Background: Plasmodium falciparum merozoite surface protein-1 (PfMSP-1) and -2 (PfMSP-2) are major blood-stage vaccine candidate antigens. Understanding the genetic diversity of the genes, pfmsp-1 and pfmsp-2, is important for recognizing the genetic structure of P. falciparum, and the development of an effective vaccine based on the antigens. In this study, the genetic diversities of pfmsp-1 and pfmsp-2 in the Myanmar P. falciparum were analysed.
Methods: The pfmsp-1 block 2 and pfmsp-2 block 3 regions were amplified by polymerase chain reaction from blood samples collected from Myanmar patients who were infected with P. falciparum in 2013-2015. The amplified gene fragments were cloned into a T&A vector, and sequenced. Sequence analysis of Myanmar pfmsp-1 block 2 and pfmsp-2 block 3 was performed to identify the genetic diversity of the regions. The temporal genetic changes of both pfmsp-1 and pfmsp-2 in the Myanmar P. falciparum population, as well as the polymorphic diversity in the publicly available global pfmsp-1 and pfmsp-2, were also comparatively analysed.
Results: High levels of genetic diversity of pfmsp-1 and pfmsp-2 were observed in the Myanmar P. falciparum isolates. Twenty-eight different alleles of pfmsp-1 (8 for K1 type, 14 for MAD20 type, and 6 for RO33 type) and 59 distinct alleles of pfmsp-2 (18 for FC27, and 41 for 3D7 type) were identified in the Myanmar P. falciparum population in amino acid level. Comparative analyses of the genetic diversity of the Myanmar pfmsp-1 and pfmsp-2 alleles in the recent (2013-2015) and past (2004-2006) Myanmar P. falciparum populations indicated the dynamic genetic expansion of the pfmsp-1 and pfmsp-2 in recent years, suggesting that a high level of genetic differentiation and recombination of the two genes may be maintained. Population genetic structure analysis of the global pfmsp-1 and pfmsp-2 also suggested that a high level of genetic diversity of the two genes was found in the global P. falciparum population.
Conclusion: Despite the recent remarkable decline of malaria cases, the Myanmar P. falciparum population still remains of sufficient size to allow the generation and maintenance of genetic diversity. The high level of genetic diversity of pfmsp-1 and pfmsp-2 in the global P. falciparum population emphasizes the necessity for continuous monitoring of the genetic diversity of the genes for better understanding of the genetic make-up and evolutionary aspect of the genes in the global P. falciparum population.
Keywords: Genetic diversity; Merozoite surface protein-1; Merozoite surface protein-2; Myanmar; Plasmodium falciparum.