Enterobius vermicularis are very hard to control and get rid of, for reasons that will soon become apparent. First off, they can survive in much more temperate climates than most helminths (though they still really like tropical and sub-tropical zones). It doesn't primarily affect low-income people either, the way most worms do. The most important reason pinworms are so common is who is most commonly infected. It's children ages ~2-5, right around the age where they're going to daycare, but before the time that they've (hopefully) learned proper hand washing and sanitation techniques. This is because pinworms eggs are spread when people scratch their peri-anal region (aka their butt) and then touch other people/surfaces without washing their hands!
The lifecycle of the pinworm is quite simple. They are small worms, rarely reaching more than 13mm long. The worms mate in the small intestine, and the females settle themselves in the intestinal mucosa down by the colon. Here they live happily, rarely causing any problems. Then, the females, drawn by some sort of biological clock, creep out of the colon through the anus, and explode themselves all over the peri-anal region, leaving sticky egg clusters in their wake. (Hope you weren't eating while reading that bit of info).
Pinworms are easily identifiable from their esophagus. It has a distinct corpus- isthmus-bulb structure, which is easily seen under a microscope.
These egg clusters then itch quite a bit, causing the infected host to scratch. The sticky eggs rapidly form into infective L3 larva, which attach to the hosts fingers, where they can then be swallowed again to repeat the lifecycle, or passed onto others. The larva are quite robust, and can survive for several days hanging out on places like doorknobs and telephones. This means that re-infection is very likely, as is infection of the whole household.
It's very rare to see adult worms outside of the body, as they mostly explode once they leave. In many cases, the only symptom is very scientifically described as "itchy butt". However, in small children it may also present as irritability and insomnia. In other words, exactly how little kids act all the time.
If one suspects a pinworm attack, you can check yourself at home, so long as you have a microscope. Simply apply some clear scotch tape to the peri-anal region, preferably in the morning before bathing has occurred, and then examine it under a microscope. The eggs are very clearly visible in clusters. They are think shelled and oval shape, typically flattened on one side. It may be possible to see the developing larva inside the egg.
Prevention includes frequent hand washing and education. Clearing up these infections can take a while, because the chances for re-infection are so high. However, repeated doses of Albendazole or Mebendazole over a few weeks should be sufficient!
Severe problems only occur with pinworm infections when the adult females accidentally migrate too far, and re-enter the body via the vagina. There, the females and their eggs can cause a granulomatous lesion which can obstruct fallopian tubes. However, most people with pinworms are asymptomatic!
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