A study of the epidemiology of theileriosis on smallholder dairy farms in Kiambu District, Keny

This thesis describes a one year longitudinal study of East Coast fever (ECF)/Theileria parva infection on 90 smallholder dairy farms, randomly selected from dairy co-operative societies in Kiambu District, Central Highlands, Kenya. A total of 535 animals were examined monthly, providing 370.3 animal years of observation, 82.3 years contributed by calves less than one year of age.;Serological samples were assessed for T. parva-specific antibodies by a standardised and quantified ELISA, allowing identification of primary and secondary infections from serological profiles. In total, 54.5% of all samples tested positive. The overall rate of secondary infections in mature cattle of 18.4% was significantly lower (p < 0.001) than the rate of seroconversion (primary infections) of 49.8% observed in calves.;While infection pressure was higher for calves, ECF disease risk was not. Although the crude mortality rate was higher (p < 0.001) in calves (30.4%) than in mature cattle (6.3%), the ECF-specific morbidity and mortality rates were not different (7.3% versus 5.6% and 1.2% versus 1.7%, respectively). These relatively low ECF risks were associated with lower intensity of tick control practices than previously reported, particularly for calves.;Risks of T. parva infection/ECF were homogeneous across agro-ecological zone (AEZ) with the most important differences by grazing management system. Generalised linear multi-level mixed models of measures of antibody activity and dichotomous (positive/negative) status both demonstrated significantly different age-profiles by grazing management system, but not by AEZ. Cattle kept under semi-/full-pasture grazing management both tested positive earlier and had higher levels of antibody activity than those housed in zero-grazing units. Strong farm clustering was observed for all outcome measures, but variability was greatest within semi-/full-pasture grazing systems.;Continued intensification of the smallholder dairy sector is expected to further depress the low level of challenge experienced by zero-grazing units such that disease control efforts are likely to be based on a risk-aversion rather than disease-reduction strategy. However, the more heterogeneous risk in grazing systems on highland margins demonstrates that these farms are likely to experience the greatest benefits of ECF control programmes.