Head injuries may waken viruses “sleeping” in the brain, causing damage that could lead to neurodegenerative diseases such as Alzheimer’s and Parkinson’s, researchers have found.
The relationship between neurodegenerative diseases and repeat concussions and head injuries in sports such football and boxing is already well known. But researchers do not yet fully understand why it happens.
A new study may help explain the link, suggesting head knocks can awaken latent viruses in the nervous system, setting off a chain of inflammation that results in damage over time. Researchers say antiviral drugs could be used to help prevent post-head injury to guard against future illness.
The body’s microbiome, which includes hundreds of bacterial species that live inside our bodies, helps aid digestion, immune system development, and protect against harmful pathogens. But it also includes dozens of viruses that lie dormant within our cells.
They include herpes simplex virus 1 (HSV-1), which is found in more than 80 per cent of people, and varicella-zoster virus, found in 95 per cent of people and which make their way into the brain and sleep within its neurons and glial cells.
Previous research has found that reactivation of HSV-1 causes the symptoms of Alzheimer’s disease in lab models of brain tissue. “In that study, another virus – varicella – created the inflammatory conditions that activated HSV-1,” said Dr Dana Cairns, research associate at Tufts University in the US state of Massachusetts and lead author of the study, which also involved researchers from the University of Oxford.
“We thought, what would happen if we subjected the brain tissue model to a physical disruption, something akin to a concussion? Would HSV-1 wake up and start the process of neurodegeneration?”
Researchers created a model to explore the idea, enclosing brain-like tissue in a cylinder, giving it a sudden jolt on top of a piston to simulate concussion.
Some of the tissues had neurons with HSV-1 and others were virus-free. The blows caused the virus in the infected cells to reactivate, resulting in markers of Alzheimer’s disease, such as amyloid plaques; the development of p-tau, which is a protein that creates fibre-like “tangles” in the brain; inflammation; the death of neurons; and the growth of glial cells called gliosis.
More strikes with the pistons led to the same reactions, which were even more severe. The cells without HSV-1 showed the growth of some gliosis but none of the other markers of Alzheimer’s.
Researchers say the findings, published in Science Signalling, are a strong indicator that athletes suffering concussions could be triggering the reactivation of latent infections in the brain that can lead to Alzheimer’s disease.
Previous research has shown repeated head injuries can significantly increase the risk of developing a neurodegenerative condition months or even years later.
“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,” said Dr Cairns.
David Kaplan, professor of engineering at Tufts, said the tissue model could be used to test new drugs for Alzheimer’s and other neurodegenerative diseases.
Researchers late last year found heading a football may cause more damage to the brain than previously believed.
They used MRI scans to analyse microstructures close to the surface of the organ, comparing the results of 352 male and female amateur footballers, with those of 77 non-collision-sport athletes, such as runners.
Most had never suffered from concussion or been diagnosed with a traumatic brain injury. But the scans showed evidence of brain damage in areas where it is seen in chronic traumatic encephalopathy (CTE), a progressive brain disease with symptoms including memory loss, confusion, mood changes and behavioural problems.
A number of sports people who have suffered brain injuries have sued their governing bodies for not doing enough to protect them from known harm. Steve Thompson is among a group of dozens of rugby players suing his sport's authorities for negligence over brain injuries they have suffered.
He was diagnosed with early onset dementia in his early 40s in 2020 and has said he cannot remember playing in England’s World Cup final win over Australia in 2003 or receiving a MBE from Queen Elizabeth II afterwards.
