Enterobius vermicularis

It is a nematode or roundworm. Also called Pinworm, it most commonly occurs among children, institutionalized persons, and household members of persons with pinworm infection. Pinworm is the most common worm infection in the United States. Infection is transmitted directly or indirectly by contaminated hands, food or water containing pinworm eggs. Once someone has ingested pinworm eggs, there is an incubation period of 1 to 2 months or longer for the adult gravid female to mature in the small intestine. Once mature, the adult female worm migrates to the colon and lays eggs around the anus at night. Reinfection is common. Rarely, eggs may become airborne and be inhaled and swallowed.

It is frequently asymptomatic. It may cause perianal pruritus at night, vulvovaginitis, pelvic or peritoneal granulomas from retroinfection and rarely eosinophilic colitis. It may cause perianal excoriations and bacterial superinfections from scratching and itching. Diagnosis is done by looking for pinworms in the perianal area 2-3 hours after the infected person is asleep as that’s the time the female worms migrate to lay eggs/ or by the “tape test” where transparent tape or NIH swab is applied to the perianal area to collect eggs which can be observed microscopically/ or by collecting samples from under the fingernails which may harbor eggs secondary to scratching. Stool examination or serology is not useful. Again, good concept to test for USMLEs!

Eggs of E. vermicularis in a wet mount.