The plague moved through Europe during the medieval period with devastating speed, causing millions of deaths as fleas spread Yersinia pestis from rodents to humans. However, long before that catastrophe, a different plague circulated across Eurasia during the Bronze Age. This earlier lineage of plague emerged about 5,000 years ago and persisted for about two millennia before disappearing. The earlier plague strain lacked the genetic traits needed for successful transmission through fleas, thus leaving scientists to wonder how it spread so widely.
A very important finding has come to light in a recent study published in Cell. An international team of researchers has found the DNA of Y. pestis in a 4,000-year-old domesticated sheep from the fortified Bronze Age settlement of Arkaim, in the southern Ural Mountains in present-day Russia, which marks the first confirmed case of a Bronze Age plague infection in a non-human host. It proves that livestock played a role in prehistoric plague dynamics.
The sheep was associated with the Sintashta-Petrovka cultural complex, which was known for its sophisticated metallurgy, horse riding, and large, mobile herds. Genetic studies indicate that the bacterium found in the sheep belongs to the Late Neolithic–Bronze Age plague lineage that had previously been identified only in ancient humans across Eurasia. This suggests that plague was associated with pastoral economies and that plague transmission did not rely solely on human movement.
Researchers claim that this early lineage of plague may have persisted in some unspecified “natural reservoir,” possibly in wild rodents or other animals living in the Eurasian steppe, “spilling over” occasionally into domesticated herds. Sheep and other livestock may have acted as “bridge hosts,” bringing the bacteria into closer contact with people through herding, butchering, or food preparation. Modern outbreaks in parts of Asia show similar patterns, where sheep become infected through contact with wild rodents and can pass the disease to humans without spreading it further among themselves.
Recovering pathogen DNA from animal remains is very rare. Most animals were consumed or discarded and not buried with care, making the possibility of preservation low. Still, this sheep genome is enough to prove that close human–animal relationships during the Bronze Age increased the risk of infection.
In addition to shedding light on an ancient mystery, this research uncovers a larger truth: as human societies expanded, domesticated animals became critical intermediaries in the emergence of infectious diseases. Understanding these deep historical connections can also help explain how environmental disruption and changing economies continue to influence disease risks today.
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