A Bangladeshi child infected with smallpox, 1973. In ordinary type smallpox the bumps are filled with a thick, opaque fluid and often have a depression or dimple in the center. This is a major distinguishing characteristic of smallpox. The last naturally occurring case of smallpox was diagnosed on 26 October 1977, and in 1979 the World Health Organization declared the disease eradicated.Photo: Centers for Disease Control and Prevention