The Black Death that killed half the people in Europe in the 14th century has long thought to have been carried by fleas on a certain type of rat. But now scientists think it was actually an Ebola-like disease.

Debora MacKenzie writes in New Scientist that researchers have long blamed the bubonic plague bacterium Yersinia pestis, but they?ve never been able to find traces of it in the remains of Black Death victims. “We cannot rule out Yersinia as the cause of the Black Death,” says researcher Alan Cooper, “But right now there is no molecular evidence for it.” After a detailed analysis of historical records, Susan Scott and Chris Duncan think it might have been caused by a virus that led to massive bleeding, like Ebola.

Yersinia still infects a small number of people and some fear it could be used as a bioweapon. The Soviet Union made 1500 tons of it a year for military use, and there may still be some of it around. However, people of European ancestry are less susceptible to whatever the disease was, since their ancestors had to have lived through it. This also gives people with that background some protection against HIV, which is one reason that, while it’s bad in Europe and the U.S., it’s much more devastating in Africa, which did not experience the Black Death. If the Black Death actually was Ebola, it’s also much less likely to cause the kind of epidemics here that it’s caused in Africa.

In 2000, Didier Raoult studied fragments of DNA extracted from the teeth of three 14th-century French, and found traces of Yersinia. But Scott and Duncan say it wasn?t clear that these people died from the Black Death.

Now Cooper and Duncan have analyzed 121 teeth from 66 skeletons found in five mass graves, including one in the U.K. that was dug especially for Black Death victims in 1349. “We detected a lot of different bacteria,” Cooper says, ?but none of the sequences were from Yersinia.” He next wants to study some victims that may be buried in permafrost in Finland, in order to get soft tissue to study, instead of just teeth and bones.

If only evil from the past could stay walled up and never touch us again. The ancient Egyptians tried to make it happen, but failed. What was unleashed from an ancient tomb? Learn a secret from the past on this week’s Dreamland.

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