Covid-19: A potential treatment for loss of smell

One of the persistent and debilitating symptoms of Covid-19 is the loss of smell (or anosmia). Scientists from INRAE and EnvA have demonstrated the effectiveness of corticosteroids in restoring olfactory abilities impacted following viral infection. These results, published on February 27 in Brain, Behavior, and Immunity, mark an important advance in understanding and treating this symptom.


Covid-19 causes some patients to lose their sense of smell. While this symptom is generally temporary, it can persist in about 10% of patients for more than 6 months.

Previous work carried out by a team of researchers from INRAE and EnvA showed that the olfactory mucosa, affected by SARS-CoV-2, was invaded by immune cells, leading to its destruction and prolonged inflammation. Building on these discoveries, the same team evaluated the effectiveness of corticosteroids, known for their anti-inflammatory properties, in the recovery of smell.

The results of this research are twofold: they confirm a direct link between the virus-induced loss of smell and the decrease in olfactory neuron populations in the nasal mucosa; and they demonstrate that early treatment with dexamethasone, a commonly used corticosteroid, improves the recovery of olfactory abilities in animals.

This recovery of olfactory abilities is associated with a reduction in the presence of immune cells in the mucosa and improved regeneration of the olfactory neuron population. These findings suggest that corticosteroid treatments currently used with little benefit in cases of prolonged anosmia could be effectively utilized if prescribed promptly upon the onset of loss of smell symptoms.

Notes:
[1] Funded by the ANR (CORAR) and ANRS (UCRAH).
[2] The olfactory neurons located in the olfactory mucosa are directly in contact with odors that enter the nose, and they are responsible for detecting odor molecules.

Reference:
Merle-Nguyen L., Ando-Grard O., Bourgon C. et al. (2024). Early corticosteroid treatment enhances recovery from SARS-CoV-2 induced loss of smell in hamster. Brain, Behavior, and Immunity, ISSN 0889-1591, https://doi.org/10.1016/j.bbi.2024.02.020.