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The nematode (roundworm) Enterobius vermicularis (previously Oxyuris vermicularis) also called human pinworm. (Adult females: 8 to 13 mm, adult male: 2 to 5 mm.) Humans are practically the only hosts of E. vermicularis.

Life Cycle:
Eggs are deposited on perennial folds. Self-infection occurs by transferring infective eggs to the mouth with hands that have scratched the perennial area. Person-to-person transmission can also occur through handling of contaminated clothes or bed linens. Enterobiasis may also be acquired through surfaces in the environment that are contaminated with pinworm eggs (e.g., curtains, carpeting). Following ingestion of infective eggs, the larvae hatch in the small intestine and the adults establish themselves in the colon. The time interval from ingestion of infective eggs to oviposition by the adult females is about one month. The life span of the adults is about two months. Gravid females migrate nocturnally outside the anus and oviposit while crawling on the skin of the perennial area. The larvae contained inside the eggs develop (the eggs become infective) in 4 to 6 hours under optimal conditions.

Geographic Distribution:
Worldwide, with infections more frequent in school- or preschool- children and in crowded conditions. The most common helminthic infection in the United States (an estimated 40 million persons infected).

Clinical Features:
Enterobiasis is frequently asymptomatic. The most typical symptom is perennial pruritus, especially at night, which may lead to excoriations and bacterial superinfection. Occasionally, invasion of the female genital tract with vulvovaginitis and pelvic or peritoneal granulomas can occur. Other symptoms include anorexia, irritability, and abdominal pain.