Anisakis – The Sushi Parasite

What the so-called sushi parasite is and what it does inside your body.
The lifecycle of the nematode the media has dubbed the “sushi parasite“.

Extensive coverage of a case of anisakiasis in Portugal has many Americans swearing off sushi, terrified of what the media has dubbed the “sushi parasite”.

But what is the “sushi parasite”, really? And do you really need to give up sushi and sashimi?

About The Recent Case of “Sushi Parasite”

Last Thursday the medical journal BMJ Case Reports published a story about a 32-year-old man in Portugal who sought medical treatment for severe abdominal pain, vomiting and fever that he reported had gone on for about a week. Doctors interviewed him extensively and learned that he had recently eaten sushi. When they performed an endoscopy, they discovered a nematode, or roundworm, attached to the lining of the patient’s stomach. They removed the parasite with a special tool known as a Roth Net and, immediately, the patient began to recover.

And that’s pretty much it. Other than warning other doctors to be on the lookout for the roundworm, which appears to be becoming more common as more of us become accustomed to consuming sushi and sashimi, the doctors who treated this patient had little to add.

 What The “Sushi Parasite” Actually Is

The roundworm found in the patient in Portugal is only one of several that can sicken people who eat raw fish and seafood. This one was a nematode known scientifically as Anisakis simplex, but flukes, like Clonorchis sinensis, and tapeworms in the Diphyllobothrium genus are also well-known culprits.

The Anisakis nematode presents 2 dangers to people–parasitic infection and an allergic reaction to chemicals released into the fish. (It can even cause an allergic reaction in people who simply handle raw fish.) Neither cooking nor freezing will prevent the allergic reaction but, if done properly, it will kill the parasite and prevent the kind of parasitic infection seen in the Portuguese case.

When the nematode sets up shop in your digestive tract, as it did in this case, the resulting infection is known as anisakiasis. Generally the “worm” is removed via an endoscope but, rarely, surgery is required. It can also be killed with medication.

Exact numbers are hard to come by but the vast majority of cases are believed to occur in Japan. That will probably change, say experts, as more of us travel more extensively and as we become accustomed to eating new foods. In 2008 the World Health Organization, or WHO, estimated that Japan had recorded around 12,000 cases of anisakiasis. The actual number may be underestimated, however, because milder symptoms may simply be dismissed as flu or food poisoning. Only rarely do symptoms last longer than a couple of weeks.

Should You Stop Eating Sushi?

Despite all the media hoopla about the case in Portugal, this infection is still rare. And while food poisoning outbreaks linked to sushi have happened in the U.S., the Food and Drug Administration, or FDA, says that you can lower your risk by freezing fresh fish used in sushi and sashimi for at least a week before you use it. Freezing it at extreme temperatures, like those used in commercial sashimi production plants, works much faster.

And while the FDA stops short of actually giving sushi lovers a green light, it does acknowledge that it may also be safer to consume farmed fish, as opposed to wild-caught specimens.

There are, of course, some people who should never eat raw or undercooked fish or seafood, say food safety experts.




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