A hunter-gatherer who lived more than 5,000 years ago is the earliest known person to have died with the plague, researchers have revealed.
Stone-age communities in western Europe experienced a huge population decline about 5,500 years ago, an event that is thought to have subsequently enabled a huge migration of people from the east.
The plague has been posited as an explanation after it was previously been found in stone-age individuals, including a 20-year-old woman from a rural farming community in Sweden.
However, researchers claim their new discovery casts doubt on the idea suggesting the nature of the strain found in hunter-gatherer would have been unlikely to cause rapid spread.
“We think that these early forms of Y.pestis couldn’t really drive big outbreaks,” said Prof Ben Krause-Kyora, co-author of the study at the Christian-Albrecht University of Kiel, Germany.
Writing in the journal Cell Reports, Krause-Kyora and colleagues describe how they analysed ancient DNA recovered from the teeth and skull bones of four individuals buried in a prehistoric rubbish tip, or shell midden, at a site in Latvia called Riņņukalns.
The remains, dating to between 5,300–5,050 years ago, were from a young woman, a baby and two men, and were unearthed in two excavations, one in the 19th century and one just a few years ago.
The team screened the genetic material for signs of known pathogens, including Y. pestis – the bacterium that causes the plague, revealing one of the men, aged 20 to 30 years old, not only had DNA fragments, but also proteins, indicating he had died with a now-extinct form of the plague in his bloodstream.
“Up to date [it is], the oldest known plague victim,” said Krause-Kyora.
Further analysis revealed the strain likely split from all other forms of Y.pestis about 7,200 years ago, making it the earliest known strain of the plague, and was clearly different from those found later in the Neolithic and bronze age.
The researchers added the strain lacked the gene that allowed plague to be spread by fleas.
“The flea seems to be one of the major vectors which are driving really fast distribution and the fast infection during the middle ages,” said Krause-Kyora, adding black buboes, caused by infected lymph nodes, are associate with this route of spread.
Instead the team say the man could have had septicemic plague, an infection of the blood, caused by a rodent bite or pneumonic plague, which affects the lungs and is spread by droplets. While the latter is usually more virulent than bubonic plague, the team say the genetics of the early strain suggest its ability to spread may have been compromised.
The researchers also said they found high levels of Y.pestis DNA in the stone age man, suggesting he might have lived with the plague for some time and hence the disease might have been mild.
Krause-Kyora said the results – together evidence of Y.pestis in ancient populations beyond western Europe, the rarity of stone age plague pits, and the careful burial of the man in Latvia – suggested it was unlikely plague was to blame for the stone age population decline. Instead he backed the idea that factors such as climate change played a role.
Prof Simon Rasmussen of the University of Copenhagen, who was a co-author of research into the Swedish stone age plague victim, welcomed the new study but said it did not rule out the possibility that the plague had caused a dramatic decline in the stone-age population, adding there was little evidence that stone-age strains only caused mild disease.
“The individual does in fact overlap with the Neolithic decline and very likely died from the plague infection,” he said.
“We know that large settlements, trade and movement happened in this period and human interaction is therefore still a very plausible cause of the spread of plague in Europe at this time.”