The pinworm Enterobius vermicularis (formerly Oxyuris) is a common parasite around the world and is the most prevalent parasitic helminth in developed countries today. Enterobiasis has afflicted and annoyed humans from ancient times; it was known to ancient Chinese, classical, and Islamic writers and was present in pre-Columbian America. Humans are the only hosts. Mature worms, ranging from 2 to 13 millimeters in length, inhabit the cecum and adjacent regions of the large and small intestines. Gravid females migrate out the host’s anus and deposit thousands of eggs on the skin of the perianal region. The eggs mature quickly and are infectious in several hours. Infection by ingestion of eggs from the hands is common, as the worms induce itching and scratching. Eggs are frequently eaten with contaminated food, and, because they are light, they are easily inhaled in household dust. Eggs hatch in the small intestine and develop into mature adults in as short a time as 4 weeks. Retroinfection, when the eggs hatch on the perianal skin and the larvae crawl back into the rectum, is possible but rare. Pinworms are especially prevalent among small children and often become a family affair.

Enterobiasis is rarely a serious disease. Intestinal disturbances, if any, are minor, but pinworms can cause great discomfort, and scratching can lead to secondary infections. Migrating worms occasionally reach the vagina or appendix, but rarely cause serious harm. Rectal itching and consequently insomnia, especially in children, are suggestive of pinworm infection.