Living in the large intestine, pinworm Enterobius vermicularis infestations may be asymptomatic or result in mild irritations of the gastrointestinal tract. A common symptom of a pinworm infestation is perianal itching associated with the nocturnal egg-laying habits of pinworm, which is complicated by secondary bacterial infections associated with scratching. Children, the most commonly infected subpopulation because of close proximity in daycare and classroom situations, and often poor sanitary habits, undergo noticeable changes associated with pinworm parasitic loads including irritability, insomnia, and restlessness. With women as hosts, adult pinworms can also enter the vagina and cause additional discomfort.
Mature female pinworms are about twice as long as the 5-millimeter-long males, which live only until copulation occurs. When she is ready to lay her 10,000 plus eggs, the female nematode crawls out of the host's anus, deposits the eggs on the perianal skin, and then dies. The eggs develop rapidly and reach their third juvenile stage as infective eggs in approximately 6 hours. The eggs are ingested by another human host and hatch in the small intestine. In about a month, the parasitic nematodes reach maturity and reproduce sexually, reinitiating the life cycle.
The pinworm is the most common nematode parasite of humans in North America and Europe. Pinworms infect more than 400 million people worldwide.