K A S H R U T . C O M_©

June 10, 2025 from Food Safety News:

"Two species of fish-borne parasites have been found in freshwater fish routinely caught for consumption. Researchers say people could be eating the fish in ways that are conducive to transmission.

"The analysis of freshwater fish collected at five fishing sites in San Diego County, CA, was published in the Journal of Infectious Diseases and showed that two species of trematodes, a type of flatworm, were prevalent in seven fish species. The infected fish species are found across the United States.

"One of the trematode varieties was found to have infected fish from all testing sites with 93 percent of the fish tested being infected. The other type of parasite was found in fish at two of the testing sites and had an overall prevalence of 89 percent.

"Researchers with the Scripps Institution of Oceanography at the University of California-San Diego discovered that fish species found to be infected with the parasites included largemouth bass, bluegill, black crappie and common carp.

"An invasive snail has been found to be a host for the parasites, which cause human illness. Trematodes have historically infected people in Southeast Asia and the Western Pacific and local transmission wasn’t a concern in the United States until the arrival of the freshwater snail that serves as a host. The snail is now found in at least 17 states and Puerto Rico. Previous research by the same team found that the snail and the two trematodes have become widespread at freshwater fishing sites in California.

"n the initial stage of their lifecycle, trematodes infect the snails, then exit the infected snails and move on to a second intermediate host — fish. The adult trematodes then infect hosts, like birds or people, that eat the infected fish. If ingested by people, trematodes infect the small intestine, causing gastrointestinal symptoms that range from mild diarrhea to weight loss and lethargy.

"People can take to reduce the risk, like properly cooking or freezing fish before consumption, which kills the parasites.