Recent research suggesting an unexpected link between a common form of herpes and Alzheimer’s disease could mean that anti-viral treatments might offer a potential preventative measure, said the scientists.
Previous studies have shown that herpes simplex virus type 1 (HSV-1) can remain dormant within human cells, only to reactivate later in life, potentially triggering dementia-like symptoms.
Experts have observed that HSV-1 induces changes in the brain that mirror those seen in Alzheimer’s patients, including the formation of amyloid plaque-like structures and inflammation.
Now, a large-scale US study involving researchers from Gilead Sciences and the University of Washington has further explored this connection, reports The Independent.
Analysing data from 344 628 individuals with Alzheimer’s and an equal number without the disease, all over 50, the researchers investigated the relationship between HSV-1 and Alzheimer’s diagnoses between 2006 and 2021.
The study revealed that those with a history of HSV-1 infection had an 80% increased risk of developing Alzheimer’s, even after accounting for other contributing factors.
Of those with Alzheimer’s, 0.44% had a prior HSV-1 diagnosis, compared with 0.24% of those without Alzheimer’s. The study group comprised 65% women, with an average age of 73.
Crucially, the research also found that people with HSV-1 who used antiviral medications to treat the virus were 17% less likely to develop Alzheimer’s than those who did not receive antiviral treatment.
Among the 2 330 individuals with a history of HSV-1 infection, 40% used antivirals after their diagnosis. These findings suggest that managing HSV-1 with antiviral medications could potentially mitigate the risk of developing Alzheimer’s disease, said the researchers.
Writing in the journal BMJ Open, the authors concluded: “Findings from this large…study implicate HSV-1 in the development of Alzheimer’s disease and highlight anti-herpetic therapies as potentially protective for Alzheimer’s and related dementia.”
The researchers also looked at the potential role of other herpes viruses, including HSV-2, varicella zoster virus (which causes chickenpox), and cytomegalovirus.
Both HSV-2 and varicella zoster virus infections were also associated with a heightened risk of Alzheimer’s.
Exactly how HSV-1 and other viruses might heighten the risk of dementia is not clear, pointed out the researchers.
“However, studies have shown that inflammatory alterations in the brain caused by HSV infection are pivotal in (Alzheimer’s) development,” they added.
HSV-1 DNA is also found in the plaques characteristic of Alzheimer’s, and people carrying the most common genetic risk factor for the disease are more susceptible to HSV infections, they said.
Professor Tara Spires-Jones, from the University of Edinburgh, said: “This is a well-conducted study adding to strong data in the field linking HSV-1 and other viral infections to increased risk of developing Alzheimer’s disease, but it is important to note that HSV-1 infection, which is extremely common in the population, is by no means a guarantee that someone will develop Alzheimer’s.
“Why viral infections may increase risk of dementia is not fully understood, but the most likely explanation is that infections increase inflammation in the body and contribute to age-related brain inflammation.
“More research is needed to understand the best way to protect our brains from Alzheimer’s as we age, including a better understanding of links between viral infection and Alzheimer’s risk.”
Dr David Vickers, from the University of Calgary in Canada, said: “The research exaggerates the role of HSV-1, failing to appreciate its absence in 99.56% of Alzheimer’s cases.”
He added: “The observed 17% hazard reduction with anti-herpetic drugs translates to a mere nine-month delay in Alzheimer’s disease onset.”
Dr Richard Oakley, director of research and innovation at the Alzheimer’s Society, said: “Results from this observational study suggested that people with recorded cold sore infections were more likely to develop Alzheimer’s disease, and interestingly those prescribed antiviral drugs had a slightly lower risk.
“But this doesn’t prove that cold sores cause Alzheimer’s disease, or that antivirals prevent it.
“The data came from insurance records, often based on self-reported symptoms which may miss or misclassify infections, and didn’t track how often people had cold sores or how consistently they took medication.
“Much more research is needed to explore exactly how viruses might be involved and before we can draw firm conclusions.”
Study details
Association between herpes simplex virus type 1 and the risk of Alzheimer’s disease: a retrospective case–control study
Yunhao Liu, Christine Johnston, Nadine Jarousse et al.
Published in BMJ Open Volume 15
Abstract
Objective
A growing body of evidence points to a role for herpesviruses in the development of Alzheimer’s disease (AD) and a reduced risk of AD among patients receiving antiherpetic medications. We investigated the association between herpes simplex virus type 1 (HSV-1) and AD using real-world data (RWD) from USA.
Design
In a matched case–control study, patients with AD aged ≥50 years diagnosed between 2006 and 2021 were identified from the IQVIA PharMetrics Plus claims database. Controls were matched in a 1:1 ratio with subjects with AD on age, sex, region, database entry year and healthcare visit numbers.
Results
The study included 344 628 AD case–control pairs. History of HSV-1 diagnosis was present in 1507 (0.44%) patients with AD compared with 823 (0.24%) controls. HSV-1 diagnosis was found to be associated with AD (adjusted OR 1.80; 95% CI 1.65 to 1.96). Patients with HSV-1 who used antiherpetics were less likely to develop AD compared with those who did not use antiherpetics (adjusted HR 0.83, 95% CI 0.74 to 0.92).
Conclusions
Findings from this large RWD study implicate HSV-1 in the development of AD and highlight antiherpetic therapies as potentially protective for AD and related dementia.
See more from MedicalBrief archives:
Corroborating the role of herpes simplex virus in Alzheimer’s
Commentary on causal link between herpes and Alzheimer’s