Contributor: Don Stader, MD Educational Pearls: Yersinia Pestis is the bacteria that caused the black plague. It was first discovered to be the cause of the bubonic plague in 1800s in China during the 3rd bubonic plague where 10-20 million people died Causes 3 types of plague: Bubonic plague: characterized by severe swelling of lymph nodes called buboes, most commonly in the groin, also axillary and olecranon lymph nodes. Septicemic plague: characterized by severe sepsis, no lymphadenopathy. This strain famously causes disseminated intravascular coagulopathy (DIC) and can lead to limb necrosis and fingers turning black. Hence the name the Black Death. Pneumonic: most dangerous of the plagues and characterized by PNA on CXR with pronounced mediastinal lymphadenopathy  Fleas are the largest reservoir, although prairie dogs and squirrels have been known to carry the bacteria as well. Yersinia Pestis creates a microfilm inside the stomach of fleas and renders them incapable of digesting your blood when they try to eat it and they vomit the bacteria into your blood. Doxycycline and Ciprofloxacin are the mainstay of treatment. References Achtman M, Zurth K, Morelli G, Torrea G, Guiyoule A. Carniel E. Yersinia pestis, the cause of plague, is a recently emerged clone of Yersinia pseudotuberculosis. Proc Natl Acad Sci U S A. 1999. doi:10.1073/pnas.96.24.14043 Galimand M, Carniel E, Courvalin P. Resistance of Yersinia pestis to Antimicrobial Agents. Antimicrob Agents Chemother. 2006;50(10):3233 LP - 3236. doi:10.1128/AAC.00306-06 Sexton D, Stout J. Clinical Manifestations, Diagnosis, And Treatment Of Plague (Yersinia Pestis Infection). Waltham, MA: UpToDate; 2020.   Summarized by Mason Tuttle & Jackson Roos, MS4 | Edited by Erik Verzemnieks, MD