Enterobius Vermicularis


Enterobius Vermicularis is the scientific name for the human pinworm.  Pinworms are very common, especially in children and especially in daycare situations.  This is because of the life cycle of the pinworm, which relies completely on ingestion of the pinworm eggs to maintain the active infestation state.  The lifespan of an individual pinworm is relatively short, a couple of months, so if no additional eggs are ingested the worms in a particular person just die off.  Not to fear, the worm has a great mechanism that leads to repeated egg ingestion and ongoing infection.

First though let’s look at how to tell if you have pinworms and how to treat them.  Pinworms live in the human intestine, and the mature female worms migrate from their home in the very distal small bowel down the colon and lay their eggs on the skin around the anus.  These eggs and the worms themselves cause itching, and as a child itches they tend to scratch, getting the eggs on their hands.  Children are always putting their hands in their mouth, and so ingest eggs that get on their fingers from the itching.  To diagnose pinworms a parent needs to use a flashlight to look at the anal area of their child during the night when the worms tend to come out to lay their eggs.  The worms are about the size of a common pin, hence their name, and are whitish colored.

If peri-anal itching and scratching are noted, but no worms seen on a nighttime search or two, a test called the scotch tape test.  This is a way to pick up the eggs from the peri-anal area and bring them to the office for a physician to look at microscopically and confirm the diagnosis.  A parent simply applies scotch tape to the anus and peri-anal skin in the morning and sticks the tape to a microscope slide. The eggs are easy to see on the slide under a microscope, and the diagnosis is confirmed.  Treatment is easy.  Mebendazole in a single 100 mg chewable tablet dose is usually effective to kill the worms of this infection.  Unfortunately reinfection is common, and it is recommended that the whole family be treated at the same time.

The life cycle of Enterobius vermicularis is simple yet amazing.  The eggs are simply ingested and after ingestion the eggs hatch in the upper small bowel called the duodenum.  The larvae migrate to the distal small bowel and the proximal colon where after maturing they mate.  The males die after mating, and the females remain in this area while the eggs mature.  After the eggs mature the females migrate down the colon to lay the eggs on the skin of the perineum.  They females die after laying their eggs.  The whole lifespan of a pinworm is about 2 months.   The worms and the eggs tend to cause a reaction in the perianal skin that induces itching and scratching.  This can facilitate the eggs getting on the fingers of the infected individual and from there being passed to others as well as being reingested by the infected person themselves.

Other symptoms of pinworms in girls can be a vaginal itching and irritation if the worms accidentally crawl into the vagina or lay eggs on the area around the external genitals.   Also on girls urinary symptoms can occur if the pinworms migrate into the urethra and deposit eggs or die there.

In summary pinworms is a common but relatively benign condition that usually affects children but can also affect adults.  Treatment is simple and easy, but recurrent infection is common, so eradication of the problem can be frustrating.