Is there a link between Alzheimer's and cold sore and shingles infections?

Research points to a possible viral connection — and possible paths to minimizing risks.

- Ruth Itzhaki

The common cold sore virus, which is often caught in childhood, usually stays in the body for life — quietly dormant in the nerves. Now and then, things like stress, illness or injury can trigger it, bringing on a cold sore in some people. This same virus — called herpes simplex virus type 1 — may also play an important role in something far more serious: Alzheimer's disease.

Over 30 years ago, my colleagues and I made a surprising discovery. We found that this cold sore virus can be present in the brains of older people. It was the first clear sign that a virus could be quietly living in the brain, which was long thought to be completely germ-free — protected by the so-called "blood-brain barrier".

Then we discovered something even more striking. People who have a certain version of a gene (called APOE-e4) that increases their risk of Alzheimer's, and who have been infected with this virus, have a risk that is many times greater.

To investigate further, we studied brain cells that we infected with the virus. They produced the same abnormal proteins (amyloid and tau) found in the brains of people with Alzheimer's.