Abstract
BackgroundIn Benin, Indoor Residual Spraying (IRS) and long-lasting insecticidal nets (LLINs) are the cornerstones of malaria prevention. In the context of high resistance of Anopheles gambiae to pyrethroids, The National Malaria Control Program (NMCP) has undertaken a full coverage of IRS in a no-flood zone in the Oueme region, coupled with the distribution of LLINs in a flood zone. We assessed the impact of this campaign on phenotypic resistance, kdr (knock-down resistance) and ace-1R (insensitive acetylcholinesterase) mutations.MethodsInsecticides used for malaria vector control interventions were bendiocarb WP (0.4 g/m2) and deltamethrin (55 mg/m2), respectively for IRS and LLINs. Susceptibility status of An. gambiae was assessed using World Health Organization bioassay tests to DDT, permethrin, deltamethrin and bendiocarb in the Oueme region before intervention (2007) and after interventions in 2008 and 2010. An. gambiae specimens were screened for identification of species, molecular M and S forms and for the detection of the West African kdr (L1014F) as well as ace-1R mutations using PCR techniques.ResultsThe univariate logistic regression performed showed that kdr frequency has increased significantly during the three years in the intervention area and in the control area. Several factors (LLINs, IRS, mosquito coils, aerosols, use of pesticides for crop protection) could explain the selection of individual resistant An. gambiae. The Kdr resistance gene could not be the only mechanism of resistance observed in the Oueme region. The high susceptibility to bendiocarb is in agreement with a previous study conducted in Benin. However, the occurrence of ace-1R heterozygous individuals even on sites far from IRS areas, suggests other factors may contribute to the selection of resistance other than those exerted by the vector control program.ConclusionThe results of this study have confirmed that An.gambiae have maintained and developed the resistance to pyrethroids, but are still susceptible to bendiocarb. Our data clearly shows that selection of resistant individuals was caused by other insecticides than those used by the IRS and LLINs.
Highlights
The present study aimed to report the first case of the impact of the three years of large scale of Indoor Residual Spraying (IRS) and long-lasting insecticidal nets (LLINs) interventions on phenotypic resistance, kdr and ace-1R alleles in natural populations of An. gambiae s.l. from southeast Benin
In 2010, heterozygous (RS) individuals of ace-1R mutation were detected in all localities 24 months after the first round of IRS, except in Adjohoun, Seme LLIN and control LLIN
The results of this study have confirmed that natural populations of An.gambiae in the Oueme region have maintained and developed their resistance to pyrethroids, but are still susceptible to bendiocarb
Summary
In the context of high resistance of Anopheles gambiae to pyrethroids, The National Malaria Control Program (NMCP) has undertaken a full coverage of IRS in a no-flood zone in the Oueme region, coupled with the distribution of LLINs in a flood zone. In subSaharan Africa, insecticide treated nets (ITNs) and indoor residual insecticide spraying (IRS) are the cornerstones of malaria vector control [3]. Several recent studies conducted in Benin [18,19,20,21] have indicated that An.gambiae is highly resistant to pyrethroids and DDT, but not to bendiocarb It is in this context that the National Malaria Control Program (NMCP) has undertaken a full coverage of the IRS in no-flood zones in the Oueme region coupled with the distribution of mosquito treated nets in flood zones. A total of 128,132 kg of bendiocarb 80% was sprayed onto the walls of 166,910 human dwellings to protect a population of 512,491 in a no-flood zone
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