I'm not sure in general but there is evidence that some dementia is down to infections and can be treated in the usual way for those - https://www.theguardian.com/lifeandstyle/2024/dec/01/the-bra...

I think I read that amyloid may be a body immune reaction to infection which is why targeting that rather than the infection is ineffective. (not expert on this but the article is interesting).