterous flies inthe family Psychodidae, known as sandflies.

Phoresy The movement of one animal byattachment to another animal.

Pinna The ear flap (plural pinnae).Pleural rod A vertical thickening of the integu-ment of the mesopleuron of fleas; known alsoas the pleural ridge or meral rod.

Pleuron The lateral region of the body, bearingthe limb bases (plural pleura).

Polychaeta An order of marine, annelid wormswith numerous chaetae borne on projections ofthe body (parapodia).

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Polyradiculoneuritis A diffuse lower motorneurone paresis.

Posterior The body of an animal furthest fromthe head.

Postscutellum A projecting posterior area of thethorax of Diptera underneath the scutellum.

Prepuce The fold of skin around the penis.Prestomal teeth Structures at the end of the

labella of some dipterous flies.Pretarsus The last segment of the leg of mites.Proboscis A general term for elongate mouth-

parts.Pronotum The upper (dorsal) plate of the pro-

thorax.Prothorax The first segment of the thorax.Protozoa Single-celled animals with at least one

well-defined nucleus, some of which arepathogenic.

Proventriculus The grinding organ of the fore-gut.

Proximal At or near the end of attachment of anappendage.

Pruritus Itching, skin irritation.Pseudotrachea A ridged groove on the ventral

surface of the labellum of some higherDiptera.

Psorogatidae A family of prostigmatid itch andforage mites.

Psycholidae A family of blood-feeding nemato-cerbus Diptera, known as the sand flies; ofimportance as vectors of Leishmania.

Ptilinum A sac everted from a suture betweenthe antennae of schizophoran Diptera.

Pulvillus The expanded terminal structure of thepretarsus of some genera of mites, which maybe membranous bell- or sucker-like discs(plural pulvilli).

Pupa The inactive stage between larva and adultin holometabolous insects.

Pupariation The process of puparium forma-tion.

Puparium The hardened skin of the final stagelarva of higher, cyclorrhaphous Diptera inwhich the pupa forms.

Pupation The process of becoming a pupa.Pustular Forming spots or pustules in the skin.Pustule A small, circumscribed elevation of the

skin filled with pus.

Pyaemia The presence of pus in circulatingblood.

Pygidium An area of sensory setae at the pos-terior of the abdomen of fleas; also known asthe sensilium.

Pyoderma A skin disease characterised by thepresence of pus or purulence, usually in theform of pustules and caused by bacteria.

Pyotraumatic Purulent skin disease associatedwith pruritus.

Pyrethrin One of the insecticidal chemicalspresent in the plant pyrethrum.

Pyrethroids Synthetic chemicals with similarstructure to pyrethrins.

Pyrexia Elevated body temperature or fever.

Reservoir An animal infected with a diseasepathogen, but not necessarily suffering clinicaldisease and acting as a source of disease whicharthropod vectors transmit to non-diseasedanimals.

Resilin A rubber-like protein in some insectcuticles, particularly important in the jumpingmechanism of fleas.

Retinula cell A sensory cell of the light recep-tors, ommatidia or ocelli, comprising a rhab-dom of rhabdomeres.

Rhabdom The central zone of the retinula con-sisting of microvilli filled with visual pigment.

Rhabdomere One of typically eight units, com-prising a rhabdom.

Rhinitis Inflammation of the internal surfaces ofthe nose.

Rhynchophthirina A suborder of lice, consistingof only two species, which are parasites ofeither elephant or warthog.

Rickettsia A group of parasitic micro-organ-isms intermediate in size between bacteria andviruses, without cellular structure, many ofwhich are pathogenic and transmitted byarthropods.

Rotenone An insecticidal chemical derived fromlegumes.

Saliva A fluid, produced by the salivary glands,containing a complex mixture of agents oftencontaining digestive enzymes. In blood-feeding

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arthropods the saliva may contain antic-oagulants.

Saprophagous Feeding on decaying organisms.Sarcophagidae A large family of grey-black,

cyclorrhaphous Diptera, known as flesh flies.Scab Skin disease caused by psororoptic mites,

usually applied to sheep infested with Psoroptesovis.

Scape The first segment of the antenna ofinsects.

Sclerite A plate on the body wall surrounded bymembrane or sutures.

Sclerotised Cuticle hardened by cross-linkage ofprotein chains.

Screwworm Common name given to the larvaeof the obligate agents of cutaneous myiasis,Cochliomyia hominivorax, Chrysomya bezzianaand, less commonly, Wohlfahrtia magnifica.

Scutellum An area of the thorax of dipterousflies at the posterior dorsal margin between thewings.

Scutum The sclerotised plate on the dorsal sur-face of ixodid hard ticks, also known as thedorsal shield.

Sebaceous gland A gland in the skin of mam-mals associated with hair follicles.

Sebum An oily secretion produced by thesebaceous glands of mammals which spreadsover the skin and hair.

Seminal vessicle Male sperm storage organs.Semiochemical Any chemical used in intra- and

interspecific communication.Sensilium An area of sensory setae on the pos-

terior abdomen of fleas; also known as thepygidium.

