Researchers have analyzed the oldest case of bubonic plague to date and revealed that humans have been suffering from the disease for much longer than previously thought.
By analyzing the genome of the plague-causing bacteria, Yestina pestis, recovered from the remains of two 3,800-year-old skeletons unearthed in the Samara region of Russia, researchers from the Max Plank Institute were able to determine that both Bronze Age people carried the ancestral strain of the plague that would eventually give rise to the Black Death.
“Both individuals appear to have the same strain of Y. pestis,” explains Kirsten Bos, co-author of the paper published in Nature Communications, in a statement. “And this strain has all the genetic components we know of that are needed for the bubonic form of the disease. So plague, with the transmission potential that we know today, has been around for much longer than we thought.”
The plague has caused some of the most devastating pandemics in human history, wiping out up to half of all western Europeans during the Black Death, killing up to 50 million in the Near East during the Plague of Justinian, and burning through India and China in major epidemics as recently as the 19th century.
Even though this one disease has shaped so much of Eurasian history, altering culture and civilization as it swept the continents, where exactly it came from – and when it gained its ruinous virulence – has remained elusive.
Some of the earliest evidence suggests that Y. pestis was living among humans during the Late Neolithic and early Bronze Age. But the genetics of these samples seem to show that it had not yet managed to be transmitted by fleas, and so the ability to inflict such deadly impact would have been significantly limited.
After studying nine individuals of the Srubnaya culture discovered in the region, however, the researchers revealed that even as early as close to 4,000 years ago, Y. pestis was likely transmitted by fleas. The evidence was found after two of the skeletons that were buried together in a single grave were found to have been carrying the bacteria.
“Our Y. pestis isolates from around 4,000 years ago possessed all the genetic characteristics required for efficient flea transmission of plague to rodents, humans and other mammals,” says co-author Maria Spyrou.
Previous studies have suggested that all the plagues were the result of a single strain that has been circulating around Eurasia, but this study now hints at the possibility that there were at least two. Whether or not both of these strains were equally virulent and deadly remains to be seen.