kiwi33 said: "I do not know of anybody who argues that AD and PD are prion diseases."

I think you may have just walked into a minefield kiwi33!

For example, have a look at this comment on PubMed Commons, from just a few days ago (about half way down the webpage):

The prion model for progression and diversity of neurodegenerative diseases. - PubMed - NCBI

Prion, prion-like, transcellular prionoid, ... I just hope they can get the terms sorted out ASAP!

Here is another relevant (and recent) reference:

Targeting α-Synuclein as a therapy for Parkinson's disease: The battle begins - Olanow - 217 - Movement Disorders - Wiley Online Library

(It's behind a paywall, but you can preview the 1st page for free. If you register as a patient or carer (patientACCESS), US$3.50 is the price you pay for the complete article.)