Parasites Found in California Freshwater Fish Pose Health Risks

More than 90% of popular freshwater fish in Southern California have been found to carry parasites that can infect humans, according to a study published in the Journal of Infectious Diseases. The study, led by Ryan Hechinger, an ecologist and parasitologist at the University of California San Diego, identified two species of trematodes, Haplorchis pumilio and Centrocestus formosanus, in fish such as largemouth bass and bluegill. These parasites can cause gastrointestinal issues, weight loss, and lethargy, and in severe cases, strokes or heart attacks.

The trematodes were likely introduced to the United States by the red-rimmed melania, an invasive aquatic snail. These snails, which were first spotted in California in 1972, serve as hosts for the parasites and have spread across 17 states and Puerto Rico. The parasites move from the snails to fish, eventually reaching humans or birds who consume the infected fish.

Researchers examined fish from five fishing locations in San Diego County and found that 93% of the fish were infected with H. pumilio, while 91% of the fish at two locations were infected with C. formosanus. The parasites can be found on different parts of the fish, including the base of the fins and the gills, and can infect the muscles and connective tissue, posing a risk to those who consume the fish.

To prevent illness, the U.S. Food and Drug Administration advises thoroughly cooking freshwater fish or freezing it before consuming it raw. However, a survey of 125 YouTube videos revealed that 65% did not mention proper cooking or freezing techniques, increasing the risk of infection. Hechinger emphasized the importance of public awareness and proper food preparation to prevent the spread of these parasites.