How did The Black Death start?

The Black Death started with a disease that infected and was carried by fleas. Soon enough, these fleas began housing themselves in the fur of rats. Since there was no source of water or food for the rats in their location, they soon started migrating to the cities. This was the beginning of a huge "slaughter" of the medieval world. People began dropping dead left and right from the horrible disease. Whole towns were wiped out in a matter of just days. This was not the end of the disease though. More rats also crept onto ships. Sailors were soon infected with the disease. When the sailors made port, the residents of that area had already heard about the disease and tried to ward them off. But it was too late. People had already made contact with the infected sailors. The proccess repeated itself. By the year 1348, the disease had reached Italy, Spain, England, and France. But, it did not stop there either. In the following year, the plague spread to Austria, Holland, Hungary, Switzerland, and Germany. In 1350, people in Scandinavia and the Baltic countries began their stuggle against the beast now known as The Black Death.