[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Nematodes](https://durgical.com/en/microbiology/groups/nematodes/) › Toxocara canis / Toxocara cati

[Microbiology](https://durgical.com/en/microbiology/) · [Nematodes](https://durgical.com/en/microbiology/groups/nematodes/)

# Toxocara canis / Toxocara cati

- Parasite
- Exam priority: medium

A roundworm of dogs and cats. A child who swallows its eggs from soil can have larvae wandering through liver, lung or eye, with no adult worm.

Updated 2026-11-01

Also called: dog roundworm, cat roundworm

## Key points

- Humans are accidental hosts: the larva does not mature and there are no eggs in stool.
- Visceral in preschoolers; ocular in older children and young adults.
- Ocular granuloma mimicking retinoblastoma.
- Diagnosis by serology; marked eosinophilia in the visceral form.
- Prevention: deworm puppies.

## At a glance

**Shape**
Microscopic larva in human tissues

**Family**
Toxocaridae

**Type**
Dog and cat nematode; humans harbour only migrating larvae

**Size**
The adult, in the dog or cat gut, is several centimetres long

## Morphology

- Humans harbour only larvae in tissue, surrounded by eosinophilic granulomas.
- Eggs (in dog and cat faeces) are subspherical, thick-walled and pitted.
- There are no Toxocara eggs in human stool.

## Transmission

- Swallowing embryonated eggs from soil in parks, sandboxes and yards with dog or cat faeces.
- Geophagia and pica in young children.
- Rarely, raw meat or offal from paratenic hosts (chicken, cattle, rabbit).

**Reservoir:** Dogs, especially puppies (T. canis); Cats (T. cati); Contaminated soil

### Isolation precautions

What the care team adds to standard precautions.

- Standard

## Life cycle

- The dog (T. canis) or cat (T. cati) passes unembryonated eggs in faeces.
- In soil they embryonate in 1–4 weeks and become infective.
- Puppies are infected mostly across the placenta and through milk; adult animals by eggs or prey.
- A child swallows eggs from soil; the larva hatches, crosses the gut and migrates in the blood.
- In humans the larva never matures: it wanders through liver, lung, eye or brain and leaves granulomas.

## Virulence factors

- Migrating larvae release antigens that drive eosinophilic inflammation and granulomas.
- In the eye, the granuloma can mimic retinoblastoma (leukocoria).
- The number of eggs swallowed determines severity.

## Diseases it causes

- Toxocariasis: visceral larva migrans (fever, hepatomegaly, wheeze, eosinophilia) [Toxocariasis (visceral and ocular larva migrans) →](https://durgical.com/en/conditions/toxocariasis/)
- Ocular larva migrans: uveitis and retinal granuloma, usually one eye [Uveitis →](https://durgical.com/en/conditions/uveitis/)

## Clinical picture

- Visceral larva migrans mainly in preschool children with geophagia.
- Ocular larva migrans in older children or young adults: one-sided vision loss, strabismus, leukocoria.
- Covert toxocariasis: abdominal pain, cough and mild eosinophilia.
- Many infections are asymptomatic.

## Diagnosis

- EIA serology with larval excretory-secretory antigens; a positive titre does not prove active infection.
- Marked eosinophilia and high IgE in the visceral form.
- Ocular form: fundoscopy and antibodies in vitreous or aqueous fluid.
- Stool exams are useless: humans pass no eggs.

## Treatment

Benzimidazole antiparasitics (albendazole) for the visceral form; the ocular form is managed with corticosteroids and sometimes vitreoretinal surgery.

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

In Pharmacology:

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

## Prevention

- Deworm puppies, kittens and adult pets under veterinary care.
- Pick up pet faeces in parks and yards.
- Handwashing after playing in soil and before eating.
- Prevent geophagia and cover sandboxes.

## In Colombia

Common where many dogs go undewormed and parks are contaminated with faeces. It is considered in children with unexplained eosinophilia and in the work-up of childhood uveitis.

## Memory aid

Undewormed puppy, eosinophilic child: the dog's larva gets lost in a human and never grows up.

## Test yourself

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

## Why is a stool exam useless for human toxocariasis?

Because in humans the larva never becomes an adult and no eggs are produced.

## Which childhood tumour can ocular larva migrans mimic?

Retinoblastoma, since both can cause leukocoria.

## What is the main route of Toxocara infection in children?

Swallowing embryonated eggs from soil contaminated with dog or cat faeces, often through geophagia.

## How are puppies mainly infected with T. canis?

Transplacentally and, to a lesser degree, through the mother's milk.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/microbiology/toxocara-canis-toxocara-cati/)

## Related

- [Ascaris lumbricoides](https://durgical.com/en/microbiology/ascaris-lumbricoides/)
- [Ancylostoma braziliense / Ancylostoma caninum](https://durgical.com/en/microbiology/ancylostoma-braziliense-ancylostoma-caninum/)

## Related conditions

- [Toxocariasis (visceral and ocular larva migrans)](https://durgical.com/en/conditions/toxocariasis/)
- [Uveitis](https://durgical.com/en/conditions/uveitis/)

## 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: Nematodes](https://durgical.com/en/microbiology/groups/nematodes/)

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

Sources: [CDC - DPDx - Toxocariasis](https://www.cdc.gov/dpdx/toxocariasis/index.html) (CDC, 2019); [About Toxocariasis | Toxocariasis | CDC](https://www.cdc.gov/toxocariasis/about/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/toxocara-canis-toxocara-cati/