East coast fever: 1. Chemoprophylactic immunization of cattle against Theileria parva (Muguga) and five theilerial strains

In one experiment, groups of cattle were immunized by chemophylaxis or therapy against Theileria parva (Muguga), and were challenged with five recently-isolated strains of Theileria. Two of the strains caused mild or inapparent reactions in the immunized animals, and three caused significant reactions. None of 25 immunized animals died on challenge, whereas 22 of 25 susceptible (non-immunized) animals died.In a second experiment, groups of cattle were immunized against five field strains using chemoprophylaxis. They had minimal reactions and were solidly immune both to isologous challenge and to subsequent challenge with T. parva (Muguga). This demonstrated that cattle could be effectively immunized against lethal challenge with several theilerial strains by inoculating them with 1 ml of an infective stabilate of the appropriate strain and the concomitant daily inoculation of 5 mg/kg of a formulation of oxytetracycline on 4 consecutive days starting on the day of infection.It is suggested that T. parva (Muguga) may be a valuable component of a polyvalent East Coast fever (ECF) vaccine in East Africa.     

East coast fever: 2. Cross-immunity trials with a Kenya strain of Theileria lawrencei

Cross-immunity trials were carried out on cattle which were immunized against theileriosis either by chemoprophylaxis or by sub-lethal challenge. In the first of two experiments, animals were immunized against either one of two strains of Theileria parva or one of two strains of Theileria lawrencei. They were then challenged with a Kenya strain of T. lawrencei (T. lawrencei KB 5). The former animals were not protected against the challenge, whereas the latter were either partially protected, when a Tanzanian strain of T. lawrencei had been used for immunization, or completely protected when another Kenyan strain of T. lawrencei had been used.In the second experiment, animals were immunized by chemoprophylaxis against T. lawrencei (KB5) and challenged with T. parva (one strain) or T. lawrencei (five strains). The cattle were protected against challenge with the identical or related T. lawrencei strains, but only partially protected against the T. parva strain and a Tanzanian strain of T. lawrencei.It appears that cattle cannot be immunized for field exposure to theileriosis throughout East Africa by chemoprophylaxis using T. lawrencei (KB5) alone, but may be able to withstand field exposure in a variety of situations if a combination of different theilerial strains is used in the vaccination procedure.     

East coast fever: 4. Further studies on the protection of cattle immunized with a combination of theilerial strains

Four experiments were carried out in which cattle immunized with three cryopreserved stabilates, Theileria parva (Muguga), T. parva (Kiambu 5) and T. lawrencei (Serengeti transformed) and simultaneously treated with a single dose of long acting tetracycline were challenged with field isolates of T. parva. Three of the challenge isolates were from Tanzania and one from Kenya. The immunized cattle showed either mild or inapparent diease reations while susceptible control cattle suffered severe disease and 72% died. These experiments further demonstrated the efficacy of the immunization method against T. parva isolates from a wide distribution within East Africa. The value of such laboratory screening of field isolates prior to field exposures is discussed.     

Theileriosis: The exposure of immunised cattle in aTheileria lawrencei enzootic area

Summary Three groups of steers were exposed to field challenge in aT. lawrencei-enzootic area of Kenya. Four out of five ECF-susceptible steers and four out of five steers immunised againstT. parva (Muguga) died of theileriosis, the surviving animals experiencing severe reactions. On the other hand, all five steers immunised againstT. parva (Muguga) and a strain of theileria probably homologous with the one present in the area of exposure, survived and only experienced mild reactions. These results indicated that immunisation of cattle withT. parva (Muguga) may not necessarily protect them against field challenge with certainT. lawrencei-type strains, but that immunisation with an apparently homologous strain of theileria may well do so.

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Sumario Tres groupos de novillos fueron expuestos al desafio de campo en un area de Kenya enzootica aT. lawrencei. Cuatro de cinco novillos susceptibles a la Fiebre de la Costa del Este y cuatro de cinco novillos inmunizados contraT. parva (Muguga) murieron de Theileriosis; los animales sobrevivientes experimentaron reacciones severas. De otra manera, todos los cinco novillos inmunizados contraTheileria parva (Muguga) y una cepa de theileria probablemente homologa con la presente en el area de exposición, sobrevivieron y solo experimentaron reacciones ligeras. Estos resultados indicaron de que la inmunización del ganado conT. parva (Muguga) puede no necesariamente proteger contra el desafio de campo con ciertas capas ó tipos deT. lawrencei, pero que la inmunizacion con una cepa de theileria aparentemente homóloga puede proteger.

