Researchers analyzing ancient DNA say they have detected the plague bacterium Yersinia pestis in the remains of a domesticated sheep from Arkaim, a Bronze Age settlement in the southern Ural region of present-day Russia. The team reports this is the first known identification of a Bronze Age plague lineage in a nonhuman host from that period, a finding that could help explain how an early, pre-flea-adapted form of plague traveled widely across Eurasia.
An international team that included University of Arkansas archaeologist Taylor R. Hermes analyzed ancient DNA from livestock remains recovered decades ago from Arkaim, a fortified Bronze Age settlement in the southern Ural Mountains region of present-day Russia, near the border with Kazakhstan.
In work published in Cell, the researchers reported detecting Yersinia pestis DNA in the remains of a domesticated sheep that lived about 4,000 years ago. The team described the result as the first evidence of a Bronze Age plague infection identified in a nonhuman host from that era.
The finding bears on a long-standing question about how early plague lineages dispersed. According to the researchers, an earlier form of Y. pestis emerged around 5,000 years ago and circulated across Eurasia for roughly two millennia before disappearing. Unlike the flea-adapted strains associated with later pandemics, this Bronze Age lineage is described by the researchers as lacking the genetic features needed for efficient flea-borne transmission.
Hermes, who co-leads research focused on ancient livestock DNA, said the technical hurdles of working with animal remains can be substantial: "When we test livestock DNA in ancient samples, we get a complex genetic soup of contamination. This is a large barrier to getting a strong signal for the animal, but it also gives us an opportunity to look for pathogens that infected herds and their handlers."
The team said the plague signal appeared unexpectedly while they were screening livestock material excavated from Arkaim in the 1980s and 1990s. "It was alarm bells for my team. This was the first time we had recovered the genome from Yersinia pestis in a non-human sample," Hermes said.
To account for long-distance spread without flea transmission, the researchers argue the evidence points to an interaction among people, livestock and a still-unidentified natural reservoir. Hermes said that reservoir could have included animals such as rodents on Eurasian steppe grasslands or migratory birds.
The paper’s author list includes researchers affiliated with Harvard University and institutions in Germany, Russia and South Korea.
Hermes has also received a five-year grant from Germany’s Max Planck Society valued at €100,000 to support continuing work on ancient plague genetics and related field research.
Beyond the historical reconstruction, Hermes said the study underscores how disease risks can rise when human economic activity expands into wildlife habitats. "We should appreciate the delicate inner workings of the ecosystems we might disturb and aim to preserve the balance," he said. "It's important to have a greater respect for the forces of nature."
