Associating Herpes with Alzheimer's Disease

We have written several times in the past about a correlation between herpes infection and Alzheimer's disease.  Correlation is not causation, and no causal relationship has been found.  Nevertheless, the correlation is intriguing.  

A couple of points, most of which we've made before:

• The implicated version of the virus is the Herpes Simplex Type 1, or HSV1.  It's known for causing cold sores.
• Most people contract the virus at some point in their lives, and it often finds a hiding place in the brain.  
• People carrying the APOE4 gene are most likely to show a correlation between a viral infection and Alzheimer's disease in their autopsies.
• There is interest in the possibility that controlling the herpes virus might control at least some forms of Alzheimer's disease.

So will fighting the herpes virus fight Alzheimer's disease?  According to a nationwide study out of Taiwan, the answer is yes.  This was reported in an April 2018 article in the journal Neurotherapeutics.  The study enrolled 33,448 subjects, 8,362 of whom were newly diagnosed with herpes infections.  The infected subjects were treated with antiherpetic medications.  The study concluded, "The usage of anti-herpetic medications in the treatment of herpes simplex virus infections was associated with a decreased risk of dementia."  The risk of dementia was reduced by a factor of 10.

The correlation with the APOE4 gene variant is significant, because it is a factor in many, but certainly not all cases of Alzheimer's disease.  Therefore, treating or preventing HSV1 infection might influence a substantial portion of Alzheimer's cases, but certainly not all.