Scientists have uncovered an intriguing link between infection and brain health, finding that a common bacterium in the eye appears to be linked to cognitive decline and Alzheimer’s disease. It's the newest evidence suggesting bacteria and infections play a significant and poorly understood role in destroying the brain as we age.

Researchers at Cedars-Sinai found traces of Chlamydia pneumoniae – a bacterium that's best known for causing respiratory infections – in the eye's retinal tissue, and higher levels of this pathogen correlated with advanced degeneration in Alzheimer’s disease patients. While this don't show causation by any means, the findings add to a growing body of evidence suggesting chronic infections play some role in neurodegenerative disease over time.

https://newatlas.com/brain/alzheimers-dementia/bacteria-dementia-alzheimers-eye-infection/

Also bacteria from the mouth entering from lesions in the gums. I have read.

It is a dangerous world out there?