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smallpox, also called variola major, acute infectious disease that begins with a high fever, headache, and back pain and then proceeds to an eruption on the skin that leaves the face and limbs covered with cratered pockmarks, or pox. For centuries smallpox was one of the world’s most-dreaded plagues, killing as many as 30 percent of its victims, most of them children. Those who survived were permanently immune to a second infection, but they faced a lifetime of disfigurement and in some cases blindness. But smallpox was also one of the first diseases to be controlled by a vaccine, particularly
Smallpox is caused by infection with variola major, a virus of the family Poxviridae. (A less-virulent form of smallpox, called alastrim, is caused by a closely related virus known as variola minor.) There are no natural animal carriers nor natural propagation of variola outside the human body.
History
The history of smallpox is uncertain. Genetic analyses of viral DNA isolated from a mummified child who had been interred in a church in Lithuania suggest that variola virus had evolved by at least the 17th century. It is likely, however, that the virus was circulating in human populations much earlier, based on the recovery of variola virus DNA from teeth and bones of human remains dated to 600–1050 that were uncovered in the region of modern-day Denmark and Russia. Prior to that discovery, the disease had been thought by some scholars to have arisen among settled agricultural populations in Mesopotamia as early as the 5th millennium bce and in the Nile River valley in the 3rd mil