Indoor residual spraying (IRS) is a key tool for controlling and eliminating malaria. Developing effective interventions requires understanding the impact of vector control tools on malaria incidence and insecticide resistance. IRS coverage data are sparse and unspecific, so we estimated the subnational coverage of IRS across 46 malaria-endemic countries in sub-Saharan Africa for the four main insecticide classes-- carbamates, organochlorines, organophosphates, and pyrethroids--from 1997 to 2017.
We collated IRS deployment data from sources such as the U.S. President’s Malaria Initiative spray reports and National Malaria Control Program reports. We mapped and calculated data for the applicable administrative divisions and the proportion of households sprayed.
The number of countries implementing IRS increased over time, although targeted deployment means the number of people protected remains low compared with insecticide-treated nets due to the complex logistics and high cost of IRS. From 1997 to 2010, DDT and pyrethroids were common. Carbamates partly replaced them in 2011. Organophosphates replaced carbamates in 2013. IRS deployment since the publication of resistance management guidelines in yeartk typically avoided overlap between pyrethroid IRS and bednet use. However, annual rotations of insecticide classes with differing modes of action are not routine.
This study highlights the gaps between policy and practice, emphasizing the continuing potential for IRS resistance. The data can improve studies on IRS’s impact on malaria incidence and inform evidence-based decisions on malaria control efforts to enhance efficacy and lower costs.
Co-authors of this article include: Julie-Anne A. Tangena, Anna E. Trett & Michael Coleman, Liverpool School of Tropical Medicine; Chantal M. J. Hendriks, Maria Devine, Jennifer Rozier & Catherine L. Moyes, Big Data Institute, Li Ka Shing Centre for Health Information and Discovery, University of Oxford; Ignatius Williams, AngloGold Ashanti Malaria Limited; Adilson José DePina, Malaria Pre-Elimination Program, CCS-SIDA/MSSS; Ecole Doctorale Des Sciences de La Vie, de la Santé et de l´Environnement (ED‑SEV), Université Cheikh Anta Diop (UCAD) de Dakar ; Achamylesh Sisay, Ethiopian Federal Ministry of Health; Ramandimbiarijaona Herizo, Programme national de lutte contre le paludisme; Hmooda Toto Kafy, Integrated Vector Management Department, Sudanese Federal Ministry of Health; Elizabeth Chizema, National Malaria Elimination Centre, Chainama Hills Hospital Grounds, Zambia