MOSCOW, June 5. /TASS/. German molecular biologists have discovered that the coronavirus infiltrates human brain via nasal receptors of smell, using them to infiltrate the central nervous system (CNS). The research results and possible outcomes are published at the bioRxiv website.
"We provide first evidence that SARS-CoV-2 neuroinvasion occurs at the neuro-mucosal interface by transmucosal trespassing via regional nervous structures followed by a transport along the olfactory tract of the CNS, thus explaining some of the well-documented neurological symptoms in COVID-19 patients including alterations of smell and taste perception," the researchers write.
Since almost the very beginning of the coronavirus outbreak in Wuhan, the scientists know that the SARS-CoV-2 infects not only the lungs, but can also penetrate certain bodies in other organs, including mucous membranes of the nose, the esophagus, the blood vessels, and the heart, among others.
It was discovered very early that the virus can penetrate the peripheral nerve cells and the brain tissue. Recently, medics from Germany and France discovered that the coronavirus cannot reproduce inside brain cells, but can cause their mass death and facilitate development of the neurodegenerative diseases.
A group of German researchers, led by Frank Heppner of the Free University of Berlin, revealed the exact mechanism of SARS-CoV-2 penetration of human brain by studying tissue specimen, extracted from 32 patients that died from the coronavirus.
Gateway for the infection
According to the researchers, four patients died from blood clots in their brains, which led Heppner and his colleagues to suspect that their formation was caused by the coronavirus infiltration of their CNS.
Guided by this idea, the scientists harvested cell samples from different regions of the patients’ brain and researched their structure under the electronic microscope, looking for traces of the SARS-CoV-2 RNA and proteins inside them. Comparing the concentration of the viral particles and copies of the coronavirus genome, the scientists were able to trace the spread of the infection through the brain to and understand how it got there in the first place.
In particular, they discovered that the most viral traces was located in the olfactory [smell] epithelium and nervous cells that connect this part of the nose with smell centers in human brain. Apart from viral DNA, this was supported by inflammatory processes in these regions, usually associated with viral infections.
In addition, in some photos of those cells, the researchers discovered structures that simultaneously resembled the SARS-CoV-2 particles in size, but differed from them in shape. This might explain why another group of German researchers was unable to find traces of viable coronavirus particles inside human brain.
In the upcoming days, Heppner and his team plans to observe how exactly the coronavirus infiltrates the olfactory epithelium, which receptor it utilizes and what facilitates infiltration of neighboring neurons by new viral particles.
Answers to these questions would make it possible to understand, how often difficulty breathing and other complications, associated with COVID-19 are caused by infection of the brain, as well as estimate the long-term consequences of such infection for the nervous system.