Resistance to drug by different isolates Trypanosoma evansi in China.

In order to understand drug resistance in Chinese Trypanosoma evansi isolates, the in vitro growth inhibition test was carried out to detect the sensitivities to suramin and antrycide of 12 T. evansi isolates. For suramin, 50% inhibitory concentrations (IC(50)) ranged from 0.041 to 0.752 microg/ml; for antrycide, the IC(50) values ranged from 0.00151 to 0.06694 microg/ml. In vivo experiments in mice with selected isolates showed that the isolate most resistant to suramin was not cured at a dosage of 10 mg/kg, while the isolate that was most resistant to antrycide showed only 50% cure rate at a dose rate of 5 mg/kg. The data presented here indicate that T. evansi isolates from China had differences in drug resistance, with some isolates exhibiting low sensitivity to suramin or antrycide, while a few isolates showed complete drug resistance to curative dosages of suramin or antrycide. No drug cross-resistance was observed between suramin and antrycide.