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Protists: A Microbial Grab Bag |
Chapter: 5
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Check Your Sushi Each year, the CDC records over 50 confirmed cases of a roundworm disease called anisakiasis. Because it is difficult to diagnose, many hundreds of cases probably go undetected or undocumented. The responsible parasite is a roundworm known as Anisakis simplex. A second roundworm, Pseudoterranova decipiens, may also be involved. The worms represent the immature larvae stage of the nematode. They initially infest tiny shrimplike ocean crusta-ceans called krill, which are eaten by many ocean creatures, including squid and small fish. The parasites are passed along when the krill or fish are eaten by larger fish, which in turn are eaten by marine mammals. During autopsies on dead animals, marine mammal organizations may find thousands of worms blocking the gastrointestinal tract. Enactment of the Marine Mammal Protection Act in 1972 has led to a great increase of mammals along U.S. coastlines and consequently, increased possibility of encountering the parasite. Seals, sea lions and walruses are heavily infected. Salmon, mackerel, herring, striped bass and cod are among the fish that can carry Anisakis and Pseudoterranova to humans. The worm larvae are a brilliant red color and may be as long as 4 cm. Usually the larvae are easy to spot but apparently many sushi and sashimi devotees fail to look carefully enough. The most usual presentation in human exposure is for the diner to regurgitate a number of worms up to 48 hours after eating. This unpleasant (and unsettling) experience rarely results in permanent illness, although some worms may cause enough distress to mimic ulcer pain, and in rare instances, migration out of the bowel may occur. As expected, cooking fish invariably destroys the parasites, and freezing for five days or more at -4° F is also said to be effective (in the Netherlands the law requires that any fish to be consumed by humans must be frozen before sale). For sushi and sashimi lovers, a reliable restaurant is strongly recommended. |
