In the Middle Ages, a devastating epidemic wiped out about a third of Europe’s population. The disease was spread through fleas, which carry bacteria plague bacterium. These fleas were transmitted from rats to humans, causing the scourge known as the Black Death.
However, the history of plague goes back even further. previous format plague bacterium It appeared during the Bronze Age about 5,000 years ago. This ancient strain infected people across Eurasia for nearly 2000 years before disappearing. However, unlike the medieval plague, this early plague could not be transmitted by fleas. Scientists have struggled for years to understand how the disease could spread across such a large area without this transmission route.
Ancient sheep provide important clues
Researchers have now uncovered a key piece of the puzzle. An international team including University of Arkansas archaeologist Taylor Hermes has identified the first evidence of Bronze Age plague in a non-human host. What scientists have discovered is that plague bacterium DNA contained in the remains of a domesticated sheep that lived approximately 4,000 years ago.
The animal was from Arkaim, a fortified settlement in the southern Ural Mountains of modern-day Russia, near the border with Kazakhstan. The discovery suggests that livestock may have been involved in the spread of plague during the Bronze Age, and helps explain how plague spread so widely across Eurasia.
This study cell Under the title, “The Y. pestis genome from a Bronze Age sheep sheds light on the evolution of hosts and prehistoric plague lineages.” This international collaboration involves researchers from Harvard University and major institutions in Germany, Russia, and South Korea.
Searching for clues in ancient DNA
Hermès is leading a major research project to study the DNA of ancient livestock. His team is tracking how livestock such as cows, goats and sheep spread from the Fertile Crescent across Eurasia by examining genetic material stored in bones and teeth. These movements were instrumental in the rise of nomadic cultures and the formation of early empires.
“Testing livestock DNA on ancient samples creates complex genetic contamination,” Hermes said. “This is a big barrier to getting a strong signal for the animals, but it also gives us an opportunity to look for pathogens that have infected the herd and its handlers.”
Working with ancient DNA is difficult and time-consuming. Scientists must separate the animal’s DNA from the many other sources found in the sample. The microorganisms that live in the soil where bones are buried leave their own genetic imprint. Researchers could also accidentally capture DNA from their own skin cells or saliva.
Fragments recovered from ancient ruins are very small. Many fragments measure only about 50 base pairs. For comparison, the complete human genome contains over 3 billion base pairs.
Animal remains tend to be less well preserved than human remains, which are usually carefully buried. Animals are often cooked and eaten, and their bones are thrown into waste piles where their genetic material is gradually broken down by exposure to heat and the elements.
moment of discovery
While studying livestock remains excavated from Alkaim in the 1980s and 1990s, Hermes and his colleagues noticed something unexpected. One sheep bone contained DNA that looked like this: plague bacterium.
“This was a wake-up call for my team. This was the first time we had recovered a genome.” plague bacterium “We found non-human samples,” Hermes said. “We were even more excited because Arkaim is linked to the Sintashta culture, known for early horse riding, impressive bronze weaponry, and a large influx of genes into Central Asia.”
How did the Bronze Age plague spread?
Researchers have previously discovered identical Bronze Age plague strains in human bones thousands of kilometers apart. The question is how did this disease travel such long distances?
“It had to be more than humans migrating. The plague sheep gave us a breakthrough. We now see it as a dynamic between humans, livestock, and an unidentified ‘natural reservoir’ of the disease, which could be steppe rodents or migratory birds in the Eurasian Steppes,” Hermes said.
Natural reservoirs are animal species that can carry pathogens without getting sick. In the Middle Ages, rats served as reservoirs of disease. plague bacteriumFleas, on the other hand, acted as vectors for spreading the bacteria. Currently, bats often play this role against viruses such as Ebola and Marburg virus.
Lessons learned from ancient plagues
Hermes recently received a five-year grant worth €100,000 from Germany’s Max Planck Society to continue excavating in the South Urals near Arkaim. His team plans to search for additional human and animal remains that may contain traces. plague bacterium.
The Bronze Age was a time when the Sintashta culture began to manage larger herds of livestock and at the same time became skilled horsemen. Increased interactions with animals and expanded movement across grasslands may expose people to reservoirs of disease in the environment.
Although these events took place thousands of years ago, Hermes believes this discovery carries an important message for today. Extending economic activity into the natural environment can disrupt ecosystems and increase the risk of disease spillover.
“We should aim to understand and maintain balance in the delicate inner workings of the ecosystems we may disturb,” Hermes said.
“It’s important to have more respect for the forces of nature,” he says.
