SAN DIEGO (FOX 5/KUSI) Nearly all freshwater game fish at popular recreational fishing areas in Southern California have been exposed to invasive parasites with the ability to infect humans, a new study published in the Journal of Infectious Diseases on Tuesday found.

The study is the first time the parasites two species of flatworms called trematodes have been recorded with such a widespread presence in the state’s fish, suggesting infections from the organisms pose a greater risk to public health nationwide than previously thought.

“It’s something we don’t want to overdramatize, but we also don’t want to underemphasize,” Ryan Hechinger, an ecologist and parasitologist at UC San Diego’s Scripps Instruction of Oceanography who is a lead author on the study, explained to affiliate KUSI.

“These intestinal small trematodes are recognized as major, serious health problems in other areas of the world,” he continued.

1B worldwide thought to at least be at risk of foodborne parasitic infections

Upwards of a billion people around the world are believed to be suffering from or at risk of foodborne parasitic infections from organisms like the trematodes identified in the study, Haplorchis pumilio and Centrocestus formosanus.

Infections can range in severity from headaches and gastrointestinal distress to prolonged malaise and weight loss. In some rare cases, people who have been infected by the parasites can also experience a stroke or heart attack.

Public health experts say parasitic infections like these are typically developed from consuming raw or undercooked food namely fish, which are often the stepping stone for the organisms from their first host to a warm-blooded vertebrate.

For American patients, doctors have long linked this consumption with international travel before diagnosing them with such an infection, given the novelty of homegrown cases in the U.S. However, the study’s findings upend this conventional line of thinking.

“We can become infected with the type of trematode parasite in the United States by eating freshwater fish. It’s something that we have not historically been thinking about,” Hechinger said. “They’re here now and we would be better off being aware of it.”

Researchers say there is no reason for alarm

That said, the researchers behind the study said there is no reason for alarm, as it is easy for freshwater anglers to avoid infection: Simply follow the Food and Drug Administration’s fish preparation guidelines before eating any catches.

This means any fish should either be cooked fully or placed in the freezer for a least a week, if being used raw.

The trematodes identified in the study are not native to Southern California, but were found in more than 90% of the game fish researchers analyzed in tandem with the California Department of Fish and Wildlife. This included largemouth bass, bluegill and sunfish.

As Hechinger explained, even where they did not observe the parasite in fish, they found its primary host, an aquatic snail native to Southeast Asia known as the red-rimmed melania or the Malaysian trumpet snail.

The invasive snail was previously documented by Hechinger and his team at fishing spots in California. It has also been recorded in 17 other states mainly those along the Gulf Coast like Florida and Texas, where it was first introduced more than a decade ago and Puerto Rico.

“Once we found that it was here in the snails in California too at fishing spots, we were quite sure they would be in the fish, given what we know about the basic biology of these things,” Hechinger said.

Parasites spread by eggs, small clones

The parasites spread by way of eggs and small clones that are ingested into their host. Once the worms make it to a human by way of consumption, their eggs can get trapped in the body, leading to the symptoms exhibited by those with an infection.

These eggs and the clone, Hechinger added, eventually pass over time, but they can build up with repeated consumption of infected food and lead to more serious ailments.

Given this, consumption habits were another core focus of the newly published study. The researchers conducted a survey of popular fishing videos posted to YouTube, noting that most either did not mention the FDA’s preparation guidelines or showed otherwise risky behaviors.

As Emma Palmer, a marine scientist at the Smithsonian Environmental Research Center who conducted field analysis for the study while in her graduate studies at Scripps, explained to FOX 5/KUSI, these behaviors included eating a whole raw fish, straight off the line.

“A lot of the areas that these parasites infect are in things like the fins or the head,” she said. “They’re concentrated typically in areas that you tend to avoid while you’re fileting the fish. So if you eat the whole fish, you’re eating all the parasites in the fish.”

Palmer added some of the videos mentioned other misconceptions about eating raw fish, like the thought that marinating it in lime juice will kill any unwanted organisms in the fish or that there are no potential health risks for fish caught from a clean water source.

Researchers to share findings with local public health agencies

Many of these organisms are also too small for the naked eye to see, she noted to emphasize the importance of following the FDA’s guidelines there can be thousands of parasites inside fish that appear to be “perfectly fine.”

The study’s authors plan to share these findings with local public health agencies in an effort to increase awareness through things like educational campaigns and improved signage around recreational fishing areas.

They are also recommending that parasitic infections be added to the list of reportable diseases to improve public health tracking and that medical practitioners take their presence in the U.S. into account when assessing patients.

“We don’t have to be overly concerned about it,” Hechinger said. “It’s pretty straightforward to diagnose and treat if we’re simply aware and take appropriate steps.”