Variola virus, a species of Orthopoxvirus
12-14 days (range 7-17 days)
From fever onset (usually 2–4 days before rash) until last scab has separated; about three weeks.
Aerosols/droplets from nasopharyngeal lesions and contact with contaminated articles.
Last naturally acquired human case in the world occurred in Somalia in 1977; global eradication was certified two years later.
There are at least 2 strains, variola major and the variola minor.
- Variola major: the more severe form with case fatality rate up to 30-50% in susceptible populations.
- Variola minor: milder form of the disease with more diminutive pox lesions; case fatality rate of 1-2% in susceptible populations.