Abstract
BackgroundThe evolution and spread of pyrethroid resistance in Anopheles gambiae s.s, the major malaria vector in sub-Saharan Africa, is of great concern owing to the importance of pyrethroid-treated nets in the WHO global strategy for malaria control. The impact of kdr (the main pyrethroid-resistance mechanism) on the behaviour of An. gambiae is not well understood. The objective of this study was to determine whether high or low doses of permethrin differ in their resistance-selection effects.MethodsThe effect of permethrin treatment was assessed under laboratory conditions using the tunnel test technique against susceptible, heterozygous and homozygous genotypes. Experimental huts trials were then carried out in Benin to assess the level of personal protection conferred by nets treated with a variety of permethrin concentrations and their impact on the selection for kdr allele.ResultsTunnel tests showed that nets treated with permethrin at 250 and 500 mg/m2 induced higher mortality and blood feeding reduction among susceptible and heterozygous (RS) females as compared to the lower concentration (100 mg/m2). The experimental hut trials showed that the best personal protection was achieved with the highest permethrin concentration (1,000 mg/m2). Mosquito genotyping revealed a non-linear relationship in the survival of kdr susceptible and resistant genotypes with permethrin dosage. Higher dosages (≥250 mg/m2) killed more efficiently the RS genotypes than did lower dosages (50 and 100 mg/m2).ConclusionThis study showed that nets treated with high permethrin concentrations provided better blood feeding prevention against pyrethroid-resistant An. gambiae than did lower concentrations. Permethrin-treated nets seem unlikely to select for pyrethroid resistance in areas where the kdr mutation is rare and present mainly in heterozygous form.
Highlights
The evolution and spread of pyrethroid resistance in Anopheles gambiae s.s, the major malaria vector in sub-Saharan Africa, is of great concern owing to the importance of pyrethroid-treated nets in the WHO global strategy for malaria control
Pyrethroids are the only insecticides currently recommended by the World Health Organization for treatment of mosquito nets owing to their strong insecticidal activity at low concentrations and their low mammalian toxicity [1]
Pyrethroid resistance in Anopheles gambiae has become widespread in different regions of Africa [7,8,9] and may represent a threat for successful and sustainable implementation of insecticide-treated net (ITN) programmes
Summary
The evolution and spread of pyrethroid resistance in Anopheles gambiae s.s, the major malaria vector in sub-Saharan Africa, is of great concern owing to the importance of pyrethroid-treated nets in the WHO global strategy for malaria control. Pyrethroid-treated nets are effective in reducing malaria morbidity and mortality [2,3,4] and may provide community protection through mass impact on vector mosquito populations, when used at a high coverage rate [5,6]. Pyrethroid resistance in Anopheles gambiae has become widespread in different regions of Africa [7,8,9] and may represent a threat for successful and sustainable implementation of insecticide-treated net (ITN) programmes. A point mutation (leucine to phenylalanine) in the S6 transmembrane segment domain II in the sodium channel sequence is associated with the kdr resistance in West Africa [10] and is characterized by a reduction in the intrinsic sensitivity of the insect nervous system to DDT and pyrethroids [11]. A second point mutation (leucine to serine) has been reported in An. gambiae from East Africa and is responsible for high level of resistance to permethrin [12]
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