Enterobius vermicularis

Enterobius vermicularis is a nematode (roundworm), also called the pinworm. It most commonly affects children, institutionalized persons, and household contacts of infected individuals. Pinworm is the most common helminth infection in the United States.

Transmission and life cycle

Infection is transmitted directly or indirectly when pinworm eggs are ingested. Common sources include contaminated hands, food, or water.

After ingestion, there is an incubation period of about 1-2 months (or longer) while the adult gravid female matures in the small intestine. Once mature, the adult female migrates to the colon and lays eggs around the anus at night.

Reinfection is common. Rarely, eggs can become airborne, be inhaled, and then swallowed.

Clinical features

Infection is frequently asymptomatic. When symptoms occur, they may include:

Perianal pruritus at night
Vulvovaginitis
Pelvic or peritoneal granulomas from retroinfection
Rarely, eosinophilic colitis

Scratching can lead to perianal excoriations and secondary bacterial superinfection.

Diagnosis

Diagnosis is made by detecting worms or eggs in the perianal region:

Look for pinworms in the perianal area 2-3 hours after the person falls asleep, when female worms migrate to lay eggs
Perform the “tape test”: apply transparent tape (or an NIH swab) to the perianal area to collect eggs, then examine microscopically
Collect material from under the fingernails, which may contain eggs after scratching

Stool examination and serology are not useful.

Eggs of E. vermicularis in a wet mount.