Together in death, early victims of plague

Bubonic plague, the lethal, virulent bacterium behind the Justinian Plague and the Black Death, emerged in humans about 4000 years ago, a millennium earlier than previously thought.

That’s the finding from research conducted by Kirsten Bos of the Max Planck Institute for the Science of Human History in Germany, and published in the journal Nature Communications.

Bos and colleagues examined nine human skeletons buried in ancient tombs at a site in Russia. One grave contained two people, and dating evidence revealed that they had been interred together 3800 years ago.

Analysis revealed that both had died of the plague – caused by a bacterium called Yersinia pestis – and that the same strain had infected them.

Bos and her colleagues retrieved Y. pestis remains from the corpses and sequenced the genomes.

Previous studies have identified Y. pestis strains from older sources, yielding different estimates for when the strain emerged. In a paper published in 2015, for instance, researchers reported DNA from the bacterium retrieved from 5000-year-old human teeth.

A 1999 paper used a genetic analysis to conclude that Y. pestis had evolved from a related bacterium, Yersinia pseudotuberculosis, between 1500 and 20,000 years ago.

Bos and her colleagues, however, say their Russian sample – and the short backtrack to its emergence – is the earliest found so far that contains the virulence factors associated with the bubonic form of the disease – and the adaptations necessary for it to use fleas as its primary vector.

“This strain has all the genetic components we know of that are needed for the bubonic form of the disease,” she says.