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Anisakiasis is a result of aberrant infection of the gastrointestinal tract by anisakid species of parasitic nematodes found in marine mammals. Infection occurs after ingestion of raw or inadequately prepared fish and is typically self-limited.
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PATHOGENESIS AND EPIDEMIOLOGY
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Adult nematodes of anisakis species (Anisakis simplex complex, Pseudoterranova decipiens complex, and Contracecum osculatum complex) reside in the gastric mucosa of marine mammals. The female adult releases unembryonated eggs into the feces of these definitive hosts which develop into free-swimming second-stage larvae in the water. These larvae are ingested by crustaceans and develop into third-stage larvae. These larvae are in turn ingested by marine (or anadromous) fish and squid. Larvae then migrate into the host tissues. Predation between these paratenic hosts can lead to high concentrations of third-stage larvae in these hosts. Definitive hosts and humans become infected by ingesting these paratenic hosts. Once ingested, the larvae penetrate the gastric or intestinal mucosa leading to symptoms of anisakiasis. Anisakiasis occurs most frequently in areas where raw or inadequately prepared fish (including sashimi, ceviche, and pickled or marinated fish) are consumed, particularly in Japan, South America, and Northern Europe.
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CLINICAL MANIFESTATIONS
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Gastric anisakiasis is characterized by abrupt-onset epigastric pain, nausea, and vomiting occurring 1 to 12 hours of ingestion. Symptoms typically resolve within a few days but can persist for months. Gastric anisakiasis is often misdiagnosed as peptic ulcer disease or gastritis. In contrast, intestinal anisakiasis occurs 5 to 7 days after ingestion of larvae and can cause severe abdominal pain and distension, and bowel obstruction due to a palpable inflammatory mass. Intestinal infection may mimic appendicitis, peritonitis, or other causes of an acute abdomen. Invasion of the gastric or intestinal wall may be associated with a severe eosinophilic granulomatous reaction that may become chronic, causing gastric or right lower quadrant pain and eosinophilia. Ectopic anisakiasis can occur from penetration of the larvae through the stomach or intestine, leading to migration into the peritoneal space and other visceral organs. Symptoms of allergic anisakiasis range from urticaria to isolated angioedema and anaphylactic shock within hours of exposure. Fevers can also occur. There is speculation that sensitization may occur from exposure to both dead and live parasitic larvae.
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Gastric anisakiasis can be diagnosed through visualization of larvae by endoscopy through which removal of the larvae can also be performed and be curative. Intestinal anisakiasis can be difficult to diagnose, but a history of raw seafood consumption and imaging findings such as irregular thickening of the bowel wall with luminal narrowing on computed tomography scan, and thread-like filling defects on barium x-ray can be useful. Serologic tests for A. simplex, particularly immunoglobulin (Ig) E, have been developed and can be suggestive of infection or allergy. However, these tests are not widely available, and are ...