Chicken pox, also spelled chickenpox, is a common childhood disease caused by the varicella-zoster virus (VZV), also known as human herpes virus 3 (HHV-3), one of the eight herpesviruses known to affect humans. It is characterized by a fever followed by itchy raw pox or open sores.
The disease is rarely fatal: if it does cause death, it is usually from varicella pneumonia, which occurs more frequently in pregnant women. In the US, 55% of chicken pox deaths were in the over-20 age group. Chicken pox has a two week incubation period and is highly contagious by air transmission two days before symptoms appear. Therefore chicken pox spreads quickly through schools and other places of close contact. Once someone was infected with the disease, they usually develop an immunity and cannot get it again. As the disease is more severe if contracted by an adult, parents have been known to ensure that their children became infected before adulthood. Aspirin shouldn't be used during a chickenpox infection because it can increase the incidence of a potentially deadly condition called Reye's syndrome.
Doctors advise that pregnant women who come into contact with chickenpox should contact their doctor immediately as the virus can cause serious problems for the fetus.
Later in life, virus remaining in the nerves can develop into the painful disease, shingles. A chicken pox vaccine is now available, and is now required in some countries for children to be admitted into elementary school. In addition, effective medications (e.g., acyclovir) are available to treat chicken pox in healthy and immunocompromised persons.
One history of medicine book claims that Giovanni Filippo (1510 - 80) of Palermo gave the first description of varicella (chicken pox). Subsequently in the 1600s, an English physician named Richard Morton described what he thought was a mild form of smallpox as "chicken pox." Later, in 1767, a physician named William Heberden, also from England, was the first physician to clearly demonstrate that chicken pox was different from smallpox. However, it is believed that the name chicken pox was commonly used in earlier centuries before doctors knew what they were seeing.  (http://www.familyeducation.com/experts/advice/0,1183,25-26758,00.html)
There are many explanations offered for the origin of the name chicken pox, from the idea that the specks that appeared looked as though the skin was picked by chickens to that the disease was named after chick peas, from a supposed resemblance of the seed to the lesions. The simplest explanation is probably that offered by Samuel Johnson, that the disease was "no very great danger" thus a "chicken" version of the pox.