We developed a new concentration kit, called the ParaEgg (PE), for easy detection trematode eggs from fecal samples in endemic areas of clonorchiasis and metagonimiasis in Korea. To create a standard of detection efficiency, 120 fecal samples were examined using the water–ether concentration method (WECM). The PE kit and Mini ParaSep (PS) kit were used to compare the detection sensitivity of 100 egg-positive and 20 egg-negative samples in WECM. Additionally, stool samples, which were intentionally spiked with 10, 20, and 30 Clonorchis sinensis eggs, were evaluated to assess the sensitivity in lowinfection cases. The PE and PS kits showed detection rates of 100% and 92%, respectively, from 100 egg-positive samples in WECM. Meanwhile, eggs were detected in 3 (PE) and 2 (PS) out of 20 egg-negative samples in WECM. The PE kit detected the highest number of eggs per gram of feces (727 on average), followed by the WECM (524) and PS kit (432). In fecal samples that were intentionally spiked with 10, 20, and 30 C. sinensis eggs, PE only detected eggs 2 out of 5 samples in 10 eggs spiked (40%), and the detection rates were 80% and 100%, respectively. The PE kit enabled a more accurate identification of trematode eggs because of the clearance of small fecal debris in the microscopic field. In conclusion, the PE kit is obviously helpful to detect and identify trematode eggs in stool examinations especially in endemic areas of clonorchiasis and metagonimiasis.

Until now, 3 Metagonimus spp. (M. yokogawai, M. takahashii, and M. miyatai) causing human metagonimiasis have been reported in Korea. In this study, we investigated the possible presence of Metagonimus spp. other than these 3 species using human fecal samples from an endemic area in Korea. DNA was extracted from Metagonimus egg-positive fecal samples collected from residents of Gurye-gun, Jeollanam-do. A total of 21 representative mitochondrial cytochrome c oxidase subunit I sequences were obtained by PCR and cloning, and sequencing. Phylogenetic analysis revealed 1 cluster corresponding to M. yokogawai (n=10) and 2 additional distinct clusters corresponding to M. kogai (n=8) and M. saitoi (n=3), which were proposed as new species in Japan in 2022. Pairwise cytochrome c oxidase subunit I distances were low for M. yokogawai and M. kogai (mean Kimura 2-parameter: 0.005–0.006), whereas M. saitoi showed higher Korea–Japan values (~0.029), a pattern consistent with geographic structuring. In conclusion, we provide the first molecular evidence for the occurrence of M. kogai and M. saitoi in human fecal samples in Korea. Further confirmation using adult morphology, additional nuclear markers, and ecological surveys are needed to clarify metagonimiasis transmission in the Seomjin-gang (river) basin.