New dietary habits also have had an impact on disease emergence. Immigration to the United States, in particular, the relatively recent heavy influx of peoples from Latin America and Asia, has introduced many U.S. residents to new foods. Although popular, some of these foods, or the ways in which they are prepared, can cause disease as a result of contamination by any number of organisms or their toxic byproducts. Ceviche—raw seafood served in lemon juice—and sushi—raw seafood and rice wrapped in seaweed—are perhaps the most obvious examples of ethnic foods that have been associated with disease transmission, in most cases caused by intestinal worms (helminths).
Trichinosis, a generally self-limiting but potentially fatal disease caused by an intestinal roundworm that migrates to and encysts in striated muscle tissue, can be contracted from improperly prepared food. Trichinosis incidence in the United States had declined nearly every year since 1947 (Bailey and Schantz, 1990). As a result mainly of a single large outbreak of trichinosis, however, the incidence of the disease increased in 1990. The largest recent outbreak in this country occurred when uncooked, contaminated commercial pork sausage was consumed at a wedding reception. Ninety individuals, most of whom were Southeast Asian immigrants who customarily eat raw sausage, developed trichinosis (Centers for Disease Control, 1991i). Although the majority of cases of trichinosis still result from eating raw or insufficiently cooked commercial pork, consumption of insufficiently frozen or cooked wild game, particularly walrus and bear, has been increasingly associated with the disease, at least since 1975 (McAuley et al., 1991).
Cases of human anisakiasis, a food-borne disease, generally are caused by either of two species of nematode worms, Pseudoterranova decipiens and Anisakis simplex, commonly referred to as codworms and herring worms, respectively. Adult worms are found in marine mammals and release eggs that hatch in seawater; they are ingested by krill, which are eaten in turn by squid or fish. Larval-stage worms penetrate the bowel of the fish and encyst in the muscle. Humans contract anisakiasis by eating raw or partially cooked seafood containing nematode larvae.
Anisakiasis occurs most commonly in people living in coastal areas or areas in which the consumption of raw fish is customary. The fish most