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Microbiology · Other parasites of interest

Gnathostoma and Anisakis !

  • Parasite
  • For completeness

Worm larvae that come with raw fish such as ceviche. One wanders under the skin; the other bites the stomach within hours.

Updated 2026-11-01

Also called: gnathostomiasis, anisakiasis, herring worm

At a glance

Family
Gnathostomatidae (Gnathostoma) and Anisakidae (Anisakis, Pseudoterranova)
Type
Nematode larvae (humans are accidental hosts)
Size
Larvae from a few millimetres to a few centimetres

Morphology

  • Gnathostoma: larva with a head bulb armed with rows of hooks.
  • Anisakis: whitish third-stage larva coiled in the flesh of marine fish.

Transmission

  • Gnathostoma: raw or undercooked freshwater fish, amphibians or birds (ceviche, river-fish sushi).
  • Anisakis: raw or undercooked marine fish or squid (herring, cod, mackerel, marine ceviche).
  • Not spread from person to person.

Reservoir: Gnathostoma: dogs, cats, pigs and other carnivores; Anisakis: marine mammals (dolphins, seals)

Isolation precautions

What the care team adds to standard precautions.

  • Standard

Life cycle

  1. Adults live in the stomach of carnivores (Gnathostoma) or marine mammals (Anisakis), which shed eggs into water.
  2. Larvae develop in small crustaceans (copepods or krill).
  3. Fish or squid that eat those crustaceans keep third-stage larvae in their flesh.
  4. A person eats the raw fish and the larva invades the stomach or bowel wall.
  5. Gnathostoma keeps migrating through tissue for months; Anisakis stays in the gut and dies without maturing.

Virulence factors

  • The larva burrows into the mucosa and causes eosinophilic inflammation and granulomas.
  • Gnathostoma migrates through skin, eye and nervous system; passage through the spinal cord or brain can be fatal.
  • Anisakis antigens, even from dead larvae, can cause allergy.

Diseases it causes

  • Gastric or intestinal anisakiasis and Anisakis allergy
  • Gnathostomiasis: migratory skin, ocular and neurological disease (eosinophilic meningitis or myeloencephalitis)

Clinical picture

  • Anisakis: severe epigastric pain, nausea and vomiting a few hours after eating raw fish; can mimic an ulcer or appendicitis.
  • Gnathostoma: itchy or painful migratory swellings that recur for months or years, with eosinophilia.
  • Gnathostoma in the nervous system: severe radicular pain followed by paralysis or altered consciousness.

Diagnosis

  • Anisakis: endoscopy that sees and removes the larva; histopathology if operated on.
  • Gnathostoma: identifying the larva removed from a lesion or in a biopsy; serology only at reference labs.
  • A history of raw fish plus eosinophilia points to both.

Treatment

Anisakis: endoscopic removal of the larva. Gnathostoma: anthelmintics (albendazole or ivermectin) and surgical removal of an accessible larva; the neurological form needs supportive care.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

Prevention

  • Cooking fish thoroughly; proper industrial freezing kills Anisakis larvae.
  • Ceviche lime juice, salting or cold smoking do not reliably kill the larvae.
  • People allergic to Anisakis can react even to frozen fish.

Test yourself

Think of the answer, then tap the question to see it.

Which picture suggests anisakiasis?

Severe epigastric pain with nausea and vomiting a few hours after eating raw marine fish or squid.

How is gastric anisakiasis diagnosed and treated?

By endoscopy, which shows the larva in the mucosa and allows its removal.

Which skin sign is typical of gnathostomiasis?

Itchy or painful migratory swellings that come and go for months, with eosinophilia.

Is ceviche lime juice enough to kill these larvae?

No. Thorough cooking or proper industrial freezing kills them reliably.

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Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: CDC - DPDx - Gnathostomiasis (CDC, 2024); CDC - DPDx - Anisakiasis (CDC, 2024).

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Representative model, for educational purposes only.