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Résumé Trois groupes de bouvillons ont été soumis à l'épreuve sur le terrain dans une région du Kenya où sévit une enzootie àT. lawrencei. Quatre sur cinq bouvillons neufs et quatre sur cinq bouvillons immunisés contreT. parva (Muguga) sont morts, les survivants éprouvant des réactions graves. D'autre part, cinq bouvillons immunisés contreT. parva (Muguga) et une souche deTheileria probablement identique à celle présente dans la région d'exposition, ont survécu et n'ont présenté que de faibles réactions. Ces résultats montrent que l'immunisation de bovins avecT. parva (Muguga) peut ne pas les protéger nécessairement de l'épreuve sur le terrain avec certaines souches de typeT. lawrencei, mais que l'immunisation avec une souche deTheileria apparemment identique àT. lawrencei peut le faire.

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On O.D.A. secondment from the A.R.C. Institute for Research in Animal Diseases, Compton, nr. Newbury, Berks., U.K. (Research Project R 2396).

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Supported by a grant from Pfizer Corporation, New York.

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On U.S.D.A. secondment from Plum Island Animal Disease Laboratory, Box 848, Greenport, Long Island, N.Y. 11944, U.S.A.

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Project supported by the United Nations Development Programme, with the Food and Agriculture Organization of the United Nations as the Executing Agency, in co-operation with the East African Community. The Project is also supported by the Overseas Development Administration of the United Kingdom (Research Projects 2396 and 2494), the United States Department of Agriculture, the Rockefeller Foundation, the International Atomic Energy Agency and the Pfizer Corporation.     

Exposure of immunized cattle to prolonged natural challenge of Theileria lawrencei derived from African buffalo (Syncerus caffer)

Cattle were immunized with Theileria lawrencei stabilates either by fortuitous recovery or intentionally by chemoprophylaxis with oxytetracycline. The immunized cattle were exposed together with susceptible control cattle in a paddock where a lethal T. lawrencei challenge derived from two African buffaloes had been established.Theileria lawrencei stabilates used for immunization were of two types: one batch was prepared from Rhipicephalus appendiculatus fed on a buffalo in the paddock, and the other was from a number of tick batches fed on the two buffaloes over a period of 3 months.All the susceptible control cattle exposed in the paddock died of acute Theileria lawrencei infections. Cattle immunized with the composite stabilates survived T. lawrencei challenge for a prolonged period without showing clinical disease. The protection to the T. lawrencei challenge persisted for at least 1.5 years after the composite stabilates had been prepared. The stabilate prepared from ticks fed on a buffalo on one occasion failed to give effective protection since half of these immunized cattle died of T. lawrencei infection when exposed. These results suggest that different immunogenic types of T. lawrencei occur in buffalo which may hinder the effectiveness of a vaccine for T. lawrencei.     

A comparative study of the diseases in cattle caused by Theileria parva or T. lawrencei: II. Hematology,clinical chemistry,coagulation studies and complement

Theileria lawrencei tick-derived stabilate infection of 8 cattle resulted in the development of panleukopenia and hypoproteinemia. In addition to these changes, T. parva infection caused mild normocytic, normochromic, non-responsive anemia at either of two dose rates. Disseminated intravascular coagulation, as indicated by positive protamine paracoagulation tests, prolonged prothrombin and partial thromboplastin times, and thrombocytopenia, developed in cattle infected with either of the Theileria spp., and was probably an important intermediary mechanism leading to death. Infection of calves with a high dose of T. parva stabilate resulted in more rapid onset of clinico-pathologic changes than did the low dose infection. Theileria lawrencei infection produced a severe, acute syndrome, the clinico-pathologic alterations of which varied in time of onset and severity between those of the T. parva high dose and low dose groups.     

