Scientists have uncovered the earliest known plague outbreaks in human history, dating to 5,500 years ago among hunter-gatherer communities near Siberia's Lake Baikal. Analysis of ancient DNA extracted from teeth found in burial sites revealed the presence of Yersinia pestis, the bacterium responsible for the plague. The findings, published in Nature, push back the timeline of plague infections by more than 2,000 years.
The discovery challenges the long-held assumption that plague outbreaks only became a threat after the rise of large, settled agricultural societies. These hunter-gatherers lived in small, mobile groups, yet the graves contained multiple individuals with the plague, suggesting recurrent lethal outbreaks. The infected individuals were buried in cemeteries, indicating the communities had complex social responses to the disease.
DNA analysis of 7 out of 133 ancient teeth tested from three burial sites returned positive for Yersinia pestis. Researchers identified two distinct strains, pointing to separate outbreaks separated by centuries. The pathogen's genome from these specimens lacked the flea-adapted gene that later enabled rapid transmission, implying the bacteria spread directly between humans without insect vectors.
The findings imply that plague could spread in low-density populations through direct contact or respiratory droplets, a mode of transmission now associated with pneumonic plague. This changes the understanding of how ancient diseases functioned and evolved. It also raises questions about whether other prehistoric communities faced similar threats from pathogens that have since adapted.
The study's authors caution that the sample size remains small and the pathogen's exact transmission mechanism among these groups is not fully resolved. Further genetic work on additional ancient remains will be needed to confirm the scale of these early outbreaks.