Scientists Have Traced The Origin Of The 14th-Century Plague That Killed More Than Half Of Europeans

Mass grave from the time of the Black Death, at the archaeological site '16 rue des Trente Six Ponts' in Toulouse, France © Archeodunum SAS, Gourvennec Michaël

DNA analysis of human remains from across nearly a dozen European archaeological sites has led an international team of scientists to believe that the Black Death spread to the continent from Russia.

Beginning in the 14th century, the Bubonic plague decimated Europe. Historical accounts suggest the bacteria responsible for the plague, Yersinia pestis, arrived at the continent via a dozen ships from the Black Sea docked in Italy, according to History.com. When the ships arrived, most of the sailors were dead and those who were still alive were riddled with horrific black boils oozing with blood and pus. In just five years, 20 million people would die from Y. pestis – nearly one-third of the population.

Waves of the Black Death would taunt Europe over the next several centuries, all the while teasing researchers trying to determine where it came from. Until now.

To determine where the plague-causing bacterium came from, and to trace its evolution, researchers reconstructed the genomes of the bacterium extracted from 34 individuals found at burial sites in England, France, Germany, Switzerland and two from the Volga region of Russia. Of the samples taken, the bacteria lacked genomic diversity and the single Russian strain was found to be ancestral to all of those ancestral to the pandemic strains.

“These findings indicate a single entry of Y. pestis into Europe through the east," explains first author Maria Spyrou in a statement. "However, it is possible that additional interpretations may be revealed with future discoveries of un-sampled diversity in western Eurasia,"

The map shows the archaeological sites of newly sequenced (circles) and already published pest genomes (triangles), stained in temporal staggering. Spyrou et al . Phylogeography of the second plague pandemic Yersinia pestis genomes, Nature Communications

Analyses from genomes later in the pandemic showed a higher genetic diversity, suggesting that perhaps it evolved after the initial plague swept Europe.

"In the later phase of the second pandemic, we see the development of multiple branches within Europe, which suggests that plague was maintained in different local foci," said study co-author Marcel Keller. "No modern descendants of this lineage have been found to date, possibly indicating the extinction of these reservoirs.”

Y. pestis is spread from person to person through the air, as well as from bites from fleas or rats. severe symptoms include onset pf fever, headaches, chills, and painful lymph nodes, according to the Centers for Disease Control and Prevention. Today the strain is treatable with antibiotics, but 700 years ago people neither knew what prompted the onset or how to cure it. The researchers say their work gives new insights into how the pandemic transpired. 

"We have shown that extensive analysis of ancient Y. pestis genomes can provide unique insights into the microevolution of a pathogen over a period of several hundred years," said senior author Johannes Krause, adding that integrating their work into disease modeling, paired with data from other areas like climate science and history, will help to understand how infectious diseases spread.

In recent years, Y. pestis has been spotted in Colorado Prairie Dogs, in a small Chinese town, in Mongolia after a couple ate raw marmot, killed dozens in Madagascar, and was rumored to be on New York Subways (though that was later proven false).

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