Until now, science has assumed that the cause is damage to the neurons in the epithelial cell layer of the upper respiratory tract. According to US scientists, 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 impede the function of the nerve cells as a consequence.
human and hamster examined
“SARS-CoV-2 infects less than one percent of the cells in the human body. Despite this, it can cause severe damage in a whole range of organs. (…) Neurological and cognitive damage are among the most poorly understood symptoms of Covid- 19 patients. Among them, disorders of the sense of smell are the most common,” wrote Marianna Zazhytska (Columbia University/New York) and her co-authors a few days ago in the journal Cell.
The scientists carried out investigations on olfactory epithelium samples from SARS-CoV-2 patients and hamsters infected with the virus. “Accordingly, as a result of the infection, a violent immune reaction set in in the hamsters, which led to local inflammation and destroyed olfactory receptors and proteins on the surface of nerve cells in the nose, which recognize and transmit information about odors. About ten days after infection, this became massive disruption corrected again”, wrote the German Pharmazeutische Zeitung (online).
Neighboring cells infected
In any case, the causes of the disturbances in the sense of smell and taste are more complicated than originally assumed. According to the US scientists, the supporting cells of the cover and gland cell layer (epithelium) of the upper respiratory tract were the first to be infected by the Covid 19 pathogen. The experts could not prove a loss of neurons, which absorb or transmit the olfactory information. Anosmia is apparently an indirect consequential damage.
“Apparently, infection of neighboring cells was sufficient to alter the function of nearby neurons. The effects unfolded via a significant down-regulation of olfactory receptor genes and other key genes of the olfactory receptor signaling pathway. This was confirmed by analysis of the olfactory epithelia of 23 Covid -19 patients”, wrote the German pharmacist magazine.
tissue damaged
The results of the laboratory studies by the US neurologists apparently confirm once again that in the long term the inflammatory reaction triggered by SARS-CoV-2 is the main problem of Covid-19 after the acute “viral” phase of the disease. The loss of smell and taste as a result of Covid-19 is apparently “collateral damage” that occurs due to an overreaction of the immune system. It is activated by the infection and leads to an excessive endogenous production of inflammatory messenger substances. The result is damage to tissue or organs.
“Possibly such indirect mechanisms can also explain part of the long-Covid pathology, which can last weeks or months after a SARS-CoV-2 infection,” said the German Pharmazeutische Zeitung. First author Marianna Zazhytska therefore spoke to the New York Times of hope that the olfactory neurons could also recover after surviving Covid 19 disease.