For years, scientists have debated whether Alzheimer’s disease is caused solely by protein buildup in the brain or whether infections may also help drive the condition.
The so-called infection hypothesis remains controversial, but new findings are adding weight to the discussion.
A study from Cedars-Sinai Medical Center, published in Nature Communications, examines whether a common respiratory bacterium could be involved in processes linked to Alzheimer’s.
Evidence from tissue
According to researchers at Cedars-Sinai, the bacterium — best known for causing pneumonia, bronchitis and sinus infections — was found at higher levels in brain and retinal tissue from people diagnosed with Alzheimer’s compared with cognitively healthy individuals.
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The study authors report that increased bacterial presence was associated with more severe cognitive decline.
Participants who carried the APOE4 gene variant, which raises Alzheimer’s risk, showed particularly elevated levels.
Inflammation link
In laboratory experiments and mouse models, infection appeared to intensify inflammatory responses and increase production of amyloid-beta, a protein widely associated with Alzheimer’s disease.
According to the researchers, this suggests the infection may contribute to processes that damage nerve cells.
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The bacterium was also detected in the retina, the light-sensitive tissue at the back of the eye. The study authors suggest retinal changes could potentially reflect disease activity in the brain.
Ongoing debate
Experts not involved in the research have long cautioned that detecting an infection does not prove it causes Alzheimer’s. Inflammation may be a consequence rather than a trigger.
Still, the study authors report that further research into treating long-term infections and reducing inflammation may be warranted.
Sources: Science Daily and Nature
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This article is made and published by Mie Hermansen, who may have used AI in the preparation.