system
Given the following post, respond as if you're commenting on Reddit:
human
Why don't viruses spread throughout your entire body?

I have viral conjunctivitis and I was cautioned about washing my hands and not sharing towels etc.

But it got me thinking, what makes certain viruses only spread via a particular vector?

For example AIDS and blood/sex, Coronavirus is airborne/fomite tramissions, etc.

Logically, it seems once you get a virus, any bodily function should be able to spread it. Why do viruses behave the way they do?

Thanks in advance for your time.
gpt
Viruses need to enter cells to replicate, they do this by binding receptors on cells' surface. Not all cells will express the same quantities of these receptors, and so viruses will prefer some cells/tissues over others.