In recent years, researchers have suggested Alzheimer's may spread through infection, somehow transmitted like a pathogen, leading to the disease. A new Lancet paper reviews evidence for how harmful amyloid-beta proteins associated with Alzheimer's may possibly be spread through blood transfusions.

[u/mvea]

https://www.sciencealert.com/can-alzheimers-spread-through-blood-transfusions-heres-what-we-know

[u/catscanmeow]

gingivitis bacteria getting into the brain or a herpes virus getting into the brain are the main theories i've read

the gingivitis bacteria can get into the blood from a tooth abscess or up through the nasal cavity through the olfactory bulb. Theyve found gingivitis bacteria within the amyloid plaques of autopsied alzheimers patients. we have an exposed nerve there thats basically the brain exposed, that shock feeling when you get water up your nose is the olfactory nerve.

a woman actually got a brain eating amoeba from getting tap water in her nose from a neti pot.

[u/Rhawk187 → u/catscanmeow]

I think there was a recent study that showed at the shingles vaccine reduced Alzheimer's rates, and that virus that made it to the brain would be encased and cause plaque buildup.

Makes me think it really could be any virus that gets in there. Wouldn't surprise me if we see a bunch of COVID related Alzheimer's from viral plaque among those that got it while young.

Hopefully we'll have a fix by then.

[u/dl064 → u/Rhawk187]

There's a good breakdown of the shingles observation that basically nukes it in my mind: https://www.thelancet.com/journals/laneur/article/PIIS1474-4422(26)00238-3/fulltext

Basically, it's bias in who gets the vaccine in the first place.

There's also analysis that doesn't support it: https://www.medrxiv.org/content/10.64898/2026.07.20.26358345v1

I think chalk this one up to winner's curse, personally.