Smallpox is a serious and often fatal viral infection. It is contagious - meaning it can spread from person to person - and can cause permanent scarring. Sometimes, it causes disfigurement. The first symptoms of chickenpox usually appear 12 to 14 days after you are exposed to the chickenpox virus. However, the virus can stay in your body for 7 to 19 days before you start to look or feel sick. This period is called incubation period. After the incubation period, sudden flu-like symptoms appear. Besides:

• fever

• Muscle aches

• headache

• Severe fatigue

• Severe back pain

• Vomiting, sometimes

After a few days, flat, red spots appear on the body. They can start in the mouth and on the tongue and spread to the skin. The face, arms and legs are often affected first, followed by the torso, arms and legs. After a few days, flat, red spots appear on the body. They can start in the mouth and on the tongue and spread to the skin. The face, arms and legs are often affected first, followed by the torso, arms and legs.