Molecular and immunological characterisation of Theileria parva stocks which are components of the 'Muguga cocktail' used for vaccination against East Coast fever in cattle

The 'Muguga cocktail' which is composed of three Theileria parva stocks Muguga, Kiambu 5 and Serengeti-transformed has been used extensively for live vaccination against East Coast fever in cattle in eastern, central and southern Africa. Herein we describe the molecular characterisation of the T. parva vaccine stocks using three techniques, an indirect fluorescent antibody test with a panel of anti-schizont monoclonal antibodies (MAb), Southern blotting with four T. parva repetitive DNA probes and polymerase chain reaction (PCR)-based assays detecting polymorphism within four single copy loci encoding antigen genes. The Muguga and Serengeti-transformed stocks exhibited no obvious differences in their reactivity with the panel of MAbs, whereas Kiambu 5 differed with several MAbs. Kiambu 5 DNA was very distinct from the Muguga and Serengeti-transformed isolates in the hybridisation pattern with all four nucleic acid probes, whereas Muguga and Serengeti-transformed isolates exhibited minor differences and could not be discriminated with one of the probes. PCR amplification in combination with restriction fragment length polymorphism analysis indicated that Kiambu 5 was also markedly divergent from the Muguga and Serengeti-transformed stocks within two of the four antigen coding genes. The T. parva Serengeti-transformed stock did not contain a 130 base pair insert within the p67 sporozoite antigen gene, which has been observed previously in most T. parva parasites isolated from buffalo, and could not be discriminated from T. parva Muguga at any of the four single copy loci. Collectively the data indicate that two of the cocktail components T. parva Serengeti-transformed and Muguga are genetically closely related, while the third component Kiambu 5 is quite distinct. Based on the findings, there may be a need to include only one of the T. parva Muguga and Serengeti-transformed components in the immunising cocktail. The study demonstrates the value of molecular characterisation data for monitoring of live vaccines.     

A comparative study of the diseases in cattle caused by Theileria Lawrencei and Theileria Parva. 1. Clinical signs and parasitological observations

A comparison was made between the clinical signs and blood and lymph node parasite levels in cattle reacting to the inoculation of tick-derived stabilates of Theileria lawrencei (TL), and T. parva at high dose (TPH) and low dose (TPL) levels. The TL and TPH infections produced acute diseases with statistically similar tines to death of 13.50 and 14.25 days, respectively, while TPL caused a more protacted but equally fatal disease of 20 days duration. In the TPL group, the local drainage lymph node (LDLN) became enlarged earlier and macroschizonts appeared later than in the TPH group. The characteristics of T. lawrencei infection which differentiated it from T. parva infection were: nervous signs; complete anorexia; low macroschizont index (MSI) levels of up to 5%; and lack of piroplasms. In T. parva groups, the high MSI levels of up to 60%, presence of piroplasms and dysentery were characteristic. In addition, the enlargement of lymph nodes in the TL group persisted to time of death, while in both T. parva infections the initial enlargement was followed by a decrease in size.The 100-fold dose difference between TPH and TPL influenced the times of onset of the majority of clinical signs, most of which occurred later in the TPL group. The MSI levels were 60% in the TPH group and 40% in the TPL group. The piroplasm parasitemia levels reached 5% in the TPH group, and 16% in the TPL group.Theileria lawrencei and T. parva caused diseases with significant differences in clinical manifestations and parasite levels in erythrocytes and lymphocytes. The size of the infecting dose influenced the time of onset of clinical signs as well as the duration of the disease.     

Immunization of cattle with a Theileria parva bovis stock from Zimbabwe protects against challenge with virulent T.p. parva and T.p. lawrencei stocks from Kenya

Following inoculation of 34 Bos indicus (Boran) cattle with a Theileria parva bovis (Boleni) stock from Zimbabwe, 18 animals underwent mild theilerial reactions, 12 underwent moderate reactions, three suffered severe reactions and one died. When these animals were subsequently challenged with different virulent stocks of either T.p. parva (Muguga, Marikebuni or Mariakani) or T.p. lawrencei (Ngong 1 or Nanyuki) from Kenya, all except two animals resisted challenge. The two reactors were part of the group challenged with the T.p. parva (Mariakani) stock. All 12 susceptible control animals underwent severe reactions and 11 died. The results of these experiments suggest that T.p. bovis (Boleni) may be used in some situations to immunize cattle against East Coast fever without the need to provide concomitant chemotherapy as in the infection and treatment method of immunization.     

