Ancient DNA Reveals Plague Outbreak in Siberia 5,500 Years Ago

Ancient DNA Reveals Deadly Plague Outbreak Among Siberian Hunter-Gatherers 5,500 Years Ago

Scientists have discovered some of the oldest known genetic evidence of plague in human remains from southeastern Siberia, revealing that the disease may have killed members of hunter-gatherer communities thousands of years before the Black Death devastated Europe. The findings challenge previous assumptions about how early plague strains spread and suggest that prehistoric communities may have experienced deadly outbreaks long before the rise of crowded cities.

Ancient DNA Uncovers an Unexpected Plague Outbreak

Researchers analysing ancient human remains from cemeteries near Lake Baikal in southeastern Siberia have identified genetic evidence of plague infections dating back approximately 5,500 years.

The discovery provides new insights into the early history of Yersinia pestis, the bacterium responsible for plague, one of the most devastating infectious diseases in human history.

The findings, published in the scientific journal Nature in June 2026, suggest that prehistoric hunter-gatherer communities experienced serious outbreaks of the disease much earlier than previously established evidence had indicated.

Scientists examined DNA recovered from human remains and discovered evidence of plague infection in 18 out of 46 individuals investigated. The remains belonged to people from small, mobile communities that lived around Lake Baikal thousands of years ago.

The discovery was particularly surprising because many of the individuals buried in the cemeteries were children and young adolescents. Their remains showed no obvious physical injuries that could explain their deaths.

Researchers believe that the findings may help explain an otherwise mysterious pattern of deaths in the ancient communities.

The results also challenge the assumption that early plague strains were generally unable to cause severe outbreaks among humans.

Although scientists have long understood that plague has ancient origins, the discovery suggests that some early forms of the bacterium may have been capable of causing substantial mortality before the pathogen developed all the characteristics associated with later forms of the disease.

What Is Plague, and Why Is It Historically Important?

Plague is an infectious disease caused by the bacterium Yersinia pestis. It can cause severe illness and, without appropriate treatment, may be fatal.

The disease is best known for the Black Death, the devastating pandemic that spread across Europe, Asia and parts of North Africa during the 14th century. The pandemic killed tens of millions of people, profoundly affecting societies, economies and population structures.

Plague has appeared in several major outbreaks throughout history. Its impact has depended on factors such as the form of the infection, the environment, patterns of transmission, access to treatment and the vulnerability of affected populations.

The bacterium can circulate among wild animals, particularly certain rodents, and can sometimes spread to humans through infected fleas. Depending on the form of plague, transmission can also occur through contact with infected tissues or, in the case of pneumonic plague, infectious respiratory droplets.

Before the latest discovery, some of the earliest known ancient strains associated with human plague dated to approximately 3,800 years ago.

The newly identified Siberian evidence pushes the known history of plague infection in humans considerably further into the past.

However, researchers caution that finding ancient bacterial DNA does not automatically establish exactly how the disease spread, how many people were infected in the wider population or whether the outbreak followed the same pattern as later pandemics.

Instead, the discovery provides new evidence that scientists can use to investigate the evolution of the pathogen.

Why the Siberian Discovery Surprised Researchers

The research began with a different archaeological question.

Scientists were investigating human remains recovered from ancient cemeteries around Lake Baikal. Archaeologists had studied the burial sites for decades, but the remains contained patterns that researchers wanted to understand more clearly.

Two of the cemeteries contained an unusually high number of children and young adolescents. Many of the individuals showed no obvious physical trauma that could explain why they died.

The researchers combined archaeological evidence, radiocarbon dating and advanced genetic analysis to investigate the possible cause.

Radiocarbon dating helped establish when the individuals lived and whether their deaths occurred around the same period.

The genetic analysis then revealed the unexpected presence of Yersinia pestis in a substantial proportion of the remains examined.

According to lead study author Ruairidh Macleod, a research fellow at the University of Oxford in the United Kingdom, the radiocarbon evidence suggested that many deaths occurred within a relatively short period.

This pattern raised the possibility that an infectious disease had spread through the communities.

The discovery was significant because hunter-gatherers generally moved across the landscape in search of food and other resources. Researchers had previously considered whether such mobility might make it more difficult for certain infectious diseases to cause large, concentrated outbreaks.

The Siberian findings suggest that mobility did not necessarily protect every community from severe disease.

The results do not prove that all hunter-gatherer societies experienced similar outbreaks. However, they demonstrate that some mobile prehistoric populations could suffer substantial losses from infectious disease.

