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Ascariasis ˌas-kə-ˈrī-ə-səs

By Richard D. Pearson, MD, Emeritus Professor of Medicine, University of Virginia School of Medicine

Ascariasis is infection caused by Ascaris lumbricoides, an intestinal roundworm.

  • People acquire the infection by swallowing the roundworm eggs, usually in food.

  • People may have no symptoms or may have fever, coughing, wheezing, abdominal cramps, nausea, and vomiting.

  • Children with a heavy infection may not grow normally, or worms can block the intestine or bile duct, resulting in severe pain and vomiting.

  • Doctors usually diagnose the infection by identifying the eggs or worms in a stool sample.

  • People are treated with antiparasitic drugs such as albendazole.

Ascariasis is the most common roundworm infection in people, occurring in about 1 billion people worldwide and 4 million people in the United States. Worldwide, about 20,000 infected people (mostly children) die each year because the worms block the intestine or bile ducts (tubes that connect the liver and gallbladder to the small intestine).

The infection is common in areas with poor sanitation and often occurs in tropical or subtropical areas. In the United States, ascariasis occurs most often in immigrants and in people who have lived abroad in areas where hygiene is poor, but it occasionally occurs in rural areas of southeastern states.

Did You Know...

  • About 1 billion people worldwide have a roundworm infection called ascariasis.

Transmission of ascariasis

Infection begins when a person swallows Ascaris eggs, often in contaminated food. Food is contaminated through contact with soil that has been contaminated by human stool (feces) containing the eggs. Ascaris eggs are hardy and can survive in the soil for years.

Once swallowed, Ascaris eggs hatch and release larvae in the intestine. Each larva migrates through the wall of the small intestine and is carried through the lymphatic vessels and bloodstream to the lungs. Once inside the lungs, the larva passes into the air sacs (alveoli), moves up the respiratory tract and into the throat, and is swallowed. The larva matures in the small intestine, where it remains as an adult worm. This process takes 2 to 3 months. Adult worms range from 6 to 20 inches in length and from 1/10 to 2/10 inch in diameter. They live 1 to 2 years. Eggs laid by the adult worms are excreted in stool, develop in the soil, and begin the cycle of infection again when they are ingested.

Symptoms of Ascariasis

Many people who have ascariasis do not develop symptoms. However, the migration of larvae through the lungs can cause fever, coughing, wheezing, and sometimes blood in phlegm (sputum).

A large number of worms in the intestine can cause abdominal cramps and, occasionally, a blockage of the intestine, most commonly in children living in areas with poor sanitation. A blockage can cause nausea, vomiting, abdominal swelling (distention), and abdominal pain.

Sometimes adult worms migrate to the mouth or nose, are vomited up, or passed in the stool—situations that can be psychologically distressing. Adult worms occasionally block the opening into the appendix, biliary ducts, or pancreatic duct, producing severe abdominal pain.

Infected children may not grow or gain weight normally.

Diagnosis of Ascariasis

  • Examination of a stool sample

Ascariasis is diagnosed by identifying eggs or adult worms in a stool sample or, rarely, by seeing adult worms that have migrated to the throat or nose.

If computed tomography (CT) or ultrasonography is done for other reasons, adult worms may be seen. Rarely, the effects of larvae migrating through the lungs can be seen on a chest x-ray.

Prevention of Ascariasis

The best strategies for preventing ascariasis include

  • Washing hands thoroughly with soap and water before handling food

  • Washing, peeling, and/or cooking all raw vegetables and fruits before eating, particularly those that have been grown in areas where human feces is used as fertilizer

  • Not defecating outdoors

Effective sewage disposal systems can help prevent this infection from spreading.

Treatment of Ascariasis

  • A drug used to treat worm infections (antihelminthic drug)

To treat a person with ascariasis, a doctor prescribes albendazole, mebendazole, or ivermectin, which are taken by mouth. However, because these drugs may harm the fetus, they should not be taken by pregnant women.

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