Researchers find tapeworms in Alaskan salmon

A study published in Emerging Infectious Diseases shows that the diphyllobothriosis (an infection caused by tapeworms of the Diphyllobothrium genus) is reemerging because of global importation and increased popularity of eating raw fish. The researchers detected the Japanese broad tapeworm (Diphyllobothrium nihonkaiense) in the musculature of wild pink salmon (Oncorhynchus gorbuscha) from Alaska. Therefore, salmon from the American and Asian Pacific coasts and elsewhere pose potential dangers for persons who eat these fish raw.

In July 2013, the researchers examined 64 wild Pacific salmon of five species: one chinook salmon (O. tshawytscha), one coho salmon (O. kisutch), 23 pink salmon, eight rainbow trout (O. mykiss), and 31 sockeye salmon in Southcentral Alaska. The salmon were collected by angling or obtained from local fishermen. The musculature was filleted to narrow slices, and internal organs were observed under a magnifying glass. Several morphotypes of diphyllobothriid plerocercoids were found, including a single larva in the musculature of pink salmon collected in Resurrection Creek (near Hope, Alaska). The sequences of the cox1 and 28S rRNA genes (lsrDNA) on this plerocercoid were almost identical to those of the Japanese broad tapeworm available in the GenBank database, thus providing unequivocal support that this plerocercoid was a larva of the D. nihonkaiense tapeworm reported from North America.

For decades, the possible occurrence of the Japanese broad tapeworm on the Pacific coast of North America was ignored, but since 2008, human infection with adult tapeworms and natural infection of carnivores (wolves and bears) with adult tapeworms have been confirmed by use of molecular markers. The researchers concluded that 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. For more effective control of this human foodborne parasite, detection of the sources of human infection and critical revision of the current knowledge of the distribution and transmission patterns of individual human-infecting tapeworms are needed.

Study