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35-24: Enterobiasis

Philip J. Rosenthal

ESSENTIALS OF DIAGNOSIS

  • Nocturnal perianal pruritus.

  • Identification of eggs or adult worms on perianal skin or in stool.

GENERAL CONSIDERATIONS

Enterobius vermicularis, the pinworm, is a common cause of intestinal infections worldwide, with maximal prevalence in school-aged children. Enterobiasis is transmitted person-to-person via ingestion of eggs after contact with the hands or perianal region of an infected individual, food or fomites that have been contaminated by an infected individual, or infected bedding or clothing. Autoinfection also occurs. Eggs hatch in the duodenum and larvae migrate to the cecum. Females mature in about a month, and remain viable for about another month. During this time, they migrate through the anus to deposit large numbers of eggs on the perianal skin (eFigure 35–37). Due to the relatively short life span of these helminths, continuous reinfection, as in institutional settings, is required for long-standing infection.

eFigure 35–37.

Life cycle of Enterobius vermicularis (pinworm). Eggs are deposited on perianal folds

image. Self-infection occurs by transferring infective eggs to the mouth with hands that have scratched the perianal area
image. 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 (eg, curtains, carpeting). Some small number of eggs may become airborne and inhaled. These would be swallowed and follow the same development as ingested eggs. Following ingestion of infective eggs, the larvae hatch in the small intestine
image and the adults establish themselves in the colon
image. The time interval from ingestion of infective eggs to oviposition by the adult females is about 1 month. The life span of the adults is about 2 months. Gravid females migrate nocturnally outside the anus and oviposit while crawling on the skin of the perianal area
image. The larvae contained inside the eggs develop (the eggs become infective) in 4–6 hours under optimal conditions
image. Retroinfection, or the migration of newly hatched larvae from the anal skin back into the rectum, may occur but the frequency with which this happens is unknown. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.)

A flowchart of the life cycle of Enterobius vermicularis.
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CLINICAL FINDINGS

A. Symptoms and Signs

Most individuals with pinworm infection are asymptomatic. The most common symptom is perianal pruritus, particularly at night, due to the presence of the female worms or deposited eggs. Insomnia, restlessness, and enuresis are common in children. Perianal scratching may result in excoriation and impetigo. Many mild gastrointestinal symptoms have also been attributed to enterobiasis, but associations are not proven. Serious sequelae are uncommon. Rarely, worm migration results in inflammation or granulomatous reactions of the gastrointestinal or genitourinary tracts. Colonic ulceration and eosinophilic colitis have been reported.

B. Laboratory Findings

Pinworm eggs are usually not ...

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