Ascaris infection
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| A: Fertilized Ascaris egg, still at the unicellular stage. Eggs are normally at this stage when passed in the stool. Complete development of the larva requires 18 days under favorable conditions. B: Unfertilized and fertilized eggs (left and right, respectively). |
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
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Overview
Ascaris is a worm that lives in the small intestine. Infection with Ascaris is called ascariasis (ass-kuh-rye-uh-sis). Adult female worms can grow over 12 inches in length, adult males are smaller.
Related Key Words and Synonyms:
Intestinal roundworm infection, Ascariasis.
Epidemiology and Demographics
Ascariasis is the most common human worm infection. Infection occurs worldwide and is most common in tropical and subtropical areas where sanitation and hygiene are poor. Children are infected more often than adults. In the United States, infection is rare, but most common in rural areas of the southeast.
How can I get ascariasis?
You or your children can become infected after touching your mouth with your hands that have become contaminated with eggs from soil or other contaminated surfaces or by ingesting contaminated food or water.
Pathophysiology & Etiology
Etiologic agent:
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:
Adult worms 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 2. Unfertilized eggs may be ingested but are not infective. Fertile eggs embryonate and become infective after 18 days to several weeks 3, depending on the environmental conditions (optimum: moist, warm, shaded soil). After infective eggs are swallowed 4, the larvae hatch 5 , invade the intestinal mucosa, and are carried via the portal, then systemic circulation to the lungs 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 7. Upon reaching the small intestine, they develop into adult worms 1. 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.
Diagnosis
Your health care provider will ask you to provide stool samples for testing. Some people notice infection when a worm is passed in their stool or is coughed up. If this happens, bring in the worm specimen to your health care provider for diagnosis. There is no blood test used to diagnose an Ascaris infection.
Treatment
In the United States, Ascaris infections are generally treated for 1-3 days with medication prescribed by your health care provider. The drugs are effective and appear to have few side effects. Your health care provider will likely request additional stool exams 1 to 2 weeks after therapy; if the infection is still present, treatment will be repeated.
I am pregnant and have just been diagnosed with ascariasis. Can I be treated?
Infection with Ascaris worms is generally light and is not considered an emergency. Unless your infection is heavy, and your health may be at risk, treatment is generally postponed until after delivery of the baby.
Pharmacotherapy
The drugs of choice for treatment of ascariasis are albendazole with mebendazole, ivermectin, and nitazoxanide as alternatives. In the United States, ascariasis is generally treated for 1-3 days with medication prescribed by a health care provider. The drugs are effective and appear to have few side effects.
Acknowledgements
The content on this page was first contributed by: C. Michael Gibson, M.S., M.D.