The innate immune system is remarkably good at providing a first line of defense. Viruses don't just march into your body uncontested. They basically have to fight for every square centimeter of ground they claim, and even then, it's a race against time before the adaptive immune system pulls facial recognition on them and sends out hit squads which targets them directly.

That means that viruses aren't necessarily able to infect all of the cells in a particular area of tissue. While viruses have some defenses against immune systems, their very simplicity limits the tricks they can use. Flesh-eating bacteria, being much larger and more complex, have more tools at their disposal when it comes to attacking host tissue.

Kurzgesagt has some really good videos on the immune system:

• https://www.youtube.com/watch?v=BSypUV6QUNw
• https://www.youtube.com/watch?v=lXfEK8G8CUI

The complement system, in particular, is especially interesting, because it's basically a free-floating chemical warfare system which passively protects virtually every part of your body 24/7. No signalling molecules or specialized immune cells are necessary for it to start interfering with foreign invaders.

The innate immune system is remarkably good at providing a first line of defense. Viruses don't just march into your body uncontested. They basically have to fight for every square centimeter of ground they claim, and even then, it's a race against time before the adaptive immune system pulls facial recognition on them and sends out hit squads which targets them directly.

That means that viruses aren't necessarily able to infect all of the cells in a particular area of tissue. While viruses have some defenses against immune systems, their very simplicity limits the tricks they can use. Flesh-eating bacteria, being much larger and more complex, have more tools at their disposal when it comes to attacking host tissue.

Kurzgesagt has some really good videos on the immune system:

• Tiny bombs in your blood - the complement system
• How the immune system actually works

The complement system, in particular, is especially interesting, because it's basically a free-floating chemical warfare system which passively protects virtually every part of your body 24/7. No signalling molecules or specialized immune cells are necessary for it to start interfering with foreign invaders.