DNA samples extracted from ancient Bronze Age skeletons unearthed in Europe and Asia show signs of plague infection dating back 4,800 years, although it would take a further thousand years for the bacteria Yersinia pestis to mutate to a form that could spread from fleas to humans in order to create the Black Death, researchers say.
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Yersinia pestis caused two of humankind’s deadliest pandemics: the 6th century Justinian Plague, named for the Byzantine emperor who was sickened but survived, and the 14th century “Black Death”. The new study suggests looked a 5000-year fossilized tooth to suggest that Y. pestis had been around for much longer than we thought. This more ancient alternate version, now known as the pneumonic plague, was passed on from person-to-person via airborne transmission rather than from flea bites. They discovered Y. pestis DNA in seven of these individuals, whose teeth were dated between 2794 BC and 951 BC (early Iron Age). But, it is not evident if Y. pestis could have been blamed for these early epidemics because direct molecular evidence for this bacterium has not been obtained from skeletal material older than 1,500 years.
There have been many plagues over time and each time a plague fell over the land, it was catastrophic.
This map of Eurasia shows where and in which cultures the plague bacteria were found and dated; the inset show a burial from the Bulanovo site. They learned that the Bronze Age plague didn’t possess a gene called Yersinia murine toxin, which allows the disease to replicate in fleas and ultimately spread like wildfire. The team’s interest was sparked by the reasons behind these migrations. “The Bronze Age is the edge of history, and ancient DNA is making what happened at this critical time more visible”.
Plague strains are also recognized to have a mutation that doesn’t enable them to generate flagellin, a protein which the mammal’s immune system can detect and eliminate.
“Perhaps people were migrating to get away from epidemics or recolonizing new areas where epidemics had decimated the local populations”, says study co-author Morten Allentoft, an evolutionary biologist at the University of Copenhagen. This suggests that the disease wasn’t fully transmissible by fleas until the start of the first millennium BC.
“Additionally, our study changes the historical understanding of this extremely important human pathogen and makes it possible that other so-called plagues, such as the Plague of Athens and the Antonine Plague, could have been caused by Y. pestis”.
“Our findings suggest that the virulent, flea-borne Y. pestis strain that caused the historic bubonic plague pandemics evolved from a less pathogenic Y. pestis lineage infecting human populations long before recorded evidence of plague outbreaks”, wrote the authors of the study. “By knowing which new genes and mutations lead to the development of plague, we may be better at predicting or identifying bacteria that could develop into new infectious diseases”.
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The study authors added, the plagues helped killing a huge number of people as well as altering the course of human history.
