http://www.newscientist.com/news/news.jsp?id=ns99994149
Case reopens on Black Death cause
Fresh controversy has broken out over the cause of the Black Death that killed up to half the people in Europe in 1348 and circulated for centuries after that.
For a century the blame has rested with the bubonic plague bacterium
Yersinia pestis, which is carried by rats and fleas. But the most ambitious effort yet to find traces of
Yersinia in the remains of Black Death victims has failed, and the researchers involved argue that a previous study that did report finding
Yersinia was flawed.
"We cannot rule out
Yersinia as the cause of the Black Death," says Alan Cooper, head of the Ancient Biomolecules Centre at Oxford University, UK, whose team did the latest work. "But right now there is no molecular evidence for it."
The dispute over what caused the Black Death is more than just a historical concern.
Yersinia still infects people in the tropics and there are fears that it might be used as a bioweapon, unleashing another "Black Death". The Soviet Union, for example, reportedly prepared 1500 tonnes of it a year for military use. Such fears have prompted much research.
Yet, a detailed analysis of historical records led Susan Scott and Chris Duncan of the University of Liverpool, UK, among others, to conclude that
Yersinia was not the cause of the Black Death (
New Scientist print edition, 24 November 2001). They think it might have been a haemorrhagic virus that caused massive bleeding, like Ebola.
Unique DNA sequences
In 2000, Didier Raoult and colleagues at the University of the Mediterranean in Marseille, France, claimed to have settled the matter by using PCR to amplify fragments of DNA extracted from the teeth of three 14th-century skeletons from nearby Montpellier. These sequences included some unique to
Yersinia, they reported.
Scott and others argued that it was not even clear if the skeletons were from people who died from the Black Death. But in June 2003, Raoult dismissed such criticism as "unsubstantiated speculation".
Now Cooper and his colleagues have analysed 121 teeth from 66 skeletons found in five mass graves, including one in East Smithfield in London, UK, dug for Black Death victims in 1349. They also looked at suspected plague pits at Spitalfields in London, Vodroffsgaard in Copenhagen, Denmark, and Angers and Verdun in France.
Not one tooth harboured identifiable
Yersinia DNA, the team will tell this week's meeting of the British Society for General Microbiology in Manchester, UK. The team used primers - DNA fragments that act as probes in the PCR test to pick up specific sequences that were unique to
Yersinia, but found nothing.
"And when we used the same primers the French used," Cooper told
New Scientist, "we detected a lot of different bacteria, but none of the sequences were from
Yersinia."
Splitting and scraping
Raoult is adamant that his team avoided contamination. But the latest study reveals how easy it can be. Splitting teeth and scraping out the inside, as the French group did, contaminated them with bacteria, Cooper's team found. After one lab did a control test with modern
Yersinia DNA, it got a positive result from a tooth - only to find it was contamination by the modern DNA.
What is more, nearly all the French samples tested positive - a suspiciously high survival rate for DNA in Montpellier's warm climate, Cooper believes. Together with the non-specificity of the primers, he thinks this makes it unlikely the French detected ancient
Yersinia DNA.
Cooper's team did find human mitochondrial DNA in the teeth, proving that DNA could survive there. But not finding
Yersinia DNA does not prove that the bacterium did not kill these people the infection might not have penetrated teeth.
"If I can get some soft tissue from the plague, I'll look again," he says. In Finland, for example, there may be victims buried in permafrost.
