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Tsetse-transmitted African Animal Trypanosomosis (AAT) constitutes a main constraint to livestock industries in sub-Saharan Africa, causing reduced productivity and fertility as well as death without treatment. Control strategies comprise trypanocidal drug use and reduction of vector populations (Glossina spp) by various methods. Vector control methods are successful but unsustainable resulting in rapid reversal of achievements after external support termination. This study evaluates an innovative approach to control Glossina palpalis palpalis using deltamethrin-treated mosquito fences protecting pig pens, finally reducing trypanosome prevalence in Ghana. Two villages comparable in pig numbers, husbandry practices, vegetation, surface water and climate (tropical rain forest zone) were selected. While one village (Zorh) served as unprotected control, the pig pens of the other village (Kwesi Konfo) were protected with 100cm high insecticide-treated mosquito fences (polyester, 150denier, 100-120mg/m2 deltamethrin) which were attached to the timber poles and planks surrounding each pig pen in May 2007. Apparent tsetse densities were monitored for six months by using geo-referenced biconical traps.
The reduction of fly numbers in Kwesi Konfo (netted pig pens) exceeded 90 % within two months. A further decline of the population during the following months led to reductions of more than 95 % until termination. This contrasted clearly with the tsetse numbers in the control village, which remained stable apart from their usual seasonal variations.
Captured tsetse flies were identified and separated according to sex and age. Non teneral and parous female flies were dissected for ovarian age grading. Net samples were taken at monthly intervals and stored for further evaluation of their bio-cidal activity through bioassays.
To monitor the persistence of the insecticide treated netting material it was tested in the laboratory before and throughout the installation using house flies (Musca domestica). The rates of paralysis five, ten and fifteen minutes after exposure decreased markedly in the six months trial corresponding with the time passing. The rates of paralysis 30 minutes, six hours and 24 hours after exposure remained at comparable levels until termination of the project. Blood samples were collected three times from about 50 % of the respective pig populations during the trial: at the onset, after three months, and at the end of experiment (six month after intervention). After the first sampling all pigs were treated with a trypanocidal drug (diminazene aceturate, Berenil®, Intervet) at a dose of 3.5mg/kg. Initially, thin blood smears revealed a trypanosome (Nannomonas) prevalence of 76 % and 72 %, respectively, in pigs from Kwesi Konfo and Zorh. The examination of the
second blood samples showed a prevalence reduction to 16 % in Kwesi Konfo whereas the infection rate in pigs of the control village had increased to 84 %; this effect was well confirmed by the results of the third examination with 8 % trypanosome prevalence in protected pigs as opposed to 60 % in the control pigs. The study confirmed that insecticide treated netting material leads into a significant reduction of tsetse flies even in dense vegetation of tropical rain forest zone and therefore considerably improves livestock industries in sub-Saharan Africa. A successful local vector control method has proven its feasibility. High practicability, easy handling and low cost of material as well as a confirmed persistence of more than six months allows independent and individual use of insecticide treated nets by farmers themselves. Future improvement of quality characteristics, concerning persistence, heat and UV-resistance of the net material is recommended.