The plague, or Black Death, killed off nearly half of the population of Europe in the 14th century, but new DNA studies suggest the bacteria has been around a lot longer and was in fact infecting people almost 5,000 years ago.
DNA samples extracted from ancient Bronze Age skeletons unearthed in Europe and Asia show signs of plague infection dating back 4,800 years, although it would take a further thousand years for the bacteria Yersinia pestis to mutate to a form that could spread from fleas to humans in order to create the Black Death, researchers say.
"We found that the Y. pestis lineage originated and was widespread much earlier than previously thought, and we narrowed the time window as to when it developed," says Eske Willerslev at the University of Copenhagen's Center for GeoGenetics, the senior author of a study appearing in the journal Cell.
The researchers were able to extract human DNA from more than 100 bones found in Asia and from between 3,000 and 5,000 years ago.
"This study changes our view of when and how plague influenced human populations and opens new avenues for studying the evolution of diseases," he says.
The date of 4,800 years ago is earlier than the previous oldest evidence of plague in humans, the Plague of Justinian, which wreaked havoc in the Byzantine Empire in the 6th century.
The earliest DNA sample showing signs of plague came from Bronze Age Siberia and dated to 2794 B.C., the researchers reported.
The finding of earlier plague episodes suggests it may have been behind the mysterious epidemics that hit ancient Greece at the end of the Classical period and for one that decimated the Imperial Roman Army, the researchers say.
It may have had other influences throughout history, driving Bronze Age movements and migrations of people, the researchers suggest.
"Perhaps people were migrating to get away from epidemics or recolonizing new areas where epidemics had decimated the local populations," says study co-author Morten Allentoft, an evolutionary biologist at the University of Copenhagen.
The new findings may have more than historic significance, says another researcher, Simon Rasmussen of the Technical University of Denmark.
"The underlying evolutionary mechanisms that facilitated the evolution of Y. pestis are still present today, and learning from this will help us understand how future pathogens may arise or develop increased virulence," he says.
