Chickenpox is caused by the Varicella zoster virus. Like measles, it is very infectious and transmitted from person to person by droplet spread. Chickenpox is most infectious at the time that the rash starts. Following chickenpox, the same virus may remain silent (dormant) in the body for many years before being reactivated to result in shingles (acute pain and vesicular rash affecting only part of the body). Children can therefore also be infected and get chickenpox from an adult with shingles.