4 thousand-year-old sheep DNA reveals livestock’s role in spreading Bronze Age plague

Four thousand years ago, a sheep in the Eurasian Steppe carried a lethal bacterium that once swept across continents. The discovery of its preserved DNA has given scientists the first direct evidence that livestock may have helped spread an ancient form of plague during the Bronze Age.

This prehistoric strain, known as the Late Neolithic and Bronze Age (LNBA) plague, emerged about 5,000 years ago and lingered for nearly three millennia before disappearing. Until now, it had only been detected in human remains, leaving its animal origins and routes of transmission a mystery.

The new find, published in Cell, links domesticated animals to the spread of this enigmatic pathogen for the first time. The sheep’s remains were uncovered at Arkaim, a fortified settlement in the southern Ural region associated with the Sintashta-Petrovka culture, known for its expertise in herding and horse use.

Researchers from institutions including the Max Planck Institute of Infection Biology, Harvard University, and the University of Arkansas believe that livestock herding over large pastures brought humans into closer contact with wild reservoirs of disease. This increased the likelihood of infections crossing between species, including the jump from wild animals to sheep and people.

The genetic evidence shows that both humans and sheep in the region were infected with nearly identical strains of Yersinia pestis, the bacterium that causes plague. Lead author Ian Light-Maka, a PhD candidate studying long-term pathogen evolution, explains the importance of finding an animal case: “We have over 200 Y. pestis genomes from ancient humans, but humans aren’t a natural host of plague.”

The matching strains suggest that people and animals contracted the disease from the same unknown wild reservoir. Sheep grazing over vast areas may have crossed paths with infected wildlife, setting the stage for disease spillover into human communities.

In the modern world, plague outbreaks in pastoral regions sometimes occur when livestock come into contact with infected carcasses, particularly rodents. If animals are not properly handled or cooked, the infection can pass to humans. The same mechanism could have operated thousands of years ago.

Dr. Christina Warinner of Harvard University and the Max Planck Institute of Evolutionary Anthropology notes, “If we didn't know it was from a sheep, everyone would have assumed it was just another human infection – it's almost indistinguishable.” This close genetic match strengthens the idea that animals were not just incidental hosts but active participants in spreading the Bronze Age plague.

This ancient plague was genetically distinct from the flea-borne strains responsible for later pandemics such as the Black Death, which wiped out a third of Europe’s population in the 14th century. The LNBA strain lacked key genes needed for flea transmission, meaning its spread followed different rules.

Scientists found that the LNBA lineage displayed remarkably little genetic diversity across thousands of kilometers. That uniformity suggests it was shaped by strong evolutionary constraints rather than rapid mutation. In fact, the team detected repeated changes in certain genes, a pattern often linked to spillovers from a reservoir host.

Dr. Felix M. Key, who leads the Evolutionary Pathogenomics Lab at the Max Planck Institute of Infection Biology, says, “The ancient sheep as well as human infections are likely isolated spillovers from the unknown reservoir, which remains at large. Finding that reservoir would be the next step.”

The Sintashta-Petrovka culture thrived in the Eurasian Steppe during the Bronze Age, developing advanced herding techniques and horse technologies. Their animals roamed vast grasslands, making contact with diverse wildlife. This mobility, while beneficial for trade and food supply, may have unintentionally opened new pathways for disease transmission.

Dr. Taylor Hermes of the University of Arkansas explains why Arkaim was an ideal site for this research: “They were early pastoralist societies without the kind of grain storage that would attract rats and their fleas – and prior Sintashta individuals have been found with Y. pestis infections. Could their livestock be a missing link?”

The evidence now points to livestock being more than just bystanders. In these communities, animals may have acted as bridges, connecting human populations to the broader disease ecology of the steppe.

Identifying ancient pathogen DNA in animal remains is far more difficult than in human bones. Many animal remains are discarded as food waste, often exposed to cooking heat and environmental damage that degrade genetic material. Sick animals might not have been eaten at all, further reducing the odds of discovery.

Despite these hurdles, the Arkaim sheep provided enough genetic material to reconstruct a complete Y. pestis genome. It closely matched a strain found in a human from a nearby site, dated to the same period. This rare match bridges a major gap in understanding the ecology of the prehistoric plague.

The work also highlights how much remains hidden in archaeological collections. Tens of thousands of animal bones from past excavations sit in storage, waiting to be tested. Each could hold clues to ancient diseases and the ways they moved between species.

The World Health Organization lists zoonoses—diseases that jump from animals to humans—as one of today’s greatest health threats. Many deadly pathogens, including tuberculosis, measles, and plague, have origins linked to animal domestication.

The shift from hunting and gathering to farming increased human population density and brought people into sustained contact with livestock. These conditions favored the emergence of diseases that could cross species barriers.

The LNBA plague’s spread across Eurasia mirrors modern concerns about how mobility, trade, and changing ecosystems can drive disease transmission. Understanding the deep history of such pathogens can help predict and prevent future outbreaks.

Genomic research on Yersinia pestis has revealed its evolution from Y. pseudotuberculosis through a series of genetic changes that enhanced flea-borne transmission. Nearly 200 plague genomes have been reconstructed from human remains, but animal evidence has been scarce.

Two incomplete plague genomes from a medieval rat and a Neolithic dog lacked enough data for full analysis. A survey of over 100 prehistoric animal teeth found no trace of the bacterium. This scarcity reflects both the difficulty of recovering DNA from animal remains and the low chance of infected animals entering the archaeological record.

The LNBA lineage had previously been identified only in human remains from across Eurasia. Despite its wide range, it remained genetically uniform for over two millennia, suggesting unique ecological and evolutionary pressures.

These findings show that domestic animals can be key intermediaries in the spread of diseases that threaten human populations. Recognizing livestock’s role in ancient pandemics can help modern researchers monitor and control emerging zoonotic diseases.

By studying ancient DNA from animals, scientists can identify overlooked transmission routes and reservoirs. This work may improve models predicting how pathogens evolve and spread, helping prepare for future outbreaks.

Understanding the ecological dynamics that allowed the LNBA plague to persist could inform strategies to manage modern zoonoses, particularly in regions where humans, livestock, and wildlife interact closely.

The search now turns to finding the wild reservoir that harbored this ancient plague. That discovery could answer lingering questions about how the disease persisted for centuries and traveled so far. As Dr. Key says, “They give us insights that no human sample can.”

Note: The article above provided above by The Brighter Side of News.

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