is the largest
nematode (roundworm) parasitizing the human intestine. (Adult females:
20 to 35 cm; adult male: 15 to 30 cm.)
in the lumen of the small intestine. A female may produce approximately
200,000 eggs per day, which are passed with the feces
Unfertilized eggs may be ingested but are not infective. Fertile eggs
embryonate and become infective after 18 days to several weeks
depending on the environmental conditions (optimum: moist, warm, shaded
soil). After infective eggs are swallowed
the larvae hatch
invade the intestinal mucosa, and are carried via the portal, then
systemic circulation to the lungs
The larvae mature further in the lungs (10 to 14 days), penetrate the
alveolar walls, ascend the bronchial tree to the throat, and are
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
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
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).
Microscopic identification of eggs in the stool is the most common
method for diagnosing intestinal ascariasis. The recommended procedure
is as follows:
specimen in 10% formalin.
using the formalin–ethyl acetate sedimentation technique.
Examine a wet
mount of the sediment.
concentration procedures are not available, a direct wet mount
examination of the specimen is adequate for detecting moderate to heavy
infections. For quantitative assessments of infection, various methods
such as the Kato-Katz can be used. Larvae can be identified in sputum
or gastric aspirate during the pulmonary migration phase (examine
formalin-fixed organisms for morphology). Adult worms are occasionally
passed in the stool or through the mouth or nose and are recognizable by
their macroscopic characteristics.
comparison with other intestinal parasites
drugs of choice for treatment of ascariasis are albendazole*,
mebendazole, and pyrantel pamoate*. 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
* This drug is
approved by the FDA, but considered investigational for this purpose.