For many people, the plague brings to mind rats, crowded medieval towns, and the devastating epidemic that spread throughout Europe during and after the Middle Ages.
New research suggests the disease’s deadly history goes back even further. Research published in nature Researchers found that plague was already killing people in small hunter-gatherer groups 5,500 years ago, 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 stored inside ancient teeth, researchers reconstructed the bacterial genome and identified a previously unknown early strain of plague.
“Whether early forms of plague were milder or more virulent is a matter of debate, but our findings show that these ancient strains were already highly lethal,” said lead author Eske Willerslev, a professor at the University of Copenhagen and the University of Cambridge.
Ancient DNA reveals prehistoric plague epidemic
Researchers combined genetic evidence with archaeological finds and radiocarbon dating to piece together what happened within these prehistoric communities.
“Based on plague DNA, genetic relationships among victims, archaeological analysis and radiocarbon dating, we have built a very clear and complete picture of what happened during these epidemics,” says lead author Ruairidh MacLeod. He conducted this research while a PhD student at Cambridge University and is currently a research fellow at Oxford University.
The research team detected DNA from plague bacteriumthe bacterium that causes plague was detected in 18 out of 46 people studied. This means that about 40% of the bodies had signs of infection. The researchers said this detection rate exceeds that reported from some medieval plague burial sites.
Evidence that early plagues were deadly
Previous research has shown that ancient strains plague bacterium They lacked some of the genetic characteristics that later allowed bubonic plague to spread efficiently through flea and rodent hosts. For this reason, many scientists believed that early forms of the disease were unlikely to have caused large-scale or deadly outbreaks.
New discoveries point in a different direction.
Researchers found an unusually large number of children and teenagers among the dead at the two largest cemeteries. For decades, archaeologists struggled to explain this pattern.
“The unusually high number and short duration of children has been a real challenge that we’ve been trying to solve since the 1990s,” said Andrei Weber, an archaeologist at the University of Alberta and lead researcher on the Baikal Archeology Project.
Radiocarbon dating revealed that many of the burials occurred over a relatively short period of time. In some cases, siblings or parents and children appear to have died at the same time and are buried together.
Inherent genetic factors may have increased severity
Researchers also identified superantigens unique to ancient plague strains. The genetic element that produces this toxin has not been found in subsequent historical plague strains.
Superantigens can trigger strong immune responses and are associated with severe inflammatory responses, which can make infections more dangerous.
“This discovery changes our understanding of early plague outbreaks. Even before the bacterium evolved efficient flea-borne infection, these ancient strains appear to have possessed a combination of potent virulence factors that could make the infection highly lethal,” said lead author Martin Sikora, associate professor at the University of Copenhagen.
This result suggests that, despite lacking the flea-borne transmission mechanism associated with bubonic plague, some of the earliest known plague epidemics may have been as deadly as later forms of plague, especially for children.
Clues to the origins of the plague
The study also supports the idea that plague first originated in central or northeast Asia and then spread across Eurasia through wild rodent populations.
Archaeological evidence shows that the hunter-gatherers studied had close contact with marmots, large burrowing rodents that still carry disease today. Researchers believe the disease may have been transmitted directly from infected marmots to humans, causing outbreaks in prehistoric communities.
