Parasitology Today, vol. I, no. 6, I985

coati-mundl (Nasua n&a) irl Costa Rica”, and marmosets (Saguinus mystax) from Iquitos, Peru’*, were also found naturally Infected.

These data suggest that AngiostrongyIus is widely prevalent providing many op- portunities for humans to become in- fected.

Parasitological diagnosis i!; very difficult because first stage larvae are not found in human stools. Instead, a higklly specific and sensitive serological test t-as been de- veloped using a suspension of polystyrene beads (averaging 0.3 pm In diameter) sen- sitized with an antigen o>tained from lyophilized worms. The test involves mix- ing one drop of the reagent with one drop of inactivated serum. By this method, IO4 cases were diagnosed in 1983 in Costa Rica. In I984 this figure reached 308, giving an approximate rate of 12 cases per IO0 000 inhabitants. This exceeds the pre-

valence of tuberculosis and other com- municable diseases in our country, and represents only those case; already sus- pected by physicians that are aware of the problem. But such physicians represent

only about 15% of the medical population of our country!

Outside Costa Rica, almost all cases of angiostrongyliasis were diagnosed in surgi- cal specimens, and few cases have been reported. Yet we do not believe that Costa Rica has such special environmental conditions to explain the huge apparent difference between our recorded preva- lence and that of our neighbouring coun- tries. More likely the apparent distributron of angiostrongyliasis is determined by awareness of the problem by the medical profession. If this is so, our figures repre-

sent ‘just the tip of the iceberg’.

Pedro Morero is Profeaor ofMedico Poros,tology ot the School of Medrcine. University of Costa Rica, PO Box 2 I I 7, Son Jose, Costa &a

References I Morera, P. and Ckspedes, R. (197 I) Acta

Medico Cmtarricense 14, I 59-I 73 2 Agostin~. A.E. et al. (1983) Rewsta AMRJGS

(Porte Akgre) 27,20&203 3 Barbosa. H. et al. (I 980) Rev da Asoc~lcac

Medico Brasileira 26, I78 4 Sauerbrey. M. (I 977)Am.J. lrw. Med. Hyg. 26,

115~1158

5

6

7

8

9

IO

I I

I2

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14

I5

16

I7

18

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Zambrano. Z. (I 973) Revm Latrnaamericana de Patalagra 12, 43-50

Zavala, 1, et al. ( 1974) Rewsta de Investi@xr6n Clinrca 26, 389-384

Z~l~otto, A. et of. (I 975) Rewsta do Insotuta de Mediona Jrqcal (Sao Pa&j 17. 3 12-3 I8

Ztifilga, S.R. Cardona-L+ez, V. and Alvarado, D. ( 1983) Revsto M&ka Hondureria 5 I, 184 192

Morera P. (1970) Boletrn Chileno de Parasrtolog!a 25, 133-l 34 Morera. P.. and Ash, L.R. (I 970) @&tin Chrleno de Parosrtologra 25, I35

Morera, P.. Arroyo. R. and Solano, E. (I 97 I) Rewsta de &ologra Traplcal (Costa Rica) 25.257- 261 Morera, P. (I 973) Am. 1. Trap. Med Hyg. 22, 613421

Robles, G. et a/. ( 1968) Revrsta Mkka del Has- pital de Nifios (Costa Rica) 3.67-80

Lona-Co&s, Rand Lobe-Sanahuja J.F. (I 98Oj Am. /. Trap. Med HE. 29,538-544 Moiera, P. et al. (I &32) Am. J. Trap. Med. Hyg 3 I, 67-70

RUIZ, P. and Morera. P. (I 983)&j. Trap Med Hyg. 32, 145% I459

Mange, E. Arroyo, R and Wax, E. (1978) / Poraxtol 64 34

Sly, D.L et al (1982) Lab. Anrm. So 32, 286 288

Heartwater Invades the Caribbean M.]. Burridge

Heatiater, or cowdriosir, is an acute tickborne disease of ruminants which is attracting considerable atterition due to its alarming spread from Africa. to the Carib- bean, where Amblyommo vcrriegotum is an effective vector. The disease is caused by infedion with the rickettsia Cow&a ruminant&m.

In Africa, heartwater is usually a mild or subclinical disease in local indigenous stock, but acute disease - leading IO convulsions and death - is more typical when suscept- ible ruminants are imported into endemic areas or when the Infection is introduced to previously uninfected regions.

