COMPARISON OF PERMETHRIN TREATMENTS FOR BEDNETS IN THE-GAMBIA

An experimental hut trial of bednets was undertaken in The Gambia to c ompare six different permethrin treatments, including a wash-resistant formulation, and to test the effect of thorough hand washing of the n ets. The wash-resistant formulation on nylon and cotton nets deterred gambiae Giles (sensu lato) from house entry. All treated bednets kille d a significantly higher number of A. gambiac (sensu lato) than untrea ted nets. The ability to kill mosquitoes was not diminished with the w ash-resistant and Wellcome formulations after washing unlike the norma l ICI formulation, this result being consistent with the permethrin re sidues found by gas liquid chromatographic (GLC) analyses to persist o n the nets after washing. The mortality on treated cotton nets was sig nificantly less than on treated nylon nets. Of the unwashed nets only the cotton net was significantly repellent. Both washed and unwashed t reated nets significantly reduced the proportion of human blood-fed mo squitoes that survived and were potentially able to transmit malaria. Although the wash-resistant formulation might prove more efficient at killing mosquitoes with time, as compared to the other treatments, in The Gambia, where women wash their nets frequently, we suggest that th e cheapest and most readily available formulation is used on nylon net s where possible.