 Volume 23, Number 2—February 2017 
 
 Research Letter 
 
 Diphyllobothrium nihonkaiense Tapeworm Larvae in Salmon from North America 
 
 Roman Kuchta , Mikuláš Oros, Jayde Ferguson, and Tomáš Scholz 
 
 Author affiliations: Biology Centre, Czech Academy of Sciences, České Budějovice, Czech Republic (R. Kuchta, T. Scholz) ; Slovak Academy of Sciences, Košice, Slovak Republic (M. Oros) ; State of Alaska Department of Fish and Game, Anchorage, Alaska, USA (J. Ferguson) 
 
 Cite This Article 
 
 Abstract Diphyllobothriosis is reemerging because of global importation and increased popularity of eating raw fish. The Centers for Disease Control recently posted an article in its Emerging Infectious Disease journal, stating that Diphyllobothrium nihonkaiense has been found in wild pink salmon from Alaska. There is some concern in regards to those who have caught the fish themselves or have bought it freshly caught from someone else, and want to eat their salmon raw — in those instances, consumers should freeze their fish first, for at least a few days. In 1986, scientists identified another member of this family, the Japanese broad tapeworm, and believed it had been responsible for about 2,000 infections reported to that point, making it the second most common cause of tapeworm infection. The validity of the Japanese broad tapeworm was later confirmed by molecular data, especially the cox1 gene sequences (1). Evidence indicates that virtually all previous cases of diphyllobothriosis in humans in Japan, South Korea, and the Pacific coast of Russia that were attributed to D. latum tapeworms were caused by D. nihonkaiense tapeworms (1,3). Studies on the transmission of the Japanese broad tapeworm in Japan and eastern Russia (Primorsky Region) have identified 4 species of Pacific salmon as the principal sources of human infection: chum salmon (Oncorhynchus keta), masu salmon (O. masou), pink salmon (O. gorbuscha), and sockeye salmon (O. nerka). Tapeworm larvae infective for humans (plerocercoids) have been described in only a few studies performed in eastern Russia and Japan, (e.g., as plerocercoids type F from the musculature of chum salmon in Kamchatka, Russia) (2,6,7). Figure 
 
 Video 
 
 In July 2013, we examined 64 wild Pacific salmon of 5 species:1 chinook salmon (O. tshawytscha), 1 coho salmon (O. kisutch), 23 pink salmon, 8 rainbow trout (O. mykiss), and 31 sockeye salmon in south-central Alaska, USA. After filleting the musculature into narrow slices, the scientists observed these and the internal organs of each fish under a magnifying glass. This report provides additional evidence that salmon from the Pacific coast of North America may represent a source of human infection. Because Pacific salmon are frequently exported unfrozen, on ice, plerocercoids may survive transport and cause human infections in areas where they are not endemic, such as China, Europe, New Zealand, and middle and eastern United States (1). However, continuing to study the tapeworms using new molecular methods, researchers funded by the Czech Science Foundation discovered they'd been wrong. After all, tapeworm infection is very unusual in the United States.
– It turns out that a parasite thought to be confined to fish from Asia is in fish around the US, too. Researchers identified the Japanese broad tapeworm, aka Diphyllobothrium nihonkaiense, in wild pink salmon caught off Alaska, they report in a study in the CDC's Emerging Infectious Diseases journal. "Therefore, salmon from the American and Asian Pacific coasts and elsewhere pose potential dangers for persons who eat these fish raw," write the researchers. However, Jayde Ferguson, a state wildlife official who co-authored the study, tells Alaska Dispatch News that the discovery shouldn't be much cause for alarm among consumers. "If it was anything that was of concern, increased risk or anything like that from a management standpoint, we would have said something," he says. "They're wild animals—they're going to have parasites, they're out in nature." The comfort for US sushi lovers is that the FDA requires that any fish sold or served raw be frozen first, which would kill any parasites, reports the Seattle Times. (Those who caught the fish themselves and planned to eat it raw would want to freeze it first as well, notes the San Francisco Chronicle.) The researchers cautioned that "Pacific salmon are frequently exported unfrozen," though that doesn't apply to the vast majority of Alaskan salmon. A preventive medicine professor at Vanderbilt University School of Medicine tells CNN most infected humans remain asymptomatic—some may feel slight abdominal discomfort or nausea—though there are rare cases in which the infection can turn serious. The CDC notes that cooking the fish also will annihilate Diphyllobothrium parasites. (A Canadian man bit into a piece of salmon and fell into a coma.)