Plague is often linked to medieval Europe, crowded cities, and rats carrying infected fleas.
However, a new study published in the journal Nature shows that the disease was already killing people thousands of years earlier.
Researchers have discovered that plague caused deadly outbreaks among hunter-gatherers in Siberia about 5,500 years ago, long before cities and farming communities existed.
An international team of scientists studied ancient DNA from human remains found in four hunter-gatherer cemeteries near Lake Baikal in East Siberia.
The researchers examined DNA preserved inside teeth and were able to reconstruct ancient versions of Yersinia pestis, the bacterium that causes plague.
The findings surprised scientists because many researchers had believed that the earliest forms of plague were relatively mild.
These ancient strains lacked some of the genetic features that later allowed plague to spread efficiently through fleas and rodents, leading experts to assume they could not have caused large, deadly outbreaks.
Instead, the new evidence tells a very different story.
The researchers found plague DNA in 18 out of 46 people examined, meaning nearly 40% of the individuals carried the disease. This detection rate is even higher than that reported in some burial sites from medieval plague epidemics.
The cemeteries had long puzzled archaeologists because they contained an unusually large number of children and young teenagers. Many of the burials also appeared to have taken place within a short period of time. In some cases, siblings or parents and children were buried together, suggesting entire families may have died during the outbreaks.
Radiocarbon dating confirmed that many of these deaths occurred over a relatively brief period. According to the researchers, this pattern strongly points to devastating disease outbreaks that swept through these small communities.
The scientists also discovered something unusual about the ancient plague strains. They carried a unique “superantigen,” a toxin-producing genetic factor not found in later historical forms of plague. Superantigens can trigger an extreme reaction from the body’s immune system, causing severe inflammation and potentially making infections much more dangerous.
Researchers believe this superantigen may explain why these early forms of plague were so deadly, even without the flea-borne transmission system that made later plague epidemics famous.
The study also provides clues about where plague may have first emerged. The evidence suggests that the disease may have originated in Central or North-East Asia before eventually spreading across Eurasia.
The hunter-gatherers around Lake Baikal are known to have interacted closely with marmots, large burrowing rodents that still carry plague today. Scientists think infected marmots may have passed the bacterium directly to humans, sparking outbreaks in these small communities.
The discovery changes our understanding of plague’s history.
Rather than becoming deadly only after cities and trade networks developed, plague appears to have been a highly lethal disease from its earliest known stages, capable of devastating even small groups of mobile hunter-gatherers thousands of years before recorded history.
Source: University of Copenhagen.
