Deadly plague strain discovered in Siberia shows it was fatal over 5,500 years ago

A study published in Nature has found that plague has been around for nearly 5,500 years, pushing back the timeline of the dreaded disease that killed millions in medieval times. The bacterium linked to the disease has been around for a much longer time, according to researchers from the University of Oxford. The discovery was made in the DNA of 42 prehistoric hunter-gatherers in Russia. These included several children and teenagers. The researchers gathered and sequenced the DNA from the teeth of the specimen found at four sites near Lake Baikal in Siberia, Russia. DNA from the individuals and the plague bacterium, Yersinia pestis, comprised the total genetic material analysed by the team.

The finding shows two things. First, this is the oldest detection of plague outbreaks known to humans. Second, it offers clear evidence that the genetically different Yersinia pestis strains were deadly for humans. Till now, the earliest known strains of the Y. pestis were potentially 5,300 years old. And likely did not cause serious disease.

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Two plagues afflicted same communities within centuries

The scientists found that two separate plagues spread in southeast Siberia. The first one approximately 5,500 years ago, and another a few centuries later. The team noted that in the first incident, several close relatives died at a site called Ust’Ida and were laid to rest in mass graves. More people were infected by the same strain 37 kilometres away in Bratskii Kamen. "The clearest explanation for this mass death is widespread infection with plague," Ruairidh Macleod, a co-author of the study, told Popular Science. He said it is similar to "human-to-human transmission of the disease."

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The same rodent caused the two outbreaks

Interestingly, the researchers identified biological relatives among victims of both outbreaks buried in separate graves. According to Macleod, this finding shows that the "same populations over hundreds of years" were exposed to new outbreaks of plague over several centuries. The pathogen responsible for the outbreaks originated from the same wild rodent host species—most likely marmots.

Several children also died in both outbreaks, and the mortality among the younger ones was high. Children between the ages of eight and 11 were seriously impacted. Scientists said that the Y. pestis strain, which had not been discovered before, may have evolved around 5,700 years ago. A gene that made the disease more fatal, especially for children, isn't present in other modern or historical Y. pestis strains.

What the study on plague discovery in Russia tells us

Till now, experts have believed that community-wide outbreaks only happened once prehistoric man moved to bigger habitations and formed cities. However, this study shows that even hunter-gatherers, who were mostly on the move, were also affected by it. The finding also thwarts the belief that prehistoric plague strains were less deadly because of the absence of particular genes linked with bubonic plague.