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.
At night, the female worm leaves her home in an infected person's lower intestinal tract. She slips out of her host's rectum and lays eggs in the folds of skin around the edge of the anus. The eggs are deposited in a sticky, jelly-like substance that, along with the wriggling of the mother pinworm, causes severe itching. The eggs can be transferred to the fingers, either by directly scratching the anal area or by way of clothing or bedding. They can then be carried to the mouth and swallowed or can be transmitted to others by touch.
Since the eggs can survive for up to 20 days, they might be found in bedding and clothing. If these materials are shaken, it is even possible to spread the eggs in the air and swallow them directly. Once eaten, the eggs hatch in the intestine and develop into adult worms within 2 to 6 weeks. Adult worms can live for approximately 3 months and an adult female can lay more than 10,000 eggs in her lifetime.
Pinworm eggs attached to the skin around the anus hatch within 6 hours, and the emerging larvae migrate back into the anus to reside and mature within the lower intestine. For the eggs that fell off onto adjacent clothing or bedding, they can survive for as long as 3 weeks at room temperature - waiting for unsuspecting hands to carry them into the mouth. Humans are the only natural host of pinworms.
Pinworms mainly infest children 5 to 10 years old, most of whom have no symptoms apart from itching around the anus, which may then become raw from scratching. Pinworms are uncommon in children less than 2 years old. In girls, pinworm infection can cause vaginal itching and irritation (vaginitis).
In severe cases, weight loss, restlessness, irritability, and loss of appetite may occur. In a few rare cases, attacks of appendicitis may have been caused by pinworms blocking the appendix.