Long-lasting insecticidal nets no longer effectively kill the highly resistant Anopheles funestus of southern Mozambique

Abstract

BackgroundChemical insecticides are crucial to malaria control and elimination programmes. The frontline vector control interventions depend mainly on pyrethroids; all long-lasting insecticidal nets (LLINs) and more than 80% of indoor residual spraying (IRS) campaigns use chemicals from this class. This extensive use of pyrethroids imposes a strong selection pressure for resistance in mosquito populations, and so continuous resistance monitoring and evaluation are important. As pyrethroids have also been used for many years in the Manhiça District, an area in southern Mozambique with perennial malaria transmission, an assessment of their efficacy against the local malaria vectors was conducted.MethodsFemale offspring of wild-caught Anopheles funestus s.s. females were exposed to deltamethrin, lambda-cyhalothrin and permethrin using the World Health Organization (WHO) insecticide-resistance monitoring protocols. The 3-min WHO cone bioassay was used to evaluate the effectiveness of the bed nets distributed or available for purchase in the area (Olyset, permethrin LLIN; PermaNet 2.0, deltamethrin LLIN) against An. funestus. Mosquitoes were also exposed to PermaNet 2.0 for up to 8 h in time-exposure assays.ResultsResistance to pyrethroids in An. funestus s.s. was extremely high, much higher than reported in 2002 and 2009. No exposure killed more than 25.8% of the mosquitoes tested (average mortality, deltamethrin: 6.4%; lambda-cyhalothrin: 5.1%; permethrin: 19.1%). There was no significant difference in the mortality generated by 3-min exposure to any net (Olyset: 9.3% mortality, PermaNet 2.0: 6.0%, untreated: 2.0%; p = 0.2). Six hours of exposure were required to kill 50% of the An. funestuss.s. on PermaNet 2.0.ConclusionsAnopheles funestus s.s. in Manhiça is extremely resistant to pyrethroids, and this area is clearly a pyrethroid-resistance hotspot. This could severely undermine vector control in this district if no appropriate countermeasures are undertaken. The National Malaria Control Programme (NMCP) of Mozambique is currently improving its resistance monitoring programme, to design and scale up new management strategies. These actions are urgently needed, as the goal of the NMCP and its partners is to reach elimination in southern Mozambique by 2020.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-015-0807-z) contains supplementary material, which is available to authorized users.

Age and geographic patterns of Plasmodium falciparum malaria infection in a representative sample of children living in Burkitt lymphoma-endemic areas of northern Uganda

“…However, mosquito bed nets only suppress mosquito populations around bed areas, which may not lead to community-wide suppression of the vector-host ratio like IRS. More worrying, the lack of impact could be an indicator of emerging pyrethroid resistance in this region as has been reported in some studies [53]. If so, the lack of impact of mosquito bed nets on geographical patterns of pfPR should be evaluated more carefully to understand its basis and to exclude more serious reasons such as emerging pyrethroid resistance in regional mosquito populations.…”

Empirical and theoretical investigation into the potential impacts of insecticide resistance on the effectiveness of insecticide‐treated bed nets

“…Due to the nature of field collections, the females were of unknown age and insecticide exposure history. The exact resistance profile was also unknown, although resistance testing of the offspring of females collected in 2013 from the same location using the WHO tube bioassay indicated high‐level resistance to deltamethrin (Glunt et al., ), as did CDC bottle bioassays using field‐collected females (5% mortality at diagnostic concentration, 68% mortality at 10X; S Huijben, unpublished data).…”

MiR-932 Regulates Pyrethroid Resistance inCulex pipiens pallens(Diptera: Culicidae)

“…Therefore, it is imperative for controlling and preventing mosquito-borne diseases. However, due to the lack of effective vaccines and drugs, vector control mostly relies on insecticides to reduce the number of mosquitoes (Glunt et al 2015). But continuous and lasting application of insecticides has led to a constant increasing resistance, which makes antivector strategies more challenging (Rasic et al 2015).…”