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A systematic analysis of 33 COVID-19 autopsies revealed small traces of viral material in the human brain, and they appear to come from the nose.
It’s a scary thought that SARS-CoV-2 could actually make its way into the human nervous system; while the results are preliminary, the signs do not look good.
The upper part of the human nasal cavity, known as the nasopharynx, is believed to be one of the primary sites of SARS-CoV-2 infection and replication, and could also be a weak point in the body’s defenses. our brain.
The human brain is separated from the rest of the body’s blood supply by a semi-permeable barrier of cells – usefully called the blood-brain barrier – that keeps toxins and pathogens away from our precious noggins, at least most of the time. .
Some viruses, including a few coronaviruses, are particularly sneaky and able to break through this barrier. Unfortunately, SARS-CoV-2 could be one of them.
In fact, some scientists believe it could be the root of many neurological symptoms associated with COVID-19, including loss of smell and taste, headaches, dizziness, nausea, and fatigue.
Recently, some studies have actually found traces of viral RNA in the brain and cerebrospinal fluid of some patients with COVID-19. Exactly how these remains got there is another question.
Some initial studies suggest that the prickly proteins on the outside of SARS-CoV-2 promote inflammation of blood-brain barrier endothelial cells, loosening connections and letting the virus escape.
The new analysis adds another possible route. Not only did the researchers find intact viral particles in endothelial cells in the nasopharynx, they also found viral RNA in the upper part of the nose – known as the mucous membrane – as well as in several regions of the brain.
The remaining genetic material was minimal, but perhaps that was because the autopsy took place a month after death on average.
While it may not be possible to see how the virus moves inside individual brain cells, in some patients the same spike proteins found outside of SARS-CoV-2 have also been found in cells that researchers have identified as neurons.
This suggests that the SARS-CoV-2 virus could somehow cross the blood-brain barrier and enter the brain via the long, thread-like projections of the olfactory nerves.
But even if it turns out that neurons in the nose carry SARS-CoV-2 to the brain, in all likelihood, that’s probably just one port of entry. In the analysis, some regions of the brain with traces of RNA had no direct connection to the olfactory lining and were more involved in respiration and cardiovascular control, suggesting that the virus also enters by another means.
It could, for example, leak through endothelial cells, as other studies suggest, or it could be hitchhiking on another cell that is allowed to cross the blood-brain barrier, for example, to transport vital resources.
At the moment, we just don’t know. The accumulation of reports and results suggests that the virus is crossing over and impacting the nervous system. We hope that time and research will reveal more and help us fight this unprecedented virus.
The study was published in Neuroscience of nature.
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