Varicella, also known as chickenpox, is a very common and highly infectious childhood disease that is found worldwide. Symptoms appear 10 to 21 days after infection and last about 2 weeks. The defining symptom is a characteristic blister-like rash, which can cause severe irritation. Most children have a relatively mild illness, but severe illness may occur in adults and people with depressed immunity because of existing illness or because of a treatment that they are receiving (e.g. chemotherapy).
Source : Public Health Agency of Canada