Among the worms of the human intestine, the pinworm, Enterobius vermicularis, has unique features (page 492). It has a simple, direct life cycle. The normal habitat of the adults is the colon. The gravid female migrates out the anus, and deposits her eggs on the perianal and perineal skin. Within 4 to 6 hours the eggs are infective and, when transported to the mouth and swallowed, institute a new cycle. Infection is from man to man, there being no need for a free-living cycle or for an intermediate, biological vector.
Many aspects of the epidemiology of pinworm infection are as yet poorly understood. The total number of cases in the world is probably on the order of a quarter of a billion. In 1955 it was termed "the most prevalent parasite encountered in the practice of pediatrics."1 It is more common in colder climates than in the tropics. Stoll's 2