Evidence of Infection Among Children and Families

One of the most striking aspects of the discovery was the apparent impact of plague on children and young people.

The ancient DNA analysis identified infections among several individuals buried in the cemeteries, including members of related families.

In some cases, the remains suggested that parents, children and siblings had been buried close together.

The researchers believe these burial patterns may reflect how the disease affected families within the communities.

When an infectious disease enters a small population, close contact between relatives can increase opportunities for transmission, particularly when people care for sick family members without understanding the cause of the illness.

However, the exact routes of transmission in the Siberian communities remain uncertain. Genetic evidence and burial arrangements can help reconstruct possible events, but they cannot establish every interaction between individuals.

Other graves contained relatives who appeared to have died at different times. The study suggests that the region may have experienced more than one outbreak, with separate episodes occurring hundreds of years apart.

These findings indicate that plague-related infections may have affected the Lake Baikal region repeatedly rather than appearing in only one isolated incident.

The researchers also identified an unusual genetic feature associated with the ancient bacterial strain that may have contributed to the severity of some infections.

Further research will be necessary to establish precisely how that feature affected the disease and whether its effects differed according to age or other characteristics of the infected individuals.

A Distinct Ancient Strain of the Plague Bacterium

To investigate the pathogen, scientists extracted ancient DNA from human remains, including teeth.

Teeth can preserve genetic material from microorganisms that were present in the bloodstream during a person’s life. Under suitable conditions, this material can survive for thousands of years.

By analysing the recovered genetic material, researchers reconstructed genomes associated with an ancient form of Yersinia pestis.

The study suggests that the strain originated approximately 5,700 years ago and differed from other previously identified ancient and modern strains.

This distinction is important because bacteria evolve over time. Genetic changes can affect their ability to survive in different environments, infect hosts and spread between individuals or animal populations.

Some earlier plague strains appeared to lack certain genetic characteristics associated with efficient flea-borne transmission.

That led researchers to question how early versions of the bacterium infected humans and whether they were capable of causing substantial outbreaks.

The Siberian discovery adds complexity to that picture.

The ancient strain appears to have possessed biological features that may have contributed to severe disease, even though its transmission characteristics differed from those of later plague strains.

Senior study author Martin Sikora, a population geneticist and associate professor at the University of Copenhagen, said the findings change how researchers understand the earliest plague outbreaks.

The evidence suggests that the severity of an infection cannot be understood solely by looking at whether a pathogen has developed the transmission mechanisms that later became important in its spread.

Nevertheless, scientists still need more evidence to determine how the ancient strain moved between people and whether it spread primarily through animal-to-human transmission, human contact or a combination of routes.

Could Marmots Have Spread the Disease?

Researchers believe wild rodents, particularly marmots, may have played an important role in the ancient outbreak.

Marmots are large ground-dwelling rodents that inhabit parts of Central and northern Asia. Some populations can carry Yersinia pestis, allowing the bacterium to persist in animal communities over long periods.

The researchers suggest that people living around Lake Baikal may have encountered the pathogen while hunting, skinning or butchering infected marmots for meat and fur.

Handling infected animals or tissues could have exposed individuals to the bacteria.

Archaeologists also discovered marmot-tooth pendants among some of the burial remains. Although these objects do not prove how the infections occurred, they provide evidence that marmots were part of the communities’ material culture.

The researchers consider the region a possible important area in the early ecological history of plague.

However, identifying where a pathogen may have circulated in ancient times is not the same as establishing a single, definitive geographical origin for the disease.

The bacterium's history is complicated by the movement of animals, changing environments and interactions between different human populations.

Further genetic evidence from other archaeological sites will be needed to reconstruct how the pathogen moved across Eurasia and how its characteristics changed over time.

A Possible Toxin Could Have Increased Disease Severity

Another important finding involved a genetic feature described by the researchers as a possible superantigen.

Superantigens are substances that can trigger an unusually strong immune response under certain circumstances. Such responses can contribute to severe inflammation and tissue damage.

The researchers identified a genetic factor in the ancient strain that may have influenced the severity of infection.

Their analysis suggested that this feature could have been particularly relevant to the high number of deaths among children in the studied communities.

However, the precise biological effects of the ancient genetic feature remain a subject for further investigation.

Scientists cannot determine every detail of an infection's severity from ancient DNA alone. The outcome of a disease also depends on the person's immune system, overall health, exposure level and other environmental or biological factors.

The researchers also noted a relationship between the identified feature and a related bacterium, Yersinia pseudotuberculosis, which naturally occurs in animals and can infect humans.