Heartwater has been reported from many countries in Africa south of the Sahara, but in most areas little IS known about the prevalence of infection or dis- ease because of the dificully of diagnosis and the lack of a satisfactory serodiagnostic test. In 1980, heartwater was diagnosed in Guadeloupe’, the first confirmation of the disease outside the African continent. Since then, heartwater has been con- firmed on two other Caribbean islands, Marie Galante and Antigua3 (Fig. I). It is most likely that C. ruminantilm was intro- duced into the Caribbean by ticks infesting cattle imported from West Africa2. Cattle, sheep, goats, and water buffalo are sus- ceptible to C. ruminantium infection. Some wild ruminant species, including antelope

and deer, are susceptible to experimental infection, with natural fata cases of heart- water seen in springbok (Antidorcas mar- supia/is) and eland (Jaurotragus oryx)4.

Great differences in susceptibility occur between different populations of domes- tic ruminants. These differences seem not to be associated with any particular breed or species but rather depend upon pre- sence or absence of resistance acquired thrbugh long natural selection. Con- sequently, in a heartwater-endemic area mortality rates are usually high in imported exotic stock, with losses of up to 60% in cattle and up to 90% in small ruminants, whereas losses in local stock are usually 1~s than 10%. Young calves and lambs possess some resistance to infection which is independent of the immune status ofthe dam: this resistance is not absolute and is shot-t-lived, lasting up to four weeks in calves and one week in lambs.

Recently, four South African strains of C. ruminantium were serially passaged in mice=. The Kumm strain kllled mice in I C- I4 days when given intraperitoneally5,

whereas the Kwanyanga, Nonile and Welgevonden strains killed mice consis- tently only when given intravenousI+,@ No loss of pathogenicity for mice occur- red with any of the mouse-infective St- rains, even after up to I20 serial passages. Intravenous inoculation of spleen or liver

homogenates from infected mice into sheep caused acute or fatal heartwater in the ruminants.

Transmission

C. rumlnantium is transmitted only by ticks of the genus Amblyomma. The natural vectors are A. gemma, A. hebraeum, A. lepidum, A. pomposum and A. variegatum in Africa, and A. variegatum alone in the Caribbean‘+. Six other species have been shown to be experimental vectors: A. astrion, A. cohaerens, A. spanum and A. tholloni from Africa, and A. cajennense and A. maculatum from the western hemis- phere? Two ofthe mouse-infective strains of C. ruminantium (Kumm and Kwanyanga) have been shown to be transmissible by A. hebraeum‘? All transmission IS trans- stadial.

Infection rates in wild tick populations tend to be low, and in heartwater- endemic areas susceptible ruminants may escape infection for a long period. Factors that limit the tick infection rate include the absence of transovarial transmission and their indiscrimlnate feeding behaviour, especially tn the immature stages which commonly feed on animals not susceptible to C. ruminant/urn infection. Ticks infected as larvae can transmit C. ruminant/urn as nymphs or on occasion, as adults, even

176 Parasitology Today, vol. 1, no. 6. I985

Table I. Occurrence of Amblmmma variepatum ticks, Cowdrio ruminantium, and acute bovine dermatopilosis in the eastern Caribbean

Islands Presence of: A. variegawm* C. ruminontium acute bovine

Puerto Rico Vieques US Virgin Islands British Virgin Islands Anguilla St Maarten/St Martin St Barthklemy Saba St Eustatius St Kii Nevis Barbuda Antigua Montserrat Guadeloupe La Desirade Marie Galante Les Saintes Dominica Martinique St Lucia Barbados St Vincent 81 The Grenadines Carriacou

+ + - - I? + - + 2 + +

+ + + + + -

+ + + k

- - - -

- - - + - +

+ - -

- -

dermatophilosis + + - -

+ +

+ + + + +

+ + + -

-

PllERTD RICO - s*an, St EU!3$T;y+

QARBUDA

NEWS e,ANTIOUA b YDNTSERRAT

CARIBBEAN SEA

B”AOELOW& *LA DESlRAce

&MARIE GALANTE

0 WMINICA ATLANTIC

Q

OCEAN MARTINIQUE

0 ST. LUCIA

ST. VINCENTO %

(pARSADDS

: e

QGRENADA 0

TRINIDAD

Fig. I. Map ofthe eastern Caribbean; underlined names are those ofislands on which hearlwater is known to occur

- = Wks absent f = occasional tick found; + = tick established.

after the nymphal ticks have fed on a non- susceptible host Ticks can remain infected for long periods, with infection surviving in adults for at least I5 months.

Once a tick has ingested infected blood, C. ruminontium invades epithelial cells of the intestine where it multiplies, especially after the tick has mouthed and resumed feeding. Infection then spills over into the lumen of the tick gut from where it is regurgitated, infecting the ruminant host Within the host the ricketiial organisms are found in closely-packed colonies inside the membrane-lined vacuoles in the cytoplasm of vascular endothelial cells, especially those in capillaries of the brain cortex. The rickettsiae also occur in cir- culating blood although the exact cell types infected remain to be determined.

