A clinically extinct viral infection, brought to the fore by recent fears of bioterrorism. It is a highly
contagious disease characterized by fever, pustular erruption, and a 20% mortality rate. Global erradication was officially announced in 1979. The virus infects the oropharynx and spreads by
inhalation. A minor illness caused by the same virus is called variola minor, with less than 1%
mortality. Previously vaccinated persons  may get infected and develop fever only without skin pustules.
The mean incubation period is 12 days. Vomiting occurs in 50% of patients, diarrhea in 10%. Rash first
appears as minute red spots on the tongue, then spreads to the face, arms, trunk then legs. Distinguishing
smallpox from chickenpox may be a problem. Vaccination during the first week of incubation reduces
the severity of the disease.