People taking acyclovir regularly (to suppress HSV1 and 2 symptoms) have been found to have a 10 fold decrease in risk of getting Alzheimer's (Taiwanese study).
Additional studies are currently ongoing to confirm this in the US.
The scientific "journalists" seem to jump to the conclusion that therefor HSV1,2 must be cuasal for Alzheimer's. But it could be that Acyclovir somehow prevents or slows the formation of AB tau prion-like forms (and has nothing to do with the herpes - Alzheimer's causality).
Or. Some Acyclovir prevents Alzheimer's through a completely different mechanism we don't know about yet.
My point: effective medication may already be there. We just don't know how it works yet.
Also by "factor" do you mean protein?
I'm just an electronics guy, would love to know more.
By "factor" I didn't mean a biological entity, but rather... well, a factor contributing to the development of the disease. (As you might have noticed, English is not my native tongue, and I couldn't come up with a sophisticated synonym to "a thing that makes a contribution to sth" ;-))
It's been long postulated that AB/tau proteins are only a symptom of Alzheimer's and not a causative agent (which would explain why, so far, no treatment has been successful despite pre-clinical successes). According to some hypotheses, what we observe is the effect of "strayed" lymphocytes going postal and attacking brain cells after being activated by a microbial agent – and HSV is one of the suspects.
Hope that helps. If something is not clear, feel free to ask and I'll try to explain :-)