Epidemiology of animal trypanosomiasis on a cattle ranch in Kilifi, Kenya.

A study of the epidemiology of animal trypanosomiasis was carried out on a 2500 ha cattle ranch, with a history of trypanosomiasis, in the Coast Province of Kenya in 1982. The tsetse survey on the ranch revealed one breeding focus of Glossina austeni in a thicket of approximately 50 ha. Trypanosomes were detected in 20% of the 46 dissected tsetse. During the study period of 9 months, 0.8% of the 3315 samples collected from 2300 Ayrshire X Sahiwal crossbred cattle were found infected with trypanosomes; 32% of 5909 samples collected from the same cattle had a packed cell volume (PCV) of 30% or less. Animals with a PCV of 30% or less were treated with a trypanocide (Berenil, Ethidium or Novidium). Antibody to trypanosomes was detected in 22.1% of the 343 sera collected from the cattle. A sentinel herd of 20 cattle was exposed for 182 days inside the tsetse infested thicket. All animals became infected with Trypanosoma congolense, on average after 53 days; they were subsequently treated with Berenil (6 mg/kg). A second, third and fourth T. congolense infection was diagnosed in 17, 11 and 1 animals, respectively. The cattle were treated similarly with Berenil after each of these infections. T. vivax and T. brucei were not diagnosed in the sentinel cattle. The results suggest that acquired immunity to T. congolense infection did not play a significant role in the sentinel cattle.