Ascaris eggs are found in the soil. Infection occurs when a person accidently ingests (swallows) infective ascaris eggs. Once in the stomach, larvae (immature worms) hatch from the eggs. The larvae are carried through the lungs then to the throat where they are then swallowed. Once swallowed, they reach the intestines and develop into adult worms. Adult female worms can grow over 12 inches (4.8 cm) in length. Adult male worms are smaller. Adult female worms lay eggs that are then passed in feces; this cycle takes between 2 and 3 months. Adult worms can live 1 to 2 years.
Infection occurs worldwide. It is most common in tropical and subtropical areas where sanitation and hygiene are poor. Children are infected more often than adults. In the US, infection is not common and occurs mostly in rural areas of the southeast.
Pigs can be infected with ascaris. Occasionally, a pig infection can be spread to humans; this occurs when infective eggs, found in the soil and manure, are ingested. Infection is more likely if pig feces is used as fertilizer in the garden; crops then become contaminated with ascaris eggs.
Infection is often silent. But if someone is heavily infected, they may have abdominal pain. While the immature worms migrate through the lungs, they may cough and have difficulty breathing. And if someone has a very heavy worm infection in the intestines, the intestines may become blocked. Chronic ascaris infection can stunt the growth of children.
The diagnosis is most commonly made by finding the worm eggs in the stool. Larvae can be identified during the lung migration phase in sputum or gastric aspirate (stomach juice). Adult worms are occasionally passed in the stool or through the mouth or nose.
To prevent infection with ascaris:
- Avoid contacting soil that may be contaminated with human feces.
- Do not defecate outdoors.
- Dispose of diapers properly.
- Wash hands with soap and water before handling food.
- When traveling to countries where sanitation and hygiene are poor, avoid water or food that may be contaminated.
- Wash, peel or cook all raw vegetables and fruits before eating.
Ascaris infection is usually treated for 1-3 days with albendazole, mebendazole, or pyrantel pamoate. These drugs are effective and appear to have few side effects. Additional stool exams are done 1 to 2 weeks after therapy; if the infection is still present, treatment is repeated.