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Ancient plague outbreaks were already deadly 5,500 years ago

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September 15, 2026
2 min read

Ancient plague outbreaks were already deadly 5,500 years ago

Plague may have been killing people thousands of years before the rise of cities and the crowded living conditions traditionally associated with its spread. New research published in Nature has found evidence that Yersinia pestis, the bacterium responsible for plague, was already causing potentially deadly outbreaks around 5,500 years ago among small, mobile hunter-gatherer communities in the Lake Baikal region of East Siberia.

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The international study examined ancient DNA from human remains recovered at four prehistoric burial sites. Researchers sequenced genetic material preserved in teeth and identified plague bacteria in 18 of the 46 people tested, nearly 40 per cent of the individuals examined.

The findings challenge the long-standing assumption that the earliest forms of plague were relatively mild because they lacked some of the genetic characteristics later associated with efficient flea-borne transmission.

Researchers instead found evidence that these early strains could have been highly virulent. They also identified a distinctive superantigen, a genetic factor associated with toxin production and potentially severe immune reactions, that has not been found in historic plague strains.

The evidence may also explain a longstanding archaeological mystery. At two of the largest burial sites, unusually high numbers of children and young teenagers had died within a relatively short period. Radiocarbon dating suggests that several deaths occurred close together, with some graves containing possible family groups, including siblings and parents with children.

The research was conducted by an international team involving scientists from the University of Copenhagen, University of Cambridge, University of Oxford and University of Alberta, among other institutions. Lead author Ruairidh Macleod carried out the work while at Cambridge and is now a Research Fellow at Oxford. Senior authors include Eske Willerslev and Martin Sikora of the University of Copenhagen.

The researchers also point to a possible connection with marmots, which lived alongside these hunter-gatherer communities and remain natural carriers of plague today. Direct contact with infected animals could have provided a route for the disease to pass into humans.

The study suggests plague did not need cities, dense populations, or flea-driven transmission to cause serious outbreaks. Its deadly history may reach much further back into human prehistory than previously understood.

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