In news that is not surprising, but still interesting, a group of German Anthropologists have confirmed once and for all that the Black Death in the 14th century was caused by Yersinia pestis, better known as bubonic plague or even just The Plague. The study, done at the Johannes Gutenberg University in Mainz, extracted DNA from mass graves for plague victims in England, France, Germany, Italy, and the Netherlands. Using a variety of tests they eventually located markers that indicated the former presence of Y. pestis.
While most of us were taught the the Black Death was indeed caused by bubonic plague, there have been some historians and scientists in recent years who have questioned that diagnosis. The traditional version was that the plague was carried by rats and transmitted from rats to people by fleas. A major line of argument in the revisionist school challenges this transmission vector, by pointing out that many of the outbreaks during the Black Death happened during the winter when fleas are not active. Another line of argument is based on the Medieval descriptions of symptoms that, while close to those exhibited by Y. pestis, are not quite the same.
The new study answers the second of those critiques. Once they found Y. pestis, the Mainz scientists attempted to identify the exact strain of the disease. What they discovered were two strains that don't match the known modern strains. One of the two appears to be completely extinct while the other appears to be related to modern strains found in Asia. If the epidemic was caused by different strains than the ones we know, then it makes perfect sense for the symptomology to be different that that which we know.
This discovery leads to a new challenge to the traditional historical narrative of the Black Death. That narrative has the plague initially being brought from the Crimea to Italy by rats on Genoese ships. From Italy the disease spread through the Western Mediterranean, up into Western Europe, then across Central and Northern Europe before disappearing back into the East. Finding two strains implies two separate epidemics at the same time. One from the Mediterranean and one from the North.
I sometimes joke that the one thing that unites history and the sciences is the sentence "It's more complicated than we initially thought." This is a perfect example of that at work. Nailing down the disease and its strains has answered one question and eliminated one challenge to the prevailing theory. At the same time, it leaves one question still open (the flea problem) and created a new challenge. This brings us to the one sentence that unites all scholarly enterprise, "We're going to need to do more work on this."