pfizer animal health european equine symposium...equine symposium meeting. we are delighted to be...
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Pfizer Animal HealthEuropean Equine Symposium
Scientific Proceedings
Vienna, November 2010
09:00 – 09:30
09:30 – 10:00
10:00 – 10:30
10:30 – 11:00
11:00 – 11:30
11:30 – 12:00
12:00 – 12:30
12:30 – 13:00
13:00 – 14:00
14:00 – 15:00
15:00 – 15:30
15:30 – 16:30
16:30
18:00 – 19:00
20:00
Opening WelcomeJolian Howell, Pfizer Animal Health
Current status and update on Equine InfluenzaRichard Newton, Animal Health Trust, UK
Current status and update on Equine HerpesvirusKees van Maanen, Animal Health Service (GD), Ne
Coffee Break
Equine Viral ArteritisAnn Cullinane, Irish Equine Centre
StranglesAndrew Waller, Animal Health Trust, UK
Current status and update on West Nile virus infectionsNorbert Nowotny, University of Veterinary Medicine, Vienna
African Horse SicknessAlan Guthrie, University of Pretoria
Lunch at Hotel
Case studies and interactive session EIV, EHV, EVARichard Newton, Kees van Maanen, Ann Cullinane
Break
Case studies and interactive session Strangles, WNV, AHSAndrew Waller, Norbert Nowotny, Alan Guthrie
Close for day
Tour of equine facility
Dinner
Meeting Agenda
Tuesday 30 November
2
09:30 – 09:45
09:45 – 10:15
10:15 – 10:45
10:45 – 11:15
11:15 – 11:45
11:45 – 12:30
12:30 – 14:00
14:00 – 15:00
15:00 – 15:30
15:30 – 16:30
16:30
20:00
Welcome
Cyathostomin resistance trial – efficacy resultsDonato Traversa, University of Teramo, Italy
Cyathostomin resistance trial – survey findingsGeorg von Samson Himmelstjerna, Freie Universität Berlin, Germany
Resistance monitoring and Sustainable Parasite ControlJane Hodgkinson, University of Liverpool, UK
Coffee Break
Sustainable parasite control Q&A panelDonato Traversa, Georg von Samson Himmelstjerna, Jane Hodgkinson
Lunch
Equine sedation and standing surgical anaesthesia (SSA)Kate White, University of Nottingham, UK
Coffee Break
Equine sedation protocolsKate White, University of Nottingham, UK
Close for day
Dinner
Wednesday 1 December
3
Contents
4
Speaker Biographies.....................................................................6
Current status and update on Equine Influenza.....................10Richard Newton, Animal Health Trust, UK
Current status and update on Equine Herpesviruses types 1 and 4...............................................................................12Kees van Maanen, Animal Health Service (GD), Netherlands
Equine Viral Arteritis.....................................................................14Ann Cullinane, Irish Equine Centre
Strangles – current status and future directions......................16Andrew Waller, Animal Health Trust, UK
Current status and update on West Nile virus infections........18Norbert Nowotny, University of Veterinary Medicine, Vienna
African Horse Sickness................................................................20Alan Guthrie, University of Pretoria
Cyathostomin resistance trial – efficacy results.......................22Donato Traversa, University of Teramo, Italy
Cyathostomin resistance trial – survey findings.......................24Georg von Samson Himmelstjerna, Freie Universität Berlin, Germany
Resistance monitoring and Sustainable Parasite Control......25Jane Hodgkinson, University of Liverpool, UK
Equine sedation and standing surgical anaesthesia (SSA)....26Kate White, University of Nottingham, UK
Thank you for travelling to Vienna to attend what promises to be a very
interesting and enjoyable meeting.
We have gathered together several leading experts on equine health
to present the most recent information and opinions on the key issues
facing equine veterinarians today. As well as updates on the current
status of important diseases such as influenza, West Nile, EHV and
Strangles, you will also have the opportunity to participate in case
studies facilitated by the speakers.
On day two the agenda will cover sustainable parasite control and
anthelmintic resistance, followed by a more detailed look at equine
sedation.
These proceedings summarise the presentations for this European
Equine Symposium meeting. We are delighted to be able to bring
together a broad and diverse group of speakers from across Europe
and would especially like to thank them for their support and effort in
making these days possible.
I hope you will have an enjoyable and rewarding time with us in Vienna.
Jolian Howell
Associate Director, Pfizer Equine Business, Europe, Africa and Middle East
Welcome to the Pfizer Animal Health European Equine Symposium
5
Speaker Biographies
6
Richard Newton BVSc MSc PhD DLSHTM DipECVPH FRCVS graduated
in Veterinary Science from Liverpool University in 1991. After several
years in mixed practice, Richard joined the Epidemiology Unit of
the Animal Health Trust in 1994. Since completing a Masters in
Communicable Disease Epidemiology at the London School of
Hygiene and Tropical Medicine in November 1998 he has worked
on the epidemiology of grass sickness, EIPH and equine infectious
diseases, including equine viral arteritis, influenza and strangles.
He completed his PhD on the epidemiology of equine infectious respiratory disease in
2002 and in 2003 was awarded both the Diploma of Fellowship from the Royal College
Veterinary Surgeons and became a de facto Diplomat of the European College of
Veterinary Public Health. He is currently Head of Epidemiology and Disease Surveillance
at the Animal Health Trust. The group at the AHT currently has programmes on infectious
disease surveillance in the UK for which it prepares quarterly disease reports for Defra; a
dedicated programme on grass sickness surveillance and a programme looking at the
epidemiology of laminitis in the UK. Richard's main area of interest is epidemiology and
surveillance of infectious diseases of the horse, including influenza, EHV, EVA, strangles
and bacterial lower airway disease. Other spheres of professional interest have included
epidemiological aspects of internal medicine and non-infectious respiratory disease,
including grass sickness, liver disease, tying up, EIPH and laminitis.
Dr. Kees van Maanen studied veterinary medicine in Utrecht, the
Netherlands. After his graduation in 1986 he became head of the
laboratory for FMD vaccine control, diagnosis of vesicular diseases,
and equine viral diseases at the Central Veterinary Institute in
Lelystad, the Netherlands. In 1992 he joined the Animal Health
Service and started a four year course in veterinary pathology.
He holds a specialist degree both in veterinary pathology and
veterinary microbiology. Since 1995 he has been the head of the
R&D laboratory of the Animal Health Service (GD) in the Netherlands, and as a virologist
is also responsible for the state-of the art performance of all routine virological and
molecular tests in the framework of the ISO 17025 accreditation of the GD laboratory.
In 2001 he completed a PhD on the subject equine herpesvirus 1 and 4 and equine
influenza virus infections: diagnosis, epidemiology and vaccinology. He is an author of
60 articles in scientific journals, has presented many papers on all sorts of subjects at
national or international scientific congresses and other meetings. He has served as a
referee for a number of journals, and is member of the advisory panel for equine
diseases of the Dutch ministry of agriculture with currently a focus on the development
of a contingency plan for African Horse Sickness. His main research interests are in
equine infectious diseases, test development and test validation, and implementation
of diagnostic strategies in the context of compulsory or voluntary disease control and
eradication programs. Currently he is also active as an FAO consultant for FMD in
Botswana and Egypt, and for Avian Influenza in Indonesia.
Richard Newton BVSc MSc PhD DLSHTM
DipECVPH FRCVS
Head of Epidemiology and
Disease Surveillance at the
Animal Health Trust, UK
Kees van Maanen DVM, PhD
Animal Health Service (GD),
GD Deventer, Netherlands
7
Ann Cullinane MVB, PhD, MRCVS has been Head of the Virology Unit
at the Irish Equine Centre since 1987. Ann is an OIE designated expert
in equine influenza and her laboratory is an OIE reference laboratory
for this disease. She obtained her MVB (Hons) from University College,
Dublin, and her PhD at the Medical Research Council Institute of
Virology, Glasgow University. Before joining the Irish Equine Centre,
Ann held research posts at the Department of Clinical Veterinary
Medicine, Cambridge University and at Applied Biotechnology,
Cambridge, Massachusetts. She has been a Member of the European Federation of
Veterinarians Biotechnology Working Party (1996-1998) and an Appointee of the Tanaiste
and Minister for Enterprise, Trade and Employment to the Irish Council for Science,
Technology and Innovation (2004-2005). In addition to her current position at the Irish
Equine Centre, Ann is also an Associate of the Faculty of Veterinary Medicine, University
College, Dublin; an appointee of the Minister for Health to the Advisory Committee for
Veterinary Medicines; and since 2007 an adjunct Professor in the Department of Life
Sciences at Limerick University. In 2007, Ann and her team in the Virology Unit received
a special recognition award from the Irish Thoroughbred Breeders Association for their
work during the Equine Infectious Anaemia outbreak. Ann’s research interests are equine
virology, clinical virology, molecular diagnostics and vaccinology, subjects about which
she has published numerous papers in peer-reviewed journals.
