ALSO KNOWN AS pinworm, Enterobius vermicularis is a parasitic intestinal worm (nematode). Humans are their only known host. Most prevalent among preschool and school-age children, pinworms infect some 40 million children and adults in the United States, according to the Centers for Disease Control and Prevention (CDC).
Small (2 to 13 mm) and white, adult pinworms live in the cecum. At night, gravid females migrate to the anus to lay eggs in perianal skin folds. The eggs usually hatch within hours. (See Short story: The pinworm life cycle.)
Activity by adult pinworms and the mobile larvae causes perianal itching, the most common symptom of pinworm infection. Other signs and symptoms include trouble sleeping and general irritability. Patients with severe infestations may experience anorexia and weight loss. However, many patients have only mild symptoms or none at all.
Because of anal irritation, the sleeping host may scratch herself, acquiring pinworm eggs and larvae under her fingernails. She may then reinfect herself if she doesn't practice scrupulous hand hygiene. Scratching may also lead to a secondary bacterial infection.
Pinworms can spread when people handle contaminated objects (fomites), such as pajamas, bed linen, and underwear, or anything the infected person has handled with unwashed hands. This is why pinworms are especially prevalent among young children in crowded settings, such as day-care centers and schools, and why mothers of infected children are far more likely to be infected than adults in the general population.
Pinning down the diagnosis
To confirm a pinworm diagnosis, eggs are recovered from the anal area and examined microscopically. Eggs can be recovered by applying transparent adhesive tape or a special pinworm paddle with an adhesive surface to perianal skin. Instruct the patient (or her parent) to apply the tape or paddle on the anus before getting out of bed in the morning, before washing, urinating, or defecating.
Treating pinworm infection
According to the CDC, the treatment of choice for pinworm infection is pyrantel pamoate, which is available as a liquid or capsule. An alternative, mebendazole (Vermox), is available as a chewable tablet. Both drugs are indicated for adults and children over age 2.
The recommended dose for pyrantel is 11 mg/kg P.O. (maximum dosage, 1 gram), taken with or without food. The patient may take a second dose in 2 weeks if pinworms persist.
Mebendazole, a chewable tablet, is normally given in one 100-mg dose. If necessary, however, the patient may take a second dose in 3 to 4 weeks. This drug may also be taken without regard to food.
In some cases of persistent infection, patients receive four to six doses of medication spaced 2 weeks apart.
Family members and other close contacts of an infected patient should be assessed and treated if necessary. Teach all patients to take their medication as directed.
Patient teaching
To eradicate pinworms and prevent reinfection, teach children, their parents, and other close contacts to perform meticulous hand hygiene throughout the day-especially before eating or food preparation, after toileting or diaper changes, after handling bed linen or underwear, and after touching any potentially contaminated objects.
Infected patients need to keep their nails short, bathe every morning upon rising (using a fresh washcloth and towel each time), and change underwear, pajamas, and bed linen daily.
Once an infected child has received one dose of medication, been bathed, and had her fingernails trimmed, she can return to school.