Smallpox, which is caused by the variola virus of the Poxviridae family and the orthopoxvirus genus, is among the most devastating human diseases. It may have originated and spread from Egypt, the Near East, or the Indus Valley 3000 to 4000 years ago, and historical reports indicate epidemics in China as early as the first century A.D. and in Europe during the 6th century. By the mid-18th century, smallpox was a worldwide endemic disease. It was eradicated after vaccination campaigns began more than 200 years ago.
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