Unraveling Haplotype Diversity of the Apical Membrane Antigen-1 Gene in Populations in Thailand.

Development of an effective vaccine is critically needed for the prevention of malaria. One of the key antigens for malaria vaccines is the apical membrane antigen 1 (-1) of the human malaria parasite , the surface protein for erythrocyte invasion of the parasite. The gene encoding -1 has been sequenced from populations of worldwide, but the haplotype diversity of the gene in populations in the Greater Mekong Subregion (GMS), including Thailand, remains to be characterized. In the present study, the -1 gene was PCR amplified and sequenced from the genomic DNA of 65 isolates from 5 endemic areas in Thailand. The nearly full-length 1,848 nucleotide sequence of -1 was subjected to molecular analyses, including nucleotide sequence diversity, haplotype diversity and deduced amino acid sequence diversity and neutrality tests. Phylogenetic analysis and pairwise population differentiation ( indices) were performed to infer the population structure. The analyses identified 60 single nucleotide polymorphic loci, predominately located in domain I of -1. A total of 31 unique -1 haplotypes were identified, which included 11 novel ones. The phylogenetic tree of the -1 haplotypes revealed multiple clades of -1, each of which contained parasites of multiple geographical origins, consistent with the indices indicating genetic homogeneity or gene flow among geographically distinct populations of in Thailand's borders with Myanmar, Laos and Cambodia. In summary, the study revealed novel haplotypes and population structure needed for the further advancement of -1-based malaria vaccines in the GMS.