COMMENTARY

Is Alzheimer Disease Caused by an Infection?

Richard S. Isaacson, MD

Disclosures

October 08, 2018

I am Dr Richard Isaacson, director of the Alzheimer's Prevention Clinic at Weill Cornell Medicine and New York-Presbyterian Hospital in New York City. I want to talk about the contagion theory of Alzheimer disease. Could Alzheimer disease be caused by an infection? Some very interesting research calls into question the precise etiology of Alzheimer disease.

Physicians and scientists have been taught for decades that amyloid causes Alzheimer disease. Although that may be true, different people may take different roads to developing the disease. Some people may be on the metabolic road; for example, having diabetes increases the Alzheimer disease risk twofold.[1] What about hormones and the menopause transition? Maybe women are in the fast lane while men are sitting in traffic. These are all very interesting questions

Recently, some very exciting work has begun on the infectious theory of Alzheimer disease.[2] For example, herpesviruses are ubiquitous. Many people have herpesvirus infections, but in some people, perhaps based on epigenetics and the environmental interaction with a person's genes, infection with the herpesvirus puts them on the fast track to Alzheimer disease.

For many years, we have thought of amyloid as the primary causative factor for Alzheimer disease. However, amyloid is also released in response to an infection in the brain. So, maybe—just maybe—that virus or another virus, or a bacteria, or another germ that has yet to be isolated, may put someone on that path to Alzheimer disease. Again, this is probably not the only cause—there may be many paths—but it is one that we need to explore.

Could Alzheimer disease be contagious? We all know about prions. Prion proteins are nonliving infectious particles that cause Creutzfeldt-Jakob, or mad cow, disease, as well as a variety of other conditions. What about Alzheimer disease? Could it be contagious? In fact, if you look at the statistics, the spouses of persons with Alzheimer disease are at a 1.6-fold risk of having the disease themselves.[3] Also, neurosurgeons are at a much higher risk for Alzheimer disease than the general population.[4] Why is this? We're not sure yet.

The goal is to conduct more research and try to isolate the various potential causes. Could it be that in some people, an infection causes an inflammatory cascade, amyloid is released to fight the virus or bacteria, and that is what eventually leads to Alzheimer disease? The infectious hypothesis of Alzheimer disease is one that we definitely should explore and consider. Perhaps using antiviral drugs could be one way to fight the condition. Maybe using antiviral drugs early could even be a way to prevent that condition.

For Medscape, I am Dr Richard Isaacson. Thanks so much.

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