Catching the chickenpox virus may increase the risk of developing Alzheimer’s, scientists at the University of Oxford have found for the first time.

The combination of the virus which causes chickenpox and shingles, with a common herpes infection which is dormant among two-thirds of under-50s, has been found to produce the proteins that cause Alzheimer’s.

Most people have had shingles or chickenpox at some point in their life but people can catch the virus – varicella zoster virus, or VZV – several times, especially if they are not vaccinated.

A chickenpox vaccine, which is a weakened version of the live virus, is available on the NHS for healthcare workers who have never had the infection and those in contact with the immunocompromised.

Most people gain immunity through natural infection during childhood.

Chickenpox virus cannot cause dementia on its own

Prof Ruth Itzhaki, an Oxford scientist, has been examining the role of herpes in Alzheimer’s for more than 30 years, previously proving that the common cold sore virus can damage neurons by creating the plaques that cause dementia and Alzheimer’s.

Her latest research, published on Tuesday in the Journal of Alzheimer’s Disease, looked at how herpes (HSV-1) in brain cells is affected when VZV is present.

The two viruses are closely related and belong to the same family. Experiments found that the chickenpox virus does not, on its own, create the proteins that cause dementia, known as beta amyloid and tau.

However, it does kickstart the immune system, which produces chemicals called cytokines that try and destroy the pathogen but also cause inflammation.

Lab-based studies show that this immune response to the chickenpox virus reawakens the herpes virus from its dormant state and allows it to start making the brain-destroying proteins again.

The researchers say that the chickenpox virus VZV is unlikely to be a direct cause of Alzheimer’s, but may have an indirect impact by aiding and reviving herpes.

Vaccines could play ‘greater role’

It is possible, the researchers say, based on their early findings, that repeated and unnoticed minor VZV infections lead to herpes flare-ups that damage the brain, and that these have a cumulative effect over time.

“This striking result appears to confirm that, in humans, infections such as VZV can cause an increase in inflammation in the brain, which can reactivate dormant HSV-1,” said Prof Itzhaki of the University of Oxford and the University of Manchester.

“The damage in the brain by repeated infections over a lifetime would lead eventually to the development of Alzheimer’s Disease/dementia.

“This would mean vaccines could play a greater role than just protecting against a single disease, because they could also indirectly, by reducing infections, provide some protection against Alzheimer’s.”

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