Pinworm infection is caused by the intestinal roundworm (nematode) Enterobius vermicularis.
People acquire the infection when they swallow eggs of the roundworm.
The infection may cause itching around the anus.
The infection can be diagnosed by finding the eggs or sometimes the adult pinworm around the anus.
Two doses of a medication used to treat worms usually cure the infection.
Helminths are parasitic worms that can infect humans and animals. There are 3 types of helminths: flukes (trematodes), tapeworms (cestodes), and roundworms (nematodes). Enterobius vermicularis is a roundworm.
Pinworm infection is estimated to be present in more than 1 billion people worldwide. Most cases of pinworm occur in school-aged children.
Because most cases of pinworm occur in school-aged children, adults who care for children or family members of an infected child are at increased risk of infection. People who live in long-term care facilities are also at increased risk of pinworm infections.
Infection can be transmitted through anal-oral contact with an infected partner during sex.
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(See also Overview of Parasitic Infections.)
Transmission of Pinworm Infection
Infection occurs after pinworm eggs (ova) are swallowed. The larvae in the eggs hatch in the small intestine, then move to the large intestine. There, the larvae mature within 2 to 6 weeks, and the adult worms mate. After the eggs develop, the adult female worm moves to the rectum and exits through the anus to lay eggs. The eggs are deposited in a sticky, gel-like substance that sticks to the skin around the anus. From there, eggs can be transferred to fingernails, clothing, bedding, toys, or toilet seats. Eggs can survive outside the body up to 3 weeks at normal room temperature.
Eggs are often introduced into the mouth from fingers or from contaminated food. Children may reinfect themselves by transferring eggs from the area around their anus to their mouth. Children who suck their thumb are at increased risk of infection, as are adults who live with infected children.
Infection can also be transmitted through anal-oral contact with an infected partner during sex.
People who live in long-term care facilities are also at increased risk of pinworm infections.
Image from the Centers for Disease Control and Prevention, Global Health, Division of Parasitic Diseases and Malaria.
Symptoms of Pinworm Infection
Most people who have pinworms do not have symptoms. However, in some, the area around the anus itches because the eggs and the sticky substance around them irritate the skin. With scratching, the skin can become raw and infected with bacteria.
In girls and women, pinworms may cause vaginal itching and irritation.
Diagnosis of Pinworm Infection
Microscopic examination of transparent tape that has been patted around the anus to collect eggs
Observation of adult worms around the anus
The diagnosis of pinworm infection is made by finding the eggs or adult pinworms around the anus. Eggs can be obtained by patting the skinfolds around the anus with the sticky side of a strip of transparent tape. This should be done in the early morning before the person defecates or wipes the area. The tape can be taken to the doctor for microscopic examination. Doctors may ask people to repeat this procedure several days in a row to make sure that they obtain eggs, if present.
If vaginal itching occurs and is possibly due to pinworms (usually this is likely in a person who recently had a pinworm infection or has close contact with a person who recently had a pinworm infection), a piece of transparent tape can be applied in a similar way to the opening of the vagina.
The best way to search for adult pinworms is to examine the anus approximately 1 to 2 hours after going to bed for the night. The worms are white and hair-thin, but they wiggle and are visible to the naked eye.
Treatment of Pinworm Infection
Medications used to treat worm infections (anthelmintics)
To treat pinworm infection, a doctor prescribes mebendazole, albendazole, or pyrantel pamoate (available over the counter). These medications are known as anthelmintics, and they are taken by mouth. Two doses of one of these medications taken 2 weeks apart usually cure pinworm infection.
Anti-itching creams or ointments, such as petroleum jelly, applied directly to the area around the anus may relieve itching.
Prevention of Pinworm Infection
Even if treatment of pinworm infection is successful, reinfection is common, partly because eggs can survive outside the body for 3 weeks and may be passed in stool for 1 week after treatment ends. Thus, some doctors recommend treating the entire family.
The following can help prevent the spread of pinworms:
Washing the hands with soap and warm water after using the toilet, after changing diapers, and before handling food (the most effective way)
Frequently washing clothing, bedding, and toys
Vacuuming the environment to try to eliminate eggs
If people are infected, showering every morning to help remove eggs on the skin
Avoiding oral-anal contact during sex
