There's really nothing we can do about prion diseases, can we? What does the FDA (or any other regulatory or research institution) even have in the way of prion detection?

Just because something can't be easily detected in a timely manner doesn't mean there's nothing to be done.

Banning offal consumption. Banning blood donations from people who could have been exposed. Detecting the disease in postmortem examinations.

https://en.wikipedia.org/wiki/United_Kingdom_BSE_outbreak