My appointment as Head of Bacteriology at the Animal Health Trust
in 2003 coincided with the genome sequencing of Streptococcus
equi strain 4047 and Streptococcus zooepidemicus strain H70 at the
Wellcome Trust Sanger Institute. My group has exploited this genome
information to learn more about the evolution of these important
pathogens and to make significant advances in the development of
new diagnostics and vaccines for the prevention of equine strangles.
Key publications: Guss B, Flock M, Frykberg L, Waller AS, Robinson C,
Smith KC, Flock JI. PLoS Pathog. 2009 Sep;5(9):e1000584. Getting to grips with strangles:
an effective multi- component recombinant vaccine for the protection of horses from
Streptococcus equi infection. Holden MT, Heather Z, Paillot R, Steward KF, Webb K, Ainslie F,
Jourdan T, Bason NC, Holroyd NE, Mungall K, Quail MA, Sanders M, Simmonds M, Willey D,
Brooks K, Aanensen DM, Spratt BG, Jolley KA, Maiden MC, Kehoe M, Chanter N, Bentley SD,
Robinson C, Maskell DJ, Parkhill J, Waller AS. PLoS Pathog. 2009 Mar;5(3):e1000346.
Genomic evidence for the evolution of Streptococcus equi: host restriction, increased
virulence, and genetic exchange with human pathogens.
Norbert Nowotny is currently Associate Professor of Virology, University
of Veterinary Medicine, Vienna, Austria and Leader of the ‘Zoonoses
and Emerging Infections Group’, University of Veterinary Medicine,
Vienna. Norbert studied Biology (Zoology/Botany) at the Faculty of
Natural Sciences, University of Vienna with a Ph.D. Thesis at the
Virology Laboratory of the Institute for Cancer Research, University
of Vienna Medical School and most recently Habilitation for Virology
at the University of Veterinary Medicine, Vienna. Norbert received
together with his group the ‘Oscar’ for their teaching performance at the main Virology
course (awarded by the Vetmeduni Vienna students). Norbert’s research interests and
current research projects include those related to all aspects of infectious diseases,
especially viral diseases, of farm, pet and zoo animals as well as wildlife, emerging
infections, zoonoses, infectious diseases at the environment/animal/human interface,
mosquito-borne viruses (West Nile virus, Usutu virus, etc.), borna disease virus and
molecular epidemiology. Norbert has 162 Publications in peer-reviewed renowned
scientific Journals, of which currently 125 are listed in PubMed. Since 1999 Norbert has
been a Member of the Bornaviridae Study Group of the International Committee on
Taxonomy of Viruses (ICTV) and from 2009 onwards Chairman of this ICTV Study Group.
Ann CullinaneMVB, PhD, MRCVS
Head of the Virology Unit
at the Irish Equine Centre
Andrew Waller Head of Bacteriology at
the Animal Health Trust, UK
Norbert NowotnyPh.D. Associate Professor of Virology,
University of Veterinary
Medicine, Vienna, Austria
Donato Traversa graduated with a DVM in 1999 and a PhD in 2002 at
the University of Bari, (Italy). In 2004 he received a European Young
Scientist Award from the European Federation of Parasitologists and
in 2006 the de facto Diploma from the European College of Veterinary
Parasitology (DipEVPC). Since 2002 as an Assistant Professor of
Parasitology and Animal Parasitic Diseases at the University of Teramo
(Italy) he has supervised (and still supervising) about 40 under-
graduates and about 15 intramural and extramural post-graduate
and PhD students. The main thrust of his research has been on myiasis causing larvae,
water-borne zoonotic protozoa and, in recent years, emerging nematodes of companion
animals (i.e. dogs, cats and horses), focusing on epidemiology, molecular diagnosis and
control and treatment of infections. Dr. Traversa is peer reviewer for 30 International
Scientific Journals on Medical Sciences, Parasitology and Molecular Biology. He has
published about 250 scientific papers, 90 of which are in international peer reviewed
journals, and has given about 40 presentations at conferences.
Donato TraversaDVM, PhD, Diplomate EVPC
Department of Comparative
Biomedical Sciences,
University of Teramo, Italy
Alan Guthrie BVSc, MMedVet, PhD is Director of the Equine Research
Centre, Faculty of Veterinary Science, University of Pretoria, South
Africa. He obtained his BVSc, BVSc (Hons) and MMedVet degrees
from the University of Pretoria. He completed his PhD at Louisiana
State University in the United States. Alan Guthrie has served as
promoter or co-promoter for 20 post-graduate students who have
been actively involved in the research activities of the Equine
Research Centre. He is an author of 65 articles in scientific journals,
has presented in excess of 100 papers at national or international scientific congresses
and made 80 presentations at other meetings. He has served as a referee for a number
Journals. His main research interests are in equine infectious diseases and equine sports
medicine. He has played an active role in coordinating South Africa’s efforts to
overcome the ‘African horse sickness ban’ which has severely limited South Africa’s
ability to export horses since its introduction in 1960. He has served as a member of the
International Movement of Horses Committee of the International Federation of Horse
Racing Authorities since 2001 and served on the OIE’s Ad Hoc Working Groups for
Equine Influenza and African Horse Sickness. Alan is an Honorary Life Member of the
Thoroughbred Breeder’s Association of South Africa due to his efforts to facilitate
international trade in South African horses.
Alan Guthrie BVSc, MMedVet, PhD
Director of the Equine
Research Centre,
Faculty of Veterinary Science,
University of Pretoria,
South Africa
Since October 2009, Georg von Samson-Himmelstjerna has been
Full Professor (W3) and director at the Institute of Parasitology and
Tropical Veterinary Medicine at the Freie Universität Berlin, Germany.
Between 1996 and 2000 he was employed by Bayer AG, Leverkusen,
where he established and was head of the laboratory for molecular
helminthology and was also active in the development of several
new antiparasiticides. At the beginning of 2001 he became head
of the molecular parasitology group at the Institute of Parasitology,
TiHo. He received his habilitation from the TiHo in 2003 and in 2005 he was appointed as
Professor (W2) for Molecular Parasitology at the Institute for Parasitology, University of
Veterinary Medicine Hannover, Foundation (TiHo) until he moved into his current position.
His main research interest are the mode of action and resistance of antiparasiticides,
development of new diagnostic tools and the identification of protective antigens from
veterinary parasites. During the past 10 years he has conducted numerous public and
industry funded research projects. Georg v. Samson-Himmelstjerna has published more
than 90 research papers in international peer reviewed journals. He is a diplomate of the
European Veterinary Parasitology College and, since 2008, a member of the editorial
board of Veterinary Parasitology (Elsevier).
Georg von Samson-Himmelstjerna Director or the Institute of
Parasitology and Tropical
Veterinary Medicine,
Freie Universität Berlin,
Germany
8
Kate White is a Clinical Associate Professor in Veterinary Anaesthesia
and Clinical Sub Dean at the University of Nottingham Veterinary
School. She graduated from Cambridge Vet School and then
worked in mixed practice. Kate then returned to Cambridge Vet
School and undertook a residency in anaesthesia funded by the
Horserace Betting Levy Board and gained her RCVS certificate and
diploma in anaesthesia. She also gained her European College of
Anaesthesia diploma. Following this she was a founding partner in
a large referral practice in Essex. She recently moved to the new veterinary school at
Nottingham and also runs an independent consultancy business offering anaesthesia
services to referral practices, pharmaceutical companies, and first opinion practices.
Her other interests are gardening, bridge, ski mountaineering, and juggling (working and
being mother of two toddlers).
Kate L White MA Vet MB DVA
Dipl ECVAA MRCVS
European Specialist in
Veterinary Anaesthesia
& Analgesia
Dr Jane Hodgkinson was awarded a first degree in Cell Biology from
the University of Manchester and a PhD from the University of
London. She has specialised in equine parasitology research at the
University of Liverpool since 1999 and was appointed Lecturer in
Veterinary Parasitology in 2002. Following her appointment she has
been awarded several grants totalling over a million pounds to
investigate anthelmintic resistance and key aspects in the biology of
the equine parasites, the cyathostomes. Her main research interests
combine molecular biology with classical parasitology and she has multiple publications
in international peer reviewed journals in the areas of molecular species identification
and mechanisms of benzimidazole resistance in cyathostomes. Anthelmintic resistance
is currently a priority research area in veterinary parasitology and her more recent work
has focussed on diagnosing resistance and the molecular mechanisms responsible for
reduced sensitivity to macrocyclic lactones in parasite populations. She has an extensive
teaching portfolio at both undergraduate and postgraduate level and is a keen
promoter of knowledge exchange to the equine community, particularly in promoting
sustainable control practices.
