The variola virus, commonly known as smallpox, was eradicated from the world
in 1977, except for stocks of it kept in two World Health Organization reference labs.
It is unknown whether it is being held in other labs in violation of WHO policy.
Smallpox comes in two forms: variola minor or the more deadly variola major.

HOW DOES IT SPREAD?
The smallpox virus is relatively stable and the dose required for infection is
small, making it a candidate for aerosol release. It could then be further
spread by the saliva droplets of infected people.

SYMPTOMS:
The incubation period is about 12 days following exposure. Symptoms include
fever, fatigue and aches, followed by a rash with lesions and can lead to death
within the first two weeks of the illness.

TREATMENT: No proven treatment at this time.

PREVENTION: Vaccine

SOURCE: CDC