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The findings of this study, which revealed that SARS-CoV-2 enters the brain through nerve cells in the nasal mucosa, are published in the journal Nature Neuroscience. For the first time, researchers were able to image intact coronavirus particles within the nasal mucosa captured with an electron microscope, writes sciencedaily.com.
It is now recognized that COVID-19 is not a mere respiratory disease. SARS-CoV-2 not only affects the lungs, it also affects the cardiovascular system, the gastrointestinal tract, and the central nervous system. More than one in three people with COVID-19 experience neurological symptoms such as changes or loss of taste and smell, headaches, tiredness, dizziness or nausea. For some people, the disease can even lead to a stroke or other serious condition.
To date, researchers have suspected that such symptoms are caused by a virus that infects specific cells in the brain. But how does SARS-CoV-2 get there? A team of field scientists, led by Frank Heppner, MD, Ph.D.
In this study, experts in neuropathology, pathology, forensic medicine, virology, and clinical care analyzed tissue samples from 33 patients with a mean age of 72 years. All of these patients died of COVID-19 at Charité Hospital or Göttingen University Medical Center.
Using the latest technology, the researchers analyzed samples taken from the nasal mucosa of dead patients and four different areas of the brain. Specific tissue and cell samples were searched for SARS-CoV-2 genetic material and spike proteins found on the surface of the virus.
The team of researchers found evidence that the virus was found in different neuroanatomical structures that connect the eyes, mouth and nose to the brain stem. Most of the virus was detected in the nasal mucosa. Using special tissue dyes, the researchers were able to extract the first electron microscope images in history to show intact virus particles in the nasal mucosa. They have been found both in nerve cells and in processes that take place in epithelial cells on the sides.
All samples used in this type of image-based analysis should be of the highest possible quality. To ensure this, the researchers ensured that all clinical and pathological processes were closely coordinated and supported by a sophisticated infrastructure.
“These data support the idea that SARS-CoV-2 has the ability to use the nasal mucosa as a gateway to the brain,” said prof. F. Heppneris. This is confirmed by the anatomical proximity of mucosal cells, blood vessels, and nerve cells in this area.
“The virus that enters the nasal mucosa uses neuroanatomical connections, such as the olfactory nerve, to reach the brain,” said the neuropathologist. – However, it is very important to note that those COVID-19 patients whose samples were used in this study had what could be called a severe form of the disease. They belonged to a small group of patients for whom the disease was fatal. Therefore, the results of our study may not be applicable to mild to moderate cases. “
The way the virus moves from nerve cells has not yet been definitively confirmed. “Our data suggest that the virus moves from one nerve cell to another until it reaches the brain,” Radbrusch explained. “However, the virus is also likely to travel through the blood vessels, as evidenced by the fact that the virus has also been found in the blood vessel walls of the brain.”
SARS-CoV-2 is certainly not the only virus that can reach the brain in certain ways. “Other examples are the herpes virus and the rabies virus,” Radbrusch explained.
The researchers also looked at how the immune system responds to SARS-CoV-2 infection. Not only did they find evidence that immune cells in the brain and nasal mucosa were activated, but they also detected immune markers for these cells in cerebrospinal fluid.
In some of the cases analyzed, the researchers also found a stroke due to tissue damage caused by thromboembolism (a blood clot in a blood vessel).
“We believe that the presence of SARS-CoV-2 in the nerve cells of the nasal mucosa explains the neurological symptoms that occur in COVID-19 patients, such as loss of taste or smell,” Heppner said. – We have also detected SARS-CoV-2 in those parts of the brain that are responsible for 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 may further impair respiratory function and contribute to respiratory problems due to the effects of SARS-CoV-2 infection on the lungs. . Similar problems can arise with regard to cardiovascular function. “
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