Jane E Hodgkinson University of Liverpool, UK
9
Equine influenza virus (EIV) causes clinically severe respiratory disease in horses.
Coughing and fever are the most common clinical signs of equine influenza,
the cough being dry, harsh and initially non-productive. The nasal discharge
is initially serous but subsequently becomes mucopurulent when secondary
bacterial infection of the respiratory tract has occurred. Increasingly it is
recognized that among vaccinated horses that have some but incomplete
immunity, outbreaks of clinically mild influenza do occur. In such outbreaks
there is frequently mild signs that may not be recognized or diagnosed as
influenza and often the first sign noted is poor training and racing performance.
The characteristic clinical features of equine influenza in susceptible animals
(rapidly spreading disease manifested by a harsh, dry cough, high temperature
and nasal discharge) are sufficiently characteristic to permit a tentative
diagnosis. However, in animals that have previously experienced the infection
or that have waning vaccinal immunity, it is difficult to differentiate influenza
from other respiratory infections. In such situations laboratory diagnosis is
required involving virus isolation, antigen detection or serology.
The dynamics of transmission of EIV are well characterised and indicate that
because, unlike other equine infectious diseases, there is no known carrier
state for this infection, propagating EIV infection requires ongoing chains of
transmission. Underlying this is the theory of the basic reproduction number (R0),
which is the number of new cases that an infectious individual gives rise to, on
average, in a fully susceptible population. Where R0 is significantly greater than
1.0 (e.g. 10) then because each infected individual may infect up to 10 others
this may give rise to an escalating epidemic. However, where R0 is less than 1.0
then this gives rise for conditions in which the virus will ultimately become
extinct as each infected individual cannot give rise to at least one other
infected individual. This theory informs control measures for EI as vaccination
that effectively reduces R0 to less than 1.0, consequently halting spread
and restrictions on movement and mixing should over a relatively short time
effectively achieve the same ends.
Figure 1: A schematic representing the dynamics of equine influenza infection
Infection⇓
HEALTHY INCUBATION HEALTHY
1-2 days
1-2 days
2-3 weeks
SUSCEPTIBLE LATENT IMMUNE then SUSCEPTIBLE
Max 10 days months or years
⇓ ⇓ ⇓ ⇓ ⇓ ⇓ ⇓ ⇓ ⇓
Current status and update on Equine Influenza
Richard Newton BVSc MSc PhD DLSHTM
DipECVPH FRCVS
Head of Epidemiology and
Disease Surveillance at the
Animal Health Trust, UK
E-mail address:
10
Antigenic variation (‘drift’) of the surface haemagglutinin protein (HA), the
major immune target of EIV, leads to reduced vaccine efficacy. As antigenic
drift is continuous, ongoing virus characterisation is necessary to inform
periodic vaccine updates. Viruses isolated around the world are submitted to
a small number of reference laboratories for antigenic and genetic analysis
so that antigenically distinct viruses can be identified and monitored for their
spread in the equine population. Veterinary practitioners are a critical part of
EIV surveillance activity as they facilitate access to information and samples
from cases in the field.
Phylogenetic analysis of HA sequences revealed that equine H3N8 viruses,
which had been evolving as a single lineage for at least two decades,
diverged into two distinct lineages during the mid-1980s. Viruses in one lineage
were predominantly isolated from horses on the continent of America;
whereas viruses in the other lineage were almost exclusively isolated from
horses in Europe and Asia. Since then American lineage viruses have come to
predominate, but the lineage has evolved into three distinct sublineages.
Within the American lineage is a variant sublineage known as the Florida
sublineage. The strains that caused the outbreak in Newmarket in 2003 and
spread across Europe shortly thereafter belonged to this sublineage, as have
the majority of strains isolated in Europe since 2003. However, two clades can
now be distinguished in this sublineage; Florida Clade 1 viruses have been
isolated in North America since 2003 (e.g. Ohio/2003) and are distinct from the
Florida Clade 2 strains that spread to Europe (e.g. Newmarket/5/03). Florida
Clade 1 viruses caused outbreaks in South Africa at the end of 2003 and
subsequently in Japan and Australia in 2007. Florida Clade 2 viruses were
responsible for major outbreaks in China, Mongolia and India from 2007–2009
and have re-emerged as the predominant clade in the UK during 2010 following
a period in the second half of 2009 when clade 1 viruses appeared to be
dominant. Overall the phylogenetic analysis points to sporadic incursions of
virus from North America into Europe and other regions, as happened around
1993 and 2003, followed by a period of more localised divergent evolution.
11
Current status and update on Equine Herpesviruses types 1 and 4
Kees van Maanen DVM, PhD
Animal Health Service (GD),
GD Deventer, Netherlands
12
Introduction
Equine herpesvirus 1 (EHV1) and equine herpesvirus 4 (EHV4) are important ubiquitous equine viral pathogens, causing much damage to the horse industry. EHV1 strains are associated with respiratory disease, abortion, and paresis/paralysis, whereas EHV4 strains are predomi-nantly associated with respiratory disease. In the past decades much research effort has gone into improving knowledge about these viruses. In this presentation the most important aspects of these virus infections are discussed.
Pathogenesis
After inhalation EHV1 and EHV4 multiply in the epithelia of the nasal cavities, pharynx, trachea and bronchi(ol)i, and subsequently spread to regional lymph nodes. In respiratory epithelia and lymphoid germinal centres, necrosis and intranuclear inclusion bodies can be observed, and viral shedding from the mucosal surfaces generally lasts for 10-14 days. Abortion can be initiated either by exogenous or endogenous infection, i.e. recrudescence of latent virus. After respiratory infection, EHV1 strains invade quickly the lamina propria and infect leucocytes and endothelial cells of blood and lymphatic vessels. The specific leucocyte subset(s) harbouring EHV1 remain poorly defined. Then infection spreads to regional lymph nodes from which infected mononuclear cells enter the circulation resulting in a cell-associated viraemia leading to placental transfer and infection of the foetus with subsequent abortion. However, foetal infection is not always a prerequisite for abortion. Experimental studies suggest that different EHV1 isolates vary in abortigenic potential. Since both viraemia and endothelial infection seem to play a crucial role in the pathogenesis of abortion and neurological disease, the current knowledge and the limitations of our understanding of the mechanisms of infection of blood mononuclear cells and transmission between endothelial cells and blood mononuclear cells at the port of entry and in the target organs will be discussed. In contrast to several other alphaherpesviruses, e.g. herpes simplexvirus (HSV), bovine herpesvirus 1 (BHV1), and pseudorabies virus (PRV) that can cause encephalitis through primary neuro-tropism with virus multiplication in neurons and neuronophagia, EHV1 seems to be non- neurotropic in equine brain, even after intracerebral inoculation. The propensity of certain EHV1 isolates to induce Equine Herpesvirus Myeloencephalopathy (EHM) does not reflect specific neurotropism but rather a marked endotheliotropism. However, the mechanism underlying CNS endothelial infection is largely unknown, as are the risk factors that determine its occurrence. Recently a point mutation in the polymerase gene of EHV1 has been shown to be strongly associated with neurological sequelae of infection. The magnitude of cell- associated viraemia seems to be an important factor for the development of EHM, although also for neuropathogenic strains considerable differences have been observed in magnitude and duration of viraemia. It is also possible that differential utilization of receptors and efficiency of virus entry or attachment to virus-infected lymphocytes to endothelial cells in response to host factors could be a determining factor in the outcome of EHM.
