Catching shingles may increase Alzheimer’s risk, scientists warn.
A study led 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 another normally harmless herpes virus that has been dormant in our bodies since childhood.
This leads to a ‘dramatic’ accumulation of plaque and inflammation in the brain – two hallmarks of Alzheimer’s disease.
Chickenpox occurs when the body is first exposed to the varicella zoster virus (VZV), usually as children. Shingles results from subsequent infections.
Researchers used lab-grown brain cells to create a three-dimensional brain to see the impact VZV has on the brain.
They found that it didn’t directly cause the signature changes associated with Alzheimer’s disease.
But it did reactivate the simplex virus (HSV-1), better known for causing cold sores, causing a rapid build-up of harmful proteins.
Study author Dana Cairns, of Tufts University in Massachusetts, said, “It’s a one-two punch of two viruses that are common and mostly harmless.
Catching shingles may raise Alzheimer’s risk by triggering brain chain reaction, scientists warn (file image)
“But the lab studies suggest that if a new exposure to VZV wakes up dormant HSV-1, they could cause problems.”
HSV-1 normal lies dormant in the body and there is strong evidence that it may be linked to dementia.
Previous research has found that older people with high levels of the virus in their brains have a much higher risk of Alzheimer’s disease.
Professor Ruth Itzhaki, from the University of Manchester, collaborated with researchers from the Oxford Institute of Population Aging and Tufts University on the latest study.
Researchers created brain-like environments in 6 millimeter wide donut-shaped sponges made of silk protein and collagen.
They populated the sponges with stem cells that grew into neurons and could transmit signals to each other, just like in the brain.
Results showed that neurons in the brain can be infected with VZV, but that alone does not lead to plaque formation and cell death.
Neurons infected with the virus could still function normally.
However, if the cells also harbored HSV-1, there was a dramatic increase in tau and beta-amyloid proteins, strongly linked to dementia.
The neuronal signals also began to slow down.
Professor Itzhaki said: ‘This striking result seems to confirm that infections such as VZV can cause an increase in inflammation in the brain in humans, which can reactivate the dormant HSV-1.
‘The damage in the brain from repeated infections throughout life would eventually lead to the development of AD/dementia.
“This would mean that vaccines could play a greater role than just protecting against a single disease, as they may 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 tend to affect people more often as they get older.
About one in five people who have had chickenpox develop shingles, and most are in their 70s.
Researchers also warn that obesity, smoking, alcohol and head trauma may also increase the risk of Alzheimer’s disease by weakening the immune system and activating dormant HSV1 in the brain.
More than 900,000 people live with dementia in the UK today, expected to rise to 1.6 million by 2040
Alzheimer’s disease is the most common form of dementia.
Current estimates are that about 5.8 million people in the US have the condition, most of whom are over the age of 65.