June 5 (UPI) -- Scientists have gained new insights into the first historically recorded plague pandemic.
To better understand the early evolution of plague-causing bacterium Yersinia pestis, scientists isolated the deadly microbe from ancient human remains recovered at 21 archaeological sites in Britain, Germany, France and Spain.
Researchers were able to reconstruct the genomes of eight different plague strains, including strains responsible for the Justinianic Plague, a pandemic that began in 541 A.D. in the Eastern Roman Empire. The pandemic lasted nearly two centuries, spreading in periodic waves across the Mediterranean and Europe.
Until now, scientists weren't sure how the Justinianic Plague, the so-called First Pandemic, lasted for so long. The latest research -- published this week in the journal Proceedings of the National Academy of Sciences -- offered scientists a detailed look at the diversity of strains of Y. pestis moving through Europe during the 6th, 7th and 8th centuries.
"The retrieval of genomes that span a wide geographic and temporal scope gives us the opportunity to assess Y. pestis' microdiversity present in Europe during the First Pandemic," Marcel Keller, who helped reconstruct the ancient plague genomes while a PhD student at the Max Planck Institute for the Science of Human History, said in a news release.
The genomic analysis showed several closely related strains fueled the Justinianic Plague. It's likely some of the strains affected the same places at the same time. Because all eight strains belonged to the same genetic lineage, scientists suggest the plague wasn't repeatedly renintroduced, but instead persisted throughout the Mediterranean and Europe between 540 and 750 A.D.
The new analysis also revealed genetic similarities between the strains responsible for the First Pandemic and the Second Pandemic, which struck Europe some 800 to 1,000 years later. Both lineages of Y. pestis evolved similar genetic deletions.
"This is a possible example of convergent evolution, meaning that these Y. pestis strains independently evolved similar characteristics," Max Planck researcher Maria Spyrou said. "Such changes may reflect an adaptation to a distinct ecological niche in Western Eurasia where the plague was circulating during both pandemics."