An acute, extremely infectious disease, usually contracted by young children. Chicken pox is caused by the varicella virus. The infection is characterized by a fever and itchy, red spots usually appearing on the chest and stomach first, then appearing in crops over the entire body. The red spots turn into small blisters that dry up and form scabs over about a week. They occasionally cause scarring (particularly if scratched) or if they become infected with bacteria. A vaccine has been available for this disease in the US since 1996.