An incomprehensible unexplained phenomenon. In patients infected with SARS-CoV-2, French researchers at the Institut Pasteur, CNRS, Inserm, University of Paris and AP-HP have explored which mechanisms are involved in the loss of odor.

Complemented by his studies on patients with Kovid-19 and analysis on an animal model (Golden Syrian Hamsters), it shows that anosmia, a persistent symptom of the disease that can persist in some people for several months, is prolonged. Causes – Permanent presence of virus and inflammation in the olfactory mucosa.

Several stages

More precisely, viral infection initially causes “disappearance of cilia made by sensory neurons”. However, “these same eyelids allow the reception of odor molecules by sensory neurons”, explains the Pasteur Institute in a press release.

The virus then terminates in sensory neurons, causing “clutter of the olfactory epithelium (sensory organ)”. The virus then enters the “first cerebral relay of the olfactory system, the olfactory bulb”, which causes “neuroinflammation and the presence of viral RNA in many regions of the brain”.

© Institutional Pasteur

“We found that sensory neurons are infected with SARS-CoV-2, but also have olfactory nerves and olfactory nerve centers in the brain”, Pierre-Marie Lledo, CNRS researcher, head of perception and thesis (Institute Pasteur / CNRS) Underlined. And co-author responsible for the study, published in the journal Science Translational Medicine.

Once entering the olfactory bulb, the virus “spreads to other neural structures where it produces a significant inflammatory response”, added Hervé Bourhy, head of the Lyssavirus, Epidemiology and Neuropathology Unit at the institute. Pastor and co-author responsible for the study. .

Infection of olfactory neurons can therefore “constitute a gateway to the brain and explain that some patients develop various clinical manifestations, psychological (anxiety disorder, depression) or neurological (cognitive decline, neurological disease). Sensitivity) develops, which should be the subject of further. Studies “.

Negative RT-PCR test despite virus

During their research, scientists also found that RT-PCR tests performed on the nasopharyngeal swab could be negative, even if the virus remained deep in the nasal cavity, in the olfactory epithelium.

This finding suggests that the disease can be diagnosed by brushing the nose in patients with this disease.