A decline and age shift in malaria incidence in rural Mali following implementation of seasonal malaria chemoprevention and indoor residual spraying

Abstract BackgroundDeclines in malaria incidence attributed to the implementation of control strategies have been reported in many African countries. The declines are often accompanied by a shift in clinical burden to older children. In Mali, artemisinin-based combination therapy (ACT) was introduced in 2004, and Long-lasting insecticide-treated nets (LLINs) have been partially distributed free of charge since 2007. In Bandiagara, a study conducted from 2009 to 2013 showed a stable incidence of malaria compared to 1999 despite the use of ACTs and LLINs. Since 2016, seasonal malaria chemoprevention (SMC) has been scaled up across the country. In addition to these strategies, the population of Bandiagara benefited the universal bed net coverage and indoor residual spray (IRS) implementation in 2017 and 2018.This study aimed to measure the incidence of malaria in the context of recent scaling-up of control strategies.MethodsA cohort of 300 children aged 6 months to 15 years was followed from October 2017 to December 2018 in Mali. Monthly cross-sectional surveys were done to measure the prevalence of malaria infection by microscopy and anaemia. The study outcomes included the monthly prevalence of malaria infection and the incidence of symptomatic malaria.ResultsThe incidence of symptomatic malaria was 0.5 episodes/person-year. The average prevalence of malaria parasitaemia was 6.7%. The incidence was higher in the oldest age group than the youngest one (0.6 episodes/person-year in children above 10 years vs 0.29 in 6 months to 5 years age group).ConclusionsThis study showed a reduction of malaria incidence compared to 1999 and 2009-2013. An age shift in the susceptibility to malaria was also observed; older children experienced more clinical malaria than younger ones. These findings suggest to extend malaria control efforts to older children.