A common bacterium usually found in the respiratory system appears to be linked to cognitive decline and Alzheimer’s disease when it’s present in the retina.

Chlamydia pneumoniae – often responsible for pneumonia and sinus infections – has previously been spotted in brains affected by Alzheimer’s. Now, a new study has detected C. pneumoniae in the vision-generating tissue that lines the back of the eye, at higher levels in people with Alzheimer’s.

Led by a team from Cedars-Sinai Medical Center in the US, the research provides fresh insight into the biological processes that may worsen Alzheimer’s progression – and could inspire new approaches to slowing the disease.

As well as potentially contributing to the cascade of mechanisms that lead to Alzheimer’s, the presence of C. pneumoniae in the retina could also one day be used to detect cognitive decline and dementia – though that possibility wasn’t directly tested here.

“The eye is a surrogate for the brain, and this study shows that retinal bacterial infection and chronic inflammation can reflect brain pathology and predict disease status, supporting retinal imaging as a noninvasive way to identify people at risk for Alzheimer’s,” says neuroscientist Maya Koronyo-Hamaoui, from the Cedars-Sinai Medical Center. (See link for article)

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