Abstract: Objective To analyze the polymorphisms of microsatellite loci flanking the K13 gene(K13) of Plasmodium falciparum in Lazan of China-Myanmar border and three areas in Thailand. Methods Forty-two P. falciparum samples were collected, including 22 from Lazan(11 with R539T mutation and 11 wild type) and 20 from three areas of Thailand(9 with R539T mutation and 11 wild type). Six microsatellite loci flanking K13 gene (31 900, 6 360, and 150 bp upstream and 11 000, 31 500, and 1 700 bp downstream) were amplified by PCR. Length of the PCR products was determined by a QIAxcel capillary electrophoresis instrument. The allele frequency and expected heterozygosity(He)were calculated by GenALEx software. Results Forty-six alleles were detected for the six microsatellite loci. The alleles of R539T mutant clustered on 286 bp(allele frequency 73%) and 278 bp (allele frequency 67%) for the locus of 6 360 bp upstream, and on 211 bp (allele frequency 55%) and 205 bp(allele frequency 44%) for 31 900 bp upstream. For the other two loci of 150 bp upstream and 1 700 bp downstream, the alleles mainly clustered on 195 bp and 209 bp. No alleles were found for the loci of 11 000 bp and 31 500 bp downstream. The haplotypes of the isolates in the three areas of Thailand(H2 type in 2 samples, and H5 and H6 in the rest samples) differed from that in Lazan(H1-H4 types). For the R539T mutant isolates from China-Burma border and Thailand, the mean He values were (0.49 ± 0.23) and (0.42 ± 0.33), respectively, while for the wild type isolates, the mean He values were (0.72 ± 0.12) and (0.67 ± 0.11), respectively. The expected heterozygosity was low at the loci closely adjacent to the K13 gene of the R539T mutant strains, with a He value of 0.17 at the 150 bp upstream locus and 0.3 at the 1 700 bp downstream locus. Conclusion P. falciparum parasites with R539T mutation of K13 gene are subjected to drug selection pressure in both China-Myanmar border and Thailand, and there is a significant allele difference at the upstream 6 360 bp and 31 900 bp loci.

Key words: Plasmodium falciparum, Microsatellite, K13 gene