EATING RAW FISH: THE DANGERS
''In the most serious cases,'' he continued, ''it penetrates the intestinal wall and enters the peritoneal cavity, where it may cause chronic lesions or prompt white blood cells to gather around to fight it off, thus forming a granuloma, which is often mistaken for a tumor. Then if surgery is performed, the worm can be found within the granuloma. Nevertheless, we do not consider it a major problem, in spite of the potential. But we will probably see more of it as the eating of raw fish increases.''
Symptoms of gastric anisakiasis are said to develop within four to 12 hours of eating contaminated fish (intestinal anisakiasis will develop within seven days).
There is no cumulative effect from eating raw fish. It is possible to eat 100 pieces and not get anisakiasis if it is not present in those pieces, and it is possible to become infected from eating only a single piece that contains larvae, usually about one to one and half inches long.
In a report on anisakiasis written in 1976 for the Armed Forces Institute of Pathology, Ronald C. Neafie and John R. Dooley, both parasitologists, said, ''Infected fish are commonly marketed in this country and elsewhere; for example about 90 percent of cod fillet sold in and around Washington, D.C., contain anisakine larvae.'' They recommended that ''public health education should discourage the eating of raw or inadequately prepared fish or squid.''
At various times, contaminated fish have been found off the waters of Massachusetts, and in 1970, the Beltsville Parasitological Laboratory in Maryland reported that infected fish were found in markets in Connecticut, Maryland and New York, as well as in fish from Canada. Fish from northern waters are generally considered more likely to have anisakis simplex larvae than those from tropical waters, and the proximity to mammals such as whales, seals and certain strains of porpoises also increase possibilities because those animals are important to the life cycle development of the parasitic nematodes.
Fish that have the anisakis larvae do not necessarily transmit it to humans. While the fish are alive, the worms live in their stomachs. Once the fish are dead, the larvae penetrate the tissue that is eaten.
It is safest, therefore, to gut fish as soon as they are caught to minimize chances of the larvae's spreading. It is also possible to remove anisakis larvae from fish as it is being cut, because such larvae are visible to the trained eye, especially those of experienced sushi cutters.
To be safe, however, responsible sushi shop owners buy only the freshest fish and never serve fish in which larvae were discovered. The most susceptible fish, such as mackerel or squid, are not served completely raw.
According to Ryudaburo Kawada, the owner of the Takezushi and Kurumazushi restaurants, all mackerel is salted and then marinated in strong vinegar and squid is purchased frozen, a process that kills the parasite. Mr. Kawada also said that all bonito is infected and so is rarely ordered by non-Japanese and the susceptible yellowtail is also purch ased frozen.
Shrimp, eel and octopus are always cooked for sushi. Nevertheless, fluke, porgy and sea trout are traditionally served raw and all have been found to have anisakis at one time or another. There are no reports citing tuna as a carrier.
Because of an outbreak of the parasite a few years ago in the raw herring favored in the Netherlands, the law there now requires that all herring must be gutted immediately, then salted and frozen at 4 degrees below zero within 12 hours of being caught and for 24 hours thereafter. Such freezing, or heating to 140 degrees, kills the larvae.
But though anisakis simplex is known in Japan, it is not considered dangerous by most experts there and no regulations have been established. Dr. Noboru Kagei, chief of the second division of parasitology at the National Health Institute of Japan in Tokyo, said that the number of cases is considered negligible, although there, too, fish from northern waters are suspect, and mackerel and squid are treated as Mr. Kawada described.
Nevertheless, there has been some increase of infection reported, most notably in the Ohita prefecture, where 42 cases were reported in 1980 as against 12 in 1977, an increase possibly a result of the eating of raw mackerel by a group of men at a party. Stating that local health centers rarely issue warnings because it is not considered one of the most dangerous diseases, Dr. Kagei said that the number of cases of anisakiasis may be much greater than reported.
Acknowledging that he eats raw fish often and that doing so is a custom in Japan, Dr. Kagei said it is difficult to require all fish to be frozen because so many varieties are eaten raw. But he also stated that he believes that some regulations are needed.
Putting the matter in perspective, Dr. Roberto said, ''There's no point in doing fish market surveys. The parasites are there all right and they can't be cleared up. You can't treat fish. People who like to eat raw fish because they enjoy it or feel it is healthful should be aware of the risk, and go only to good clean places and if they feel any gastric symptoms should see a physician.''