Dormant viruses and microbes are found in the brains of most elderly people, but they can be reactivated after stress or by a weakened immune system, says the group of 31 scientists and clinicians from research centres such as from Oxford, Cambridge and Imperial universities.

An activated herpes virus, for instance, can cause damage in areas of the brain associated with memory and cognition.

They say there is growing evidence of a link with viruses and more than a hundred papers now support the belief.

If viruses are indeed a cause of Alzheimer’s and dementia, a whole new way of treating the diseases opens up.