[Efficacy of permethrin-impregnated Olyset Net mosquito nets in a zone with pyrethroid resistance vectors. II. Parasitic and clinical evaluation].

The efficacy of permethrin-treated Olyset Net mosquito nets in preventing transmission and morbidity of malaria was studied in Kafine, a village in the rice-growing region of the Cote d'Ivoire. Entomological data demonstrated that permethrin-treated mosquito nets failed to reduce transmission of malaria. Laboratory tests showed that Anopheles gambiae s.s. in Kafine were resistant to permethrin and other pyrethroids. Study included a cohort of 163 children under five years of age who did or did not use mosquito nets. The number of patients seeking treatment for malaria attacks with fever was recorded weekly. No difference was found between the user and non-user groups with regard to the percentage of children exhibiting Plasmodium flaciparum trophozoites or gametocytes or to the mean parasite load. However the rate of high density parasitemia and malaria attacks was twice as high in the non-user group. This difference between users and non-users of mosquito nets cannot be explained only as the result of a physical barrier against bites. In areas where mosquitoes are resistant to pyrethroids, tests conducted in experimental huts have shown that impregnated mosquito nets reduce host/vector contact. However further study will be need to evaluate the overall impact of impregnated nets on malaria in the areas where mosquitoes are resistant to insecticides.