Drug sensitivity screening in vitro of populations of Trypanosoma congolense originating from cattle and tsetse flies at Nguruman, Kenya.

An in vitro assay that utilises in vitro-derived metacyclic trypanosomes was used to determine the drug sensitivity of 7 populations of Trypanosoma congolense collected from cattle and tsetse flies at Nguruman; a trypanosomiasis-endemic area in southwest Kenya. The metacyclic trypanosomes used in the assay were obtained from cultures initiated directly from either the blood of cattle with low levels of parasitaemia or from guts of infected tsetse flies. Sensitivities to isometamidium chloride, diminazene aceturate and homidium salts were assessed at various drug concentrations (0.5 ng-50 micrograms/ml). The results were compared with those obtained with two characterised laboratory populations. In spite of the fact that isometamidium chloride had not been widely used at Nguruman, two of the stocks (KE 3302 and KE 3303) expressed high levels of resistance to this drug (resistant to 100 ng/ml and 1000 ng/ml, respectively). In contrast, all of the populations examined were as sensitive, or more so, to diminazene aceturate than the sensitive laboratory clone IL 1180; two stocks (KE 3305 and KE 3306) were more sensitive (resistant to 0.5 microgram/ml, sensitive to 1 microgram/ml) and three stocks expressed the same level of sensitivity as IL 1180 (resistant to 1 microgram/ml, sensitive to 5 micrograms/ml). Since the results of the in vitro assay correlated well with field observations it was concluded that the assay would be a useful tool in epidemiological studies to determine the resistance phenotypes of trypanosome populations in the field, thereby enabling development of appropriate control measures for particular areas.