Pinworm (Enterobius vermicularis) Infection
Pinworm (Enterobius vermicularis) Infection
Pinworm infection, or enterobiasis, is a common helminth infection that arises when humans drink water or eat food contaminated by eggs of parasitic pinworms. Enterobiasis is considered the most common roundworm infection in the United States. Although it can affect any human, it is more common in children.
Pinworms live in the general area of the body known as the rectum (lower part of intestine). The small, thin (threadlike), white pinworm is about 0.4 in (1 cm) in length, with the adult male ranging from 0.04–0.16 in (0.1–0.4 cm) in length and the adult female having a length of 0.32–0.50 in (0.8–1.3 cm). A pinworm possesses a long, pin-shaped posterior, which gives the worm its common name. Pinworms are nematodes in the family Oxyuridae, genus Enterobius. Pinworm infection is most commonly caused by the species Enterobius vermicularis, the threadworm. A second species, Enterobius gregorii, recently has been found to cause the infection in Africa, Asia, and Europe.
The pinworm is a roundworm, which is the common name of any non-segmented worm located in freshwater, marine, or terrestrial environments. Roundworms are found almost anywhere around the world, living frequently in the surface layers of soils.
Pinworms develop to adulthood within the host's intestines, specifically in the lower small intestine and the upper colon. On rare occasions they are found in the abdominal lining, fallopian tubes, liver, uterus, and vagina. Generally, they are not found in the bloodstream or in other organs besides the intestines.
The male pinworm dies after mating. The female moves from the intestine to the anal area where she lays 10,000–20,000 eggs. Within four to six hours, the eggs become mature and, thus, infectious. The female soon expels a sticky substance that causes itching in the host. Intense itching causes the human to transfer eggs to the fingers, which then transfer the eggs to other objects. The eggs can live outside of a host for up to two weeks— in some cases, three weeks. The eggs are often accidentally ingested. The larvae then hatch and move to the intestine. They mature within 30–45 days. Their overall lifespan is about 60 days. The larvae can also hatch outside the host and then move through the anus and into the intestines. In some cases, the eggs become airborne and are inhaled by the host.
Symptoms are usually mild, and sometimes there are no symptoms at all. When present, symptoms include itching, intestinal problems, vomiting, nervousness and irritability, restless sleep, and sometimes skin reddening and infection around the anus. Other than these mild symptoms, the infection usually does not cause permanent damage.
WORDS TO KNOW
HELMINTH: A representative of various phyla of wormlike animals.
HOST: Organism that serves as the habitat for a parasite, or possibly for a symbiont. A host may provide nutrition to the parasite or symbiont, or simply a place in which to live.
LARVAE: Immature forms (wormlike in insects; fishlike in amphibians) of an organism capable of surviving on its own. Larvae do not resemble the parent and must go through metamorphosis, or change, to reach the adult stage.
NEMATODES: Also known as roundworms; a type of helminth characterized by long, cylindrical bodies.
IN CONTEXT: TRENDS AND STATISTICS
The Division of Parasitic Diseases at the Centers for Disease Control and Prevention (CDC) states that “pinworm is the most common worm infection in the United States. School-age children, followed by preschoolers, have the highest rates of infection. In some groups nearly 50% of children are infected. Infection often occurs in more than one family member. Adults are less likely to have pinworm infection, except mothers of infected children. Child care centers, and other institutional settings often have cases of pinworm infection.”
Pinworm infection is found worldwide, although it is found more commonly in temperate regions of Western Europe and North America. It is only occasionally found in tropical areas. The infection is frequently found when humans live in crowded environments. It is estimated that between 200 million and 500 million people world-wide are infected annually. The Division of Parasitic Diseases (DPD) of the National Center for Infectious Diseases (U.S. Centers for Disease Control and Prevention) estimates that approximately 40 million people are infected each year in the United States. About 50% of all children become infected at some time during their childhoods.
In the United States, according to the DPD, pinworm infection is most common in school-age children, followed by preschool-age children and people in institutional care facilities and children at day care facilities. Mothers are also frequently infected.
Diagnosis of pinworm infection is made by an examination of the patient's anal region. A tape test is usually used, which involves placing the sticky side of a transparent adhesive or cellophane tape against the skin around the anus. The procedure should be performed immediately after waking up, before bathing and using the toilet, so that any eggs in the anal area will be picked up. The materials that stick to the tape are then examined under a microscope for the presence of pinworms. The infected person may also see worms crawling on bed sheets or clothing.
Treatment includes various antiparasitic drugs that have been found effective in treating the infection. These drugs include albendazole, mebendazole, piperazine, and pyrantel pamoate. If one person in a household has the infection, all family members are often advised to take the drug treatment.
These medicines kill the worms about 95% of the time. However, they do not kill the eggs. To kill the eggs, a second round of medicine is recommended two weeks after the completion of the first round. If this treatment does not eliminate the infection, then additional treatments should be administered. In addition, a thorough search should be made for the source of the infection, including other children, household members, and anyone or anything else that has come in contact with the infected person. Four to six treatments spaced two weeks apart are sometimes recommended for difficult cases.
To avoid becoming re-infected, an array of hygiene practices are advised, including disinfecting eating utensils and bed linens; cleaning the toilet daily; keeping fingers away from the nostrils and mouth; bathing when first waking; changing and washing underwear daily; changing bed clothing frequently and after each treatment; providing plenty of sunlight or artificial light (pinworms are light sensitive); trimming fingernails (scratching of anal area may place pinworms underneath nails); and not scratching bare anal areas.
When treated properly, pinworm infection is fully curable. Even though the prognosis for pinworm infection is very good, complications can set in. Among the most common complications are salpingitis (pelvic inflammatory disease, an infection of the lining of the uterus, fallopian tubes, or ovaries), vaginitis (any infection or inflammation of the vagina), and reinfestation (further reoccurrence of the infection).
Children who are being treated for pinworm infection need not be kept home from school, and it is not appropriate to conclude that a child with pinworms has an unclean environment. Pinworm infections are extremely common among children, with half of all children eventually becoming infected due to the large amount of time spent outdoors playing in dirt and sand. Parents can minimize the chances of their children getting the infection by promoting handwashing and sanitation within and outside the home. Prompt medical care, medication, and preventive hygiene practices will eliminate pinworms from children and adults in a quick and safe manner.
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KidsHealth for Parents. “Infections: Pinworm.” April 2005. <http://www.kidshealth.org/parent/infections/parasitic/pinworm.html> (accessed March 16, 2007).
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