The Black Death, which ravaged Europe between 1347 and 1351, has been blamed on fleas from rats passing the plague bacterium to people, but some experts question this.
Credit: iStockPhoto
Yersinia pestis seen at 200x magnification. This bacterium, carried and spread by fleas, is generally thought to have been the cause of millions of deaths.
Credit: Wikimedia
DUBLIN: An extinct form of bacterium could have been responsible for the Black Death plague that devastated Europe in the 14th century.
A recent analysis of skeletal remains from a mass grave at East Smithfield in London has revealed that victims harboured the DNA of a plague bacterium called Yersinia pestis, which places it at the scene of the medieval catastrophe. Y. pestis infection takes three forms: pneumonic, septicemi and bubonic, and thousands of cases of plague per year are still reported to the World Health Organisation.
New technologies have enabled scientists to acquire the genomes of ancient pathogens, according to Hendrik Poinar of McMaster University in Ontario, Canada, who is the co-author of a new study published in Proceedings of the National Academy of Sciences today. "This will allow us a chance to understand what caused major pandemics in the past," he said.
Medieval pestilence
The Black Death ravaged Europe between the years 1347 and 1351, with historians estimating that more than one-third of the continent's population perished because of it. The plague killed most of its victims within a week.
The pestilence has been blamed on fleas from black rats passing the plague bacterium to people, but some experts question this explanation. There is also debate as to whether the plague bacterium was actually the culprit, given the difference between the medieval outbreak and the disease we see today.
Poinar and his colleagues analysed the DNA of 109 human skeletal remains excavated from the Smithfield site in the 1980s and archived at the British Museum, London. They also studied DNA from the remains of 10 people unearthed at a site that pre-dates the Black Death medieval plague as a control sample.
The Smithfield skeletons were shown to have harboured plague bacteria genes, which the authors sequenced to form one of the oldest genetic assemblages from an ancient pathogen, proving that the plague microbe was present among the Black Death victims.
Death in London
The genetic sequences differed from the sequences of other known versions of the plague bacteria, the authors reported, suggesting that the particular variety of the pathogen responsible for the Black Death is no longer among us. This may explain why the Black Death plague differs so strikingly from the modern disease.
Modern plague continues to affect an estimated 2,000 people around the world each year, but it does not cause outbreaks on a scale anything like the medieval plague. At the time of the medieval plague, the existence of pathogenic microbes like Y. pestis was unknown and bad air was believed to be the possible cause.
"This will be the nail in the coffin for other theories," said Poinar. "That said, we cannot rule out, at this stage, that other co-circulating strains weren't also there," though he added that this is "unlikely".
In his recent book The Black Death in London, historian Barney Sloane claimed that people, not rats, carried the bubonic plague. "I have been waiting for this piece of research," said Sloane, "and it is really very good news for the debate". However, he noted that Y. pestis was recovered in just five out of the 109 skeletal remains and that the control sample of 10 individuals seems low. "I would prefer an earlier mass grave to be studied with the rigour of this one (they do exist and are well dated), in order to dismiss any suspicion of pestis presence in London before the 1348 outbreak."
