Smallpox (also known by the Latin names Variola or Variola vera) is a highly contagious disease unique to humans. It is caused by two virus variants called Variola major and Variola minor. V. major is the more deadly form, with a typical mortality of 20-40 percent of those infected. The other type, V. minor, only kills 1% of its victims. Many survivors are left blind in one or both eyes from corneal ulcerations, and persistent skin scarring - pockmarks - is nearly universal. ...