lurkingforacure said: "... how does it get in the brain?"

Personally, I find the Braak staging hypothesis fairly convincing (i.e. PD starts in the olfactory bulb and the gut wall, and then travels via nerve fibres to the brain stem and beyond).

In this regard I found the following article very interesting. It discusses the case for the "travelling" being done by alpha-syn oligomers and fibrils, rather then by traditional pathogens.

Pathology: The prion principle : Nature : Nature Research