An Alaska pink salmon and the booby trap waiting inside/CDC
As Alaska heads into the season of the salmon, it is worth noting the story of a raw-fish eater who made the news at the end of last week for the tapeworm he was found to be carrying in his gut.
The 32-year-old “man from Lisbon, Portugal, is featured in the medical journal BMJ Case Report,” CBS News reported. “The man was suffering from a bout of stomach pain for more than a week, and experienced vomiting and a fever.
“When doctors questioned him about his symptoms and history, he revealed that he had recently eaten sushi.”
Sushi, as the story notes, is generally considered very healthy. But in this case it was made with fish infected with parasites, a fairly common phenomenon .
What kind of parasite-laden fish the man ate was not mentioned in the story, although reporter Mary Brophy Marcus did note the danger of “raw or undercooked seafood such as cod, fluke, haddock and monk fish.”
Somehow she left out the species about which the Centers for Disease Control warned last February: salmon, particularly Alaska salmon.
The CDC cited the Japanese broad tapeworm as an “emerging infectious disease” in Alaska salmon.
“Recent studies that used molecular methods indicate that the number of human cases caused by this tapeworm may have been highly underestimated,” the CDC reported. “In addition, increasing popularity of eating raw fish is probably responsible for the increased number of imported cases in regions where this infection is not endemic.”
A group of Czech and Slovak scientists, working in cooperation with the Alaska Department of Fish and Game, in 2013 went looking for salmon infected with this parasite. They examined 64 fish from Southcentral Alaska and found tapeworms in many of them, including one with the Japanese broad tapeworm.
It was a pink salmon pulled from Resurrection Creek near Hope, just across Turnagain Arm from Alaska’s cities. The tapeworm inside was “found unencysted, deep in the musculature of the anterior part of the fish near the spinal cord,” the scientists reported. “It was highly motile.”
It was also the first Japanese broad tapeworm found in an Alaska fish in the wild. The parasite had been thought to be limited to northeastern Asia where a couple thousand people have been known to have been stricken by the parasite, which is far from the only tapeworm found in salmon.
Hidden dangers
“Diphyllobothriosis, a human disease caused by tapeworms of the genus Diphyllobothrium, is the most important fish-borne (disease) caused by a cestode parasite. Up to 20 million humans are estimated to be infected worldwide,” Tomas Scholz and colleagues reported in Clinical Microbiology Reviews back in 2009.
They noted 14 species of “broad tapeworms” or “fish tapeworms” that can make people sick, and they cited Alaska and Finland as places where parasite-related illnesses were high but appeared to be declining.
That might now have changed given the growing interest in eating raw fish, and the surprising number of Alaskans unaware of the potential downside given that Alaska salmon have been cited as one of the most common carriers of tapeworms of various sorts.
“…Fish that spend part of their life in freshwater such as salmon may carry Diphyllobothrium tapeworm larvae,” they warned. “These small, whitish, and somewhat flabby worms are common in salmon from some areas of Alaska.”
Most Alaskans who’ve handled a lot of fish – be they commercial, sport, personal-use or subsistence fishermen – have run into these small, whitish and somewhat flabby worms at some time.
YouTube these days has quite a collection of wormy salmon videos. Here’s one featuring wild sockeye salmon from Costco, and another of a live worm in “cooked” (obviously not cooked well enough) wild coho salmon from Whole Foods, and yet another worm in “rather pricey fresh wild pacific salmon fillets from a high-end fish market.”
The good news is that these worms won’t hurt you unless you eat them live, and even then they might not be a serious problem.
“Swallowing a live nematode larva can cause severe gastric upset called anisakiasis. This happens when the nematode attaches to or penetrates the intestinal lining. Nematodes do not find humans to be suitable hosts (however) and will not live longer than 7-10 days in human digestive tracts,” the Oregon paper said.
But it also warned that “swallowing live tapeworm larvae can cause a tapeworm infestation. The tapeworms may live in the human intestinal tract for several years. Symptoms can include abdominal pain, weakness, weight loss and anemia. Doctors successfully treat tapeworm infections with medicines,” if – of course – the condition is properly diagnosed.
Best news
Now, for the really good news. There are two simple ways to avoid problems with any of these parasites.
Number one: Cook your fish to an internal temperature of 140 degrees.
OK, so you don’t like overcooked salmon.
Number two: Put your fish in the freezer until they’re frozen solid and leave them there for a week. Or, if you’ve got a cold enough freezer – minus-31 degrees or colder – you can kill them in 15 hours, according to the Food and Drug Administration.
The FDA also says flash freezing at minus-31 degrees or colder and then storing the fish for 24 hours at minus-4 degrees or colder will work.
“Brining and pickling may reduce the parasite hazard in a fish, but they do not eliminate it, nor do they minimize it to an acceptable level,” the federal agency cautions. “Nematode larvae have been shown to survive 28 days in an 80° salinometer brine (21% salt by weight).”
So if you’re going to cold smoke the fish or make ceviche, it would be a good idea to freeze the fish first. And the same for any salmon intended for that sushi.
As for that first, fresh salmon of the season that Alaskans so much love to toss on the barbecue, well, there is one thing on which all the authorities agree: Cook it well. It might not taste as good as that filet that still has a hint of red inside, but it is a lot safer.
And you can always put some of the fresh salmon down in the freezer for a week and still have it essentially fresh the next week. Think of it as “aging,” as with wine.
If nothing else, it might make life better in the kitchen. Even if you know that worm crawling out of your salmon won’t kill you, and even if you are well aware cooking will kill it and any others still in the salmon flesh, small, whitish and somewhat flabby worms slithering around on your fish are just not very appetizing.
Unless, maybe, you’re a serious survivalist.