Japanese Tapeworm Found in American Wild Salmon

For those who like their salmon on the rare side, time to be more careful as that prime piece of wild Alaskan salmon may be infected by D. nihonkaiense, a member of a genus of tapeworms that can infect humans. This particular species, the Japanese broad tapeworm is the second leading cause of diphyllobothriasis (tapeworm infection) in humans. The tapeworm is usually transferred to humans when they consume raw or under-cooked fish that contain the eggs or larvae.

About the Tapeworm Diphyllobothrium nihonkaiense

D. nihonkaiense is commonly known as the Japanese broad tapeworm, and resides in the intestines of marine mammals, fish and fish-eating birds. The parasite is distinctive for utilizing salmonids (salmon, trout) as intermediate hosts. As the chart above shows, salmon get infected by the parasite by eating infected crustaceans. Its incredible adaptability allows the tapeworm to infest various marine and non-marine species.

tapeworm

The creature’s segmented body is armed with specialized structures called bothria, which help it latch onto the host’s intestinal wall. Once there, the parasite’s prolific reproductive capabilities take over, generating thousands of eggs daily, and starting the whole cycle over again.

Mature diphyllobothriids are large tapeworms reaching 2—15 meters in length, with occasional larger specimens. The scolex always has two bothria (grooves). The general size and shape of the scolex may be subject to intraspecific variability, though some species-level differences have been described historically. Proglottids are broader than long, with a single genital pore that opens in the middle of the ventral surface; fully mature specimens may be comprised of a 2,000—5,000 proglottids. The ovaries are characteristically rosette-shaped.

Source: CDC

This has been a long-standing and probably under reported issue in Japan and could be growing due to the popularity of sushi worldwide. Now the CDC has a report that states that this tapeworm species has been found in North American salmon for the first time. According to the report, chum, masu, pink, and sockeye salmon are the species most likely to carry D. nihonkaiense.

How Does it Spread?

The CDC states the parasite’s eggs and larvae are spread usually from fresh fish shipped on ice but not frozen fish. Which makes sense, since frozen fish is at a temperature and for a duration that will kill off fish parasites. However, you are still are at risk before your nigiri is even at the table. If the fish in your sushi was not handled properly through the entire supply chain, you still run the risk of diphyllobothriasis. Expect abdominal cramping, diarrhea, weight loss (not the good kind) and possible neurological issues.

If clean fish is cross-contaminated by fish with tapeworm eggs, by using the same cutting board for instance, then all the safeguards were for naught. This is the main reason why sushi-grade fish is not about the quality of the fish, but how it was handled. Although the major news outlets have grabbed onto this story, keep in mind this is not the only tape worm or other parasite that infects salmon, not to mention various other popular fish.

Simple Rules to Keep you Parasite-Free

For the home chef, make sure your fish is thoroughly cooked or brined. An alternative strategy is to freeze the fish down to -4F (-20C) for between a minimum of 3 days before preparing sushi.