Tick-Borne Diseases

TICK-BORNE DISEASES by R.E. Purnell Agricultural Research Council Institute for Research on Animal Diseases, Compton, Newbury, Berks.

INTRODUCTION If you are concerned because the reindeer which you herd on the edge of the Siberian taiga or the camels which you graze at oases in the Sahara desert are feverish and anaemic , you should be aware that they may have contracted a tick-borne disease . Alternatively, your responsibility may be for some of the 1000 million cattle in the world , which have a three to one chance of being infected by tick-borne pathogens . Tick-borne disease is thus one of the major problems facing the world livestock industry, second only perhaps to sleeping-sickness . In 1975, the FAO proposed that global programmes for the control of tick -borne diseases of livestock should be established within 20 years . Success of this programme will depend on transfer of information from scattered groups of research scientists. so that their results can be translated into positive action .

LIFE CYCLES Piroplasms and rickettsiae are transmitted by ticks of the order Ixodoidea , the hard ticks. There are four stages in the life cycle of such ticks . Adults. They feed and mate on the host, after which the engorged female drops to the ground and lays eggs . Eggs. Each female lays 1000 to 5000 eggs. Larvae. Each egg hatches to a larva , which actively seeks a new host by climbing a grass stem in order to increase the possibility of contact with a potential host. Once on the host , the larva feeds , engorges and then moults to a nymph , either in situ or on the ground . Nymphs. The emerged nymph either attaches itself to the same host or finds a new host. It then feeds . engorges and moults to an adult , either in situ or on the ground . Ticks may have one, two or three hosts during their life cycle. One-host ticks. e.g. Boophilus spp. undergo both their larval and nymphal moults on the same host. Two-host ticks. e.g . several Hyalomma spp. undergo their larval moult on the host, but their nymphal moult occurs on the ground . Three-host ticks. e.g. most Rhipicephalus spp . (Fig . 1). undergo both moults on the ground , each stage seeking a new host.

This paper is designed to bring attention to the hazard that animals face from tick -borne diseases , to suggest up-to-date diagnostic procedures and , finally , to discuss the latest methods of prevention .

TICK-BORNE DISEASES CLASSIFICATION Tick-borne pathogens may be classified into three main groups : Piroplasms Identifiable in th e red blood cells of the host. Babesia - divide in red blood cells. Theileria - divide principally in wh ite blood cells. Rickettsiae Anaplasma - fou nd in red blood ce lls. Cytoecetes - found in white blood cells. Cowdria - found in brain capil laries. Viruses Found in, or associated with, a variety of organs, they are outside the scope of this paper.

Fig . 1. Ixodes ricinus : vector of several ti ckborne disease agents in Europe, e.g. Babesia divergens. It is a three-host tick which undergoes both moults on the ground, each stage seeking a new host.

TRANSMISSION Piroplasma and rickettsiae pass to ticks during their blood meal on infected animals. There are two method s of transmission : Trans-ovarial transm ission, as seen in Babesia spp. and rickettsiae, is when a female tick picks up th e parasite, lays her eggs and the hatched larvae transmit the disease to a new host during feeding. Trans-stadial transmission , as seen in Theileria spp . and rickettsiae , is when larvae pick up th e parasite and moulted nymphs transmit the disease to a new host, or when nymphs pick up the parasite and moulted adults transmit th e disease. 22 1

222

BRITI H V TE RI ARY JOU R AL, 137,2 TABLE I TICK-BORNE PIROPLASMS AND RICKETTSIAE OF CATTLE

B. bigemina B. bovis B. major

Babesia

B. divergens B. jakimovi Piroplasms

T. annulata

T. sergenti T. parva

Theileria

T. lawrencei T. mutans Anaplasma marginale Cowdria ruminantium Rickettsiae

Cytoecetes phagocytophila Cytoecetes ondiri

TICK-BORNE DISEASES OF CATTLE

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Much research has been carried out on tick -borne diseases of cattle since the first recorded outbreaks of babesiosis occurred in 1880-81 , near Darwin, Australia . During the following 10 years, the disease which had originated in Indonesia, moved eastwards, so that by 1900, babesiosis had killed millions of cattle including over three million in Queensland, Australia.

BIGEMINA IN NIGERIAN CATTl.E

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The tick-borne blood parasites of cattle are listed in Table I.

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Piroplasms DISEASES CAUSED BY BAB ESIA SPP. Piroplasms of the family Babesiidae are responsible for babesiosis, also known as redwater. This disease is an enormous problem in the tropics, where ticks have an ideal climate for rapid development and often have a wide variety of wild animal reservoirs. Although there is a lower incidence of the disease in temperate countries, it is still a problem in so far as animal movement between tick-infested and tick-free zones has to be restricted.

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Fig . 2. Babesia bigemina : forms seen in red blood cells of infected cattle. :

The main Babesia species afflicting cattle are: Tropical and sub-tropical B. bigemina, B. bovis Temperate regions B. major B. divergens Siberia B. (= Piroplasma) jakimovi

Babesia bigemina Description. This large species , whose piroplasms are longer than half the width of a red blood cell , is usually seen in blood smears as double pear-shaped forms , connected at the narrow end (Fig . 2) .

DISTRIBUTION

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TI CK -BO RNE DI SEA SES Distribution . It is not considered to be such an important pathogen as B. bovis, at least in Australia, but virulent forms exist in Africa and South America. where it often occurs together with other tick-borne pathogens , causing synergistic pathogenicty. Fig . 3 shows the areas of the world where cattle are at risk from redwater caused by B. bigemina.

haemoglobinuria , this species also causes cerebral babesiosis. This results from the tendency of infected erythrocytes to clump, thus blocking the capillary blood vessels of the cerebral cortex . This can be clearly seen in stained squashes of brain tissue (Fig . 5). Distribution.

See Fig . 6.

Vectors. In Central and South America, Asia and Eastern Australia , the vector species concerned is the one-host tick Boophilus microplus , found in the neck and brisket and in the axillae . In Africa , the vector is the one-host tick , Boophilus decoloratus .

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Description . This is a small Babesia , whose piroplasms are less than half the width of a red blood cell ; round or oval single forms are often seen in blood smears (Fig . 4) .

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Vectors. In Central and South Am erica, Asia and Eastern Australia the vector is Boophilus microplus; in Africa the vector is Boophilus decoloratus. Babesia major Description . Babesia major (Fig. 7), although apparently rare and non -pathogenic , becomes virulent on syringe passage in splenectomized calves.

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Babesia major in infected red blood cells.

