Abstract
BackgroundThe detection of insecticide resistance in natural populations of Anopheles vectors is absolutely necessary for malaria control. In the African region, the WHO insecticide susceptibility test is the most common method for assessing resistance status. In order to search for a simple, rapid and more reliable technique in the assessment of insecticide resistance in malaria vectors, we compared the WHO tests with the CDC bottle bioassay in the Ouemé province of southern Benin where insecticide resistance has been widely reported.MethodsLarvae and pupae of Anopheles gambiae s.l. mosquitoes were collected from the breeding sites in Ouemé. WHO and CDC susceptibility tests were conducted simultaneously on unfed female mosquitoes aged 2–5 days old. WHO bioassays were performed with impregnated papers of deltamethrin (0.05%) and bendiocarb (0.1%), whereas CDC bioassays were performed with stock solutions of deltamethrin (12.5 μg per bottle) and bendiocarb (12.5 μg per bottle). PCR techniques were used to detect species, Kdr and Ace-1 mutations. CDC biochemical assays using synergists were also conducted to assess the metabolic resistance.ResultsA slight decrease in mortality rates was observed with 97.95% and 98.33% obtained from CDC and WHO bioassays respectively in populations of mosquitoes from Adjara and Dangbo. PCR revealed that all specimens tested were Anopheles gambiae s.s. The Kdr mutation was found at high frequency in all populations and both the Kdr mutation and mono-oxygenase enzymes were implicated as mechanisms of pyrethroid resistance in An. gambiae from Misserete.ConclusionThis study emphasizes that both WHO and CDC bioassays give similar results with regards to the susceptibility of mosquitoes to insecticides in southern Benin. There were complementarities between both methods, however, some specificity was noted for each of the two methods used. Both Kdr and metabolic mechanisms were implicated in the resistance.
Highlights
The detection of insecticide resistance in natural populations of Anopheles vectors is absolutely necessary for malaria control
Susceptibility of An. gambiae populations to pyrethroids and carbamates The results of 24 hours mortality recorded after exposure of mosquitoes to impregnated papers of deltamethrin and bendiocarb were compared to those recorded from CDC bottle bioassays at the susceptibility threshold of
WHO susceptibility tests require more mosquitoes (4 test tubes containing 20 to 25 mosquitoes each plus one control tube) than those of CDC technique (4 test bottles containing 15 to 20 mosquitoes each plus one control bottle), the concordance between the results obtained with both methods is clear
Summary
The detection of insecticide resistance in natural populations of Anopheles vectors is absolutely necessary for malaria control. Most commonly, when the frequency of resistant insects in a vector population increases, efficacy of the treatment decreases up to the point where the insecticide has to be replaced by another one. The management of insecticide resistance is a major issue, which must interest the different National Malaria Control Programmes. This management requires two kinds of information: sound knowledge of the mechanisms of resistance and a thorough resistance monitoring programme. Routine monitoring of insecticide resistance in the natural populations of vectors helps us to detect early resistance and improve effectiveness of operational control strategies
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