Siberian graves point to earliest known plague outbreak

Researchers have identified what they describe as the oldest known evidence of a plague outbreak, based on ancient DNA recovered from prehistoric graves in Siberia. The findings push the history of plague into hunter-gatherer communities about 5,500 years ago and challenge the idea that major infectious outbreaks began mainly with farming societies.

The study, published Wednesday in Nature, examined skeletons from burial sites near Lake Baikal and the Angara River in modern-day Siberia. The graves contained remains from several generations, along with artifacts including arrowheads that helped date the sites.

Researchers tested DNA from teeth and found genetic traces of Yersinia pestis, the bacterium that causes plague, in 18 of 46 skeletons analyzed, according to the study. That detection rate, about 40%, led the researchers to conclude that plague probably caused many of the deaths at the sites.

Ruairidh Macleod, a postdoctoral fellow at the University of Oxford and the study’s lead author, said one grave held three young girls, ages 4 to 9, who were buried at the same time and all carried substantial amounts of plague DNA. Macleod said the pattern showed a severe effect on children in those communities.

Several graves held multiple children who appear to have been buried together without signs that the graves were reopened, according to the study. One shared grave contained a boy between 12 and 15 and a girl between 13 and 16 who were not close biological relatives, but both yielded plague DNA. Another held two half-sisters and an unrelated boy, with plague DNA found in the boy.

Evidence of spread within families

The researchers said the findings point to two separate plague outbreaks among the hunter-gatherer groups. They also said the evidence suggests an early form of plague spread among relatives and close contacts, rather than appearing as an isolated infection.

A prior study found plague in a single hunter-gatherer who died about 5,000 years ago in what is now Latvia, but it did not show an outbreak or transmission between people. Nicolás Rascovan, an ancient DNA researcher at the Institut Pasteur in Paris who was not involved in the new research, told NBC News the Siberian findings provide clear evidence of a prehistoric outbreak and weaken the view that agriculture was the main driver of plague’s emergence.

Scientists have often linked the rise of epidemic diseases to the Neolithic Revolution, when many groups began farming, living in denser settlements and keeping domesticated animals. The new study suggests plague also emerged in some hunter-gatherer groups that lived near wild animals carrying the bacterium, according to the researchers.

Eske Willersev, an evolutionary geneticist at the University of Copenhagen and a contributor to the study, said the findings undercut the idea that hunter-gatherer life was largely free of dangerous pathogens. He said plague may have struck such communities repeatedly.

An older form of plague

The bacterium identified in the Siberian graves is the same species responsible for the Black Death, the pandemic that began in 1347 and killed about half of Europe’s population, according to NBC News. Researchers said the ancient strain likely lacked later genetic features that allowed plague to spread through flea bites and cause bubonic disease.

Scientists think those traits emerged about 3,800 years ago, according to the study. Macleod said the Siberian outbreaks were more likely pneumonic plague, which infects the lungs and can spread through coughing.

The skeletons used in the study were excavated by Russian archaeologists in the 1980s and later preserved. Because ancient DNA often degrades, Macleod said the absence of plague DNA in some remains does not rule out infection; he compared the Siberian results with a medieval London plague pit where researchers detected plague DNA in only 20% of known victims.

Plague still appears occasionally in rural areas and can be treated with antibiotics if caught early. Madagascar reported more than 2,400 pneumonic plague cases in 2017, and NBC News reported that a person in Arizona died of plague last year, the first recorded U.S. plague death since 2007.

This story draws on original reporting from NBC News.