Ancient hunter-gatherers in southeastern Siberia faced a deadly plague 5,500 years ago, according to new research.

University of Oxford researchers uncovered DNA from the Yersinia pestis bacteria – known for causing the Black Death – within teeth from victims at four ancient cemeteries around Lake Baikal. This marks the earliest known outbreak of this devastating disease and the oldest strain ever sequenced, challenging previous assumptions about its origins.

The findings suggest that plague could have emerged in hunter-gatherer communities long before dense settlements with farmers and domestic animals appeared. This challenges long-held theories that the spread of plague was linked to urbanization.

‘Our research shows that the earliest known outbreaks of plague occurred in prehistoric hunter-gatherers centuries before infections are observed in Neolithic farmers,’ Ruairidh Macleod, an ancient DNA researcher, stated in a press conference. ‘This challenges the traditional view that plague spillover was linked to people adopting farming and living closer together.’

While it is believed that hunter-gatherers constantly moved around due to their small group sizes, this research suggests infectious diseases could still devastate entire communities.