What is chickenpox?
Chickenpox is a highly contagious illness
caused by the varicella-zoster virus (VZV), a type of herpes virus. It is often a mild illness, characterized by an itchy rash on the face, scalp and trunk with pink spots and tiny fluid-filled blisters that dry and become scabs four to five days later. Serious complications, although rare, can occur mainly in infants, adolescents, adults and persons with a weakened immune system. These complications include bacterial infections of skin blisters, pneumonia, and encephalitis (inflammation of the brain). In temperate climates, such as the Northeast, chickenpox occurs most frequently in the late winter and early spring.
http://www.health.state.ny.us/diseases/communicable/chickenpox/fact_sheet.htm