• Over 90% of popular freshwater fish in Southern California are infected with human-infecting parasites.
• The trematodes, Haplorchis pumilio and Centrocestus formosanus, pose significant health risks if fish are consumed improperly.
• Precautions include thorough cooking or freezing fish intended for raw consumption.
• The parasites are linked to an invasive snail species that arrived in the U.S. over a decade ago.
• Public health officials recommend awareness and proper reporting of infections.

Researchers have found that more than 90% of popular freshwater game fish sampled in Southern California contain invasive parasitic worms that could pose a health risk to humans. These parasites belong to two species of flatworms known as trematodes: Haplorchis pumilio and Centrocestus formosanus. The alarming findings, published in the Journal of Infectious Diseases, indicate that consumption of infected fish may lead to gastrointestinal problems, weight loss, lethargy, and in severe cases, strokes or heart attacks, according to The Hill, Los Angeles Times, SFGate, and Newsweek.

The study conducted involved sampling 84 fish from five different fishing spots in San Diego County, revealing that approximately 93% were infected with H. pumilio and 91% with C. formosanus, indicating a significant health threat within aquatic ecosystems. The parasites were likely introduced to the U.S. via the invasive Malaysian trumpet snail, which has spread to various parts of California since its first sighting in 1972, as noted by Los Angeles Times and SFGate.

According to senior author Ryan Hechinger, “Americans don’t usually think about parasites when they eat freshwater fish because it hasn’t historically been an issue here.” Hechinger emphasized that consumers of these fish must be made aware of the risks, especially since many health professionals might not consider parasitic infections related to locally caught fish, according to Newsweek and The Hill.

Preventive measures recommended by health officials include thoroughly cooking any freshwater fish that might be infected or, if consuming raw fish, freezing it for at least one week. The U.S. Food and Drug Administration also supports these guidelines, highlighting that freezing parasites can effectively reduce infection risk, as reflected in research conducted by Los Angeles Times and Newsweek.

A survey conducted as part of the study analyzed 125 YouTube videos totaling nearly 5 million views and found that approximately 65% of them failed to mention necessary cooking procedures, which could further exacerbate the potential for infection. This lack of awareness accentuates the urgency for public health initiatives aimed at educating consumers on safe fish consumption practices, according to SFGate and Los Angeles Times.