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It is not infected neurons of the nose that cause the common symptom but damaged neighboring cells.
Disturbances of the sense of smell are, in many cases, the leading symptoms of a SARS-CoV-2 infection. Until now, scientists assumed that the cause was damage to the neurons in the epithelial cell layer of the upper respiratory tract. According to US scientists, however, experiments in the laboratory with tissue samples from covid 19 patients and infected hamsters show a different picture: the defects affect supporting cells and only hinder the function of the neurons.
“SARS-CoV-2 infects less than one percent of the cells in the human body. Nevertheless, it can cause severe damage to a whole range of organs. (…) Neurological and cognitive damage are among the least understood symptoms of covid-19 patients to date. Among them, disorders of the sense of smell are the most common,” Marianna Zazhytska (Columbia University/New York) and her co-authors wrote a few days ago in the scientific journal “Cell”.
Samples from covid patients and hamsters
The scientists conducted olfactory epithelium samples from SARS-CoV-2 patients and hamsters infected with the virus. “According to the results, as a consequence of the infection, a violent immune reaction started in the hamsters, which led to local inflammation and destroyed odor receptors as well as proteins on the surface of the nerve cells in the nose, which recognize and transmit information about odors. About ten days after the infection, this massive disturbance was corrected again,” wrote the German Pharmaceutical Newspaper.
The cause of the disturbances of the sense of smell and taste are, in any case, more complicated than initially assumed. In the first place, according to US scientists, supporting cells of the covering and epithelial cell layer (epithelium) of the upper respiratory tract were infected by the Covid 19 pathogens. The experts could not prove a loss of neurons that record or transmit the olfactory information. The anosmia is indirect, consequential damage.
Infection of neighboring cells
“An infection of neighboring cells was sufficient to change the function of the nearby neurons. The effects unfolded via a significant down-regulation of odor receptor genes and other key receptor signaling pathway genes. This was confirmed by analyzing the olfactory epithelia of 23 Covid-19 patients,” wrote the German pharmacy journal.
The results of the US neurologists’ laboratory studies seem to confirm that in the longer term, the inflammatory response triggered by SARS-CoV-2 is the main problem of Covid-19 after the acute “viral” phase of the disease. It appears that the loss of smell and taste in the aftermath of Covid-19 is “collateral damage” that occurs due to an overreaction of the immune system. The immune system is activated by the infection and leads to excessive pro-inflammatory messenger substances in the body. The result is then damaging to tissue or organs.
“It is possible that such indirect mechanisms can also explain part of the long-covid pathology that can persist weeks or months after a SARS-CoV-2 infection,” the German pharmaceutical newspaper said. In an interview with the New York Times, first author Marianna Zazhytska also spoke of a hope that the olfactory neurons could also recover after the covid-19 disease has been overcome.
- source: kurier.at/picture: Image by silviarita from Pixabay
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