Variola virus (or variola major virus) is the virus that causes smallpox. The virus is one of the members of the poxvirus group (Family Poxviridae). The virus particle is brick shaped and contains a double strand of deoxyribonucleic acid. The variola virus is among the most dangerous of all the potential biological weapons.

Variola virus infects only humans. The virus can be easily transmitted from person to person via the air. Inhalation of only a few virus particles is sufficient to establish an infection. Transmission of the virus is also possible if items such as contaminated linen are handled. The various common symptoms of smallpox include chills, high fever, extreme tiredness, headache, backache, vomiting, sore throat with a cough, and sores on mucus membranes and on the skin. As the sores burst and release pus, the afflicted person can experience great pain. Males and females of...