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Yersinia pestis bacteria are found in animals throughout the world, most commonly in rats but occasionally in other wild animals, such as prairie dogs. Most cases of human plague are caused by bites of infected animals or the infected fleas that feed on them. In almost all cases, only the pneumonic form of plague can be passed from person to person.​


A healthcare provider can diagnose plague by doing laboratory tests on blood or sputum, or on fluid from a lymph node, from an infected person.


If a healthcare provider suspects plague and diagnoses it early, they can prescribe specific antibiotics.

Untreated bubonic plague bacteria can quickly multiply in the bloodstream causing septicemic plague, or even move to the lungs, causing pneumonic plague.



Health experts recommend antibiotics if you have been exposed to wild rodent fleas, during a plague outbreak in animals, or to a possible plague-infected animal. Because there are so few cases of plague in the United States, experts do not recommend taking antibiotics unless it's certain a person has been exposed to plague-infected fleas or animals.


Currently, there is no commercially available vaccine against plague in the United States.

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Last Updated May 20, 2015