Chickenpox, also known as VARICELLA, is a highly contagious viral infection that is characterized by an itchy rash with blisters. It is caused by the VARICELLA-zoster virus and is most common in children, although adults can also be affected. Symptoms usually last for about two weeks and can include fever, fatigue, and loss of appetite. Treatment typically involves rest and over-the-counter medications to reduce itching and discomfort.