Portugal Colonial - Plague was killing hunter-gatherers 5,500 years ago: study

The plague is generally associated with rats spreading the disease through crowded medieval cities, sparking pandemics such as the Black Death that killed tens of millions of people across Europe from the 1300s to 1800s.

This was a long way from the rugged vistas surrounding Lake Baikal in the Russian region of Siberia, where archaeologists have spent decades studying the burial sites of pre-historic hunter-gatherers.

One of these sites has been particularly mystifying because of its "very unusual mortality profile" -- many children and adolescents appear to have died over a short period, Oxford University researcher Ruairidh Macleod told journalists.

The skeletons also bore no signs of violence or trauma, meaning there was "no reasonable explanation" for this catastrophic event, said the lead author of the new study in the journal Nature.

When the team of researchers sequenced ancient DNA from 46 people across four sites near the lake, they found Yersinia pestis -- the bacteria responsible for the plague -- in 18 of them.

This means nearly 40 percent of these people had the plague -- a higher rate than has been detected in some medieval mass graves. Trying to identify plague in such ancient DNA also throws up many false negatives.

The results were therefore "consistent with pretty much everybody having died of plague" at the burial sites across two outbreaks, the earliest of which was 5,500 years ago, Macleod said.

This was a "complete surprise," he added.

- Not a 'golden age' -

Until this discovery, the oldest traces of plague had been detected among farming communities in northern Europe around 5,300 years ago.

However exactly how deadly these ancient strains were has been "hotly debated" in the scientific community, according to the new study's senior study author Eske Willerslev.

It had been thought that this kind of outbreak could not occur among hunter-gatherers, said the geneticist at Cambridge University and the University of Copenhagen.

Because they lived in small groups and were constantly moving around, it was believed that "infectious disease can't really take a hold and devastate entire communities", he said.

This led the authors of some best-selling pop science books such as Yuval Noah Harari of "Sapiens" and Jared Diamond to portray the time of hunter-gatherers as a "kind of golden age" without disease or illness, Willerslev said.

"Well, it wasn't that easy to be a hunter-gatherer," he said, adding that it now looks like the plague was probably "very common" for them.

It was famously rats that spread the plague in the Middle Ages, but for these prehistoric Siberian outbreaks, a different animal was likely to blame: the Tarbagan marmot.

"Marmots are thought to be the original host species that plague first evolved in," Macleod explained.

Even today, cases of plague spread by marmots are regularly recorded in Siberia and Mongolia, where the rodents are hunted for their fur and meat.

This could have also been how the hunter-gatherers originally caught the virus.

"Presumably the first infection was from an animal interaction and then spread among humans" via respiratory droplets, said study co-author Astrid Iversen, a virology professor at Oxford.

She pointed out that today, the World Health Organization estimates three-quarters of all new infectious diseases jump over from animals into humans.

So these unlucky ancient-gatherers can provide a lesson for modern humans.

"Being able to understand the links between when they infect humans from animals and how they've evolved to be able to do that at different contexts and different places in time and space is really important for understanding the risk of that happening in the future," Macleod said.

A.Magalhes--PC