Covid-19 enters the brain via nerve cells in the olfactory mucosa, which lies in the roof of the nasal cavity, a study has found.
The researchers from Charité-Universitätsmedizin in Berlin have been able to produce electron microscope images of coronavirus particles inside the olfactory mucosa for the first time.
Dr Frank Heppner, director of the university’s neuropathology department and who co-led the study, said ‘the virus appears to use neuroanatomical connections, such as the olfactory nerve, in order to reach the brain’ once it is inside the olfactory mucosa.
He continued: ‘In our eyes, [the findings] provide good explanation for the neurologic symptoms found in Covid-19 patients, such as a loss of the sense of smell or taste.’
The scientists studied tissue samples from the olfactory mucosa and brain of 33 patients who had died at either Charité or the University Medical Center Göttingen after contracting Covid-19.
They found evidence of the virus in different neuroanatomical structures which connect the eyes, mouth and nose with the brain stem. The highest viral load was revealed in the olfactory mucosa.
Covid-19 was also found in areas of the brain controlling vital functions such as a breathing. Professor Heppner suggested this could ‘add to breathing problems’ in patients with severe infection.
Researchers had previously suspected that the virus entered specific cells in the brain, but this study is the first to show how the virus gets there.
Dr Helena Radbruch, who jointly led the study, said the findings suggest that the ‘virus moves from nerve cell to nerve cell’ to reach the brain and may also be transported via blood vessels in the brain.
The scientists pointed out that the Covid-19 patients in the study had severe disease, so the results are not necessarily applicable to those with mild or moderate forms.
More than one in three people with Covid-19 report neurological symptoms such as loss of, or change in, their sense of smell or taste, headaches, fatigue, dizziness, and nausea. The disease can even result in a stroke or other serious conditions for some people.
NHS England said last month that it would launch over forty ‘Long Covid’ specialist clinics in England for patients suffering from the debilitating symptoms of Covid- 19 months after catching the virus.