This digitally colorized image shows the yellow-colored Yersinia pestis bacteria, the pathogen that causes bubonic plague, on part of a flea's digestive system. National Institute of Allergy and Infectious Diseases via CDC hide caption

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Gerbils are harmless... Right? Peter Knight/Flickr hide caption

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Mary Mallon, known as "Typhoid Mary," was immune to the typhoid she carried. Working as a cook, she spread the disease in New York and ended up quarantined on Brother Island (above) for more than two decades. Bettmann/Corbis hide caption

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Graduate student Jennifer Klunk of McMaster University examines a tooth used to decode the genome of the ancient plague. Courtesy of McMaster University hide caption

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Yoset, a spiritual healer near Arua, Uganda, works with the Centers for Disease Control and Prevention to detect the plague in his village. Courtesy of Mary Hayden hide caption

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A copper engraving from 1656 shows a plague doctor in Rome wearing a protective suit and a mask. Artwork by Paul Furst /Wikimedia.org hide caption

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Victims of the plague are consigned to a communal burial during the Plague of London in 1665.

Universal Images Group/Getty Images hide caption

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