Smallpox is fatal in 30% of cases. Early symptoms include high fever and fatigue. Later, the virus causes a characteristic rash, especially on the face, arms, and legs. The spots become filled with clear fluid, turn to pus, and then form a crust, which eventually dries and falls off.

Smallpox is a disease caused by a virus. The initial symptoms of the disease such as fever, rash... are easily confused with other infectious diseases.