Man with Smallpox in isolation, 1890. Smallpox is an acute, infectious viral disease transmitted by direct contact with infected people. Fever symptoms commence 8-18 days after exposure. After 3 days, red spots appear on the face and body and develop into pea-size pustules. Scabs formed by the drying of the pustules leave permanent scars. Most patients recover, but nephritis and pneumonia occur as complications.