Pinworm Infection, Life Cycle, Spread, Symptoms, Tests, Treatment

Many different types of worms can parasitize the human gut. The pinworm is one of them. Also known as the seat worm, roundworm or threadworm, the pinworm is a helminth that causes intestinal infection in children. In fact, infection by pinworms is the most common childhood worm infection in the United States. The scientific name of pinworm is Enterobius vermicularis.


The pinworm is a nematode that is slender and white in color. The females of this species are longer than the males. The average length of a female pinworm is about 10mm, whereas the average length of a male pinworm is about 4mm. The adults worms are big enough to be seen by the naked eye.

Pinworm Infection

Pinworm infection usually does not cause any symptoms or serious complications. When present, the most common symptom of a pinworm infection is an itching sensation around the anus (technically referred to as pruritus ani). This is often the only symptom that may be evident.

Children are most commonly affected by pinworm infections. For this reason, pinworm is also sometimes referred to as the “childhood worm”. When children complain of an itchy bum, they may be having a pinworm infection that needs to be treated. Parents should, therefore, be aware of this particular parasite. Apart from children, pinworm infections may also occur in adolescents and adults.

Infections in older individuals is more likely if they live in close contact with young children who already have pinworm infections. However, older individuals may not show any obvious symptoms of pinworm infection (such as an itchy bottom).

Life Cycle of Pinworms

Pinworm infection begins when the eggs of pinworm enter the mouth. As the eggs (technically referred to as the ova) migrate through the gut, they hatch and the larvae emerge in the duodenum. The larvae then moult twice to become adult worms while moving through the other parts of the small and large intestine (ileum, cecum, appendix, and ascending colon).

The adult male and female pinworms mate within the ileum, and the pregnant females stay at the ileocecal junction (the junction between the ileum and the cecum in the intestine) till they are ready to lay eggs. In order to lay eggs, the pregnant females move through the large intestine and emerge from the anal canal. They deposit their eggs in the perianal region after piercing the skin with their “pins”.

Upon hatching, the larvae can cause retrograde infection by migrating back into the anus and the colon. The eggs may also be released into the environment where they are free to infect another host, thus beginning another cycle of infection. The male pinworms live for approximately 7 weeks, whereas the female pinworms may survive for about 5 to 7 weeks.

How pinworm infection spreads?

Pinworm infection can spread from an infected person to an uninfected person. The main route of transmission is through the oral cavity. The eggs of pinworms may find their way into the oral cavity via direct contact with an infected person, or via inanimate objects or food that are contaminated. The eggs of pinworm may latch onto inanimate objects such as utensils, furniture, toilets, towels, bed linen, door knobs, and a variety of other surfaces.

The eggs can survive for about 2-3 weeks on such surfaces. The risk of contracting pinworm infection is greater when living with an infected person. For example, nannies and daycare workers who spend a lot of time with different children are at a relatively higher risk of getting pinworm infections.

The spread of pinworm infections can be arrested through certain hygienic measures that should be adopted by both children and adults. These measures include washing hands thoroughly with soap and water after going to toilet and avoiding touching or scratching the anal region. Re-infection with pinworms is also common in children. It is advisable to treat all close contacts (including family members) simultaneously with an infected child.

Signs and Symptoms

In many cases, pinworm infection does not cause any obvious symptoms. This is likely to be the case when the pinworms are localized within the ileocecal region of the intestine. Symptoms typically begin when the eggs are laid in the perianal region by the pregnant female pinworms. Hatching of eggs may also cause some symptoms to appear.
The most common symptoms of a pinworm infection include:

  • Itching in the anal area (also referred to as an itchy bottom or pruritis ani).
  • Itching in the vaginal area in infected females.
  • A prickly pain instead of an itching sensation around the anus.
  • Restlessness and irritability that make it difficult to sleep at night.
  • Nausea and abdominal pain.

It is important to note that the majority of cases of pinworm infection do not present with any symptoms. A person may remain unaware of being infected. Symptoms are most likely to appear in infected children.

Tests for Pinworm Infection

Adult pinworms are large enough to be seen by the naked eye. The female pinworms that migrate to the perianal region to deposit eggs may be visible in some cases. However, better diagnostic tests for pinworm infection depend on the detection of pinworm eggs. The following diagnostic tests are typically used for detecting pinworm infections:

Tape test

The tape test involves trapping the eggs in the perianal region onto the sticky side of an adhesive tape. The tape is then examined under a microscope for the presence of pinworm eggs. The tape test is typically conducted in the early morning before a person uses the toilet or bathroom. A single tape test has a sensitivity of around 50%. Therefore, the tape test might be done three days in a row to increase the sensitivity of detection to 90%.

Stool test

A stool test might be conducted in case of recurrent pinworm infections and persistent itching in the anal area. Persistent anal itching may also be caused by intestinal parasites other than pinworms. A detailed laboratory analysis of a stool sample helps in identifying the cause of the symptoms.

It is important to stress that people who collect the stool samples (such a parents of the infected children) should wear gloves during the procedure and wash hands thoroughly afterwards with a soap or disinfectant. There is a high risk of contracting pinworm infection during such procedures.

Treatment for Pinworm Infection

Anthelmintic drugs are used to treat pinworm infections. Two of the most commonly used drugs are albendazole and mebendazole. These medications kill the parasitic worms specifically. However, the effectiveness of the drug may vary depending on the type or stage of the life cycle of the worm. Younger worms may show some resistance to the drugs. However, it is still possible to eradicate them with an appropriate dosage of drugs.

The most optimal drug regimen for anthelmintic drugs is three doses separated by three week intervals. In severe cases, symptomatic treatment to relieve itching may also be given. Re-infection with pinworms is a common occurrence. Therefore, it is advisable to treat an infected person along with close family members or other close contacts.

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