Enterobius vermicularis is a threadlike white worm that infects the colon and causes intense nocturnal perianal pruritus when the gravid adult female migrates to deposit eggs at night. Female worms measure 8 to 13 mm in length and can be observed moving about the perianal area at night. On rare occasions, this nematode can lead to vulvovaginitis. The diagnosis can be made by direct visualization of the nematode by the parents or by using a piece of transparent adhesive tape and touching it to the perianal area upon awakening in the morning. This tape is then applied to a glass slide for microscopic examination under low power to look for “bean-shaped” eggs. The differential diagnosis includes perianal irritation, perianal group A Streptococcus infection, cellulitis, fissures, hemorrhoids, and contact dermatitis.
Management and Disposition
Stool studies are not warranted as the eggs are not generally passed in the stool. The treatment of choice is the anthelmintic agents, albendazole or mebendazole. The initial single dose is repeated in 2 weeks to treat secondary Enterobius hatchings. Because of the high frequency of reinfection, families should be treated as a group, and household bedding and clothes should be washed.
Reinfection from other infected individuals (daycare cohorts) or autoinfection is necessary to maintain enterobiasis in the individual, since these nematodes usually die after depositing their eggs in the perianal region. Frequent hand washing may reduce chances of infection as transmission occurs by the fecal-oral route.
E vermicularis is the most common intestinal nematode in the United States, affecting 5% to 15% of the population. Many infections are asymptomatic.
Suspect pinworm infection in children who present with nocturnal restlessness. These patients are often evaluated for urinary tract infection because the scratching of the perineal area is misinterpreted by the parents and treating clinicians as painful urination.
Pinworms. Multiple tiny pearly white worms are seen at the anus. (Photo contributor: Lawrence E. Heiskell, MD.)