Pinworms are another type of roundworm. They infect Americans more often than any other intestinal worm and are sometimes called threadworms. They are most common in children under the age of ten. Adult female pinworms lay microscopic eggs in the small folds of skin around the anus. Like Ascaris roundworms, swallowing fertile pinworm eggs causes infection. The thin, white worms can live in the intestine for up to six weeks.

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