Five thousand years ago, a rodent bit a Stone Age hunter-gatherer. The creature carried a strain of pernicious bacteria called Yersinia pestis – the pathogen that caused the Black Death, or bubonic plague in the 1300s.
The bacteria likely killed the Stone Age man, who died in his 20s, according to a study published Tuesday. It’s the oldest strain of plague known to science so far.
The strain’s genome closely resembles the version of plague that wrecked medieval Europe more than 4,000 years later, killing up to half the region’s population over the course of seven years. But it’s missing a few key genes – notably, traits that helped it spread.
Unlike its microbial descendants, the plague that sickened the ancient hunter was a slow-moving disease and not very transmissible, according to Ben Krause-Kyora, a professor of ancient DNA analysis at Kiel University in Germany.
“It lacked the genes that enabled transmission by flea,” Krause-Kyora, who co-authored the new study, told Insider. During the Black Death, bites from fleas and lice were the key source of infections.
So in the millennia between the hunter-gatherer’s demise and the Black Death, Y. pestis bacteria mutated in a way that gave it the ability to jump between species via fleas.
“The change was a major driving force of a fast and widespread plague,” Krause-Kyora said.
Bacteria in the bloodstream
The Stone Age hunter-gatherer died in a region that’s now Latvia. Near his bones, anthropologists also excavated the remains of another man, a teenage girl, and a newborn, but none had been infected.
Krause-Kyora’s group hadn’t gone looking for ancient plague victims – rather, they wanted to see if the four buried people were related. But before completing their planned genetic analysis, the team screened ancient DNA extracted from the bones and teeth for traces of pathogens. That’s how they found the bacteria.
The researchers then compared the bacteria’s genome to other ancient plague strains. A previous study described other strains that are roughly 5,000 years old, but Krause-Kyora said this particular one is a couple hundred years older. So his team concluded it was the earliest-known version of Y. pestis.
The hunter-gatherer’s DNA also showed that he had a large quantity of bacteria in his body, which suggests that he died from it. His grave site indicated that other members of his group meticulously buried him, according to the study.[…]