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Medscape
23-05-2025
- Health
- Medscape
Cold Sore Virus Implicated in Alzheimer's Disease
Herpes simplex virus 1 (HSV-1) infection is associated with an increased risk of developing Alzheimer's disease (AD), but treating the viral infection may offer protection, a new study found. In a matched case-control study of nearly 700,000 older adults, HSV-1 was more common in those with AD, and antiviral therapy for HSV-1 was associated with a lower risk of developing AD. However, the authors and outside experts cautioned that no firm conclusions can be drawn from this observational study and called for more research. The study was published online on May 20 in BMJ Open . It was funded by Gilead Sciences, which is actively involved in the research and development of treatments for HSV. Mixed Data HSV-1, a common virus that causes cold sores, affects more than two thirds of the global population younger than 50 years. An association between HSV-1 and AD has been reported previously, albeit with conflicting results across various studies. One recent Taiwanese cohort study found that symptomatic HSV infection was associated with a threefold increased risk of developing dementia. Antiherpetic medication reduced the risk by 90%. However, a study of US veterans failed to link HSV infection with an increased risk for dementia. Although, like the Taiwanese findings, antiherpetic medication was associated with a protective effect against dementia. To investigate further, researchers led by Yunhao Liu, PhD, data scientist with Gilead Sciences, used the IQVIA PharMetrics Plus claims database to match 344,628 people with AD to an equal number of control individuals without AD. Compared with 823 (0.24%) control individuals without an AD diagnosis, 1507 (0.44%) individuals diagnosed with AD had a history of HSV-1. Among those with AD, nearly two thirds were women (65%), their mean age was 73 years, and they tended to have more coexisting conditions. After adjusting for relevant confounding factors, the likelihood of an HSV-1 diagnosis was 80% higher in those with AD (adjusted odds ratio [aOR], 1.80; 95% CI, 1.65-1.96). In a stratified analysis, the association of HSV-1 with AD was more pronounced in older age groups — with an aOR of 2.10 in those aged 75 years or older vs an aOR of 1.14 in those aged 50-70 years. 'These findings are consistent with studies suggesting that the neurodegenerative impact of HSV-1 becomes more apparent with age and cumulative exposures,' the authors noted. Among the 2330 adults with a history of HSV-1, 931 (40%) were treated with antiherpetic medication, which was associated with a 17% reduced risk for AD compared with no treatment (adjusted hazard ratio [aHR], 0.83; 95% CI, 0.74-0.92). 'While the molecular mechanisms remain to be fully elucidated, these results are indicative of a possible role for antiherpetic therapy in mitigating dementia risk,' the authors wrote. Caveats and Cautionary Notes F. Perry Wilson, MD, Yale School of Medicine, New Haven, Connecticut, and Medscape's Impact Factor commentator, noted in a recent commentary that studies that use administrative data have limitations and said the author's suggestion that antiherpetic therapies are potentially protective for AD-related dementia 'feels like a bit of a leap to me at this point.' On the other hand, Wilson said, 'for those who suffer from cold sores, a study like this may push you a bit toward treatment, at least during an outbreak. Short-term valacyclovir is relatively safe and reduces the duration of the cold sore by about a day, which is nice. But if it reduces your risk of dementia as well, well, it might be a no-brainer.' Several outside experts also weighed in on the study in a statement from the UK nonprofit Science Media Centre. Sheona Scales, PhD, director of research at Alzheimer's Research UK, Cambridge, England, cautioned that 'despite the large sample size, this research has limitations partly due to only using health records and administrative claims data.' 'Most people infected with HSV-1 don't have any symptoms, so some infections might not have been recorded. Infections predating the information recorded are also not available. Although cases were matched with controls, diagnosing Alzheimer's disease, especially in the early stages, remains a challenge,' Scales commented. While the study found that some people receiving medicines to treat HSV-1 infections had a lower risk for AD, 'a lot more work is needed to unpick this,' she added. 'We know there are 14 established risk factors for dementia, and there's not enough evidence to include infections in this list. This study doesn't tell us if infections are causing the risk, it only shows an association. Further research is needed to understand what the underlying biology around this is,' Scales said. Tara Spires-Jones, PhD, director of the Centre for Discovery Brain Sciences at The University of Edinburgh, Edinburgh, Scotland, said the study adds to a growing body of data linking HSV-1 and other viral infections to the risk for AD. However, '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,' Spires-Jones noted. '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 disease as we age, including a better understanding of links between viral infection and Alzheimer's risk,' Spires-Jones said. Richard Oakley, PhD, director of Research and Innovation at Alzheimer's Society, London, England, cautioned that the study 'doesn't prove that cold sores cause Alzheimer's disease, or that antivirals prevent it. Much more research is needed to explore exactly how viruses might be involved and before we can draw firm conclusions.'
Daily Mirror
20-05-2025
- Health
- Daily Mirror
Common virus could leave people at far higher risk of developing Alzheimer's
Researchers have found that the herpes virus, which causes cold sores, increases Alzheimer's risk by as much as 80% by looking at medical records of over 300,000 Americans People who get a cold sore appear to be at 80% greater risk of developing Alzheimer's, research shows. Scientists behind a huge study into how viruses could increase the risk of dementia in later life also found treating cold sores with antivirals could lower this risk. Previous studies have found that the herpes simplex virus type 1 (HSV-1) can lie dormant in human cells for a lifetime before "re-awakening", leading to dementia symptoms. Researchers, including from pharmaceutical firm Gilead Sciences and the University of Washington in Seattle, used the medical records of 344,628 Americans with Alzheimer's and matched with the same number of people without the disease. The study, published in the journal BMJ Open, found that people who had suffered the herpes virus had an 80% increased risk of Alzheimer's, even when other factors were taken into account. But those with HSV-1 who used anti-virals to treat the virus were 17% less likely to develop Alzheimer's compared with those who did not the medicines. Author Dr Yunhao Liu, of Gilead, said: 'Findings from this 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 smaller heightened risk of Alzheimer's disease. Dr Sheona Scales, research director at Alzheimer's Research UK, said: 'There's an increasing amount of evidence that suggests our body's response to certain viruses could put us at an increased risk of developing Alzheimer's disease in later life. These recent findings from a large study using US health records propose that infection with HSV-1 - a common virus that causes cold sores – may be associated with an increased risk of Alzheimer's disease. The researchers also state that taking medicines to treat HSV-1 infections could reduce the risk, but this is still very early work and needs more investigation.' Experts have previously discovered that HSV-1 causes changes that resemble those in the brains of dementia patients, such as amyloid plaque-like formations and inflammation. In the new study all participants were aged over 50 and the diagnosis of Alzheimer's was made between 2006 and 2021. A history of HSV-1 diagnosis was noted for 1,507 (0.44%) patients with Alzheimer's, compared with 823 (0.24%) of those without. Some 65% of those with Alzheimer's disease were women, with an average age of 73. In the UK, the drug aciclovir is one of those available for treating cold sores, chickenpox, shingles and other herpes virus infections. The researchers admit that exactly how HSV-1 and other viruses might heighten the risk of dementia is not clear. Dr Liu added: "However, studies have shown that inflammatory alterations in the brain caused by HSV infection are pivotal in (Alzheimer's disease) development.' 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 disease as we age, including a better understanding of links between viral infection and Alzheimer's risk."
