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What About Eating Raw or Undercooked Fish and Parasites?

Question

A reader wrote: I was in a fancy restaurant last night and ordered wild salmon. I had already eaten half of it when I noticed a skinny 2 inch long bright pink worm wriggling on my plate. It had been hiding in the salmon. Do you know what kind of worm it was and if it will make me sick?

Answer

Trish Barbash, USFWS Fish Pathologist at the This link opens in a new windowLamar Fish Health Unit in Lamar, Pennsylvania responded: I suspect that the worm observed on the plate of salmon is a nematode. They are a member of the roundworm family (Anisakidae) and are the most common parasite found in marine fishes. They can reside in the intestines, organs as well as the flesh of fish. There are many different species, and exact identification can only be made with microscopic examination of body structures.

Freshwater fish, like trout, and fish that spend part of their life in freshwater such as salmon, may carry Diphyllobothrium tapeworm larvae. These small, whitish, and somewhat flabby worms are common in salmon from some areas of Alaska. 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. However, the worm described by this woman does not sound like a tapeworm larvae.

Most adult salmon served commercially are from the ocean. I strongly doubt that she was actually served "wild" salmon. Since both the fish and the worm had the same extremely pink color, it suggests that a flesh colorant was fed to the fish prior to harvest. Many commercial salmon farms feed colorants in the fish food to make the flesh look pink and thus more attractive to customers.

The worm was obviously residing in the muscle flesh, and absorbed the colorant. The restaurant may or may not have known they were serving farmed fish. The nematodes are usually white, and curled up in a ball in the muscle.

Nematodes rarely cause health problems because normal cooking easily destroys them. If this worm was in a properly cooked fillet, it would be dead!!! But this one was alive; therefore, the fish was definitely not properly cooked - period. I understand her concern for her own health, but in most cases, swallowing a live nematode is harmless. The nematode passes through the intestine without causing problems. In rare cases, 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 and will not live longer than 7-10 days in human digestive tracts.

Personally, I would be more concerned about contracting a horrible bacterial infection from the undercooked fish.

So if she does experience any of these symptoms related to either tapeworms, nematodes, or any intestinal disruption, she should tell her doctor about the worm incident and the fact that the fish was under-cooked. If she does not get any symptoms - the prognosis is good (but not for the restaurant that served her!!!!).



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