Pathogenic bacteria are very diverse, they multiply easily and quickly in favorable conditions, and are quickly

Pathogenic bacteria are very diverse, they multiply easily and quickly in favorable conditions, and are quickly transmitted from person to person. It is known that in the Middle Ages, entire cities died out from diseases caused by bacteria. Why didn’t bacteria kill all people?

Mechnikov discovered in daphnia and sea urchins special cells – phagocytes, which destroyed foreign objects (both living and nonliving) that got into the body of crustaceans and hedgehogs. In fact, he discovered the simplest immunity. In humans, the immune system is very complex: specialized cells can reshuffle their genome, becoming masters at neutralizing an individual pest. Therefore, humanity will never die out from a bacterial or parasitic disease – there are lucky ones who have developed effective immunity before the disease kills them.