Capture–recapture analysis of East Coast fever in smallholder dairy herds in the Dar es Salaam region of Tanzania

The prevalence of and case fatality rate due to East Coast fever (ECF) were estimated in 1402 dairy cattle in 87 small herds in the Dar es Salaam region of Tanzania, from January 2003 to January 2005 using a capture–recapture method. Information on clinical cases and deaths due to ECF were obtained from farm records and from a questionnaire-based cross-sectional survey conducted between July 2003 and March 2005 as part of longitudinal studies of bovine mastitis in these herds. The number of clinical cases identified was 567 (from farm records) and 496 (from the questionnaire), and the number of deaths recorded were 305 (from farm records) and 251 (from the questionnaire).In all, 450 clinical cases and 191 deaths due to ECF were identified from the two sources, giving an observed prevalence of 32% (CI95% 30–35%) and observed case fatality rate of 42% (CI95% 38–47%). Following application of the capture–recapture method, the estimated number of clinical cases and deaths was 625 (CI95% 617–633) and 401 (CI95% 384–418), respectively. The respective prevalence and case fatality rates were 45% (CI95% 41–48%) and 64% (CI95% 60–68%). The estimates obtained using the capture–recapture method are higher than those identified by traditional cross-sectional studies conducted in the same study area, and probably provide a more accurate epidemiological picture of ECF in this region of Tanzania.