Aspiring author looking for theories.... Hi :) I'm looking for some information / theories for a sci-fi book I'm working on. I have no medical or biology background so I'm kind of starting from scratch with this. I'm specifically looking for theories regarding parasites, virus's, things of that nature that would effect the brain. Some questions I'm trying to work out are: 1. Is there any factors that could theoretically cause a virus/parasite-host relationship to change from an antagonistic relationship to a mutualistic one? 2. Plausibility of parasite/virus causing neurological phenomenons. 3. Could a naturally occurring parasite/virus theoretically mutate quickly (perhaps spontaneously) as opposed to over thousands of years, without using external stimulus like radiation? I'm very new to writing and researching so any thoughts, idea, resources would be greatly appreciated! Thanks!