Plague is a bacterial disease that has played an important role in the history of Europe. Three different plague pandemics have occurred in the past centuries, the latest one at the turn of the 19th century, and all with significant mortality worldwide. Plague has been absent from Europe for over half a century now, but is still widespread in the Americas, Africa and Asia. On an annual basis, a few thousands of cases are reported worldwide.
Plague is caused by the bacillus Yersinia (Y.) pestis, belonging to the family of the Enterobacteriaceae. It evolved several thousand years ago from Y. pseudotuberculosis.