\u2018We spray and walk away\u2019: wall modifications decrease the impact of indoor residual spray campaigns through reductions in post-spray coverage

Mercy A Opiyo,Krijn P Paaijmans

doi:10.1186/s12936-020-3102-6

Abstract

Malaria prevalence has significantly reduced since 2000, largely due to the scale-up of vector control interventions, mainly indoor residual spraying (IRS) and long-lasting insecticide-treated nets (LLINs). Given their success, these tools remain the frontline interventions in the fight against malaria. Their effectiveness relies on three key ingredients: the intervention, the mosquito vector and the end-user. Regarding the intervention, factors such as the insecticide active ingredient(s) used and the durability and/or bio-efficacy of the tool over time are critical. For the vectors, these factors include biting and resting behaviours and the susceptibility to insecticides. Finally, the end-users need to accept and properly use the intervention. Whilst human attitude and behaviour towards LLINs are well-documented both during and after distribution, only initial coverage is monitored for IRS and in a few geographic settings the residual efficacy of the used product. Here, the historical evidence on end-users modifying their wall surfaces post-spraying is presented, a behaviour that has the potential to reduce actual IRS coverage, effectiveness and impact, as fewer people are truly protected. Therefore, clear guidelines on how to monitor IRS acceptability and/or coverage, both before, during and after spraying, are urgently needed as part of the Monitoring and Evaluation of malaria programmes.

Highlights

Insecticide-treated nets (ITNs), later replaced by longlasting insecticidal nets (LLINs), and indoor residual spraying (IRS) are core vector control interventions in malaria-endemic settings and have averted 663 million clinical malaria cases between 2000 and 2015 [1].Albeit the huge success in the fight against malaria, malaria cases are on the rise again since 2016 [2, 3] which endangers the long-term goals of the Global Technical Strategy (GTS) for Malaria [4]
Whilst many studies focus on the vector, the critical component of how human behaviour impacts the efficacy of vector control tools has been largely overlooked for IRS
What is the true impact of the IRS? To date, the studies from India and South Africa provide the only longitudinal data on wall modifications post-IRS. Whilst it is not known how representative the data from India and South Africa are to other settings in Africa where IRS has been or is being implemented, wall modifications could reduce or potentially completely remove the bioavailability of insecticides. This may change the outcomes of IRS impact evaluations, as this indicator is not included in models that estimate the efficacy of IRS campaigns [14, 37,38,39]

Summary

Introduction

Insecticide-treated nets (ITNs), later replaced by longlasting insecticidal nets (LLINs), and indoor residual spraying (IRS) are core vector control interventions in malaria-endemic settings and have averted 663 million clinical malaria cases (three-quarters of the gains achieved) between 2000 and 2015 [1].Albeit the huge success in the fight against malaria, malaria cases are on the rise again since 2016 [2, 3] which endangers the long-term goals of the Global Technical Strategy (GTS) for Malaria [4]. For IRS, apart from assessing the initial coverage (at time of application), only the quality of the IRS product may be assessed post-spraying through standard residual efficacy tests using WHO cone bioassays [19, 28]. Current guidelines to assess the effectiveness of IRS programmes include initial coverage (number of structures covered) and the residual efficacy of the product sprayed [19] (Table 1).

Results

Conclusion