Yersinia pestis is the bacteria widely believed to have been behind the plague that ravaged the world in the Middle Ages and may have wiped out half of the entire population of Europe in what became known as the Black Death. The disease was spread by fleas on rats, and began to spread further into Europe from Asia due to trade routes.
But while the disease first became known in the Middle Ages, and scientists believed it may have originated around 2,000 years ago, recent findings suggest the disease may be far older than previously thought.
As detailed in a new study, published in the peer-reviewed academic journal Cell Reports, a 5,000-year-old Yersinia pestis genome was reconstructed by scientists from the bones of a 5,000-year-old hunter-gatherer (dubbed RV 2039) found buried in Latvia.
This, the researchers believe, was likely one of, if not the earliest known strain of what would become known as the plague.
The hunter-gatherer was likely bitten by a rodent and died of shock following infection, the researchers theorize.
It should be noted that despite the prevailing consensus for years that the plague originated in Asia, scientists had begun finding evidence of a European origin. In 2018, a study published in the academic journal Cell found an ancient case of the plague in a 4,900-year-old tomb in Sweden.
In a 2015 study in the same journal, scientists presented evidence that Yersinia pestis infected humans in Bronze Age Eurasia.
However, it is widely agreed upon that these earlier variants were not as infectious, and the genome notably did not posses the necessary factor that would allow it to be transmissible from fleas to humans. Another 2018 study in Cell found that two individuals in Russia 3,800 years ago were infected by the more virulent version, as was an individual from Iron Age Armenia 2,900 years ago.
In the 2018 study, the researchers theorized that an early plague pandemic contributed to the decline of Neolithic populations in Europe.
However, a few things stand out in this latest study.Most notably, the strain is different in that it marks the beginning of the evolution of Yersinia pestis, and is on a separate branch from the one found in Sweden. It further adds to other early genomes of the bacteria found in eastern Europe.Furthermore, the researchers have reason to suspect that though the genome was found on 5,000-year-old bones, this strain of Yersinia pestis may have evolved around 7,000 years ago. This would put it not at the end of the Neolithic period as earlier theories suggested, but at the beginning.
The plague famously spread throughout Europe and wiped out around a third of the global population. Though now treatable by antibiotics, the disease remains a persistent threat in parts of the world, and occasional outbreaks do still happen, but it has mostly been found in animals. Most human cases have been seen in Africa.
However, humans can still catch the disease, either by being bitten by a flea carrying Yersinia pestis or by handing an animal infected with the disease.