Co-transmission of Related Malaria Parasite Lineages Shapes Within-Host Parasite Diversity

In high-transmission regions, we expect parasite lineages within complex malaria infections to be unrelated due to parasite inoculations from different mosquitoes. This project was designed to test this prediction. We generated 485 single-cell genome sequences from fifteen P. falciparum malaria patients from Chikhwawa, Malawi-an area of intense transmission. Patients harbored up to seventeen unique parasite lineages. Surprisingly, parasite lineages within infections tend to be closely related, suggesting that superinfection by repeated mosquito bites is rarer than co-transmission of parasites from a single mosquito. Both closely and distantly related parasites comprise an infection, suggesting sequential transmission of complex infections between multiple hosts. We identified tetrads and reconstructed parental haplotypes, which revealed the inbred ancestry of infections and non-Mendelian inheritance. Our analysis suggests strong barriers to secondary infection and outbreeding amongst malaria parasites from a high transmission setting, providing unexpected insights into the biology and transmission of malaria.