How One Strain of Plague Bacterium Ravaged Eurasia

A mass burial site in Ellwangen, Germany. (Credit: Rainer Weiss) Even today, the specter of the Black Death looms over society. The disease, caused by the bacterium Yersinia pestis, began a deadly march through Eurasia starting in the mid-14th century, killing hundreds of thousands along the way. And researchers from the Max Planck Institute for the Science of Human History believe that a single strain of the bacterium is to blame, and it remains the source of modern plague epidemics. The disease was likely introduced in Europe via fleas that had feasted on infected ship rats. Symptoms of the Black Death were first reported in port cities on the Mediterranean, and it spread quickly from there. Whole villages were nearly wiped out, and in total, some 60 percent of Europe's population would succumb to the disease, which was characterized by an extreme swelling of the lymph nodes and the gradual blackening of the fingertips and toes as the tissues died. Many of those infected died within a week.