The effect of diminazene aceturate and isometamidium chloride on cultured procyclic forms of susceptible and drug-resistant Trypanosoma congolense.

Cultures of insect forms of Trypanosoma congolense stocks and clones with different susceptibilities to trypanocidal drugs in vivo were initiated from bloodstream trypomastigotes harvested from mammalian hosts and maintained axenically in vitro at 27 degrees C. Growth inhibition of procyclic forms of susceptible and drug-resistant T. congolense occurred after incubation for 48 h with 0.1 ng isometamidium chloride ml or 500 ng diminazene aceturate/ml. Procyclic forms were propagated in vitro in the presence of 10 or 100 ng diminazene aceturate/ml for 20 days without or with only minor loss of growth. In the presence of 0.1 or 1 ng isometamidium chloride/ml the trypanocidal effect was detectable after 6-8 days and the cultures died after 10-12 days. Concentrations of 1 or 10 ng isometamidium chloride/ml had an irreversible effect when the trypanosomes were exposed to the drug for 24 h. Both drugs used in this study thus showed antitrypanosomal activity on T. congolense procyclic forms but it was not possible to distinguish between drug-resistant and susceptible stocks or clones employing the criteria of growth inhibition or death of trypanosomes in culture.