Summary: A large study suggests that symptomatic
infection with herpes simplex virus 1 (HSV-1)—best known for causing
cold sores—may significantly raise the risk of developing Alzheimer’s
disease. Researchers found that people with HSV-1 were 80% more likely
to have Alzheimer’s, while those treated with antiviral medications had a
17% lower risk.
The findings align with other evidence that HSV-1
may trigger inflammation and amyloid-beta accumulation in the brain,
hallmarks of Alzheimer’s pathology. Although the study is observational
and can’t prove causation, it highlights the potential for antiviral
therapy as a protective strategy and urges greater public health focus
on herpes virus prevention.
Key Facts:
- 80% Higher Risk: People with HSV-1 were significantly more likely to develop Alzheimer’s.
- Antiviral Benefit: HSV-1 patients who took antiviral drugs had a 17% lower Alzheimer’s risk.
- Biological Link: HSV-1 may drive brain inflammation and amyloid buildup, contributing to dementia.
Source: BMJ
Symptomatic
infection with the virus responsible for cold sores around the
mouth–herpes simplex 1, or HSV-1 for short—may have a key role in the
development of Alzheimer’s disease, suggests a large pharma
industry-funded US study published in the open access journal BMJ Open.
But treatment with antiviral therapy seems to be linked to a lower
risk of this type of dementia, suggesting that treatment to quell HSV-1
symptoms may be protective, the findings indicate.
Currently,
around 35.6 million people worldwide live with dementia, and 7.7million
new cases are diagnosed every year, say the researchers. Alzheimer’s
disease comprises 60%–80% of all dementias, with total costs for its
treatment reaching US$305 billion in 2020, they add.
Various infectious agents have been implicated in the development of
Alzheimer’s disease, and the most studied of these is HSV-1, which
affected more than two-thirds of under 50s around the globe in 2016
alone.
To shed further light on the mooted role of HSV-1 in
Alzheimer’s disease and the potential protective effects of antiherpetic
drugs, the researchers drew on a large set of US administrative claims
data (IQVIA PharMetrics Plus) for the period 2006-21.
People
diagnosed with Alzheimer’s disease were matched for age, sex,
geographical region, database entry year, and number of healthcare
visits with those without any history of neurological disease, resulting
in a total of 344,628 case–control pairs.
Nearly two thirds (65%)
of those with Alzheimer’s disease were women. Their average age was 73
and they tended to have more co-existing conditions—all risk factors.
In
all, 1507 (just under 0.5%) people with Alzheimer’s disease had been
diagnosed with HSV-1 (0.44%) compared with 823 (just under 0.25%) of
those in the comparison (control) group.
Unsurprisingly, the risk
of Alzheimer’s disease rose in tandem with age. But, overall, the
likelihood of an HSV-1 diagnosis was 80% higher among those with
Alzheimer’s disease, after adjusting for potentially influential
factors.
Among the 2330 people with a history of HSV-1 infection,
931 (40%) used antiherpetic medication after their diagnosis. And they
were 17% less likely to develop Alzheimer’s disease than those who
didn’t use these treatments.
The researchers also looked at the
potential role of other herpes viruses, including HSV-2, varicella
zoster virus, and cytomegalovirus. Both HSV-2 and varicella zoster virus
infections were also associated with a heightened risk of Alzheimer’s
disease.
Exactly how HSV-1 and other neurotropic viruses might heighten the risk of dementia isn’t clear, point out the researchers.
“However,
studies have shown that inflammatory alterations in the brain caused by
HSV infection are pivotal in [Alzheimer’s disease] development,” they
explain.
“It has been reported
that Aβ peptides are deposited in response to HSV infection and protect
host cells by blocking viral fusion with the plasma membrane, pointing
to HSV as a potential risk factor for [Alzheimer’s disease].
Consistently, Aβ exhibits antimicrobial properties against various
pathogens, including HSV-1,” they add.
HSV-1 DNA is also found in the plaques characteristic of Alzheimer’s
disease, and people carrying the ApoE ε4 allele, the most common genetic
risk factor for the disease, are more susceptible to HSV infections,
they note.
This is an observational study, and as such, no firm
conclusions can be drawn about cause and effect. And the researchers
acknowledge that HSV-1 infections before the patient’s inclusion in the
database weren’t known, added to which many people with the infection
don’t have symptoms, while others might not seek treatment when they
do–all factors that might influence the findings.
But their
findings are in line with those of other studies. And they suggest:
“While the molecular mechanisms remain to be fully elucidated, these
results are indicative of a possible role for antiherpetic therapy in
mitigating dementia risk.”
And they conclude: “These findings
place an even greater emphasis on viewing the prevention of herpes
viruses as a public health priority.
About this virology and Alzheimer’s disease research news
Author: Emma Dickinson
Source: BMJ
Contact: Emma Dickinson – BMJ
Image: The image is credited to Neuroscience News
Original Research: The findings will appear in BMJ Open
