The black death is thought of to be caused by a virus.
However when the black death first started it was thought that the black death was caused by and spread from infected rats.
But as research has been done after all those years the evidence shown now through research suggests that the black death was actually caused by a virus and not by rats.
Although the rats may have spread that virus to humans which caused it to affect people and kill those people.
Some viruses can be spread from rats to humans and other viruses can be spread from other animals to humans as well.
As for the black death an E Bola like virus is thought to be the cause of the black death.
The black death is also known as the Bubonic Plague.