Plague Was Killing Whole Families Thousands of Years Before the Black Death

An international team of researchers has found that plague was already a deadly threat 5,500 years ago, striking small hunter-gatherer communities near Lake Baikal in East Siberia long before farming and crowded cities created the conditions typically linked to major outbreaks. The findings, published in Nature, come from ancient DNA extracted from human remains at four burial sites in the region.

By sequencing genetic material preserved in teeth, scientists reconstructed ancient bacterial genomes and identified previously unknown early forms of plague. Senior author Eske Willerslev, of the University of Copenhagen and University of Cambridge, said the findings settle a long-standing debate: these ancient strains were already highly lethal, not mild as some had assumed.

Out of 46 individuals tested, DNA from the plague-causing bacterium Yersinia pestis was found in 18 — nearly 40 percent, a higher detection rate than at some medieval plague burial sites.

A Decades-Old Puzzle Solved

At the two largest cemeteries, archaeologists had struggled since the 1990s to explain an unusually high number of children and young teenagers buried within a short timespan. Radiocarbon dating showed many deaths occurred close together, with siblings, and sometimes parents and children, apparently dying during the same outbreak. Researchers now believe plague explains this pattern.

The ancient strains also carried a distinctive superantigen — a toxin-producing genetic factor absent from historic plague strains — which can trigger an unusually intense immune response and severe inflammation, making infections far more dangerous even without the efficient flea-borne transmission that later characterized bubonic plague.

The findings support the theory that plague first emerged in Central or Northeast Asia and spread through wild rodent populations. Archaeological evidence shows the Lake Baikal hunter-gatherers had close contact with marmots, burrowing rodents that still carry plague today, suggesting some outbreaks may have jumped directly from marmots to humans — proving the disease could devastate small communities thousands of years before cities and flea-driven epidemics made it infamous.