Differences in the epidemiology of theileriosis on smallholder dairy farmsin contrasting agro-ecological and grazing strata of highland Kenya

A prospective cohort study was conducted in five purposively-sampled agro-e cological zone (AEZ)-grazing system strata in Murang'a District, Kenya, bet ween March 1995 and June 1996. The study strata were selected based on a pr eliminary characterization study to represent the widest range of risks to East Coast fever (ECF) in the District and included zero-grazing and open-g razing farms. In total, 225 calves from 188 smallholder farms were examined from birth to 6 months of age and visited within the first 2 weeks of life and thereafter at bi-weekly intervals for up to 14 visits. The purpose of the study was to characterize the differences in epidemiolog y (risks of infection, morbidity and mortality) and potential control of EC F between the selected strata. Evidence of Theileria parva infection was as sessed by increased antibody levels as measured in an indirect ELISA assay by the percent positivity (PP) of serum samples relative to a strong positi ve reference serum. Sero-conversion risks of T. parva were highest in the open-grazing strata. Antibody prevalence in adult cattle and ECF morbidity and mortality risks w ere also highest in open-grazing strata, While different, all five AEZ-graz ing strata were considered to be endemically unstable for ECF, East Coast f ever challenge was low in all zero-grazing strata and this challenge is lik ely to remain low due to continuing intensification of smallholder farming in the central highlands. In the open-grazing strata, there was higher chal lenge and a greater impact of ECF.