The varicella zoster virus (VZV) is transmitted via droplets, aerosol or direct contact, or indirectly by touching freshly soiled contaminated items. Patients are usually contagious from a few days before onset of the rash until the rash has crusted over.
Varicella (“Chickenpox”) is an acute, highly contagious disease. In temperate climates most cases occur before the age of 10 years. While mostly a mild disorder in childhood, varicella tends to be more severe in adults. It is characterized by an itchy, vesicular rash, initially accompanied by fever and malaise. The disease may be fatal, especially in neonates and immunocompromised individuals.
Complications include VZV-induced pneumonitis or encephalitis and invasive group A streptococcal infections.
Source: World Health Organization