Distinct Allelic Diversity of Merozoite Surface Protein 3-Alpha () Gene in Thailand Using PCR-RFLP

Considering the importance of merozoite surface proteins (MSPs) as vaccine candidates, this study was conducted to investigate the polymorphism and genetic diversity of merozoite surface protein 3-alpha () in Thailand. To analyze genetic diversity, 118 blood samples containing were collected from four malaria-endemic areas in western and southern Thailand. The DNA was extracted and amplified for the gene using nested PCR. The PCR products were genotyped by PCR-RFLP with I and I restriction enzymes. The combination patterns of I and I RFLP were used to identify allelic variants. Genetic evaluation and phylogenic analysis were performed on 13 sequences, including 10 sequences from our study and 3 sequences from GenBank. The results revealed three major types of , 91.5% allelic type A (∼1.8 kb), 5.1% allelic type B (∼1.5 kb), and 3.4% allelic type C (∼1.2 kb), were detected based on PCR product size with different frequencies. Among all , 19 allelic subtypes with I RFLP patterns were distinguished and 6 allelic subtypes with I RFLP patterns were identified. Of these samples, 73 (61%) and 42 (35.6%) samples were defined as monoallelic subtype infection by I and I PCR-RFLP, respectively, whereas 77 (65.3%) samples were determined to be mixed-allelic subtype infection by the combination patterns of I and I RFLP. These results strongly indicate that gene is highly polymorphic, particularly in blood samples collected from the Thai-Myanmar border area (the western part of Thailand). The combination patterns I and I RFLP of the gene could be considered for use as molecular epidemiologic markers for genotyping isolates in Thailand.