Dormant viruses lurking in the brain could be activated by a head injury and trigger Alzheimer’s, research has suggested.
Studies have long warned that concussions and blows to the head may raise the risk of neurodegenerative conditions.
But now, scientists believe such injuries could ‘wake-up’ dormant viruses in the brain triggering inflammation and longer-term damage that leads to dementia.
The main concern is around herpes viruses, including herpes simplex virus (HSV-1), which causes cold sores — and is carried by four in five adults.
Up to 95 per cent are also estimated to carry the varicella-zoster virus, another type of herpes virus that causes chickenpox and shingles.
The scientists, from the UK and US, hope the promising findings — conducted in laboratory settings not on humans — could help speed up research into antiviral drugs for herpes that may slow the onset of degenerative diseases.
Professor Ruth Itzhaki, a visiting fellow at the University of Oxford‘s Institute of Population Ageing, said: ‘What we’ve discovered is that in the brain model these injuries can reactivate a dormant virus, HSV-1.
‘This sets off inflammation which, in the brain, would lead to the very changes we see in Alzheimer’s patients.’
Scientists believe head injuries could ‘wake-up’ dormant herpes viruses in the brain triggering inflammation and longer-term damage
Studies have long warned that concussions and blows to the head may raise the risk of neurodegenerative conditions. Former rugby union player Steve Thompson was diagnosed with with early onset dementia at 43-years-old
Dr Dana Cairns, a biomedical engineering research associate at Tufts University in Boston, added: ‘This opens the question as to whether antiviral drugs or anti-inflammatory agents might be useful as early preventive treatments after head trauma to stop HSV-1 activation in its tracks, and lower the risk of Alzheimer’s disease.’
In the study, researchers recreated a model brain in the lab, putting it into a cylinder to mimic the skull.
Some of the brain cells had been infected with dormant herpes simplex virus (HSV-1) which causes cold sores.
They then gave the mini-brains either a single hard blow with a piston to mimic a traumatic head injury or a series of smaller jolts to mimic the effects of periodic milder concussion.
When the brain tissues were exposed to repeated ‘mild blows,’ the previously dormant HSV-1 virus became active.
This reactivation triggered inflammation, beta-amyloid plaque build-up, and the formation of harmful tau proteins, signature markers of Alzheimer’s disease.
There was also evidence of diminished function of brain cells.
Further strikes to the brain tissue, mimicking repetitive head injuries, saw more severe damage – but brain cells without a herpes infection did not exhibit the same problems from the blows.
Alzheimer’s disease is the most common cause of dementia. The disease can cause anxiety, confusion and short-term memory loss
Writing in the journal Science Advances, the scientists said: ‘We suggest that after brain injury from repeated mechanical blows in life, the resulting HSV-1 reactivation in the brain leads to the development of Alzheimer’s disease/dementia.
‘[This suggests] that HSV-1 is a major cause of Alzheimer’s.’
However, other scientists not involved in the study have urged caution over the findings.
Professor Robert Howard, a professor of old age psychiatry at University College London, said: ‘The study is interesting and raises a potential mechanism for the observed association between infection with the cold sore virus, brain injuries and Alzheimer’s disease.
‘However, as so often in science, it is very important to bear in mind that association does not mean causation.
‘Much more research will be needed before this can be seriously considered a plausible mechanism for the development of dementia.
‘Avoidance of brain injuries, such as those encountered in some contact sports, is already known to be an important way to prevent dementia and I’m unconvinced that this reflects anything more complicated than mechanical damage causing death of brain cells.’
Research has suggested that multiple blows to the head can more than double the chance of having a neurodegenerative condition months or years down the line.
Sir Bobby Charlton (pictured holding a ball with United written on it during an interview with local press at a hotel in Hong Kong in 2005) died , 86, with dementia in 2023
Former England and West Bromwich Albion striker Jeff Astle died aged 59 from early-onset disease — reportedly due to repeated head trauma
Contact sports have been marred in controversy due to links with dementia and other brain diseases in players, thought to be a result of frequent impact to the head.
Most famously, former England football player Sir Bobby Charlton died aged 86 in 2023, years after he was diagnosed with dementia.
Former England and West Bromwich Albion striker Jeff Astle died aged 59 from early-onset disease — reportedly due to repeated head trauma.
Former rugby union player Steve Thompson was also diagnosed with early onset dementia at 43-years-old.
A 2023 study commissioned by the Football Association and Professional Footballers’ Association, found professional footballers are three times more likely to be diagnosed with dementia than the general population.
But research published last year by scientists at University of New South Wales in Australia found those who experienced concussion while playing sports during their lifetime had marginally better cognitive performance than those who reported no concussions.
Recent analysis by the Alzheimer’s Society estimates the overall annual cost of the dementia to the UK is £42billion a year, with families bearing the brunt.
An ageing population means these costs – which include lost earnings of unpaid carers – are set to soar to £90billion in the next 15 years.
Around 900,000 Brits are currently thought to have the memory-robbing disorder. But University College London scientists estimate this will rise to 1.7million within two decades as people live longer. It marks a 40 per cent uptick on the previous forecast in 2017
Around 944,000 in the UK are thought to be living with dementia, while the figure is thought to be around 7million in the US.
Alzheimer’s affects around six in 10 people with dementia.
Memory problems, thinking and reasoning difficulties and language problems are common early symptoms of the condition, which then worsen over time.
Dementia are expected to sky-rocket in the coming years, making a cheap screening tool vital to get to grips with the challenge.
Alzheimer’s Research UK analysis found 74,261 people died from dementia in 2022 compared with 69,178 a year earlier, making it the country’s biggest killer.
