Characterization and application of multiple genetic markers forPlasmodium malariae

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Abstract
SUMMARY: Plasmodium malariae, a protozoan parasite that causes malaria in humans, has a global distribution in tropical and subtropical regions and is commonly found in sympatry with otherPlasmodiumspecies of humans. Little is known about the genetics or population structure ofP. malariae. In the present study, we describe polymorphic genetic markers forP. malariaeand present the first molecular epidemiological data for this parasite. Six microsatellite or minisatellite markers were validated using 76P. malariaesamples from a diverse geographical range. The repeat unit length varied from 2 to17 bp, and up to 10 different alleles per locus were detected. Multiple genotypes ofP. malariaewere detected in 33 of 70 samples from humans with naturally acquired infection. Heterozygosity was calculated to be between 0·236 and 0·811. Allelic diversity was reduced for samples from South America and, at some loci, in samples from Thailand compared with those from Malawi. The number of unique multilocus genotypes defined using the 6 markers was significantly greater in Malawi than in Thailand, even when data from single genotype infections were used. There was a significant reduction in the multiplicity of infection in symptomatic infections compared with asymptomatic ones, suggesting that clinical episodes are usually caused by the expansion of a single genotype.