Research by Australian academics revealed that injury to the nasal lining may provide an entry point into the brain for bacteria capable of initiating processes resembling the progression of Alzheimer’s disease. The work appears in the scientific journal Scientific Reports.
A team of neurobiologists led by James St. John from Griffith University examined the bacterium Chlamydia pneumoniae, known as a cause of pneumonia. It had previously been found in the brains of most patients with late-stage dementia, but how it reached there remained unclear.
Experiments on mice demonstrated that the bacterium can penetrate the brain directly via the olfactory nerve, which connects the nasal cavity to the central nervous system. This occurred particularly quickly when the animals had damage to the nasal mucous membrane; such an injury can arise, for instance, from vigorous nose-picking or hair pulling.
In infected mice, beta-amyloid proteins began to accumulate in the brain within just 24–72 hours. Aggregations of these proteins (amyloid plaques) are a characteristic hallmark of Alzheimer’s disease in people. The investigators posited that their formation might be part of the immune reaction to the infection.
As the study’s leader, James St. John, noted, researchers managed for the first time to show that Chlamydia pneumoniae can directly enter the brain via the nose and trigger pathological changes similar to Alzheimer’s disease. Moreover, the speed of the infection’s spread proved to be very quick.
It remains uncertain whether amyloid accumulation is the cause of the illness or a temporary protective response by the body. Furthermore, all conclusions are drawn from experiments with animals. Nevertheless, the study supports the hypothesis that neurodegenerative disorders may be linked not just to age and genetics, but also to exposure to environmental bacteria or viruses.
The scientists intend to continue their work involving humans to verify if a similar mechanism functions in people. For now, they advise avoiding damage to the nasal lining, as it serves as a vital barrier protecting the brain from external dangers.
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