Distribution. Found in small foci in coastal regions in Britain , Germany and the Netherlands. Vectors. It is transmitted by the three-host tick Haemaphysalis punctata (Fig . 8) .

BRIT ISH VETE RI ARY JO U R AL , 137,2 Distribution. Fig. 10 clearly shows that B. divergens is of greatest importance to European farmers . Vectors. The vector of B. divergens is the three-host tick, Ixodes ricinus , the sheep tick (Fig . 1). which is found in the axillae , on the brisket and the perineal reg ion .

Babesia(= Piroplasma) jakimovi This is a large Babesia resembling B.

Descriptio n. bigemina .

Fig. 8. Haemaphysalis punctata: vector of several tick-borne disease agents in Europe, e.g. Babesia major, Theileria sergenti.

Distributio n. This is a serious pathogen in cattle in Siberia . As the roe deer acts as a reservoir of infection , the potential exists for the disease to spread into northern Europe . Vectors. This species is transmitted by Ixodes ticks. and probably by biting fl ies.

Babesia divergens Description . This small Babesia (Fig . 9) takes a variety of forms , but early in the disease , ring-forms predominate, followed later by double pear-shaped parasites, at an obtuse angle to each other.

DISEA SES CAUSED BY THEILERIA SPP. The other family of piroplasms is the Theileriidae , which cause the death of hundreds of thousands of cattle annually.

Theileria annulata BABES4A OIVERGEN$

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Descri ption . Piroplasms can be detected in blood smears taken at the time when infected cattle begin to show loss of condition and haemoglobinuria is present . They have a variety of forms , of which the most common are round or oval (Fig. 11 ). Developmental forms (schizonts) can be identified in the white blood cells of blood obtained by needle biopsy from swollen lymph nodes (Fig . 12). Symptoms. T. annulata can cause a mortality of up to 90% in infected animals. Characteristic symptoms include fever and swollen , palpable superficial lymph

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Known d istribution of Babesia divergens.

Fig . 11. Theileria annulata: common fonns In Infected red b lood cells.

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Known distribution of Theileria sergenti.

Theileria paiva nodes. Subsequently, cattle rapidly lose condition and haemoglobinuria may occur. At post-mortem examination , the spleen and liver are enlarged , there are kidney infarcts and pulmonary oedema. Distribution . T. annulata is distributed in a broad belt of the tropical and sub-tropical zones , from Portugal . Spain and Morocco in the west, to China in the east (Fig . 13).

Description. This is the most notorious tick-borne pathogen and is the chief causative organism of East Coast fever , which causes high mortality in cattle in Africa south of the Sahara. The piroplasms are similar in size to those of T. annulata , but rod-shaped forms predominate (Fig . 15).

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Vectors. The vectors of T. annulata are two-host ticks of the genus Hyalomma , which have characteristically striped legs and are found particularly in the perineal region .

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Theileria sergenti Description . This parasite, which is larger than T. annulata , occurs in the red blood cells in a number of different forms , including both single pear-shaped and rod-shaped forms. It multiplies by division in the red blood cells. The schizonts are very difficult to detect in white blood cells. Distribution . T. sergenti often occurs in the same part of the world as T. annulata (Fig. 14), and may combine with it to cause a pathogenic syndrome . In Europe and Australia, it is not pathogenic, but in the Far East, notably Japan and Korea, and to a lesser extent in the southern USSR , it causes severe problems . Vectors. T. sergenti can be most easily distinguished from T. annulata by th e fact that it has different tick vectors, namely Haemaphysalis longicornis in the Far East and H. punctata in Eu rope.

Fig. 15.

Theileria parva in infected red blood cells.

The most pathogenic stage ofT. p arva is the schizont , which occurs in the white blood cells and part icularly in the superficial lymph nodes , which become enlarged and palpable (Fig. 16). The pathogenic effect of T. p arva is often enhanced by synergistic infections with T. la wrencei and T. mutans. Distribution. T. parva.

Fig. 17 shows the distribution of

Vectors. Transmission is via the three-host tick Rhip icephalus appendiculatus, the brown ear tick (Fig. 18).

B RI T ISH VETE RI

ARY J OU R AL . 137 .2

Theileria mutans Description . This species as only recently been differentiated from T. sergenti. It is transmissable by blood inoculation, and has large schizonts (Fig . 19) wh ich are rarely encountered in the circulating white blood cells . Although previously thought to be harmless, it has recently been shown to be pathogenic on its own account .

Fig. 16. Theileria parva: macro and microschizonts in infected lymphocytes (courtesy C.G.D. Brown).

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Fig . 19. Theileria mutans: schizont in Infected lymphocyte (courtesy of C.G.D. Brown). Distribution. T. mutans occurs mainly in Africa and in limited foci in Central and South America . Vectors. In Africa it is transmitted by Amblyomma variegatum (Fig . 20} , found in the axillae and perineal region. In Central and South America , Amblyomma cayennense is thought to be the vector. Both vectors are three -host ticks.

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Fig. 17.

Known distribution of Theileria parva.

Fig . 18. Rhipicephalus appendiculatus: vector of several tick-borne disease agents in Africa, e.g. Theileria parva.

Theileria lawrencei Description. This species, which originates from the African buffalo, has piroplasms identical to those of T. parva , but neither they nor the schizonts occur in large numbers before animals die of the infection. Distribution. The distribution of corresponds with that of T. parva.

T. lawrencei

Vectors. T. lawrencei is transmitted by the brown ear tick . R. appendiculatus , a three-host tick (Fig . 18).

Fig . 20. Amblyomma variegatum: vector of several tick-borne disease agents in Africa, e.g. Theileria mutans.

T l K -BO R E D ISEASES

227

Rickettsiae Only two of the rickettsiae have been recogn ized as causing widespread mortality in cattle. DISEASES CAU SED BY ANAPLASMA SPP. Anaplasma marginale

Description. Th is is the most important rickettsia in cattle. It is a parasite of red blood cells, in which it appears as a small , dense structure towards the cell margin (Fig. 21 ). Fig . 22. Cowdria ruminantium in brain capillary of an animal with heartwater.

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DISEASES CA USED BY CYTOECETES SPP. Fig . 21. Anaplasma marginale in infected red blood cells (courtsey of C.G.D. Brown). Symptoms.

The symptoms in animals infected with

Anaplasma are similar to those of babesiosis, and

there is a severe anaemia. Vecto rs. Since A. marginale shares tick vectors of the genus Boophilus with the two tropical cattle Babesia spp., B. bigemina and B. bovis , it often occurs with them and causes the syndrome known in Australia as tick fever.

