There are many examples of epidemics in history. Probably the most famous such example is the Black Death, or bubonic plague, that decimated fourteenth-century Europe. It has been estimated that this outbreak killed a third to more than a half of the population of Europe at the time. Bubonic plague is caused by a bacteria called Yersinia pestis and was conveyed, in this particular case, by infected fleas carried by common sewer rats. Death from bubonic plague generally resulted from pneumonia and related respiratory failure or overwhelming systemic infection.