Molecular characterization of live Theileria parva sporozoite vaccine stabilates reveals extensive genotypic diversity

The current Infection and Treatment Method of vaccination against East Coast fever comprises an inoculation of live Theileria parva sporozoites and simultaneous administration of oxytetracycline. Immunization with a combination of parasite types has been shown to provide broader protection than inoculation of individual strains. In this study, we used a high-throughput capillary electrophoresis system to determine the genotypic composition of the Muguga Cocktail, a widely used vaccine stabilate derived from three seed stabilates-Muguga, Serengeti-transformed and Kiambu 5. Five satellite markers were used to genotype the vaccine and reference stabilates from two commercial-scale preparations of the vaccine. In addition, 224 cloned cell lines established by infection of bovine lymphocytes with T. parva parasites from the component stabilates were genotyped. The results indicate that, for the recently prepared batch, there are at least eight genotypes in each of the Muguga and the Serengeti-transformed stabilates, while parasites from the Kiambu 5 stabilate showed no diversity at the five loci. The Serengeti-transformed stabilate contained parasites of the Kiambu 5 genotype and of two genotypes present in the Muguga stabilate, whereas there were no genotypes common to the Muguga and Kiambu 5 stabilates. When stabilates from the two vaccine batches were compared, no allelic variations were identified between the Muguga and Kiambu 5 parasites, while lack of sufficient clones prevented a full comparison of the Serengeti-transformed stabilates. The findings will facilitate examination of the extent to which the vaccine strains become resident in areas under vaccination, the identification of 'breakthrough' strains and the establishment of the quality assurance protocols to detect variations in the production of the vaccine. The cloned cell lines will be useful for further understanding the antigenic diversity of parasites in the vaccine.     

Four p67 alleles identified in South African Theileria parva field samples

Previous studies characterizing the Theileria parva p67 gene in East Africa revealed two alleles. Cattle-derived isolates associated with East Coast fever (ECF) have a 129 bp deletion in the central region of the p67 gene (allele 1), compared to buffalo-derived isolates with no deletion (allele 2). In South Africa, Corridor disease outbreaks occur if there is contact between infected buffalo and susceptible cattle in the presence of vector ticks. Although ECF was introduced into South Africa in the early 20th century, it has been eradicated and it is thought that there has been no cattle to cattle transmission of T. parva since. The variable region of the p67 gene was amplified and the gene sequences analyzed to characterize South African T. parva parasites that occur in buffalo, in cattle from farms where Corridor disease outbreaks were diagnosed and in experimentally infected cattle. Four p67 alleles were identified, including alleles 1 and 2 previously detected in East African cattle and buffalo, respectively, as well as two novel alleles, one with a different 174 bp deletion (allele 3), the other with a similar sequence to allele 3 but with no deletion (allele 4). Sequence variants of allele 1 were obtained from field samples originating from both cattle and buffalo. Allele 1 was also obtained from a bovine that tested T. parva positive from a farm near Ladysmith in the KwaZulu-Natal Province. East Coast fever was not diagnosed on this farm, but the p67 sequence was identical to that of T. parva Muguga, an isolate that causes ECF in Kenya. Variants of allele 2 were obtained from all T. parva samples from both buffalo and cattle, except Lad 10 and Zam 5. Phylogenetic analysis revealed that alleles 3 and 4 are monophyletic and diverged early from the other alleles. These novel alleles were not identified from South African field samples collected from cattle; however allele 3, with a p67 sequence identical to those obtained in South African field samples from buffalo, was obtained from a Zambian field isolate of a naturally infected bovine diagnosed with ECF. The p67 genetic profiles appear to be more complex than previously thought and cannot be used to distinguish between cattle- and buffalo-derived T. parva isolates in South Africa. The significance of the different p67 alleles, particularly the novel variants, in the epidemiology of theileriosis in South Africa still needs to be determined.     

East coast fever: Field challenge of cattle immunised againstTheileria parva (Muguga)

Summary This paper describes some of the work of the Edinburgh University East African Veterinary Expedition of 1969, carried out in conjunction with the F.A.O. Tickborne diseases project at Muguga. Cattle of proven immunity toT.parva (Muguga), together with controls, were exposed to field theirleriosis in two experiments. In both all animals died, though some protective effects of immunisation were demonstrable. The death of immunised animals is considered to be a result of aT.parva challenge by a strain of partial immunogenic difference fromT.parva (Muguga) concurrent with a profound anaemia caused byT.mutans infection.

