Scientists discover plague bacteria in ancient Bronze Age sheep from Russia

Long before the Black Death killed millions of people in Europe in the Middle Ages, an older, elusive version of the plague spread across much of Eurasia.

For years, scientists were unsure how the ancient disease spread so widely during the Bronze Age, which lasted from about 3300 to 1200 BCE, and managed to stick around for nearly 2,000 years, especially because it was not spread by fleas like later epidemics. Now researchers say a surprising clue may help explain this: a domesticated sheep that lived more than 4,000 years ago.

According to a study published recently in southern Russia, researchers found DNA from the plague bacterium Yersinia pestis in the tooth of a Bronze Age sheep found in what is now southern Russia. Cell magazine. This is the first known evidence that the ancient plague infected not only humans but also animals, and offers a missing clue as to how the disease spread.

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“This was alarm bells for my team,” said study co-author Taylor Hermes, a University of Arkansas archaeologist who studies ancient livestock and the spread of disease. in a statement. “This was the first time we obtained the Yersinia pestis genome in a non-human sample.”

According to the researchers, this was a lucky discovery.

“When we test animal DNA in ancient samples, we get a complex soup of genetic contamination,” Hermes said. “This is a big hurdle… but it also gives us the opportunity to look for pathogens that are transmitting to herds and their caretakers.”

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The highly technical and time-consuming work requires researchers to separate small, damaged fragments of ancient DNA from pollution left behind by soil, microbes, and even modern humans. The DNA they obtain from ancient animals is often fragmented into small pieces, sometimes only 50 “letters” long, compared to a full human DNA strand containing more than 3 billion of these letters.

Animal remains are particularly difficult to study because they are often less well preserved compared to carefully buried human remains, the researchers noted.

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The findings shed light on how plague spread through close contact between humans, livestock and wild animals as Bronze Age societies began to raise larger herds and travel further afield on horses. The Bronze Age saw more widespread use of bronze tools, large-scale animal herding, and increased travel; These conditions may have facilitated the transmission of diseases between animals and humans.

The plague known as the Black Death in the 1300s killed an estimated one-third of Europe’s population when it returned in the Middle Ages.

The discovery was made at Arkaim, a fortified Bronze Age settlement in the Southern Ural Mountains near modern-day Russia’s border with Kazakhstan. (iStock)

“There had to be more than just people moving,” Hermes said. “Our plague sheep gave us a breakthrough. We now see this as the dynamic between humans, animals, and some still unidentified ‘natural reservoirs’.”

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Researchers believe the sheep likely picked up the bacteria from another animal, such as rodents or migratory birds, carried it without getting sick and then transferred it to humans. The findings underscore how many deadly diseases start in animals and spread to humans; This risk continues today as humans move to new environments and interact more closely with wildlife and livestock.

“It is important to have more respect for the forces of nature,” Hermes said.

They noted that the study was based on a single ancient sheep genome, which limits the conclusions scientists can draw and that more samples are needed to fully understand the spread.

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Researchers plan to examine older human and animal remains from the region to determine how widespread the plague was and which species played a role in its spread.

Researchers (not pictured) found DNA of Yersinia pestis, which causes plague, in the remains of a Bronze Age sheep. (iStock)

They also hope to identify the wild animal that first carried the bacteria and better understand how human movement and animal herding help the disease spread across large distances, insights that could help them better predict how animal-borne diseases continue to emerge.

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The research was led by scientists at the Max Planck Institute for Infection Biology, senior authors Felix M. Key of the Max Planck Institute for Infection Biology, and Christina Warinner of Harvard University and the Max Planck Institute for Geoanthropology.

The research was supported by the Max Planck Society, which also funded follow-up studies in the region.