Getting shingles can increase the risk of Alzheimer’s disease, scientists have warned.
A study conducted by the University of Oxford found that the infection can trigger a chain reaction in the brain linked to dementia.
It does this by waking up a different, normally harmless herpes virus that has lain dormant in our bodies since childhood.
This leads to a “dramatic” buildup of plaque and inflammation in the brain – two hallmarks of Alzheimer’s disease.
Chickenpox occurs when the body is first exposed to varicella zoster virus (VZV), usually during childhood. Shingles is the result of subsequent infections.
The researchers used lab-grown brain cells to create a three-dimensional brain to see the impact of VZV on the brain.
They found that it did not directly trigger the signature changes associated with Alzheimer’s disease.
But it reactivated the simplex virus (HSV-1), best known for causing cold sores, triggering a rapid buildup of harmful proteins.
Study author Dana Cairns, from Tufts University in Massachusetts, said: ‘It’s a double punch of two viruses that are very common and generally harmless.
Getting shingles may increase the risk of Alzheimer’s disease by setting off a chain reaction in the brain, scientists have warned (file image)
“But lab studies suggest that if further exposure to VZV awakens dormant HSV-1, it could cause problems.”
HSV-1 normally lies dormant in the body and there is strong evidence that it could be linked to dementia.
Previous research has indicated that older people with high levels of the virus in their brains are at a much higher risk of developing Alzheimer’s disease.
Professor Ruth Itzhaki, from the University of Manchester, worked with researchers from the Oxford Institute for Population Aging and Tufts University on the latest study.
The researchers recreated brain-like environments in 6-millimeter-wide doughnut-shaped sponges made of silk proteins and collagen.
They populated the sponges with stem cells that grew into neurons and were able to transmit signals to each other, just as they do in the brain.
The results showed that brain neurons can be infected with VZV, but this alone does not lead to plaque formation and cell death.
Neurons infected with the virus were still able to function normally.
However, if the cells also harbored HSV-1, there was a dramatic increase in tau and beta-amyloid proteins, which are strongly linked to dementia.
Neural signals also began to slow down.
Professor Itzhaki said: ‘This striking result appears to confirm that, in humans, infections such as VZV can cause increased inflammation in the brain, which can reactivate dormant HSV-1.
“Damage to the brain from repeated infections throughout life would eventually lead to the development of Alzheimer’s disease and dementia.
“This would mean that vaccines could play a bigger role than just protecting against a single disease, because they could also indirectly, by reducing infections, provide some protection against Alzheimer’s disease.”
The study was published in the Journal of Alzheimer’s Disease.
Shingles can be very painful and tends to affect people more frequently as they get older.
About one in five people who have had chickenpox develop shingles, and most are in their 60s.
Researchers also warn that obesity, smoking, alcohol and head trauma could also increase the risk of Alzheimer’s disease by weakening the immune system and activating dormant HSV1 in the brain.
Over 900,000 people are now living with dementia in the UK, which is expected to rise to 1.6 million by 2040
Alzheimer’s disease is the most common type of dementia.
Current estimates indicate that approximately 5.8 million people in the United States suffer from the disease, most of whom are over the age of 65.