<em>Yersinia pestis</em> is the bacterium responsible for the infamous Black Death, an epidemic that cause millions of deceases in Europe during the fourteenth-century. Black Death left a mark of people in Europe not only in their history, but also in their genome, since several studies have revealed that they immune system respond differently than people in other countries. People who survived Black Death had shown to be immune when reexposed to plague, since the bacterium responsible of plague is <em>Yersinia pestis</em> itself.