Herpes simplex virus 1 may be associated with increased risk for Alzheimer's, dementia

Key takeaways:

• Some studies found herpes simplex virus 1 increased dementia risk by about 2.5 vs. controls.
• In another study, antiviral treatment for herpes was associated with decreased risk of dementia (HR = 0.89).

Mounting evidence suggests that herpes simplex virus 1 may be associated with an increased risk for Alzheimer’s disease and dementia, according to a systematic review of published studies.

“The underlying cause of Alzheimer’s disease, a progressive neurologic disorder that is the most common cause of dementia, is poorly understood,” Marc Cohen, BS, of the department of dermatology at the State University of New York, Downstate Medical Center, and colleagues wrote. “The neurotropic nature of [Herpes simplex virus 1 (HSV-1)], as well as its ability to establish dormancy in the sensory root ganglia of the trigeminal nerve, have made it a target of research as a potential infectious etiology for [Alzheimer’s disease].”

To evaluate the epidemiological associations between HSV-1 and Alzheimer’s disease, the authors conducted a systematic review consisting of 21 studies published between 1997 and 2021.

The evidence showed that there is an increased risk for Alzheimer’s disease when HSV-1 is present in the brain vs. controls (OR = 1.38; 95% CI, 1.14-1.66), according to a meta-analysis with a 4,353-person sample size. Another study with 3,566 subjects found similar results with an odds ratio of 1.4 (95% CI, 1.13-1.75) linking HSV-1 with the risk of Alzheimer’s disease.

In a subgroup analysis, the presence of HSV-1 along with apolipoprotein E (APOE) epsilon 4 allele, a genetic variant known to be associated with an increased risk for Alzheimer’s disease, was also found to increase a person’s risk of contracting the disease by almost threefold compared with the presence of APOE epsilon 4 allele alone.

Many of the studies that the researchers evaluated, including one of the retrospective cohort studies of 33,448 subjects, showed that HSV-1 increased a person’s risk for dementia, with two of the studies approximating a 2.5-fold risk increase compared with controls.

Further, in one of the studies including 265,172 subjects, antiviral treatment for HSV-1 was associated with decreased risk of dementia (HR = 0.89; 95% CI, 0.86-0.92).

“Recent studies demonstrate a strong correlation between HSV-1 and [Alzheimer’s disease]; however, treatment of HSV-1 for prevention of [Alzheimer’s disease] is not currently the standard of care,” the authors wrote. “Due to the high prevalence of HSV-1 in the adult population, focusing on HSV-1 anti-viral suppression may be a reasonable course of action.”

In their review, Cohen and colleagues concluded with a call to dermatologists to help in the “fight against Alzheimer’s disease,” as dermatologists may be at the frontline of HSV-1 treatment.

“Ultimately, understanding the connection between HSV-1 infection and neurodegenerative brain changes may become an integral part of the future of [Alzheimer’s disease] prevention and treatment,” they concluded.