Bronze Age sheep DNA reveals how plague spread across Eurasia

DNA from the plague bacterium Yersinia pestis has been found in a 4,000-year-old Bronze Age sheep tooth, offering the first direct evidence that animals could harbor the pathogen alongside humans and hinting at how the disease moved across Eurasia long before the medieval outbreaks.

Researchers reported the finding in the journal Cell, describing how they isolated tiny, damaged fragments of ancient DNA from the sheep and separated them from soil and modern contaminants. The genome was identified in a domesticated sheep discovered at Arkaim, a fortified Bronze Age settlement in the Southern Ural Mountains near the Kazakhstan border. The work was led by scientists at the Max Planck Institute for Infection Biology, with senior authors Felix M. Key and Christina Warinner from the Max Planck Institute for Geoanthropology and Harvard University.

"It was alarm bells for my team," study co-author Taylor Hermes, an archaeologist at the University of Arkansas who studies ancient livestock and disease spread, said in a statement. "This was the first time we had recovered the genome from Yersinia pestis in a non-human sample." The team noted that recovering pathogen DNA from ancient animal remains is exceptionally challenging because the DNA is often broken into tiny fragments and heavily contaminated by soil microbes or later human handling.

The Bronze Age, spanning roughly 3,300 to 1,200 B.C., saw growing livestock herding, larger cattle and sheep herds, and longer-distance travel with horses. Those changes created more opportunities for pathogens to move between animals and people. The Bronze Age finding provides a potential mechanism for how plague could spread across vast regions where people and animals lived in close quarters, even before fleas, which later spread the disease during the medieval Black Death, were a dominant factor.

The discovery was made at Arkaim, a Bronze Age settlement in the Southern Ural Mountains of present-day Russia near the Kazakhstan border. Hermes said the result suggests a dynamic network of connections among people, their livestock, and wildlife, rather than a simple movement of infected humans alone.

It is possible the sheep contracted the bacteria from another animal, such as rodents or migratory birds that carried Y. pestis without showing illness, and then transmitted it to humans through close contact or shared environments. The researchers emphasized that the finding points to a broader pattern: many deadly diseases begin in animals and jump to humans, a risk that persists today as people move into new environments and intensify interaction with wildlife and livestock.

The study is based on a single ancient sheep genome, which limits what scientists can conclude about the prevalence or geographic spread of the plague in Bronze Age Eurasia. The team plans to study additional ancient human and animal remains from the region to determine how widespread the plague was and which species might have served as reservoirs or conduits for transmission. They also aim to identify the wild animals that originally carried the bacterium and to better understand how human movement and livestock herding shaped disease transmission across large distances.

The research was led by scientists at the Max Planck Institute for Infection Biology, with senior authors Felix M. Key and Christina Warinner, and supported by the Max Planck Society, which funded follow-up work in the region. The discovery underscores the enduring link between animal husbandry, mobility, and the emergence of zoonotic diseases—and how modern science can illuminate the deep past to inform present-day public health.

The bottom line, researchers say, is that Bronze Age societies’ expanding herding and trade networks likely created new paths for pathogens to move beyond human carriers, a finding that resonates with ongoing work on how animal reservoirs influence disease dynamics today. The scientists cautioned that more samples are needed before they can map the spread with confidence, but the Bronze Age sheep genome already offers a pivotal piece of the puzzle in understanding the long, complex history of plague transmission across Eurasia.

This line of inquiry helps scientists connect the dots between human expansion, animal husbandry, and the emergence of pandemic threats—an intersection that remains central to predicting and mitigating future zoonotic spillovers.