An international research team studying ancient DNA from burial sites in the Lake Baikal region of East Siberia has determined that plague posed a significant threat to human populations approximately 5,500 years ago, challenging conventional understanding of the disease’s origins and early impact.
Scientists sequenced genetic material recovered from human remains at four hunter-gatherer burial sites, identifying previously unknown early forms of the plague bacterium Yersinia pestis. Analysis revealed that 18 of 46 individuals tested carried DNA from the pathogen, representing a detection rate of nearly 40 percent—a proportion exceeding levels found at some medieval plague burial sites. Researchers combined genetic evidence with archaeological analysis and radiocarbon dating to reconstruct what occurred during these ancient outbreaks.
The discovery challenges earlier assumptions about early plague strains. Previous research suggested that ancient variants of Yersinia pestis lacked genetic features necessary for efficient transmission through fleas and rodents, leading scientists to theorize that early versions could not produce severe epidemics. However, the new findings indicate these ancient strains were already highly lethal. At the two largest cemeteries studied, researchers observed an unusually high concentration of child and adolescent deaths occurring within a short timeframe. Radiocarbon dating suggested many fatalities occurred in close temporal proximity, with genetic evidence indicating some family groups—including siblings and parents with children—may have perished during the same outbreaks.
A distinctive superantigen present in the ancient plague strains may explain their virulence. This toxin-producing genetic factor, absent in later historic plague strains, can trigger unusually intense immune responses, potentially causing severe inflammation and increased lethality. The presence of this virulence factor suggests early plague outbreaks could have been comparably deadly to later historical epidemics, particularly for younger populations, despite occurring before the bacterium evolved efficient flea-based transmission.
The research supports theories that plague may have originated in Central or Northeast Asia before spreading across Eurasia through wild rodent populations. Archaeological evidence indicates the Lake Baikal hunter-gatherers maintained close contact with marmots, large burrowing rodents that continue carrying plague today. Researchers theorize certain prehistoric outbreaks may have resulted from direct transmission of infected marmots to humans, suggesting plague was capable of generating deadly episodes in small communities millennia before urbanization facilitated the disease’s later notoriety.
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