Epidemiology
Latency As all alphaherpesviruses, EHV1 and EHV4 appear to establish life-long latent infections. Both viruses could be reactivated experimentally with very high doses of cortico- steroids and mild nasal trauma. The most important site of latency is still controversial. Latency has been demonstrated for both viruses predominantly in lymphoid tissues and peripheral leucocytes on one hand, and predominantly in trigeminal ganglia on the other hand. Reactivation and shedding of EHV1 and EHV4 creates the opportunity for transmission to other horses, which is considered important in the epidemiology of EHV1 and EHV4 and might explain why these diseases can occur in closed populations. With the availability of sensitive PCR methods, in recent years more information has become available with respect to the occurrence of latent infections. For practical purposes, however, clinicians should presume that the majority of horses are latently infected with EHV1 and EHV4. During the 6- to 8-month period following weaning the majority of foals experience repeated respiratory infections with EHV4. The majority of such infections pass unnoticed. Circulation of EHV1 in unweaned and weaned foals supports the long standing management practices of separating pregnant mares from other groups of horses, especially lactating mares with unweaned foals,
13
and groups of weaned foals, to reduce the incidence of EHV1 abortion. Interestingly enough, recent observations in Australia and the USA question the paradigm of common subclinical shedding of EHV1, at least in the absence of neonatal and juvenile horse populations, and suggest that spread of EHV1 among adult horses is typically accompanied by clinical disease, either abortion or EHM. The occurrence of infections very early in life should also have implications for vaccine efficacy criteria and vaccination regimens, as the efficacy of vaccination in already latently infected horses is unknown.
Diagnosis
For nasal swabs, PCR appears to be more sensitive than virus isolation. Also local antibodies do not interfere with nucleic acid amplification methods, whereas they may interfere with virus isolation. Therefore, virus shedding can be demonstrated with PCR for a longer time, which is especially advantageous when samples are not taken in the acute phase of respiratory disease or after a relatively long incubation period as described for EHV1 neurological disease. A significant increase in EHV1/4 cross-reactive antibodies or type-specific antibodies by different serological assays can also be considered proof of infection. The foetus is the speci-men of choice for diagnosis. EHV1 or EHV4 infection can be demonstrated in relevant organs either directly by IFT or immunohistochemistry in sections from frozen or paraffin embedded tissues, or by virus isolation or PCR. In the acute phase of neurological disease an EHV1 infection can be diagnosed by virus isolation or PCR from nasopharyngeal swabs, from white blood cells or from cerebro- spinal fluid (CSF). CSF analysis often reveals xanthochromia and increased protein concentrations, reflecting vasculitis and protein leakage into the CSF. Presumptive evidence of infection is provided by showing a seroconversion or significant increase in titre in acute and convalescent sera. However, antibody titres often rise already during the incubation period and may have peaked by the time neurological signs appear. Since a point mutation in the polymerase gene of EHV1 is strongly associated with the neurological potential of EHV1 strains, allele-specific PCRs are nowadays available to differentiate between neurological and non-neurological strains. However, the relevance of pathotyping is debatable, at least for diagnosis and management purposes. The most important reason to perform this testing is to increase our knowledge about EHV1 epidemiology.
(Immuno)prophylaxis
Preventive management Epizootics of EHV1 respiratory disease are often associated with bringing together groups of susceptible horses under circumstances that produce stress, like weaning, long distance transport, intermingling of young horses originating from different locations for sales, training and performing. Preventive management should therefore involve avoidance of stress, prevention of introduction from an exogenous source by isolation practices by keeping incoming horses isolated from the resident population for at least three weeks, and division of the farm or track population into discrete, small units. Management has to be mainly concentrated on prevention of the more serious sequelae of an EHV1 infection like abortion storms and outbreaks of neurological disease, and should therefore aim at reducing the chance for exogenous introduction of EHV1 into a population of brood mares, reducing the chance for reactivation from latently infected carriers, and limiting the spread in the case of introduction of infection. Under the acronym SISS (Segregation, Isolation, Subdivision and Stress reduction) the main principles will be discussed.Vaccination Efficacy of vaccination against the different sequelae of EHV1 and/or EHV4 infections will be discussed on an individual level and on a population level. On a population level virological protection, i.e. reduction of virus excretion, is as important as clinical protection. Since latency is important in the epidemiology of EHV1 and EHV4 infections, as for other alphaherpesviruses inducing latent and recurrent infections, the goal of vaccination is different and more ambitious than for many other viruses. The aims for alpha-herpesvirus vaccines are not limited to prevention of the first episode of disease but also the control of recurrent infections. Also reduction of re-excretion after stressful events in horses that are first infected and then vaccinated might be an important efficacy criterion for EHV1/4 vaccines. Efficacy of vaccines for protection against clinical disease and reduction of virus excretion after exogenous infection can be different from that after reactivation. Since the ideal EHV1/EHV4 vaccine has not yet been developed, current developments and research priorities will be discussed.
Introduction
Equine viral arteritis (EVA) is caused by an arterivirus equine arteritis virus (EAV)
which was first isolated in 1953 during an outbreak of respiratory disease and
abortion in Ohio, USA. Since then outbreaks have occurred all over the world.
Evidence of exposure to EAV has been reported in Standardbreds, Thorough-
breds, Quarter horses, Arabian and Warmbloods. Considerable variation in the
prevalence of seropositive horses occurs between certain breeds within a
country. In America, Australia and New Zealand, EAV is endemic in Standard-
bred horses but rare in Thoroughbred horses.
In spite of the apparent worldwide distribution of EAV, disease outbreaks appear
to be infrequent and sporadic in nature. In 1984 an outbreak in Kentucky
affected some 41 Thoroughbred stud farms and led to the temporary embargo
on the import of horses of all breeds from the USA by several other countries.
However, current international movement restrictions relate primarily to carrier
stallions and infected semen.
Transmission
The two important routes of EAV transmission are venereal and aerosol but the
virus can be transferred by personnel or fomites and aborted fetuses are often
heavily contaminated with virus. The most effective transmission is the venereal
infection of mares by stallions during mating or when artificially inseminated
with semen from a carrier stallion. There is no evidence of the carrier state in
mares but after infection a mare may shed virus in all her bodily fluids for a
limited period. Initial viral transmission is frequently followed by lateral spread to
the mares cohorts, usually mares and foals. This in turn may lead to the infection
of other stallions and the establishment of further venereal shedders. Stallions
infected by aerosol transmission or by direct contact with an acutely infected
mare may become short-term (convalescent) or long-term venereal shedders
of virus. Carrier stallions shed EAV in the sperm rich portion of their semen and
infect virtually every mare they cover. The virus localises in the reproductive
tract principally the ampulla of the vas deferens and the maintenance of the
carrier status is testosterone dependent.
Clinical signs
Clinical signs of EAV infection are extremely variable and the majority of infections
appeared to be subclinical. The most common clinical signs are fever, depression,
inappetance, limb oedema especially of the hind limbs, stiffness in gait,
inflammation of the conjunctiva (’pink eye’) and nasal mucus membranes,
urticarial rashes and oedematous plaques, ocular and nasal discharge,
palpebral oedema and oedema of the orbital fossa. Oedema of the mammary
gland is frequently seen in mares and the majority of stallions develop scrotal
oedema. The oedema is a result of the vasculitis which characterises the
disease. EAV is usually self-limiting and most horses make an uneventful recovery
within 14 days. However a fatal pneumonia can occur in foals. Abortion can
occur from 3 months of gestation and appears to be due to myometrial
necrosis and oedema leading to placental detachment and fetal death.
Equine Viral Arteritis
Ann Cullinane MVB, PhD, MRCVS
Virology Unit,
Irish Equine Centre,
Johnstown, Naas,
Co. Kildare, Ireland
Tel: +353 45 866266
E-mail address:
14
Diagnosis
The diagnosis of EVA cannot be made based solely on the clinical signs without
corroborative virus isolation and/or serology. The variability in pathogenicity
among strains of EAV means that the absence of clinical signs cannot be taken
as evidence of the absence of virus infection. Acute EVA may be diagnosed
by virus isolation or detection using the polymerase chain reaction (PCR). The
virus can be isolated/detected in nasal secretions, semen, urine, buffy coats and
fetal tissues. Serological diagnosis of EAV infection is based on seroconversion
i.e. a significant rise in antibody titres between two samples. If the first sample
is collected during the acute stages of the disease the convalescent sample
should be taken 14–28 days later. The serum neutralisation test (SNT) is the
internationally recognised test but ELISA tests have also been developed. All
long-term carrier stallions are seropositive but not all seropositive stallions are
carriers. Many stallions only shed virus for weeks or months but their antibody
titre remains stable for years. The shedding status of a putative carrier stallion
can be determined by virus isolation/detection from entire ejaculates or by
test mating seronegative mares.
