Abstract
Malaria infections containing multiple parasite genotypes are ubiquitous in nature, and play a central role in models of recombination, intra-host dynamics, virulence, sex ratio, immunity and drug resistance evolution in Plasmodium. While these multiple infections (MIs) are often assumed to result from superinfection (bites from multiple infected mosquitoes), we know remarkably little about their composition or generation. We isolated 336 parasite clones from eight patients from Malawi (high transmission) and six from Thailand (low transmission) by dilution cloning. These were genotyped using 384 single-nucleotide polymorphisms, revealing 22 independent haplotypes in Malawi (2–6 per MI) and 15 in Thailand (2–5 per MI). Surprisingly, all six patients from Thailand and six of eight from Malawi contained related haplotypes, and haplotypes were more similar within- than between-infections. These results argue against a simple superinfection model. Instead, the observed kinship patterns may be explained by inoculation of multiple related haploid sporozoites from single mosquito bites, by immune suppression of parasite subpopulations within infections, and serial transmission of related parasites between people. That relatedness is maintained in endemic areas in the face of repeated bites from infected mosquitoes has profound implications for understanding malaria transmission, immunity and intra-host dynamics of co-infecting parasite genotypes.
Highlights
People living in malaria-endemic regions are often infected with Plasmodium falciparum infections containing multiple parasite haplotypes [1,2]
multiple infections’ (MIs) play a prominent role in the models of parasite virulence evolution [7], drug resistance [8,9], sex ratio [10], transmission [11] and population genetics [1], we have minimal understanding of the composition of MIs or the manner in which they are generated
Malaria transmission is intense in Malawi, with entomological inoculation rates (EIR) as high as 180 infective bites per year [20] and mean malaria prevalence rates of more than 25 per cent in children less than 10 years old [21], and MI carriage rates more than 75 per cent
Summary
People living in malaria-endemic regions are often infected with Plasmodium falciparum infections containing multiple parasite haplotypes [1,2]. Multiple sporozoites from a single mosquito bite establish infections, which will result in related parasite haplotypes within MIs (figure 1).
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