A prospective cohort study was conducted in five purposively-sampled agro-ecological zone
(AEZ)-grazing system strata in Murang’a District, Kenya, between March 1995 and June 1996.
The study strata were selected based on a preliminary characterization study to represent the
widest range of risks to East Coast fever (ECF) in the District and included zero-grazing and
open-grazing 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 epidemiology (risks of
infection, morbidity and mortality) and potential control of ECF between the selected strata.
Evidence of Theileria parva infection was assessed by increased antibody levels as measured in
an indirect ELISA assay by the percent positivity (PP) of serum samples relative to a strong
positive 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 were also highest in open-grazing strata. While different, all five AEZ-grazing strata were considered to be endemically
unstable for ECF. East Coast fever challenge was low in all zero-grazing strata and this
challenge is likely to remain low due to continuing intensification of smallholder farming in the
central highlands. In the open-grazing strata, there was higher challenge and a greater impact