Control
Adequate rest, with supportive therapy if necessary, allows the majority of
horses to make a speedy and uneventful recovery. The spread of EAV can be
limited by restriction of movement of horses from affected premises until there
is no virological evidence of active virus infection. Most control programmes
only allow carrier stallions to breed under very restricted circumstances i.e.
they are kept physically isolated and bred only to mares that are seropositive
to EAV. EVA is a notifiable disease in many countries. European Union (EU)
legislation concerning EAV testing exists in relation to the importation of horses
from third countries but there is no mandatory testing for horses moving within
the EU. Thus the horse industry is extremely reliant on compliance with voluntary
codes of practice for the control of EVA.
It is strongly recommended that all stallions are vaccinated against EAV each
breeding season. A modified live EAV vaccine (Arvac) is available in North
America and a killed vaccine (Artervac) is available in Europe. All stallions should
be serologically tested immediately prior to and 2 to 3 weeks after vaccination
to indicate that their antibody titre is a consequence of vaccination and not
natural infection. The keeping of adequate records obviates the need for
investigations into the carrier status of the horse at a future date particularly if
the owner wishes to sell or export the horse.
15
Strangles caused by the bacterium Streptococcus equi sub-species equi
(S. equi) continues to be the most frequently diagnosed infectious disease of
horses world-wide with over 700 outbreaks identified in the UK alone during
2008. The disease is characterised by abscessation of lymph nodes in the head
and neck resulting in high morbidity and occasional mortality. S. equi shed from
ruptured abscesses can transmit to naïve horses directly via nose to nose
contact or via fomites such as water troughs, feed utensils, tack and other
equipment. As a result the management practices implemented in the face of
an outbreak can greatly impact its severity and duration.
Suspected strangles cases and healthy direct or indirect contacts should be
immediately isolated into RED or AMBER groups, respectively. Those that have
not had contact with any horse showing clinical signs form GREEN groups.
Buckets and other equipment should be colour-coded to ensure that mixing
between groups does not occur. Staff should always move from the lowest risk
to highest risk groups i.e. GREEN to AMBER to RED. The temperature of all horses
should be taken daily and any horse showing an increase in temperature
(>38.9C) should be moved to the RED group. Using such a management
strategy can dramatically reduce the impact of a strangles outbreak. However,
given that outbreaks should be readily identified and contained, the world
wide prevalence of strangles is unexpectedly high. One explanation for the
global success of S. equi is its ability to persistently infect the guttural pouches
of a proportion of horses (approximately 10%) after clinical signs have resolved.
These apparently healthy carriers intermittently shed S. equi, which can trigger
new outbreaks.
S. equi evolved from an ancestral strain of Streptococcus equi sub-species
zooepidemicus (S. zooepidemicus), which is associated with a wide variety of
diseases in horses and other animals including humans, through a process of
gene loss and gain1. Recent analysis of high resolution draft genome
sequences of 51 isolates has defined the global and temporal diversity of
S. equi. These data demonstrate that outbreaks are often multi-focal, that
persistently infected carriers can be reinfected with the circulating outbreak
strain and that super-infection of horses permits the exchange of genetic
material from one strain to another. The S. equi genome is subjected to a
continual process of decay and modification, particularly associated with
isolates recovered from the guttural pouch, providing one explanation to why
S. equi has become host-restricted. The analysis of this data has increased our
understanding of S. equi evolution and diversity, but it is also important to
translate this knowledge into improved diagnostic tests and vaccines for the
prevention of strangles.
In contrast to S. zooepidemicus, S. equi lacks the ability to ferment ribose,
sorbitol and lactose as a consequence of independent lesions in its genome.
This difference in metabolism is commonly used to differentiate cultures of
S. equi from S. zooepidemicus. However, the identification of horses infected
with S. equi by culture techniques is confounded by low sensitivity, the presence
of contaminating bacteria and intermittent shedding.
PCR techniques exploit genome data to target genes unique to S. equi. This
sensitive technique is able to detect S. equi DNA even in the presence of
contaminating bacteria and has the potential to be used as a point of care
Strangles – current status and future directions
Andrew Waller Head of Bacteriology
at the Animal Health Trust, UK
16
test. However, intermittent shedding of S. equi necessitates the taking of three
consecutive swabs at weekly intervals or guttural pouch lavages for the
identification of persistently infected carriers.
The absence of some S. equi genes from the S. zooepidemicus population has
also enabled the development of a specific blood test for the identification of
horses recently exposed to S. equi. The test quantifies the amount of antibodies
present in the blood sera of a horse that target two S. equi proteins. Following
exposure it may take 14 days before antibody levels reach sufficient levels
to be detected in this assay. However, the test does not rely on intermittent
shedding of S. equi and a single blood sample can identify horses that did not
have clinical signs of strangles, but which were exposed to S. equi during the
course of an outbreak. These horses can then be targeted for culture and PCR
testing either using three nasopharyngeal swabs or guttural pouch lavages to
identify and treat persistently infected carriers.
The application of new diagnostic techniques can prevent and reduce the
impact of S. equi infection, but they cannot eliminate all risk. Horses frequently
and unavoidably mix with one another during competition, events, transport
or sales. Therefore, a key preventative element involves enhancing the ability
of the equine immune response to combat S. equi infection through the
development of safe and effective vaccines. Again the S. equi genome
sequencing data is proving to be an invaluable resource and a new safe
multi-component protein vaccine protected 87% of ponies from developing
lymph node abscesses following S. equi infection2.
The progress being made towards improving management practices, rapid
and sensitive diagnostics and developing an effective strangles vaccine should
finally enable us to break the strangles hold.
References:1. Holden, M.T. et al. Genomic evidence for the evolution of Streptococcus equi: host restriction, increased virulence, and genetic exchange with human pathogens. PLoS Pathog 5, e1000346 (2009).2. Guss, B. et al. Getting to grips with strangles: an effective multi-component recombinant vaccine for the protection of horses from Streptococcus equi infection. PLoS Pathog 5, e1000584 (2009).
17
Background information
In 1999, a lineage 1 strain of West Nile virus (WNV) emerged in the New York
area, and spread rapidly within a few years throughout North and Central
America, causing significant morbidity and mortality in avian species, horses
and human beings.
In August 2004, a lineage 2 WNV was identified in a goshawk (Accipiter gentilis)
fledgling, which died due to severe CNS disease in a national park in south-
eastern Hungary. This was the first time that a WNV of lineage 2 was identified in
Europe (Bakonyi et al., Lineage 1 and 2 strains of encephalitic West Nile virus,
Central Europe. Emerg Infect Dis. 2006;12:618-623). Before that, the occurrence
of lineage 2 WNV was restricted to sub-Saharan Africa and Madagascar. Most
likely this exotic virus strain was introduced to Hungary by viraemic migratory
birds. Competent mosquito vectors, such as Culex pipiens, were present, and
passed the virus on to local bird species.
Objectives
The objectives were to closely monitor whether this exotic WNV strain is able to
establish a successful mosquito-bird transmission cycle,
survive the cold Central European winters,
become a resident pathogen in Hungary,
and to spread within Hungary and to other European countries.
Methods
A dead bird surveillance system was initiated. Birds found dead were submitted
to necropsy, and specific tests were performed in order to identify WNV as well
as other infections.
Results
In 2005 and 2007 further WNV cases were observed in the same region, whereas
the 2007 cases showed already a certain dispersal of the infection. In summer
2008 the infection suddenly spread all over Hungary and to the eastern part
of Austria, and West Nile disease was seen in several different species of birds
(though the ‘indicator bird’ for this particular WNV strain remained to be the
goshawk and other birds of prey), in horses, and even in a sheep. In Hungary,
also humans became infected and some of them developed meningitis.
It was also demonstrated that mosquitoes carried the virus. Molecular studies
showed that the 2008 outbreak was caused by essentially the same virus,
which was introduced to Hungary in 2004.
Interestingly, in summer 2008 a widespread WNV outbreak in human beings,
horses and birds was also observed in northern Italy, though the etiologic virus
of the Italian outbreak was a lineage 1 WNV, which circulated in Europe
already for a long time, but rarely had caused outbreaks, and if so, then such
outbreaks were limited in time and geographic range. It seems that in spring
and summer 2008 there were extremely favourable conditions for the spread
of WNV in Central Europe.
Current status and update on West Nile virus infections
Norbert Nowotny Zoonoses and Emerging
Infections Group,
Clinical Virology,
Department of Pathobiology,
University of Veterinary
Medicine, Vienna, Austria
18
In 2009 West Nile disease was observed in the same large areas as in 2008,
which include the whole of Hungary and the eastern part of Austria for lineage
2 and northern Italy for lineage 1.
