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Ascariasis, or roundworm infection of the intestines, is common throughout the world in both temperate and tropical areas where sanitation and hygiene are poor. In those areas, everyone may be harboring the parasite that causes the infection.

According to the Centers for Disease Control and Prevention (CDC), ascariasis is estimated to affect between 807-1,221 million people in the world. It is most common in children between 3 and 8 years old.


Ascaris infection is caused by a parasitic roundworm called Ascaris lumbricoides. This worm resembles the common earthworm. Ranging in length from 6 to 13 inches, the female worm may grow to be as thick as a pencil. Up to 100 worms could potentially infect the human body.


Almost more than any other parasitic disease, inadequate personal hygiene leads to ascariasis. Human feces found in fields, streets, and yards are a major source of infective eggs in heavily populated areas.

The eggs do not infect humans when first excreted by the roundworm. They usually are transmitted by hand to mouth. The use of human feces as fertilizer also may permit transmission of infective eggs through food that is grown in the soil and eaten without being thoroughly washed. The eggs are resistant to extremes of temperature and humidity.

The eggs need several weeks to develop and become infective. If you swallow infective eggs, they pass into your intestines where they hatch into larvae and then begin their journey through your body.

  • Once through your intestinal wall, the eggs reach your lungs by means of the bloodstream or lymphatic system.
  • In your lungs, they pass through the air sacs, are carried up the bronchial tree with respiratory fluids and into your throat.
  • When in your throat, you re-swallow them, and they return to the small intestine where they grow, mature, and mate.

The worms become mature in about 2 months.


If you have only a few roundworms in your intestines, you might not have symptoms. If you do have symptoms, you may have vague or off-and-on abdominal pain.

The first sign of infection may be the presence of a live worm in your vomit or stool. If the larvae have migrated to your lungs, you may have an illness resembling pneumonia with wheezing, cough, and fever. This stage of the disease happens before the intestinal phase by weeks, and the symptoms are difficult for a healthcare provider to diagnose.

If you have a heavy infection of the worms, you may have a partial or complete blockage of the small intestine and have the following symptoms:

  • Severe abdominal pain
  • Vomiting
  • Restlessness
  • Disturbed sleep

The heavier or greater the worm infection, the more severe your symptoms are likely to be. Your pancreas might become inflamed. Serious infections, especially those causing blockages, can be fatal.


Once mature female roundworms are in your intestines, a healthcare provider can diagnose the infection by finding the eggs (or live worms) in your stool.

Lung infection is more difficult to diagnose, but your healthcare provider can confirm it by finding evidence of the larvae in lung or stomach fluids.


Your healthcare provider can treat ascariasis with mebendazole, albendazole, or ivermectin, according to the CDC.


Researchers supported by NIAID are conducting basic and clinical research on the prevention, control, and treatment of a variety of parasitic diseases, including some caused by parasitic roundworms.

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Last Updated September 23, 2015