( = Cytoecetes) are rickettsiae whose pathogenicity for cattle may well have been underestimated . They live in wh ite blood ce lls, be1ng most read ily detected in the neutrophils.

Ehrlichiae

Cytoecetes phag ocytophila

Description. C. phagocytophila (Fig. 23) looks very similar to Cyoecetes ondiri, which causes the severe disease bovine petechial feve r, in East Africa.

Although at least 20 tick species have been shown to be capable of transmitting rickettsiae, they can also be transmitted mechanically on the mouth parts of biting flies, such as horse-flies (Tabanus spp.). Cow dria ruminantium

Description. The other important pathogenic rickettsi a is Cowd ria ruminantium , the cau sative organism of heartwater. The role of this species in tick-borne disease syndromes, particularly in Africa, has so far been underestimated, primari ly because it is difficult to diagnose infection since the rickettsia does not have an identifiable blood stage. The disease is confirmed by the detection of rickettsiae in Giemsa-stained smears of brain tissue (Fig. 22), and by subinoculation of blood into a susceptible animal. Sym ptoms. Symptoms of infection are a fever and a variety of nervous signs, such as incoordination, continuous chewing movements, twitching and blinking . Unfortunately, by the time these symptoms are observed, the animal is beyond treatment. Postmortem examination shows extensive oedema, with the characteristic hydropericardium in acute cases.

Fig . 23. Cytoecetes phagocytophila in neutrophil of an animal w ith tick-borne fever.

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Sy mptoms. In some cases this rickettsia appears to accentuate redwater reactions, but it is also capable of causing anaemia, and a transient fever known as tick-borne fever. Distri bution. It commonly infects cattle in Europe, but similar organisms may be cattle pathogens in other parts of the world, particularly in Asia. Vect or. It shares with Babesia divergens the tick vector Ixodes ricinus .

229

T ICK -BOR E 01 EASES case of equine babesiosis was recorded in Australia in 1976, and sporadic cases do occur in the United States. THEIL£ I! lA OVIS IN BRrTISH SHEEP

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DISEASES CAUSED BY BABESIA SPP. Horses are infected by two species of Babesia, B. caballi and the more pathogenic B. equi.

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Distribution . and in Africa .

It is found in Europe , throughout Asia

Vectors. T. ovis has been shown to be transmitted by Rhipicephalus evertsi, the red-legged tick, which is found in the perineal region , and by Haemasyphalis punctata. Various guesses have been made about other possible vectors.

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Other Tick-Borne Pathogens in Sheep and Goats Sheep are also known to have other tick-borne pathogens wh ich are similar or identica l to those of cattle . These are Cowdria ruminantium (causes heartwater), Anaplasma ovis , and Cytoecetes

phagocytophila .

TICK-BORNE DISEASES OF HORSES The main interest in tick-borne diseases of horses has been to prevent them entering developed western countries. For example, there are very stringent checks on the movement of horses , and the serum of animals destined for the United States must be tested by the complement fixation test. Nevertheless, the first

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Babesia caballi and Babesia equi Description . B. caballi has a pear-shaped form when seen in blood smears , whereas B. equi, which is smaller, has predom inantly round forms . Division in B. equi, can be into four daughter organisms, form ing a characteristic Maltese cross (Figs. 29 and 30). Symptoms. Both species are known to occur in a pathogenic syndrome and may also be found together with Ehrlichia equi, a tick-borne rickettsia very similar to Cytoecetes phagocytophila , the cause of tickborne fever in cattle . Distribution.

Fig. 31 shows the distribution of horse

Babesia . B. equi has a wider distribution that B. caballi because it is transmitted by a variety of tick vectors. It also occurs in mules and donkeys, and the zebra acts as a wildlife reservoir of infection .

Vectors. B. equi is transmitted by a variety of tick vectors, namely, Hyalomma spp. wh ich occur at the edges of deserts, Rhipicephalus spp. from the African savannah and Dermacentor spp. (Fig . 32) from the forests of northern Europe .

BRI T ISH VET E RINARY JO URNAL. 137 .2

TICK-BORNE DISEASES OF PIGS

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Little is known about the incidence of tick -borne diseases of pigs. Although pigs in developed countries have little contact with ticks, in Italy, nonMuslim Africa and in the Far East they are less rigidly confined and can easily become infested with ticks whilst rooting through the undergrowth .

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DISEASES CAUSED BY BABESIA SPP. Two species of Babesia , B. trautmanni and B. perroncitoi, are known to infect pigs.

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Descri ption .. Both B. trautmanni and the smaller B. perroncitoi occur in a variety of forms , as shown in Figs 33 and 34 . Distrib ut ion . The geographical distribution of B. trautmanni is supposedly wider, but this may be because it is easier to see in blood smears. It has been recorded from the Soviet Union , southern Europe and various African countries . It seems likely that it will be found to be a pig pathogen throughout Africa. and that the warthog and bushpig will be shown to be signifi cant natural reservoirs . Lo L , , , , , , J Y f'jU

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Fig . 32. Dermacentor reticulatus: vector of several t ick -borne d isease agents in Europe, e.g . Babesia

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CONST RUCTING A CRUSH

Ideally, a crush should be constructed in a shady area under trees, and preferably at the corner of a paddock so that use can be made of the existing fences to drive the animal into the pre-crush enclosure. A simple crush , requires the use of 20 stout 2 metre stakes. These are arranged to form two parallel lines. one metre apart, thus enabling poles to be inserted across the crush in order to restrain the animals and separate them one from the other. The stakes in each row are connected using branches 5 to 8 em in diameter and nailed at levels of 60 em and 11 0 em above the ground. These measurements are only an approximate guide and should be varied to enable easy access to the animals ' necks and tails over the top of the side rails. At the entrance to the crush the stakes furthest from the fence are spread out to form a funnel , in order to enable animals to be driven into the pre-crush enclosure .

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Taking a blood sample and exam ining the animal

With the animal restrained in the crush , about 2 ml of blood can be drawn from its jugular vein , using either a 2 ml disposable syringe and size 25 x 0·9 mm disposable needle. The blood is transferred straight into a plastic EDTA bottle, or a 7 ml heparinized vacutainer with a fine needle. At the same time , an assistant can take the animal 's rectal temperature.

Vectors. The tick vectors of both species have not yet been proven . although circumstantial evidence suggests that they may be Rhipicephalus sanguineus .

