Baffled for years, scientists have been trying to figure out how some infections might impact brain health, especially in diseases like Alzheimer’s. Driven by these questions, they explored whether the common respiratory germ Chlamydia pneumoniae, a type of bacteria that usually causes lung infections, could sneak into the brain and possibly play a role in dementia. Small injuries to the nose, such as from nose picking, might also increase the risk by weakening the natural barrier, allowing bacteria easier access to the brain.
Carefully working on this, scientists led by Dr. Jenny Ekberg from Griffith University. Their findings are shared in the journal Scientific Reports, a respected publication that features scientific discoveries. The team found that C. pneumoniae can quickly travel to the brain by hitching a ride along the nerves that link the nose and brain.
During tests on mice, the scientists discovered that live C. pneumoniae reached the brain and the olfactory bulb—an important smell-processing area in the brain—within a short time after being introduced through the nose. This quick journey stood out because the bacteria managed it without appearing in the bloodstream, which is the system that carries blood throughout the body. They also spotted clumps of amyloid beta, a sticky protein that forms plaques and is tied to Alzheimer’s, forming next to the bacterial gatherings. Damage to the nasal lining made infections worse in the nearby nerves but did not seem to increase the spread deeper into the brain, hinting at strong natural defenses. The study emphasized that injuries to the nasal lining significantly boost the bacteria’s ability to invade nerve pathways, suggesting that everyday actions causing minor nasal damage might unintentionally raise infection risks.
Curiously, one important observation was how the infection seemed to connect with processes related to Alzheimer’s. “We found that Chlamydia pneumoniae can infect and survive inside support cells in the nervous system, called glial cells, which help protect and maintain nerve cells. This infection disrupts important genetic processes involved in Alzheimer’s disease,” explained Dr. Ekberg. These glial cells include olfactory support cells that assist the sense of smell, Schwann cells that help nerve signals travel faster, astrocytes that provide nutrients to nerve cells, and microglia that act like the brain’s immune cells. They seem to allow the bacteria to persist longer than expected.
Dr. Ekberg and her team also noticed that infections might cause not just inflammation, meaning swelling and irritation, but also set off changes in how genes and proteins behave in the brain. These changes could be linked to diseases that damage the brain over time. After a few weeks of infection, they saw significant shifts in the way important brain pathways operated. Pathways are the routes that signals take to travel across different parts of the brain. “The infection triggered stress responses inside cells, which are the ways cells react to threats, and chemical imbalances that are often seen early in Alzheimer’s,” Dr. Ekberg added.
Clearly, this work highlights an important idea: some bacteria can impact brain health much earlier and faster than many had assumed. Although this research was done in mice, it mirrors findings from studies on human brains of Alzheimer’s patients, where signs of C. pneumoniae have been detected. Altogether, the results suggest that the nerves linking the nose to the brain could act as an unexpected but vulnerable entrance for infections that might contribute to brain diseases.
Journal Reference
Chacko A., Delbaz A., Walkden H., Basu S., Armitage C.W., Eindorf T., Trim L.K., Miller E., West N.P., St John J.A., Beagley K.W., Ekberg J.A.K. “Chlamydia pneumoniae can infect the central nervous system via the olfactory and trigeminal nerves and contributes to Alzheimer’s disease risk.” Scientific Reports, 2022; 12:2759. DOI: https://doi.org/10.1038/s41598-022-06749-9
About the Author
Dr. Jenny Ekberg is a leading neuroscientist specializing in nerve regeneration, neurodegenerative diseases, and microbial interactions with the nervous system. Based at Griffith University in Australia, she holds key research roles at both the Menzies Health Institute Queensland and the Griffith Institute for Drug Discovery. Her work focuses on understanding how infections might influence brain health, including pioneering studies on how common bacteria can invade the brain via nasal pathways. Dr. Ekberg’s research bridges cellular neuroscience and clinical applications, aiming to find new strategies to treat conditions like Alzheimer’s disease. She is passionate about uncovering the hidden mechanisms that drive neurological disorders, often exploring how everyday environmental exposures might contribute to disease risks. Throughout her career, Dr. Ekberg has contributed significantly to advancing our knowledge of nerve injury, repair, and protection. Her work is recognized internationally, and she actively mentors the next generation of researchers in neuroscience and regenerative medicine.
