Abstract
Anopheles gambiae s.l. (Diptera: Culicidae) in Muleba, Tanzania has developed high levels of resistance to most insecticides currently advocated for malaria control. The kdr mutation has almost reached fixation in An. gambiae s.s. in Muleba. This change has the potential to jeopardize malaria control interventions carried out in the region. Trends in insecticide resistance were monitored in two intervention villages using World Health Organization (WHO) susceptibility test kits. Additional mechanisms contributing to observed phenotypic resistance were investigated using Centers for Disease Control (CDC) bottle bioassays with piperonylbutoxide (PBO) and S,S,S‐tributyl phosphorotrithioate (DEF) synergists. Resistance genotyping for kdr and Ace‐1 alleles was conducted using quantitative polymerase chain reaction (qPCR). In both study villages, high phenotypic resistance to several pyrethroids and DDT was observed, with mortality in the range of 12–23%. There was a sharp decrease in mortality in An. gambiae s.l. exposed to bendiocarb (carbamate) from 84% in November 2011 to 31% in December 2012 after two rounds of bendiocarb‐based indoor residual spraying (IRS). Anopheles gambiae s.l. remained susceptible to pirimiphos‐methyl (organophosphate). Bendiocarb‐based IRS did not lead to the reversion of pyrethroid resistance. There was no evidence for selection for Ace‐1 resistance alleles. The need to investigate the operational impact of the observed resistance selection on the effectiveness of longlasting insecticidal nets and IRS for malaria control is urgent.
Highlights
IntroductionCurrent strategies for malaria vector control rely heavily on chemical means for both the indoor residual spraying (IRS) of insecticide and the use of insecticide-treated nets (ITNs) [World Health Organization (WHO), 2013a]
The percentage of households in Tanzania that owned at least one insecticide-treated nets (ITNs) increased from 23% in 2005 to 92% in 2012 and the use of ITNs by household members increased from 15% in 2005 to 68% in 2012 [Tanzania Demographic and Health Survey (TDHS), 2005; Tanzania HIV/AIDS and Malaria Indicator Survey (THMIS), 2012]
The present study found no further selection for the kdr-based resistance to pyrethroids between the pre- and post-intervention years and neither was the Ace-1 (G119S) allele, which confers resistance to organophosphates and carbamates, detected
Summary
Current strategies for malaria vector control rely heavily on chemical means for both the indoor residual spraying (IRS) of insecticide and the use of insecticide-treated nets (ITNs) [World Health Organization (WHO), 2013a]. Indoor residual spraying has been deployed in several areas of sub-Saharan Africa, including in settings of high and medium rates of malaria transmission (Kolaczinski et al, 2007; Kigozi et al, 2012; Kim et al, 2012; Fullman et al, 2013). In order to reduce the burden of malaria morbidity and mortality in Tanzania, the National Malaria Control Programme (NMCP) adopted the WHO-recommended strategies for the distribution and consistent use of LLINs, and spraying of houses with a safe and efficacious insecticide (IRS). The percentage of households in Tanzania that owned at least one ITN increased from 23% in 2005 to 92% in 2012 and the use of ITNs by household members increased from 15% in 2005 to 68% in 2012 [Tanzania Demographic and Health Survey (TDHS), 2005; Tanzania HIV/AIDS and Malaria Indicator Survey (THMIS), 2012]
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