The oldest strains of the plague were already ‘highly lethal’ thousands of years before the Black Death, according to new research.
The Black Death, which peaked between 1347 and 1353, was the most devastating pandemic in human history, leading to the death of up to 50 million people – around half of Europe’s 14th Century population.
Typically, the plague has been associated with rats and crowded medieval cities.
However, according to a new study published in the journal Nature, the disease that swept across Europe during the Middle Ages was already killing humans in small hunter-gatherer communities 5,500 years ago.
A team of researchers analysed ancient DNA from human remains found at four hunter-gatherer cemeteries in the Lake Baikal region of East Siberia.
Using advanced DNA sequencing techniques, the researchers revealed previously unknown early strains of plague.
Study senior author Professor Eske Willerslev, of the University of Cambridge and the University of Copenhagen, said: ‘Whether the earliest forms of plague were mild or virulent has been a matter of debate, but our findings demonstrate that these ancient strains were already highly lethal.’
Lead author Dr Ruairidh Macleod, a Research Fellow at the University of Oxford, also added: ‘Based on the plague DNA, the genetic relationships between the victims, the archaeological analysis and the radiocarbon dating, we’ve built a really clear, complete picture of what happened during these outbreaks.’
In total, DNA from Yersinia pestis, which is the bacterium that causes a plague, was detected in 18 of 46 individuals.
At 39%, the figure is higher than the detection rate reported from some medieval plague pits.
Previous studies led many scientists to believe that the earliest forms of plague were unlikely to have caused major outbreaks.
However, this latest study challenges that assumption.
Two of the largest cemeteries showed an ‘exceptionally’ high number of children and young teenagers dead, which was something that puzzled archaeologists for decades.
Dr Andrzej Weber, of the University of Alberta, explained: ‘The unusually high number of children and the short timespan was a real puzzle that we’ve been trying to solve since the 1990s.
‘Finding out that plague was the cause is extraordinary, but it makes so much sense.’
The ancient plague strains also carried a unique ‘superantigen’ – a toxin-producing genetic factor not seen in historic plague strains.
Professor Martin Sikora, from the University of Copenhagen, added: ‘This finding changes our understanding of the earliest plague outbreaks.
‘Even before the bacterium evolved efficient flea-borne transmission, these ancient strains appear to have carried a potent combination of virulence factors that could make infection highly lethal.’
He says the findings suggest that the earliest known outbreaks may already have been as deadly as later historical forms of the plague, especially for children, even without flea-borne transmission.
‘The study also supports the idea that plague may have originated in Central or North-East Asia before later spreading across Eurasia through wild rodent reservoirs,’ Professor Sikora continued.
‘Archaeological evidence suggests these hunter-gatherers interacted closely with marmots – large burrowing rodents that still carry plague today.’