Ascariasis is an infection caused by Ascaris lumbricoides, an intestinal roundworm (nematode), or occasionally by Ascaris suum, a roundworm that also causes ascariasis in pigs.
People become infected by swallowing the roundworm eggs, usually in food.
When first infected, people may have no symptoms or may develop 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 medications used to treat worm infections.
Helminths are parasitic worms that can infect humans and animals. There are 3 types of helminths: flukes (trematodes), tapeworms (cestodes), and roundworms (nematodes). Ascaris is a roundworm.
Ascariasis is the most common roundworm infection in people, occurring in 819 million people worldwide. The infection is most common among school-aged children. It can cause undernutrition.
Approximately 2,000 to 10,000 people die each year of ascariasis. Most of the deaths occur in children as a result of worms blocking the intestine or bile ducts (tubes that connect the liver and gallbladder to the small intestine).
The infection is common in tropical or subtropical areas with inadequate sanitation where water, soil, and food are contaminated with human stool (feces). In the United States, ascariasis occurs most often in refugees, immigrants, and people who have traveled to or lived in areas where the infection is common.
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(See also Overview of Parasitic Infections.)
Transmission of Ascariasis
Infection begins when a person swallows fertilized Ascaris eggs. Only fertilized eggs can cause infection. People may swallow the eggs in food that came in contact with soil contaminated by human stool (feces) containing the eggs. Infection can also occur when people come in contact with contaminated dirt and put their hands or fingers in their mouth. 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 (tubes that carry a fluid called lymph through the body) 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. 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.
Adult worms are large. Adult females range from 8 to 14 inches (20 to 35 centimeters), and adult males range from 6 to 12 inches (15 to 30 centimeters) in length. They live 1 to 2 years.
CLOUDS HILL IMAGING LTD/SCIENCE PHOTO LIBRARY
Image from the Centers for Disease Control and Prevention, Global Health, Division of Parasitic Diseases and Malaria.
People can also be infected with Ascaris suum, which is a roundworm closely related to Ascaris lumbricoides that infects pigs. Infection begins when a person swallows fertilized eggs because their hands were contaminated from touching infected pigs or from consuming undercooked vegetables or fruits contaminated with pig feces.
Symptoms of Ascariasis
The migration of Ascaris larvae through the lungs can cause fever, coughing, wheezing, and sometimes blood in phlegm (sputum).
A small number of worms in the intestine do not usually cause digestive symptoms. A large number of worms can cause abdominal cramps and, occasionally, a blockage of the intestine. A blockage can cause nausea, vomiting, abdominal swelling (distention), and abdominal pain. Adult worms occasionally block the opening into the appendix, biliary ducts, or pancreatic duct, causing severe abdominal pain.
Sometimes adult worms migrate to the mouth or nose, are vomited up, or are passed in the stool—situations that can be psychologically distressing.
Undernutrition may develop in infected children. Children with a heavy infection 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 in stool or coming out of the mouth, nose, or rectum. Sometimes larvae are found in sputum.
If a computed tomography (CT) scan or ultrasound is done for other reasons, adult worms may be seen. Rarely, the internal problems caused by larvae migrating through the lungs can be seen on a chest x-ray.
Treatment of Ascariasis
Medications used to treat worm infections (anthelmintics)
To treat a person with ascariasis, a doctor usually prescribes albendazole, mebendazole, or ivermectin, which are taken by mouth. These medications are not safe for use during pregnancy because of potential harm to the fetus, so a different medication, pyrantel pamoate, is used in pregnant women. If a medication known to be safe in pregnancy is not available, doctors must balance the risk of treating an infected pregnant woman.
If people have lived in areas of central Africa where a roundworm called Loa loa is transmitted, doctors check them for Loa loa infection (loiasis) before giving them ivermectin because ivermectin can cause serious brain inflammation (encephalitis) in people who have a severe Loa loa infection and ascariasis at the same time.
If people have a mild ascariasis infection, doctors may give them nitazoxanide. This medication is used to treat parasite infections of the intestines, and it is taken by mouth.
When Ascaris worms cause a blockage in the intestines, people may be treated with one of the anthelmintics, or the worms may be removed surgically or through an endoscope (a flexible viewing tube) inserted through the mouth into the intestine.
When the lungs are affected, doctors focus on relieving symptoms. Treatment includes bronchodilators and corticosteroids. Anthelmintics are typically not used to treat the lungs.
Prevention of Ascariasis
The best strategies for preventing ascariasis include
Washing hands thoroughly with soap and water before handling food or after handling pigs
Washing, peeling, and/or cooking all raw vegetables and fruits before eating, particularly those that have been grown in areas where human or pig feces is used as fertilizer
Not defecating outdoors except in latrines with proper sewage disposal
Effective sewage disposal systems can help prevent this infection from spreading.
