No abstract

Background: An investigation aimed to confirm whether immunisation with the “benign” buffeli genotype of Theileria orientalis could reduce the parasitosis of the virulent ikeda genotype. Methods: Calves were inoculated intravenously or subcutaneously with bovine blood containing merozoites of T.orientalis buffeli. When recipients became positive, they and control animals were challenged with unfed nymphs of Haemaphysalis longicornis ticks infested as larvae with T.orientalis ikeda. Results: All calves became positive for the challenge within 12 days after tick application. In the immunised calves, the first wave of parasitosis with T.orientalis ikeda from 4-6 weeks was reduced significantly by >80% before the infestation declined into the carrier state by 9 weeks. Conclusions: The results confirm the field experience with theileriosis in endemic zones where the carrier state appears to prevent clinical disease despite repeated, seasonal tick infestations with virulent genotypes of the parasite. This method offers a means to reduce the severity of the first wave of theilerial parasitosis after tick challenge and recover associated production losses.