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The epidemiology, pathogenesis, and clinical manifestations of smallpox

Harvey M Friedman, MD
Stuart N Isaacs, MD
Section Editor
Martin S Hirsch, MD
Deputy Editor
Jennifer Mitty, MD, MPH


Variola virus is the causative agent of smallpox, a highly infectious disease characterized by fever, rash, and a high mortality rate that was eradicated globally by 1979 through a program that included widespread immunization [1]. In the past, smallpox accounted for 10 percent of all deaths in the world.

The virology, pathogenesis, epidemiology, clinical manifestations, and treatment of smallpox will be reviewed here. Issues related to bioterrorism and vaccinia virus vaccination for the prevention of smallpox are discussed separately. (See "Vaccinia virus as the smallpox vaccine".)


The global eradication of smallpox was announced in 1979, marking one of the greatest achievements of modern medicine [1]. An unusual combination of factors facilitated eradication [2]:

Human beings were the only known reservoir for the virus

No asymptomatic carrier state existed

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Literature review current through: Nov 2017. | This topic last updated: Aug 13, 2017.
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