Confirmed: Y. pestis bacteria caused the Black Death

Yersinia pestis in the lymph of a plague patientMost microbiologists, epidemiologists and historians agree that the Black Death, the plague that devastated Europe between 1347 and 1353 killing at least a third of the population, was caused by the bacteria Yersinia pestis. Endemic to rodent fleas in China, Y. pestis is thought to have made its way to Europe over the Silk Road and/or sea trade routes.

There are, however, people who disagree that the Black Death was actually bubonic and pneumonic plague caused by Y. pestis. The primary alternate theory was that it wasn’t a bacterial disease spread by parasites on vermin, but rather an infectious Ebola-like viral hemorrhagic fever that was spread from person to person. The evidence for this was primarily historical — the effectiveness of quarantine, for instance, in stopping the spread of disease.

Now a new study (pdf) from an international team of researchers appears to have conclusively demonstrated that Y. pestis was indeed the cause of the Black Death and all subsequent outbreaks of the plague in Europe. Researchers tested the DNA in tooth pulp recovered from the plague victims buried in plague pits in Hereford, England, Saint-Laurent-de-la-Cabrerisse, France, Bergen op Zoom, the Netherlands, Augsburg, Germany, and Parma, Italy, among others.

They were able to identify the DNA and protein signatures for Y. pestis, and while they were at it, they also discovered two previously unknown clades of the bacterium, both of them ancestors of the Orientalis (the one that devastated India and China in the late 19th century) and Medievalis (the Black Death one) biovars. This suggests that the plague didn’t just come to Europe once over one route. There were at least two distinct pathways Y. pestis took to get to Europe.

Several historical epidemic waves of plague have been attributed to Yersinia pestis, the etiologic agent of modern plague. The most famous of these was the second pandemic which was active in Europe from AD 1347 until 1750, and began with the ‘Black Death’. The most informative method to establish the etiological nature of these ancient infections should be the analysis of ancient DNA, but the results of this method have been controversial. Here, by combining ancient DNA analyses and protein-specific detection, we demonstrate unambiguously that Y. pestis caused the Black Death. Furthermore, we show that at least two variants of Y. pestis spread over Europe during the second pandemic. The analysis of up to 20 diagnostic markers reveals that the two variants evolved near the time that phylogenetic branches 1 and 2 separated and may no longer exist. Our results thus resolve a long-standing debate about the etiology of the Black Death and provide key information about the evolution of the plague bacillus and the spread of the disease during the Middle Ages.

If you’d like to read more about the arguments for and against Y. pestis causation, I highly recommend this excellent series of articles by epidemiologist and Aetiology blogger Tara Smith. They’re from three years ago so they don’t address the recent study, of course, but they’re eminently readable and thoroughly address the issues on all sides.

10 thoughts on “Confirmed: Y. pestis bacteria caused the Black Death

  1. Are you hitting on me? :p

    Another argument I’ve read against Y. Pestis is the rapidity of its spread throughout Northern Europe. I can’t remember the book, but the idea was that the rat vector wouldn’t allow for the plague to have spread like the historical records show. I’ve never really bought that, but haven’t seen an actual rebuttal either.

    Something that muddies the water a bit is that we have to rely on Medieval records and they weren’t that precise in describing symptoms. Sometimes they described symptoms that were downright fantastic and sometimes so generic that it’s impossible to say if it was plague. So the presence of anomalous cases isn’t really evidence against Y. Pestis being the cause of the plague itself. The individual case or outbreak might have been another disease, or just misreported.

    :skull: :skull: :skull: :skull:

    1. I saw a show on NatGeo or THC that argued against Y. pestis based on evidence that rats weren’t a major issue in rural England in the 14th century, even in towns that were devastated by the plague. It was quite reasonable. They presented some interesting architectural evidence from medieval dovecots that people were not overrun by rats since they had nesting cubicles starting down at floor level, for instance. Entirely fair, as far as it goes. It just doesn’t go very far.

      That show also mentioned the diversity of contemporary descriptions as an argument against Y. pestis. But like you said, that doesn’t really affect the general case.

      1. Now that you mention that, it occurs to me that my problem is trying to disprove scientific conclusions (such as the plague pit data*) using circumstantial evidence. At best, such evidence makes the hypothesis seem less plausible but does nothing to falsify it. I became pretty irritated over a similar attempt regarding the Battle of Gettysburg on a TV documentary once. In that case, there were also serious problems with their methodology.

        *This isn’t the first report of testing of plague pit victims showing Y. Pestis, btw.

  2. When I first looked up info regarding the Black Death(Black Plague), there are three strains of it. Pneumonic(which can be contracted by airborne pathogens and the most dangerous), Bubonic (this one relates to rats being bitten by fleas) and Septisemic(basically blood poisoning as a result of an injury).

  3. Actually, all three forms of the plague are caused by Y. pestis bacteria. They’re just different infection sites — lungs (pneumonic), lymph nodes (bubonic), blood (septicemic). Pneumonic can indeed be spread from person to person via inhaled air-borne Y. pestis, but it can also develop from the bubonic form spreading to the lungs.

  4. Disagree with your assertions. Black death is an extra terrestrial disease which was first introduced to the planet through China. Its arrival was probably around 1100AD or thereabouts, and it took nearly a century to get going properly.

    Black death bacteriumata DNA has been sequenced from freshly arrived meteorite particles.

  5. “Black death bacteriumata DNA has been sequenced from freshly arrived meteorite particles.” Presumably there was a peer-reviewed paper in a scientific journal on this? I’m sorry I missed it. Can you give a reference?

  6. You missed it, because there isn’t one. If there had been, it would have been sensational international news that virtually EVERYONE would be talking about. Golenticatum is BSin’. lol.

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