Studies on prevalence of trypanosomosis and drug sensitivity on trypanosome congolenes in Wolayita and Dawero zone of Southern Ethiopia
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Date
2007-06
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Abstract
The current study was conducted in tsetse and non tsetse controlled areas of the Southern
Nation Nationalities and Peoples Regional State (SNNPRS) of Ethiopia. A cross sectional
study to determine the prevalence of bovine trypanosomosis as well as a drug sensitivity tests
on T. congolense in both naturally and experimentally infected cattle and mice, respectively
were carried out. In the first study area, Humbo district, a total trypanosome prevalence of
4.8% (95% CI: 1.8–7.5) was recorded. In the second study area, Mareka district, a total
prevalence of 20.4 (95% CI: 14–26.8) was recorded. There was statistically significant
difference in the mean prevalence of trypanosomosis between the two areas (P<0.001). The
mean PCV value for Humbo and Mareka was 26.2 (95%: 25.7-26.7) and 22.7 (95% CI: 22.1-
23.3), respectively. There was statistically significant difference in the mean PCV value
between the two study areas (P<0.001). To assess the prophylactic activity of isometamidium
chloride a field trial was conducted in Humbo on nine parasitological positive zebu cattle. A
breakthrough case of 66.7% (6/9) was recorded in less than five weeks. A qualitative mice
assay was conducted on two T. congolense isolates obtained from the break through cases
with ranges of doses of isometamidium chloride and diminazene diaceturate. Thereafter the
mice were followed for relapse infection. Isometamidium at doses 0.5-4mg/kg b.w and
diminazene at doses of 3.5-28mg/kg b.w failed completely to cure T. congolense infections in
any of the mice. A quantitative mice assay was conducted on four T. congolense isolates
obtained from Mareka. The four isolates were pooled into two pools (Pool-1 and Pool-2) for
the quantitative mice assay. The pooled isolates were tested with the same trypanocidal drugs
and ranges of doses as it was used for the qualitative mice assay. The minimum curative dose
(MCD) of isometamidium chloride and diminazene diaceturate that cleared the trypanosome
from mice infected with Pool-1 was found to be 4mg/kg b.w and 28mg/kg b.w, respectively.
For mice infected with Pool-2 the MCD of isometamidium chloride and diminazene
diaceturate that cleared the trypanosme was found to be 2mg/kg b.w and 14mg/kg b.w,
respectively. Even though cloned populations were not used to proof the observed resistance
was at the individual level or not the result indicated that there is the possibility of failure of
“sanative pair” between the two drugs.
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Keywords
Trypanosoma congolense, drug resistance, cattle, mice assay, diminazene diaceturate