Asian tapeworm found in Alaskan salmon

(Graphic: Jayde Ferguson)

Scientists recently announced they had found an Asian tapeworm species in pink salmon caught off the coast of the Kenai Peninsula.

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Humans can contract the tapeworm by eating raw or under-cooked fish, but researchers say the risk is low.

For years, researchers have suspected the Japanese broad tapeworm was present on the Pacific Coast of North America. But with improved genetic techniques, they can now be sure.

In a recent study, a team of scientists identified a Japanese broad tapeworm larva in pink salmon caught in Resurrection Creek near Hope.

The tapeworm larva, which was about 10 mm long, had burrowed deep into the fish’s muscle near the spinal cord.

Jayde Ferguson is a fish pathologist with the Alaska Department of Fish and Game and one of the study co-authors. He said the Japanese species looks remarkably similar to another fish tapeworm already present in North America.

“There’s been growing evidence that it’s been here, it’s just the ability to differentiate it with the similar looking species has now improved with molecular testing,” Ferguson said.

Japanese broad tapeworm eggs were first found in wolf feces in British Columbia back in 2008.

This is the first time larvae in fish have been found in North America, but it’s likely this species has been present here for many years. That’s why Ferguson said the name Japanese broad tapeworm is somewhat misleading.

“Pacific salmon are on both sides of the Pacific Ocean. They’ve evolved on those sides for thousands and thousands of years as have their parasites,” Ferguson said. “There’s really no increased risk, no need to be alarmed.”

Since it was first identified in 1986, the tapeworm has been found in several salmon species, including sockeye, chum and pinks.

Tapeworm larvae in raw or under-cooked fish can infect humans and other carnivores. An estimated 2,000 people have contracted the tapeworm worldwide, mostly in northeast Asia.

The risk of contracting the parasite in Alaska, either from raw fish in a restaurant or at the store, is low. According to the Alaska Food Code, businesses must freeze all fish prior to serving to kill parasites.

To ensure the safety of personally caught fish, Ferguson said there are simple precautions to take.

“There are FDA guidelines on how to prepare your fish properly to basically avoid any risk of infection,” Ferguson said. “That would be freezing your fish in your standard household freezer for one week or cooking it to the standard recommended cooking temperature of 140 degrees Fahrenheit.”

The study appears in the February issue of Emerging Infectious Diseases.

For more information on common fish diseases and parasites in Alaska, consult the Alaska Department of Fish and Game’s illustrated handbook.

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Shahla Farzan is a reporter with KBBI - Homer. Shahla first caught the radio bug as a world music host for WMHC, the oldest college radio station operated exclusively by women. Before coming to KBBI, she worked at Capital Public Radio in Sacramento and as a science writer for the California Environmental Legacy Project. She is currently completing her Ph.D in ecology at the University of California-Davis, where she studies native bees. When she's not producing audio stories, you can find Shahla beachcombing or buried in a good book.

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