A new explanation for loss of smell affecting people affected by Covid comes to us from the results of a study recently published in the prestigious journal Cell.
As a reminder, this symptom is one of those commonly observed. The loss of smell (and usually taste) can be partial or total, and last up to several months after an infection in some cases.
Thus, according to the researchers who worked on this study, Covid would indirectly affect olfactory receptors – proteins on the surface of nerve cells present in the nose and which allow us to smell odors – by decreasing (hyposmia) or even inhibiting completely (anosmia) their action. In some cases, some patients even confuse odors (parosmia).
Immune Response in Olfactory Tissues Leads to Loss of Smell
Researchers speak of a generalized persistent and negative regulation of these famous olfactory receptors. In the process, the presence of the virus near the olfactory tissues will trigger a response from the immune cells. The latter will thus produce and release proteins called cytokines in order to fight the infection.
However, these cytokines will alter gene activity olfactory nerve cells themselves, according to the researchers. And since we’re in the brain, the immune response persists with the infection. This will have the effect of reducing the activity of the genes necessary for the construction and functioning of olfactory receptors.
Clearly, the proteins on the surface of nerve cells will no longer function properly and we can no longer smell odors as long as the infection persists.
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A more contained immune response to limit the damage?
Still according to these researchers, the understanding of this mechanism – starting from an infection of the olfactory tissues with Sars-Cov-2, passing through an immune response which will then affect the expression and the proper functioning of the genes responsible for the sense of smell – can serve as a sign that the virus is indirectly damaging the brain tissue.
From there, a new way of understanding the effects of the disease presents itself to us. Especially by acting on the immune response which affects the expression and functioning of certain genes.
Moreover, these researchers are currently looking into the use of steroids on hamsters in order to reduce the immune response and thus limit the damage of an infection at the level of the olfactory nerve cells.
Details of this study are available here.
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