That said, the respiratory route is very distinct from the oral, genital and anal route.

On a spectrum of frequency of contact, respiratory is the most frequent, then comes oral/digestive, then genital, and finally anal.

The more frequent and vital a route is, the more natural and artificial resources we can allocate to combat infections.

So infections spread by talking to each other, being vital, gets a vaccine developed in less than a year, and gets diverse natural antibodies.

On the other hand, a disease that spreads among adults who seek pleasure, will be allocated less resources, more so if it spreads preferentially through non reproductive sex.

Aids on the respiratory system would be fucking deadly, but my guess is that it would never spread there because there's more protection mechanisms, respiratory is like a process running unprivileged on an open port 80. Genital is port 22 and anal-genital is rdp or teamviewer with admin privileges on a server.