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A systematic analysis of 33 autopsies of COVID-19 has found tiny traces of viral material in the human brain, and they appear to come from the nose.
It is a scary thought that SARS-CoV-2 can actually reach the human nervous system; While the results are preliminary, the signs are not looking good.
The upper part of the human nasal cavity, known as the nasopharynx, is believed to be one of the earliest sites of infection and replication of SARS-CoV-2, and could also be a weak point in our brain’s defenses.
The human brain is separated from the rest of the body’s blood supply by a semi-permeable cell barrier, usefully called the blood-brain barrier, which keeps toxins and pathogens away from our prized noggins, at least most of the time.
Some viruses, including a couple of coronaviruses, are especially sneaky and capable of breaking through this barrier. Unfortunately, SARS-CoV-2 could be one of them.
In fact, some scientists think this could be what is causing many of the neurological symptoms associated with COVID-19, including loss of smell and taste, headaches, dizziness, nausea, and fatigue.
Recently, some studies have discovered traces of viral RNA in the brain and cerebrospinal fluid of some COVID-19 patients. Exactly how those remains got there is another matter.
Some early studies suggest that the spikey proteins on the outside of SARS-CoV-2 promote inflammation in the endothelial cells of the blood-brain barrier, loosening the connections and allowing the virus to leak out.
The new analysis adds another possible route. The researchers not only found intact viral particles within the endothelial cells of the nasopharynx, they also found viral RNA in the upper part of the nose, known as the mucous membrane, as well as in various regions of the brain.
Leftover genetic material was minimal, but that could be because the autopsy was performed a month after death on average.
While it may not be possible to see how the virus travels inside individual brain cells, in some patients the same spike proteins found on the outside of SARS-CoV-2 were also found in the cells the researchers identified. like neurons.
This suggests that the SARS-CoV-2 virus may somehow be crossing the blood-brain barrier and into the brain through the long, threadlike projections of the olfactory nerves.
But even if it turns out that neurons in the nose are carrying 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 mucosa and were more involved with respiration and cardiovascular control, suggesting that the virus is also entering by other means.
It could, for example, leak through endothelial cells, as other studies suggest, or it could be mounting on another cell that is allowed to cross the blood-brain barrier, for example, to transport vital resources.
For now, we just don’t know. Reports and cumulative results suggest that the virus is somehow penetrating and impacting the nervous system. Time and research are expected to reveal more, helping us fight this unprecedented virus.
The study was published in Neuroscience of nature.
