Smallpox is a potentially deadly infection caused by the variola
virus. The infection causes severe illness, including a high fever, followed by a rash all over the body that looks like blisters.
Smallpox symptoms develop about 12 days after exposure. The disease
usually is not contagious until the rash first appears. As scabs form, the chance of
passing on the disease decreases.
Smallpox was a worldwide problem in the past. But because of a widespread
vaccination program, it was declared eradicated (no longer a naturally occurring
disease) by the World Health Organization (WHO) in 1980.
There may be
a risk that the smallpox virus could be stolen by people in order to
threaten or harm others.