Anisakiasis, a zoonotic disease associated with the consumption of raw seafoods, has been the recipient of much media attention and public concern in recent years. One reason for this attention is due to the increased incidence of reported human cases throughout the world. Obviously, the majority of cases occur in areas where seafood constitutes a major portion of the protein intake of a population. The annual incidence of anisakiasis in Japan, for example, is estimated in excess of 1,000 symptomatic episodes per year. In 1984, Japan reported 3,141 confirmed cases of stomach anisakiasis (cases of intestinal anisakiasis were not included).

Fortunately, the United States has a relatively low incidence of anisakiasis. This is probably because most fishery products in this country are effectively processed and/or cooked. The changing dietary habits of our cosmopolitan society and the current trend of cooking seafoods for shorter lengths of time are increasing the chances of consumers to become infected with these invasive anisakid larvae. For example, some common raw fish dishes known to transmit the infective form of the anisakid parasites to humans are: Japanese sushi and sashimi, South American ceviche, Dutch green herring, Scandinavian gravlax, Hawaiian lomi lomi salmon, and Pacific Island poison cru. Our increased consumption of raw or "lightly done" seafoods closely corresponds with the noticeable increase in the incidence of case reports of anisakiasis. The majority of the cases of human anisakiasis in the United States resulted from home-prepared meals; however, restaurants have been confirmed to be involved in the transmission process.

The U.S. Food and Drug Administration is interested in preventive measures to neutralize the invasive potential of anisakid larvae encapsulated in infected fishery products. Several parasite control measures have been suggested and, for a variety of reasons, rejected. Examples of control measures that have been considered are: candling (a procedure utilizing bright lights above and below transparent fish fillets to visualize the encapsulated nematodes); species avoidance (elimination of commercially important species known to vector the disease); and training (education of food handlers and consumers).

Temperature extremes appear to be most effective in controlling the parasites. The heat from thorough cooking seafoods kills the larval nematodes. However, heating fishery products is not always desirable. Currently, freezing is regarded as the most promising preventive measure against infection with anisakid larvae. The specified times and temperatures required to kill these roundworm larvae are being evaluated.

The commercial fishing industry commonly uses a process called blast-freezing which rapidly freezes the fishes to -40'C. A recently completed study demonstrated that commercial blast-freezing is extremely effective in killing larvae in fishes. A summary of some of these data are presented in Table 1.

Table 1. Viability of Anisakis Larvae Following Blast-freezing

The study concluded that blast-freezing could effectively prevent anisakiasis when thorough cooking of fishery products is not desired. Not only does blast-freezing kill parasites, it is cost-effective, causes little change in the flavor or texture of the fishes, and is of practical importance because the commercial fishing industry currently uses the process.

Evisceration of some fishes after capture will lessen the worm burden because most infective larvae reside in the viscera. Table 2 shows that, for rockfish, 75% of the anisakid larvae were encapsulated in the viscera; therefore, removing viscera would eliminate the majority of the helminths. Salmon, unfortunately, are an exception to the statement that most infective larvae reside in inedible portions. Salmon usually have more worms in the edible musculature than in the viscera (see Table 2). Still, evisceration of all fishes-including salmonids-immediately after capture is recommended because it will eliminate the potential for these anisakid larvae to migrate from the decomposing abdominal mesentery of the dead fish to the muscle. This migratory phenomenon is well-documented in the literature.

Table 2. Worm Burden in Whole Fishes

Because of the risk of becoming infected with parasites in fishery products and our increased knowledge concerning the effects of temperature extremes on parasites, the Food and Drug Administration on 21 August 1.987 released the following Code Interpretation:

"Fishery products which are not cooked throughout to 14°F (60°C) or above, must have been or must, before service or sale in ready-to-eat form, be blast frozen to ­31°F (-35°C) or below for 15 hours or regularly frozen to -10°F (-23°C) or below for 168 hours (7 days). Records which establish that fishery products were appropriately frozen on-site must be retained by the operator for 90 days."

This FDA Code Interpretation defines "fishery products" as fin fish; bivalve (scallops), gastropod (abalone) and cephalopod (octopus, squid) mollusks; and crustaceans (lobsters, crabs) from both fresh and salt water. Clams, mussels and oysters are specifically excluded from this interpretation because of the controls imposed by states under the provisions of the National Shellfish Sanitation Program.

The United States is not the first country to address this problem. The Netherlands established legislative regulations concerning consumption of raw herring. The regulations, known as The Green Herring Laws, stated that fresh herring should be frozen in such a manner as to reach a temperature of at least -20°C within 12 hours and stored for a period of 24 hours prior to being released to the public. The regulations also address marination and smoking procedures. Previous to the implementation of this legislation, 160 proven or highly suspected cases of human anisakiasis had been reported. As a direct result of The Netherland's legislative actions, the number of human cases was dramatically reduced.

Although Japan has no freezing regulations or policy with regard to prevention of an1sakiasis at present, the country reports that it is common practice to freeze Pacific salmon (Oncorhynchus spp.) in order to kill worm parasites. (Note: Pacific salmon are most commonly implicated as the agent of transmission in U.S. cases.)

While adequate freezing or thorough cooking of fishery products are good preventive measures against anisakiasis and other parasitic diseases, these practices are not always followed and are difficult to enforce. Prevention of this disease, therefore, is probably best accomplished by educating the public to the health risks of eating raw fishery products.