chicken pox or varicella, infectious disease usually occurring in childhood. It is believed to be caused by the same herpesvirus that produces shingles. Chicken pox is highly communicable and is characterized by an easily recognizable rash consisting of blisterlike lesions that appear two to three weeks after infection. Usually there are also low fever and headache. When the lesions have crusted over, the disease is believed to be no longer communicable; however, most patients simultaneously exhibit lesions at different stages of eruption. Chicken pox is usually a mild disease requiring little treatment other than medication to relieve the troublesome itching, but care must be taken that the rash does not become secondarily infected by bacteria. Pneumonia and encephalitis are rare complications. A vaccine for chicken pox was approved for use in the United States in 1995. The drug acyclovir may be used to treat the disease, particularly in older patients.

or varicella

Contagious viral disease producing itchy blisters. It usually occurs in epidemics among young children, causes a low fever, and runs a mild course, leaving patients immune. The blisters can scar if scratched. The virus that causes chickenpox (varicella-zoster virus) can reactivate years later, causing shingles. Zoster immune globulin (ZIG) can prevent chickenpox in children with leukemia or immunodeficiency disorders who are exposed to the virus. A vaccine has also been developed.

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