[PUGACHEV]

There has been speculation that the Black Death was not caused by the Bubonic Plague, but by some unidentified type of hemorrhagic fever, like Ebola. One argument in favor of that theory is that the supposed vector of Bubonic Plague, rats and their fleas, could not travel fast enough to account for the reported spread of the Black Death, whereas hemorrhagic fever, spread by direct contact from one infected person to another, could.

[DakotaGator]

There has been speculation that the Black Death was not caused by the Bubonic Plague, but by some unidentified type of hemorrhagic fever, like Ebola.

This wouldn't surprise me. Have always suspected we know less of the plague than we commonly believe.