Anisakiasis

Anisakiasis is infection of the gastrointestinal tract by larvae of Anisakis simplex and related nematodes, acquired by eating raw or undercooked marine fish or squid. Larvae burrow into the gastric or intestinal wall and may cause allergic reactions.

It is reported mainly in Japan (over 2,000 cases each year), Korea, Spain, the Netherlands and the Pacific coast of Latin America. The incidence is rising with the popularity of raw fish dishes (sushi, sashimi, ceviche, pickled herring).

Pathophysiology.

Third stage larvae from fish penetrate the mucosa, causing eosinophilic granuloma and local oedema. Allergens (including heat stable allergens in cooked fish) can provoke urticaria and anaphylaxis.

Gastric form: severe epigastric pain, nausea and vomiting within 1 to 12 hours of eating fish. Intestinal form: abdominal pain, vomiting and obstruction or peritonitis 5 to 7 days later, usually in the ileum. Allergic form: urticaria, angio oedema and anaphylaxis. Chronic eosinophilic granuloma mimics a tumour.

Red flags.

• Anaphylaxis.
• Intestinal obstruction or perforation.
• Peritonitis.

Ask about raw fish within the past days. Endoscopy shows a worm embedded in the gastric mucosa with surrounding oedema (gastric form). Eosinophilia and specific IgE support the diagnosis. CT or ultrasound of the intestinal form shows segmental oedematous thickening, ascites and proximal dilatation. Histology of resected tissue or a larva identifies the parasite.

Differential diagnosis.

• Peptic ulcer disease.
• Acute appendicitis.
• Crohn disease.
• Gastric or small bowel tumour.
• Acute gastroenteritis.
• Fish allergy.

Remove larvae endoscopically with forceps or biopsy forceps in gastric disease, which relieves symptoms at once. Intestinal disease is usually self-limited and is managed with fluids, analgesia and bowel rest; operate for obstruction or perforation.

• Albendazole (intestinal or persistent disease; limited evidence): 400 mg orally twice daily with a fatty meal for 6 to 21 days; maximum 800 mg daily; monitor blood counts and liver tests; avoid in pregnancy and reduce in hepatic impairment.
• Adrenaline (anaphylaxis): 0.5 mg (0.5 mL of 1 mg/mL) IM into the anterolateral thigh, repeated every 5 minutes as needed; maximum 3 doses before escalation to infusion; monitor heart rate, blood pressure and oxygen saturation (94% to 98%); use 0.01 mg/kg in children (maximum 0.5 mg).
• Cetirizine (urticaria): 10 mg orally once daily for 5 to 7 days; maximum 20 mg daily in this use; monitor sedation; reduce to 5 mg daily when creatinine clearance is under 30 mL/min.

Prevent infection by cooking fish to 63 C or freezing at minus 20 C for 24 hours or at minus 35 C for 15 hours, and by gutting fish promptly.

Monitoring. Observe after larva removal for 24 hours for recurrent pain or allergic symptoms; repeat endoscopy if symptoms continue.

Referral and escalation. Gastroenterology; surgery for obstruction or perforation; emergency care for anaphylaxis.