Researchers from France, Sweden and Denmark found the oldest ever evidence of plague-causing Yersinia pestis bacteria after studying the genetic material of a 20-year-old woman who died around 5,000 years ago in Sweden. According to the team, the strain was a completely new type never before seen, and was also the oldest discovered at the time of the study.
It had the same genetic makeup as strains of pneumonic plague still in existence today.
Traces of it were also found in another deceased person who was buried at the same site.
This suggested the young woman probably died of the disease, the team added.
The finding also offers scientists a new insight into how plague can spread between people, and provides a new theory into how the civilisations of the time were affected.
The strain that was found was believed, at the time of the study, to be the closest known genetic origin of the Y. pestis bacteria.
This particular strain is thought to have diverged from other strains around 5,700 years ago.
By contrast, huge human migrations from Eurasia and into Europe occurred about 700 years later, and the way in which this led to the decline of Neolithic farming culture is not known for certain.
Studies before this one had suggested the travellers brought the disease with them which subsequently killed Stone Age farmers.
“This is exactly what was observed in these settlements after 5,500 years ago.”
Mr Rasmussen said the plague would have spread along trade routes and eventually reached Sweden, where the traces of it were found.
Mr Rasmussen also said plague is “maybe one of the deadliest bacteria that has ever existed for humans.”
He told Science Daily: “And if you think of the word ‘plague,’ it can mean this infection by Y. pestis, but because of the trauma plague has caused in our history, it’s also come to refer more generally to any epidemic.
“The kind of analyses we do here let us go back through time and look at how this pathogen that’s had such a huge effect on us evolved.”
The team’s findings, published in the journal Cell in 2018, were based on publicly available data.