Molecular identification of heterophyids in human stool samples from the Philippines

The family Heterophyidae includes endoparasitic minute intestinal flukes that are primarily transmitted through the consumption of raw or undercooked fish, causing heterophyidiasis. Several heterophyid species have been reported to infect humans in the Philippines. Heterophyidiasis is diagnosed by detection of parasite ova in stool samples through Kato-Katz stool microscopy, but species identification is challenging due to the morphologically similar eggs of different heterophyid species and other minute intestinal flukes such as Clonorchis and Opisthorchis. This study addresses the need for accurate species identification by employing molecular techniques, specifically nested PCR and DNA sequencing of the 5.8S-ITS2 rDNA region, to identify heterophyid eggs in human stool samples in the Philippines. This study detected 10 human stool samples infected with Haplorchis taichui from Leyte and Davao del Norte, with all ten sequences clustering with H. taichui sequences from Vietnam. One sample contained Opisthorchis viverrini, an opisthorchiid that is nested inside Heterophyidae. The study also identified two novel genotypes of Haplorchis sp. These results contribute to our knowledge of the diversity of medically important trematodes in the Philippines and emphasize the usefulness of molecular techniques for the accurate identification of heterophyid parasite eggs.