Varicella (also known as chickenpox) is an acute infectious disease caused by the varicella-zoster virus.  It is highly contagious and is spread by airborne transmission of droplets from the respiratory tract or from the vesicle fluid of the skin lesions of chickenpox or herpes zoster infection. 

Affected persons present with fever and itchy rash.  The rash usually develops over 5 days with formation of vesicles and appears first on the scalp and face, moves to the trunk and then to the limbs.  The rash occurs mainly over the trunk.  The vesicles are itchy, and then dry up and form a scab in around 3 days. 

Varicella can also cause fever, tiredness, loss of appetite, and headache. 

Varicella is usually a mild disease of childhood. Affected persons usually recover in 2 to 4 weeks. Varicella is more severe in adults and in individuals of any age with impaired immunity.  The disease may be complicated by skin infections, pneumonia, inflammation of the blood vessels, aseptic meningitis, encephalitis and/or spinal cord covering, and infections of the bloodstream, bone, or joints. Infection in early pregnancy may be associated with congenital malformation of the foetus.

Although almost all persons develop lifelong immunity after varicella infection, the virus may remain latent in the body and recur many years later as herpes zoster (shingles).