Bacteria in Ancient Teeth Push Back Origins of the Bubonic Plague

The deadly disease may have been transmitted to humans at least 800 years earlier than previously believed

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Double burial of two plague victims in the Samara region, Russia V.V. Kondrashin and V.A. Tsybin; Spyrou et al. 2018; Nature Communications

There are three major documented episodes of the plague. The first pandemic is the so-called “Justinian Plague,” which began in 541 C.E. during the reign of Byzantine emperor Justinian I, and is believed to have killed more than 25 million people. The Black Death followed, which decimated nearly one-third of Europe’s population in the 14th century. The third major pandemic originated in China in the 1860s and spread to port cities across the globe, killing an estimated 10 million people.

But for all the devastation that plague outbreaks have inflicted upon human history, researchers still have unanswered questions about the pandemics. When, for instance, did the plague bacteria first acquire the deadly properties that allowed it to spread among humans? As Ike Swetlitz reports for STAT, a new study of ancient skeletal remains suggests that the deadly disease was circulating in Bronze Age Eurasians around 800 years earlier than previously recorded.

Several years ago, archaeologists found the bodies of a man and a woman interred in a Bronze Age burial mound near Russia’s Volga River. Analysis revealed the remains to be approximately 3,800 years old. The individuals’ teeth were removed and sent to researchers at the Max Planck Institute in Germany, who performed genetic testing on the ancient tooth pulp.

As the researchers reveal in a paper published in Nature Communications, they were surprised to find that the teeth harbored the same strain of Yersinia pestis—a bacterium that has been linked to the plague pandemics.

Y. pestis lives in rodents and is transmitted to humans when fleas that bite infected rodents also chomp down on people. Recent studies have found that Y. Pestis variants were infecting humans as early as Late Neolithic/Early Bronze period. But these strains lacked the genetic adaptations that made the plague so efficient—“namely, adaptation to survival in fleas, which act as the main vectors that transmit the disease to mammals,” the Max Planck Institute explains in a statement.

According to a 2015 study, the bacterium only acquired the changes that made it a “highly virulent, flea-borne bubonic strain” around 3000 years ago.

The recent analysis of the Volga River remains, however, suggest that a flea-adapted strain of bubonic plaguewas infecting humans at least 800 years earlier.

Kirsten Bos, one of the authors of the new paper, tells Andrew Masterson of Cosmos that the strain extracted from the teeth of the Volga individuals “has all the genetic components we know of that are needed for the bubonic form of the disease.”

And that, as Swetlitz of STAT points out, raises an interesting question: were there major out breaks of the plague prior to 541 C.E. that historians simply do not know about?

The study authors think it’s possible. In the Bronze Age, transport and trade routes were being established between Europe and Asia, and this “likely contributed to the spread of infectious disease,” the study authors write. But they also note that analyzing genomes from more ancient individuals is necessary to “pinpoint key events that contributed to the high virulence and spread of one of humankind’s most notorious pathogens.”

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