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Sumario Este artículos describe parte del trabajo de la Expedición Veterinaria al Africa Oriental de la Universidad de Edimburgo en 1969 la cual, se realizó de acuerdo con el proyecto de “enfermedades transmitidas por garrapatas”, de FAO en Muguga. Ganado bovino de inmunidad probada haciaT. parva (Muguga), conjuntamente con controles, fueron expuestos a Theileriosis de campo en dos experimentos. Todos los animales de ambos grupos murieron, aunque se demostraron algunos efectos protectivos de inmunización. La muerte de los animales inmunizados se considera ser un resultado del desafió conT. parva con una cepa de una differencia inmunogénica parcial deT. parva de Muguga, concurrente con una profunda anemia causada por la infección conT. mutans.

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Résumé L’article décrit une partie du travail de l’expédition vétérinaire de l’Université d’Edinburgh, réalisé en Afrique de l’Est en 1969, en collaboration avec le projet de la FAO pour les maladies transmises par les tiques à Muguga. Des bovins dont l’immunité àT. parva (Muguga) avait été prouvée, ont été exposés, avec des témoins, à la theilériose naturelle au cours de deux expériences. Dans les deux cas, tous les animaux sont morts, bien qu’un certain effet protecteur de l’immunisation ait pu être démontré. On considère que la mort des animaux immunisés est due à l’infection par une souche deT. parva ayant une structure immunogène partiellement différent de celle deT. parva (Muguga), combinée à une anémie intense causée par une infection parT. mutans.

     

A pathogenic theilerial syndrome of cattle in the Narok District of Kenya

Summary Two theilerial parasites, both pathogenic for cattle, which had been isolated during a field trial conducted in Kenya, were studied in the laboratory. One of the parasites was mechanically transmissible and the other tick-transmitted. The sera of two groups of cattle, each infected with one of these parasites, were studied by the indirect fluorescent antibody technique, using both standardTheileria parva andT. mutans antigens and antigens prepared from the infective parasites under study. From the results obtained it was concluded that in the indirect fluorescent antibody test the mechanically transmissible parasite behaved antigenically likeT. mutans and the tick-transmitted parasite likeT. parva. Transmission studies on the infections are published in preceding article of this issue of the journal.

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Sumario Dos parasitos Theileria, ambos patogenicos para bovinos, los cuales habian sido aislados durante un trabajo de campo en Kenya, fueron estudiados en el laboratorio. Uno de los parasitos fue mecanicamente transmitido y el otro transmitido por una garrapata. Los sueros de dos grupos de bovinos, cada uno infectado con uno de estos parasitos fueron estudiados por la prueba indirecta de los anticuerpos fluorescentes, usando antigenos estandard deTheileria parva y Theileria mutans y antigenos preparados de los dos aislamientos infecciosos. Con excepcion de un solo bovino de los 18 inoculados mecanicamente, con el parasito asi transmitido, todosmostraron una marcada respuesta serologica al antigeno deT. mutans, la excepcion muriendo de la infeccion en tres semanas despues de la inoculacion. Todos los cuatro bovinos que se recuperaron a la exposicion del parasito transmitido por garrapatas mostraron una marcada respuesta serologica aTheileria parva. (Muguga). Reacciones cruzadas entreT. parva y el antigeno doT. mutans fueron solo detectadasen dos bovinos infectados con el parasito mecanicamente transmitido. Se concluyo que en la prueba indirecta de los anticuerpos fluorescentes el parasito transmitido mecanicamente se comportaba antigenicamente comoT. mutans y el parasito transmitido por qarrapatas comoT. parva.

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Résumé Deux.Theileria pathogènes pour le bétail, isolées au Kenya au cours d'essais sur le terrain, only été étudiées en laboratoire. L'un des parasites a été transmissible mécaniquement et l'autre par les tiques. Les sérums de deux groupes de bovins, infectés chacun d'un des parasites, ont été étudiés par la technique indirecte des anticorps fluorescents, en utilisant des antigénes standardisés deTh. parva etTh. mutans et des antigenes préparés à partir des deux souches isolées. Sur 18 bovins infectés par la souche transmissible mécaniquement, un seul a montré une réponse sérologique marquée à l'antigène deTh. mutans, et est mort dans les 3 semaines suivant l'inoculation. Parmi les bovins infectés par lesTheileria transmises par les tiques, 4 animaux guéris ont donné une réponse marquée à l'antigène deTh, parva (Muguga). Des réactions croisées entre les antigènes deTh. parva etTh. mutans ont été détectées seulement chez deux animaux infectés par le parasite transmissible mécaniquement. En conclusion de l'épreuve indirecte par les anticorps fluorescents, le parasite transmissible mécaniquement s'est comporté antigéniquement commeTh. mutans, et le parasite transmis par les tiques commeTh. parva.

