People get ascariasis by consuming food or drink that is contaminated with roundworm eggs. Ascariasis is the most common intestinal worm infection. It is related to poor sanitation. People who live in places where human feces (stool) are used as fertilizer are also at risk for this disease.

Once consumed, the eggs hatch and release immature roundworms called larvae inside the small intestine. Within a few days, the larvae move through the bloodstream to the lungs. They travel up through the large airways of the lungs and are swallowed back into the stomach and small intestine.

As the larvae move through the lungs they may cause an uncommon form of pneumonia called eosinophilic pneumonia. Eosinophils are a type of white blood cell. Once the larvae are back in the small intestine, they mature into adult roundworms. Adult worms live in the small intestine, where they lay eggs that are present in feces. They can live 10 to 24 months.

An estimated 800 to 900 million people are infected worldwide. Ascariasis occurs in people of all ages, though children are affected more severely than adults.

Most of the time, there are no symptoms. If there are symptoms, they may include:

• Bloody sputum (mucus coughed up by the lower airways)
• Cough, wheezing
• Low-grade fever
• Passing worms in stool
• Shortness of breath
• Skin rash
• Stomach pain
• Vomiting or coughing up worms
• Worms leaving the body through the nose or mouth

The infected person may show signs of malnutrition. Tests to diagnose this condition include:

• Abdominal x-ray or other imaging tests
• Blood tests, including complete blood count and eosinophil count
• Stool exam to look for worms and worm eggs

Treatment includes medicines such as albendazole that paralyze or kill intestinal parasitic worms.

If there is a blockage of the intestine caused by a large number of worms, a procedure called an endoscopy may be used to remove the worms. In rare cases, surgery is needed.

People who are treated for roundworms should be checked again in 3 months. This involves examining the stools to check for eggs of the worm. If eggs are present, treatment should be given again.

Most people recover from symptoms of the infection, even without treatment. But they may continue to carry the worms in their body.

Complications can be caused by adult worms that move to certain organs, such as the:

• Appendix
• Bile duct
• Pancreas

If the worms multiply, they can block the intestine.

These complications may occur:

• Appendicitis
• Blockage in the bile ducts of the liver
• Blockage in the intestine
• Hole in the gut

Contact your health care provider if you have symptoms of ascariasis, particularly if you have traveled to an area where the disease is common. Also contact your provider if you have any of the following:

• Symptoms get worse
• Symptoms do not improve with treatment
• New symptoms occur

Improved sanitation and hygiene in developing countries will reduce the risk in those areas. In places where ascariasis is common, people may be given deworming medicines as a preventive measure.

Intestinal parasite - ascariasis; Roundworm - ascariasis

Centers for Disease Control and Prevention website. Soil-transmitted helminths. About ascariasis. www.cdc.gov/sth/about/ascariasis.html. Updated June 13, 2024. Accessed November 22, 2024.

Diemert DJ. Nematode infections. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 327.

Mejia R, Weatherhead J, Hotez PJ. Intestinal nematodes (roundworms). In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th ed. Philadelphia, PA: Elsevier; 2020:chap 286.

Updated by: Jatin M. Vyas, MD, PhD, Professor in Medicine, Harvard Medical School; Associate in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital, Boston, MA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.