Ancient DNA recovered from human remains in southeastern Siberia has provided new evidence about the devastating history of plague, suggesting that the disease was already capable of causing deadly outbreaks among humans around 5,500 years ago.

The discovery was made at several ancient cemeteries near Lake Baikal, where researchers studied the remains of prehistoric hunter-gatherers.

Scientists identified previously unknown strains of Yersinia pestis, the bacterium responsible for plague. The newly identified strains may represent some of the oldest evidence of plague infection ever found in humans.

Before this discovery, some of the earliest known strains associated with bubonic plague were estimated to be around 3,800 years old.

The findings challenge the earlier assumption that prehistoric strains of the bacterium were too limited in their ability to cause serious outbreaks.

Evidence of a deadly outbreak

Researchers became interested in the Lake Baikal cemeteries because an unusually large number of children and young teenagers had been buried there. Many of the remains showed no obvious signs of physical trauma or another explanation for their deaths.

Using ancient DNA analysis, archaeological evidence and radiocarbon dating, scientists identified plague bacteria in 18 of 46 individuals examined.

The researchers also found evidence suggesting that a large number of deaths occurred within a relatively short period. Some graves contained several members of the same family, including parents, children and siblings.

Scientists believe this pattern could indicate that the disease spread between relatives as they cared for sick family members.

Other relatives were buried separately, which may reflect different waves of infection occurring over time.

Researchers believe at least two major outbreaks occurred in the region, separated by several hundred years.

Children appear to have been particularly affected

One of the most striking findings involved young children.

Scientists discovered genetic evidence of a unique toxin, known as a superantigen, in the ancient plague strain. Such microbial toxins can trigger powerful immune responses and potentially make infections more severe.

The researchers found indications that this factor may have had a particularly serious effect on children between approximately 7½ and 11 years old.

In one particularly tragic grave, three young girls were apparently buried after dying around the same time. The girls were related, with two being sisters and the third their cousin.

The youngest was estimated to be around 4 or 5 years old, while the oldest was approximately 9.

Researchers said the discovery demonstrates that early plague strains may have possessed combinations of characteristics that made them highly dangerous even before the bacterium developed the efficient flea-based transmission associated with later forms of plague.

How did prehistoric people become infected?

Scientists believe the hunter-gatherers may have contracted the disease through contact with marmots, large rodents that remain an important natural host for plague in the region today.

The communities are believed to have hunted and processed marmots for meat and fur. Handling infected animals could have exposed people to Yersinia pestis.

Archaeologists also discovered marmot teeth used as pendants among some of the burials, providing additional evidence of the close relationship between the communities and these animals.

Lead researcher Ruairidh Macleod said the findings support the possibility that marmots may have played an important role in the early history of plague.

Some scientists have proposed that plague originated somewhere in Central or northeastern Asia before eventually spreading across Eurasia.

A new understanding of prehistoric disease

The discovery also challenges the idea that infectious diseases could not seriously affect highly mobile hunter-gatherer societies.

Because these communities frequently moved across the landscape, scientists had previously expected infectious diseases to have difficulty establishing sustained outbreaks.

However, the evidence from Lake Baikal suggests that plague may have caused severe mortality even within relatively small and mobile prehistoric populations.

Researchers say the findings provide a more complicated picture of how zoonotic diseases evolved and spread. Hunter-gatherers and other mobile populations may have played an important role in the development and transmission of diseases through their interactions with animals.

Many questions remain

Despite the discovery, scientists still do not know exactly how plague moved across Eurasia.

The researchers noted that similar evidence of the disease appears in Northern Europe only a few hundred years after the outbreaks identified around Lake Baikal.

That raises questions about whether the bacterium spread rapidly through wild animals, moved between human populations or followed a combination of both routes.

Understanding this ancient history could help scientists better understand how infectious pathogens evolve and adapt over time.

Although plague is strongly associated with historic catastrophes such as the Black Death, cases of plague still occur today. Researchers say studying its ancient evolution can therefore provide important insight into the disease’s continuing presence.

Source: CNN, “Oldest known evidence of plague reveals the disease’s deadly impact 5,500 years ago,” by Ashley Strickland, June 18, 2026.