The ears, neck, axillae and perineal region should be checked for ticks. To assist disease diagnosis, a few flat ticks should be removed and placed in a Universal, or similar, bottle for subsequent identification.

The seven major genera of ixodid ticks responsible for disease transmission are shown in Table II.

If facilities are available, or samples can be sent away for laboratory examination , blood should be taken for serum . This should either be placed in a glass Universal bottle , using a 20 ml disposable syringe and a size 32 x 1·2 mm disposable needle, or a sample of blood should be collected in a vacutainer without anticoagulant.

THE DIAGNOSIS OF TICK-BORNE DISEASES

Cattle in the tropics are likely to be infected with Babesia bovis , the parasites accumulating in the capillaries. To obtain a bead of blood with which to make a blood smear, the tail tip should be washed , clipped and then stabbed with a fine needle.

TICK VECTORS

Most of the tick-borne diseases run such a severe and rapid course, that a delay of 24 hours can make the difference between life and death. Consequently, rapid diagnosis is essential , so that treatment may commence as quickly as possible .

Diagnostic Procedures With the exception of heartwater, initial diagnosis is from a blood smear taken from the sick animal in the field . To obtain the blood smear, the sick animal should be isolated from the herd and driven into a crush .

Where theileriosis is suspected - usually evidenced by the presence of swollen lymph nodes nearest the site of attachment of infected ticks, i.e. the node behind the ear or the prescapular node - a biopsy sample should be taken. This can be done by punching a broad needle into the swollen node, then, after attaching the syringe to the needle , a small amount of lymphoid material can be withdrawn and expelled onto a glass slide and spread with the point of a needle. When making smears at the crush , clean slides should be carried in a wooden slide box , which should always be kept closed to prevent flies from attacking biopsy samples.

232

BRITISH VETERINARY JOURNAL. 137,2 If it is intended that blood spots should be sent to a diagnostic laboratory, then a few drops of blood should be used to make a spot in the middle of a 9 em

Whatmans No. 1 filter paper. When dry , the filter paper should be labelled and put into a plastic bag for transport to the laboratory.

TABLE II TICK GENERA RESPONSIBLE FOR TRANSMITTING PIROPLASMS AND RICKETTSIAE OF LIVESTOCK

Zone

Temperate

Tick genus

Ixodes

Disease agent

B. divergens

Host

Cattle

B. jakimovi

Haemaphysalis

C. phagocytophila

Cattle and sheep

T. sergenti

Cattle

B. major B. motasi

Sheep

T. ovis Dermacentor

A. marginale

Cattle

B. caballi

Horses

B. equi B. trautmanni

Pigs

B. perroncitoi

Tropical

Rhipicephalus

T. parva

Cattle

T. lawrencei

A. marginale T. ovis

Sheep

B. ovis B. equi

Horses

B. trautmanni

Pigs

B. perroncitoi Boophilus

B. bigemina

Cattle

B. bovis

A. marginale Hyalomma

Amblyomma

T. annulata

Cattle

T. hirci

Sheep and goats

B. equi

Horses

T. mutans

Cattle

C. ruminantium

Cattle and sheep

TICK-BORN E DISEASES Preparing and transporting laboratory analysis

samples

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Preparing blood samples. If blood has been taken for serum , take the serum from the clot with a pipette and place it in a labelled centrifuge tube . Balance the tubes and then spin them at 2000 rev./min for 15 min. Pipette off the clear supernate into two bijou bottles and store them in a deep freeze . If they are to be sent to a laboratory for serological diagnosis, add a drop of 1% thiomersalate. Labelling samples. It is essential that all smears and samples, including ticks, are labelled accurately and in a consistent style, so that they can be correlated with each other. A pencil should be used for labelling dry smears and a felt-tip marker pen for labelling bottles and bags. Packaging of samples. Blood or serum samples for diagnosis should be sent packed in polystyrene, preferably together with a cooler pack from a camping ice-box or with a sealed plastic bag containing ice cubes. Packed in this way, blood samples particularly in vacutainers- stay fresh for a week.

DIAGNOSTIC PROCEDURES IN THE LABORATORY

Blood can be kept overnight - preferably in a refrigerator - before being examined . Serum should be separated from the blood clot as soon as possible, but the Universal bottles can be left overnight on the bench. However, serum should not be separated and left overnight in an open tube on the bench, since it will become contaminated . Making thin blood smears Thin blood smears are made i) using slides which have been soaked in alcohol and then dried with a clean cloth . Make smears with a definite tail , as infected cells are most easily found there . ii) When the smears are dry and labelled, fix them by pouring methyl alcohol from a dropper bottle over them, and allow it to evaporate. iii) Next, stain the smears with Giemsa stain, putting the smears back to back in a glass staining dish. This stain varies a great deal , depending not only on the manufacturer but also on the batch . However, staining for 45 min with a 1:10 dilution in buffered (pH 7·2) distilled water, should prove satisfactory. iv) After 4S min, wash off the stain with cold , running water, and put the smears in a grooved wooden rack to dry. v) Examine the tail ends of the smears, using an X100 oil immersion lens for 5 min . Making thick blood smears If it is suspected that an animal is ill, even when its parasitaemia is low and no parasites are found in a thin blood smear, then a thick blood smear should be made . This can either be carried out at the crush (as in the case of B. bovis from tail-tip blood) or in the laboratory, using the EDTA blood sample.

i)

ii)

iii) iv)

233

Place a drop of blood in the centre of the slide and spread it with a needle or capillary-tube tip, so that it is just possible to see print through it. Let it dry thoroughly, but do not fix it. Briefly immerse the slide in 1% aqueous methylene blue, then stain it with 1:10 Giemsa stain for 20 min. After staining , wash the slide in cold, running water for 1 h. Examine the slide under oil-immersion , using a green filter, if possible, and look for the refractile nuclear cytoplasm of the parasite. The parasite should sparkle slightly as it goes in and out of focus.

Tissue smears Diagnosis of heartwater is very difficult and relies on brain biopsy. This can only be carried out on living animals by specialists, but the veterinarian can confinm his suspicions at post-mortem examination by means of tissue smears. The procedure is as follows: i) Place a small piece of grey matter (about the size of a matchstick) between two slides and compress firmly . Move the upper slide briskly in a zig-zag fashion from one end to the other of the lower slide . ii) Air-dry the smear and fix it in methyl alcohol before staining for 1 h in Giemsa. iii) Examine the completed smear for clusters of rickettsia associated with white cell nuclei. This technique can also be used to confinm B. bovis infection of brain capillaries. Haematology If possible , haematology should be perfonmed on blood samples. since the blood parasites genercilly cause anaemia. Ideally, however, the sample should be sent to a regional diagnostic laboratory, particularly if it is equipped with a Coulter counter. Serological tests for use in the field These are best carried out by a regional or national diagnostic laboratory capable of processing large numbers of samples routinely, and where staff are familiar with the specialized techniques.

