A drug incubation glossina infectivity test (DIGIT) to assess the susceptibility of Trypanosoma congolense bloodstream forms to trypanocidal drugs (Xenodiagnosis)

Blood was collected from two Sahelian goats, experimentally infected with e ither a drug-sensitive cloned population of Trypanosoma congolense (IL 1180 ) or a multiple drug-resistant T, congolense stock (Samorogouan/89/CRTA/267 ) and incubated at 37 degrees C for 30 min and 12 h, respectively, in the p resence of different drug concentrations (0.5, 1.0, 10.0 and 100.0 mu g/ml blood) of diminazene aceturate or isometamidium chloride. After that, the t rypanosome/blood/drug suspensions were offered to tsetse flies (2100 tenera l Glossina morsitans submorsitans) through an in vitro feeding system, usin g a silicone membrane. All tsetse flies were dissected and examined for the presence of trypanosomes in labrum, hypopharynx and midgut 20 days after t heir infective blood-meals. Infectivity of the drug-sensitive cloned popula tion was already completely abolished after incubation with 0.5 mu g/ml of both drugs; however, 13.6-42.2% of tsetse having been fed on untreated bloo d had developed an infection. In contrast, no significant differences were observed in the infection rates between the experimental groups and their c ontrol groups when fed on blood infected with the multiple drug-resistant s tock after incubation for 30 min with up to 10 mu g/ml of diminazene or iso metamidium. In consequence, tsetse appear to be a useful tool in the assess ment of drug susceptibility of typanosome populations. (C) 1999 Published b y Elsevier Science B.V. All rights reserved.