Parasitic Threat Found In U.S. Fish
A recent study has revealed that many freshwater game fish commonly caught in the United States—such as bluegill, largemouth bass, and black crappie—are infected with parasitic flatworms that could pose health risks to humans. Researchers found that over 90% of fish sampled from several fishing spots in Southern California were hosts to illness-causing trematodes. These findings were published in The Journal of Infectious Diseases and signal a need for greater awareness about the potential dangers of consuming raw or undercooked freshwater fish.
Lead researchers from institutions like the University of California-San Diego and the Smithsonian Environmental Research Center emphasized that while Americans generally do not worry about parasites in freshwater fish, the spread of trematodes across U.S. waters demands more attention. Cooking fish thoroughly or freezing it for at least a week before eating can kill the parasites. However, online videos showing people eating raw, unfrozen freshwater fish suggest that unsafe practices may be more common than previously thought.
The parasites found in the study, such as Haplorchis pumilio and Centrocestus formosanus, are known to cause gastrointestinal issues, fatigue, and in severe cases, organ damage. These flatworms typically target the liver, lungs, and bile ducts, and though they have historically been linked to infections in Southeast Asia, invasive snails have likely introduced them to U.S. ecosystems. In this study, some fish were found to carry thousands of these parasites, and two locations showed especially high infection rates.
Despite the risks, there have been no officially documented cases of these infections in Americans—likely because they are not being actively looked for or reported. Researchers suggest that some unexplained gastrointestinal illnesses might actually be linked to these parasites. They urge doctors and public health officials to consider these parasites when diagnosing symptoms and to educate the public on the importance of properly preparing freshwater fish.
The study was funded by the National Institutes of Health and highlights the importance of government-supported research into public health risks. Researchers emphasized that such work is essential for protecting the public, especially since it is unlikely to attract private sector funding. As the presence of these parasites grows in the U.S., both awareness and preventative measures are key to minimizing potential health threats.
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