Sensillum A sense organ.Seta A long, thin, cuticular extension, produced

by an epidermal cell; flexible at the base; maybe called a hair; large setae are called bristles.

Simuiidae A family of nematocerous Diptera,including the genus Simulium, known as blackflies.

Soft tick Ticks of the family Argasidae, whichdo not have a hard scutum on the dorsal idio-soma.

Species A group of organisms that can inter-breed in natural populations producing fullyfertile offspring.

Spermatophore An encapsulated package ofspermatozoa.

Spine An unjointed cuticular extension.Spiracle An external opening of the trachaealsystem.

Spirochaetosis Infection with spirochaete bac-teria, such as Borrelia.

Spur A long, sharp, articular, multicellularprojection of the integument.

Squama Membranous flaps at the base of thewings of Diptera; typically the alula, the alarsquama and the thoracic squama (also knownas a calypter).

Squamous A condition in which the skin of thehost forms thick scales, as in some forms ofdemodecosis.

Stadium The period between moults.Stemma The simple eye of many larval insects.Sternum The ventral surface of a segment.Stigmata External openings of the trachaealsystem in the integument of ticks and mites.

Stipes The distal part of the maxilla.Stomoxyinae A subfamily of dipterous flies,including the stable fly Stomoxys calcitrans.

Striations Fine grooves in the integument ofsome mites and ticks forming complexpatterns.

Strike Name commonly given to cuteneousmyiasis by fly larvae, usually applied to myia-sis of sheep by Lucilia sericata or Luciliacuprina.

Stylostome A feeding tube produced around themouthparts of trombiculid mites in the skin ofthe host.

Subcutaneous Beneath the skin of vertebrates.Sucker Name commonly given to the pulvillusat the end of the legs of some types of mite.

Suture A groove on the arthropod that mayshow the fusion of two exoskeletal plates.

Synanthropic Associated with humans.Systematics The practice of biological classifi-cation.

Systemic insecticide An insecticide taken intothe body of a host that kills insects feeding onthe host.

Tabanidae A family of Diptera, including thehorse flies, deer flies and keds.

Glossary 251

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Tagma The group of segments that form amajor body unit (head, thorax, abdomen).

Tarsomere A subdivision of the tarsus.Tarsus The leg segment distal to the tibia,

bearing the pretarsus; in insects composed ofup to five tarsomeres (plural tarsi).

Taxonomy The theory and practice of namingand classifying living organisms

Teneral The condition of a newly emerged, notyet fully mature, adult insect.

Tergum The dorsal surface of a segment.Thorax The middle of the three major body

divisions of insects; composed of the pro-,meso- and metathorax.

Thrombocytopenia Reduced numbers of plate-lets circulating in the blood.

Tibia In insects: the fourth leg segment follow-ing the femur; in Acari: the fifth leg segmentfollowing the genu.

Tormogen cell The socket forming epidermalcell associated with a seta.

Toxaemia Illness caused by poisoning.Trachaea A tubular element of the gas exchange

system in insects and some Acari.Tracheole Fine tubules of the gas exchange

system in insects and some Acari.Transovarial transmission The transmission of

pathogens between generations via the eggs.Transtadial transmission The transmission of

pathogens between stadia.Transverse At right angles to the longitudinal

axis.Trichogen cell A hair-forming epidermal cell

associated with a seta.Trochanter In insects and Acari, the second leg

segment following the coxa.Trombiculidae A family of prostigmatid mite,

parasitic only in the larval stage, including theharvest mites and chiggers.

Trypanosomiasis A disease caused by Trypano-soma protozoans.

Tubercle A large rounded projection from thesurface of an arthropod.

Udder The milk-producing organ of domesticanimals such as cattle, sheep, pigs and goats.

Urticaria Inflammation and irritation of theskin associated with allergic or similar reac-tions.

Vas deferens The ducts that carry sperm fromthe testes.

Vector An arthropod that transmits a patho-genic organism.

Vein Tubes of cuticle in a network that supportthe wings of insects.

Ventral Towards or at the lower surface.Vertebrate An animal with a skull which sur-rounds the brain and a skeleton of bone orcartilage, including the spine of vertebral bonessurrounding a spinal cord of nerves; includesmammals, birds, fish, reptiles and amphibians.

Virus Nucleic acid within a protein or proteinand lipid coat that is unable to multiply outsidethe host tissues. Many are pathogenic.

Vitellogenesis The process by which oocytesgrow by yolk deposition.

Viviparity Producing live offspring.

Warble Swelling in skin caused by infectionwith larvae of flies causing furuncular myiasis.

Wax layer The lipid or waxy layer outside theepicuticle of some arthropods.

Zoogeographic region Areas of the world con-taining characteristic animal and plant specieswhich have been isolated from each other.

Zoonosis A disease on animals that may becommunicated to humans.

252 Glossary

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veterinary ectoparasites - biology, pathology and control

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