Dynamics of Parasitaemia in <i>Trypanosoma evansi</i> Infection in Donkeys and the Efficacies of Buparvaquone and Isometamidium chloride Treatments

Abstract

The aim of this study was to evaluate the efficacies of Buparvaquone (an anti-theilerial drug) and Isometamidium chloride (a standard trypanocide) in the treatment of experimental Trypanosoma evansi infection in donkeys. Out of a total of 24 donkeys, 6 were assigned to each of the experimental groups A1, A2, A3 and B at random. About 2.0x106 T. evansi parasite in 2 mL inoculum was used to infect each of the donkeys in groups A1, A2 and A3 through jugular vein while group B remained as Un-infected control. On day 28 post-infection, animals in groups A2 and A3 were treated with Isometamidium chloride and Buparvaquone respectively. Parasitaemia levels were evaluated post-infection and post-treatment using Haematocrit Centrifugation Technique and supported with mice inoculation tests to ascertain effectiveness of treatments. Group means of parasitaemia were presented on graphs. Result showed that parasites were first detectable from peripheral blood of the infected animals from day 3 and by day 4 post-infection all animals were parasitaemic and the levels fluctuated in subsequent days. The infected-untreated group of animals was aparasitaemic on day 100 post-infection onward using haematocrit centrifugation technique test but mice inoculation test detected relapse with death of all mice used due to heavy parasitemia. Similarly, the buparvaquone-treated group was aparasitemic on day 49 post-treatment (corresponding to day 77 post-infection) but mice inoculation test detected relapse of parasitaemia in the group and all mice used also died. Isometamidium-treated animals were negative for parasitaemia for 50 days on mice inoculation test but later on day 100 post-treatment, showed 60% relapse with parasiaemia level of 1+ in the mice used and they did not die within 48 days of observation. In conclusion, experimental Trypanosoma evansi infection in donkeys have pre-patent period of 3-4 days, parasitaemia pattern is undulating and infected-untreated animals became subclinical carriers from day 100 post-infection. The parasites in untreated, carrier animals maintained their virulence and pathogenicity. Buparvaquone on the other hand, depressed parasitaemia but the parasites were virulent and pathogenic to mice. Isometamidium chloride treatment resulted in incomplete clearance of parasitaemia due to Trypanosoma evansi and the relapsed parasites were avirulent and apathogenic. This is also the first report on the trial of buparvaquone for anti-Trypanosoma evansi effect in donkeys.