The Black Plague was probably the worst pandemic in the history of mankind. It first hit Western Europe in 1347, when people noticed that there were a rather large number of dead bodies piling up in the streets. The usual culprit, runaway ox carts, could not be blamed for all of them. Something was amiss, so the learned scholars gathered together in the same room, examined the putrefying corpses, consulted amongst themselves, and finally informed the waiting public that the victims had each succumbed to a new form of pestilence. Then they keeled over and died.
The moment that you exhibited one of the warning signs, your number was pretty much up. Even if it turned out you had just eaten a bad bit of porridge and that was why you got sick all over the barn floor, the town elders would immediately proclaim you a dead peasant walking and imprison you in your home for the next four to six weeks. By the end of this time period, if you hadn’t succumbed to disease, then you had likely starved to death. Red X’s were customarily painted over the doorways in these cases, so that anyone passing by would know to avoid you like… the plague.
At the time, the notion that rats might be responsible for the deaths was considered to be completely ludicrous. Did people think that the rats bit the victims on the leg? Ha! The horrible suffering was obviously a result of an imbalance of the four humours (too much black bile). It wasn’t until the 19th century that the true correlation between vermin and sickness would be confirmed, more specifically that the fleas which danced on the backs of the rodents were actually carriers of the disease.
The black plague ultimately killed about 70 million people. There would be serious labor shortages throughout Europe, leading to a large number of peasant revolts, and the church lost a great deal of power when monks purporting to have a cure suddenly dropped dead in their tracks. Mostly, though, it led to an overwhelming morbidity in the populace, who believed that all hope had been lost. As it turned out, it was merely misplaced, and would be found a few centuries later when someone glanced behind the wood shed.