Conclusions
An exotic lineage 2 WNV strain was introduced to Hungary in 2004, and
emerged as a significant disease of several animal species and human beings
in 2008. Also in 2008, a severe and widespread lineage 1 WNV outbreak was
recorded in northern Italy. In 2009 the same areas were affected. The exotic
lineage 2 WNV strain became a resident pathogen to Central Europe, and will
during the upcoming years certainly spread to further areas. As a conse-
quence, WNV monitoring systems should be established urgently in Central
Europe and the awareness of the general public must be increased.
Note added in proof
In summer and autumn 2010 a huge lineage 2 WNV outbreak was going on in
Central Macedonia (northern Greece) with 191 laboratory-diagnosed human
neuroinvasive cases including 32 fatalities, all of them elderly.
19
African horse sickness (AHS) is a non-contagious, infectious, insect-borne
disease of equids caused by African horse sickness virus (AHSV). In horses the
disease is usually peracute to acute and in naive animals more than 90% of
those affected die. Clinically, the disease is characterized by pyrexia, oedema
of the lungs, pleura and subcutaneous tissues and haemorrhages on the
serosal surfaces of organs. Mules are less susceptible than horses. Donkeys and
zebras rarely show clinical signs of disease.
The first known historical reference to a disease resembling AHS was reported in
Yemen in 1327. Documents reporting on the travels of Portuguese explorers in
East Africa in 1569 report AHS affecting horses imported from India. Neither horses
nor donkeys were indigenous to southern Africa but were introduced shortly after
the arrival of the first settlers of the Dutch East India Company in the Cape of
Good Hope in 1652. Dutch East India Company records make frequent reference
to ‘perreziekte’ or ‘pardeziekte’ in the Cape of Good Hope. In 1719 about 1,700
horses died due to AHS in the Cape of Good Hope. Major epizootics of AHS
occurred in southern Africa prior to the 1950’s at intervals of roughly 20-30 years.
Severe losses were reported in 1780, 1801, 1839, 1855, 1862, 1891, 1914, 1918, 1923,
1940, 1946 and 1953. The 1854/55 epizootic was the most severe with almost
70,000 horses (40% of population) dying in the Cape of Good Hope.
In the early 1900’s, Theiler and others succeeded in transmitting AHS with
a bacteria-free filtrate of blood from infected horses confirming that the
disease was caused by a virus. Sir Arnold Theiler described the plurality of
‘immunologically distinct strains’ of AHSV, since immunity acquired against one
‘strain’ did not always afford protection against infection by ‘heterologous strains’.
The proposal in 1903 by Pitchford and Theiler that AHS may be transmitted by
biting insects was finally confirmed in 1944 when Du Toit showed that Culicoides
species were probably vectors of AHSV.
Alexander and co-workers showed that AHSV could be attenuated after
serial intracerebral passage in mice. This led to the development of the first
polyvalent vaccine against AHS in the 1930’s. In the 1970’s Erasmus successfully
attenuated AHSV using serial tissue culture passage and plaque selection.
The tissue culture attenuated AHS vaccine strains are used exclusively in the
polyvalent AHS vaccine currently marketed by Onderstepoort Biological
Products in South Africa. An inactivated vaccine was produced against AHSV
serotype 4 for use during the outbreak of AHS in Spain, Portugal and Morocco
in 1987 to 1990. This vaccine has since been discontinued.
A number of different approaches have been used in an attempt to develop
new generation vaccines to AHSV. Vaccination with baculovirus expressed
proteins, DNA vaccine and a modified Ankara virus have been shown to
produce immune responses to AHSV in horses. Recently, a canarypox vectored
vaccine containing the genes encoding the VP2 and VP5 proteins of AHSV
serotype 4 has been described which provided a solid protective immunity to
challenge with AHSV serotype 4 in horses. This vaccine also has DIVA properties.
Confirmation of the diagnosis of AHS has traditionally relied on virus isolation
and typing using neutralization tests. Originally these tests were performed in
suckling mice but these techniques have generally been superseded by tissue
culture techniques. These assays take 1 to 3 weeks to complete. Antigen
African Horse Sickness
Alan Guthrie BVSc, MMedVet, PhD
Director of the Equine
Research Centre,
Faculty of Veterinary Science,
University of Pretoria,
South Africa
20
capture ELISA’s have been described which can be applied directly to blood
and tissue samples and which can accelerate the diagnosis of AHS. These
techniques have since been replaced by molecular techniques although the
majority of these assays have not been evaluated on incurred field samples from
cases of AHS. A duplex RT-qPCR has recently been described and well charac-
terised using incurred field samples. Further refinement of this assay to include
an external control will allow one to certify animals free from infection with AHS.
These techniques allow one to complete sample analysis within a few hours and
appear to be considerably more sensitive than virus isolation. It is anticipated
that these techniques will replace virus isolation for primary diagnosis of AHS.
Accidental aerosol infection of four humans working with mouse brain
attenuated strains of AHS in the vaccine packing section at Onderstepoort
Biological Products has been demonstrated. They suffered from non-fatal
encephalitis and chorioretinitis which resulted in partial loss of vision or blindness.
These mouse brain attenuated strains have since been removed from the AHS
vaccine produced by Onderstepoort Biological Products.
AHS is endemic in eastern and central Africa and spreads regularly to southern
Africa. In endemic areas, different serotypes of AHS may be active simultaneously
but one serotype usually dominates during a particular season. AHS has been
recorded in Egypt in 1928, 1943, 1953, 1958 and 1971, in Yemen in 1930 and in
Palestine, Syria, Lebanon and Jordan in 1949. In 1959, AHS serotype 9 occurred
in the south-eastern regions of Iran. This was followed by outbreaks during 1960
in Cyprus, Iraq, Syria, Lebanon and Jordan as well as in Afghanistan, Pakistan,
India and Turkey. Between 1959 and 1961 this region lost more than 300,000
equids. In 1965 AHS occurred in Libya, Tunisia, Algeria and Morocco and
subsequently spread to Spain in 1966. Between 1987 and 1990, AHS serotype 4
occurred in Spain with the virus being introduced by zebra (Equus burchelli)
imported from Namibia. AHS was also confirmed in southern Portugal in 1989
and Morocco between 1989 and 1991 with these outbreaks being extensions
of the outbreak in Spain. In 1989 an outbreak of AHS serotype 9 occurred in
Saudi Arabia. AHS was also reported in Saudi Arabia and Yemen in 1997 and
on the Cape Verde Islands in 1999. Serotypes 6 and 9 of AHSV were isolated
from samples collected from equids in Ethiopia in 2003 and serotype 2 has
resulted in the death of approximately 2000 horses in Ethiopia in 2008. Serotypes
2 and 7 of AHSV were isolated in Senegal in 2007 and serotype 2 was isolated
in Nigeria in 2007 and 2009 and in Ghana in 2009. AHS was also reported in The
Gambia in 2007. To date, the only epizootic of AHS that has been associated
with the legal movement of equids (albeit under suboptimal sanitary conditions)
was the outbreak in Spain, Portugal and Morocco from 1987 to 1990.
In endemic areas, severe losses due to AHS have ceased since the development
of polyvalent vaccine. However, epizootics in countries outside the endemic
regions in Africa serve as a warning that AHS may spread to areas traditionally
free of the disease. AHS is one of the important diseases to consider when
moving equids internationally but movement can be accomplished safely
following appropriate quarantine and testing procedures. The recent outbreaks
of Bluetongue in Europe which have been associated with changes in vector
range and capacity due to climate change suggest that the epidemiology of
AHSV may be very different if an epizootic of AHS were to reoccur in Europe.
21
Strongylid nematodes ranked within the Cyathostominae Subfamily (known as
cyathostomins or small strongyles) are equine pathogens, causing symptoms
such as lethargy, weight loss, debilitation, and diarrhoea. Moreover, at the onset
of larval invasion of the host, thousands of third larval stages may encyst in the
intestine wall, causing serious damage to the mucosa and reducing nutritional
intestinal metabolism. Even more dangerous is the simultaneous re-emergence
in the lumen of the developed fourth stage larvae to continue their cycle to the
adulthood, causing ‘larval cyathostominosis’, a syndrome mainly characterized
by diarrhoea and potentially serious colic, with a fatality rate up to 50%.
