Development of multiple drug resistance of Trypanosoma congolense in Zebu cattle under high natural tsetse fly challenge in the pastoral zone of Samorogouan, Burkina Faso.

Preliminary data from an ongoing epidemiological survey in the pastoral zone of Samorogouan (Kénédougou) indicate the occurrence of multiple-drug-resistant Trypanosoma congolense. Despite frequent trypanocidal drug treatments with diminazene aceturate (Berenil, Hoechst) at 7 mg/kg body weight (bw) at intervals of 2 to 4 weeks, no significant drop in the prevalence of African animal trypanosomosis (AAT) was observed. To examine a suspected drug resistance, 20 Zebu cattle, naturally infected with T. congolense and/or T. vivax, were transferred in December 1989 from Samorogouan into a fly-proof stable. Diminazene aceturate at 7 mg/kg bw cured infections of T. vivax, but was ineffective against T. congolense. Likewise, treatments with homidium bromide (Ethidium, FBC) at 1 mg/kg bw and isometamidium chloride (Trypamidium, Rhône Mérieux) at 1 mg/kg bw, respectively, proved to be ineffective. Corresponding chemotherapeutic trials in previously unexposed Zebu bulls and Sahelian goats infected with one primary T. congolense isolate from Samorogouan demonstrated a high level of resistance to diminazene aceturate (7 mg/kg bw in cattle and 17.5 mg/kg bw in goats), isometamidium chloride (1 and 2 mg/kg bw i.v. in goats) and quinapyramine sulphate (Trypacide'S', Rhône Mérieux) at 5 mg/kg bw in goats. The appearance of a multiple-drug-resistant strain of T. congolense emphasizes the urgent need for new chemical substances as trypanocidal drugs and the increasing importance of efficient vector control.