Abstract
Tick-borne diseases are a major impediment to improved productivity of livestock in sub-Saharan Africa. Improved control of these diseases would be assisted by detailed epidemiological data. Here we used longitudinal, serological data to determine the patterns of exposure to Theileria parva, Theileria mutans, Babesia bigemina and Anaplasma marginale from 548 indigenous calves in western Kenya. The percentage of calves seropositive for the first three parasites declined from initial high levels due to maternal antibody until week 16, after which the percentage increased until the end of the study. In contrast, the percentage of calves seropositive for T. mutans increased from week 6 and reached a maximal level at week 16. Overall 423 (77%) calves seroconverted to T. parva, 451 (82%) to T. mutans, 195 (36%) to B. bigemina and 275 (50%) to A. marginale. Theileria parva antibody levels were sustained following infection, in contrast to those of the other three haemoparasites. Three times as many calves seroconverted to T. mutans before seroconverting to T. parva. No T. parva antibody response was detected in 25 calves that died of T. parva infection, suggesting that most deaths due to T. parva are the result of acute disease from primary exposure.
Highlights
Tick-borne diseases are thought to constitute one of the major constraints to cattle productivity and the improvement of dairy industries in Africa (Perry and Young, 1995)
The study area is within a 45 km-radius semi-circle radiating from the field laboratory. It was stratified across four agro-ecological zones (AEZ): Lower Midland 1 (LM 1), Lower Midland 2 (LM 2), Lower Midland 3 (LM 3) and Upper Midland 3 (UM 3)
For T. parva, A. marginale and B. bigemina, this decrease continued until week 16, after which the percentage of seropositive calves showed a general increase up to and including the final visit at 1 year
Summary
Tick-borne diseases are thought to constitute one of the major constraints to cattle productivity and the improvement of dairy industries in Africa (Perry and Young, 1995). Well-structured epidemiological studies on tickborne diseases to estimate morbidity, mortality, case fatality rates and associated risk factors have been conducted in different production systems in eastern Africa (Gitau et al 1997; Maloo et al 2001; Muraguri et al 2005; Okuthe and Buyu, 2006; Swai et al 2007). The studies reported here are part of one such project: the Infectious Diseases of East Africa Livestock (IDEAL). The IDEAL project was a large, 3-year epidemiological study of calves in western Kenya aimed at alleviating the widely recognized lack of baseline epidemiological data on the dynamics and impacts of infectious diseases of cattle in eastern Africa
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