Variation of sensitivity of Trypanosoma evansi isolates from Isiolo and Marsabit counties of Kenya to locally available trypanocidal drugs

Trypanocidal resistance is a major cause of treatment failure. This study evaluated the sensitivity of Trypanosoma evansi field isolates collected from Marsabit and Isiolo counties, Kenya. A total of 2,750 camels were screened using parasitological tests for trypanosomes. Of the screened camels, 113 tested positive from which 40 T. evansi isolates were tested using the single dose mice sensitivity test. Five treatment groups each comprising of 6 mice were inoculated intraperitoneally with 1x105 trypanosomes of each isolate and treated 24 hours later with isometamidium chloride at 1 mg/kg, homidium chloride at 1mg/kg, diminazene aceturate at 20 mg/kg and quinapyramine sulphate & chloride at 1 mg/kg. The fifth group was left untreated (positive control). The mice were monitored daily for 60 days. A survey on camel owners' practices that influence development of resistance to trypanocidal drugs was then conducted. Results indicated presence of drug resistance in all the 7 study sites that had infected camels. Seven of the isolates tested were resistant to diminazene aceturate whereas, 28, 33 and 34 were resistant to isometamidium chloride, quinapyramine sulphate & chloride and homidium chloride, respectively. Seven (17.5%) isolates of the 40 tested were sensitive to all 4 drugs, whereas, 7.5%, 10%,55% and 10% were resistant to 1,2,3 and 4 drugs, respectively. The prevalence of multiple drug resistance was 75%. Survey data indicated that camel management practices influenced the prevalence and degree of drug resistance. In conclusion, the multiple drug resistance observed in the two counties may not be an indication of total trypanocidal drug failure. Judicious treatment of confirmed trypanosomiasis cases with correct dosage would still be effective in controlling the disease since the observed resistance was at the population and not clonal level. However, integrated control of the disease and the vectors using available alternative methods is recommended to reduce drug use.