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[Microbiology](https://durgical.com/en/microbiology/) · [Other parasites of interest](https://durgical.com/en/microbiology/groups/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

## Key points

- Ceviche + epigastric pain within hours = Anisakis; diagnosed and treated by endoscopy.
- Freshwater ceviche + migratory swellings with eosinophilia = Gnathostoma.
- Gnathostoma can cause eosinophilic meningitis or myeloencephalitis.
- Lime does not cook the larvae: cooking or proper freezing is what protects.

## 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

- Adults live in the stomach of carnivores (Gnathostoma) or marine mammals (Anisakis), which shed eggs into water.
- Larvae develop in small crustaceans (copepods or krill).
- Fish or squid that eat those crustaceans keep third-stage larvae in their flesh.
- A person eats the raw fish and the larva invades the stomach or bowel wall.
- 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:

- [Albendazole](https://durgical.com/en/pharmacology/albendazole/)
- [Ivermectin](https://durgical.com/en/pharmacology/ivermectin/)

## 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.

## In Colombia

In the Americas, Gnathostoma binucleatum causes cases in Mexico and Ecuador; anisakiasis is more frequent on the Pacific coast of South America, where raw fish is common. Both are uncommon in Colombia, but ceviche and sushi make the history worth asking.

## Memory aid

Ceviche needs fire: lime does not kill the worm; Anisakis bites the stomach early and Gnathostoma goes for a walk under the skin.

## 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.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/microbiology/gnathostoma-and-anisakis/)

## Related

- [Angiostrongylus (A. costaricensis, A. cantonensis)](https://durgical.com/en/microbiology/angiostrongylus/)
- [Dibothriocephalus latus](https://durgical.com/en/microbiology/dibothriocephalus-latus/)
- [Clonorchis sinensis / Opisthorchis spp.](https://durgical.com/en/microbiology/clonorchis-sinensis-opisthorchis-spp/)
- [Toxocara canis / Toxocara cati](https://durgical.com/en/microbiology/toxocara-canis-toxocara-cati/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

[← Back to the group: Other parasites of interest](https://durgical.com/en/microbiology/groups/other-parasites-of-interest/)

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](https://www.cdc.gov/dpdx/gnathostomiasis/index.html) (CDC, 2024); [CDC - DPDx - Anisakiasis](https://www.cdc.gov/dpdx/anisakiasis/index.html) (CDC, 2024).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/gnathostoma-and-anisakis/