Anisakiasis

Essentials of Diagnosis

• Nausea, vomiting, and progressive epigastric pain

• Occasionally, acute infection is followed by a chronic course

• Infection is by larval invasion of the stomach or intestinal wall by anisakid nematodes

General Considerations

• 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

Demographics

• Most common in Japan

Symptoms and Signs

• Clinical manifestations follow burrowing of worms into the stomach or intestinal wall, leading to

  • Localized ulceration

  • Edema

  • Eosinophilic granuloma formation

• Acute infection

  • Causes severe epigastric or abdominal pain, nausea, and vomiting (usually within 2 days of parasite ingestion)

  • May cause allergic symptoms (eg, urticaria, angioedema, and anaphylaxis)

  • Generally resolves within 2 weeks

• Chronic symptoms suggest

  • Inflammatory bowel disease

  • Diverticulitis

  • Carcinoma

• Rarely, worms may migrate to other sites or be coughed up

Differential Diagnosis

• Norwalk virus or rotavirus

• "Food poisoning" by toxins from Bacillus cereus, Staphylococcus aureus, Clostridium perfringens

• Appendicitis

• Peptic ulcer disease or gastritis

• Inflammatory bowel disease

Laboratory Tests

• Eosinophilia is not usually seen

Imaging Studies

• Radiographs may identify stomach or intestinal lesions

Diagnostic Procedures

• Diagnosis is suggested in persons with acute abdominal symptoms after eating raw fish

• Endoscopy may allow visualization and removal of the worm

Medications

• Specific therapy is not indicated

Surgery

• When surgery is performed due to consideration of other diagnoses, eosinophilic inflammatory lesions and invading worms are found

Therapeutic Procedures

• Endoscopic worm removal hastens recovery

• Parasites are killed by cooking or deep freezing fish

Complications

• Chronic intestinal anisakiasis

When to Refer

• Refer for consideration of mechanical removal of the worm

Prevention

• Avoidance of ingestion of raw or incompletely cooked squid or marine fish, especially salmon, rockfish, herring, and mackerel; early evisceration of fish is recommended

• Larvae within fish may, with difficulty, be seen as colorless, tightly coiled or spiraled worms in 3-mm whorls or as reddish or pigmented larvae lying open in muscles or viscera

• The larvae are killed by temperatures above 60°C or by freezing at –23°C for 7 days or at –35°C for 15 hours

• Smoking procedures that do not bring the temperature to 60°C, marinating in vinegar, and salt-curing are not reliable