In terms of malaria prevalence, The Gambia can be divided into two strata: low prevalence in the western part and relatively high prevalence in the eastern part. Nevertheless, within these two strata, prevalence can vary substantially by village. Transmission is seasonal (August-December) and the country aims at reaching the pre-elimination status by 2018. Coverage of interventions (LLIN, IRS, IPTp, SMC) is apparently good. Nevertheless, there is still some residual transmission that in the eastern part is moderate to high during the period August-December. Samples contributed are from clinical and asymptomatic infections from communities in the east, central and west of The Gambia. The overall objective is to understand the determinants of malaria heterogeneity and the spatial and temporal spread of malaria infections. This project is characterizing the human reservoir of infection in a cohort of 4,300 individuals across six sites in the Gambia. It has implemented two rounds of mass drug administration with dihydroartemisinin-piperaquine. Blood samples (dried blood spots) are collected monthly from all residents in the study villages between June and December. Passive detection of clinical malaria cases among the study population is done at the local health facilities. Genotyping of parasites in samples collected from these patients will be analysed for relatedness and gene flow between villages. The fine scale resolution of parasite population structure found among clinical and asymptomatic carriers of infection is targeted.