The DNA of a strain of bacteria responsible for the infamous Black Death The plague has been found in the teeth of three individuals who were found buried in the UK thousands of years before the deadly pandemics raged in Europe.
Two of those individuals, determined to be young adolescents, were buried in a mass grave at Charterhouse Warren in Somerset; the third was a middle-aged woman between the ages of 35 and 45, buried in a ringcairn memorial at Levens in Cumbria. All three lived around the same time, although it is unclear whether the plague was the cause of their deaths.
The tension of the Yersinia pestis The bacteria identified was different from the strain that caused the Black Death, an outbreak that caused a plague pandemic that lasted 500 years and killed millions across Europe and the Middle East.
Yet these are the oldest cases of Y pestis infection has been identified in Britain, suggesting that the plague spread readily even before it developed the mutations that would contribute to recurrent bouts of deadly virulence from the 14th century.
“The ability to detect ancient pathogens from degraded samples, from thousands of years ago, is incredible,” explains genomicist Pooja Swali from the Francis Crick Institute in the United Kingdom.
“These genomes can inform us about the distribution and evolutionary changes of pathogens in the past, and hopefully help us understand which genes may be important in the spread of infectious diseases. We see that this Yersinia pestis lineage, including genomes from this study, lose genes over time, a pattern that has emerged with subsequent epidemics caused by the same pathogen.”
The second plague pandemic was quite a large series of events in human history that not only changed economics, politics and culture, but possibly even moot – our own genome.
While we know a lot about the history of the disease, its genesis and spread is something genetic detectives are still working to figure out. Traces of it have been found from Eurasia dating back to around 5,000 years agoto the Late Neolithic and Bronze Age (LNBA).
There are two forms of the disease: bubonic plague or septicemia, transmitted by flea bites; and pneumonic plague, spread by human-to-human aerosol transmission. The most common LNBA strains of the bacteria lack the adaptations for flea transmission, suggesting that earlier forms of plague weren’t so horribly deadly.
But how transmissible was pneumonic plague? Swali and her colleagues examined the early spread of Y pestis in Britain by extracting DNA from the teeth of 34 individuals. Our helicopters have a reputation for preserving identifiable bits of microbial DNA in detectable levelsproviding researchers with a valuable resource for tracking the histories of many diseases.
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Swali’s team discovers Y pestis in three of the individuals’ teeth, all of the radiocarbon dates to about 4,000 years ago.
Interestingly, the mass grave at Charterhouse Warren containing the two children is not typical of that period. In addition, many of the bones of the 28 individuals therein showed signs of fatal trauma, suggesting that the site was used for the disposal of bodies following a violent event.
There is a strong possibility that the children were infected with the plague at the time of their deaths, but it is unlikely that the infection was the primary cause of their deaths.
By contrast, how the elderly woman buried in the ring cairn died is impossible to say.
In all three, the bacterial DNA lacked the genetic mutation for flea transmission. The earliest identification of this mutation remains about 3800 years ago.
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However, what the new discovery tells us is Y pestis had spread from mainland Europe to the British Isles sooner than we knew. This early, wide geographic distribution seems to indicate that pneumonic plague did not just spread far, and therefore quite easily. Further research could help reveal the impact this had on humanity at the time.
“We understand the massive impact of many historical plague outbreaks, such as the Black Death, on human societies and health, but ancient DNA can document infectious diseases much further into the past,” says geneticist Pontus Skoglund from the Francis Crick Institute.
“Future research will do more to understand how our genomes responded to such diseases in the past, and the evolutionary arms race with the pathogens themselves, which may help us understand the impact of diseases in the present or in the future.”
The research has been published in Nature communication.