Fans of salmon rolls and sashimi beware — you may be at risk of ingesting a Japanese broad tapeworm.
The Japanese broad tapeworm, scientifically known as Diphyllobothrium nihonkaiense, was commonly believed to only be found inside fish from Asia. However, a recent study published by the Centers for Disease Control and Prevention in the journal Emerging Infectious Diseases says that the tapeworm may have found its way inside wild salmon caught in Alaska and along the Pacific coast of North America.
Previously, the most common type of tapeworm found in fish was believed to be Diphyllobothrium latum, but in 1986 scientists discovered another member of that family — the Japanese broad tapeworm. They believe that the Japanese broad tapeworm was actually responsible for about 2,000 reported infections, making it the second most common type of tapeworm infection.
Further research found that past cases of tapeworm infections in Japan, South Korea and the Pacific coast of Russia had been caused by Japanese tapeworms, not D. latum tapeworms as previously thought. The researchers also discovered that Japanese tapeworm larvae, known as plerocercoids, was found in salmon caught off the coasts of eastern Russian and Japan.
But the question remains — how did this tapeworm find its way into the United States?
In 2013, a team of scientists examined 64 wild Pacific salmon from four different species of the fish: chinook salmon, coho salmon, pink salmon and sockeye salmon. All 64 salmon were caught in south-central Alaska.
After observing the internal organs of each of the fish, the scientists discovered larvae between eight and 15 millimeters long, which elongated and contracted in the same manner worms do. After gene sequencing, the larvae were identified as Japanese tapeworms.
The researchers said their new findings present evidence that this salmon may be a source of human infection, because it is often transported on ice — not frozen — which creates an ideal environment for the tapeworms to survive transport. This salmon often ends up in restaurants in China, Europe and even the U.S.
D. latum — including the Japanese tapeworm — can grow up to a horrifying 30 feet long, according to the CDC. What’s even more alarming is that many people don’t even realize that they have been infected.
“Actually, most of the people who are infected don’t have symptoms,” Dr. William Schaffner, a professor of Preventive Medicine at Vanderbilt University School of Medicine who was not involved in the new study, told CNN.
Some people may feel a bit of abdominal discomfort, nausea, loose stools and sometimes weight loss. However, in some rare cases, the infection can turn into a serious medical problem.
“Massive infections may result in intestinal obstruction and painful inflammation of the bile ducts,” said Roman Kuchta, lead author of the study and a research scientist at the Academy of Sciences of the Czech Republic. “The infections can have a substantial emotional impact on patients and their families, because segments are evacuated over a long period of time. More severe cases may require specialized consultations and complementary analyses, which are costly.”
If you can’t kick your salmon habit, the CDC recommends sticking with adequately frozen or cooked fish. Cooking the fish at 145 degrees or freezing the fish under certain conditions should destroy the tapeworm and its larvae.
Danielle Tarasiuk is a multimedia journalist based in Los Angeles. Her work has been published on AllDay.com, Yahoo! Sports, KCET, and NPR-affiliate stations KPCC and KCRW. She’s a proud Sarah Lawrence College and USC Annenberg alumn.