Abstract:
In 2030, World health organization’s target is to eliminate malaria at least in 35 countries. At present, Thailand is low risk of malaria so that, it has the potential to eliminate. About 10 years ago, malaria prevalence was high along the country border areas. To prevent the recurrence in those areas, evaluation of drug susceptibility of parasites and vaccine are important. Therefore, basic knowledge on genetic diversity in malaria parasite is needed. Merozoite surface protein 1(msp1), one of the vaccine candidate genes, is useful for monitoring genetic diversity of the parasite and the potential gene of vaccine. However, high diversity of block 2 region in msp1 is the barrier of vaccine design.
Therefore, in this study, genotyping of different msp1 alleles from endemic areas of Thailand was crucial for control program. Two-hundred and thirty-six P. falciparum-infected blood samples collected during 2013-2017 from five endemic regions were amplified by nested PCR to detect the block 2 region of msp1 gene; K1, MAD20 and RO33 allelic type. The DNA samples used in this study were extracted by using Chelex-100 method. These alleles were investigated with 2.5% agarose gel electrophoresis and fragment sizes were analyzed. The msp1, block 2 region of the isolates with mono-infection was determined by direct sequencing method. The sequences were aligned and constructed to get the phylogenetic tree.
The overall prevalence of MAD20, R033 and K1 allelic types in P. falciparum isolates were 57.2% (135/236) and 31.3% (74/236) and 15.7% (37/236) respectively. The number of alleles for MAD20, R033 and K1 were 46, 11 and 16 respectively. K1 type is comprised of 2-7 repetition of SGT and 2-3 repetition of SGP. Moreover, MAD20 is also comprised of different repetition of SGG, SVA and SVT. However, R033 is comprised of sequences without repetition. MAD 20 type was the most prevalent allele type found in this study. Multiplicity of infection of parasites in five provinces ranges from 1.0 to 1.2. The phylogenetic trees show that the isolates in five provinces are related each other. The fluctuation of allele is observed in Thailand by comparing with the previous studies. The high diversity of block 2 region indicates that high transmission intensity of parasites still present.
