A study that appears in The Journal of Alzheimer’s Disease. from researchers at Tufts University in Medford, Massachusetts reports that a combination of very common viruses may be a leading cause of Alzheimer’s disease (AD).
The virus responsible for chickenpox and shingles may activate a dormant herpes virus strongly associated in its active state with AD. Varicella zoster virus (VZV) is the virus that causes varicella or chickenpox in childhood and can cause zoster shingles later in life.
The corresponding author of the study, Tufts’ Prof. David Kaplan told Medical News Today that “[m]ore than 95% of adults have experienced chickenpox during childhood and adolescence.”
The virus remains in the body afterward.
Co-author Dr. Ruth Itzhaki, visiting professor at Oxford University and professor emeritus at Manchester University, told MNT that “age and the decline in the immune system with age, and immunosuppression” are factors that can reawaken VZV as shingles in an adult. Before the new study, “VZV has been linked to AD, but the linkage was unclear, and the mechanisms not understood,” said Dr. Itzhaki.
The study found that when VZV becomes activated as shingles, it reactivates dormant herpes simplex virus type 1Trusted Source (HSV-1). In 2021, Dr. Itzhaki published a study compiling a significant body of research showing an association between activated HSV-1 and AD.
HSV-1 is also extremely common, with 50% to 80% of American adults carrying the virus. While either the oral or genital form of VZV is active, it can cause painful blisters at the site of infection.
Dr. Itzhaki noted that “What is known now is that infectious diseases, in general, confer a risk of AD, and our results explain this for shingles. We are now investigating if it is the case for some other infections. If it is, then it would explain the major risk posed by infectious diseases.”
“If we shift paradigms,” said Prof. Kaplan, “to focus efforts more on preventive strategies of treating these microbial species before they get a chance to wreak this havoc, we might have a better handle on preventing this disease.”
Parvathy Sukumaran 