The control of infections by small strongyles usually relies on three major classes
of anthelmintics: benzimidazoles - BZs (e.g. fenbendazole - FBZ); tetrahydro-
pyrimidines - THP (i.e. pyrantel-PYR salts); and macrocyclic lactones - MLs
(i.e. ivermectin-IVM and moxidectin-MOX). In recent decades the spread of
cyathostomin populations resistant to parasiticides has become a serious
threat to horse health and welfare. In several European and US areas, resistance
to BZs is widespread and resistance to THP is also presently increasing. MLs have
demonstrated efficacy against cyathostomins until the last few years; specifically,
some cases of reduced efficacy of IVM have been recently described in
Europe and USA, and failure of MLs to provide control of cyathostomins in Brazil
has been reported as well.
Although in Europe cyathostomin populations resistant to one (’single resistance’)
or more (’multiple resistance’) parasiticide class have been described from a
range of countries, the vast majority of the studies have been carried out on a
small number of horse yards in limited areas. Therefore, with the aim of enhancing
our knowledge on the presence of drug resistance on horse farms, a large
scale study evaluated the efficacy of FBZ, PYR, IVM and MOX (i.e. the major
anthelmintics used in current equine practice) in 2008 in three key countries for
the horse industry in Europe.
A total of 146 yards and 4280 horses were screened with a faecal egg count
(FEC) for cyathostomins: 84 yards and 2105 horses from Italy, 32 and 1059 from
UK, and 30 and 1116 from Germany. A FEC value of 50 eggs per gram (EPG) of
faeces in 12 to 20 horses was used as a cut-off for inclusion of yards in the study.
Overall, 102 yards and 1704 horses were enrolled in the three countries: 60 yards
and 988 horses from Italy, 22 and 396 from the UK, 20 and 320 from Germany.
All horses were subjected to a Faecal Egg Count Reduction Test (FECRT), in
which a random selection of animals in each yard was performed to obtain
equally sized treatment groups of 4 or 5 horses. On Day 0, animals enrolled in
each group were orally treated by veterinary practitioners for the different
yards (see acknowledgments) with either FBZ, PYR, IVM or MOX at the dosages
recommended for the treatment of horse cyathostominosis. Faecal samples
were collected for each animal at Day 0 (prior to treatment) and at Day 14 to
determine the individual pre-treatment and post-treatment EPG values with a
quantitative coproscopic analysis.
The calculation of the FECR percentages was performed using the computer
program ‘BootStreat’ and arithmetic means of the pre- and post-treatment FEC
were used to calculate the group FECR according to the formula FECR= 100*
(1 - FEC post-treatment/ FEC pre-treatment), and the lower and upper 95%
confidence limits. The FECRs were categorized for all tested compounds as
Cyathostomin resistance trial – efficacy results
Donato TraversaDVM, PhD, Diplomate EVPC
Department of
Comparative Biomedical
Sciences, University of
Teramo, Italy
Tel: +39 (0) 861 266870
Fax: +39 (0) 861 266873
E-mail address:
22
follows: (I) resistance present if FECR <90% and the lower 95% confidence limit
(LCL) <90%, (II) resistance suspected if FECR 90% and/or LCL <90% and (III) no
resistance if FECR 90% and LCL >90%. Post-treatment larval cultures from each
yard were performed from pooled faecal samples collected from each treatment
group and, after incubation, third-stage larvae were collected and identified.
FBZ was excluded in 22 yards (10, 5, 7 from Italy, UK, Germany respectively),
where a smaller number of horses was available; all four compounds were
evaluated in 80 yards (50, 17 and 13 from Italy, UK, Germany respectively).
The efficacy range in individual animals was 0-100% for FBZ and PYR in each of
the three countries and for IVM in UK and Italy. In Germany IVM showed a
range of efficacy from 78.5 to 100%. MOX was 100% effective in all treated
horses from the three countries with the exception of a single horse in a yard
from Germany. Treatment with FBZ resulted in resistance present in 19 out of 50
(38%), 14 out of 17 (82.4%) and 11 out of 13 (84.6%) yards, resistance suspected
in 8 (16%), 2 (11.8%) and 0 (0%) yards and no resistance in 23 (46%), 1 (5.8%)
and 2 (15.4%) in Italy, UK and Germany, respectively. With regard to PYR,
resistance present was detected in 18 out of 60 (30%), 4 out of 22 (18.2%) and
4 out of 20 (20%) yards, resistance suspected was individuated in 17 (28.3%),
2 (9.1%) and 4 (20%) yards and no resistance in 25 (41.7%), 16 (72.7%) and 12
(60%) for Italy, UK and Germany, respectively. Treatment with IVM resulted in
resistance present in only 1 out of 60 (1.7%), 2 out of 22 (9.1%) and 0 (0%),
resistance suspected in 3 (5%), 1 (4.5%) and 1 (5%) and no resistance in 56 (93.3%),
19 (86.4) and 19 (95%) for Italy, UK and Germany, respectively. Treatment with
MOX was 100% effective in all yards examined in Italy and UK, and in all German
yards as well, with a single exception.
On farms where all four compounds were tested, the occurrence of multiple
resistance was found on 10 Italian, 5 UK and 3 German farms. Multiple resistance
always included FBZ and PYR, except for one Italian (FBZ and IVM) and two UK
(FBZ and IVM, and FBZ and PYR and suspected for IVM) yards. The microscopic
examination of the in vitro grown larvae demonstrated that they belonged
exclusively to the Cyathostominae subfamily.
This survey demonstrated that single and/or multiple anthelmintic resistance to
horse cyathostomins is present in UK, Germany and Italy, with higher prevalence
for FBZ followed by PYR, while IVM and MOX proved to be the most effective
drugs. In fact, efficacy reduction for IVM was rarely detected and highest activity
of MOX was assessed, despite a single case of reduced efficacy in Germany.
This picture is, in turn, an alarm bell ringing if one considers the important
pathogenic potential of cyathostomins at both the adult and larval stages.
Hence, given the strong impact resistant cyathostomins can have on horse
health and welfare, owners, managers and veterinary practitioners should have
active and leading roles in planning and monitoring effective and appropriate
horse nematode control programs.
This study calls for studies to explore the presence of drug resistant populations
in other European countries, to limit their expansion and to use anthelmintics
that are still effective in a manner that preserves their efficacy as long as possible.
Finally, further investigations to elucidate the susceptibility and/or resistance
status in cyathostomin populations according to their epidemiological and
biological features and use of drugs are warranted.
This study has been published: Traversa et al. 2009. Parasites & Vectors, Suppl.: ‘Equine parasites: diagnosis and control – a current perspective’, 2: S2, and reviewed in Traversa, 2010. Scientia Parasitologica, 11(1):1-6 and Traversa 2010. Parassitologia, 52 (n. 1-2), 83-86.The author is especially grateful to Albert Boeckh (Pfizer Animal Health) and expresses his gratitude to Rami Cobb, Helen Barnes, David Bartram, P. Traill, S. Hooper, T. Pollard - Fort Dodge Animal Health (USA and UK) for their collaboration on drug resistance in small strongyles in 2008-2010. The author also thanks all friends and colleagues for the productive works carried out in 2008-2009 on anthelmintic resistant cyathostomins in Italy, UK and Germany: G. von Samson-Himmelstjerna, D. Otranto, P. Milillo, R. Lia, A. Frangipane di Regalbono, S. Perrucci, P. Beraldo, J. Demeler, S. Schurmann, R. Bartolini, V.D. Tarallo, C. Basile, G. Benvenuti, M. Boschi, E. De Angelis, S. Di Maria, A. Ducci, S. Genero, G. Incastrone, R. Leone, A. Leto, G. Mazzotta, F. Pagano, F. Parente, D. Pellegrini, V. Ricci, M. Spinelli, R. Codolo.
23
Worm infections constitute a permanent threat to the health, well being
and performance of those horses having access to pasture. Nowadays the
cyathostomins or small strongyles and the ascarid Parascaris equorum, the
former and later being both gastro-intestinal nematodes species, represent the
most prevalent and significant infectious agents in horses. The control of these
worm infections to date is mainly attempted by using anthelmintic chemo-
therapeutics and to a limited extend by employing complementary worm
control procedures like stable and pasture cleaning, specific pasture and farm
management procedures. The success of the chemotherapeutic approach
has lately become more and more endangered by the appearance of worm
populations which show a reduced or even no susceptibility against the used
drugs. The currently available horse anthelmintics belong to only three classes,
each with a different mechanism of action; the benzimimidazoles (BZs), the
tetrahydropyrimidines (THP) and the macrocyclic lactones (ML). As suggested
by a recent faecal egg count reduction test (FECRT) survey in horse farms from
Italy, the UK and Germany, on average the BZs and the THPs are facing resistant
cyathostomin populations on most or at least a third, respectively, of the tested
horse farms. Too frequent usage or repeated underdosage of anthelmintics are
considered as main reasons for the selection of resistance. Further issues like
lack of quarantine treatments or certain pasture management procedures
may also contribute to the occurrence and spread of resistance. Our current
scientific knowledge on the actual effects of pasture, farm and even chemo-
therapeutic procedures on the farm prevalence of gastro-intestinal nematodes
is very limited. We therefore undertook a questionnaire survey in context with
the above mentioned FECRT survey and a thorough statistical analysis of the
combined data sets.
