Author: John Winkler, MD Educational Pearls: The plague (black death) is caused by the Yersinia Pestis bacteria. This bacteria is spread by fleas and carried by rats. It is very contagious and only needs ~ 100 bacteria to cause an infection.  The pulmonary form presents with cough, fever, night sweats, hemoptysis and has a near 100% fatality rate if not treated in the first day of symptoms The bubonic form causes buboes, which are necrotic, purulent lymph nodes that can lead to sepsis.  Prairie dogs are a common carrier in modern times References https://www.cdc.gov/plague/index.html Summarized by Will Dewispelaere, MS4 | Edited by Erik Verzemnieks, MD