Derivation and characterization of a quinapyramine-resistant clone of Trypanosoma congolense.

Over a period of 208 days a quinapyramine-resistant population was derived in vivo from a quinapyramine-susceptible clone of Trypanosoma congolense: IL 1180. While the dose of quinapyramine sulfate required to cure 50% of mice infected with the parental clone was 0.23 mg/kg of body weight, the 50% curative dose for the resistant derivative, IL 1180/Stabilate 12, was greater than 9.6 mg/kg. This approximately 40-fold increase in resistance to quinapyramine was shown to be associated with an 8-fold increase in resistance to isometamidium, a 28-fold increase in resistance to homidium, and a 5.5-fold increase in resistance to diminazene. Cross-resistance to homidium and diminazene was also demonstrated in goats. Two clones derived from the drug-resistant derivative underwent cyclical development in Glossina morsitans centralis, producing mature infection rates of 39.6 and 23.9%. Thus, induction of resistance to quinapyramine in T. congolense IL 1180 was associated with cross-resistance to isometamidium, homidium, and diminazene and did not compromise the population's ability to undergo full cyclical development in tsetse flies.