Anisakiasis is caused by infection with larvae of parasites of saltwater fish and squid. Multiple species of the family Anisakidae may occasionally infect humans. Definitive hosts for these parasites are marine mammals. Eggs are passed in the feces and ingested by crustaceans, which are then eaten by fish and squid. When ingested by humans in undercooked seafood, larvae penetrate the stomach or intestinal wall but cannot complete their life cycle. The disease is most common in Japan.
Clinical manifestations of anisakiasis follow burrowing of worms into the stomach or intestinal wall, leading to localized ulceration, edema, and eosinophilic granuloma formation. Symptoms usually occur within 2 days of parasite ingestion and include severe epigastric or abdominal pain, nausea, and vomiting. Intestinal involvement can mimic appendicitis. Allergic symptoms, including urticaria, angioedema, and anaphylaxis, have also been attributed to acute infection. Acute symptoms generally resolve within 2 weeks, but chronic symptoms may also be seen, suggesting inflammatory bowel disease, diverticulitis, or carcinoma. Rarely, worms may migrate to other sites or be coughed up. Eosinophilia is usually not seen.
The diagnosis is suggested in those with acute abdominal symptoms after ingestion of raw fish. Radiographic studies may identify stomach or intestinal lesions, and endoscopy may allow visualization and removal of the worm (eFigure 35–46). When surgery is performed due to consideration of other diagnoses, eosinophilic inflammatory lesions and the invading worms are found.
Live anisakid larva observed by endoscopy. (Used, with permission, from N Kagei.)
Specific therapy is not indicated, but endoscopic worm removal hastens recovery. The parasites are killed by cooking or deep freezing fish.
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