What Is a Pinworm Infection?

Illustration of pinworms in the intestines

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Pinworm infection (enterobiasis vermicularis or oxyuriasis) is an intestinal infection with parasitic worms known as a pinworms (a.k.a. threadworms or seatworms), which are able to live in the human colon and rectum. It is highly contagious and caused by fecal-oral transmission of pinworm eggs, most often in young children, though adults can also be affected. While pinworm infection can cause intense anal itching, it is not a serious health threat and treatment is available.

According to the Centers for Disease Control and Prevention (CDC), pinworm infection is the most common worm infection in the United States.

Pinworm Symptoms

Pinworm commonly causes itching, typically in the rectal area. In women and girls, pinworms can also cause vaginal itching and discharge.

It's usually worse at night and the itching sensation can be irritating enough to interfere with sleep. Adults and children who have pinworm may spend a long time in the shower or pool because the water can feel soothing (or due to an urge to clean the itchy area).

Bedwetting is another possible symptom of enterobiasis, especially among young children who have recently learned to control their bladder at night. This occurs because the worms can irritate the urethra, the thin tube by which urine leaves the bladder and passes out of the body.

Complications

Children and adults who develop a pinworm infection may scratch the irritated area. This can cause swelling, redness, and bleeding. Skin wounds from scratching can become infected with bacteria, resulting in a rectal abscess or a condition called perianal cellulitis.

Sometimes, pinworms cause digestive symptoms such as abdominal pain or nausea. Weight loss can occur due to loss of appetite if stomachaches persist. As parasites, pinworms can leech essential nutrients from the body, resulting in malnutrition.

Sometimes pinworms can spread to the female reproductive tract, leading to complications such as urinary tract infections, vaginitis, and even endometriosis.

Causes

Pinworm is very contagious. Enterobius vermicularis eggs are transmitted from one person to another when they somehow make their way from the infected individual's feces to the mouth or nose of someone else.

The eggs can enter the body after an infected surface has been touched—and those surfaces can be just about anything.

The eggs can survive on food and drinks, utensils, countertops, doorknobs, linens, clothing, toilets, fixtures, toys and sandboxes, classroom desks, and so on. They do not, however, live on animals, so you can't get pinworms from your dog or cat (or pass the parasite along to a pet if you're infected).

Note that pinworm eggs can live on surfaces outside of the body for as long as two to three weeks.

It's also possible to breathe in the eggs because they are so tiny (they can only be seen with a microscope). And if you are infected and get the eggs on your hands, it is also possible for you to transmit the infection back to yourself.

People do not frequently discuss pinworm infection—so it can be hard to know whether you got it from your work or from a public place, or whether a family member brought it home.

Lifecycle in the Body

The Enterobius vermicularis parasites are small and thin. They belong to a category of parasites described as nematodes or roundworms.

  • Once the eggs are inside the body, they travel to the small intestine to hatch.
  • The larvae then move on to the large intestine where they live as parasites while maturing.
  • After a month or two, adult female pinworms take yet another trip, this time to the area around the rectum, to lay eggs and then die.

The total lifespan of a pinworm is about 13 weeks.

The tremendous discomfort and itching associated with pinworm infection are caused by the presence of the Enterobius vermicularis eggs near the rectum. You can get the eggs on your hands and underneath your fingernails by scratching the infested area. Unfortunately, this can set off an entirely new pinworm lifecycle.

Diagnosis

Pinworm is usually diagnosed based on the symptoms. There are other causes of anal itching, however, including skin irritation, diarrhea, and infections other than pinworm. The diagnosis of pinworm can be confirmed by identifying the eggs or the worms in samples examined under a microscope.

Tape Test

Your doctor may ask you to conduct a tape test to collect a sample for examination. This involves just what you might imagine given the name: Pressing tape on to the affected area to capture pinworm eggs.

Your doctor may give you the materials for this test. The worms tend to lay eggs at night, so the morning is the best time to do a tape test.

Instructions are typically as follows:

  1. Before bathing, press the sticky side of an inch-long piece of clear tape against the anal area. Hold it there for a few seconds to give the eggs time to adhere firmly to the tape. 
  2. Transfer the tape sticky-side down to a glass slide and place it in a clean plastic bag. Seal the bag and wash your hands.
  3. You can repeat the test on three separate days to increase the chance of picking up the eggs.
  4. Take the slides to your doctor for an examination.

You can actually see the worms (but not the eggs) even without a microscope, and a microscopic examination of the material obtained from a tape test can show eggs, worms, or both.

Live worms may be seen near the rectum or on clothes. They look like thin white threads, and they may or may not be alive and moving.

Treatment and Prevention

There are several prescription medications for treating pinworm infection, such as Emverm (mebendazole) for adults and children age 2 and up and Albenza (albendazole) for adults and children age 6 and up.

Over-the-counter (OTC) pyrantel pamoate, which comes as a liquid, is safe for kids ages 2 and up. You also can sometimes find this medication sold under a drugstore brand.

These medications are all taken in two doses. The second dose is taken two weeks after the first dose. Your doctor may recommend that family members get treated as well, even if they are not exhibiting symptoms of infection.

In addition to using medication to get rid of pinworm infection, there are measures you should take to prevent it from spreading (and to avoid reinfecting yourself).

Learning how to keep your hands and body clean after using the toilet—especially after a bowel movement, is an important strategy for keeping this parasite from spreading. You may need to be extra mindful about helping potty-training children with this.

Other steps you need to take include:

  • Cutting nails very short to avoid getting the eggs trapped underneath and to prevent scraping open skin when scratching
  • Making sure everyone in the household washes their hands frequently and thoroughly with warm, soapy water
  • Washing all clothing, bed linens, and towels that might have had contact with the pinworms in hot water
  • Not shaking fabric items out before they've been washed
  • Wiping down any surfaces or items that could be harboring pinworm eggs
  • Vacuuming all carpets regularly
  • Keeping rooms well-lit during the day, as pinworm eggs are sensitive to light
  • Bathing children separately and daily
  • Washing pajamas every few days and putting clean underwear on every day

It may take a little time and effort, but by following these strategies you should be able to get your household free of pinworms within a few weeks.

A Word From Verywell

Pinworm is relatively common, especially among children. If you or your child or another loved one (such as a parent with chronic illness) develops pinworm, there is no need for alarm. It does not reflect on your cleanliness or hygiene. This is simply an infection that happens to be present in most communities—and spreads through regular day-to-day contact with other people.

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  1. Centers for Disease Control and Prevention. Pinworm Infection FAQs. Updated January 10, 2013.

  2. KidsHealth. Pinworm. Updated July 2017.

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