Anatomic barriers protect the brains against the coronavirus

12 December 2022

COVID-19 is often accompanied by partial or complete loss of the sense of smell. It was long thought that the coronavirus could reach and infect the brains via the nasal mucosa. An international research team, including UZ Leuven doctors, checked samples of over 100 deceased COVID-19 patients. The good news is that they found no proof that the coronavirus can infect nerve cells in the nose or in the brain, or reach the brain tissue. Certain cell in the olfactory mucosa reukslijmvlies seem to form a protective barrier. 

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Tekening van hoe het coronavirus het neusslijmvlies infecteert

Prof. dr. Laura Van Gerven, nose-throat-ear specialist: "We found no proof whatsoever that the coronavirus could penetrate the brain via the nose. It seems that certain cell types in the olfactory mucosa form an efficient anatomic barrier."

The nasal mucosa is one of the most important places where a virus penetrates our body. Early on in the pandemic it was thought that the virus could infect the cells of the olfactory mucosa in the nose and hitchhike its way via the olfactory nerve to the brain. 

First study

Last year, an international research team, led by UZ Leuven and the Max Planck Research Unit for Neurogenetics in Germany, set up a large trial in deceased COVID-19 patients in order to unravel how the virus could cause loss of smell. The study showed that the coronavirus infects the supporting cells of the olfactory mucosa, but not the nerve cells with the olfactory receptors. 

New findings

Recently the team published a second trial in which they assessed quite some additional tissue samples, including from people infected with the Delta and Omicron variants of the coronavirus. They also examined whether there were traces of the coronavirus in the frontal lobe, close to the olfactory nerves. 

"We could not find any proof that the coronavirus can penetrate the brain via the nasal mucosa. This is very good news and this insight will help us unravel the exact mechanism of loss of smell further."
Prof. dr. Laura Van Gerven, nose-throat-ear specialist at UZ Leuven

Prof. dr. Laura Van Gerven, nose-throat-ear specialist at UZ Leuven and principal investigator of the study: “All samples came back negative: we did not see any infected nerve cells anywhere. We also did not find any virus particle in the cerebral fluid. So we could not find any proof that the coronavirus could penetrate the brain via this route. It seems that certain cells in the olfactory mucosa form an efficient anatomic barrier against the virus (and probably also many other pathogens that infect the olfactory mucosa). This is very good news and this insight will help us unravel the exact mechanism of loss of smell through SARS-CoV-2 further.”

Last edit: 2 January 2023