A man who died more than 5,000 years ago in Latvia was infected with the earliest-known strain of the disease, according to new evidence.
"Up to now this is the oldest-identified plague victim we have," Dr Ben Krause-Kyora of the University of Kiel in Germany said of the 5,300-year-old remains.
The man was buried with three others at a Neolithic burial site in Latvia by the side of the River Salac, which flows into the Baltic Sea.
They were surprised to find one hunter-gatherer - a man in his twenties - was infected with an ancient strain of plague, caused by the bacterium, Yersinia pestis.
"He most likely was bitten by a rodent, got the primary infection of Yersinia pestis and died a couple of days [later] - maybe a week later - from the septic shock," said Dr Krause-Kyora.
The researchers suggest the ancient strain emerged about 7,000 years ago, when agriculture was starting to appear in central Europe.