(CN) – New genetic evidence suggests nomads migrating into Europe during the Stone Age might have been trying to escape the plague, but instead brought it with them.
These findings stem from an analysis of the plague-causing bacterium Yersinia pestis by scientists at the Max Planck Institute for the Science of Human History in Germany.
After screening more than 500 ancient skeletal samples, the team was able to recover the full genomes of the plague bacteria from six individuals.
The team’s analysis of these samples, published Wednesday in the journal Current Biology, reveals the plague entered Europe about 4,800 years ago and coincides with a large-scale migration of people from the Caspian-Pontic Steppe – in present-day Ukraine and Russia – into Europe.
The Y. pestis genomes, which were found in different parts of Europe, are fairly closely related, according to the team.
“This suggests the plague either entered Europe multiple times during this period from the same reservoir, or entered once in the Stone Age and remained there,” said first author Aida Andrades Valtuena, a researcher at the Max Planck Institute.
To determine which scenario was more likely, the team reviewed their data in the context of existing ancient DNA and archeological evidence of the movements of the steppe migrants.
The group’s distinct genetic markers allowed the scientists to trace their movements and genetic influence, which is present in nearly all modern-day Europeans. The team’s analysis determined the earliest signs of the plague in Europe overlap with the arrival of steppe ancestry.
This finding supports the “view that Y. pestis was possibly introduced to Europe from the steppe around 4,800 years ago, where it established a local reservoir before moving back towards Central Eurasia,” according to co-lead author Alexander Herbig, also of the Max Planck Institute.
The team’s analysis of the genomes also confirmed that genes related to plague virulence were changing during this period, as suggested in previous studies. Additional research will be needed to determine how these changes impacted the severity of the disease.
However, Y. pestis – which has been responsible for several major pandemics, including the Black Death in the 14th century – might have been capable of causing large-scale epidemics before these genetic changes occurred.
Fear of the plague could have spurred the flight of the steppe migrants, according to co-lead author Johannes Krause, director of the Department of Archaeogenetics at the Max Planck Institute.
“The threat of Y. pestis infections may have been one of the causes for the increased mobility during the late Neolithic-early Bronze Age period,” Krause said.
Madagascar is currently experiencing a wave of Y. pestis infections. More than 2,200 people in the African nation have been infected by the bacterium, in what has been described as the “worst outbreak in 50 years.”
The outbreak has killed 195 people so far, according to World Health Organization statistics.