[Impact of pyrethrin resistance on the efficacity of impregnated mosquito nets in the prevention of malaria: results of tests in experimental cases with deltamethrin SC].

The effects of impregnated bednets treated with deltamethrin at a dosage of 25 mg a.i./m2 were evaluated at two testing stations in Côte d'Ivoire. The first one was located in Yaokoffikro, where Anopheles gambiae s.s. are resistant to pyrethroids (including deltamethrin), and the second in M'be, close to a large rice-growing area where An. gambiae s.s. are susceptible pyrethroids. In both situations, treating bednets with deltamethrin was very effective in limiting contact between man and vector. 72% fewer female An. gambiae entered the huts in the susceptible area, whereas a decrease of 43% was recorded in the resistant area, indicating that deltamethrin still has a certain repellent effect on resistant populations of An. gambiae s.s. Overall mortality induced by bednets treated with insecticide was significantly higher in the resistant area (56.4% as versus 44.3%). An explanation for this apparent paradox is that the mosquitoes being less repelled by the insecticide remain on the treated material for longer periods of time and most of them eventually die. The results of this study indicate that bednets treated with deltamethrin are an effective prophylactic measure even in areas where An. gambiae s.s. are resistant to pyrethroids and should still be considered as a practical means of personal protection against malaria even in pyrethroid resistance areas with high frequency of kdr resistance genes.