Epidemiology of bovine trypanosomiasis in the Ghibe valley, southwest Ethiopia. 3. Occurrence of population of Trypanosoma congolense resistant to diminazene, isometamidium and homidium
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Acta Tropica;53(2): 151-163
Permanent link to this item: http://hdl.handle.net/10568/27972
Blood samples were collected from parasitaemic cattle in the Ghibe Valley, Ethiopia, frozen in liquid nitrogen and transported to Nairobi, Kenya. Twelve of the stabilates were inoculated into individual Boran (Bos indicus) calves and characterised for their sensitivity, in turn, to diminazene aceturate (Berenil), isometamidium chloride (Samorin) and homidium chloride (Novidium). All 12 stabilates produced infections which were shown to be Trypanosoma congolense and resistant to treatment with diminazene aceturate at a dose of 7.0 mg kg -1 body weight (b.w.). Eleven of the infections were also resistant to isometamidium chloride at a dose of 0.50 mg kg -1 b.w. The drug - sensitivity phenotypes of three of the same isolates were also determined in goats which were each treated with only one of the three trypanocides: all expressed the same phenotypes as the populations expressed in the aforementioned Boran calves. Five clones were derived from one of the isolates which expressed a high level of resistance to all three trypanocides: each alone expressed high levels of resistance to all three trypanocides when characterised in mice. Thus, the multi-resistance phenotype of the parental isolate was associated with expression of multi-resistance by individual trypanosomes. Finally, molecular karyotypes and electrophoretic variants of six enzymes were determined for seven and eight of the isolates, respectively. Six different karotypes were observed and all light of the latter isolates belonged to different zymodemes, indicating that the multi-resistance phenotype at Ghibe was associated with many genetically distinct populations.