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 A study unveiled on Thursday of DNA from Bronze Age people in
Europe and Asia showed the bacterium, Yersinia pestis, afflicted
humans as long ago as about 2800 BC, more than 3,000 years earlier
than the oldest previous evidence of plague.
The plague has killed untold millions of people over the centuries
in pandemic flares that reshaped human society.
"It seems to have started impacting human populations over large
geographical scales way earlier than we thought," said evolutionary
geneticist Eske Willerslev of the University of Copenhagen and
University of Cambridge.
They studied DNA from the teeth of 101 people from six sites: three
in Russia, one in Poland, one in Estonia and one in Armenia. Seven
had evidence of Yersinia pestis infection.
 The researchers also tracked the timing of a pivotal event in plague
evolution, a mutation that made the germ capable of being
transmitted by fleas. They found Yersinia pestis with this mutation
in a person who died in Armenia in about 951 BC, the most recent of
the 101 studied.
The study, published in the journal Cell, showed plague was
widespread across Europe and Asia during the Bronze Age. The oldest
evidence of infection was found in the DNA of people from about 2782
BC and 2794 BC buried in a mass grave in Bateni, Russia, in Central
Asia's Altai mountains.
Previously, the oldest evidence of plague came from about 540 AD in
Germany, Technical University of Denmark geneticist Simon Rasmussen
said.
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"The Bronze Age plague represents an intermediate state where it had
not yet evolved the capabilities to be transmitted by fleas or cause
bubonic plague. However, it was still able to cause septicemic and
pneumonic plague," Rasmussen added.
Septicemic plague infection is confined to the blood. In bubonic
plague, it infects lymphatic tissue. In pneumonic plague, it spreads
to the lungs and can be transmitted person-to-person via droplets.
The germ was spread mainly by such human-to-human contact until a
genetic mutation allowed it to survive in fleas' guts, choking their
digestive tract and causing them to bite anything they can, wildly
spreading plague.
Yersinia pestis caused two of humankind's deadliest pandemics: the
6th century Justinian Plague, named for the Byzantine emperor who
was sickened but survived, and the 14th century "Black Death."
(Reporting by Will Dunham; Editing by Sandra Maler)
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