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

Introduction: Seasonal malaria chemoprevention (SMC) reduces malaria incidence in children under five in Mali, yet transmission persists likely due to chronic low density Plasmodium falciparum infections which are often asymptomatic and undetectable by routine field diagnostics. This study characterises the P. falciparum reservoir in two distinct Malian settings with routine SMC. Methods: We conducted a cohort study (2021 to 2022) of 670 participants from four Malian villages (two in Kati, two in Dire). During four survey visits (T0 to T3), infection was detected using rapid diagnostic tests (RDTs) and quantitative PCR (qPCR). Weekly clinical malaria incidence, P. falciparum PCR prevalence, parasite density and multiplicity of infection (eMOI) were calculated. We evaluated factors associated with P. falciparum carriage using multivariable regression. Results: In Kati, incidence followed rainfall, peaking in 20 to 24 year olds (T1 to T2), while in Dire it peaked during Niger River flooding, mainly in 5 to 24 year olds (T2 to T3). qPCR prevalence reached 33.3% in Kati and 60% in Dire, RDT sensitivity was low, over half of the infections were <100 parasites/μL and eMOI was higher in Kati peaking in 10 to 25 year olds. Discussion Our findings show that asymptomatic and subpatent infections sustain transmission in Mali with 5 to 24 years olds as major parasite reservoirs due to their high infection prevalence, parasite densities, and multiplicity. Predominance of polyclonal infections indicates ongoing exposure despite reduced clinical incidence. Conclusion: SMC has shifted malaria incidence from under fives to older age groups now sustaining transmission. Targeting asymptomatic carriers beyond SMC coverage is essential to further reduce transmission and advance elimination in seasonal settings.