Enterobiasis is caused by the pinworm Enterobius vermicularis, a strictly human parasite infecting the gastrointestinal tract.
PATHOGENESIS AND EPIDEMIOLOGY
Infection occurs by ingestion of embryonated eggs by hand-to-mouth transmission or by oral contact with infected fomites, such as toys, bedding, or clothing. The incubation period from ingestion of an egg until an adult gravid female migrates to the perianal region is 1 to 2 months or longer. Ingested eggs hatch in the duodenum, and the larvae develop into adults in the cecum, where they mate. The yellow-white gravid female pinworms measuring 8 to 13 mm detach from the cecal mucosa and migrate out of the anus onto the perianal and perineal skin, leaving a trail of eggs on the surface of the skin. They do not lay eggs in the colon. Female pinworms usually die after depositing up to 10,000 fertilized eggs within 24 hours on the perianal skin. Eggs average 55 μm by 35 μm and appear flattened on one side and convex on the other. They are fully mature and infective 3 to 8 hours after being deposited, but at normal room temperature, less than 10% of eggs live for 48 hours. Eggs remain infective in an indoor environment usually for 2 to 3 weeks.
Since the female pinworm dies after ovipositing is completed, repeated infections are the result of reinfection from other environmental sources and not from retrograde infection.
Infection occurs worldwide, and clustering of cases in families is common. Prevalence estimates suggest there are 40 million infected persons in the United States, and infection rates in school-aged children vary from 10% to 45%. Infection is unrelated to poor sanitary facilities or tropical climates. Young girls have pinworms more frequently than boys of the same age, and whites are more often infected than African Americans. Infection is most common between early fall and late spring, perhaps related to transmission in schools. For unknown reasons, some individuals seem to be predisposed or vulnerable to reinfection. Unlike soil-transmitted helminths such as Ascaris, enterobiasis is more common in urban settings.
Pinworms rarely produce serious pathology, and many infections are asymptomatic. The most common presentation is perianal and perineal pruritus, typically felt at night. Although pruritus probably results from crawling worms, some patients with heavy pinworm infections and many worms in the rectum have little or no itching. Pruritus may provoke such severe scratching that local bleeding, secondary pyogenic infection, and lichenification can occur. Abdominal pain, nausea, and vomiting have been described with heavy worm burden. Adult pinworms may be found in normal and inflamed appendices following surgical removal, but whether or not they cause appendicitis is debated. Eosinophilic enterocolitis has been noted in the presence of pinworms usually without peripheral eosinophilia being observed. Vaginitis and discharge have been observed in young girls. Rarely, pinworms have been found in ...