Comparison of deltamethrin tablet formulation with liquid deltamethrin and permethrin for bednet treatment in The Gambia

The study aim was to compare three formulations, tablet deltamethrin, liquid deltamethrin and liquid permethrin, for their impact on vector behaviour and persistence. Product acceptance, perceived side-effects and user's perceptions of effectiveness were also investigated. At the beginning of the 1998 rainy season, 255 nets in a Gambian village were dipped in one of the three insecticides. Chemical residue analysis immediately after dipping showed that the target doses were reached for the liquid insecticides, but tablet deltamethrin deposited significantly less. Insecticide persistence at 5 months, however, was highest for the tablet formulation. Susceptibility tests established that Anophelines in this area were sensitive to both insecticides. All three formulations appeared effective as very few live Anophelines, or other mosquitoes, were caught under the treated nets. This conclusion was supported by the bioassay data with both deltamethrin formulations giving over 90% mortality soon after dipping and at 3 months, and at 5 months 70.8 and 79.6% were obtained for deltametrin liquid and tablet, respectively. Permethrin appeared less effective at all times (72.4, 86.8, 59.0%). There were no serious side-effects reported by the villagers following dipping. All three treatments were perceived as effective by the majority (92%) of users and most (93%) wanted to use the insecticide again. Deltamethrin tablets thus appear as good as permethrin for treating bednets in The Gambia. In addition, a tablet formulation is considerable easier to pack and distribute.