How did the bubonic plague spread so quickly throughout Europe?

Answer 1

Sanitation was extremely poor during the Middle Ages. Baths were uncommon and sewers were almost non-existant in crowded cities. There was no 'garbage' service, the water was polluted and rats, the primary carriers of the infected fleas, were rampant.

Answer 2

Bubonic Plague is spread by fleas in what is called as geometric proportion. When people started dying of plague, others fled to other towns. Some of them were in the incubation period and carried the disease to the next say ten towns.

When the phenomena got repeated, the number of towns was 10*10. In the next tern the number was 10*10*10. In the next tern the number was 10*10*10*10. In the next turn the number was 10*10*10*10*10. In the next turn the number was 10*10*10*10*10*10. Means 1,000,000.

Probably that number was equal to the number of villages and towns of the entire Europe.

Answer 3

To put things simply, lack of sanitation. People had no concept of how a disease actually worked, so they had no idea that being clean would protect them. Take the leaving of dead bodies in the street for example.