It was recorded that all farms involved in the study used routine/preventive
anthelmintic treatments for worm control. On none of the farms the success of
anthelmintic treatment was assessed. Reliable testing of horse weight before
dosing was performed on only less than 10% of the farms. While approx. 50% of
Italian farms stated that they use pasture cleaning only, less than a quarter of
the UK or German farms did so. However, neither for the Italian nor the UK or
German data an effect on strongyle prevalence by pasture cleaning was
seen. When the effect of treatment frequency was examined it was found that
in adult horses higher treatment frequencies correlated with a statistically
significant reduced stronglye infection risk. On farms performing more than one
annual treatment, faecal samples were significantly less often positive. The
comparison of FECR data from individual horses with their pre-treatment faecal
egg counts (FEC) showed that high pre-treatment FEC were associated with
a significantly higher probability for a FECR below 90%. This observation and
the consistent finding of younger horses being more often strongyle positive,
as well as showing higher FECs, suggests for a focus on horses showing high
pre-treatment FEC when monitoring anthelmintic treatment efficacy in the field.
Cyathostomin resistance trial – survey findings
Georg von Samson-Himmelstjerna Director or the Institute of
Parasitology and Tropical
Veterinary Medicine,
Freie Universität Berlin,
Germany
24
Anthelmintic resistance threatens the current and future control of parasites of
horses. In particular the cyathostomes, the primary parasitic pathogen of horses,
have a great propensity to develop resistance to the commonly used drugs.
The worldwide prevalence of resistance to each of the three anthelmintic
classes, the benzimidazoles (BZs), the tetrahydropyrimidines (PYR) and the
macrocyclic lactones, ivermectin (IVM) and moxidectin (MOX), in cyathostome
populations is not known. However resistance is evident for some drugs e.g BZs
whilst for others e.g IVM and MOX it is still emerging.
Resistance monitoring in cyathostome populations is not common practice but
it is essential to establish the efficacy of a given anthelmintic, particularly if the
same drug has been given frequently and repeatedly. There are diagnostic
tools in development to assist in identifying resistant parasites and monitoring
resistance in the field however, to date, the most accessible and practical tool
remains the faecal egg count reduction test (FECRT). The practicalities of the
FECRT, sample collection and interpretation of data are discussed and key issues
are highlighted. The phenomenon of anthelmintic resistance is outlined as are
some of the important issues of resistant parasites and factors predisposing to
their selection.
Sustainable control of parasites in horses is an achievable goal that relies on a
sound knowledge of parasite epidemiology combined with an understanding
of the efficacy of anthelmintic drugs to employ them strategically against
parasite species and stage. The underlying principle of using faecal egg counts
(FECs) during the peak period of parasite transmission in order to identify the
minority of horses contributing the most to pasture contamination is discussed
in the context of cyathostomes. The ability to use this information to allow
targeted treatments to those individual animals responsible for the majority of
parasite transmission is highlighted. The benefits this delivers in terms of reducing
parasite transmission by reducing levels of pasture contamination are presented,
whilst the ability to reduce the frequency of anthelmintic treatment via strategic
control programmes demonstrates how to prolong the effective life of the drugs
and reduce the selection pressure for resistance. The balance that is necessary
to apply drugs strategically whilst avoiding clinical disease is acknowledged as
is the need to support sustainable parasite control with appropriate monitoring
and diagnostic tools, not least resistance monitoring, as ultimately strategic,
sustainable programmes will only be successful if effective drugs are employed.
Resistance monitoring and Sustainable Parasite Control
Jane E Hodgkinson University of Liverpool, UK
25
Safe and effective chemical restraint of horses is an important tool for all
equine practitioners. Often a clinician will have several recipes (or maybe just
one!) that they use on most of their patients. The first part of this presentation is
designed to demonstrate the variety of approaches and drug combinations
that are possible, and give guidelines for the more challenging cases.
Prior to sedating a horse, consideration should be given to any underlying
pathology and the environment and degree of stimulation the horse may
experience during the procedure. Temperament of the horse will also affect
the approach to sedation. It should be borne in mind that most sedative drugs
can also be used as premedicant drugs, and it is often just the dose that differs.
All sedative drugs should be given in a quiet environment to ensure efficacy.
The horse should not be aroused or stimulated ideally for 20 minutes following
sedation. It must also be remembered that despite a horse appearing well
sedated they can still respond in an unexpected manner.
The most commonly used phenothiazine is acepromazine and this is a useful
anxiolytic and tranquilliser that can calm a nervous horse without causing
excessive ataxia or drowsiness. The drug can be administered intramuscularly
or intravenously and oral formulations are also useful. Peak effect is often slow
irrespective of the route of administration. Caution should be exercised with its
use in breeding stallions as occasionally priapism or paraphimosis can occur.
Acepromazine can be combined with many other drugs to improve the
degree of chemical restraint. Acepromazine should be avoided in hypo-
volaemic horses.
Alpha 2 adrenoceptor agonists represent the most commonly used class of drug
for providing sedation. These drugs provide a rapid onset of action following
intravenous administration and horse will become profoundly sedated and
adopt a wide based stance with a lowered head. The ataxia can be marked.
The most commonly used alpha 2 agonists in equids are detomidine, romifidine
and xylazine. The newer more alpha 2 selective drugs (medetomidine and
dexmedetomidine) are currently being trialled in some European countries.
These latter drugs are currently only licensed for small animals. It is possible to
administer infusions of the alpha 2 agonists during anaesthesia (some have
MAC reducing capabilities), or for standing sedation. Alpha 2 agonists are very
versatile drugs and can be combined with acepromazine, opioids, benzo-
diazepines, ketamine/tiletamine and guaiphenesin. The alpha 2 antagonist
atipamazole can be used if inadvertent overdose has occurred. Alpha 2
agonists are also useful in the recovery period after anaesthesia and are given
in small increments (im) smoothing and improving the quality of recovery.
Recently detomidine has been licensed as an oral paste.
The opioids represent an important tool in equine sedation/analgesia and are
most frequently combined with acepromazine or the alpha 2 agonists. Opioids
given alone to horses can in some situations cause excitement and stimulation,
but given in combination with other drugs represent an essential drug class for
sedation and analgesia.
The benzodiazepines are not routinely used in adult horses because of the
ataxia they cause from weakness, however in foals the benzodiazepines can
be a useful tool for non painful diagnostics such as imaging.
Equine sedation and standing surgical anaesthesia (SSA)
Kate L White MA Vet MB DVA
Dipl ECVAA MRCVS
European Specialist in
Veterinary Anaesthesia
& Analgesia
26
With more and more procedures being done in standing horses (e.g. laparo-
scopy) the necessity has arisen for standing surgical anaesthesia (SSA). The
challenge is to provide a safe environment for the surgeon to work in and
produce minimal ataxia. SSA avoids some of the problems associated with
general anaesthesia and is in general safer for the horse. There may be more
risk however to the surgeon in these cases. Local anaesthetic techniques are
essential in conjunction with standing chemical restraint to ensure safety and
efficacy. This second part of the presentation will focus on the approach to SSA.
Drugs used in SSA
As with many things in equine anaesthesia, success is often multifactorial rather
than being solely dependent on the drug that was used. The drugs used are
similar to those used for sedation, but are often administered in increments or
as infusions.
Acepromazine is a useful drug that augments the effects of other sedative
agents, and if there is no contraindication to its use it is an economical drug to
minimise side-effects and lower dosages of subsequent drugs. The main drug
recipes for SSA focus on the alpha 2 agonist drugs. However these drugs should
not be relied upon alone for analgesia and a multimodal approach should be
adopted. The consensus is that the alpha 2 agonists provide better visceral
rather than somatic analgesia. In combination with alpha 2 agonists, local
anaesthesia is strongly advised. Examples of protocols using increments and
infusions will be given during the presentation.
27
For further information please contact
Pfizer Animal Health Europe,
23-25 Avenue du Dr Lannelongue,
F-75668 Paris Cedex 14, France
P +33 (0) 158 07 50 01
F +33 (0) 158 07 51 78
www.pfizerah.com