They definitely can cause it as shown in multiple inoculation experiments unless there is some other kind of contamination happening - which is unlikely.
Their presence in high enough numbers also starts the runaway process.
But those misfolded proteins do not start making themselves on their own...
And if the cascade is indeed immune related then stopping progression should be potentially as easy as targeted immune suppression combined with amyloid treatments. (Not easy at all but easier than doing it outside the brain.)
And obviously getting the cause too if possible. So far, few successes in treating, say, later stage Lyme disease...
[1]https://www.cbc.ca/radio/quirks/dec-8-2018-why-are-users-tak...