Herpes causes Alzheimer's ... or does it?

It was almost exactly one year ago we posted on the unfolding story of the relationship between Alzheimer's disease and the herpes simplex virus.  What we said then was that the research results have been conflicting.  A year later, more research has been done, but little has changed.  Research results have still been conflicting.

According to an article this week in ALZForum, some new research in European health databases found correlations between herpes infection and Alzheimer's disease in some countries, but much less so in others.  There were also conflicting results regarding anti-viral treatments and their influence on Alzheimer's disease.  In some cases it looked like treating with certain drugs actually helped, but in other places it did not.  And then, is it herpes, or any virus -- like, for example, covid-19?

The manifestation of a herpes infection most easily followed is herpes zoster, or shingles.  Shingles is usually considered to be a late appearance of the virus following its first appearance as a childhood chicken pox infection.  But there was evidence in the research of elevated incidence of Alzheimer's disease from most any virus, not just herpes.  And then, what about bacterial infection?  They found evidence that hospitalization for any infection increased the probability of Alzheimer's disease by a factor of 1.6.  (Correlation is not causation...)

Have there been previous studies of national health databases looking for correlations?  A few years ago, three studies of the Taiwanese national healthcare database found that a severe herpes infection raised the risk of Alzheimer's disease by a factor of 2.5 to 3 times.  Consistent -- and inconsistent -- with the results of the European study, treatment with the drugs acyclovir and valacyclovir dramatically diminished the odds of getting dementia in these situations.

Of course, some to the inconsistencies may be consequences of inconsistencies in research methodologies.

This seems to be a topic of heated discussion.  To resolve the matter, several incentives have been offered.  Most notably, anyone “who provides persuasive evidence that an infectious agent is the root cause of Alzheimer's disease,” will be awarded a $1 million prize by Leslie Norins at ALZgerm.org.