Genetic variation of Enterobius vermicularis among schoolchildren in Thailand

Enterobiasis, caused by the nematode Enterobius vermicularis, is a common health problem among schoolchildren in Thailand. We provide the first molecular identification of this nematode from Thai schoolchildren and document genetic variation among E. vermicularis eggs using sequence analyses of the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene and the nuclear ribosomal DNA second internal transcribed spacer (ITS2). A cross-sectional parasitological survey was conducted in schoolchildren (n = 491) in five regions of Thailand between May 2015 and December 2016. The diagnosis of Enterobius infection was made using the adhesive tape perianal swab technique. Enterobius eggs were recovered from 43 participants (8.75%). DNA was extracted from these eggs and the cox1 gene and partial ITS2 region amplified using the polymerase chain reaction (PCR). Nineteen amplified PCR products of the cox1 gene (441 bp) and 18 of the ITS2 region (623 bp) were subsequently sequenced. All sequences were identified as belonging to E. vermicularis based on database searches. Phylogenetic analysis and a median-joining network of available E. vermicularis cox1 sequences showed 66 haplotypes. We found haploclusters (types A and B) represented among the Thai sequences. Six haplotypes from Thailand fell into type A (of Nakano et al., 2006) (along with sequences from Japan and Korea) and five haplotypes into type B (with sequences from Japan, Iran, Czech Republic, Greece, Denmark and Sudan). The overall haplotype diversity (Hd) was 0.9888. Transmission of worms with type B haplotypes from primates to humans in Asia or from humans in Europe possibly occurs in Thailand.