Problem:

The primary reason the body raises its temperature (via the Hypothalamus in this case) is that bacteria and viruses tend to optimally thrive at 98.6F, which is also your body's optimal operating temperature.

Question: I am just wondering if there are any viruses or bacteria that have gained the ability to prosper under fever temperatures through evolution?If not, why not?

Question: Is there any biological restriction stopping such viral evolution?

I will try to explain my question. As far as I know, evolution helps species to adapt to their environment. For example, when people started using antibiotics we got new bacteria resistant to those antibiotics.

If fever is part of the innate immune reaction to viruses and bacteria, why hasn't this resulted in selection for fever-resistant variants?

Why has evolution apparently stopped in this case?