Clinical Findings

The incubation period after natural transmission by ticks ranges between one and five weeks, with a mean of about two weeks. The acute disease is manifested clinically by a sudden rise in temperature to over 40°C. In the majorii of cases, the onset offever is followed within a few days by nervous symptoms, ranging from twitching of muscles and hypersensitivity to touch, to staggering, circling, and aggres- sive behaviour in cattle. Once nervous symptoms appear, the disease normally progresses rapidly and the animal col- lapses with fits and convulsions occurring prior to death. In some bovine cases, the

major symptom of disease may be a pro- fuse haemorrhagic diarrhoea. Respiratory involvement is common, with an increase in respiration rate and bronchial rales frequently evident. Peracute disease is seen particularly in cattle and goats, and is manifested by sudden collapse with con- vulsions and rapid death.

The most common gross lesions seen at necropsy are pulmonary oedema with froth in the trachea and bronchi, hydro- pericardium (hence the name heartwater for the disease), hydrothorax, and ascites. Other frequently seen lesions are petechiae and haemorrhages in various mucosae and serous membranes, and enteritis, sometimes haemorrhagic, espec- ially in cattle. In peracute cases, pulmonary oedema is often the only gross lesion evident.

Diagnosis and Treatment

At present, a definitive diagnosis of heattwater can be made only by demonstration of C. ruminontium or- ganisms in Giemsa-stained smears of brain biopsy material. This diagnostic method has been used for many years on post mortem brain material, but it was only re- cently modified for use in the live anima19. An indirect fluorescent antibody test and an enzyme-linked immunosorbent assay have been developed for heartwaterlO,l I, but their value in field diagnosis remains to be determined.

The tetracyclines are the most active

drugs against C. ruminontium. However, treatment with tetracyclines is usually un- successful once clinical symptoms other than fever have developed, and therapy is rarely possible under field conditions.

Immunity

All strains of C. ruminantium so far examined appear to be completely cross- protdve, with the exception of three of the mouse-infective strains (Kumm, Kwanyanga, and Nonile) from South Africa4. In experiments with sheep, little or no cross-immunity was found between the Kumm strain and the standard Ball 3 strains, whereas there was an inter- mediate degree of cross-immunity between the other two mouse-infective strains and the Ball 3 strair-67. In cross- immunity tests in mice between the Kumm and Kwanyanga strains, the only evidence of any cross-protection was an increase in the mean survival time on heterologous challenge6

The nature and mechanism of immunity to heartwater are unknown. Data on duration of immunity after recovery from heartwater are inconsistent and indicate a need for further studies.

Prevention and Control

The control of heartwater in Africa has relied on control of its tick vectors by dip- ping or spraying domestic ruminants with acaricides. This has proved a difficult task

Parasitology Today, vol. 1, no. 6, I985

because Amblyomma are three-host ticks which can survive on many wild and domestic animal species. To be successful, tick control by dipping or spraying re- quires regular and continuclus application of acaricides, which is an expensive under- taking especially in economically develop- ing countries. Breakdowns In tick control programmes can have disastrous results as, for example, in Zimbabwe during the 1970s when the dipping service collapsed, resulting in the loss of one rnillion head of cattle (or nearly 20% of the national herd) from heat-twater and other tickborne dis- eases12. It has since been argued that con- trol of tickborne diseases in southern, Africa would be safer and more cost- effective if it was based on integrated con- trol strategies utilizing host immunity ratherthan on intensive use Iof acaricides13.

The situation in the Caritlbean is some- what different It may be possible to eradi- cate heartwater from the Caribbean by elimination ofthe vector A. rariegatum, be- cause this tick has a limited distribution in the Caribbean and few wildlife species are present in the region to act as alternative hosts for the tick. An added incentive for an A. variegotum eradication programme would be to rid the Caribbean of acute bovine dermatophilosis, a severe bacterial disease causing major economic losses to

cattle production that is only experienced in herds infested with A. variegatum ticks (Table I)‘?

Attempts to immunize ruminants against heattwater have met with only very limited success. Animals have been immunized by intravenous injection with blood infected with C. ruminant&m, fol- lowed by treatment with tetracyclines at the beginning of the febrile response4,Js. Results with this so-called ‘infection and treatment’ method of immunization have been inconsistent, with some mortality and some breakdowns of immunity. Furthermore, the method is expensive, laborious and time-consuming, and it re- quires relatively sophisticated laboratory faolities and technical skills. Acceptable methods of immunization against heart- water on a herd basis are not available. However, they may soon be developed following recent successful in-vitro cuttivation of C. rummantiumlb.

Michael J Burridge is director of the Centre for Jropcd Animal Health, College of Vetennory Medrcine, Unrvenity offlorida. GamewIle, Florida 326 IO, USA.

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MPdecrne Wt&noire des Pays Trop~coux 33,

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Uilenberg, G. et al. (I 984) Preventwe Vet Med.

