Field Investigation on the Appearance of Drug-Resistant Populations of Trypainosomes in Metekel District, North-West Ethiopia
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Date
1998-01
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Addis Ababa Universty
Abstract
The objectives of the present study were (1) to determine the prevalence rate of trypnnosome
infections in the village cattle populations of Metekel district, North-west Ethiopia, (2) to
assess the prophylactic activity of isometnmidium chloride to natural trypanosome infections
and (3) to monitor the trypanocidal activity of diminazene acelurate and isometamidium
chloride in mice experimentally infected with trypanosome field isolates.
In order to obtain information on the prevaknce rate of trypanosome infections in the area and
to identify cattle herds highly suspected to be infected with drug resistant trypanosome
populations. questionnaire surveys and cross sectional studies were carried out from March to
October 1997 in four villages. The results of these studies showed that trypanosomosis is a
major constraint to livestock production in the area with an overall prevalence rate of 17.2%
(95% CI: 14,20.8). Trypanosoma congolense was the dominant species accounting fo r 47.6%
of the overall infections. The overall mean
PCV
value of the total cattle tested was found to be
4.9 ± 0.20% Parasitaemic cattle had significantly lower mean PCV values(21.6 + 0.47) than
aparasitaemic cattle (25.5±0.21 ) (p<0.05) Moreover. there is indiscriminate use of
trypanocidal drugs and exposurte of cattle in the area to subcurative doses of trypanocidal
drugs and farmers complaine about failure of treatment to cure infections in cattle.
Based on the results of the cross sectiona l study and the questionnaire, two villagec were
selected for longitudinal field study on the occurrence of drug resistant trypanosome
populations. From these villages 50 Zebu cattle naturally infected with trypanosomes. 52.4%
of the infections being due to T congolense, were selected and infected with a prophylactic
dose (1 mg /kg bw) of isomctamidium chloride (Trypamidium ®. Lot No. U6962 /E. Rhone
Merieux). The findings in the field demonslrmed 6 (13% ) relapse/ breakthrough infections. all
of them being T. congolensl.within 4 weeks of treatment In the same study 18 (37. 9%) and
25 (50%) relapse/breakthrough infections were recorded within 8 and 12 weeks of treatment,
respectively. The result also indicated that 20 cases (80%) of the overall relapse/breakthrough
infections were due to T. congolensel.
Field isolates were obtained from relapse/ breakthrough infections one. two and three months
after treatment and injected in mice. To confirm the field results and to study the therapeutic
activity of diminazent.: accturate in experimental animals, three field isolates of T.congole
nse
were ranuomly selected from the relapse populations. Investigations were conducted on the
sensitivity of these isolates to isometamidium chloride Trypamidium ®. Rhone Merieux) and
diminazene aceturate ( Bereni l ®, Hoechst). Mice infected and treated with ranges of doses of
isomelamidium chloride and diminazene oceturate were followed for relapse injections.
isometamidium chloride at doses of 0.5 to -t mg lkg b\\ failed completely 10 cllre T
congohmse infections. Similarly, diminazene acelurate at doses of 3.5 to 28 mg /kg bw did not
clear the parasites in all or the mice infected. There was a correlation of drug-dosage used and
the lime of relapse: mice treated with lower doses showed relapse earlicr than mice treated
with higher doses.
Based on these studies it is concluded that the duration of prophylactic activity of
isometamidium chloride ( 1 mg/kg, bw) to trypanosome populations circulating in the study
cattle of Metekel region is less than 1 month. Tryplanosoma cogolense field isolates
expressed resistance to both isometamidium chloride and diminazene aceturate in mice.
However, it was not known whether this double resistance was expressed by trypanosome populations or by two different populations each of which expressing resistance
to one of the drugs.
The results indicated that there is an urgent need to extend and inlensif) field and laboratory
works to monitor the development of drug resistance of pathogenic trypanosomes and its
impact on livestock productivity in Metekel region in particular and across the tsetse infested
zone of Ethiopia in general.
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Keywords
Trypainosomes in Metekel District,