" " A skeleton and victim of the Black Death, unearthed during London Crossrail excavations, is displayed at the London Charterhouse on Jan. 27, 2017, in London, England. Jack Taylor/Getty Images

Textbooks tell us that the bubonic plague caused the Black Death. But not everyone is convinced. Since 1984, scientists have put forward alternative explanations for the Black Death. For example, sociologist Susan Scott and biologist Christopher J. Duncan claim that a hemorrhagic fever, similar to the Ebola virus, caused the Black Death. And others blame anthrax or say that some now-extinct disease was the culprit.

Bubonic plague just doesn't make sense, they argue. The symptoms, the high mortality rate, the speed at which the disease spread, and the way the disease spread -- none of it jibes with typical bubonic plague.



Medieval accounts of symptoms don't match the symptoms of modern-day bubonic plague, either. Accounts describe buboes covering the entire body. But today, buboes would most commonly show up in the groin area, and aren't likely to spread all over the body. Additionally, medieval accounts mention awful odors, bruise-like splotches and disrupted nervous systems that resulted in delirium and stupor -- none of this happens with modern-day bubonic plague.

If the Black Death was caused by the bubonic plague, then the mortality rate was much higher than it should have been, they argue. The bubonic plague is fairly curable; even untreated, bubonic plague has a mortality rate of about 60 percent [source: Kelly]. If mostly everyone affected died, some feel that a hemorrhagic fever, with no cure, was the more likely culprit.

Proponents of these new theories also point out that bubonic plague usually moves very slowly. But the Black Death swept across Europe at enormous speed, especially given the fact that transportation was pretty undeveloped at the time. A hemorrhagic fever, in comparison, has a longer incubation period, in which people are contagious, but not yet symptomatic. People might have spent that incubation period traveling, inadvertently spreading the fever more rapidly. Writings from the Black Death also indicate that people were extremely contagious, so much so that people were scared to be in the same town as the infected. But modern-day plague outbreaks are nowhere near as contagious.

Virus advocates find other problems with the rat-and-flea bacterial infection theory. Since fleas only attack humans after all rat hosts have died, then there should have been a large die-off of rats before the Black Death. There's no evidence for a rat disappearance. Additionally, fleas require high temperatures and humidity to survive, which means that the plague should have essentially died out in winter months. It did not.

None of this reasoning has won over the scientific community yet. It's difficult to truly know what the Black Death was like. The only evidence we have are the written accounts of the time, and these accounts provide few details. Obviously, the people who wrote them didn't use our technical language for diagnosing and describing diseases. What they described as a tumor may not have been a tumor at all, by our modern-day medical standards.

To learn more about the Black Death and its aftermath, take a look at the links that follow.

DNA Evidence In an attempt to determine if Yersinia pestis was to blame for the Black Death, scientists have been turning to DNA evidence. In the late 1990s, a group of paleomicrobiologists was able to remove dental pulp from corpses buried in mass gravesites in France. They reported finding the DNA of Y. pestis in the samples, seeming to confirm the plague theory. However, in a later study, samples from five gravesites from all over Europe were used, and scientists were unable to confirm these results. The teeth exhumed from other gravesites did not contain elements of Y. pestis.

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