5500-Year-Old Plague DNA Shows Deadly Outbreaks

Ancient DNA taken from hunter-gatherers buried near Lake Baikal in Siberia carries traces of Yersinia pestis, the bacterium behind historic plague pandemics. The findings suggest devastating community outbreaks as much as 5500 years ago—long before farming spr

A boy and a girl were laid to rest in the same shared grave near Lake Baikal, in what is now Siberia. What researchers later found in their remains changes a long-standing story about plague: ancient DNA traces point to Yersinia pestis, the bacterium behind some of history’s deadliest pandemics.

The work suggests deadly outbreaks of plague among hunter-gatherers as long as 5500 years ago. pushing back against the idea that large disease outbreaks emerged only with the spread of farming during the so-called Neolithic revolution. Ruairidh Macleod at the University of Oxford puts it bluntly: “The expectation is that big outbreaks of disease affecting entire communities didn’t exist at all before the Neolithic revolution. What we see here is clear evidence for a really devastating outbreak of plague that’s affecting an entire community of hunter-gatherers at Baikal. and that flies in the face of that.”.

Yersinia pestis is notorious for its reach through different forms of illness. It can infect people’s lungs or their blood, leading to pneumonic or septicaemic plague. But it is more commonly bubonic plague. where flea bites enable the bacterium to infect lymph nodes. causing them to swell hugely and form large “buboes”.

In recent years, sequencing ancient DNA has made it possible to detect Y. pestis in bones and teeth from people buried hundreds or thousands of years ago. Earlier studies using those techniques had already shown plague infecting farming communities in places such as Sweden as long as 5000 years ago. The new findings now move the story dramatically farther back—and farther east.

Some researchers had proposed that plague’s ability to unleash major. deadly outbreaks only arrived after the bacterium acquired a key gene that allows it to spread via flea bites. That gene. called ymt. works in a specific. gut-clogging way: in an infected flea. the protein encoded by ymt clogs up its gut. starving it and allowing plague bacteria to accumulate near its mouthparts. “This deprives the flea of the blood meal from its host and causes it to bite anything it can like crazy. ” Macleod says.

The question was whether strains from earlier periods were already capable of causing community-scale devastation. Macleod’s team found Y. pestis in 18 of 42 hunter-gatherers recovered from four sites around Lake Baikal. “We do finally have really compelling evidence that the strains of plague at this time were deadly as well. ” he says.

The pattern that emerges points to more than one outbreak. The first appears to have started around 5500 years ago. There are graves that link victims who died around the same time—siblings buried together. and shared graves containing up to four or five people. “We see cases of siblings being buried in the same graves. apparently having died around about the same time. ” Macleod says. “And we see shared graves with up to four or five people, all apparently having died at the same time.”.

Many of the likely victims were children or teenagers. a fact that had puzzled researchers who excavated the sites in the 1980s. Now it fits with what historical records suggest about plague: children were much more likely to die of it. At the same time. the evidence also shows some people survived long enough to bury the dead using the usual ceremony. “It’s really touching that we have that insight as to how these hunter-gatherer communities responded,” Macleod says.

There is also a broader ecological story tying hunter-gatherers to the bacterium. Compared with farmers, Macleod says hunter-gatherers would have had more contact with wild animals. That meant a higher chance of exposure to animal viruses and bacteria that could infect humans. The team thinks these communities probably caught plague from marmots, described as the main reservoir of Y. pestis. They point to evidence from nearby sites where marmots were hunted for food.

Plague persists in this region today as well. People still sometimes get the plague from coming into contact with marmots or from eating undercooked marmot meat.

Once infection spread, it may not have stayed inside animals for long. The team suggests it could have moved as pneumonic plague—spreading through people coughing—after one hunter-gatherer became infected.

The evolutionary timeline matters too. Based on analysis of bacterial genomes, the researchers think Y. pestis first evolved between 9800 and 5700 years ago, with the more recent date considered more likely. That leaves the door open to even older outbreaks, but the study suggests they weren’t much older.

Nicolás Rascovan at the Pasteur Institute in Paris says the study stands out for how it reframes the geography and social setting of plague’s earliest known victims. “There are many elements that make this study unique,” he says. “It deals with the oldest known plague outbreak, the furthest to the east and one in hunter-gatherers rather than farmers.”.

Rascovan argues that the findings challenge agricultural lifestyles as the main driver of plague emergence. “It is clear evidence of an outbreak in prehistoric times that argues against agricultural lifestyles as the major driver of plague emergence. ” he says. He adds that while the discovery shows deadly outbreaks in non-agricultural societies. it may also connect to later demographic collapse: “The study demonstrates that [Y. pestis] was already producing deadly outbreaks in non-agricultural societies. which is certainly very interesting. but I believe that during the decline of European populations at the end of the Neolithic. it may well have played an important role in decimating these populations. ” he says.

Taken together, the shared graves near Lake Baikal do more than document an old disease. They put a human community—children. teenagers. siblings and families—into the timeline of plague’s deadliest potential. long before farming reshaped Europe. The unsettling detail is that the plague wasn’t waiting for history’s big transitions to begin.

ancient DNA Yersinia pestis plague Lake Baikal hunter-gatherers Neolithic decline ymt gene marmots bubonic plague pneumonic plague