Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. One such highly contagious viral disease is chickenpox, caused by primary infection with varicella zoster virus (VZV). It usually starts with vesicular skin rash mainly on the body and head rather than at the periphery and becomes itchy, raw pockmarks, which mostly heal without scarring. Chickenpox is an airborne disease spread easily through coughing or sneezing of ill individuals or through direct contact with secretions from the rash. A person with chickenpox is infectious one to two days before the rash appears and remains contagious until all lesions have crusted over, which usually takes approximately six days. Learn more about chickenpox, its effects on human health and the virus that causes the illness in this book.