Where does the plague come from?

Plague is an infection transmitted by mice (and some other animals) and fleas. Fleas are insects that feed on blood. When they bite infected mice, they become a carrier of the plague. The bacteria begin to multiply massively and rapidly inside the flea, causing a blockage in its digestive tract. After that, a flea, if it gets on a person, bites him. But due to the blockage by bacteria, it cannot digest more blood and regurgitates whatever was inside. Thus, it regurgitates the plague bacteria into the wound. The wound begins to itch, which leads to the fact that the person himself rubs the plague bacteria into the wound, causing infection.