Ascaris is a genus of nematode worms, including the species of roundworm that can infect the intestines of humans (A. lumbricoides) and pigs (A. suum). Members of this genus look like unsegmented earthworms and have three-lipped mouths.

Ascaris lumbricoides is a very common parasite in humans; medical researchers estimate that over 650 million people around the world are infected by this roundworm. Some surveys have indicated that infections of this roundworm are very common in rural parts of the southeastern U.S. and in Appalachia.

People get infected with these parasites by eating food contaminated with their microscopic eggs; a common way of getting them is by eating unwashed root vegetables. Children may get them after playing in the dirt and putting their fingers in their mouths.

The eggs are extremely durable; they may survive long dormant periods in extremely hot or dry enviroments. There have also been reports of people becoming infected after handling roundworms in the laboratory that have been preserved in alcohol.

After the eggs are swallowed, they hatch into tiny worms that bore through the intestinal wall into the host's blood vessels or lymph vessels. They then travel through the veins and vessels into the lungs, where they can cause potentially fatal pneumonia. The tiny worms are coughed up in mucus and re-swallowed, where they then grow and mature in the intestines. The worms absorb food directly into their bodies; they don't suck blood as hookworms do. A worm reaches maturity in about two months; mature females may lay up to 20,000 eggs per day.

Infection with these worms can cause pain, malnutrition, severe allergic reactions, and, if the infestation is severe, potentially-fatal intestinal blockages and perforations. Adult worms may also wander through the gastrointestinal tract and emerge through the throat or lodge in the sinuses.

Ascaris infections can usually be cleared up with antihelminthic drugs like Mebendazole (Vermox), Albendazole (Albenza), and piperazine citrate. However, in severe cases, surgery may be necessary.


Integrated Principles of Zoology by Hickman, Roberts, and Hickman.

Biology by Helena Curtis.

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