The only prion diseases I know of are BSE (a.k.a. Mad Cow Disease), scrapie (in sheep), vCJD (which I think is Mad Cow except in humans) and kuru, prevalent in cannabal societies in New Guinea.
Are any other prion diseases known? The ones that exist seem to be quite particular: they are primarily transmitted through cannabalism of neural tissues (hence BSE in cows fed on ground up cow scraps) and they cause degenerative brain diseases. Is there any particular reason that they couldn’t affect other tissues? Or is only one particular protein susceptible, one that happens to be in the brain? Do kuru and vCJD affect the same protein?
Naturally these diseases are hard to trace - testing for them is quite complicated. Is there any possibility that other degenerative neural diseases that appear to be genetic could actually be prions? Are there any convincing modes of transmission for prion diseases that don’t involve eating the tissue (e.g. could a mother pass it to her spawn in utero?)
Oh, and, uh, I’ve probably forgotten some questions, so feel free to chime in with whatever else you care to add.