The Black Death is one of the most infamous pandemics in human history, killing roughly a third of Europe’s population during the Middle Ages.
That outbreak was caused by the bacterium Yersinia pestis and spread mainly through fleas that lived on rats.
But thousands of years earlier, during the Bronze Age, a different form of plague swept across Eurasia for nearly 2,000 years — and scientists have long struggled to explain how it spread so widely.
Now, researchers believe a sheep may hold the answer.
An international team of scientists has discovered the first known evidence of Bronze Age plague in a non-human animal.
By analyzing ancient DNA, they identified Yersinia pestis in the remains of a domesticated sheep that lived about 4,000 years ago.
The sheep was found at Arkaim, a fortified Bronze Age settlement in what is now southern Russia, near the border with Kazakhstan.
The study was published in the journal Cell and includes researchers from the University of Arkansas, Harvard University, and institutions across Europe and Asia.
This discovery helps solve a major puzzle.
Unlike the plague that caused the Black Death, the Bronze Age strain of Y. pestis could not be transmitted by fleas. Yet it still infected people across vast distances, from Europe to Central Asia.
Finding the bacterium in livestock suggests the disease may have spread through close interactions between humans, their animals, and a still-unknown natural reservoir.
The finding emerged from a broader research project led in part by archaeologist Taylor Hermes, who studies ancient livestock DNA. By examining genetic material from animal bones and teeth, his team traces how sheep, goats, and cattle spread across Eurasia and supported the rise of nomadic cultures.
Ancient DNA work is notoriously difficult. Animal remains are often poorly preserved, damaged by cooking, weather, and time. The DNA fragments recovered are tiny, mixed with genetic material from soil microbes and modern human contamination. Despite these challenges, the team detected unmistakable signs of Y. pestis in one sheep bone.
For the researchers, this was a breakthrough moment. It was the first time a full genome of the plague bacterium had been recovered from an animal rather than a human, offering a crucial missing link in understanding how the disease circulated.
Previously, scientists had identified the same Bronze Age plague strain in human remains found thousands of kilometers apart. Human movement alone did not seem sufficient to explain such widespread transmission. The infected sheep suggests a more complex system, involving people, their livestock, and a natural reservoir that carried the bacteria without becoming ill. This reservoir may have been wild rodents on the Eurasian steppe or possibly migratory birds, though this remains an open question.
The timing is significant. During the Bronze Age, cultures such as the Sintashta began keeping larger herds of animals and traveling more frequently, aided by early horse riding. These changes would have increased contact between humans, livestock, and wild animals, creating new opportunities for disease to spread.
Hermes plans to continue excavating human and animal remains near Arkaim to look for additional evidence of plague infections. Beyond solving an ancient mystery, he believes the research carries a modern warning. History shows that when humans push into new environments and alter ecosystems, dangerous pathogens can emerge.
Even after 4,000 years, the ancient plague reminds us that the balance between humans, animals, and nature is fragile — and that disrupting it can have deadly consequences.
Source: University of Arkansas.
