Bacteria Behind London's Great Plague ID'd

For the first time, scientists have found evidence of the bacteria from London's Great Plague.

Using DNA testing, scientists have confirmed the identity of the bacteria that caused London's Great Plague in the 17th century, reports the BBC.

From 1665 - 1666 the bubonic plague killed 100,000 people in London, almost a quarter of the city's entire population. The disease spread rapidly and burial pits were sometimes created to accommodate the overwhelming number of bodies.

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Last year, archaeologists in London believe they came upon one of these pits as excavations were underway at a former burial ground at Liverpool Street for a new rail link across the city, reported CNN. The bodies looked to be buried on the same day as others in the nearby Bedlam cemetery with headstones reading 1665, further leading scientists to believe those in the burial pit were killed by the plague.

During the course of this year-long excavation, 3,500 skeletons have been uncovered.

The osteology department at the Museum of London Archaeology, where all the finds from the Liverpool Street excavation were examined, searched for Yersinia pestis in the skeletons, a bacterium known to cause plague. Teeth were removed from the other remains and sent to the Max Planck Institute for the Science of Human History in Germany for further testing.

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Molecular palaeopathologist Kirsten Bos found positive results for Yersinia pestis in the teeth of five out of 20 skeletons she examined, confirming this is the bacteria that caused the bubonic plague.

"We could clearly find preserved DNA signatures in the DNA extract we made from the pulp chamber and from that we were able to determine that Yersinia pestis was circulating in that individual at the time of death," she told the BBC.

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DNA of the full genome will also be sequenced by Bos and her team as they continue to search for clues that can tell us how the disease evolved and spread so rapidly.

The Yersinia pestis bacterium is still present today, though it's nowhere near the level it reached in the 17th century. Between 10 - 20 people in the United States are infected each year from flea or rodent bites, mainly in the rural southwest where prairie dogs sometimes carry the bacterium. About one in seven people actually dies from infection, but there has been no known transmission of the disease from person to person in 90 years.

If you're worried that excavating Yersinia pestis from the skeletons uncovered in London will cause another breakout -- fear not! The bacterium is not capable of surviving underground.