Alzheimer's disease, the most prevalent type of dementia, is believed to have genetic and environmental causes. Studies suggest that pathogens may also contribute, but until recently, how they infiltrate the brain was unclear.
A 2022 Australian study reveals that Chlamydia pneumoniae bacteria can enter the brain through the olfactory nerve from the nose, resulting in the formation of Alzheimer's characteristic amyloid beta plaques. The authors suggest that nose-picking may damage the nasal mucosa, enabling easier access for the bacteria to the olfactory nerve and, subsequently, the brain.
Pneumonia Bacteria Linked to Alzheimer's Disease
Science Alert reported that a group of scientists from Griffith University in Australia conducted experiments on Chlamydia pneumoniae, a bacterium that can cause pneumonia in humans and is present in the brains of most individuals with late-onset dementia.
During their mice studies, they found that the bacteria traveled through the olfactory nerve, which connects the nasal cavity and the brain, and that damage to the nasal epithelium led to an increase in nerve infections and a higher deposit of the amyloid-beta protein, which is known to be present in significant concentrations in Alzheimer's patients.
The findings showed that Chlamydia pneumoniae could enter the brain through the nose and cause pathologies that resemble Alzheimer's disease, as observed in their mouse model, and the speed at which the infection occurred, within 24 to 72 hours, suggested that bacteria and viruses may view the nose as a quick route to the brain.
While there is no certainty that these effects will be replicated in humans, the study offers a promising lead in understanding the neurodegenerative condition and the need to follow up on the same pathway operating in humans.
Nonetheless, neuroscientist James St John said in a press release that it is vital to understand the role of these bacteria in the development of Alzheimer's disease as the same bacteria are present in humans, and the pathway by which they enter the brain is not yet known.
The Link Between Bacteria, Viruses, and Neurological Diseases
Several studies have suggested a connection between pathogens and dementia, and this research adds to that evidence. For example, a study from 2008 suggested that C. pneumoniae infection might trigger late-onset Alzheimer's disease. Likewise, a 2010 study found C. pneumoniae, amyloid deposits, and neurofibrillary tangles in the brain.
Professor St. John, who led the 2022 study, believes that many microorganisms may contribute to the onset of Alzheimer's. According to Medical News Today, the herpes simplex virus is implicated in several studies.
He also thinks that a combination of microbes and genetics may lead to pathologies and symptoms. While all have bacteria and viruses in their brains, not everyone gets Alzheimer's disease.
He believes that the progression of pathologies that may take decades before resulting in symptoms is a long, slow process. So, getting bacteria in the brain does not mean an individual will get dementia next week.
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