Biased distribution of msp1 and msp2 allelic variants in Plasmodium falciparum populations in Thailand

TLDR

The study examines the epidemiological relevance of allele distribution patterns in Plasmodium falciparum isolates from Thai border patients. Researchers collected isolates from Thai‑Kampuchean border patients during four quarterly surveys and used nested PCR to genotype polymorphic regions of msp1, msp2, and glurp. Despite high genetic diversity, the parasite population remained stable over time, with msp2 showing the greatest polymorphism and higher multiplicity of infection—76 % of samples had ≥2 lines, especially at the start and end of the rainy season—while two allelic variants displayed nonrandom associations (msp1 MAD20 dissociated, msp2 FC27 associated).

Abstract

Plasmodium falciparum isolates were obtained from Thai patients attending a malaria clinic on the Thai-Kampuchean border over 4 cross-sectional surveys carried out at 3-monthly intervals. The genetic structure of the parasite populations was determined by nested polymerase chain reaction (PCR) amplification of polymorphic regions of 3 P. falciparum antigen genes: msp1, msp2 and glurp. Although a high degree of diversity characterized these isolates, the overall population structure of the parasites associated with patent malaria infections was observed to remain relatively stable over time. The highest degree of polymorphism was observed with msp2, and the mean number of lines per infection (multiplicity of infection) calculated with this marker was higher than that obtained using msp1 or glurp alone, or combined. Infections with > or = 2 parasite lines were seen in 76% of the samples, and were proportionally more numerous at the start and end of the rainy season. Two interesting exceptions to the random distribution were observed and involved 2 allelic variants which in one case were found dissociated (msp1 MAD20-family) and in the other were associated (msp2 FC27-family). The epidemiological significance of these types of data is discussed.