What are or would be good time frames and causes for a POD focused on the mutation and spread of a disease or virus that pretty much becomes a plague and a pandemic. I know their was one good TL a few years ago, I think it was called The Horse Plague or Horse Death. What are historical epidemics that could have become worse or could have been less so? I do have in my mind a thought of the creation of a new plague, basically called The Rot, in which it becomes viral in a corpse through physical contact and gaseous transmission through quite active decomposition which leads to Cremation being the popular form of burial.