How Was Plague Spread?

Plague was a disease that was spread by rats. People at the time did not know this and thought that a 'bad air' was responsible, or that the plague was a punishment from God.

In Europe, the species of rat that was very common was the Norwegian Black rat. This carried fleas that, in turn, carried the fleas that carried the plague bacterium, Yersinia pestis. The fleas would feed on the rat and take in a meal of blood rich in bacteria. The fleas and rats were unaffected by the infection but, when one of the rat fleas jumped onto a human and bit them, the bacteria entered a new host.

In humans, Yersinia pestis is very virulent and causes the plague, an awful diseases that could kill very rapidly. Once the disease was caught by one person, they would then pass it on directly to other people close to them. No further flea bites were necessary.

Some monastaries thought they could hide from the plague by shutting themselves inside their building but they didn't realise that the rats and their fleas spread the disease. The sewers brought the rats in and, once one monk was bitten by a flea, the rest of the monks all succumbed very rapidly and whole communities were wiped out in days.