Alzheimer’s disease could be caused by viruses like herpes, a group of renowned dementia experts have warned, as they call for urgent investigation into the link.
The worldwide team of 31 senior scientists and clinicians, which include specialists from Oxford, Cambridge, Edinburgh and Manchester Universities and Imperial College, have written an editorial which suggests that microbes are the major cause of dementia.
The herpes virus – the type which causes cold sores – and chlamydia bacteria are named as the major culprits, as well as a type of corkscrew-shaped bacteria called spirochaete.
Currently most scientists are trying to find treatments which prevent the build of sticky amyloid plaques and misfolded tau proteins in the brain which prevent neurons from communicating with each other, leading to memory loss and cognitive decline.
But in an the editorial in the Journal of Alzheimer’s Disease, it is suggested that it is a viral or bacterial infection which triggers the plaque build-up in the first place. Targeting them specifically with antimicrobial drugs could halt dementia.
Professor Douglas Kell of the University of Manchester’s School of Chemistry, said “We are saying there is incontrovertible evidence that Alzheimer’s Disease has a dormant microbial component. We can’t keep ignoring all of the evidence.”
There are currently 850,000 people living with dementia in Britain which is due to rise to one million by 2025 and two million by 2050. But despite 412 drugs trials taking place between 2002 and 2012, nothing has been shown to combat the disease.
The authors say that viruses and bacteria are common in the brains of elderly people, and although they are usually dormant, they can ‘wake up’ after stress or if the immune system is compromised. Around two thirds of people will acquire the herpes virus at some point in their lives, and many will not realise they have it.
The herpes virus in particular is known to damage the central nervous system, and the limbic system in the brain which regulates mood and instinct and is associated with mental decline and personality changes.
They also point to the fact that a gene mutation – APOEe4 – which makes one in five people more susceptible to Alzheimer’s disease, also raises their susceptibility to infectious disease. Viral infections in the brain are already known to cause symptoms similar to Alzheimer’s and the experts say the link has been ‘neglected’ for too long.
“Alzheimer’s disease causes great emotional and physical harm to sufferers and their carers as well as having enormously damaging economic consequences,” they write.
“We write to express our concern that one particular aspect of the disease has been neglected, even though treatment based on it might slow or arrest Alzheimer’s disease progression.
“We refer to the many studies, mainly on humans, implicating specific microbes in the elderly brain, notably herpes simplex virus type 1, chlamydia pneumoniae and several types of spirochatete.
“We propose that further research on the role of infectious agents in Alzheimer’s disease causation, including prospective trials of antimicrobial therapy, is now justified.”
They say new findings could also have implications for the future treatment of Parkinson’s Disease, and other progressive neurological conditions.
Professor Resia Pretorius of the University of Pretoria, who worked with Prof Kell on the editorial, said “The microbial presence in blood may also play a fundamental role as causative agent of systemic inflammation, which is a characteristic of Alzheimer’s disease.
“Furthermore, there is ample evidence that this can cause neuroinflammation and plaque formation.”
Dementia charities said they had noticed that viruses and bacteria were more common in people with Alzheimer’s disease.
Dr James Pickett, Head of Research at Alzheimer’s Society said: “A large number of different microbes including viruses, bacteria and fungi have been found in the brains of older people – but there do appear to be more of them in the brains of people who have died with Alzheimer’s disease.
“While these observations are interesting and warrant further research, there is currently insufficient evidence to tell us that microbes are responsible for causing Alzheimer’s disease in the vast majority of cases. We would like to reassure people that there remains no convincing evidence that Alzheimer’s disease is contagious or can be passed from person to person like a virus.
“Given the enormous global impact of dementia, there is intense interest from the research community to understand all the potential contributing factors. We welcome research that explores all possible avenues and have committed £100 million over the next decade to more fully understand the causes of dementia and to improve diagnosis, treatment and prevention of the condition.”
Last year, researchers found that the ‘seeds’ of Alzheimer’s could be passed through blood transfusions and medical accidents.
Prof John Hardy, Professor of Neuroscience, UCL, said: “This is a minority view in Alzheimer research. There had been no convincing proof of infections causing Alzheimer disease. We need always to keep an open mind but this editorial does not reflect what most researchers think about Alzheimer disease.”
Dr Simon Ridley, Director of Research at Alzheimer’s Research UK, said: “There is growing evidence for the role of the immune system in Alzheimer’s and active ongoing research looking at how an inflammatory response might contribute to the disease. There is some evidence to suggest that infections in general could ramp up the immune system and contribute to the progression of
Alzheimer’s, but there isn’t conclusive evidence to suggest that a particular infectious agent or microbe could be directly responsible for causing the disease.
“There are many avenues being explored to understand the initial events that trigger the development of Alzheimer’s and this is an important part of the research process for ruling in and out particular hypotheses. There is no evidence that Alzheimer’s can be passed from person to person like a virus. Continued research funding into diseases like Alzheimer’s is important to build a clearer picture of the genetic and lifestyle risk factors for the disease and use this knowledge to develop preventions or treatments.”
By Sarah Knapton, Science Editor
09 Mar 2016