Black Plague
The rat was a major effect in the Black Plague. Its the one that spreaded it to human to human. It got its disease by fleas.
Black Plague
The flea was the one that landed on the rat and put the disease into the rat. When the rats died, the flea moved to live on humans and the Black Plague germ got into there blood system.
Black Plague
It killed an estimated 75 million to 200 million people in the 14th century. It killed this many people because there was no cure because they didn't have the latest technology as we do today.