Researchers from the National Institute of Health and Medical Research (Inserm), the Institut Pasteur, the National Center for Scientific Research (CNRS) and the Hospitals of Paris have succeeded in unraveling the mystery of anosmia . They succeeded in highlighting the mechanisms involved in the loss of smell linked to Covid-19.

Until then, scientists did not understand why people infected with Covid-19 exhibit such a symptom, which usually appears early. To explain this sudden loss of sense of smell, professionals carried out a study including patients infected with Covid-19 at several stages of the disease. They made several discoveries. The ” neuro-invasion By Sars-Cov-2 in the nasal mucosa occurs in four steps. First, the viral particles manage to infect sensory neurons and destroy sensory cilia. The latter are receptors for odorous molecules. Then, the olfactory epithelium, which is the sensory organ, becomes disorganized and disintegrates because of the virus. This invades the olfactory bulb, which is responsible for decoding the olfactory message. 

On the other hand, at this stage, neuroinflammation is present as well as the pathogen, the coronavirus, in several areas of the brain. The sensory organ which is located at the bottom of the nasal cavities is degraded. This results in the loss of smell. As Pierre-Marie Llebo, CNRS researcher and head of the study explains, “ In fact, we have found that sensory neurons are infected by SARS-CoV-2, but also the olfactory nerve and olfactory nerve centers in the brain. ».

This is not the only information the study reveals. Indeed, one of the managers, Hervé Bourhy, details that “ the virus, once it enters the olfactory bulb, spreads to other nerve structures where it induces a significant inflammatory response “. He specifies that infection of olfactory neurons can constitute a ” gateway to the brain “. This could be the reason why some Covid-19 patients present with psychological (anxiety, depression) or neurological (cognitive decline) disorders. It will therefore be the subject of a future scientific study. For the time being, the mechanism involved in the loss of smell must be considered in order to better adapt the management of patients, especially in the long term. Indeed, the virus can ” persist within the olfactory epithelium for several months ». 

In addition, scientists recommend performing a nasal brushing (exploration of the pits), because PCR tests can turn out negative even while the virus persists in the cavities of the nose.