New treatments for dementia patients could be a major step nearer after a group of influential scientists identified microbes as a cause.
An editorial in the Journal of Alzheimer's Disease brings together evidence linking microbes - a virus and two kinds of bacteria - to the development of the illness.
The authors are calling for more research into the area, including clinical trials of antimicrobial drugs as potential Alzheimer's treatments.
The editorial claims are based on substantial published evidence implicating the microbes - a virus and two specific types of bacteria - in the cause of the degenerative illness.
However scientists say the work has been largely ignored or dismissed as controversial, despite the absence of evidence to the contrary.
It is hoped the findings set out in the editorial could also have implications on the future treatment of Parkinson's disease and other progressive neurological conditions.
Researchers say the opposition to microbe theories is similar to hostility see some years ago against studies which showed viruses cause certain types of cancer and bacterium causes stomach ulcers, which eventually proved to be correct, leading to new treatments.
Scientists also say the research into the microbe cause of Alzheimer's can no longer be ignored.
One of the editorial’s authors is Professor Douglas Kell, of Manchester University's School of Chemistry, who says supposedly sterile red blood cells were seen to contain dormant microbes, which also has implications for blood transfusions.
He said: "We are saying there is incontrovertible evidence that Alzheimer's Disease has a dormant microbial component, and that this can be woken up by iron dysregulation.
"Removing this iron will slow down or prevent cognitive degeneration - we can't keep ignoring all of the evidence."
Professor Resia Pretorius, of the University of Pretoria in South Africa, who also worked 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 - particularly, the bacterial cell wall component and endotoxin, lipopolysaccharide. "
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."
Alzheimer's Society research shows that 850,000 people in the UK have a form of dementia. And in less than 10 years a million people will be living with dementia.