Oxytetracycline (OTC) significantly inhibited cytochrome c oxidase activity in bovine lymphocytes infected with Theileria parva and in uninfected mitogen-stimulated lymphocytes. The inhibitory effect was detected in vitro within 24 h of treatment with drug concentrations as low as 1 µg/ml. Following mitogen stimulation of lymphocytes, concentrations of 3 and 10 µg/ml OTC completely inhibited an increase in cytochrome c oxidase activity for 48–72 h. This inhibitory activity was considered to be due to a direct effect on lymphoblast mitochondrial protein synthesis. As a consequence, adenosine triphosphate activity was significantly reduced in lymphocytes stimulated either by infection with T. parva sporozoites or by mitogen and then treated with OTC. The results also indicated that parasite mitochondrial protein synthesis was inhibited by OTC. The activity of OTC reported in this study could explain the suppression of disease following ‘infection and treatment’ immunization against East Coast fever and the in vitro drug-inhibition of schizont development.

When bovine peripheral blood leucocytes were infected with Theileria parva sporozoites, immediate treatment with oxytetracycline (OTC) inhibited the development of sporozoites to mature schizonts. The extent of inhibition was dependent on drug concentration and duration of treatment. Concentrations of 5 μg/ml OTC, or higher, for 8 days completely inhibited the establishment of schizonts and their ability to transform host cells. A cytostatic effect on schizont-infected cell lines was found with three tetracyclines and was also demonstrated on uninfected lymphoblasts. The parasites were found to be sensitive t OTC during development to schizonts, but when mature and established within host cells, schizonts were not demonstrably affected. The infectivity of sporozoites and the binding of sporozoites to lymphocytes were not directly inhibited by OTC. The results may explain the action of tetracyclines when used prophylactically during immunization against East Coast fever, and also the reasons for the ineffectiveness of these drugs when used therapeutically during patent disease.

In bovine theileriosis the use of chemotherapy to control an infection sufficiently long to permit the establishment of a solid protective immune response has been developed as a routine vaccination procedure. Infections with Theileria parva and T. annulata can be prevented by the administration of carefully controlled numbers of sporozoites simultaneously with a long acting tetracycline and this form of immunization has been widely used for the control of East Coast fever in Africa with considerable success. In this review, the nature of the chemotherapy, the immune response and the interactions between chemotherapy and immunity in the development of infection-and-treatment immunization procedures are discussed.

Two mathematical models are developed that investigate the transmission dynamics of Theileria parva by the ixodid tickRhipicephalus appendiculatus to cattle in endemically stable areas. A method of estimating the rate of infection to cattle ofT. parva at the endemically stable state is given. Empirical estimates of ail the parameters in the model are available. The degree to which animals that have recovered from theileriosis (the ‘carrier’ state) are able to transmit the infection to tick nymphs or larvae is a crucial determinant of the dynamics of infection in a herd. Two control methods influencing the transmission of infection are considered – infection and treatment immunization and the reduction in tick feeding by acaricide application. The impact of each method on the transmission of infection is evaluated. Future developments and the data required to predict the dynamics of T. parva infections in cattle and ticks are discussed.

East Coast fever (ECF) is a fatal disease of cattle caused by the protozoan parasite Theileria parva. The development of a subunit vaccine, based on the sporozoite-specific surface antigen p67, has been hampered by difficulties in achieving high-level expression of recombinant p67 in a near-authentic form. Therefore two sets of recombinant baculovirus vectors were constructed. The first set, encoding various regions of p67, produced low levels of the corresponding p67 domains in High Five™ cells, despite the presence of large amounts of p67 RNA. The second, consisting of p67 domains fused to the carboxy-terminus of GFP expressed significantly higher levels of p67 protein. The GFP[ratio ]p67 fusion proteins were recognized by a sporozoite-neutralizing monoclonal antibody (TpM12) raised against native p67 whereas non-fused full length p67 expressed in insect cells was not recognized. GFP-tagging therefore, appeared to enhance the stability of p67 and to conserve its folding. The high-level expression of p67 domains in a more authentic form is an important step towards the development of an effective subunit vaccine against ECF.

Two-dimensional gel electrophoresis was used to compare the protein profiles of two geographically isolated populations of the tick Rhipicephalus appendiculatus Neumann (Acari: Ixodidae) in Kenya. Most of the protein spots were common to both populations, but a number were specific to each population. Since proteins are encoded by genes, the presence of population-specific proteins suggests that there may be genetic differences between the two populations. It is proposed that some of these population-specific proteins might be related to the differences in susceptibility of the ticks to Tlwileria pnrva infection.

A statistically derived disease reaction index based on parasitological, clinical and haematological measurements observed in 309 5 to 8-month-old Boran cattle following laboratory challenge with Theileria parva is described. Principal component analysis was applied to 13 measures including first appearance of schizonts, first appearance of piroplasms and first occurrence of pyrexia, together with the duration and severity of these symptoms, and white blood cell count. The first principal component, which was based on approximately equal contributions of the 13 variables, provided the definition for the disease reaction index, defined on a scale of 0–10. As well as providing a more objective measure of the severity of the reaction, the continuous nature of the index score enables more powerful statistical analysis of the data compared with that which has been previously possible through clinically derived categories of non-, mild, moderate and severe reactions.

In Kenya, there are at least seven distinct tick-borne diseases (the ileriosis, anaplasmosis, babesiosis, heartwater, Nairobi sheep disease, sweating sickness and erhlichiosis in dogs). Theileriosis causes major economic losses arising from deaths of infected cattle.

Control of these diseases is almost exclusively by the application of chemical acaricides to cattle. Use of acaricides is regulated and only those passing field tests are permitted to be marketed in Kenya. Field trials on immunization against East Coast fever (ECF) by infection and treatment are still continuing. Chemotherapy treatment is also available but quite expensive.

The Veterinary Department continuously evaluates acaricides which have been documented to have activity against ticks. These acaricides have been grouped into four groups ranging from organophosphorus compounds in Group I to synthetic pyrethroids in Group IV. To-date Groups III and IV acaricides are kept as reserve, although amitraz in Group III can be used on a limited scale on privately owned farms.

ECFXPERT is a microcomputer software tool which can be used to investigate tick populations and the control of East Coast fever. The package contains four simulation models: a model for predicting the abundance and seasonality of Rhipicephalus appendiculatus ticks; a model for predicting East Coast fever prevalence within a herd of cattle; and two models for the study of disease control using either acaricidal dipping strategies or chemotherapy. In this paper, the philosophy of the ECFXPERT package, and the underlying assumptions and mathematical techniques employed are presented, along with the results of a number of computer experiments designed to validate and illustrate potential use of the model.

The paper analyses the extent to which ticks and tick-borne diseases, particularly East Coast Fever (ECF), are an economic problem in Kenya. It qualitatively argues that several socio-economic factors, viz. inadequate information, indivisibility of the main tick control facilities, externalities, and risk make individual farmers undertake less control efforts than is optimal for the society. This fact is used to justify a more active role for the state in tick control efforts. A simple regression model that tests the impact of ECF on the cattle breed portfolio in the country is presented.