Human pinworms, Enterobius vermicularis (en-tuh-ROH-be-us ver-MIH-kyoo-lar-is), are a species of roundworm* about the size of a staple. People become infested when they swallow tiny pinworm eggs, usually after touching something that a person with pinworms has touched. The eggs travel to the small intestine* and hatch into larvae*. The larvae then migrate to the colon*, where they grow into adult worms. Female adult pinworms emerge from a person’s anus* at night to lay their eggs on the skin of the perianal region*. The worms return to the colon, where they usually die, but the eggs can survive for up to 2 weeks outside the human body. If the person scratches around the anus and later touches the lips, it is possible to transfer the eggs from the hands to the mouth, where they are swallowed and begin a new cycle of infestation.

*roundworm: is one of several types of cylinder-shaped worms that live in people. Roundworms are also known as nematodes (NEE-muh-todes).

*small intestine: is the part of the intestine—the system of muscular tubes that food passes through during digestion—that directly receives the food after it passes through the stomach.

*larvae: (LAR-vee) are the immature forms of an insect or worm that hatches from an egg.

*colon: (KO-lin), also called the large intestine, is a muscular tube through which food passes as it is digested, just before it moves into the rectum and out of the body through the anus.

*anus: (A-nus) is the opening at the end of the digestive system, through which waste leaves the body.

*perianal: (pair-e-A-nul) region is the area of skin surrounding the anus.

How Common Is It?

The U.S. Centers for Disease Control and Prevention estimates that about 40 million people, or 1 person in 7, in the United States have pinworms, making it the most common worm infestation in the country. Children in school and preschool are most frequently infested, and pinworms are also common in people living in crowded conditions. When one person in a household becomes infested, other family members often wind up with the worms as well.

Is Pinworm Infestation Contagious?

Pinworms can spread directly from person to person. Someone with an infestation may unknowingly leave the parasite’s eggs in their clothes or bed or anywhere that they put their hands after scratching the anal area. When another person picks up the clothes or makes the bed, he or she may get the eggs on the fingers. By touching the mouth, this person can swallow the eggs and start an infestation. Young children have the greatest chance of becoming infested, because they often put their hands in their mouths. The parasites spread easily in preschools, schools, and child-care settings.

What Are the Signs and Symptoms of Infestation?

Many people with pinworms have no symptoms at all. In others, symptoms are generally mild. The most common symptom is itching around the anus. The sensation becomes strongest at night, when the female worms are active on the skin; this may lead to restless sleep or even trouble sleeping. Children with infestations may become irritable from lack of peaceful sleep, and they occasionally lose their appetites. If a child constantly scratches around the anus, the skin there can become raw and infected. In girls, adult worms sometimes enter the vagina* instead of returning to the anus, which may cause vaginal itching.

*vagina: (vah-JY-nah) is the canal, or passageway, in a woman that leads from the uterus to the outside of the body.

How Is the Diagnosis of Pinworm Infestation Made?

Doctors usually use the “tape” test to diagnose a suspected pinworm infestation: a piece of transparent tape is applied briefly over the anus and then removed. If a person has pinworms, the worms or their eggs may stick to the tape. The tape then is taken to the doctor’s office for examination, because the evidence is visible only under a microscope. The doctor may provide a special adhesive “pinworm paddle” to conduct this test. The tape is applied at home as soon as the person wakes up, because bathing or having a bowel movement can dislodge the eggs. The patient may need to take several tape tests if the first one or two do not show the presence of worms. The doctor also might examine scrapings from under the fingernails, where pinworm eggs can become stuck after the patient scratches the anal area. In some cases, the worms, which look like fine threads, can be spotted at night around the anus or in the bed sheets.

What Is the Treatment?

Once an infestation is confirmed, the doctor generally prescribes medication to get rid of the worms. The patient takes the first dose, often in the form of a chewable pill, right away and a second dose 2 weeks later. Sometimes doctors recommend that all people who live in the same house with the infested person take the medicine as well. Patients may need more than one round of treatment to get rid of the worms entirely, if they become infested a second time.

Are There Complications of Pinworm Infestation?

Complications of pinworm infestation are uncommon and generally minor, such as the development of a bacterial infection of the perianal skin from scratching.

What Are the Preventive Measures?

Practicing good personal hygiene is the best way to avoid infestation. For example, it is a good idea to wash the hands after going to the bathroom and before eating and to avoid scratching the anal area and biting the nails. To limit the spread of pinworms, people with the parasites are advised to change into clean underwear every day and frequently change their nightclothes. Taking a bath or shower after waking up in the morning can help get rid of pinworm eggs, and trimming fingernails short can prevent eggs from lodging there and later being deposited somewhere else. Doctors advise that after each course of treatment for pinworms, sheets and sleeping clothes be washed, to lower the risk of re-infestation.

See also

Resources

Organization

American Academy of Family Physicians, 11400 Tomahawk Creek Parkway, Leawood, KS 66211. The American Academy of Family Physicians publishes fact sheets about pinworms at its website.

Telephone 800-274-2237 http://familydoctor.org

U.S. Centers for Disease Control and Prevention (CDC), 1600 Clifton Road, Atlanta, GA 30333. The CDC is the U.S. government authority for information about infectious and other diseases. It provides a fact sheet and other information on pinworm infestation through the website of the National Center for Infectious Diseases.

Telephone 800-311-3435 http://www.cdc.gov/ncidod/

Complete Human Diseases and Conditions