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ANISAKIASIS

INTRODUCTION

Anisakiasis is a zoonotic nematode infection that can cause gastric, intestinal, and rarely, ectopic infections in humans. The third-stage larvae of Anisakis simplex and Pseudoterranova decipiens are the most common parasites to cause this infection after ingestion of raw or insufficiently cooked marine fish, as in sushi, sashimi, ceviche, and salted or smoked fish.

PATHOGENESIS AND EPIDEMIOLOGY

Adult nematodes are found in the gastrointestinal tract of cetaceans (dolphins, porpoises, and whales), and nematode eggs shed in the feces of these definitive hosts are ingested by small crustaceans, where they develop into third-stage larvae. Crustaceans infected by larval forms are eaten by the fish and cephalopod mollusks, and once infected, the larvae invade the tissues of the fish. Definitive hosts and humans become infected by eating fish containing these larval stages. Most cases are associated with mackerel, squid, yellow tail, cod, haddock, herring, blue fin tuna, and salmon, but other fish may be infected. Once ingested, the larvae usually penetrate the gastric wall, leading to rapid onset of acute abdominal pain, nausea, and vomiting.

There has been a dramatic increase in the incidence of anisakiasis since 1980. This is in part due to (1) improvement in endoscopic procedures needed to make the definitive diagnosis; (2) increasing global demand for seafood and a growing preference for raw or lightly cooked food, especially in Western countries; and (3) the impact of regulatory controls on harvesting of marine mammals, leading to increased populations of potential definitive hosts. Human infection is most common in Japan, where consumption of raw fish is common and approximately 2000 anisakiasis cases are reported annually (accounting for 90% of reported cases worldwide). Incidence is also high in other countries in Asia and is increasing in the United States (approximately 50 annual cases) and Europe (approximately 500 annual cases).

CLINICAL MANIFESTATIONS

There are 4 major clinical syndromes in humans: gastric (most common), intestinal, ectopic, and allergic disease. Clinical manifestations vary depending on where the worm localizes. In the gastric type, acute gastritis with abrupt onset of severe epigastric pain, nausea, and vomiting may occur, often within the first 12 hours of ingestion. Acute symptoms resolve within a few days, but some may report vague abdominal pain, nausea, and vomiting for weeks to months afterward. More severe symptoms with fever, chills, and urticaria may develop with repeated exposure because of Arthus-type allergic reactions. The relationship between anisakiasis and strong allergic reactions, ranging from urticaria to isolated angioedema and life-threatening anaphylaxis within hours of exposure, has become clearer in recent years. Most cases of allergic manifestations reported have demonstrated elevated immunoglobulin (Ig) E responses against A simplex. There is also speculation that initial sensitization may occur from exposure to both dead and live parasitic larvae.

Intestinal anisakiasis may not become symptomatic for up to a week after initial infection. ...

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