Expression of resistance to isometamidium and diminazene in Trypanosoma congolense in Boran cattle infected by Glossina morsitans centralis

Investigations were conducted on the sensitivity to isometamidium chloride (Samorin R ) and diminazene aceturate (Berenil R ) of derivatives of three of the Trypanosoma congolense stocks isolated between 1978 and 1983 from Zebu cattle in the Bobo-Dioulasso region of Burkina Faso. Boran cattle were used in the drug-sensitivity tests and were infected using Glossina morsitans centralis . The results showed that T. congolense stock IL 2466 isolated in 1978 was sensitive to the standard therapeutic dose of isometamidium chloride (0.25 mg kg −1 ) and of diminazene aceturate (a.i. 3.5 mg kg −1 ). However, T. congolense stock IL 2468 isolated in 1982 was resistant to both the prophylactic (0.5 and 1.0 mg kg −1 ) as well as the therapeutic doses of isometamidium chloride (up to 1.0 mg kg −1 ) although the sensitivity to the theapeutic dose of diminazene aceturate (3.5 mg kg −1 ) was not affected. The T. congolense stock IL 2856 isolated in 1983 was highly resistant to the therapeutic action of diminazene aceturate (up to 10.5 mg kg −1 ), as well as to the prophylactic (up to 1.0 mg kg −1 ) and therapeutic action of isometamidium chloride (up to 2.0 mg kg −1 ). The infection rates of the drug-resistant stocks of T. congolense in G.m. centralis , when goats were used as reservoir hosts, were as high (range, 22.3–56.3%) as of the drug sensitive stock (49.5%). The resistance trait in the two stocks remained stable after their cyclical development in the tsetse vectors. The rate of transmission of the drug-resistant stocks to mice by the infected tsetse was also high (mean 81.3%).