Molecular differentiation of echinostomes occurring in Asia with description of Echinostoma mekongi n. sp. from humans in Cambodia

Abstract

Echinostomes (family Echinostomatidae) of the 37-collar-spined or the revolutum group are recognized as zoonotic, food-borne intestinal trematodes that can cause echinostomiasis worldwide. Patients who suffer from echinostomiasis can complain severe epigastric or abdominal pain with diarrhea, easy fatigue, malnutrition and anemia. It is difficult to identify the species among the 37-collar-spined members because a large number of morphological characters are very similar in their adult stages. To avoid the taxonomic confusion, molecular techniques have been used based on variable genetic markers. In total, 17 Echinostoma spp. adult specimens collected in Cambodia (13), Vietnam (2) and Thailand (2) were included in the study. Most specimens were assigned as Echinostoma revolutum based on morphological findings. For identification and phylogenetic study of the specimens, nested polymerase chain reaction (nested-PCR) was conducted using specific primers designed to amplify partial adenine dinucleotide dehydrogenase subunit 1 (ND1), cytochrome c oxidase subunit 1 (CO1) and internal transcribed spacer (ITS1-5.8S rRNA-ITS2) genes. The results indicated that here are no reference sequence of ND1, CO1 and ITS region of revolutum members in GenBank highly matched with the sequence which newly analyzed in this study. As shown by phylogenetic studies, the isolates from Cambodia, Vietnam and Thailand conducted a new monophyletic lineage. According to the comparisons based on the molecular data, the samples newly analyzed in this study are a distinctive species from other 37-collar-spined members. In conclusion, we propose our echinostome specimens from humans in Cambodia as a new species, Echinostoma mekongi n sp.