For serological tests it is essential that: Samples of blood are clean. The serum is preserved by adding thiomersalate. The sample is sent to the laboratory as soon as possible The importance of speed in diagnosing tick-borne diseases cannot be overstressed , and for this reason simple tests are being developed which will enable the veterinary practitioner to make an assessment in the field . Test for Babesia. In America, a babesiosis card agglutination test for B. bigemina has been developed. The agglutinating antigen has been prepared from the blood of a heavily-infected splenectomized calf, and then preserved with 0·2% formalin and stained with fast green dye. The procedure is simple: One drop of this antigen and two drops of plasma or serum are mixed on a card by rotating the card for 5 min .

BRIT ISH VETE R INARY JOU R AL . 137.2

If the plasma or serum contains antibodies, then agglutiniation occurs, formi ng clumps of greenstained antigen.

th e serum, mixing it with antigen, so that it covers th e test area. iv)

In Australia, a similar test is used: Plasma is obtained by centrifuging a blood sample on a portable centrifuge . Next, a drop of seru m is added to a drop containing antigen adsorbed onto latex particles contained in a circular well, a standard serological plate or a marked square on a glass plate . If the plasma is from an animal with antibodies th e ' latex particles agglutinate.

If card s with a circular test are a are used, th e cards should be rotated on a mechanical rotator for 4 min at 100 rev ./min . If cards with teardrop test areas are used, the cards should be tilted to and fro for 4 min by hand .

v)

Read and record th e results .

Caution

The test should not be performed under extremely hot conditions. If carried out in the open, a moist chamber must be used to prevent the samples drying out.

Test for Theileria. Tests for the field diagnosis of theileriosis have not been extensively developed , ' Test for heartwater. Recently, th ere has been a preliminary report from West Africa of a capillary flocalthough a capillary tube agglutination test ofT. parva and T. mutans has been described . The crude antigen culation test for the diagnosis of heartwater. Thi s may prove to be an important breakthrough in the current is prepared by centrifugation and sonication of the efforts to control this serious disease. blood of a laboratory-infected donor animal. In use , the antigen is first thoroughly mixed in its vial and then The antigen is made from the cerebral cortices of a drop is drawn into a capillary tube and followed by the brains obtained from cattle and goats killed at the test serum . After about an hour, agglutination can be terminal phase of a laboratory infection with Cowdria observed in oblique light against a dark background ; ruminantium . These are homogenized and th en doubtful reactions may be left to develop overnight. evaporated with acetone to form a dry material , whi ch IS then ground to a powder and extracted in phosphate-buffered saline . Finally, an active fraction is dispensed into 1 ml plastic tubes, which are sealed and snap frozen to - asoc or - 196°C. The antigen is used in a test similar to the capillary agglutination test for anaplasmosis .

Fig. 35. Carrying out card agglutination test for Anap lasma (courtsey of G.G. Wagner) .

Test for Anaplasma. A rapid card agglutination test for anaplasmosis was developed in Amenca more than a decade ago, for routine field use. The antigen used is prepared by centrifugation of blood from a donor animal , followed by French pressure cell rupture and washing of the antigen pellet. Finally, 1 ml volumes of antigen are sealed in glass ampoules and stored in a refrigerator until used. Card test kits are commercially available and are used as follows (Fig. 35): i)

ii )

iii)

Attach a small rubber bulb to the capillary tube and draw up the test serum to the red line on the tube . Expel the serum onto each of the test areas of the card. Holding the antigen dispenser vertically , add a drop of antigen next to each drop of serum in each of the test areas of the card . Using a clean toothpick for each sample, spread

Other serolog ical tests There are other tests available which are superior in accuracy to the field tests described above. However their major disadvantage is that the amount oi apparatus needed for a test, such as the indirect fluorescent antibody test (IFA), wh ich is the preferred test for Theileria , is not easily portable . Consequently, the tests have to be carried out in a reg ional diagnostic laboratory, where faci lities for fluorescent microscopy ex 1st. The micro-ELISA test. In th e future, tests will most certainly be developed requ iring less and/or more compact and portable equipment. Already a test, the micro-ELISA test, is being developed which will probably succeed the IFA test. When problems relating to the specificity of antigens are resolved . this new test should prove to be more appropriate in the field situation than the IFA test, as it has the following advantages: There is no operator bias . the result being read numerically using a spectrophotom eter. There is reduced operator stress. since there is no need for an ultra-violet light source. The test is more accurate than the IFA test in whi ch doubling dilutions are used , because read ings are of the spectrophotometer are infinitely variable . The test can be carried out in the field , since the spectrophotometer can be used coupled to a car battery .

PREVENTION OF TICK- BORNE DISEASES Tick Control

lf J

Tick -borne diseases of livestock can be prevented if ticks are denied the opportunity of feeding on susceptible animals for a period of time suHicient to allow them to transmit disease . This can be achieved by the methods described below.

KEEPING STOCK PERMANENTLY INDOORS This is an easy method of preventing tick-borne diseases when , for example , imported Eu ropean animals are introduced into an area where tick-borne disease is endemic. In such cases, it is essential to make sure th at straw and hay brought into the pens is tick-free , by fumigating all fodder with , for example , methyl bromide .

I I

•

Q

"..

•

Fig . 36. Voller).

Principle of ELISA test (courtesy of A.

PREVENTING STOCK FROM COMING INTO CONTACT WITH TICKS If stock are to be grazed where ticks are known to occur, contact must be prevented , either by killing the free-living stages of the tick on the ground or by regularly treating the stock with an acaricide .

The micro-E LI SA test is simple to perform . Like the IFA test, it uses serum which is el uted from dried blood , collected in the field , on filter papers. Fig . 36 shows the procedure: i)

Add crude an tigen, prepared from infected red cells , to the plastic agglutination plates, so that it is adsorbed on to the wells.

ii)

Add a dilution of the test serum . This results in any antibody in the serum linking to the antigen .

iii)) Add the conj ugate - an enzyme-labelled antibody to immunoglobulin of the appropriate species, for example, bovine. This conjugate will attach itself to any an tibody-antigen complex formed at step ii) . iv)

Add the enzyme substrate .

v)

Using a spectrophotometer, measure the depth of colou r in the well on the plate . The rate of hydrolysis (depth of colou r) of the enzyme substrate is proportional to the amount of fixed conjugate , and thus to the amount of antibody in the test serum .

