Smallpox was a uniquely human disease, caused by the virus variola. It was deadly infection, killing hundreds of millions during the 20th century before the virus was successfully eradicated among humans. The characteristic result was blistering on the skin, resulting in residual pock marks, especially on the face, among those who survived. There is evidence that it appeared among humans probably around 10,000 B.C., although the molecular clock puts its appearance, as a variation of a virus found in rats, much earlier.
The earliest procedure for the prevention of smallpox was inoculation, which is the process of deliberately introducing the body to the virus so as to boost the immune response and prevent a full outbreak. Since it nevertheless involved exposure to the real virus, it carried the possibility of transmitting the disease inadvertently and perhaps causing death. This made inoculation very controversial, although the death rate after inoculation was far below that experienced in epidemics.
Cotton Mather, mostly known for regressive ideas, advocated inoculation, also known as variolation. An avid reader, he came across a description of the method as practiced in Turkey and advocated to the Boston physician Zabdiel Boylston that he inoculate his patients. Boylston inoculated his own son in 1721. Although opposition and even mob violence developed, the death rate among those inoculated that year was a small fraction of those who were untreated.
Vaccination, the use of a similar virus from a cow (Latin vacca), produced the same immunity without the risk. It was introduced into America by another Boston physician, Benjamin Waterhouse, who followed Boylston`s precedent and first vaccinated his own son. Thomas Jefferson, who vaccinated his own family and some of his neighbors near Monticello.
Smallpox was eradicated in the late 20th century. At mid-century, around 20 million cases were occurring annually with some two million deaths. The World Health Assembly resolved in the late 1950`s to undertake a global program to eradicate the disease. An aggressive policy of locating outbreaks and isolating them was undertaken. The last European outbreak was in Yugoslavia in 1972; the last naturally occurring case worldwide was in 1977.