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.

Trypanosoma congolense: drug resistance during cyclical transmissions in tsetse flies and syringe passages in mice.

A drug-resistant Trypanosoma congolense strain with predetermined curative doses (CD50 and CD90) of samorin at 13.9 +/- 1.02 and 20.3 +/- 1.13 mg/kg body weight, respectively, was cyclically transmitted through tsetse flies and by syringe passages in mice in the absence of drug pressure. The changing levels of drug sensitivity were determined after every 3rd cyclic and 5th syringe passage intervals. It was noted that when the strain was maintained in tsetse flies through 12 cyclical transmissions, the CD50 and CD90 dropped slightly from 13.9 to 11.9 +/- 1.06 and from 20.3 to 18.0 +/- 1.08 mg/kg body weight, respectively. This decrease in the level of resistance was not significant (P greater than 0.05). However, when the trypanosomes were maintained by syringe passages in mice, there was a significant reduction (P less than 0.05) in the degree of resistance (CD50 from 13.9 to 11.4 +/- 1.07 and CD90 from 20.3 to 16.7 +/- 1.16 mg/kg), by the 15th syringe passage.

Detection of trypanosome infections in the saliva of tsetse flies and buffy-coat samples from antigenaemic but aparasitaemic cattle.

Relatively simple protocols employing non-radioactive DNA probes have been used for the detection of African trypanosomes in the blood of mammalian hosts and the saliva of live tsetse flies. In combination with the polymerase chain reaction (PCR), the protocols revealed trypanosomes in buffy-coat samples from antigenaemic but aparasitaemic cattle and in the saliva of live, infected tsetse flies. Furthermore, the protocols were used to demonstrate concurrent natural infections of single tsetse flies with different species of African trypanosomes.