Loss of smell or anosmia is one of the earliest and most commonly reported symptoms of COVID-19. At the same time, the mechanism of its appearance was not known until now.
Scientists from the Pasteur Institute, the National Center for Scientific Research (France) and the University of Paris, with the participation of other scientific organizations, have explained the mechanisms of the main symptom in coronavirus – the loss of smell. For almost a year and a half of the pandemic, it was anosmia that was diagnosed in patients with COVID-19 most often, and at different stages of the disease. The results of the study are published in the journal Science Translational Medicine.
Until recently, it was unclear whether the virus plays a direct role in anosmia. According to one of the generally accepted hypotheses, it was assumed that temporary swelling of the olfactory gaps suppresses the air currents that transport odor molecules to the olfactory neurons.
French scientists have shed light on the mechanisms involved in anosmia during coronavirus infection. The study was conducted with the participation of patients with COVID-19 and supplemented with tests on model organisms.
Due to a viral infection, sensory neurons lose their olfactory cilia, which are necessary to “catch” stimulus molecules. The virus also enters sensory neurons, disrupting their function, and contributes to the death of epithelial cells as a result of apoptosis (programmed cell death). In the future, the coronavirus enters the olfactory bulb, where it provokes inflammatory reactions, and from there spreads to other nerve structures.
The study demonstrates that loss of smell is also caused by damage to the sense organ in the back of the nasal cavities. Scientists have noticed that SARS-CoV-2 affects not only sensory neurons, but also the olfactory nerve and olfactory nerve centers in the brain.
Another key finding from this study came from observation in animal models, which showed that once a virus enters the olfactory bulb, it spreads to other neural structures, where it causes a severe inflammatory response.