Fig. 37. A Northern Ireland pasture infested with Ixodes ricinus. Unlike certain pests which have well-defined ecological niches, such as black-fly and riverine tsetse flies , ticks exist under a variety of conditions (Figs 37) . Consequently, any attempt to eliminate the m from a particular si te, will necessitate aerial spraying over a wide area - a costly exercise. A more economical method is to at a particular time.

It is also possible to gauge if the test serum is positve, by compari son with a colou r standard . Unquestionably, the micro-ELISA oHers great hopes for the near future, particularl y for field diagnosis . It must be understood that any of th e serological tests described will, with in limits, detect antibodies wh ich may be present in serum samples. To assess the diagnostic significance of positive results, it is essential to take into account the known incidence of tick-borne disease in the area , together with the history and symptoms of th e an imals involved .

Fig . 38. An animal being dipped in acaricide (courtesy of S.M. Taylor).

BRITISH VETERINARY JOURNAL. J:\7. 2

such as when the ticks have begun active hostseeking after rain , but this is not a very practicable method of eliminating ticks .

Fig . 39. An animal going through spray-race (courtesy of Boots Pure Drug Co. Ltd.).

.When planning an installation , several important points shou ld be borne in mind : Animals must be dipped regularl y, but herdsmen are not prepared to drive their animals over long distances to be dipped . Treks of large numbers of cattle along defined pa th s hasten soi l erosion . Provided dipping can be adequately supervised , it is preferable to instal as many dips as possible in a given area, and to subsidize the cost from Government sources. A dipping bath should be strongly constructed . and be roofed to prevent dilution of the contents with rainwater and to check evaporation . It is import ant to check the streng th of the dip solution regularly . since the use of a weak dip will fail to kill ticks and encourage the development of acaricide resistance . The dip should be sited so that cattle do not have to swim to or from dipping. There must be adequate access along the length of the dip, so that animals can be easily reached . This ensures that th eir heads are properly dipped. and that they can be rescued should they get into difficulty. Before entering the dip. animals should pass through a footbath , which should measure 7 to 8 m in length and have a concrete floor with longitudinal corrugations . These corrugations assist in the removal of mud and faeces from feet , which would otherwise dirty the dip and also absorb acaricide thereby red ucing the dip strength . Spray-races

During the past 20 years, there has been a movement to replace dips with mechanical spray-races. These have many advantages . but need supervision to check that blocked nozzles and burst washers are repaired or replaced . A spray-race consists of a system of pipes fitted with spraying nozzles , fixed to a concrete base, between walls. Cattle enter and leave through stoutly-built races . The wash is drawn up from a sump and forced through the spray nozzles by means of a centrifug al pump driven by a petrol engine . electric motor or the power take-off of a tractor.

Fig. 40.

Communal cattle dip in Kenya .

Spray-races have significant advantages over dips. Spraying is safer for the animals than dipping. as there is less chance of accidental injury . It is possible to have a more accurately gauged

TREATING ANIMALS WITH ACARICIDES

This is undoubtedly the best way of preventing ticks from transmitting disease , since it not only kills ticks already attached , but prevents the attachment of ticks in the future . Traditionally, acaricides are applied as dips (Fig . 38) or sprays (Fig . 39) . Dips On a large farm , building a dip, although costly, is worthwhile , whereas stock-owners with small herds are best advised to construct a communal dip. In certain ci rcumstances , a Government-sponsored dip installation is logical , and may attract funds from International Agencies (Fig . 40).

Fig . 41. The use of a spray-lance on animals in crush in Korea .

TI C K-BOR NE DIS E AS ES concentration of acaricide, which can be freshly made up for each spray. Where a farmer finds it necessary to change from one wash to another, to cope with a particular dip problem , this can be done simply , without the expense and difficulty of discarding thousands of litres of wash . Once animals become accustomed to passing through a spray-race, it is possible to treat up to 500 head/ h. Hand-spraying Where it is impracticable to build either a dip or a spray-race, it is easy to hand-spray cattle held in a crush (Fig . 41 ). Using a spray-lance , the wash can be delivered either by using a hand-operated pump and a bucket of acaricide, or by using a mechanical pump driven by a small petrol engine or electric motor. Care should be taken to ensure that obscured sites are sprayed , particularly inside the ears and under the tai l, both favoured sites for ticks . The importance of using acaricides regularly It should be emphasized that acaricide treatment of livestock should not be carried out haphazardly , but on a regular, well -planned basis, appropriate to the local conditions. In the tropics in particular, it is very bad practice to become complacent about the dangers of ticks and to gradually increase the dipping interval. There have been many disappointed farmers whose dead cattle bear witness to a decreased vigilance . Even well -kept cattle can easily fall victim to disease introduced by ticks feeding on wild animals or on alien cattle straying through bwken fences .

In some parts of the tropics , stock requires regular weekly treatment if control measures are to be fully effective . In other parts of the world , such as East Africa , where the brown ear tick transmits East Coast fever (Theileria parva infection), animals require treatment as often as twice a week (see Fig . 42).

sufficient to treat them at an interval sufficient to reduce tick populations on the pasture, whilst dipping the exotic stock more frequently to prevent the development of disease . In contrast to the situations described above , in temperate zones it is only necessary to treat animals strategically at times when it is known that ticks are active, such as in the Spring . Recent developments in the use of acaricides Such developments include the use of PVC ear-tags, or neck or horn bands, impregnated with acaricide which is slowly released . When field-testing has been com pleted , they should prove of value in circumstances where it is difficult to use dips and spray-races . The research and development of acaricides Originally acaricides were based on arsenic, but these were superseded by the less toxic chlorinated hydrocarbons when ticks began to develop resistance . However, ticks are now becoming resistant to certain of these acaricides, necessitating the development of new and more effective forms of treatment. Research , apart from concentrating on finding new acaricides, is also being directed towards the development of such substances as juvenile hormone mimics , which will enable the life cycle of the ticks to be interrupted permanently, using toxic analogues of substances vital to their own reproduction .

