Plasmodium falciparum Carriage in central and northern Mali amid Seasonal Malaria Chemoprevention implementation

IntroductionSeasonal malaria chemoprevention (SMC) reduces malaria incidence in children under five in Sahelian countries. However, transmission persists at substantial levels and incidence is re-increasing. Addressing Plasmodium falciparum carriage in asymptomatic individuals could represent a relevant intervention to complement current access to care- and vector-control-based strategies. In this study, we aim to characterise the parasite reservoir dynamics over one year in the general population of two sites of central and northern Mali. MethodsWe included members of randomly selected households in four villages (2 in Kati and 2 in Dire districts). At four planned visits, infection was detected using rapid diagnostic tests (RDTs) and qPCR. Clinical malaria incidence was recorded passively at local health facility and Plasmodium positive samples were genotyped. We analyse clinical malaria incidence, P. falciparum PCR prevalence, parasite density and multiplicity of infection (eMOI) at different seasons, as well as factors associated with P. falciparum carriage. ResultsMalaria seasonal dynamics was driven by rainfall in Kati (Central Mali) and by flooding in Dire (Northern Mali). In Kati, prevalence rose from 21.5% at the dry season 2021 baseline to 33.5% in December after the rainy season. Prevalence was lowest in SMC-eligible children across 3 of 4 surveys. Prevalence was highest (40-50%) for 10-24 years old in December. Median parasite densities were generally <10 parasites/{micro}L except for 10-24 years old, who also presented higher eMOI. In Dire, prevalence was high at both baseline and December survey (60%) but dropped in September and in May 22. SMC was not distributed in 2021, and prevalence was homogenously high (50-70%) across groups in December. Parasite densities and eMOI fluctuated strongly across age-groups and survey. DiscussionOur findings show that in the "classic" Sahelian, rainfall-driven setting of Kati, a high prevalence of asymptomatic infections among 10-24 year-olds likely represents the reservoir for transmission. In the understudied Northern Mali, our results suggest generalized high burden and complex dynamics. Continuous SMC modifies the age-distribution of the parasite reservoir. Targeting asymptomatic carriers beyond SMC coverage could represent a relevant strategy to further reduce transmission in seasonal settings.