Sounds like a crock.
1) The infectious agent in prion diseases is filterable. Spiroplasma
is not.
2) UV inactivation data suggests a very small genome size (of course
that is because we know there is no genome). The genome size of
Spiroplasma is well out of the range of this data. I'm not aware of UV
inactivation data on Spiroplasma but I'll bet they don't match.
That's just for starters. Incidentally, can you please post the source
of this "hypothesis" so I can take a look.
Martin