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Blrnle. E.F. et al. ( 1985) Vet Rec. I 16, I 2 I - I23

Uilenberg, G. (I 983) Adv. Vet. Ser. Camp Med. 27,427480

du Plessls. J.L. and Kumm, N.A.L. (I 97 I)]. 5. Afr.

Vet. Assoc. 42,2 17-22 I

Mackewe. P.K.I. and van Rooyen. RE. (I 98 I)

I” Tuck B~ofo~ and Control (Whitehead, G.B..

Glbsxx. J.D. eds). pp. 33-39, Tick Research

Unit. Rhodes Unwewty, Grahamstown, South

Afnca

Mackenzie. P.K.I. and McHardy. N. (I 984) Pre-

ventwe Vet Med. 2,227-237

du Plessls, J.L. (I 985) Onderstepoort/. Vet. Res.

52,55&l

Synge, B.A. ( 1978) Trap. Anrm. Hwhh Prod. IO,

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du Plessis, J.L. ( I98 I ) I” Tick 810&y and Control

(Whrtehead, G.B. and Gibson, J.D. eds). pp.

47-52. Tick Research Unit. Rhodes Unlverslty.

Graharnstown, SC&I Afrtca

V~l~oen. G.L. et al. (I 986) Ondentepoort] Vet.

Res. (I” press)

Lawrence, ].A., Fomn, C.M.M. and NorvaIl,

RA.1. (I 980) Vet Rec. 107.82-85

Norval, RA.I. (I 983) Lmbobwe Vet.]. 14. l9-

25

Burndge, M.J. et al. (I 984) in Proceedings of

Xllfth World Congrea on &eases ofCattle (Vol.

I). pp. 542-546, South African Veterinary As-

soc~at~on. Pretoria, Soti Africa

du PIesIs, J.L.. Jansen, B.C. and Prozesky, L.

(I 983) OnderstepoortJ. Vet. Res. 50, I 37-l 43

Bezutdenhcwt I.D., Paterson, CL. and Barnard,

B.J.H. (I 985) Ondentepoort]. Vet Res 52, I I3-

120

Airport Malaria and Jumbo Vector Control

G.B. White

Among passengers leav ng London’s Heathrow airport on the evening of Satur- day I I th June I983 for holidays in Italy were Miss EM of Neasden and Mrs LB of Durham. To this day they have not met each other, but both developed almost fatal Infections of Plasmodi~m folciparum malaria within 2 weeks of travelling on the same flight from London to Rome’. Neither of them had ever visited a malari- ous country. Their malaria could not have originated from Italy where the disease was eradicated In the l95Os, and malaria died out in Britain during the 1920~2. But the plane on which they went to Rome was operated by EthIopiai? Alrlines and had left Africa the previous day. Presuma- bly malana was transmitted to the women on board by the bites of one or more in- fective ‘stow-away’ Anophe;es mosquitoes from Africa.

Since I970 when long-h.wl ‘jumbo jets’ were Introduced, at least 23 cases of ‘air- port malaria’ have been detected3,4, meaning InfectIons in people who have not

been to an endemic area but who have contracted malaria in the environs of an airport with the source of infection attri- buted to tropical mosquito vectors arriv- Ing in aeroplanes. To prevent such insects escaping alive from planes unloading at Charles de Gaulle airport, Pans, the en- closed passageways for people and bag- gage have been regularly treated with re- sidual insetiicidess. Unfortunately, the ever-Increasing volume and speed of air traffic gives rise to more opportunities for accidential transportation and introduction of various agricultural pests as well as med- ically important mosquitoesb, so that planes themselves can be viewed as ‘jumbo vectors’. It has even been suggested that discharge of toilet effluent at high altitude may disseminate dysentenc diseases such as choleraT.

The world-wide number of alr-travel- let-s on scheduled flights (i.e. excluding cargo and charters) has surpassed ICOO millions annually during the I98Os, with ris- ing proportlons of passengers from

warmer countries where parasitic diseases are more prevalent8. The affluence of many hot tslamlc countries, for example, gives rise to many pilgrims to Mecca carry- ing microfilariae of Wuchereria bancroft; transmissible by Culev pipiens in Saudi Arabia where Bancroftian filariasis has not been endemic (A.M. Amin, unpublished). Comprehenslve records on diagnosis of imported infections are kept by few coun- tries. Those available for Britain show ap- proximately 2000 cases of imported malaria annually since I 9784,9, with re- cently aroused interest in how Ascaris lum- brrcofdes is being imported and transmitted autochthonously’o. . In order to limit the spread of com-

municable diseases such as yellow fever and formerly smallpox, the International Health Regulatlonsl2 make specific Im- munizatlons mandatory for certain categories of International travellers. Also, to prevent unintentional transportation of vectors or other pests, Annex VI of the Regulations describes dislnsection proce-