Could Alzheimer disease (AD) be caused in part by a viral infection? Such an association seems bizarre and yet the evidence is accumulating that certain strains of herpes virus infections and Alzheimer disease are connected. And yes, we are talking about cold sores, also known as herpes simplex virus type 1 (HSV-1) infections of the lips. A study published in the Journal of Virology (Oct. 30, 2024) is compelling.
The authors conclude:
“These findings provide critical insights into the region-specific dissemination of HSV-1 within the CNS [central nervous system], elucidating potential mechanisms linking viral infection to neurological and neurodegenerative diseases.”
What is the Connection Between Herpes Virus Infections and AD?
The authors of the study in the Journal of Virology report that 2/3 of the world’s population has evidence of HSV-1 in their bodies. The virus hangs out in the brain (trigeminal ganglion or TG). Most of the time it is in a latent state. Think of the herpes virus as a bit like a bear hibernating.
When this viral “bear” is poked or reactivated (hormonal changes, psychological stress, sun exposure, etc), it emerges from its TG cave, starts multiplying and shows up on the lip as a core sore. But there is growing evidence that the virus can also move up into the brain.
Could HSV-1 damage parts of the brain and create an immunological cascade of events that ultimately leads to dementia? This has been called the “pathogen hypothesis of Alzheimer’s.”
One of the co-authors of a prior study (Neuron, June 21, 2018) commented:
“This is the most compelling evidence ever presented that points to a viral contribution to the cause or progression of Alzheimer’s.”
Such a statement will likely shake up brain scientists. Yet the author of this conclusion is a heavy hitter. Sam Gandy, MD, PhD, is Professor of Neurology and Psychiatry and Director of the Center for Cognitive Health and NFL Neurological Care at Mount Sinai Health System. He cannot be ignored as a crackpot.
Herpes Virus Infections and Alzheimer Disease Data:
The researchers examined postmortem brain tissues from 600 patients with and without Alzheimer disease. They found a robust association between the likelihood of this form of dementia and the presence of human herpes virus 6A (HHV-6A) and human herpes virus 7 (HHV-7). Genes from these herpes viruses in brain tissue were linked to amyloid plaque, brain tangles and the severity of Alzheimer disease.
The researchers went on to investigate an additional 800 tissue samples from the Mayo Clinic and Rush Alzheimer’s Disease Center. Again they found a link between levels of HHV-6A and HHV-7 and Alzheimer’s dementia.
The Link Between Herpes Virus Infections and Alzheimer Disease is NOT New:
It will likely come as a huge shock to the scientific community to learn that this new discovery is not really new. On October 30, 2014 we reported on Swedish research:
Do Cold Sores Increase the Risk for Alzheimer Disease?
But wait…there’s more! When we started researching a relationship between herpes virus infections and Alzheimer disease, we discovered work carried out by pathologist Melvyn J. Ball. In August 1982, he reported in the Canadian Journal of Neurological Sciences that the herpes simplex virus might be contributing to the underlying pathology of Alzheimer’s dementia.
Read about Dr. Ball’s research and newer Swedish epidemiology at this link.
What Can We Do About Herpes Virus Infections and Alzheimer Disease?
If this research continues to hold up, neuroscientists will have to reconsider their entire understanding of the causes of this disease. The body’s immune system may be reacting to the presence of invading viruses. If so, there might be something we could do to alter the course of the disease.
Dr. Gandy of Mount Sinai offers this ray of hope:
“A similar situation arose recently in certain forms of Lou Gehrig’s disease. In those patients, viral proteins were discovered in the spinal fluid of some Lou Gehrig’s patients, and patients with positive viral protein tests in their spinal fluid showed benefit when treated with antiviral drugs.”
It is premature to imagine that antiviral drugs might alter the course of Alzheimer disease. On the other hand, virtually all the drugs that have been studied for this form of dementia have flamed out during the last couple of decades. Perhaps it is time to consider the “pathogen hypothesis of Alzheimer’s.” It is not out of the question that antiviral medications could make a difference against this dreaded disease.
We’re hardly the first to propose such a strategy.
Scientists writing in the journal Future Microbiology (March, 2012) wrote:
“One strategy might be to use antiviral agents to combat the disease. This possibility is based on data suggesting that herpes simplex virus type 1 (HSV1), the virus responsible for herpes labialis (cold sores), is a cause of AD [Alzheimer Disease].”
We hope researchers soon begin testing antiviral drugs to see whether they can make a difference against this horrific disease. A preliminary study (the VALZ-Pilot) tested the antiviral drug valacyclovir in 33 subjects with mild dementia (Alzheimer’s & Dementia, March 14, 2022).
The authors wrote:
“This report describes the results of an open phase II dual‐site pilot trial of a 4‐week high‐dose valacyclovir intervention for subjects with early‐stage AD [Alzheimer’s disease]. The intervention was found to be feasible, tolerable, and safe for the duration of the trial.”
We are still awaiting data to find out if antiviral drugs like valacyclovir provide any actual benefit for people with Alzheimer Disease.
