DNA from 17th-Century Teeth Confirms Cause of London’s Great Plague

Skeletons excavated from a mass grave during London’s Crossrail project yield new clues about the ancient mystery

Suspected 1665 Great Plague pit unearthed at Crossrail Liverpool Street site
Suspected 1665 Great Plague pit unearthed at Crossrail Liverpool Street site Crossrail Project via Flickr

DNA testing on teeth has officially confirmed the cause of London’s 1665-1666 Great Plague, which tore through the city killing almost a quarter of its population in just 18 months. The final diagnosis: Bubonic plague.

Researchers recovered the teeth from suspected plague victims who were were buried in the old Bedlam Burial ground, used from 1569 to the early 1700s, Roff Smith reports for National Geographic. When construction of a commuter rail line cut through the burial ground, workers found more than 3,300 skeletons, including 42 suspected plague victims buried in a mass grave.

Analysis of samples collected from the teeth of 20 of those skeletons indicate they were exposed to Yersinia pestis, the plague bacteria, not long before they died. “Owing to the disease’s virulence, it is likely they died of the exposure,” according to a release from Museum of London Archaeology (MOLA). Researchers from the museum oversaw the excavation and MOLA osteologists collected the samples that were later tested at the Max Planck Institute.  

Teeth are a good source for ancient DNA, because their enamel shell helps to preserve its delicate structure and protect it from contamination. “In essence, the teeth can act as little time capsules,” according to the release.

The 1665-1666 outbreak was the last major occurrence of plague in Britain. At its peak, the bacteria killed 8,000 people per week, according to a Harvard University report. In the resulting chaos, quarantine measures were abandoned and wealthy Londoners fled to the country, leaving the poor in the city, according to the report.

Crossrail Archaeology: Great Plague DNA identified

The plague that hit London at that time didn’t behave like the bubonic plague we know today, according to Don Walker, one of the MOLA osteologists who was involved in taking the samples. It’s possible there was some kind of mutation in the bacteria, Walker told Smith, or that poor nutrition and other aspects of its victims’ health made them more susceptible.

Daniel DeFoe’s A Journal of the Plague Year was one of several first-hand witness stories that record these dark days. His account, first published in 1722, describes a London where regular life is on hold. Though the account is considered a work of fiction, its central concepts parallel other accounts of the period.

“The shrieks of women and children at the windows and doors of their houses, where their dearest relations were perhaps dying, or just dead, were so frequent to be heard as we passed the streets, that it was enough to pierce the stoutest heart in the world to hear them,” he writes.

Popular imagination holds that the Great Fire of London in 1666 ended the plague outbreak, but by that time the worst had abated in the city, Walker says. “The majority of deaths by then were occurring in the suburbs outside the area of the fire, so the fire itself may not have had that much impact,” Walker tells Smith.

This week’s results are the first identification of plague DNA from 17th-century Britain, according to MOLA. By sequencing the DNA from the 1665 plague and comparing it with 14th-century plague DNA from an older burial pit, researchers hope to tease out the details of how the plague came to Europe, Smith reports. Were rats driving the outbreak? Or was it coming over from Asia?

The burial pit is just one of many archaeological finds that have happened as a result of the Crossrail project, a underground commuter rail link that started being dug in 2009. Since then, thousands of artefacts spanning the last 70,000 years have been uncovered.

Editor's Note November 15, 2016: Errors in the dates of the burial ground use, the title of DeFoe’s book and the cause of death have been corrected. We regret the mistakes.

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