The oldest strain of the Plague bacteria

Yersinia pestis is the culprit bacterium of the disease popularly known as Plague. In the 14th century, it caused a terrible pandemic that decimated humanity. According to some calculations, in the case of the European population this was reduced by half.

A strain of Yersinia pestis has been found in the mortal remains of a hunter-gatherer 5,000 years ago. This strain is now the oldest known.

The plague-bearing hunter-gatherer was a man in his 20s and 30s who has been given the identification “RV 2039”. He was one of two people whose skeletons were unearthed in the late 19th century in a region called Rinnukalns, today within Latvia. Shortly after, the remains of both disappeared until 2011, when they reappeared as part of the collection of the German anthropologist Rudolph Virchow. After this rediscovery, the mortal remains of two other individuals were found at the original site, bringing the number of people unearthed from that place to a total of four. All four were most likely part of the same hunter-gatherer group.

In the new research, Ben Krause-Kyora’s team from the University of Kiel in Germany used samples of teeth and other bones from the four hunter-gatherers to sequence their genomes and then analyzed them for bacterial and viral pathogens. Scientists were surprised to find evidence of Yersinia pestis in RV 2039.

After reconstructing the genome of the bacterium and comparing it with that of other ancient strains, the researchers determined that the Yersinia pestis of RV 2039 was indeed the oldest strain of all those discovered so far. It was likely part of a lineage that emerged about 7,000 years ago, just a few centuries after Yersinia pestis evolutionarily separated from its predecessor, Yersinia pseudotuberculosis.

This image shows the available bones from the skull of the man buried in Rinnukalns, Latvia, about 5,000 years ago. (Photo: Dominik Göldner, BGAEU, Berlin)

“The surprising thing is that we already see in this early strain more or less the complete genetic set of Yersinia pestis, with only a few genes missing. But even a small change in genetic makeup can have a dramatic influence on virulence,” he says. Krause-Kyora. In particular, this ancient strain was missing a crucial component: the gene that first allowed fleas to act as vectors spreading plague in the 14th century human population.

Judging from its genetic makeup, this 5,000-year-old strain was probably less contagious and not as deadly as the medieval strain.

Over time, the bacteria underwent the mutations that allowed transmission from rats to humans through fleas.

The study is titled “A 5,000-year-old hunter-gatherer already plagued by Yersinia pestis.” And it has been published in the academic journal Cell Reports. (Source: NCYT from Amazings)

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