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Smallpox was an infectious disease caused by either of two virus variants, Variola major and Variola minor. The disease is also known by the Latin names Variola or Variola vera, derived from varius or varus. The disease was originally known in English as the \"pox\" or \"red plague\"; the term \"smallpox\" was first used in Britain in the 15th century to distinguish variola from the \"great pox\". The last naturally occurring case of smallpox was diagnosed on 26 October 1977.

Infection with smallpox is focused in small blood vessels of the skin and in the mouth and throat before disseminating. In the skin it results in a characteristic maculopapular rash and, later, raised fluid-filled blisters. V. major produced a more serious disease and had an overall mortality rate of 30–35 percent. V. minor caused a milder form of disease which killed about 1 percent of its victims. Long-term complications of V. major infection included characteristic scars, commonly on the face, which occur in 65–85 percent of survivors. Blindness resulting from corneal ulceration and scarring, and limb deformities due to arthritis and osteomyelitis were less common complications, seen in about 2–5 percent of cases.

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