Human infection with Y. pseudotuberculosis may occur through contaminated food or water. This connection could provide clues about the ecological relationships between early Yersinia bacteria, animals and humans.

However, it does not establish that the Siberian plague outbreak was caused by contaminated food or water. The precise route of infection remains uncertain.

Did Plague Spread Between Humans?

One of the central questions raised by the study concerns whether plague spread directly between members of the prehistoric communities.

The presence of bacterial DNA in numerous individuals suggests that infections were not limited to a single person.

The burial patterns also indicate that related individuals may have died during the same period, potentially reflecting the spread of disease within families or close social networks.

Independent expert Ian Light-Maka, a postdoctoral associate at the Max Planck Institute for Infection Biology in Berlin, described the proportion of individuals with evidence of infection as unusually high compared with previous research into early plague strains.

He noted that earlier studies had often identified apparently isolated infections, leaving scientists uncertain about whether the earliest strains could sustain transmission among people.

The new findings provide evidence that challenges that interpretation.

Nevertheless, Light-Maka cautioned that more research at other archaeological sites and from the same historical period is needed to confirm the extent of human-to-human transmission.

The discovery of bacterial DNA in multiple individuals does not, by itself, reveal the exact chain of transmission.

The infections could have resulted from direct contact between people, repeated exposure to infected animals, environmental factors or several mechanisms operating together.

Understanding these possibilities is essential to reconstructing how plague evolved into a pathogen capable of causing major historical pandemics.

How the Discovery Changes Our Understanding of Ancient Societies

The research also highlights the importance of infectious disease in shaping human history before the development of large cities and densely populated agricultural societies.

Many accounts of historical epidemics focus on urban centres, trade routes and crowded settlements, where people and goods moved through extensive networks.

The Siberian findings suggest that serious outbreaks could also affect smaller communities whose members travelled across the landscape.

Hunter-gatherer populations maintained close relationships with the natural environment. They depended on animals and plants for food, clothing, tools and other resources.

These relationships offered opportunities for survival but could also expose people to microorganisms circulating among wildlife.

The study therefore contributes to a broader understanding of how human behaviour, animal ecology and environmental conditions influenced the evolution of infectious diseases.

It also demonstrates the value of combining archaeology and genetics. Human remains provide evidence about past lives, while ancient DNA can reveal biological information that would otherwise remain invisible.

Together, these methods allow scientists to investigate events that occurred thousands of years before written historical records existed.

What Ancient Plague Research Means Today

Although the Siberian outbreak occurred thousands of years ago, understanding the evolution of Yersinia pestis remains relevant today.

Plague has not disappeared from the modern world. Cases continue to occur in some regions, particularly where the bacterium circulates among wild rodents and other animals.

Modern medicine provides diagnostic tools and effective antibiotics for treating plague when appropriate treatment is available promptly. Early recognition and medical care are important because the disease can progress rapidly.

The discovery does not mean that the world is facing a new plague pandemic. It is evidence about the disease's ancient history, not a warning that a comparable outbreak is imminent.

Instead, the findings may help scientists understand how the bacterium evolved, how it interacted with animal populations and how its ability to cause severe disease changed over time.

This information can contribute to wider research into zoonotic diseases, which are infections that can pass between animals and humans.

As human populations interact with wildlife through hunting, farming, travel and environmental change, understanding the history of such pathogens can provide useful context for modern disease research.

However, ancient DNA findings must be interpreted alongside contemporary epidemiological evidence before drawing conclusions about present-day risks.

More Questions Remain About Plague’s Ancient Journey

Despite the breakthrough, scientists still have important questions about how plague spread across northern Eurasia.

Researchers have found evidence of ancient plague in the Lake Baikal region and in other parts of Eurasia, but the routes connecting these discoveries remain uncertain.

The study authors have raised questions about how the disease may have reached northern Europe within a few hundred years of the Siberian outbreaks.

Possible explanations include the movement of infected animals, transmission between human populations or separate spillover events from wildlife into people.

Changes in climate, animal distribution and patterns of human movement may also have influenced the pathogen's spread.

Researchers will need to compare more ancient bacterial genomes from different places and periods to determine which explanations are best supported by the evidence.

The Siberian discovery is therefore an important step rather than the final answer to the history of plague.

The study's central finding is that deadly plague infections may have affected prehistoric hunter-gatherer communities approximately 5,500 years ago, challenging previous assumptions about the disease's early spread and severity. As scientists continue examining ancient DNA, they may uncover further evidence of how interactions between humans, animals and their environment shaped one of history's most consequential infectious diseases.