The pinworm (in the United States of America) (genus Enterobius), also known as threadworm (in the United Kingdom) or seatworm, is a nematode (roundworm) and a common human intestinal parasite, especially in children. The medical condition associated with pinworm infestation is known as enterobiasis, or less precisely as oxyuriasis in reference to the family Oxyuridae.
The pinworm (genus Enterobius) is a type of roundworm, and three species of pinworm have been identified with certainty. Humans are hosts only to Enterobius vermicularis (formerly Oxyuris vermicularis). Chimpanzees are host to Enterobius anthropopitheci, which is morphologically distinguishable from the human pinworm. Hugot (1983) claims there is another species affecting humans, Enterobius gregorii, which is supposedly a sister species of E. vermicularis, and has a slightly smaller spicule (i.e., sexual organ). Its existence is controversial however; Totkova et al. (2003) consider there to be insufficient evidence, and Hasagawa et al. (2006) contend that E. gregorii is a younger stage of E. vermicularis. Regardless of its status as a distinct species, E. gregorii is considered clinically identical to E. vermicularis.
Pinworms spread through human-to-human transmission, by ingesting (i.e., swallowing) infectious pinworm eggs. The eggs are hardy and can remain viable (i.e., infectious) in a moist environment for up to three weeks. They do not tolerate heat well, but can survive in low temperatures: two-thirds of the eggs are still viable after 18 hours at negative 8 degrees Celsius. After the eggs have been initially deposited near the anus, they are readily transmitted to other surfaces through contamination. The surface of the eggs is sticky when laid, and the eggs are readily transmitted from their initial deposit near the anus to fingernails, hands, night-clothing and bed linen. From here, eggs are further transmitted to food, water, furniture, toys, bathroom fixtures and other objects. Household pets often carry the eggs in their fur, while not actually being infected. Dust containing eggs can become airborne and widely dispersed when dislodged from surfaces, for instance when shaking out bed clothes and linen. Consequently the eggs can enter the mouth and nose through inhalation, and be swallowed later. Although pinworms do not strictly multiply inside the body of their human host, some of the pinworm larvae may hatch on the anal mucosa, and migrate up the bowel and back into the gastrointestinal tract of the original host. This process is called retroinfection. According to Burkhart (2005), when this retroinfection occurs, it leads to a heavy parasitic load and ensures that the pinworm infestation continues. This statement is contradictory to a statement by Caldwelli (1982), who contends that retroinfection is rare and not clinically significant. Despite the limited, 13 week lifespan of individual pinworms, autoinfection (i.e., infection from the original host to itself), either through the anus-to-mouth route or through retroinfection, causes the pinworms to inhabit the same host indefinitely.

Enterobiasis: Human Infection with Pinworms

A pinworm infection or enterobiasis is a human parasitic disease and one of the most common childhood parasitic worm infections in the developed world. It is caused by infestation with the parasitic roundworm Enterobius vermicularis, commonly called the human pinworm. Infection usually occurs through the ingestion of pinworm eggs, either through contaminated hands, food, or less commonly, water. The chief symptom is itching in the anal area. The incubation time from ingestion of eggs to the first appearance of new eggs around the anus is 4 to 6 weeks. Pinworms are usually considered a nuisance rather than a serious disease. Treatment is straightforward in uncomplicated cases, however, elimination of the parasite from a family group or institution often poses significant problems either due to an incomplete cure or reinfection. Pinworm infection has no association with any socioeconomic level, race or culture.

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