High prevalence of large trematode eggs in schoolchildren in Cambodia

Large trematode eggs (LTE) resembling Fasciola spp. eggs were reportedly found in the stools of schoolchildren in Kandal province, Cambodia. This study aimed to assess the prevalence of LTE in the stools of children attending the affected school, identify potential risk factors for infection and ascertain the trematode species. We performed a cross-sectional study involving an in-depth questionnaire administered to schoolchildren at the affected school, and examined cattle droppings in the surrounding area and the livers of slaughtered cattle. Three stool samples were examined per child, using Kato-Katz and formalin-ether concentration techniques. In addition, blood serum enzyme-linked immunosorbent assay (ELISA) and coprological polymerase chain reaction (PCR) was conducted for species clarification. Cattle droppings were examined by cup sedimentation and coprological ELISA. LTE were observed in the stools of 106 schoolchildren (46.5%). Two blood serum samples from schoolchildren were positive for Fasciola hepatica in a first ELISA but were negative in a confirmation immunofluorescence antibody test. Out of 221 PCR samples, only one tested positive for Fasciola spp. and none for Fasciolopsis buski. The consumption of raw aquatic plants (odds ratio (OR)=3.3) and fermented fish sauce (OR=2.1) were significantly associated with LTE in the stool. Fasciola spp. flukes were observed in 18.3% of 191 cattle livers. The prevalence of fascioliasis in cattle droppings was 88.8%. The low prevalence of schoolchildren that tested positive for Fasciola spp. with specific molecular diagnostics and who had no diagnostic evidence of F. buski strongly indicates that the majority of microscopically observed LTE are from Echinostoma spp. Fasciola spp. transmission from cattle to human is possible and public health services need to be alerted accordingly.