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 ("spotted") or varus ("pimple"). 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" (syphilis).