Medical

Bacteria could travel from the nose to the brain and trigger Alzheimer's

Bacteria could travel from the nose to the brain and trigger Alzheimer's
A new study has found evidence that nose bacteria could move into the brain through the nerves and trigger a cascade of events that can lead to Alzheimer's disease
A new study has found evidence that nose bacteria could move into the brain through the nerves and trigger a cascade of events that can lead to Alzheimer's disease
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A new study has found evidence that nose bacteria could move into the brain through the nerves and trigger a cascade of events that can lead to Alzheimer's disease
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A new study has found evidence that nose bacteria could move into the brain through the nerves and trigger a cascade of events that can lead to Alzheimer's disease
A microscope image of the olfactory bulb in the brain of a mouse – blue indicates brain cells, green indicates Chlamydia pneumoniae bacteria, and red indicates beta amyloid plaques
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A microscope image of the olfactory bulb in the brain of a mouse – blue indicates brain cells, green indicates Chlamydia pneumoniae bacteria, and red indicates beta amyloid plaques

Researchers in Australia have found evidence that bacteria that live in the nose can make their way into the brain through nasal cavity nerves, setting off a series of events that could lead to Alzheimer’s disease. The work adds to the growing body of evidence that Alzheimer’s may be initially triggered through viral or bacterial infections.

Chlamydia pneumoniae is a common bacterium that, as its name suggests, is a major cause of pneumonia, as well as a range of other respiratory diseases. But worryingly, it’s also been detected in the brain on occasion, indicating it could cause more insidious issues.

For the new study, researchers at Griffith University and the Queensland University of Technology set out to investigate how C. pneumoniae might get into the brain, and whether it could cause damage once there. The team already had an inkling about how this nose-dwelling bug might make the trek.

“Our work has previously shown that several different species of bacteria can rapidly, within 24 hours, enter the central nervous system via peripheral nerves extending between the nasal cavity and the brain,” said Jenny Ekberg, lead author of the study.

In tests in mice, the team found that within 72 hours of its introduction to the nose, C. pneumoniae can infect the olfactory and trigeminal nerves, then the olfactory bulb – the small neural structure in the forebrain that processes the sense of smell. From there it’s a short jaunt to the rest of the brain.

Most intriguingly, the researchers found that after the bacteria had gotten into the central nervous system, it triggered several changes that are associated with Alzheimer’s disease. Within a few days, deposits of beta amyloid plaques began to build up – a distinctive feature of the disease. After a few weeks, the team detected dysfunctions in several gene pathways that are linked to Alzheimer’s.

A microscope image of the olfactory bulb in the brain of a mouse – blue indicates brain cells, green indicates Chlamydia pneumoniae bacteria, and red indicates beta amyloid plaques
A microscope image of the olfactory bulb in the brain of a mouse – blue indicates brain cells, green indicates Chlamydia pneumoniae bacteria, and red indicates beta amyloid plaques

This new finding joins an expanding body of work that points towards Alzheimer’s being initially triggered through infections by viruses and bacteria. The common herpes virus is the most consistent suspect, but imbalances in mouth bacteria, particularly increases in those that cause gum disease, seem to be predictors of Alzheimer’s.

“We have suspected for a long time that bacteria, and even viruses, can lead to neuroinflammation and contribute to initiation of Alzheimer’s disease, however, the bacteria alone may not be enough to cause disease in someone,” said Ekberg. “Perhaps it requires the combination of a genetic susceptibility plus the bacteria to lead to Alzheimer’s disease in the long term.”

The team says that finding ways to target these bacteria could lead to new preventative treatments for Alzheimer’s.

The research was published in the journal Scientific Reports.

Source: Griffith University

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