[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/) › Enterobius vermicularis

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

# Enterobius vermicularis

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- Exam priority: high

A tiny white worm that lays eggs around the anus at night and causes itching. Very common in children; it spreads at home and at school.

Updated 2026-11-01

Also called: pinworm, threadworm (UK)

## Key points

- Night-time anal itching in a child = pinworm until proven otherwise.
- Diagnosis with the tape test, not a stool exam.
- Egg flattened on one side (D-shaped).
- Treat the whole household and repeat treatment.
- Humans only; no soil or lung stage.

## At a glance

**Shape**
Thin white worm; the female has a long pointed tail

**Family**
Oxyuridae

**Type**
Intestinal nematode (pinworm), not soil-transmitted

**Size**
Female 8–13 mm; male 2–5 mm

## Morphology

- Oval egg, 50–60 × 20–30 µm, flattened on one side (D-shaped).
- Transparent, sticky shell; passed partly embryonated.
- Sticks to clothing, sheets, fingernails and surfaces.

## Transmission

- Anus-hand-mouth autoinfection from scratching.
- Eggs on bedding, underwear, toys and surfaces.
- Spread within households, day-care centres and schools; rarely by inhaled eggs.

**Reservoir:** Humans only

### Isolation precautions

What the care team adds to standard precautions.

- Standard

## Life cycle

- Eggs are swallowed from hands, nails, bedding or surfaces.
- Larvae hatch in the small bowel and adults settle in the caecum.
- At night the gravid female crawls out of the anus and lays eggs on the perianal skin.
- The eggs become infective within hours; scratching carries them to fingernails and mouth.
- Retroinfection: larvae hatching on the perianal skin may crawl back into the rectum.
- About a month passes from ingestion to new egg-laying.

## Virulence factors

- The female's night-time migration causes intense anal itching.
- In girls it can migrate to the vulva and cause vulvovaginitis.
- Scratching causes excoriation and bacterial superinfection.
- It is occasionally found in a removed appendix.

## Diseases it causes

- Enterobiasis (pinworm infection)
- Vulvovaginitis in girls from pinworm migration

## Clinical picture

- Night-time anal itching.
- Restless sleep, irritability.
- Perianal scratch marks.
- Several household members with symptoms.

## Diagnosis

- Clear adhesive tape test in the morning, before bathing or a bowel movement; repeated on several days.
- Stool exams rarely show the eggs.
- Adult worms seen in the perianal area.

## Treatment

Benzimidazoles (mebendazole or albendazole) or pyrantel pamoate; treatment is repeated because the drugs do not kill eggs, and the whole household is treated at once.

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

In Pharmacology:

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

## Prevention

- Handwashing and short fingernails.
- Morning bath and daily change of underwear.
- Wash bedding and pyjamas without shaking them.
- Treat all household members at the same time.

## In Colombia

Common in children at day-care centres and schools, in cities and the countryside alike; because it does not depend on soil, it persists even with good sanitation.

## Memory aid

Morning tape catches the night shift: pinworms lay at night, the tape test catches them at dawn.

## Test yourself

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

## What is the test of choice for pinworm?

The clear adhesive tape test on the perianal skin in the morning, before bathing.

## Why is pinworm itching worse at night?

Because the gravid female crawls out of the anus at night to lay eggs on the perianal skin.

## Why is pinworm treatment repeated?

Because the drugs kill the worms but not the eggs, which can start a new infection.

## What does the Enterobius vermicularis egg look like?

Oval, transparent and flattened on one side, D-shaped.

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

## Related

- [Trichuris trichiura](https://durgical.com/en/microbiology/trichuris-trichiura/)
- [Ascaris lumbricoides](https://durgical.com/en/microbiology/ascaris-lumbricoides/)

## 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 - Enterobiasis](https://www.cdc.gov/dpdx/enterobiasis/index.html) (CDC, 2019); [About Pinworm Infection | Pinworm Infection | CDC](https://www.cdc.gov/pinworm/about/index.html) (CDC, 2024); [Pinworms: MedlinePlus](https://medlineplus.gov/pinworms.html) (MedlinePlus (NLM), 2024).

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Representative model, for educational purposes only.

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