I guess it only takes one bad pathogen to get in and it's hard to know what happened without scientific testing. The Guardian article I linked in another comme

I guess it only takes one bad pathogen to get in and it's hard to know what happened without scientific testing. The Guardian article I linked in another comment has for one guy "sample of his cerebrospinal fluid was taken and revealed a fungal infection..." which it shows it's possible at least to some extent to test for this kind of stuff. (article https://www.theguardian.com/lifeandstyle/2024/dec/01/the-brain-microbiome-could-understanding-it-help-prevent-dementia?lid=unhn64q4wvgg https://www.theguardian.com/lifeandstyle/2024/dec/01/the-bra...) It seems a bit of an under explored area. I suspected something like that with my dad who had a long deterioration of nerves/mind but current medics don't seem to regard it as a thing to do. It's more get your affairs together before the care home/death. While the guy in the Guardian article guesses that likely more than 50% of dementias are treatable infections.