Trypanosoma congolense: manifestation of resistance to Berenil and Samorin in cloned trypanosomes isolated from Zambian cattle.

Four Trypanosoma congolense clones derived from a Mumbwa field isolate proved to be resistant to Berenil with a minimum curative dose (MCD) value of 40 mg/kg and to Samorin with an MCD of 4 mg/kg for mice. Two other clones, one being resistant to Berenil with an MCD of 45 mg/kg but susceptible to 1 mg/kg Samorin, and the other being resistant to Samorin with MCD of 16 mg/kg but susceptible to 7 mg/kg Berenil, were experimentally rendered resistant to each of the respective drugs they were susceptible to by subcurative treatments in mice. The original trypanosome strains and their derivative clones were then screened for their sensitivity to Berenil or Samorin. Three clones derived from the Mumbwa isolate were resistant to Berenil, with MCD's of 14 to 28 mg/kg, and to Samorin, with MCD's of 4 mg/kg. A single Mumbwa derivative clone was relatively sensitive to both Berenil with an MCD of 7 mg/kg and to Samorin with an MCD of 2 mg/kg. The reciprocal drug induction results confirmed that although trypanosomes can acquire tolerance to both Berenil and Samorin, no cross-resistance between the two was evident.