The virus has found a loophole
The mechanism of coronavirus penetration into the brain is revealed
German scientists have found that the SARS-CoV-2 virus enters the brain through nerve cells in the olfactory mucosa. Their paper is published in the journal Nature Neuroscience (Meinhardt et al., Olfactory transmucosal SARS-CoV-2 invasion as a port of central nervous system entry in individuals with COVID-19).
It is now recognized that COVID-19 is not a purely respiratory disease. In addition to lung damage, SARS-CoV-2 affects the cardiovascular system, gastrointestinal tract and central nervous system. One in three patients with COVID-19 reports neurological symptoms such as loss or change of sense of smell and taste, headaches, fatigue, dizziness and nausea. In some patients, coronavirus infection is accompanied by a stroke or other serious diseases, the cause of which is the penetration of the virus into the brain.
German scientists decided to investigate the mechanisms by which the new coronavirus can reach the brain, and find out how the immune system reacts to it.
Biologists from the Charite University Clinic in Berlin, together with specialists in neuropathology, pathology, forensic medicine, virology and clinical medicine, studied tissue samples from 33 patients who died from COVID-19 in the Charite clinics and the University Medical Center Gottingen.
Using the latest technology, they analyzed samples taken from four different brain regions. All tissues were tested for genetic material and spike protein of the SARS-CoV-2 virus.
As a result, the researchers found evidence of the presence of the virus in the neuroanatomic structures connecting the eyes, mouth and nose to the brain stem, and using an electron microscope for the first time obtained an image of the coronavirus penetrating into the olfactory mucosa. Here, the researchers recorded the maximum viral load – both inside nerve cells and in the processes emanating from the nearest epithelial cells.
Immunofluorescence staining shows a neuron (pink) in the olfactory region of the nasal mucosa infected with SARS-CoV-2 (yellow). The surrounding epithelial cells are colored blue. Photo: Jonas Franz / Universitätsmedizin Göttingen. Figure from the press release How SARS-CoV-2 reaches the brain - VM.
"These data confirm the hypothesis that SARS-CoV-2 uses the olfactory mucosa as an entrance to the brain," the words of the head of the study, Professor Frank Heppner, are quoted in the press release of the Charite clinic.
According to scientists, the anatomical proximity of the cells of the mucous membrane, blood vessels and nerve cells in this area also indicates this path of penetration.
"Once inside the olfactory mucosa, the virus uses neuroanatomic connections, such as the olfactory nerve. Our data show that the virus moves from nerve cell to nerve cell to reach the brain," added another author of the article, Dr. Helena Radbruch from the Department of neuropathology at the Charite Clinic. – However, it remains to be fully figured out how the virus spreads from nerve cells. It is likely that the virus is also carried through blood vessels, since it has also been found in the walls of blood vessels of the brain."
The researchers note that SARS-CoV-2 is far from the only virus capable of entering the brain in this way.
"Other examples include herpes simplex virus and rabies virus," says Dr. Radbruch.
"In our opinion, the presence of SARS-CoV-2 in the nerve cells of the olfactory mucosa well explains the neurological symptoms found in patients with COVID-19, such as loss of sense of smell or taste," continues Professor Heppner. – We also found SARS-CoV-2 in areas of the brain that control vital functions such as breathing. It cannot be ruled out that in patients with severe COVID-19, the presence of the virus in these areas of the brain exacerbates breathing problems caused by lung infection. Similar problems may arise with regard to cardiovascular function."
The authors emphasize that all patients who participated in this study suffered from COVID-19 in severe form, so the results obtained cannot be distributed without additional verification to all patients with coronavirus infection.
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