Trypanosoma congolense: the in vitro akinetoplastic induction sensitivity assay.

Incubation of Trypanosoma congolense in diminazene aceturate (Berenil) or isometamidium chloride (Samorin) induced akinetoplastic (AK) forms in vitro. The AK values (expressed in percent) obtained were found to be useful for rapid assessment of relative drug sensitivities. In susceptible clones, AK forms were induced at all drug concentrations tested, whereas in resistant clones they were induced only at higher concentrations. The Berenil-resistant clone exhibited AK values of 0.9% +/- 0.6%--8.9 +/- 2% at concentrations of 1-100 micrograms/ml at 4-10 h post-inoculation (p.i.), whereas the Berenil-susceptible clone displayed values of 9.3% +/- 13%--19.2% +/- 5% at 0.1-50 micrograms/ml. Motile trypanosomes were not seen at 100 micrograms/ml at 4 h p.i. or at 10 or 50 micrograms/ml at 10 h p.i. The Samorin-resistant clone showed AK values of 0.5% +/- 0.1%--43% +/- 3% at concentrations of 0.1-100 micrograms/ml at 4 and 10 h p.i., whereas the Samorin-susceptible clone exhibited values of 5.3% +/- 2%--45% +/- 4% at 0.0005-100 micrograms/ml. These results were supported by the findings obtained using a mouse infectivity test.