In the Middle Ages, living conditions were so unbearable that most of the rodents died.
Fleas attacked the remaining animals en masse. The rodents, in turn, weakened by the disease, looked for places to live in which to get food, and found them near people. So the bubonic plague spread among the population. Bubonic plague begins to develop from the moment you are bitten by an infected flea. Bacteria enter the lymph nodes and begin their vital activity. Suddenly, a person is overcome by chills, his body temperature rises, the headache becomes unbearable, and facial features become unrecognizable, black spots appear under the eyes.