October 10, 2010
Researchers Confirm Black Death Killer Bacteria
Black Death, one of the deadliest pandemics in human history, has been confirmed by anthropologists to have been caused by a germ called Yersinia pestis.
Researchers studied tooth and bone samples from 76 skeletons discovered in "plague pits" in France, Germany, Italy and the Netherlands and found DNA evidence that Y. pestis was to blame for the plague that wiped out nearly a third of Europe's population during the Middle Ages.
It was believed for more than a century that Y. pestis was the source of the so-called Black Death, which plagued Europe from the 1300s to the 1700s and possibly early 1800s. But scientific data to prove the bacterium was the actual culprit has been sketchy at best.
Because of this, many rival theories have come about, including opinions that an Ebola-style virus or the anthrax germ was to blame.
The new evidence also sheds light on the geographical route the germ took, which is believed to have originated in central or southern Asia before making its way into Europe through trade routes.
In the samples that researchers found Y. pestis genes, they ran a test for 20 DNA markers to identify a particular bacterial strain.
They wanted to know if it matched either of the other two Y. pestis strains that are floating around today, mostly in Africa, America, the Middle East and Russia. But neither of the two modern types, Orientalis and Medievalis, showed up.
Instead, two previously unknown types were found, both of them older than today's strains and different from each other.
"The history of this pandemic is much more complicated than we had previously thought," said Stephanie Haensch, a co-leader of the research, at Johannes Gutenberg University in Mainz, Germany.
Y. pestis showed up in Western Europe in November 1347, believed to be driven by fleas living on rats which made it to land from a merchant ship docked at the Mediterranean French port of Marseille.
After making landfall, it took six years for it to spread through western France to northern France and then over to England, again through commerce.
However, a different strain was discovered in a mass burial site in Bergen op Zoom, a port in the southern Netherlands, suggesting that Y. pestis also made entry from the north, perhaps from Norway via the Dutch province Friesland.
After its initial surge in 1347, the pandemic progressively spread around Europe, reducing the population by as much as 60 percent throughout its 4 century run, and causing far-reaching social and political impacts.
The findings were published in the open-access journal PLoS Pathogens.
Image Caption: A scanning electron microscope micrograph depicting a mass of Yersinia pestis bacteria. Credit: Rocky Mountain Laboratories, NIAID, NIH
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