Plague infected 18 of 46 people buried at Siberian hunter-gatherer cemeteries 5,500 years ago

The evidence comes from burials in Siberia, and detected infection is not an established cause of death for each person. The finding, from a Nature paper led by Ruairidh Macleod, pushes lethal plague outbreaks back to a time before farming villages or cities were thought to have made them possible.

The team worked on teeth from four cemeteries in the Baikal region and reconstructed bacterial genomes from the DNA preserved inside them.

Children, siblings and graves dug in a hurry

Plague DNA was detected in 18 of the 46 people tested from hunter-gatherer cemeteries beside Lake Baikal in Siberia, and the burials date to about 5,500 years ago. According to the University of Copenhagen release carried by ScienceDaily (the university’s own Globe Institute announcement is also online), Yersinia pestis was present in 18 of the 46 people tested, close to 40 percent. The Cambridge account of the same work adds that this detection rate is higher than the rate reported from some medieval plague pits, a comparison that makes the Siberian numbers hard to dismiss as a stray infection or two. The pattern in the cemeteries is as telling as the percentage. The two largest sites held an unusually large number of children and young teenagers, and radiocarbon dating showed that many of the deaths fell close together in time. In several graves, siblings or parents and children appear to have died and been buried together. A photograph released with the Cambridge material shows a brother and sister from the Ust’-Ida burial site who both carried plague DNA.

Science News reported that the study began because of the large number of children’s graves at these sites, with researchers hoping that family ties might explain them. The burials were also described as mass graves, apparently filled in a hurry, at sites that were used only once, which fits a fatal outbreak better than a slow accumulation of deaths over generations. Macleod, then a PhD student at Cambridge and now at the University of Oxford, told the outlet the result was unexpected. Andrzej Weber, an archaeologist at the University of Alberta and principal investigator of the Baikal Archaeology Project, said that “Finding out that plague was the cause is extraordinary, but it makes so much sense.”

A toxin missing from later strains

The bacterium itself was a surprise. Earlier genetic work had suggested that the oldest plague lineages lacked the features that later let the disease spread efficiently through fleas and rodents, so researchers doubted such strains could drive major outbreaks. The Baikal genomes cut against that view. They carry a superantigen, a toxin-producing genetic factor that the release says has not been seen in historic plague strains, and superantigens are known to provoke extreme immune responses that can worsen the severity of an infection.

Eske Willerslev, who led the research at the University of Cambridge and the University of Copenhagen, said the findings “demonstrate that these ancient strains were already highly lethal.” Martin Sikora, a senior author and associate professor at Copenhagen, said they “appear to have carried a potent combination of virulence factors.” The full results are in the Nature paper, which has 21 authors and combines genetic, archaeological and radiocarbon evidence. For scale, the Cambridge release notes that the Black Death killed up to half of Europe’s population.

Marmots as the likely source

If fleas were not the main route, the question becomes how the infection reached people. The researchers point to marmots, large burrowing rodents that still carry plague today and that the Baikal hunter-gatherers lived alongside. The suspicion is that some outbreaks began when the disease passed directly from infected marmots to humans. The authors also see the work as support for the idea that plague first emerged in Central or North-East Asia before spreading across Eurasia through wild rodent reservoirs.

Science News adds that the analysis places the split from a less lethal relative at least 5,700 years ago, probably in Central Asia, and that the Baikal genomes are the oldest and most original form of the pathogen found so far. The previous oldest traces came from a single grave in Latvia and a mass grave at a Neolithic farming site in Sweden, both roughly 5,000 years old, which had fit the idea that plague turned dangerous only after farming and crowded living.

What remains uncertain

Outside experts are cautious about how far the story can be pushed. Nicolás Rascovan, a molecular biologist at the Institut Pasteur in Paris who led the Swedish ancient plague research, called the Baikal result “clear evidence of an outbreak in prehistoric times that argues against agricultural lifestyles” as the precondition for such epidemics. He also warned that it is difficult to pin down exactly which species or strain drove an ancient outbreak, and that several thousand years of Y. pestis evolution and spread remain poorly documented, so further surprises are possible.

The marmot link is likewise presented as the most likely origin and not a confirmed one. Science News notes that the pathogen could first have infected another animal the people dealt with, such as a bird, though that is raised as a possibility and not a finding. The count of 18 of 46 also refers to people in whom plague DNA was detected, which Science News describes as infection at the time of death; the sources do not report a separately established cause of death for each individual, and the outbreak interpretation rests on the burial evidence.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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