A fungus previously perceived as harmless can cause memory problems and brain abnormalities that resemble those characteristics of Alzheimer's disease.
Researchers at the Baylor College of Medicine have discovered that the common yeast Candida albicans, a type of fungus that grows naturally in the human gut, mouth, and vagina, can cross the blood-brain barrier and trigger an inflammatory response which results in the formation of granuloma-type structures and temporary mild memory impairments in mice.
The granulomas share features with plaques found in Alzheimer’s disease, supporting future studies on the long-term neurological consequences of sustained Candida albicans infection.
“An increasing number of clinical observations by us and other groups indicates that fungi are becoming a more common cause of upper airway allergic diseases such as asthma, as well as other conditions such as sepsis, a potentially life-threatening disease caused by the body's response to an infection,” said report author Dr David Corry.
Fungal infections causing airway allergic diseases and sepsis have also been associated with increased risk for dementia later, Dr Corry explained.
“These observations led us to investigate the possibility that fungus might produce a brain infection and, if so, the consequences of having that kind of infection,” said Dr Corry.
The researchers began their investigation by developing a mouse model of a low-grade fungus infection with the common yeast Candida albicans that would not cause severe disease but might carry implications for brain function. They tested several doses and finally settled on one dose of 25,000 yeasts.
They injected Candida albicans into the blood stream of mice and were surprised to discover that the yeast can cross the blood-brain barrier, which is usually a robust protective mechanism the brain employs to exclude all kinds of large and small molecules, as well as a number of microorganisms that can potentially damage the brain.
“We thought that yeast would not enter the brain, but it does,” Dr Corry said.
“In the brain, the yeast triggered the activity of microglia, a resident type of immune cell. The cells became very active ‘eating and digesting’ the yeast. They also produced a number of molecules that mediated an inflammatory response leading to the capture of the yeasts inside a granule-type structure inside the brain.”
Dr Corry and his colleagues also tested the animals’ memory in both yeast-infected and non-infected mice. They found that infected mice had impaired spatial memory, which reversed when the infection cleared.
The mice cleared the yeast infection in about 10 days; however, the microglia remained active and the granulomas persisted well past this point, out to at least day 21.
“The results prompted us to consider the possibility that in some cases, fungi also could be involved in the development of chronic neurodegenerative disorders, such as Alzheimer’s, Parkinson’s and multiple sclerosis. We are currently exploring this possibility,” Dr Corry explained.
Have you ever suffered from a yeast infection? Are you worried about these findings?
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