Dr. Greene’s Answer:
The pinworm, or Enterobius vermicularis, is one of the most common parasitic infections of humans. Somewhere between 10% and 40% of children have pinworms at any given time (Pediatric Consult, Williams and Wilkins 1997). The infections are usually limited to children below the age of twelve.
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 testical, 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.
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 (Parasitic Diseases, Springer-Verlag 1982). 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. The girls who develop vaginal pinworm infections often develop vaginal itching and sometimes a vaginal discharge. Attempts to link pinworm infection to bed wetting or grinding of the teeth have been unsuccessful.
Stool and blood tests are not very helpful in diagnosing pinworms. Seeing a worm clinches the diagnosis. Check your child’s skin with a flashlight during the night and first thing in the morning. Look for white, wiggling threads. If it’s not wiggling, it’s probably just lint. Occasionally a wiggling worm will be seen on the surface of a stool. Pinworms are so common that children with nighttime anal itching are often treated without any lab test at all. The classic diagnostic tool is to apply a piece of transparent tape to the skin near the anus first thing in the morning. This tape can then be attached to a glass slide and examined under a microscope for the presence of eggs. Your doctor can supply you with a pinworm lab kit, if necessary.
Treatment is with a single dose of an anti-pinworm drug such as Vermox (mebendazole). Vermox comes as a chewable tablet. Most children and adults experience no side effects. Hives or other allergic rashes have been reported only rarely. Very rare cases of convulsions have occurred. This medicine kills the worms 95% of the time, but does not kill the eggs. Hence, retreatment in two weeks is a good idea. Girls with vaginal itching alone do not necessarily need treatment, since the problem will often disappear on its own.