For years researchers have been investigating what they believed was the link between the herpes virus and Alzheimer’s disease.

Laboratory tests have consistently shown that there was probably some sort of connection, but scientists have been stymied trying to untangle exactly how the presence of the herpes virus in brain tissue might bring on the neuronal damage that could lead to full-blown Alzheimer’s.

Finally, scientists believe they’ve discovered the missing part of the puzzle… another virus.

In the lab, scientists have been able to build models of mini-brains that demonstrate how an infection with the cold sore virus herpes simplex-1 (HSV-1) may set off processes among neurons that are characteristic of the destructive progress of Alzheimer’s disease in the human brain.

However, they’ve recognized that their grasp of what happens in the brain during this memory-robbing illness was incomplete.

For example, many people carry around copies of dormant HSV-1 in their bodies for years without the virus creating health problems of any sort. So, why would this virus sometimes rest harmlessly in brain tissue but at other times set off swaths of brain cell destruction?

The answer, according to research at Tufts, is that it may take a second viral infection to reawaken HSV-1. It is that reawakening that initiates the early stages of Alzheimer’s disease.

A Second Virus Triggers HSV-1 To Damage Memory 

Tests show that when the varicella zoster virus (VZV), which can cause chickenpox and shingles, arrives on the scene, it can stimulate HSV-1 to become destructive within the brain.1 What’s more, an VZV infection may not be the only inflammatory event that could set HSV-1 in motion.

“Our results suggest one pathway to Alzheimer’s disease, caused by a VZV infection which creates inflammatory triggers that awaken HSV in the brain,” says researcher Dana Cairns, PhD, who is in the Biomedical Engineering Department at Tufts. “While we demonstrated a link between VZV and HSV-1 activation, it’s possible that other inflammatory events in the brain could also awaken HSV-1 and lead to Alzheimer’s disease.”

Why You Are At Risk 

Unfortunately, statistics show that both viruses are widespread. The World Health Organization reports that among the 6.5 billion people around the world under the age of 59, more than half (3.7 billion) are infected with HSV-1. And half of all Americans carry the virus around in their bodies and may occasionally experience mild swelling and pain from the virus. Or it can remain quietly dormant for decades.

The VZV virus is even more widespread. It is estimated that about 95 percent of people around the world have been infected with it before the age of 20. Interestingly, VZV, which is also a type of herpes virus, can get into nerve tissues and remain dormant for prolonged periods.

As you grow older, VZV’s activity can cause shingles, a disease that gives rise to painful nodules and blisters on the skin. This isn’t rare: It takes place in about one in three people.

The Tufts researchers report that the Alzheimer’s danger arrives only after VZV leads to HSV-1 reactivation which, in turn, gives birth to blisters, sores and other inflammatory difficulties.

Dr. Cairns issues this warning, “It’s a one-two punch of two viruses that are very common and usually harmless, but the lab studies suggest that if a new exposure to VZV wakes up dormant HSV-1, they could cause trouble.

“It’s still possible that other infections and other pathways of cause and effect could lead to Alzheimer’s disease, and risk factors such as head trauma, obesity, or alcohol consumption suggest they may intersect at the re-emergence of HSV in the brain.”

Vaccines May Help Keep Alzheimer’s At Bay 

A study in Europe shows that getting a vaccination for VZV, which is meant to ward off chickenpox and shingles, can also lower your risk of dementia.2

The Tufts researchers believe that the reduced risk occurs when the vaccine interrupts the process of viral reactivation, inflammation and neuronal damage that can lead to Alzheimer’s disease.

My take on this is that this research may convince a lot of people to get a shingles vaccine. But it also presents good evidence to, as I’ve often urged, keep your immune system strong by eating a healthy diet, limiting processed foods and getting consistent daily exercise. This helps protect you from any type of infection and is linked to a lower risk of all types of dementia.


  1. https://content.iospress.com/articles/journal-of-alzheimers-disease/jad220287 
  2. https://pubmed.ncbi.nlm.nih.gov/35434253/

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