Smallpox is a potentially deadly infection caused by the variola virus. It causes severe illness including a high fever, and is followed by a blisterlike body rash.

Smallpox symptoms develop about 12 days after exposure. The disease is not contagious until the rash first appears. As scabs form, the chance of passing on the disease decreases.

Smallpox was once a worldwide problem, but due to a widespread vaccination program, was declared eradicated (no longer a naturally occurring disease) by the World Health Organization (WHO) in 1980. However, there may be a risk that the smallpox virus could be manufactured by people in order to threaten or harm others.