Ancient DNA from Late Stone Age cemeteries in southeastern Siberia provides the earliest evidence so far of plague outbreaks, according to research reported in Nature. The evidence indicates that the disease affected hunter-gatherer communities along the Angara River beginning about 5,500 years ago, with a second outbreak occurring roughly 400 to 600 years later.
Researchers analyzed dental pulp from the remains of 42 people buried at four cemeteries. Yersinia pestis DNA—the bacterium responsible for plague—was identified in 18 individuals, or 39% of those examined. Because degraded ancient DNA can produce false-negative results, the researchers suspect that plague may have caused the deaths of more people buried at the sites than the tests confirmed.
The cemeteries include Ust-Ida, located on the Angara River northwest of Lake Baikal. Shared graves there predominantly contained children. Across two of the cemeteries, at least two-thirds of those who died were younger than 15, and many individuals were buried with siblings or other relatives. The researchers suggest that children may have been especially vulnerable, while older hunter-gatherers could have survived earlier exposure and acquired some immunity.
The team included researchers from institutions in Copenhagen, Alberta, Cambridge and London. Their genetic analysis indicates that Y. pestis emerged at least 5,700 years ago, after diverging from Yersinia pseudotuberculosis, a bacterium associated with abdominal pain, fever, diarrhea and vomiting. The outbreaks identified at the cemeteries therefore began at least two centuries after the plague bacterium first appeared.
The hunter-gatherers most likely contracted pneumonic plague, which affects the lungs. The source reporting says they may have been exposed while butchering or eating raw marmots, described as the primary animal reservoir in the area. The disease could then have spread between people in close contact.
The Y. pestis recovered from the remains carried a superantigen, or toxic protein, capable of triggering severe immune reactions. Researchers said this could have increased the disease’s lethality, particularly among children. The findings also indicate that dangerous plague outbreaks were possible in small, mobile communities, not only in later densely populated settlements.
