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Clinical Summary

Ascaris lumbricoides is the most common human intestinal roundworm infection. The parasites are found worldwide and are highly endemic where sanitation and hygiene are poor; they commonly cause infection in regions where human feces are used as fertilizer. Adult worms live in the small intestine and produce enormous numbers of eggs, which are excreted in the feces. Passed eggs require at least several weeks in warm, moist soil before embryonating into an infective egg. Ingested eggs hatch in the jejunum, migrate through the intestinal wall into the bloodstream, and are transported to the lungs. Larval worms burrow through the alveolar walls, ascend through the trachea, and are swallowed back into the small intestine where they develop into adults.

Most infections are asymptomatic. Patients may present for care if they pass a worm in their stool. A heavy worm burden may lead to abdominal pain, pancreatic/biliary disease, or intestinal obstruction. Failure to thrive and decreased cognitive development are seen in heavily infected children. Migrating worms may cause biliary obstruction, appendicitis, or liver abscesses.

Diagnosis is from identification of a passed worm or examination of stool for eggs.

Management and Disposition

Outpatient treatment with mebendazole or albendazole is usually effective but only on worms in the adult intestinal stage. Thus, it is recommended that a stool examination be done at 2 to 3 months and retreatment initiated if positive for eggs.


Ascariasis. Worms spontaneously extruding from the anus of a boy with a high fever. Worms often migrate in patients with fever. (Photo contributor: Seth W. Wright, MD.)


  1. Marked peripheral eosinophilia can be seen during the migratory stage.

  2. While in the lungs, migrating worms can cause an eosinophilic pneumonitis with asthma-like symptoms, or Löffler syndrome.

  3. Ascaris worms occasionally migrate from the anus, mouth, or nose following antihelmintic treatment.

  4. Ascaris is the most common cause of acute abdominal surgical emergencies in some highly endemic countries.


Ascariasis. Adult ascaris worm after passage from the anus. (Photo contributor: Seth W. Wright, MD.)

FIGURE 21.10

Ascariasis. Distended abdomen of a Haitian girl with a large ascaris worm burden. (Photo contributor: Seth W. Wright, MD.)

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