Related concepts:

Worms, Nematodes, Enterobiasis, Enterobius vermicularis

Introduction to pinworms:

Although adults often shudder at pinworm infections, most kids don't have this same gut response. In any case, pinworms are mostly harmless and inhabit people in every socioeconomic group and culture.

What are pinworms?

The pinworm, or Enterobius vermicularis, is one of the most common parasitic infections of humans. Somewhere between 10 percent and 40 percent of children have pinworms at any given time.

The adult pinworms are white and measure less than one half inch long, with the diameter of a strand of thread. These tiny roundworms are quite complex. Like us, they have mouths, throats, and gastrointestinal tracts. Like us, they have nervous systems. The females have a vagina, a uterus, and ovaries. The males have a testicle, vas deferens, seminal vesicle, and ejaculatory duct. They eat, drink, pee, poop, and reproduce sexually.

The adult worms live in the colons (large intestines) of human children and apparently feed on human fecal matter.

When adult male and female worms copulate, each female pinworm produces about 10,000 fertilized eggs. At night, the pregnant female migrates from the colon, out through the child's anus and onto the skin of the buttocks. There she violently expels all of her eggs and dies. Some of the eggs become airborne and land elsewhere in the child's room, but the great majority of the fertilized eggs stay on the skin of the child's buttocks. The eggs mature within six hours of being laid.

The adult worms and the eggs on the skin of the buttocks can cause intense itching in the child. When the sleeping child scratches, the eggs often get on the fingers and under the fingernails. If the child sucks his or her thumb or otherwise brings his or her hand to the mouth (perhaps while eating breakfast), the pinworm eggs are swallowed. They usually hatch within the small intestine and mature there. When they become adults, they move to the colon where they take up residence. The entire life cycle lasts four to six weeks.

Occasionally the story goes a little differently. Sometimes a child can inhale airborne eggs and become infected that way. Every now and then the eggs will hatch on the skin of the buttocks, and the immature larvae will crawl back through the anus, up into the rectum and eventually arrive in the colon. Also, the eggs can hatch on the skin of girls and the larvae crawl into the vagina instead of the rectum. This happens in up to 20% of girls with pinworms. The vaginal pinworms usually die out with no outside help.

Who gets pinworms?

Pinworms are found worldwide and can affect people of all ages, although the great majority of cases occur before age 12. Pinworms occur in all socioeconomic groups, but are more common wherever children are in close contact with each other.

What are the symptoms of pinworms?

Most children with pinworms have no symptoms at all. In the same way that many bacteria live in our intestines without making us sick, pinworms can live happily in our intestines without causing any problems. Since the pinworm almost always stays in the gastrointestinal tract (or vagina), there is usually no systemic illness.

Some children, however, develop nighttime itching of the skin around the anus. For a small number of these children, the itching can be quite intense.