The effects of indoor residual spraying (IRS) on malaria transmission have been documented. However, the impact on morbidity has not always been highlighted. The aim of this study was to evaluate the effects of IRS on malaria incidence, parasitemia and parasite density among children less than five years of age in Benin. We conducted a cohort study in sprayed and unsprayed areas during the malaria transmission season in 2017. At inclusion, finger prick blood samples were used to assess baseline parasitemia by microscopy and rapid diagnostic tests (RDT), and children were then followed up over 7 months during which thick blood smear microscopy and RDT were repeated every month. Prevalence of parasitemia at baseline was 40.70% in the sprayed, 25.3% in the unsprayed area and remains high over the entire monitoring period with the exception of month 4. We noticed a decrease in the incidence rate in the sprayed area of 8% over the period of persistence of the insecticide, while in the unsprayed area the incidence increased by 17%. This study demonstrated that IRS can effectively reduce malaria incidence in an area of high endemicity. We recommend a larger scale study to evaluate the effects of IRS on malaria morbidity after several rounds of spraying.
Key words: Effects indoor residual spraying, malaria incidence, parasitemia, parasite density, children less than 5 years, Benin.
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