Isolation of drug-resistant strains of Trypanosoma congolense from the lower Shabelle region of southern Somalia.

Drug resistance by pathogenic trypanosomes in Somali livestock has been suspected for some time but there have been few attempts to examine this problem in detail. Field isolations from two areas in the Lower Shabelle Region were obtained by injecting blood from trypanosome infected cattle into a recipient calf. Once the calf became parasitaemic it was treated with a standard dose of isometamidium chloride (Samorin, RMB) at 0.5 mg/kg. When a subsequent relapse infection developed, indicative of drug resistance, blood was taken and injected into groups of cattle and mice and these were treated with a range of doses of isometamidium chloride and diminazene aceturate (Berenil, Hoechst AC) to determine the degree of drug resistance. Both isolates showed remarkably high levels of drug resistance to both isometamidium chloride and diminazene aceturate, with minimum curative doses in cattle of > 2.0 mg/kg and 7.5 mg/kg for the two drugs respectively. Minimum curative doses in mice were approximately ten-fold those in cattle. Fortunately there have been a very few reports from Africa of such high levels of resistance of Trypanosoma congolense to this normal "sanative pair" of drugs. The results indicate that drug resistance could be an important constraint on the use of trypanocidal drugs to control trypanosomosis in Somalia.