Ascariasis
Ascariasis is infection caused by Ascaris lumbricoides, an intestinal roundworm.
Ascariasis is the most common roundworm infection in people, occurring in over 1 billion people worldwide. The infection is most common in areas with poor sanitation, where it persists largely because of indiscriminate defecation and other unsanitary practices. In the United States, infections are most often encountered in people who have traveled to areas with poor sanitation.
Infection begins when a person swallows food contaminated with Ascaris eggs. Food usually becomes contaminated through contact with soil or other objects. Ascaris eggs are hardy and can survive in the soil for years.
Once swallowed, Ascaris eggs hatch and release larvae into 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 is swallowed. The larva matures in the small intestine, where it remains as an adult worm. Adult worms range from 6 to 20 inches in length and from 1/10 to 2/10 inch in diameter.
Symptoms and Diagnosis
Many people who have ascariasis do not develop symptoms, although the migration of larvae through the lungs can cause fever, coughing, and wheezing. A large number of worms in the intestine can cause abdominal cramps and, occasionally, a blockage of the intestine, most commonly in children. Sometimes adult worms are vomited up or passed in the stool, a situation that can be psychologically distressing. Adult worms occasionally block the appendix, biliary tract, or pancreatic duct, producing severe abdominal pain.
Diagnosis of ascariasis is made by identifying eggs or adult worms in a stool sample, or rarely by seeing adult worms that have migrated to the throat or nose. Rarely, the effects of larvae migrating through the lungs can be seen on an x-ray of the chest.
Prevention and Treatment
The best strategies for preventing ascariasis include using adequate sanitation and avoiding uncooked foods.
To treat a person with ascariasis, a doctor prescribes mebendazole, albendazole, or pyrantel pamoate. However, these drugs cannot be taken by pregnant women, because they may harm the fetus.
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