The pinworm, or Enterobius vermicularis, is a small parasitic worm that can live inside the human lower intestine. Only 3 mm to 10 mm long, it causes an intense itching in the area of an infected person's anus, especially at night.
Pinworms usually infect people as a result of overcrowding in schools and family groupings or due to unsanitary living conditions and poor food preparation. However, they usually don't indicate poor personal hygiene. They can be commonly found in institutional settings such as dormitories and mental health hospitals or homes.
They're the most common parasite to affect North American children, with estimates that one-third of Canadian children will have pinworms at some time in their life.