Meanwhile , acaricides are being used with great success, either alone or often in combination so that they can supplement each other's potential deficiencies: An excellent combination comprises toxaphene , a chlorinated hydrocarbon with very good residual properties, and dioxathion , an organo-phosphorus that is highly effective against Boophilus ticks . In Africa , pyrethrum is grown and processed into a very good contact acaricide; recently synthetic pyrethroids have been developed . Perhaps the best of the new acaricides is amitraz NN-di-(2,4-xylyliminomethy)methylamine, a diamidide with the following major advantages : i)

It can be used safely in dip tanks or by spray application .

ii)

It is highly effective against single and multi-host ticks .

iii)

It is effective against strains of ticks resistant to other acaricides .

iv)

One of the outstanding features of amitraz is its cosmetic effect on cattle . Following treatment , feeding stages are seen to actively detach themselves , with the result that rapid clearance of the infestation is obtained .

v)

New formulations have been developed whi ch can be poured on the backs of animals and will keep them tick- free for several weeks .

vi)

Amitraz can significantly reduce tick populations when aerially sprayed .

Fig . 42. An animal in East Africa , heavily infested with Rhipicephalus appendiculatus , the brown ear tick.

In certain countries, such as Australia, where the most important tick vectors of disease are Boophilus spp., the dipping intervals can be safely extended to two to three weeks , since Boophilus ticks are one-host ticks Nhich remain on the animal for about 20 days . In parts of the world where indigenous cattle are both more tolerant of existing tick-borne diseases and less manageable than exotic imported cattle, it may be

vii) It is consi dered safe , since it is rapidly inactivated by the soil and has a very low toxicity, leaving no tissue residue .

BRITISH VETERINARY JOURNAL, 137,2

238

Vaccination There are vaccines available against all the tick-borne diseases of cattle and against many of the tick-borne diseases of other livestock. They may not be perfect, but if limitations on their use were removed millions of animals could be prevented from dying annually while the search continues for improved vaccines.

Thus, preparation and storage of the vaccine needs care, and vaccinated animals need watching, particularly in the second week after vaccination. In parts of the tropics where a severe challenge is anticipated, it may be best to give animals a booster dose of a different strain on the parasite a month after primary vaccination .

Vaccines for the prevention of specific tick-borne infections TYPES OF VACCINE Diluted blood vaccine This is the simplest vaccine, many doses of which can be prepared from the blood of a splenectomized calf artificially injected with a laboratory strain of a particular parasite. Such vaccines are currently prepared in Australia for use against Babesia bovis, Anaplasma marginale (where Anaplasma centrale provides cross-protection) and Babesia bigemina . Following the Australian lead, similar vaccines are now prepared in South Africa and in several South American countries. Whole blood vaccine On very rare occasions, the vaccination of animals using the original whole blood vaccine has resulted in problems associated with iso-immunity, notably haemolytic disease of calves produced by vaccinated cows. To minimize this risk, the Australian vaccine consists of washed infected red blood cells in a plasma-based diluent. Combined vaccines The use of a combined vaccine is invaluable when European breeds of cattle, or indeed sheep and goats, are to be introduced into an enzootic disease situation in the tropics. For example, recent experience in Trinidad has demonstrated the advantages of using indigenous strains of Babesia bigemina and Anaplasma marginale to vaccinate imported Canadian Holstein cattle. However, it was found necessary to examine blood smears of inoculated cattle on days 8 and 30 after vaccination, so that occasional untoward reactions could be controlled by chemotherapy. Susceptible cattle have also been successfully introduced into other Central and South American countries after vaccination with heterologous strains of parasites isolated in other countries and maintained before use as deep-frozen stabilates.

Vaccines against Anaplasma marginale . In several countries Anaplasma centrale has been found to give insufficient protection, while a commercially available killed vaccine (Anaplaz) has not been totally effective. However, an extended research programme at the University of Illinois in the United States has resulted in the production of a promising vaccine, consisting of Anaplasma marginale organisms which have been attenuated by irradiation and passage through a series of nonbovine hosts. This vaccine is currently being tested in a few countries, and if it proves to be a highly immunogenic but non-pathogenic strain, with a broad-spectrum of activity against strains of Anaplasma marginale, it will prove invaluable in the struggle against this very serious pathogen. Vaccines against Cowdria ruminantium . In South Africa, a vaccine is produced against Cowdria ruminantium , the other tick-borne rickettsia of cattle, sheep and goats, and the causative organism or heartwater. However, this vaccine is not an attenuated vaccine, but simply sheep blood infected with heartwater organism. Consequently, the reaction of inoculated animals has to be carefully observed and any febrile response treated with tetracycline at a· recommended dose of 8 to 10 mg/kg. If the febrile response persists, the dosage should be increased . For the vaccine to be fully effective it is essential that animals should be exposed in heartwater country within two months of infection, so that immunity can be boosted by natural challenge. Clearly, the vaccination of animals against heartwater is not without risk and should not be undertaken lightly, although , where the disease is severe, vaccination will enable animals to survive its onslaught.

Preparation and storage of vaccines Strict control of the preparation of these vaccines is essential, because the strain of parasite is live and could change its virulence, either becoming too mild to give protection or too potent. Also, recipient animals may vary in their susceptibility; a sustained febrile response or inappetance should receive prompt treatment with a drug such as amicarbalide or imidocarb.

Vaccines against Theileria annulata . In Israel, an attenuated Theileria annulata tissue culture vaccine has been developed. To produce the vaccine, Theileria-infected lymphoctyes recovered from infected animals are cultured in vitro in a monolayer. After a number of passages, the parasites become attenuated, and inoculation of 2 x 106 infected cells will confer immunity. The vaccine is frozen in the form of small pellets, each containing five to 10 vaccine doses, and is transported in small liquid nitrogen containers.

Storage of the vaccine has been a problem, since its shelf-life, even in the refrigerator, is only about a week. Recently, however, · stabilates have been cryopreserved in portable liquid nitrogen containers and used successfully in Bolivia.

In certain circumstances where animals are vaccinated before movement to an area with a severe Theileria annulata problem, immunity can be boosted by inoculation of a stabilate derived from groundinfective ticks.

TICK-BORNE DISEASES Vaccines against Theileria parva. Stabilates derived from ground-infective Rhipicephalus appendiculatus ticks form the basis of the so-called 'infection and treatment vaccine ' against Theileria parva, currently undergoing extensive field testing in Sub-Sahelian Africa. The East African Veterinary Research Organization in Kenya has devised a method of immunizing cattle with a cryopreserved tick-derived mixture of field strains of the parasite, coupled with treatment with four doses of tetracycline 5 mg/kg. Immunized cattle resist lethal challenge with strains of the parsite isolated from parts of East Africa not only geographically remote from each other, but also remote from the places of origin of the vaccinating strains. In the meantime research continues in an attempt to develop tissue culture vaccine strains of Theileria parva attenuated by irradiation or continuous passage.

