Pre- history of Bubonic Plague

".. in the journal Cell, researchers report that the bacterium was infecting people as long as 5,000 years ago.

"...Exactly what those early outbreaks were like is impossible to know. But the authors of the new study suggest that plague epidemics in the Bronze Age may have opened the doors to waves of migrants in regions decimated by disease.

“To my mind, this leaves little doubt that this has played a major role in those population replacements,” said Eske Willerslev, a co-author of the new study and the director of the Center for GeoGenetics at the University of Copenhagen.

"David M. Wagner, a microbial geneticist at Northern Arizona University who was not involved in the study, said that the new research should prompt other scientists to look at mysterious outbreaks in early history, such as the epidemic that devastated Athens during the Peloponnesian War. “It opens up whole new areas of research,” he said...."
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http://www.nytimes.com/2015/10/23/science/in-ancient-dna-evidence-of-plague-much-earlier-than-previously-known.html?_r=0