Usually developed during childhood, the varicella zoster virus (VZV) may increase the risk of Alzheimer’s disease. Approximately 95% of people have been infected before reaching the age of 20. If it is most of the time without consequence, this virus can manifest itself later in adults who have already had chickenpox as a child, resulting in shingles, an infectious disease more common after 50 years and causing a skin rash mainly at chest level.
Often, this virus wakes up during a temporary drop in immune defenses (fatigue, stress) or during a disease resulting in an immune deficiency (HIV, cancer, infectious disease, etc.).
A study published in the Journal of Alzheimer’s Disease and conducted by researchers from Tufts University and the University of Oxford found that shingles infection can trigger a “chain reaction” in the brain, which may increase the risk of dementia. “After recovering from chickenpox, the varicella zoster virus remains dormant at the root of the nerves in the nerve ganglia”noted Ameli.fr.
HSV-1 virus awakening
In order to test the impact of varicella zoster virus on the brain, the researchers used brain cells analyzed in the laboratory. And if it did not directly trigger changes associated with Alzheimer’s disease, VZV allowed the reactivation of a virus usually responsible for herpes or cold sores (HSV-1). In general, this virus remains dormant, but when activated, it causes an accumulation of tau and beta-amyloid proteins, two hallmarks of Alzheimer’s disease.
“It’s a double punch of two viruses that are very common and generally harmless”, said Dana Cairns, author of the study. “But lab studies suggest that if further exposure to VZV awakens dormant HSV-1, it could cause problems..”
VZV infection alone would therefore not be sufficient for plaque formation and cell death: it is only if the infected cells harbor HSV-1 that an increase”spectacular” proteins was observed.
“Damage to the brain from repeated infections throughout life would eventually lead to the development of Alzheimer’s disease and dementia. This would mean that vaccines could play a bigger role than just protecting against a single disease, because they could also indirectly, by reducing infections, provide some protection against Alzheimer’s disease.”concludes Professor Ruth Itzhaki who participated in the study.
Sources:
- Potential involvement of varicella zoster virus in Alzheimer’s disease via reactivation of quiescent herpes simplex virus type 1, Journal of Alzheimer’s diseaseAugust 2, 2022
- Shingles or reactivation of the varicella virus, Ameli.fr
