The orthopoxvirus Variola virus is the only member species of the Orthopoxvirus genus which is a solely human pathogen.
Variola virus was the only species of smallpox known until late in the nineteenth century, when a new type of mild smallpox, subsequently named Variola minor, was recognized in Southern Africa and the West Indies and later spread to Brazil, North America and parts of Europe.
During the mid 1930s, Ernst Ruska and his colleagues turned the electron microscope they invented to the study of viruses.
In 1958, Dr P von Magnus and his colleagues at the State Serum Institute in Copenhagen discovered an orthopoxvirus from the skin lesions of a cynomolgus monkey during an outbreak of a pox disease in their laboratory monkeys.
It was a new orthopoxvirus, which they called ‘monkeypox virus’.
Variola major and Variola minor were only reliable differentiated in the laboratory in the late 1950s.
A related virus with similar, but distinct characteristics intermediate between Variola major and Variola minor, with fatality rate of about 12, was first distinguished by Bedson and his colleagues in East and West African in 1963. It was labeled as Variola intermedius.
The term variola was derived in AD 570 by Bishop Marius of Avenches (near Lausanne, Switzerland) from the Latin varius, meaning spotted, or perhaps from another Latin term equally descriptive of the disease, varus, meaning pimple.
The original smallpox vaccine was derived from the work of Edward Jenner, a rural physician in 1798, who discovered that scab material from cowpox lesions on dairy cows could be used to inoculate naïve individuals who became immune to infection by variola virus.
Jenner described the clinical signs of cowpox in cattle, and humans and how human infection provided protection against smallpox.
History of Variola virus