Smallpox, a contagious disease produced by the variola virus (genus Orthopoxvirus), was eradicated in 1977. The word smallpox is believed to come from the Latin word pocca meaning ‘pouch,’ and variola from varius or varus meaning ‘spotted pimple.’ There were three subspecies of variola: variola major, intermedius, and minor. The milder form of the disease, variola minor, had a case-fatality rate of less than 1%, whereas the rate for variola major was 25% to 50%. Ten percent of the smallpox cases involved hemorrhagic smallpox that was quickly fatal.

Smallpox was found only in humans and was usually transmitted through droplet nuclei, dust, and fomites (inanimate objects such as blankets that can transmit germs). The incubation period was between 12 and 14 days, with the respiratory tract ...

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