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Worm Dangers From Sushi
NEW YORK, Jul 21 (Reuters) -- Tiny parasites in sushi can trigger a serious gastrointestinal illness called anisakidosis, researchers warn.
"Reported cases are increasing and are suspected to be just the proverbial tip of the iceberg," say a team of investigators at Yokohama City University School of Medicine in Yokohama, Japan. Their report appears in the July issue of the American Journal of Gastroenterology.
They describe the case of a 60-year-old habitual sushi eater, admitted to a Japanese hospital after having slipped into a coma. Close examination revealed what the authors call a "strangulating obstruction" in her small bowel. The woman required immediate surgery, including bowel resection. She eventually regained consciousness, and progressed to complete recovery.
The experts diagnosed her condition as anisakidosis, a condition caused by the ingestion of the larval form of a nematode of the anisaki species. They explain that the worm's natural home lies in the intestinal systems of marine mammals (such as dolphins), but it can also live in commercially-harvested fish including mackerel, tuna, or cod.
Normally, cooking kills the organism. However, sushi consumption can bring the live anisaki worm into direct contact with the digestive tract, where it can trigger severe illness. The authors report that "recently, anisakidosis has begun to be regarded as a public health problem in Japan, with more than 2,000 cases reported by physicians every year."
In the rarest and most life-threatening cases of anisakidosis, the body's immune response attempts to isolate and surround the worm with a mass of white blood cells, forming a mass called a granuloma. In the case of the 60-year-old woman, a bowel granuloma became so large that it blocked her bowel.
Heating (above 60 degrees Celsius for 1 minute) or freezing (to -20 degrees Celsius for 24 hours) all sushi prior to consumption should help destroy the anisaki worm. The authors point out that "in Holland, where this treatment is carried out compulsorily, the disease has been virtually eradicated."
However, safety precautions like these may not be popular among sushi purists, since either can alter the taste of raw fish. The researchers therefore recommend that sushi lovers who insist on taking their chances with the delicacy should have their fish "prepared fresh, (with) the viscera... removed as soon as possible." All chopping boards should be thoroughly washed after being used in the preparation of raw fish, and cooks should look closely at fish for evidence of the worm, which "can be seen by the unaided eye."
The authors also urge that sushi lovers "avoid raw mackerel or cod from sea locations where many marine mammals live." This advice could be difficult to follow, however, since marine mammal populations seem to be on the increase in American and Japanese coastal waters.
The researchers also warn that vinegar, such as that used to prepare some forms of mackerel sushi, "cannot remove or inactivate the nematode, which can survive in the vinegar for up to 51 days."
SOURCE: American Journal of Gastroenterology 1998;93:1172-1173
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