Studies on the epidemiology of trypanosoma evansi infection in camels in selected areas of Kenya

Abstract

Studies on the Epidemiology of Trypanosoma evansi infection in Selected areas of Kenya: The study covered four camel herds namely: KULAL, NGURUNIT, OLMAISOR and GALANA. All these herds, except GALANA, are north of the Equator. The Indirect haemaggulutination test (IHA) was developed and used as the main serological test. In addition, the mercuric chloride (MC) and mouse inoculation (MI) were used. In the IHA Test, Trypanosoma evansi protein extract was used as the antigen. Sheep red blood cells were used in the IHA Test. The cells were fixed with 1% buffered glutaraldehyde solution. The antigen (T. evansi) was coupled to such cells after tanning them with 1:20,000 tannic acid solution. Altogether, 2,100 camel serum samples were tested using the two serological tests and blood from the same number of camels inoculated into mice (in the MI test). Camel bleeds were done at monthly intervals or longer intervals. The IHA detected the largest number of positives. 47.9% of all the cases were positive by the IHA test, 31.8% by the MC test and 6.3% by the MI test. Of the MI positive cases, the IHA detected 94.7% and MC 66.4%.

Therefore, the IHA test was found to be more sensitive in detecting patent cases. Point prevalence rates (PPR) and Incidence rates (IR) are given. High PPR and IR rates were observed in all herds. Therefore, the disease is endemic in the camels of Kenya. Isoenzyme characterization revealed that 95.2% of the isolates were T. evansl and 4.8% T. congolense. It was possible to characterize the disease into 4 types namely: Type 1 - acute trypanosomiasis, Type 2 - chronic trypanosomiasis (showing some clinical signs), Type 3 - chronic trypanosomiasis (showing no clinical signs and characterized by low patency rate) and Type 4 - chronic trypanosomiasis (showing no clinical signs and characterized by a nil patency rate on MI and a normal PCV and WBC count values). From the PPR, IR results and the variance of PCV and total WBC counts between the 4 herds over the whole study period, disease stability occurs in NGURUNIT and GALANA herds. It was hard to explain why the disease should be stable in some herds and unstable in others. However, management differences, fly incidence, trypanosome species and £train differences may be some of the reasons.