Abstract
SummaryBackgroundScale-up of insecticide-based interventions has averted more than 500 million malaria cases since 2000. Increasing insecticide resistance could herald a rebound in disease and mortality. We aimed to investigate whether insecticide resistance was associated with loss of effectiveness of long-lasting insecticidal nets and increased malaria disease burden.MethodsThis WHO-coordinated, prospective, observational cohort study was done at 279 clusters (villages or groups of villages in which phenotypic resistance was measurable) in Benin, Cameroon, India, Kenya, and Sudan. Pyrethroid long-lasting insecticidal nets were the principal form of malaria vector control in all study areas; in Sudan this approach was supplemented by indoor residual spraying. Cohorts of children from randomly selected households in each cluster were recruited and followed up by community health workers to measure incidence of clinical malaria and prevalence of infection. Mosquitoes were assessed for susceptibility to pyrethroids using the standard WHO bioassay test. Country-specific results were combined using meta-analysis.FindingsBetween June 2, 2012, and Nov 4, 2016, 40 000 children were enrolled and assessed for clinical incidence during 1·4 million follow-up visits. 80 000 mosquitoes were assessed for insecticide resistance. Long-lasting insecticidal net users had lower infection prevalence (adjusted odds ratio [OR] 0·63, 95% CI 0·51–0·78) and disease incidence (adjusted rate ratio [RR] 0·62, 0·41–0·94) than did non-users across a range of resistance levels. We found no evidence of an association between insecticide resistance and infection prevalence (adjusted OR 0·86, 0·70–1·06) or incidence (adjusted RR 0·89, 0·72–1·10). Users of nets, although significantly better protected than non-users, were nevertheless subject to high malaria infection risk (ranging from an average incidence in net users of 0·023, [95% CI 0·016–0·033] per person-year in India, to 0·80 [0·65–0·97] per person year in Kenya; and an average infection prevalence in net users of 0·8% [0·5–1·3] in India to an average infection prevalence of 50·8% [43·4–58·2] in Benin).InterpretationIrrespective of resistance, populations in malaria endemic areas should continue to use long-lasting insecticidal nets to reduce their risk of infection. As nets provide only partial protection, the development of additional vector control tools should be prioritised to reduce the unacceptably high malaria burden.FundingBill & Melinda Gates Foundation, UK Medical Research Council, and UK Department for International Development.
Highlights
Deployment of insecticide-based interventions has been the principal driver of reductions in the global malaria burden since 2000
KwaZulu-Natal, South Africa in the late 1990s, where because of its primary focus on switching chemical despite good indoor residual spraying coverage, a classes for indoor residual spraying.[4,10] ten-times increase in malaria cases was reversed This multicountry prospective study was coordinated by when pyrethroid spraying was replaced with dichloro-WHO to assess the effect of insecticide resistance on diphenyltrichloroethane (DDT) spraying in response to malaria disease burden and on the performance of reported pyrethroid resistance in a local malaria vector, long-lasting insecticidal nets.[11]
Pyrethroid long-lasting insecticidal nets were the principal form of malaria vector control in all study areas; in Sudan this approach was supplemented by indoor residual spraying.[12]
Summary
Deployment of insecticide-based interventions has been the principal driver of reductions in the global malaria burden since 2000. The massive scale-up of insecticidetreated nets resulted in more than 50% of people in malaria endemic areas in sub-Saharan Africa sleeping under nets in 2016.1 Of 663 million clinical malaria cases averted in sub-Saharan Africa since 2001, 78% were averted thanks to the use of insecticide-treated nets and indoor residual spraying.[2] Any loss of effectiveness of these interventions could cause a catastrophic rebound in disease incidence and mortality. Pyrethroids are increasingly less effective at killing mosquitoes[3,4] and mathematical models predict this drop in effectiveness could lead to increased malaria incidence.[5] little evidence has been reported of an epidemiological effect resulting from resistance. We aimed to investigate whether insecticide resistance was associated with loss of effectiveness of long-lasting insecticidal nets and increased malaria disease burden
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