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Project supported by the United Nations Development Programme/Special Fund, with the Food and Agriculture Organization of the United Nations as the Executing Agency, in co-operation with the East African Community. The project is also assisted by the Overseas Development Administration of the United Kingdom (Research Projects 2396 and 2494), the United States Department of Agriculture, the Rockefeller Foundation, the International Atomic Energy Agency, and the Pfizer Corporation.     

Causal agents of bovine theileriosis in southern Africa

Summary One pathogenic and 4 mild bovineTheileria strains from southern Africa, all transmitted byRhipicephalus appendiculatus, were compared amongst themselves as well as to bovine and buffalo strains of theT. parva complex from eastern and southern Africa and to bovine strains ofT. taurotragi from Tanzania considered to be derived from eland antelope. Criteria used were parasitological, clinical, serological and cross-immunity characters.The mild strains are similar to bovineT. taurotragi. Serological evidence suggested thatT. taurotragi is also infective to sheep. The pathogenic strain belongs to theT. parva complex; the latter consists of a series of types with different behaviour ranging from thelawrencei-type (of buffalo) causing Corridor disease, through thebovis-type causing Rhodesian malignant theileriosis to theparva-type causing classical East Coat fever. Seven cattle-tick passages of abovis-type strain did not result in transformation into aparva-type.Four species of bovineTheileriae are now known to occur in southern Africa:T. parva (lawrencei- andbovis-types) andT. taurotragi, both transmitted byR. appendiculatus, andT. mutans andT. velifera both withAmblyomma spp. as vectors.

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Agentes Causales De Theileriosis En El Sur De Africa

Resumen Se compararon 5 cepas deTheileria del sur de Africa, 1 patógena y 4 benignas, todas transmitidas porRhipicephalus appendiculatus, entre si y también con cepas derivadas de bovinos y búfalos, del complejoT. parva, del sur y este de Africa, y con cepas bovinas deT. taurotragi de Tanzania derivadas de antílope eland. Los criterios de evaluación utilizados fueron parasitológico, clínico, serológico, utilizando también los caracteres de inmunidad cruzada.Las cepas benignas son similares aT. taurotragi de bovinos. Las pruebas serológicas indicaron que esta última es también infectiva para ovejas. Las cepas patógenas pertenecen al complejoT. parva; este último consiste de un rango de tipos con diferente comportamiento que van desde el tipolawrencei (búfalo) que causa la enfermedad Corridor, a través del tipobovis que causa la theileriosis maligna de Rodesia, hasta el tipoparva que causa la típica Fiebre de la Costa Este. Siete pasajes a través de bovinos y garrapatas de un tipobovis, no produjo transformación alguna al tipoparva.Se conocen entonces 4 especies deTheileriae bovina en el sur de Africa :T. parva (tiposlawrencei ybovis) yT. taurotragi, ambas transmitidas porR. appendiculatus, yT. mutans yT. velifera, ambas transmitidas porAmblyomma spp.

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Agent De La Theileriose Bovine En Afrique Australe

Résumé Une souche pathogène et quatre souches bovines bénignes deTheileria d'Afrique australe, toutes transmises parRhipicephalus appendiculatus ont été comparées entre elles, puis avec des souches de bovins et de buffles du complexe deT. parva de l'Afrique australe et orientale et enfin avec des souches bovines deT. taurotragi de Tanzanie considérées comme originaires de l'Elan du Cap. Les critères utilisés ont été d'ordre parasitologique, clinique, sérologique avec recherche des caractères d'immunité-croisée.Les sourches bénignes sont similaires àT. taurotragi. La sérologie a suggéreré queT. taurotragi est également infectieuse chez le mouton. La souche pathogène appartient au complexe deT. parva ; ce complexe consiste en une série de types présentant divers comportements depuis le typelawrencei du buffle causant l'affection Corridor, et le typebovis cause de la theileriose maligne de Rhodésie jusqu'au type parva cause de l'East Coast Fever classique. 7 passages bétail-tique d'une souche de typebovis n'ont pas réussi à la transformer en typeparva. 4 espèces de Theileries bovines sont maintenant connues en Afrique australe :T. parva (typeslawrencei etbovis) etT. taurotragi toutes deux transmises parR. appendiculatus, T. mutans etT. velifera avec toutes deuxAmblyomma spp. comme vecteurs.

