Enterobiasis

Definition

Enterobiasis or pinworm infection, as it is commonly called, is an intestinal infection caused by the parasitic roundworm called Enterobius vermicularis. The most common symptom of this irritating, but not particularly dangerous, disease is itching around the anal area.

Description

Enterobiasis is also called seatworm infection or oxyuriasis. In the United States, enterobiasis is the most common worm infection, and some estimate that approximately 10% of the United States population is infected. Worldwide, approximately 200 million people are infected. Enterobiasis can affect people of any age, but is most common among children ages 5-14 and particularly affects those in the daycare setting.

Causes and symptoms

The disease is highly contagious and is caused by a parasitic worm called Enterobius vermicularis. The adult female worm is about the size of a staple (approximately 1 cm long and 0.5 mm wide) and has a pointed tip. The disease is transmitted by ingesting the eggs of the pinworm. These eggs travel to the small intestine where, after approximately one month, they hatch and mature into adult worms. During the night, the female adult worms travel to the area around the anus and deposit eggs in the folds of the anal area. A single female pinworm can lay 10,000 eggs and, after laying eggs, dies. The eggs are capable of causing infection after six hours at body temperature.

Significant itching in the anal region is caused by the movement of the adult worm as the eggs are deposited. When an individual scratches the anal region, the tiny eggs get under the finger nails and in the underwear and night clothes. Anything the individual touches with the contaminated fingers, for example, toys, bedding, blankets, bathroom door knobs, or sinks, becomes contaminated. The eggs are very hardy and can live on surfaces for two to three weeks. Anyone touching these contaminated surfaces can ingest the eggs and become infected. An individual can also become infected by inhaling and swallowing the eggs, for example, when the bedcovers are shaken.

Many individuals with enterobiasis exhibit no symptoms. When present, however, symptoms of the infection begin approximately two weeks after ingesting the pinworm eggs. The main symptom is itching around the anus. Because the itching intensifies at night, when the female worms comes to the anus to lay eggs, it often leads to disrupted sleep and irritability. Poor sleeping at night in small children can be related to pinworms. Occasionally, the itching causes some bleeding and bruising in the region, and secondary bacterial infections can occur. In females, the itching may spread to the vagina and sometimes causes an infection of the vaginal region (vaginitis). Enterobiasis usually lasts one to two months.

Diagnosis

First, a physician will rule out other potential causes of the itching, such as hemorrhoids, lice, or fungal or bacterial infection. Once these have been ruled out, an accurate diagnosis of enterobiasis will require that either the eggs or the adult worms are detected. Rarely, the adult worms are seen as thin, yellowish-white threads, about 1 cm long, in the stools of the infected person. Usually, an hour or so after the individual goes to sleep, the adult female worms may be seen moving around laying eggs if a flashlight is shone at the rectal area.

An easier method is to observe the eggs under the microscope. In order to collect a specimen for laboratory diagnosis, the physician may provide a paddle with a sticky adhesive on one side, or an individual may be instructed to place a piece of shiny cellophane tape sticky side down against the anal opening. The best time to perform this test is at night or as soon as the individual wakes up in the morning, before having a bowel movement or taking a bath or shower. The pinworm eggs will stick to the tape, which can then be placed on a specimen slide. When under a microscope in the laboratory, the eggs will be clearly visible.

Treatment

In order to treat the disease, either mebendazole (Vermox) or pyrantel pamoate (Pin-X) will be given in two oral doses spaced two weeks apart. These medications eradicate the infection in approximately 90% of cases. Re-infection is common and several treatments may be required. Because the infection is easily spread through contact with contaminated clothing or surfaces, it is recommended that all family members receive the therapeutic dose. Sometimes a series of six treatments are given, each spaced two weeks apart. If family members continue to be infected, a source outside the house may be responsible.

To relieve the rectal itching, a shallow warm bath with either half a cup of table salt, or Epsom salts is recommended. Also, application of an ointment containing zinc oxide or regular petroleum jelly can be used to relieve rectal itching.

Prognosis

Pinworms cause little damage and can be easily eradicated with proper treatment. Full recovery is expected.

Prevention

The disease can be prevented by treating all the infected cases and thus eliminating the source of infection. Some ways to keep from catching or spreading the disease include the following recommendations:

• Wash hands thoroughly before handling food and eating.
• Keep finger nails short and clean.
• Avoiding scratching the anal area.
• Take early morning showers to wash away eggs deposited overnight.
• Once the infection has been identified, and treatment is started, change the bed linen, night clothes, and underwear daily.
• Machine wash linens in hot water and dry with heat to kill any eggs.
• Open the blinds or curtains since eggs are sensitive to sunlight.

Key Terms

Anus

The opening through which feces are eliminated.

Hemorrhoid

An area around the anus where veins become dilated and the tissue swells, causing itching and pain.

Rectum

The end of the large intestine in which feces collects for elimination through the anus.

Vaginitis

Inflammation of the vagina.

Further Reading

For Your Information

Books

• Merck Manual of Diagnosis and Therapy, 16th edition, edited by Robert Berkow, et al. Rahway, NJ: Merck Research Laboratories, 1992.
• Plorde, James J., and Paul G. Ramsey. "Nematodes, Cestodes and Hermaphroditic Trematodes" In Harrison's Principles of Internal Medicine, edited by Jean D. Wilson, et al. New York: McGraw Hill, 1991.
• Zinsser, Hans. Zinsser Microbiology, 19th edition, edited by Wolfgang K. Joklik, et al. Stamford, CT: Appleton Lange, 1988.

Gale Encyclopedia of Medicine. Gale Research, 1999.