Traces of fungus have been discovered in the brains of Alzheimer's sufferers, researchers said Thursday (local time), relaunching the question: might the disease be caused by an infectious microbe?
There is no conclusive evidence but if the answer turns out to be "yes", it means Alzheimer's Disease may be targeted with antifungal treatment, a Spanish team reported in the journal Scientific Reports.
"The possibility that Alzheimer's Disease is a fungal disease or that fungal infection is a risk factor for the disease opens new perspectives for effective therapy for these patients," they wrote.
The five-member team had found cells and other material from "several fungal species" in the brain tissue and blood vessels of all 11 deceased Alzheimer's patients analysed but not in ten Alzheimer's-free controls.
The findings are published just a month after scientists warned in the sister journal Nature of a risk of accidental surgical transmission of Alzheimer's "seeds" from one person to another.
Alzheimer's Disease is the most common form of dementia, which the World Health Organisation says affects nearly 50 million people worldwide - some 7.7 million new cases per year.
Old age is the major risk factor, and there is no therapy to stop or reverse Alzheimer's symptoms, which include memory loss and disorientation, as well as anxiety and aggressive behaviour.
Some researchers have suggested Alzheimer's may be an infectious disease or, at least, that infection with certain microbes may boost Alzheimer's risk.
Genetic material from viruses and bacteria had previously been found in the brains of Alzheimer's patients and viruses which cause herpes and pneumonia have been suggested as potential "agents", according to the study authors.
The main suspect in Alzheimer's to date has been brain "plaques" caused by a build-up of sticky proteins. But trials with drugs targeting these have yielded disappointing results.
The new study adds another possible cause to the list of hypotheses.
Traces of several fungal species were found, which "might explain the diversity observed in the evolution and severity of clinical symptoms in each Alzheimer's patient," they wrote.
A fungal cause would fit well with the characteristics of AD, the researchers added, including the slow progression of the disease and inflammation, which is an immune response to infectious agents such as fungi.
The researchers did point out, however, that fungal infection may be the result, not the cause, of AD.