Research has suggested a link between herpes simplex virus type-1 (HSV-1) and an increased risk of Alzheimer's disease.
The HSV-1 infection is most commonly associated with cold sores. Individuals with a history of the infection have been found to have an 80 per cent higher risk of developing Alzheimer's, according to a large-scale US study by pharmaceutical company Gilead Sciences and the University of Washington in Seattle.
The study also found that antiviral medications used for treating HSV-1 can potentially lower the risk of Alzheimer's by 17 per cent.
But, what is the HSV-1 virus and why is it being linked to dementia? How true are these findings?
What is the HSV-1 virus?
Herpes simplex virus type 1 affects more than 3.8 billion people under the age of 50 globally; that’s more than half of the global population.
It is the main cause of oral herpes and is spread by oral contact. It can also cause genital herpes.
The infection can cause painful blisters and ulcers near the mouth, known as cold sores. Whilst there is not a cure, the condition is treatable. Most people with HSV-1 do not show any symptoms.
Why are cold sores being linked with dementia?
The study by Gilead Sciences and the University of Washington analysed 344,638 individuals with Alzheimer's, and the same number without the disease.
The researchers found that of the participants with Alzheimer's, 0.44 per cent had a prior HSV-1 diagnosis, compared to 0.24 per cent of those without.
According to the study, the exact mechanism linking HSV-1 and Alzheimer’s is unclear, but researchers suspect that inflammation caused by the virus plays a role.
Previous studies have shown that HSV-1 can remain dormant within the body’s cells and reactivate in later life, potentially triggering dementia-like symptoms.
The studies have said that HSV-1 induces changes in the brain that mirror those seen in Alzheimer's patients, including the formation of amyloid plaque-like structures.
Can cold sore medications help treat dementia?
More pressingly, the study found that those who used antiviral medications to treat HSV-1 were 17 per cent less likely to develop Alzheimer's compared to those who did not receive antiviral treatment.
Findings suggested that managing HSV-1 with antiviral medications could potentially mitigate the risk of developing Alzheimer's disease.
Currently in the UK, the drug acyclovir is used to treat cold sores, chickenpox, shingles, and other herpes virus infections.
Other herpes viruses such as HSV-2 and varicella zoster virus (chicken pox) have been associated with a heightened risk of Alzheimer’s disease, though it not clear how they might heighten the risk.
What do the experts say?
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.”
Dr Richard Oakley, director of research and innovation at the Alzheimer’s Society, added: “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 anti-virals prevent it.
