Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at April 20, 2016

Ascariasis is an infection in the lungs and small intestine that is caused by roundworms. It is a fairly common disorder in places where there is little modern sanitation, and the drinking water or food has been contaminated by human feces.


Definition & Facts

The disorder gets its name from the Ascaris lumbricoides roundworm. It is the largest roundworm that parasitizes the intestine, with females from 8 to 14 inches long and males from 6 to 12 inches long. Ascaria roundworms live between one and two years.

The worm lives in the central cavity of the small intestine, and a female produces as many as 200,000 eggs every day. These are eliminated in the stool, where the embryos develop in the eggs. If the contaminated feces in turn contaminate food or contaminated water and the food or water is ingested, the larvae hatch in the intestines.

They are then carried to the lungs, where they continue to develop. They bore through the walls of the tiny air sacs called alveoli and enter the bronchial tubes and reach the throat, where they are again swallowed. When they return to the small intestine, they grow into adults, and the cycle begins again. This takes about two or three months.

Symptoms & Complaints

Some people who have ascariasis do not have symptoms. Symptoms tend to arise when the infestation of roundworms is heavy. In this case, they include persistent coughing, gagging, wheezing, or vomiting if the roundworms are caught in the respiratory system. If there is a heavy infestation in the small intestines, the symptoms include:

In some cases, the worms can actually be seen in the feces when it is passed or in vomit. Complications of ascariasis include a mass of worms blocking the intestines. This causes pain and vomiting and is considered a medical emergency.

A group of worms can also block the ducts in the pancreas, liver or gallbladder. The worms can also cause infections that cause poor appetite or malabsorption. Children, whose intestines are still immature, are at greater risk for these complications.


Ascariasis is transmitted via the fecal-oral route when food or water is contaminated with the maturing eggs of the roundworm. The eggs need to be alive, for infertile eggs don't cause infection. The eggs can contaminate water because the water has been contaminated with feces that contain the parasite eggs. Food that is washed in this water can also become contaminated and cause ascariasis when consumed. Children also play in dirt that contains the eggs, then put their dirty fingers in their mouths.

Diagnosis & Tests

Doctors take stool samples and perform blood tests on patients who are suspected to have ascariasis. The doctor may also order X-rays of the patient's abdomen or chest. These X-rays can reveal masses of adult worms or larvae either in the intestines or the lungs.

If ascariasis is diagnosed, the doctor may order more tests to see how many adult worms are in the patient's system, where most of them are and whether they have migrated toward the vital organs besides the intestines. This helps the doctor determine how long the worms have been in the body. The longer they've been in the body, the more at risk the patient is for complications.

One of the other tests the doctor may use is endoscopy. During this procedure, a tiny camera connected to a flexible tube is placed inside the patient. What the camera sees is then projected onto a monitor. The doctor can also order CT scans, MRIs, and ultrasounds.

Treatment & Therapy

Mild ascariasis often goes away on its own. However, if the ascariasis is causing symptoms, it is treated with drugs meant to expel or kill parasites. These drugs are called anthelmintics. Three of the drugs are albendazole (Albenza®); ivermectin (Stromectol®) or mebendazole. In very severe cases, surgery may be needed to remove masses of roundworms that have blocked the patient's intestines or ducts or caused an inflammation that leads to a condition such as appendicitis.

Albendazole attacks the just-hatched larvae. It prevents them from reaching adulthood and thus from reproducing in the body. It is taken in tablet form with food, and can be crushed or broken to give to a child who can't swallow a whole tablet. It is important that the drug be taken for as long as the doctor prescribes, even if the patient feels well. Because albendazole can impair the immune system, it is important that the patient keep check-up appointments with the doctor for blood and liver function tests.

Ivermectin is used to treat many parasitic infections. It is taken at least one hour after a meal and is not prescribed for a child who weighs under 33 pounds. It comes in tablet form and a single dose is all it takes to combat the infestation by the roundworm.

Mebendazole works by killing the worms and allowing the body to expel them. It comes in tablet form and is taken with meals or on an empty stomach. It needs to be chewed thoroughly. It is best not given to children who are less than two years old. These drugs have few side effects and are very effective. Most patients make a full recovery after completing a course of these drugs.

Prevention & Prophylaxis

Ascariasis is rare in places where there is modern sanitation. People who are going to visit an area where there's little or no sanitation infrastructure or a place where human feces or contaminated water are used to fertilize crops need to boil their water before they drink it, and make sure the place where their food is prepared is hygienic.

Communal baths should also be avoided in places where the cleanliness of the water is uncertain. Hands should be carefully washed before eating or preparing food, and vegetables need to be washed, peeled and thoroughly cooked, especially if they have been grown in night soil, or soil fertilized with human feces.