     

Epidemiological observations on theileriosis following field immunisation using infection and treatment

Thirty-seven high grade cattle were immunised against Corridor disease (Theileria parva lawrencei infection) on a farm with a history of heavy and often lethal theilerial challenge. Nineteen cattle were immunised by treating with two doses of long-acting oxytetracyclines given at 20 mg/kg on days 0 and 4 after sporozoite stabilate inoculation, while the other 18 were treated with naphthoquinone buparvaquone, given as a single dose of 2.5 mg/kg simultaneously with stabilate inoculation. All the cattle underwent subclinical theilerial reactions with all but two developing high antibody titres on the IFAT test against T. parva schizont antigen by day 35 after the immunisation. Both buparvaquone and long-acting oxytetracycline appeared equally effective in the immunisation. To date, 26 months later, only two cases of theileriosis parasitologically characteristic of T. p. parva have been reported in the immunised cattle. Following the two cases, investigations showed that when uninfected Rhipicephalus appendiculatus nymphal ticks were deliberately fed on healthy resident cattle on the farm, the resultant adult ticks transmitted acute and lethal theilerial infections to five out of five susceptible cattle. The resultant infections were parasitologically characteristic of T. p. parva infections. Furthermore, the monoclonal antibody profiles of schizont infected cell lines from these infections appeared to be characteristic of T. p. parva. It was thus concluded that resident cattle on the farm could be a potential source of T.p. parva infection which had broken through the immunity of T.p. lawrencei immunised cattle and could constitute a reservoir of theilerial infection for ticks and hence to susceptible stock on the farm.     

Isolation and characterization of bovine Theileria parasites in Zimbabwe

Theilerial parasites of cattle were isolated by a variety of methods from the Harare area of Zimbabwe. Parasite stocks were established in lymphoid cell cultures and as cryopreserved sporozoite stabilates in the laboratory. Fourteen stocks in culture were characterized by testing them with monoclonal antibodies (MAb) raised against T. parva parva and T. parva lawrencei antigen. Two of these stocks had profiles similar to T. taurotragi isolates from East Africa, the other stocks had profiles similar to T. parva parva, however, many of them failed to bind MAb No. 7, and this may be a distinctive feature for T. parva bovis. Three T. p. bovis stocks were titrated by injecting different doses of the respective stabilates into pairs of cattle. Reactions ranged from severe to inapparent according to the stocks and dose used, but no fatal reactions were recorded, even at the highest dose rate. On recovery, all cattle were given homologous and then heterologous challenge. The results of the latter challenge showed that the Boleni stock gave good cross-protection against challenge with two other Zimbabwean stocks. This stock may therefore be a candidate for immunizing cattle, under field conditions, to protect them against T. p. bovis in Zimbabwe. Non-pathogenic strains of T. p. bovis may be difficult to distinguish from T. taurotragi unless cross-challenge experiments can be conducted and/or MAb profiles have been made. An improved serological test is needed to differentiate antibodies to these parasites in the sera of recovered cattle.     

Lack of reactivity of sera from Theileriaparva-infected and recovered cattle against cell membrane antigens of Theileria parva transformed cell lines

Sera from $\text{Theileria}$$\text{parva}$ infected, recovered and rechallenged cattle were tested in complement-dependent cytotoxicity, membrane immunofluorescence and antibody-dependent cellular cytotoxicity assays for the presence of antibodies against cell membrane antigens of $\text{T}$. $\text{parva}$ transformed cell lines.In the complement-dependent antibody-mediated cytotoxicity assay, sera from lethally infected animals were negative. Some recovered cattle showed a positive reaction, but such reactions were also observed when an eland cell line infected with $\text{T}$. $\text{taurotragi}$, and bovine lymphoblastoid cells were used as targets. Reaction was less against Ig-negative peripheral blood lymphocytes.Evidence is presented that these reactions could be evoked by attachment of immune complexes to Fc-receptors. It is concluded that cattle exposed to $\text{T}$. $\text{parva}$ infection do not develop antibodies against specific $\text{T}$. $\text{parva}$ (or $\text{T}$. $\text{parva}$-induced) cell surface antigens.     

