Systematic review of indoor residual spray efficacy and effectiveness against Plasmodium falciparum in Africa

Ellie Sherrard-Smith,Constant Edi,Mark Rowland,Natacha Protopopoff,Pie Müller,Peter Winskill,Jason H Richardson,Vincent Corbel,Jamie T Griffin,Raphael N’Guessan,Cédric Pennetier,Richard Oxborough,Fiacre Agossa,Thomas S Churcher,Armel Djénontin,Sarah Moore

doi:10.1038/s41467-018-07357-w

Abstract

Indoor residual spraying (IRS) is an important part of malaria control. There is a growing list of insecticide classes; pyrethroids remain the principal insecticide used in bednets but recently, novel non-pyrethroid IRS products, with contrasting impacts, have been introduced. There is an urgent need to better assess product efficacy to help decision makers choose effective and relevant tools for mosquito control. Here we use experimental hut trial data to characterise the entomological efficacy of widely-used, novel IRS insecticides. We quantify their impact against pyrethroid-resistant mosquitoes and use a Plasmodium falciparum transmission model to predict the public health impact of different IRS insecticides. We report that long-lasting IRS formulations substantially reduce malaria, though their benefit over cheaper, shorter-lived formulations depends on local factors including bednet use, seasonality, endemicity and pyrethroid resistance status of local mosquito populations. We provide a framework to help decision makers evaluate IRS product effectiveness.

Highlights

The use of indoor residual spray (IRS) to supplement LLINs for malaria control and elimination is increasing in part due to concerns of pyrethroid resistant mosquitoes impeding bednet efficacy and the drive for malaria elimination
This modelling exercise highlights that the added public health benefit of the WHO policy to add IRS to LLINs can be substantial in areas where bednet usage is low and pyrethroid resistance is a concern
An RCT in Southern Benin showed no additional epidemiological benefit of annual bendiocarb-IRS over LLINs alone[6] our analyses show that the residual half-life of bendiocarb is relatively short compared to the long transmission season in Benin which may partially explain this lack of additional benefit

Summary

Methods

Whilst experimental hut trials cannot account for all of the effects of IRS alone[58] they provide a relatively standardised method to assess IRS efficacy and are considered the entomological equivalent of a Phase II trial[31]. They are a pivotal part of the testing of new products and are required by WHO Prequalification[29] which enables products to be bought by international procurers for low-income countries. To the author’s knowledge, there has been no previous published systematic meta-analysis on IRS compounds tested in experimental hut trials. Studies are limited to trials conducted in Africa (where the biggest burden of falciparum malaria is found) and to mosquito species belonging to the Anopheles family (vectors of the disease)

Results

Discussion

Conclusion