Oldest plague outbreak found in Siberian hunter-gatherers 5 500 years ago, rewriting disease history
Ancient DNA from teeth in four Siberian burial sites shows that plague killed mobile hunter-gatherers long before agriculture and crowded cities, challenging deep assumptions about how epidemics begin.
An international team of geneticists has uncovered the oldest known plague outbreak, dating to about 5 500 years ago among hunter-gatherer communities near Lake Baikal in Siberia. The study, published on 17 June 2026 in Nature, identifies Yersinia pestis DNA in the teeth of 18 out of 46 individuals unearthed from four prehistoric cemeteries along the Angara River.
A surprise in the Siberian forest
For decades archaeologists had been puzzled by an unusual mortality profile at the Baikal sites – an excess of children and adolescents buried within a very short period, without signs of violence or trauma. “No clear explanation as to why that was the case” existed, said study lead author Ruairidh Macleod, a palaeogenomicist at the University of Oxford, during a press briefing. When the team screened ancient dental pulp, they found Y. pestis in nearly 40 % of the tested individuals, a prevalence higher than some medieval plague pits.
Finding out that plague was the cause is extraordinary, but it makes so much sense.
Radiocarbon dating revealed two distinct epidemic waves. The first struck between 5 520 and 5 265 years ago; a second followed between 5 315 and 4 425 years ago. Multiple family members – aunts, nephews, cousins – were buried in separate graves at slightly different times, showing that the disease circulated within small kin groups.
A deadly germ well before cities
Earlier strains of Yersinia pestis had been debated as possibly mild. The Siberian genomes settle that argument. “Our results show that these ancient strains were already very deadly,” said senior author Eske Willerslev, an evolutionary geneticist at the University of Copenhagen and the University of Cambridge. Children aged 8 to 11 years made up a large share of the victims, likely because their immune systems were still developing.
The findings fundamentally change how we think about the origins and early impact of one of humanity’s most consequential pathogens.
- First known plague outbreak among Baikal hunter-gatherers, 18 of 46 individuals infected.
- Second plague wave in the Baikal region, roughly 5 300 years ago.
- Next oldest plague evidence found in Latvia, about 5 000 km to the west.
Marmots, not rats
The bacterium probably spilled over from marmots, large rodents that the Baikal hunter-gatherers hunted for meat and fur. Researchers think the infection passed to humans when people handled raw organs or infected hides during butchering, and later spread through coughing and sneezing within families. This adds weight to the hypothesis that plague originated in central or northeastern Asia and that marmots were the bacterium’s original reservoir.
Rewriting the textbook
The discovery overturns the long-held view that significant epidemics required settled agriculture and high population densities. The Baikal groups were mobile foragers with no contact with Neolithic farmers in western Eurasia. “The classic theory in the epidemiology of ancient diseases is that this kind of epidemic outbreak should not occur among hunter-gatherers,” Willerslev noted. The next oldest plague evidence comes from Latvia 5 300–5 000 years ago, roughly 5 000 km to the west, showing that the pathogen was already spreading across Eurasia millennia before the Justinianic Plague or the Black Death.
It’s only with the development of methods for studying ancient DNA that we’ve discovered it’s been around a lot longer than what we know from historical records.