Prevalence and risk factors associated with <Emphasis Type="Italic">Theileria parva</Emphasis> infection in cattle in three regions of Tanzania

Ticks and tickborne diseases (TBDs) are serious constraints to cattle production in Tanzania and other tropical and subtropical countries. Among the TBDs, East Coast fever (ECF) is the most important as it causes significant economic losses to the cattle industry in Tanzania. However, control of ECF in Tanzania has continued to be a challenge due to inadequate epidemiological information. The main objective of this study was to determine the epidemiological situation of Theileria parva infections in cattle kept under pastoral and agro-pastoral farming systems in Mara, Singida, and Mbeya regions of Tanzania. Blood samples were collected from 648 cattle in the three regions. Genomic DNA was extracted and amplified in a polymerase chain reaction (PCR) using T. parva-specific primers targeting the 104-kD antigen (P104) gene. In addition, information was collected on the possible risk factors of T. parva infection (animal age, region, animal sex, tick burden, tick control method, and frequency of acaricide application). The prevalence of T. parva across the three regions was 14.2%. There was variation in prevalence among the three regions with Mara (21.8%) having a significantly higher (p = 0.001) prevalence than the other regions. Moreover, Mbeya exhibited relatively lower prevalence (7.4%) compared to the other regions. Factors found to be significantly associated with an animal being PCR positive for T. parva were region (p = 0.001) and tick burden (p = 0.003). Other factors were not found to be significant predictors of being PCR positive for T. parva. The present study showed high variation in tick burden and T. parva prevalence across the regions. Therefore, different strategic planning and cost-effective control measures for ticks and T. parva infection should be implemented region by region in order to reduce losses caused by ticks and ECF in the study area.     

Genotypic diversity,a survival strategy for the apicomplexan parasite Theileria parva

The tick-borne protozoan parasite Theileria parva causes East Coast fever (ECF), a severe lymphoproliferative disease of cattle that is a major constraint to the improvement of livestock in eastern, central and southern Africa. Studies in cattle experimentally infected with T. parva have shown that the protective cytotoxic T lymphocyte (CTL) response is tightly focused, with individual animals recognizing only one or two dominant antigens, the identity of which varies with MHC class I phenotype. It is well known that cross-protection between T. parva stocks is limited, but precise evaluation of genetic diversity in field populations of the parasite has been hampered by a lack of molecular markers spanning the genome. A recently described panel of satellite markers has provided evidence for substantial genotypic diversity and recombination but does not provide cover for large segments of the genome. To address this deficiency, we undertook to identify additional polymorphic markers covering these regions and we report herein 42 newly identified PCR-RFLP markers distributed across the 4 T. parva chromosomes, as well as 19 new satellite markers for chromosomes 1 and 2. This brings the total number of available polymorphic markers to 141 for the 8.5 Mb genome. We have used these markers to characterise existing parasite stabilates and have also shown that passage of the parasite through naïve cattle and ticks can lead to substantial changes of parasite populations in resulting stabilates. These markers have also been used to show that passage of mixed parasites through an immunised calf results in the removal of the immunising genotype from the parasite population produced by ticks fed on this animal.     

PCR-based detection of blood parasites in cattle and adult Rhipicephalus appendiculatus ticks

To ascertain the infection rate for tick-borne pathogens in Zambia, an epidemiological survey of Theileria parva, Babesia bigemina and Anaplasma marginale in traditionally managed Sanga cattle was conducted using PCR. Of the 71 native Zambian cattle, 28 (39.4%) were positive for T. parva, 16 (22.5%) for B. bigemina and 34 (47.9%) for A. marginale. The mixed infection rate in cattle was 8.5% (6/71), 16.9% (12/71), 7.0% (5/71) and 2.8% (2/71) for T. parva/B. bigemina, T. parva/A. marginale, B. bigemina/A. marginale and T. parva/B. bigemina/A. marginale, respectively.To predict the risk for transmission of tick-borne pathogens from ticks to cattle, a total of 74 Rhipicephalus appendiculatus ticks were collected from a location where cattle had been found positive for T. parva. Of the ticks collected, 10 (13.5%) were found to be PCR-positive for T. parva. The results suggest that the infection rate for tick-borne pathogens was relatively high in Sanga cattle and that adult R. appendiculatus ticks were highly infected with T. parva.