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DPDx

DPDx is an education resource designed for health professionals and laboratory scientists. For an overview including prevention and control visit www.cdc.gov/parasites/ascariasis.

Ascariasis

[Ascaris lumbricoides]

 Adult female A. lumbroides.

Adult female A. lumbricoides.


Unfertilized egg of A. lumbricoides in an unstained wet mount, 200x magnification.

Unfertilized egg of A. lumbricoides in an unstained wet mount, 200x magnification.


Fertilized egg of A. lumbricoides in unstained wet mounts of stool, with embryos in the early stage of development.

Fertilized egg of A. lumbricoides in unstained wet mounts of stool, with embryos in the early stage of development.

Causal Agents

Ascaris lumbricoides is the largest nematode (roundworm) parasitizing the human intestine. (Adult females: 20 to 35 cm; adult male: 15 to 30 cm.)


Life Cycle:

Life cycle of ascariasis

Adult worms The Number 1. live in the lumen of the small intestine. A female may produce approximately 200,000 eggs per day, which are passed with the feces The Number 2. Unfertilized eggs may be ingested but are not infective. Fertile eggs embryonate and become infective after 18 days to several weeks The Number 3, depending on the environmental conditions (optimum: moist, warm, shaded soil). After infective eggs are swallowed The Number 4, the larvae hatch The Number 5, invade the intestinal mucosa, and are carried via the portal, then systemic circulation to the lungs The Number 6. The larvae mature further in the lungs (10 to 14 days), penetrate the alveolar walls, ascend the bronchial tree to the throat, and are swallowed The Number 7. Upon reaching the small intestine, they develop into adult worms . Between 2 and 3 months are required from ingestion of the infective eggs to oviposition by the adult female. Adult worms can live 1 to 2 years.

Geographic Distribution:

The most common human helminthic infection. Worldwide distribution. Highest prevalence in tropical and subtropical regions, and areas with inadequate sanitation. Occurs in rural areas of the southeastern United States.

Clinical Presentation

Although infections may cause stunted growth, adult worms usually cause no acute symptoms. High worm burdens may cause abdominal pain and intestinal obstruction. Migrating adult worms may cause symptomatic occlusion of the biliary tract or oral expulsion. During the lung phase of larval migration, pulmonary symptoms can occur (cough, dyspnea, hemoptysis, eosinophilic pneumonitis - Loeffler's syndrome).

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  • Page last reviewed November 29, 2013
  • Page last updated November 29, 2013
  • Content source: Global Health - Division of Parasitic Diseases and Malaria
  • Notice: Linking to a non-federal site does not constitute an endorsement by HHS, CDC or any of its employees of the sponsors or the information and products presented on the site.
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