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 :-)