Plasmodium falciparum genetic diversity in border areas of Myanmar assessed by genotyping merozoite surface protein genes

Abstract

Background

The description of genetic diversity of malaria parasite populations in malaria-endemic areas may help determine the effectiveness of malaria interventions in the region. This study aimed to evaluate the genetic diversity and allele frequencies of the merozoite surface protein 1 gene (Msp1) and merozoite surface protein 2 gene (Msp2) in Plasmodium falciparum populations collected from Paletwa Township in western Myanmar and two regions along the China-Myanmar border (the Myitsone and Bhamo regions of Myanmar).

Methods

Between 2013 and 2022, malaria cases in China were predominantly imported, with border counties in Yunnan reporting the highest number of cases nationwide. Furthermore, malaria transmission rates in adjacent townships in Myanmar remained relatively high. A total of 176 P. falciparum-infected blood samples were collected from local residents with infections in Bhamo and Paletwa Township in Myanmar, as well as from migrant malaria patients from Yunnan, China, who had worked in Myitsone, Myanmar. Among them, 96 samples were collected from Paletwa Township, Myanmar in 2015, and 28 from Bhamo, Myanmar in 2018–2019, both from local residents. In 2013, 55 samples were obtained from Chinese migrant workers returning from Myitsone, Myanmar, via the Tengchong border checkpoint in Yunnan, China. The genomic DNA was extracted, and the Msp1 and Msp2 genes were genotyped by nested PCR using allele-specific primers for P. falciparum.

Results

A total of 176 and 162 samples were successfully genotyped at the Msp1 and Msp2 genes, respectively. Among them, 54 samples were successfully amplified for the Msp1 allelic families in Myitsone, 27 samples in Bhamo, and 95 samples in Paletwa Township. Additionally, 46 samples were successfully amplified for the Msp2 allelic families in Myitsone, 24 samples in Bhamo, and 92 samples in Paletwa Township. Among the three cities, MAD20 was the most frequent allele in the Msp1 gene, while 3D7 was the most frequent allele in the Msp2 gene. The MAD20 allele predominated with 89% (48/54), 85% (23/27) and 67% (64/95) in Myitsone, Bhamo and Paletwa Township respectively, followed by K1 with 65% (35/54) and 44% (12/27) in Myitsone and Bhamo, respectively. The second most frequent allele in Paletwa Township was RO33, representing 47% (45/95) of the population. In migrant workers, residents of Bhamo and residents of Paletwa Township, the multiplicity of infection (MOI) estimated from Msp1 was 1.87, 1.33 and 1.56, respectively And meanwhile, the MOI estimated from Msp2 was 1.17, 1.29 and 1.35 respectively. Migrant workers harbored MOI and rate of multi-infections more frequently (72%) than residents of Bhamo or Paletwa Township (43% and 45%, respectively) based on Msp1.

Conclusions

The Msp1 revealed higher genetic diversity than Msp2. The prevalence of MOI and multi-infections among local residents was lower than that among migrant workers based on Msp1. The migrant workers in Myitsone exhibited higher MOI and the proportion of multi-infections compared to the locals, suggesting that low immunity among the migrant workers might be the primary reason for this observation, or that the transmission level in Myitsone is higher than in the local areas.