Smallpox is one of the most potent bio-terror weapons available.
It is a highly contagious disease that is unique to humans and
caused by the Variola virus. Smallpox transmission generally occurs
through face-to-face contact, direct contact with contaminated
fluids and objects, and through the air. About 30 percent of those
who become infected with smallpox die from the illness.
However, it is anticipated that transmission rates and
mortality would be much higher if the virus was used in a
deliberate attack today, as the immunity in the population is
extremely low and dropping day by day. Few illnesses have had as
profound an effect on human health as smallpox. In the 20th century
alone, an estimated 300 million people died of smallpox.