The coronavirus sneaks into the brain through the nose

Science

By CAPosts 01 December, 2020 - 05:30pm 56 views

In this section of a cell of the olfactory mucosa seen under the electron microscope, the coronavirus particles are observed in red (the color is not real) .Charité

The coronavirus reaches the brain by climbing up the nose. That is the option defended by a group of German scientists who have analyzed tissues from around thirty of those who died from COVID. In their autopsy, they have found traces of the virus from the olfactory mucosa to the brain region.

Since the beginning of the pandemic, many of the patients have reported having neurological symptoms , such as muscle pain of nervous origin (myalgia), disorders of the consciousness or the better known, loss of smell (anosmia) or taste. The involvement of the central nervous system was evident, but there is no unanimity on how the coronavirus got there. For some, more than from the virus, the damage is due to the overreaction of the immune system itself. Others have found in the analysis of brain tissues evidence that the disease comes from the breakdown of the blood-brain barrier , which protects the brain from what the bloodstream carries.

The results of the autopsies of 33 covid patients now show another possibility : that the route of entry of the virus to the brain is the nasal. This work, published in Nature Neuroscience , has found significant amounts of SARS-CoV-2 RNA (ribonucleic acid) and proteins in the olfactory mucosa. This membrane located at the end of the nostrils houses the nerve cells that allow the brain to translate the smells that enter through the nose.

"Once in the olfactory mucosa, the virus appears to use neuroanatomical connections, such as the olfactory nerve, to reach the brain" Frank Heppner. director of the department of neuropathology at Charité, the university hospital in Berlin.

"These data support the idea that SARS-CoV-2 is capable of using the olfactory mucosa as a gateway to the brain", says in a note the director of the department of neuropathology of Charité, the university hospital of Berlin (Germany ), Professor Frank Heppner. The most frequently cited neurological symptom is anosmia, the loss of smell. In addition, the physical closeness in this area of the cells of the mucosa, the blood vessels and the nerve cells, reinforced this pathway. "Once in the olfactory mucosa, the virus appears to use neuroanatomical connections, such as the olfactory nerve, to reach the brain," adds Heppner.

The olfactory mucosa appears with the highest viral load, but doctors also found its remains more there. They also found genetic material for the virus in other parts of the olfactory system, such as the olfactory bulb, which is nominally part of the brain, and in the olfactory tuber, the sensory processing center already housed in the cerebral cortex itself. "In some cases, we confirm the presence of the virus in the brain by visualizing it through the use of stains, which represent virus proteins, thus validating our findings," Heppner says in an email.

For his colleague in Charité and co-author of the study, the Dr. Helena Radbruch, "the virus moves from nerve cell to nerve cell until it reaches the brain." However, they have not found their trace in the nerve endings that, from the mucosa and the bulb, end in the brain. So they do not rule out other options, such as that of propagation through blood vessels. This could explain that they have found remains of coronavirus in other parts, such as the cerebellum, that do not intervene in the smell.

A data revealed by this research draws the attention of the member of the Spanish Society of Neurology David García Azorín: “The probability of finding the virus in the olfactory mucosa is inverse to the duration of the disease ”. This indicates that the impact of the coronavirus on the nervous system occurs from the beginning. "Headaches and anosmia appear in the first two or three days," he adds. For this neurologist, this work in which he has not intervened suggests that the virus could reach the central nervous system, but "they need to demonstrate the second part, find it in the brain."

It is the same skepticism shown by the head of the neurology service at the Albacete University Hospital Tomás Segura, who has also analyzed brain samples from those who died from covid. A first objection is that the study sample is very small and, furthermore, of such extreme cases that its results cannot be extended to the rest of the patients. Segura has observed such damage to the endothelial cells (which form the inner layer) of the blood capillaries, which leads him to think that this pathway is the entry of the virus into the brain: “We see the brain seeded with destruction, in which the virus has loaded the brain endothelium. ”

What the authors do agree on is raising the neurological side of a virus that, by definition, is respiratory. In their conclusions, the German scientists suggest that the presence of the virus in the brain stem, where among other things resides the control of breathing or heart rhythm, could be influencing respiratory or heart problems in many of the severe cases. "In certain patients with a severe course of covid who do not obtain the necessary oxygen due to the pneumonia they suffer, the presence of SARS-CoV-2 in the brain area that controls respiration can aggravate the problem of lack of oxygen, reducing, for for example, the automatic and normal impulse to breathe properly ”, he says. It is just a theory that will require further testing, but it is disturbing.

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Source: Elpais

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