Co-transmission of related parasite lineages shapes within-host parasite diversity

Malaria patients frequently carry one or more clonal lineage of the parasite, Plasmodium falciparum. In regions of high transmission, we might expect component parasites within complex infections to be unrelated as a result of parasite inoculations from different mosquitos. This project was designed to directly test this prediction. We generated 485 near-complete single-cell genome sequences isolated from fifteen P. falciparum patients from Chikhwawa, Malawi, an area of intense malaria transmission. Matched single-cell and bulk genomic analyses revealed that patients harbored up to seventeen unique lineages. Current statistical approaches were unable to accurately reconstruct infection composition from bulk sequence data. Surprisingly, our analysis demonstrated that parasite lineages within infections tend to be related, suggesting that superinfection by repeated mosquito bites is rarer than co-transmission of parasites from a single mosquito. Our single-cell analysis indicates strong barriers to establishment of secondary infections, providing new insights into the biology and transmission of malaria.