[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/) › Ascaris lumbricoides

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

# Ascaris lumbricoides

- Parasite
- Exam priority: high

The largest human gut worm. People swallow its eggs from soil; in children with many worms it can block the bowel.

Updated 2026-11-01

Also called: large roundworm, giant intestinal roundworm

## Key points

- Lung passage in the cycle: Löffler (cough + infiltrate + eosinophilia).
- Fertile egg with a thick mammillated coat.
- Bowel obstruction in heavily infected children.
- Ectopic migration to the bile duct and pancreas.
- Treatment: benzimidazoles; periodic school deworming.

## At a glance

**Shape**
Pinkish-white cylindrical worm; mouth with three lips

**Family**
Ascarididae

**Type**
Intestinal nematode (soil-transmitted helminth)

**Size**
Female 20–35 cm; male somewhat smaller

## Morphology

- Fertile egg, round, 45–75 µm, with a thick mammillated outer coat stained brown by bile.
- Unfertilized egg more elongated (up to about 90 µm), thin-walled and full of refractile granules.
- Decorticated eggs: lacking the mammillated outer layer.

## Transmission

- Swallowing embryonated eggs in soil contaminated with human faeces.
- Poorly washed produce, unsafe water and dirty hands to the mouth.
- No direct person-to-person spread: the egg needs weeks in soil to become infective.

**Reservoir:** Humans; Faecally contaminated soil

### Isolation precautions

What the care team adds to standard precautions.

- Standard

## Life cycle

- Adults live in the small bowel; the female lays thousands of eggs that leave in stool.
- In moist, shaded soil the egg embryonates within weeks and becomes infective.
- Once swallowed, the larva hatches, crosses the gut wall and travels in the blood to the liver and lung.
- In the lung it matures for about 10–14 days, enters the alveoli, climbs the airway and is swallowed.
- Back in the small bowel it becomes an adult; from egg swallowed to new eggs takes 2–3 months.

## Virulence factors

- Larval lung migration causes transient eosinophilic pneumonitis (Löffler syndrome).
- A bolus of adults can block the ileum, especially in heavily infected children.
- Adults wander to ectopic sites (common bile duct, pancreatic duct, appendix), especially with fever or anaesthesia.
- They compete for nutrients and add to malnutrition and stunting.

## Diseases it causes

- Intestinal ascariasis [Soil-transmitted helminthiasis (ascariasis, hookworm, trichuriasis) →](https://durgical.com/en/conditions/soil-transmitted-helminthiasis/)
- Bowel obstruction by a worm bolus in children [Small bowel obstruction →](https://durgical.com/en/conditions/small-bowel-obstruction/)
- Cholangitis from Ascaris migrating into the bile duct [Acute cholangitis →](https://durgical.com/en/conditions/acute-cholangitis/)
- Acute pancreatitis from Ascaris in the pancreatic duct [Acute pancreatitis →](https://durgical.com/en/conditions/acute-pancreatitis/)

## Clinical picture

- Many infections are asymptomatic.
- Lung phase: cough, wheeze, low fever and eosinophilia.
- Abdominal pain, bloating and worms passed in stool, mouth or nose.
- Right upper quadrant pain and jaundice if it migrates into the bile duct.

## Diagnosis

- Eggs on stool microscopy, ideally after formalin-ethyl acetate concentration; Kato-Katz measures the burden.
- Larvae in sputum or gastric aspirate during the lung phase.
- A passed adult worm, recognisable by its three lips.
- Ultrasound for Ascaris in the biliary tree or bowel.

## Treatment

Benzimidazoles (albendazole or mebendazole); pyrantel pamoate is an alternative. Obstruction is first managed conservatively, then by endoscopy or surgery if that fails.

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

In Pharmacology:

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

## Prevention

- Basic sanitation: latrines or sewerage and safe water.
- Handwashing and careful washing of fruit and vegetables.
- Periodic deworming of school-age and preschool children in at-risk areas (WHO preventive chemotherapy).
- Health education in schools and homes.

## In Colombia

In the national school parasitism survey (2012–2014), 11.3% of children had Ascaris. The Ministry of Health has a mass deworming guideline for school-age children based on the WHO preventive chemotherapy strategy.

## Memory aid

Soil to mouth, lung to gut: Ascaris takes a lung tour before it settles in the belly.

## Test yourself

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

## Which lung syndrome does Ascaris larval migration cause?

Löffler syndrome: cough, wheeze and transient lung infiltrates with eosinophilia.

## What does a fertile Ascaris egg look like?

Round, 45–75 µm, with a thick mammillated outer coat stained brown.

## What is the typical mechanical complication in children with heavy Ascaris loads?

Bowel obstruction by a bolus of worms, usually in the ileum.

## Why is Ascaris not spread directly from person to person?

Because its eggs need weeks in soil to embryonate and become infective.

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

## Related

- [Trichuris trichiura](https://durgical.com/en/microbiology/trichuris-trichiura/)
- [Necator americanus / Ancylostoma duodenale](https://durgical.com/en/microbiology/necator-americanus-ancylostoma-duodenale/)
- [Toxocara canis / Toxocara cati](https://durgical.com/en/microbiology/toxocara-canis-toxocara-cati/)

## Related conditions

- [Soil-transmitted helminthiasis (ascariasis, hookworm, trichuriasis)](https://durgical.com/en/conditions/soil-transmitted-helminthiasis/)
- [Small bowel obstruction](https://durgical.com/en/conditions/small-bowel-obstruction/)
- [Acute cholangitis](https://durgical.com/en/conditions/acute-cholangitis/)
- [Acute pancreatitis](https://durgical.com/en/conditions/acute-pancreatitis/)

## 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 - Ascariasis](https://www.cdc.gov/dpdx/ascariasis/index.html) (CDC, 2019); [Soil-transmitted helminth infections](https://www.who.int/news-room/fact-sheets/detail/soil-transmitted-helminth-infections) (WHO, 2023); [Ascariasis: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000628.htm) (MedlinePlus (NLM), 2024); [Geohelmintiasis](https://minsalud.gov.co/salud/publica/PET/Paginas/geohelmintiasis.aspx) (Ministerio de Salud y Protección Social de Colombia, 2014).

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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/ascaris-lumbricoides/