Abstract
In spite of widespread insecticide resistance in vector mosquitoes throughout Africa, there is limited evidence that long‐lasting insecticidal bed nets (LLINs) are failing to protect against malaria. Here, we showed that LLIN contact in the course of host‐seeking resulted in higher mortality of resistant Anopheles spp. mosquitoes than predicted from standard laboratory exposures with the same net. We also found that sublethal contact with an LLIN caused a reduction in blood feeding and subsequent host‐seeking success in multiple lines of resistant mosquitoes from the laboratory and the field. Using a transmission model, we showed that when these LLIN‐related lethal and sublethal effects were accrued over mosquito lifetimes, they greatly reduced the impact of resistance on malaria transmission potential under conditions of high net coverage. If coverage falls, the epidemiological impact is far more pronounced. Similarly, if the intensity of resistance intensifies, the loss of malaria control increases nonlinearly. Our findings help explain why insecticide resistance has not yet led to wide‐scale failure of LLINs, but reinforce the call for alternative control tools and informed resistance management strategies.
Highlights
About 1 billion long-lasting insecticidal bed nets (LLINs) have been distributed in Africa in the last 10 years, and these have contributed to substantial declines in the burden of malaria (Bhatt et al., 2015)
Given that malaria parasites take about 2 weeks to develop within the mosquito, transmission might still be halted if older mosquitoes remain susceptible to insecticides, even where younger mosquitoes can survive exposure (Read, Lynch, & Thomas, 2009; Saddler & Koella, 2015)
Malaria epidemiology is the outcome of complex interactions among a multiplicity of factors, and so, assessing the contribution of any one factor to changes in disease prevalence is difficult (Kleinschmidt et al, 2015)
Summary
About 1 billion long-lasting insecticidal bed nets (LLINs) have been distributed in Africa in the last 10 years, and these have contributed to substantial declines in the burden of malaria (Bhatt et al., 2015). Widely used for detecting resistance in field populations, it is becoming clear that this phenotypic assay tells us little about how resistance interacts with malaria epidemiology (Bradley et al, 2017; Ochomo et al, 2017; Oxborough et al, 2015; Ranson & Lissenden, 2016; World Health Organization 2016a). The reasons for this disconnect could be manifold (Rivero, Vézilier, Weill, Read, & Gandon, 2010). This model indicates that even modest lethal and sublethal effects, when accrued across the lifetime of the mosquito, can have substantial impact on malaria transmission potential, especially under conditions of high LLIN coverage
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