LETTERS

fed to farm cats, which are major res-ervoir hosts for fishborne liver and in-testinal trematodes. Infections (preva-lence 8.3%) in snakehead fish (Channa spp.) also represent a food safety risk, because snakehead fish are cultured in Vietnam and are sometimes eaten raw or inadequately cooked. In addition to O. viverrini flukes, metacercariae of the zoonotic intestinal flukes Cen-trocestus formosanus, Haplorchis tai-chui, and H. yokogawi were recovered from snakehead and barb fish (online Technical Appendix Table 1), all of which are common throughout South-east Asia (1). The results of this study demon-strate that the human liver fluke O. viverrini is endemic to Vietnam and that it is being naturally transmitted to fish species that are often con-sumed raw or inadequately cooked. For determination of the prevalence, distribution, and epidemiology of O. viverrini flukes in fish, humans, and reservoir hosts (e.g., cats and dogs), these results need to be extended, especially because aquaculture is a growing industry in Vietnam. Acknowledgments We thank Henry Madsen for his ex-pert ecologic and malacologic advice, Jesper Clausen for his valuable assistance, PhanThi Van and Anders Dalsgaard for their strong support and advice, and the staff of the Research Institute for Aquacul-ture No.3 for their support and contribu-tions in the field and laboratory. This study is part of the research capacity building project “Fishborne Zoo