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 human when they consume raw or under-cooked fish that contain the eggs or larvae.
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.
The CDC states the tapeworm eggs and larvae are spread usually from fish shipped on ice but not frozen. Although the major news outlets have grabbed onto this story, keep in mind this is not the only tape worm that infects salmon, not to mention various other popular fish.
This is the main reason why sushi-grade fish is not about the quality of the fish, but how it was handled. If the fish in your sushi was not handled properly through the entire supply chain, you run the risk of diphyllobothriasis. 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.