Other methods of preventing tick-borne diseases It is important to remember that treatment with acaricides is not a replacement for good management, which can permanently reduce tick populations of farms. II has been demonstrated in Australia that pasture spelling can be combined with a programme of strategic dipping. This technique requires that animals are prevented from grazing on a tick-infested pasture when infective Boophilus larvae are actively hostseeking . if starved for three months or more many of the larvae will die, especially.if the climatic conditions are unfavourable. The cattle then return to the pasture but may become infested with larvae that have managed to survive . When the numbers of attached ticks reach a predetermined low level, e.g. an average of 20 female ticks on an animal's right flank , strategic dipping can reduce the number of ticks substantially. Unforunately, wild animals not only perpetuate tick populations by providing blood meals, but they also carry diseases which may be transmitted via the ticks to livestock. Furthermore, many tick-borne diseases may be passed through generations of ticks, even if they feed on non-susceptibre hosts. For these reasons, fencing of pastures is particularly important because, by keeping out game, the spread of tickborne diseases can be checked . Other aspects of good farm management which reduce tick populations include: the burning off of grass in the tropics before the new growing season ; ploughing as part of the rotation of a mixed farm ; and, in countries with temperate climates, draining and liming wetter areas of the pasture where ticks are most commonly found.

239

TREATMENT OF TICK-BORNE DISEASES Chemotherapy Although drugs are available to cure most of the tickborne diseases, treatment is often commenced too late. Successful treatment of tick-borne diseases rel ies on good management and daily observation of stock to detect the early stages of disease. DRUGS FOR THE TREATMENT· OF BABESIOSIS

Amicarbalide This is the drug of choice against babesiosis of cattle and horses: For cattle , the recommended dose is 10 mg/ kg intramuscularly, but this depends on the species of cattle Babesia involved and the stage of development of the infection. In horses, Babesia caballi is much more responsive to chemotherapy than Babesia equi. The recommended dose rate is 8·8 mg/kg given intramuscularly for two consecutive days. Unfortunately, problems can arise after successful drug treatment of Babesia infections since, if a high dose is used, the infection may be sterilized before immunity can be engendered. Consequently, drugs must be employed with care, particularly if they are used to provide chemoprophylactic control of live vaccines. Diminazene This drug has proved to be a successful chemotherapeutic agent against Babesia canis infection of dogs. Several reports have been produced demonstrating its potential value against babesiosis of sheep and goats, and against Ba{?esia caballi infection ot horses. lmidocarb As initial doubts over mammalian toxicity are resolved , imidocarb is emerging as a babesicidal drug of importance. An advantage over amicarbalide is that it can be used at a much lower dose, for example 0-4 to 2 mg/kg being the dose generally used against cattle babesias. However, more research is required to evaluate the minimum dose for use in individual situations where chemoprophylaxis or urgent chemotherapy are required. lmidocarb has been shown to be effective against Babesia caballi infection of horses when given on two consecutive days at a dosage of 2 mg/kg, but higher doses are required to eliminate Babesia equi infections. Results of a laboratory trial have indicated that imidocarb is also active against Babesia ovis infection of sheep.

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BRITISH V ETERINARY JOU RNA L. 137 . 2

DRUGS FOR THE TREATMENT OF THEILERIOSIS Although chemotherapy against Babesia spp . is effective, this is not the case with species of Theileria . Theileria annulata A variety of optimistic claims have been made for the treatment of Theileria annulata infection, but a more real istic interpretation is made by the Israelis, who state that diminazene and certain anti-malarial drugs show a selective action against the erythrocytic forms of the parasite . There are no drugs having activity against the schizonts.

Theileria parva There is guarded optimism about prospects for chemotherapeutic agents against Theileria parva . There is certainly a value in close monitoring of at-risk animals, since infections detected at an early stage, following the finding of schizonts in swollen lymph glands, can be effectively term inated with tetracyclines at a dose of 15 mg/kg for five consecutive days. A new drug , menoctone (2-hydroxy-3-(8-cyclohexyloctyl)-1.4.napthoquinone), has been shown to have a high level of anti-theileria! activity in vitro, and subsequent experimentation in artificially-infected cattle has confirmed this activity. Menoctone 5 mg/kg was given intravenously to a group of infected cattle on their first day of fever, and then at a dosage of 1 mg/kg/ day for the next five days. All the treated animals survived , wh ilst all the untreated control animals died. The anti-coccidial drug halopuginone (di-trans-7bromo-6-chloro -3-3(3-hydroxy-2-piperidyl)acetonyl 4(3H)-chinazolinon-hydrobromide) has also given encouraging results in initial laboratory trials against both T. parva and T. annulata infections in cattle.

DRUGS FOR ANAPLASMOSIS

THE

TREATMENT

OF

Oxytetracycline Treatment of cattle suffering from anaplasmosis is effective if oxytetracycline is used, but infections should be treated early, since chemotherapy may involve as many as 10 intravenous inoculations of 11 mg/kg, which could prove to be very expensive. Alternatively, oxytetracycline administered orally, at a lower dosage and for a longer period , is a regime which has proved particularly effective in eliminating the carrier state in recovering animals. lmidocarb This drug may well prove to be a less costly alternative for the treatment and chemoprophylaxis of anaplasmosis, but more critical studies need to be carried out. However, it is currently recommended in Bolivia that Anaplasma marginale infections should be treated with imidocarb at a dosage of 3 mg/kg. Since it is also highly effective against the Babesia spp. which commonly occur concurrently with infections of Anaplasma , it has much to recommend it.

DRUGSFORTHETREATMENTOFHEARnNATER Tetracyclines There is no drug known to be effective against heartwater in its later stages, although large doses of tetracycline may save suspect animals, if given at the first sign of fever.

Transfusion Since Anaplasma and Babesia are both primarily parasites of red blood cells , their most severe pathogenic effects result from anaemia. Consequently, when infection is detected late in valuable animals, it is worthwhile giving a blood transfusion at the same time as administering a chemotherapeutic drug. Blood for transfusion should be collected from the jugular vein of a healthy animal into anticoagulant, preferably acid citrate dextrose (ACD) , and stored in a refrigerator until use . Generally, with adult cattle, a minimum of 2 litres of blood should be transfused into the sick animal. It must be emphasized that all equipment used for transfusion should be clean and sterile, and the recipient animal should be given precautionary anti biotic cover (unless oxytetracycline therapy of anaplasmosis is already underway) .