Earlier quoted context omitted.
Prions are exactly the tiny, hard to detect things that could make Alzheimers transmissible. There are likely to remain many questions to resolve, but this sure suggests a line of inquiry: Is Alzheimer's one distinct disease? Can a prion be isolated as the cause? Can a diagnostic test be designed that detects this prion? Etc.
There is no reason to assume this is a matter of proteins. It could just as easily be viral or bacterial infection. Classically, people always just assumed that brains had no such infections. Until somebody checked, and they turn out to be very common. But they still don't look for infections in Alzheimer's patients' brains, probably because it would make them seem negligent. (Which they are.)
Except that there's increasing evidence that specific proteins do in fact play a part in various forms of dementia.