UC San Diego

Although over a billion people are at risk of foodborne trematodiases globally, such diseases have not been a public health concern in the United States, likely given the historical lack of suitable first intermediate host species. However, the introductions of one such snail species, Melanoides tuberculata, and two of its trematodes, Haplorchis pumilio and Centrocestus formosanus, to freshwater bodies throughout the United States pose potential public health threats. People can become infected with these foodborne trematodes by eating improperly prepared fish from trematode-infested localities. As these species were documented in their first intermediate host throughout Southern California, we examined commonly consumed second intermediate fish species to assess the risk of trematode transmission to humans. Of the five Southern California fishing locations surveyed, H. pumilio occurred across all locations and infected all seven surveyed fish species, and C. formosanus occurred at two localities and infected four host species. Host species, location, and host size influenced the abundance of H. pumilio and C. formosanus in bluegill (Lepomis macrochirus) and largemouth bass (Micropterus salmoides). To explore the risk of consuming improperly prepared fish within the United States, we searched YouTube™ for videos portraying the high-risk consumption of common Southern California freshwater fish species. Twenty-seven of the forty-two (64%) videos demonstrating raw freshwater fish consumption did not appear to follow FDA fish preparation recommendations. Given the distribution of M. tuberculata throughout the United States, our confirmation and discovery of H. pumilio and C. formosanus in several second intermediate host species within California and the presence of risky raw fish consumption behaviors call for an increased awareness of these trematodes among the public and clinicians.