Selection for drug resistance in Trypanosoma congolense during cyclic transmissions through Glossina morsitans morsitans and drug treated rabbits.

A drug-sensitive Trypanosoma congolense (IL 1180 strain), with a known CD50 and CD90 (doses required to cure 50 and 90% of the infected animals) was cyclically passaged through tsetse flies. The infected flies were then fed on rabbits which received weekly prophylactic treatment of Samorin. It was observed that the infections arising from flies maintained for over 60 days on drug-treated rabbits required higher curative doses to achieve a 50 and 90% cure. The results of this work suggest that a selection for drug resistance occurs when trypanosome stage in Glossina is continuously exposed to drug-treated animals.