Researchers at the University of Copenhagen, with the aid of Bronze Age skeletons, have found that the plague dates back a few millennia more than previously thought. Their findings trace the deadly disease’s evolution and show how it has changed over time.
Prior to these findings, the earliest suspected case of plague was in Athens in 430 BC, but this has never been established definitively. The earliest known plague pandemic was the Plague of Justinian in 541 AD, which killed more than 25 million people. This was followed by the infamous Black Death in 1334 and the Modern Plague in the 1860s.
The Copenhagen researchers had been looking at 101 Bronze Age skeletons and found that seven of them, which were from locations across western Europe and central Asia, showed evidence of having been infected by the plague bacteria Yersinia pestis. Genetic sequencing revealed that the oldest of these strains—dating back 5,783 years—is an ancestor of modern Yersinia bacteria. Further analysis reveals a fascinating history of the deadly pathogen.
According to the findings, the plague originally existed only in its septicemic or pneumonic versions. This would explain why, despite how endemic the skeletons show the plague having been, there were few known or suspected outbreaks. The plague’s septicemic and pneumonic forms are highly lethal and have limited ability to spread. Any outbreaks would “burn out” before becoming pandemics as only infected spittle could provide transmission.
It took until 1000 BC for Yersinia pestis to evolve the “ymt gene” that allowed it to survive in a flea’s gut. This development opened new transmission methods and resulted in the bubonic variant. These two changes may have made the plague more survivable on an individual basis, but it resulted in the ability for continent-wide pandemics to emerge.
This research, published in the journal Cell, offers an intriguing look at the evolution of diseases in general and a glimpse at the origin of the bacteria that once brought Europe to its knees.
Sources for Today’s Article:
Gallagher, J., “Plague Traced Back to Bronze Age,” BBC News web site, October 23, 2015; http://www.bbc.com/news/health-34603116.
Rasmussen, S., et. al. “Early Divergent Strains of Yersinia Pestis in Eurasia 5,000 Years Ago,” Cell 2015; 163(3): 571–82, doi: http://dx.doi.org/10.1016/j.cell.2015.10.009.