Yeah. HIV is a good example of this. Without treatment, it is deadly pretty much 100% of the time. However, it takes a long time after the shut down of the immune system before a systematic infection takes over and kills you.
That allowed for a deadly disease that's somewhat hard to spread (mostly just through sex) to ultimately go on a rampage.
I never thought about this.
So without concern for the humans with HIV* there an argument to be made that treating symptoms without curing made it spread more?
*obviously, this is just hypothetical. It’s important to care about the life of those with HIV. No banish them all to something like a leper-colony. Although it explains the logic for those at the time they existed better than a religious one did.