Moreover,early studies showed that experimental infections with Trypanosoma brucei rhodesienseand Trypanosoma brucei brucei mostly caused the death of untreated chimpanzees, while infections with Trypanosoma brucei gambiensewere mild and did not result in apparent clinical symptoms (Baker, 1962, 1968; Baker and Taylor, 1971; Godfrey and Killick-Kendrick, 1967; Hoare, 1972).