Susceptibility status of An. gambiae.s.l to 7 different insecticides in 15 sites in Ethiopia

Objective of this study: To assess the susceptibility status of An. gambiae.s.l mosquito to seven insecticides approved for malaria control (DDT, Bendiocarb, Propoxur, Malathion, Fenitrothion, Deltamethrin and Lambdacyhalothrin) in 15 districts in Ethiopia. Data used and methods: Standard WHO insecticide susceptibility tests were conducted in September 2010 on adult female mosquitoes which were reared from larvae and pupae. Insecticide impregnated papers with discriminating concentrations of all seven insecticides were used to test susceptibility to various insecticides. Main results: The WHO characterizes insecticide susceptibility as mosquito mortality rates >98% after 24 hours post-exposure to insecticide. The overall mortality due to Deltamethrin ranged from 34.0% in Gelana district to 100% in Hawi-gudina and Miesso districts. Vector populations in ten districts showed evidence of resistance to Deltamethrin, while susceptibility to DDT in all districts was very low (0-78.8% mortality). Resistance to Lambdacyhalothrin was detected in all sites (30-94% mortality). Susceptibility to Malathion was observed in five sites, whereas eight sites appeared to contain resistant populations (89-97% mortality). Vector susceptibility to Fenitrion ranged from 97-100%, whereas for Bendiocarb and Propoxur it was above 99 % in all tested sites. Recommendations: These results demonstrate the importance of sustained monitoring of mosquito susceptibility to specific insecticides. Given the significant role of US government funding in malaria control in Africa, targeted insecticide selection based on susceptibility monitoring data could significantly improve effectiveness of existing malaria control activities.