For many people, the plague reminds them of rats, crowded medieval cities, and the devastating epidemics that swept Europe during and after the Middle Ages.
New research suggests the disease’s deadly history goes back much further. A study published in Nature He discovered that the plague was already killing people 5,500 years ago in small groups of hunter-gatherers, thousands of years before agricultural communities and cities emerged.
An international team of scientists examined ancient DNA from human remains recovered from four hunter-gatherer cemeteries near Lake Baikal in Eastern Siberia. By sequencing genetic material preserved within ancient teeth, researchers reconstructed bacterial genomes and identified previously unknown early strains of plague.
“It has been a topic of debate whether early forms of plague were mild or virulent, but our findings demonstrate that these ancient strains were already highly lethal,” says lead author Eske Willerslev, a professor at the University of Copenhagen and the University of Cambridge.
Ancient DNA reveals outbreaks of prehistoric plagues
The researchers combined genetic evidence with archaeological finds and radiocarbon dating to reconstruct what happened within these prehistoric communities.
“Based on plague DNA, genetic relationships between victims, archaeological analysis and radiocarbon dating, we have built a really clear and complete picture of what happened during these outbreaks,” says lead author Ruairidh Macleod, who carried out the work while a PhD student at the University of Cambridge and is now a researcher at the University of Oxford.
The team detected DNA from Yersinia pestisthe bacteria responsible for the plague, in 18 of 46 individuals studied. That means almost 40 percent of the remains had evidence of infection. According to the researchers, this detection rate exceeds those reported at some medieval plague burial sites.
Evidence Suggests Early Plague Was Highly Lethal
Previous research had indicated that ancient strains of Yersinia pestis it lacked some of the genetic characteristics that later allowed bubonic plague to spread efficiently through flea and rodent hosts. Because of this, many scientists believed that the earliest forms of the disease were unlikely to have triggered large or deadly outbreaks.
The new findings point in a different direction.
In the two largest cemeteries, investigators found an unusually large number of children and teenagers among the dead. For decades, archaeologists had struggled to explain this pattern.
“The unusually high number of children and the short period of time were a real puzzle that we have been trying to solve since the ’90s. Finding out that the cause was the plague is extraordinary, but it makes a lot of sense,” says archaeologist Andrzej Weber of the University of Alberta, principal investigator of the Baikal Archeology Project.
Radiocarbon dating revealed that many of the burials took place over a relatively short period. In some cases, siblings or parents and children appear to have died at approximately the same time and were buried together.
Single genetic factor may have increased severity
The researchers also identified a distinctive superantigen in ancient plague strains. This toxin-producing genetic factor has not been found in later historical plague strains.
Superantigens can trigger powerful immune reactions and are linked to severe inflammatory responses, potentially making infections much more dangerous.
“This finding changes our understanding of early plague outbreaks: even before the bacteria evolved for efficient transmission via fleas, these ancient strains appear to have carried a potent combination of virulence factors that could make the infection highly lethal,” says senior author Martin Sikora, associate professor at the University of Copenhagen.
The results suggest that some of the earliest known plague outbreaks may have been as deadly as later forms of the disease, especially in children, despite lacking the flea transmission mechanisms associated with bubonic plague.
Clues to the origins of the plague
The study also supports the idea that the plague first emerged in central or northeastern Asia before spreading across Eurasia through wild rodent populations.
Archaeological evidence indicates that the hunter-gatherers in the study had close contact with marmots, large burrowing rodents that still transmit the plague today. Researchers believe the disease may have jumped directly from infected groundhogs to humans, causing outbreaks in these prehistoric communities.