USE OF INSECTICIDE-IMPREGNATED TARGETS FOR THE CONTROL OF TSETSE-FLIES (GLOSSINA SPP) AND TRYPANOSOMIASIS OCCURRING CATTLE IN AN AREA OF SOUTH-WEST ETHIOPIA WITH A HIGH PREVALENCE OF DRUG-RESISTANT TRYPANOSOMES

In the Ghibe valley, south-west Ethiopia, a tsetse control trial using deltamethrin-impregnated targets was started in May 1990. The mean re lative density of the main vector, Glossina pallidipes, fell from 2.1 flies per trap per day in the 12 months prior to introduction of tsets e control to 0.41 flies per trap per day in the 12 months after tsetse control was initiated. The annual mean prevalence of Trypanosoma cong olense infections in cattle fell from 32% in the 2 years before tsetse control to 13% in the 2 years following deployment of targets. The la rgest reduction occurred in the first quarter of 1991 when the mean mo nthly trypanosome prevalence was 5%. There was also a decrease of appr oximately 75% in the estimated rate of relapse of trypanosome infectio ns in cattle after treatment with diminazene aceturate. However, in Ju ne 1991, socio-political disturbances occurred in Ethiopia and were as sociated with substantial thefts of targets. Following these thefts, t he mean relative density of G. pallidipes rose from 0.41 flies per tra p per day in the period May 1990-April 1991, to 1.29 flies per trap pe r day in the period April 1932-March 1993. Associated with this rise, the mean trypanosome prevalence in cattle increased from 13% in the pe riod May 1991-April 1992 to 28% in the period May 1992-April 1993. Thi s was similar to the mean trypanosome prevalence in cattle during the pre-control period. Thus, while effective tsetse control methods can b e used to reduce the transmission of trypanosomes their long-term impa ct is dependent on their sustainability.