Oxyuriasis – infection with Enterobius vermicularis

What is the worm Oxiurus vermicularis?

The pinworm (some call it oxiurrus), known scientifically as Enterobius vermicularis or Oxiurus vermicularis, is a white, cylindrical helminth nematode (worm) that measures about 1 cm and causes an intestinal worm disease called enterobiasis, oxiuriasis, or oxiurosis. In popular parlance, the oxiurus is known as tuxina.

Oxyuriasis is a parasitic disease whose main symptom is an anal itch, usually intense and predominantly nocturnal, which usually disturbs the sleep of affected individuals.

Humans are the only natural host of the pinworm, and its infection occurs in all countries and socioeconomic groups. Enterobiasis can appear at any age, but is most frequently seen among schoolchildren between the ages of 5 and 10, and is relatively rare in children under the age of 2.

Enterobius vermicularis is a worm that lives in the intestines of humans, more specifically in the region of the cecum (beginning of the large intestine) and the appendix.

After mating, the male dies and is eliminated in the feces. Pregnant females remain in the cecum, and at night they move through the intestine toward the anus, where they usually implant their eggs. Each female can lay up to 10,000 eggs.

After the eggs are laid, the female tries to return to the anus, some succeed, others do not, and are eliminated in the feces.

Pinworm worm transmission

The Enterobius vermicularis has a relatively simple life cycle, which begins with the deposition of the pregnant females eggs mucosal perianal region. From this moment on, the infection usually follows three paths:

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1. Autoinfection

The presence of eggs causes intense anal itching. If the patient scratches the anus region, he can contaminate his hands and nails with the worm eggs. If the contaminated hand is brought to the mouth at any time, the patient becomes contaminated again. Ingested eggs hatch in the small intestine, giving rise to a new generation of Enterobius vermicularis .

2. Retroinfection

After 3 weeks, the eggs implanted in the perianal region hatch and give rise to new worms. These worms can enter through the anus and proceed towards the cecum, where they will mate again.

3. Heteroinfection

Transmission of the pinworm to other people can occur through hands contaminated with eggs.

The patient scratches the anus, contaminates their hands and can transmit eggs when preparing food, handling objects or greeting other individuals.

People who live in the same environment as contaminated patients are at the highest risk of being contaminated. Towels and bedding are often infected with Enterobius vermicularis eggs , which facilitates the spread to spouses.

Eggs begin to lose their ability to infect after 1 or 2 days under hot, dry conditions, but can survive for more than two weeks in cool or moist environments.


Most patients infected with pinworms have no symptoms. In general, the symptoms appear when the patient has been reinfected successively, to the point of having a large amount of worms in their intestinal tract, which may only occur months after the initial contamination.

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When the worm causes symptoms, the most common is anal itching. In some cases, the itching is intense and makes the patient restless and having difficulty sleeping. Adult worms can migrate to places beyond the anus, such as the vaginal region. In women there may be vulvovaginitis (inflammation of the vulva and vagina), itching and vaginal discharge .

Oxyuriasis - infection with Enterobius vermicularis

Occasionally, in patients who repeatedly self-infect themselves, the burden of worms in the intestines may be so high that the patient experiences typical symptoms of intestinal parasites, such as abdominal pain, pain in bowel movements, nausea, and vomiting. Obstruction of the appendix by the worms is possible, which can lead to acute appendicitis .

Patients who frantically scratch the anal area can cause excoriation of the mucosa, facilitating the infection of wounds by bacteria.


As the elimination of Enterobius vermicularis by the feces can be erratic, that is, it does not have a regular or predictable schedule, the common parasitological exam of feces is usually not positive for the worm or its eggs. With this test, only 10% of infected patients can be diagnosed.

Oxyuriasis is more easily diagnosed using the Graham method, in which an adhesive tape is used on the skin around the anus so that eggs located in this region adhere to the tape. These eggs are then placed on a glass slide and viewed under a microscope.

Material taken from the nails of infected children may also be useful for microscopic evaluation, as they often contain pinworm eggs.


The treatment of oxyuriasis is simple and should be done preferably in all people who live in the same house.

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The most used options to treat oxyuriasis are:

  • Albendazole , 10 mg/kg in a single dose, up to a maximum of 400 mg. Repeat the dose in two weeks.
  • Mebendazole, 100 mg, twice a day* for 3 consecutive days. Repeat the dose in two weeks.
  • Pyrantel pamoate, 10 mg/kg, single dose, up to a maximum of 1000 mg.

* 100 mg in a single dose is an alternative suggested by some authors.

The cure rate with these regimens is very high, above 95%. However, if people living in the same household are not also treated, the risk of reinfection is high.

Also, in order to prevent reinfections, bed linen, towels, underwear, panties and pajamas must be washed and changed daily for at least 2 weeks. Toys must be washed every 3 days for at least 3 weeks. The nails should be cut very close to make it difficult to lay eggs between them during the act of scratching the anus.

As the worm usually lays its eggs at night, bathing and washing the perianal region in the morning, as soon as you wake up, helps to eliminate these eggs, reducing the risk of a new generation of worms appearing within 3 weeks. It is also important to wash your hands thoroughly before each meal and after any bowel movement.