Smallpox was an infectious disease caused by one of two virus variants, variola major and variola minor. The last naturally occurring case was diagnosed in October 1977 and the World Health Organization certified the global eradication of the disease in 1980. The risk of death following contracting the disease was about 30%, with higher rates among babies. Often those who survived had extensive scarring of their skin and some were left blind.
The initial symptoms of the disease included fever and vomiting. This was followed by formation of sores in the mouth and a skin rash. Over a number of days the skin rash turned into characteristic fluid filled bumps with a dent in the center. The bumps then scabbed over and fell off leaving scars. The disease used to spread between people or via contaminated objects. Prevention was by the smallpox vaccine. Once the disease had developed certain antiviral medication may have helped.
The origin of smallpox is unknown. The earliest evidence of the disease dates back to the 3rd century BC in Egyptian mummies. The disease historically occurred in outbreaks. In 18th century Europe it is estimated 400,000 people per year died from the disease, and one-third of the cases resulted in blindness. These deaths included those of at least five reigning monarchs. In the 20th century it is estimated that smallpox resulted in 300–500 million deaths. As recently as 1967, 15 million cases occurred a year.
There were two clinical forms of smallpox. Variola major was the severe and most common form, with a more extensive rash and higher fever. Variola minor was a less common presentation, and a much less severe disease, with historical death rates of 1 percent or less. Subclinical (asymptomatic) infections with variola virus were noted but were not common. In addition, a form called variola sine eruptione (smallpox without rash) was seen generally in vaccinated persons. This form was marked by a fever that occurred after the usual incubation period and could be confirmed only by antibody studies or, rarely, by virus isolation.