Abstract
BackgroundIndoor residual spraying (IRS) is a key tool for controlling and eliminating malaria by targeting vectors. To support the development of effective intervention strategies it is important to understand the impact of vector control tools on malaria incidence and on the spread of insecticide resistance. In 2006, the World Health Organization (WHO) stated that countries should report on coverage and impact of IRS, yet IRS coverage data are still sparse and unspecific. Here, the subnational coverage of IRS across sub-Saharan Africa for the four main insecticide classes from 1997 to 2017 were estimated.MethodsData on IRS deployment were collated from a variety of sources, including the President’s Malaria Initiative spray reports and National Malaria Control Programme reports, for all 46 malaria-endemic countries in sub-Saharan Africa from 1997 to 2017. The data were mapped to the applicable administrative divisions and the proportion of households sprayed for each of the four main insecticide classes; carbamates, organochlorines, organophosphates and pyrethroids was calculated.ResultsThe number of countries implementing IRS increased considerably over time, although the focal nature of deployment means the number of people protected remains low. From 1997 to 2010, DDT and pyrethroids were commonly used, then partly replaced by carbamates from 2011 and by organophosphates from 2013. IRS deployment since the publication of resistance management guidelines has typically avoided overlap between pyrethroid IRS and ITN use. However, annual rotations of insecticide classes with differing modes of action are not routinely used.ConclusionThis study highlights the gaps between policy and practice, emphasizing the continuing potential of IRS to drive resistance. The data presented here can improve studies on the impact of IRS on malaria incidence and help to guide future malaria control efforts.
Highlights
Indoor residual spraying (IRS) is a key tool for controlling and eliminating malaria by targeting vectors
Little is known about the large-scale deployment of IRS over the last 20 years and the impact it has had on the development of insecticide resistance in malaria vectors
Despite the important implications associated with the choice of compounds sprayed [8], studies that have considered the impact of heterogeneous IRS coverage on malaria transmission in Africa typically consider it a single intervention without distinguishing between the different insecticides used [1, 2, 9]
Summary
Indoor residual spraying (IRS) is a key tool for controlling and eliminating malaria by targeting vectors. Indoor residual spraying (IRS) is a key insecticide-based vector control tool for controlling and eliminating malaria in a Tangena et al Malar J (2020) 19:150 variety of malaria epidemiological settings, yet very little information is available on which insecticides have been sprayed, where, and how much across sub-Saharan Africa. By 1978, the GMEP had resulted in the elimination of malaria from 37 countries This success led to the expansion of IRS use in Africa where, subsequently, many IRS campaigns have been successful in controlling malaria in a range of different environments [2, 3, 6, 7]. The main classes are carbamates, organochlorines, organophosphates and pyrethroids, with neonicotinoids recently added These insecticide classes have different residual activity, cost and efficacy in the field (Table 1). The various insecticide classes have different residual activity, impact on local malaria vector populations, cost implications and levels of social acceptance [8]. The different IRS formulations can be considered as distinct control methods
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