A new virus linked to Alzheimer's disease - this one in your gut

We've written before about the herpes zoster virus as a potential culprit in the development of Alzheimer's disease -- the virus that causes chickenpox and shingles.  So we quoted some authorities who concluded from their research that the shingles vaccine may provide some protection from Alzheimer's disease originating from that source.  But now there's another virus under the Alzheimer's microscope, another member of the herpes family.  But, while herpes zoster inhabits the nervous system, this one lives in your gut.

The virus is called cytomegalovirus, or HCMV.  You may acquire it as a child and experience an apparently innocuous chronic infection in your gut.  Based on autopsy results, about 80% of us show evidence of having had an HCMV infection by age 80.  So it's pretty common. 

But the trouble starts when the virus either escapes the gut into the blood stream or follows the vagus nerve to the brain.  There it comes into contact with the brain's immune cells -- microglia.  In Beating the Dementia Monster we discussed the role that microglia may play in the development of the disease, notably by way of inflammation.  This somehow triggers the syndrome of amyloid plaques and clumps of microtubules with a defective form of tau protein that we associate with Alzheimer's disease. 

I choose my words carefully here.  It's increasingly clear that what we call Alzheimer's disease comes in different flavors which have different causes.  For example (as we explained in Beating the Dementia Monster), "young onset Alzheimer's disease" or "familial Alzheimer's disease" (which often strikes in someone's 40s or 50s) occurs in a different genetic environment from "sporadic Alzheimer's disease."  The latter is the common version, where symptoms begin to appear after the age of 65.  Are familial and sporadic Alzheimer's diseases exactly the same disease but with different causes, or are they distinct but slightly different diseases?  How many forms of the disease are there?  Or how many different disease are there that we label "Alzheimer's disease?"  Opinions vary.

There was a new study conducted by researchers from Arizona State University and Banner Alzheimer’s Institute on the possible role of HCMV in the development of Alzheimer's disease.  The findings were just published (December 2024) in Alzheimer’s & Dementia: The Journal of the Alzheimer’s Association, with the title, "Alzheimer's disease-associated CD83(+) microglia are linked with increased immunoglobulin G4 and human cytomegalovirus in the gut, vagal nerve, and brain."  The researchers concluded "[HCMV-microglia biochemistry] is consistent with an active HCMV infection, which may indicate an opportunity for the administration of antiviral therapy in subjects with AD."  Translation: "Stopping or preventing HCMV infections may be a way preventing or treating Alzheimer's disease."  But ... more research is required. 

Click here for more of a deep-dive on this topic.

We said here that there may be different varieties of Alzheimer's disease or even different diseases all labeled "Alzheimer's."  But, from everything I've read, they all respond to the lifestyle tools of the Dementia Toolkit.