Scientists may have found the remains of the first man to ever be infected with the plague which caused the Black Death.
The man died more than 5000 years ago in Latvia and new evidence suggests he was infected with the earliest-known strain of the disease.
Dr Ben Krause-Kyora of the University of Kiel in Germany told the BBC the man was buried with three others beside the River Salac.
Researchers sequenced DNA from the bones and teeth of all four skeletons and tested them for bacteria and viruses.
The patient zero contender, a man in his 20s when he died, 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 ancient plague began around 7000 years ago when agriculture began to appear in central European, reports the BBC.
It would have leapt between animals and humans without causing large outbreaks, until it adapted to infecting humans.
Then, it became the bubonic plague, also known as the Black Death which ravaged medieval Europe, killing millions.
At least a third, and up to half the population of Europe were killed by the plague in the 1300s.