Smallpox (variola) no longer is an active infection. Its virus exists only in laboratories. It was an acute viral disease usually transmitted by airborne droplets and entering the body through the upper respiratory tract. It infected as many as 90 percent or more of people at risk. It affected all races, and neither age nor gender seems to have influenced susceptibility directly. There never was a cure, but during its last decades of existence antibiotics were often prescribed to prevent or limit secondary infections. Closely related diseases exist, like cowpox and monkeypox, but smallpox appears to have been an exclusively human infection. Virologists recognized two kinds of smallpox: Variola major, with a mortality rate commonly of 25 to 30 percent; and Variola minor, with mild symptoms and a death rate of 1 percent or less. The characteristics of smallpox viruses varied over the centuries, and strains intermediate in virulence between V. major and V. minor in all probability existed. The worst strains, of course, attracted the most attention, and the recorded history of smallpox is for the most part a history of V. major.

Etiology and Epidemiology

Within the range of recorded history, as far as we know, the source of smallpox was always a human being with the infection. There was no animal reservoir. The virus could survive in scabs for considerable periods, and laundry workers on occasion contracted the disease from clothing and bedding of smallpox patients, but most transmissions were airborne and occurred over distances of no more than a few meters.