1665 Great Plague of London Cause Identified

The 1665 Great Plague of London was caused by Yersinia pestis bacteria, thought to be spread by rodents, according to new research that looked at skeletons found last year in the New Churchyard area of the city.

Yersinia pestis was found in the skeletons that were uncovered during the city's Crossrail dig at Liverpool Street in 2015, The Telegraph reported. The discovery, made through DNA analysis at the Max Planck Institute, was the first time a cause has been identified, the publication noted.

The outbreak was the last bubonic plague wave in Britain, killing almost a quarter of London's population, BBC News noted.

"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," Kirsten Bos, who led the DNA analysis at the Max Planck Institute, said, according to The Telegraph.

"We don't know why the Great Plague of London was the last major outbreak of plague in the UK and whether there were genetic differences in the past, those strains that were circulating in Europe to those circulating today; these are all things we're trying to address by assembling more genetic information from ancient organisms," Bos continued.

Excavators found about 3,500 burials at the site.

"To dig below London is frequently to travel back in time," The Guardian reported last year. "Since 2013, archaeologists working on the Crossrail project have excavated plague victims from a burial ground built at the notorious Bedlam mental asylum.

"The (Bills of Mortality) recorded 68,594 plague deaths in 1665 but this is likely to be far short of the true total. The searchers, shunned because of their contact with victims, were suspected even at the time of using catchall terms like 'fever' and 'consumption.' This would have increased with people's reluctance to admit to plague in their households," The Guardian continued.

Richard Stabler, associate professor at the London School of Tropical Medicine, told The Telegraph that the new confirmation made by the institute definitively solves any previous misconceptions about what was the cause.

"There was always debate around whether the great plague was actually 'plague,'" Stabler said. "The discovery of this bacteria puts such controversy to rest."

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