Characterisation of the drug sensitivity and species of trypanosomes isolated from camels in Marsabit, Kenya, between 1979 and 1993

Abstract

Trypanosomiasis is one of the most important diseases in the tropics and especially Africa due to its negative impact on livestock productivity. For effective chemotherapeutic control, it is necessary that constant evaluation of the sensitivity of trypanosomes to the available trypanocides be carried out. In this study, T evansi strains isolated in 1970, 1990 and 1993 were characterised for drug sensitivity to melarsomine, suramin and quinapyramine. Initially, the trypanosomes were characterised to confirm the species usmg kDNA minicircle analysis. Trypanosome kDNA minicircles were PCR-amplified and the products digested with Mho! restriction endonuclease. The minicircles were cut once yielding two fragments of 3~Obp and 650bp. On comparison to known T evansi restriction patterns it was confirmed that the trypanosomes were indeed T evansi and that there was no mixture with other species. Subsequently, 1x 10 trypanosomes were inoculated into mice which were then treated 6 hours later with titrated dosages of melarsomine, suramin and quinapyramine. The mice were examined thrice a week for 60 days by observing wet smears of tail blood under the microscope. After 60 days, non-parasitaemic mice were deemed cured. The proportion of mice cured to the total were recorded and used to determine curative doses for 50% and 99% of the mice infected i.e. CD50 and CD99 values for each strain. All the T evansi strains were sensitive to low levels of suramin, 0.51 - 3.69 mg/kg body weight (BW), and to melarsomine, 0.25 -1.7 mg/kg BW. This .shows that there is no substantial resistance of the T evansi populations to either melarsomine or suramin. The two drugs can therefore be effectively used for treatment of such infections. The T evansi strains, however, displayed significant levels of resistance to quinapyramine with CD50 values ranging from 1.42 mg/kg to 8.35 mg/kg. On the basis of CD50 values sensitivity of the T. evansi populations to suramin and quinapyramine was not significantly different for populations collected in 1979, 1990 and 1993. Therefore, the resistance of T. evansi populations in northern Kenya to these two compounds did not appear to have increased significantly over a 14-year period despite widespread use of quinapyramine and suramin. The three T. evansi populations did not differ significantly in their sensitivity