Loss of smell, or anosmia, is one of the earliest and most commonly reported symptoms of COVID-19. But the mechanisms involved had yet to be clarified. Scientists determined the mechanisms involved in the loss of smell in patients infected with SARS-CoV-2 at different stages of the disease.
They discovered that SARS-CoV-2 infects sensory neurons and causes persistent epithelial and olfactory nervous system inflammation. Furthermore, in some patients with persistent clinical signs, anosmia is associated with prolonged epithelial and olfactory nervous system inflammation and lasting presence of the virus in the olfactory epithelium. These findings were published in the journal Science Translational Medicine.
Although COVID-19 caused by the SARS-CoV-2 virus is principally a respiratory disease, many patients present with non-respiratory symptoms. These include a sudden loss of smell in individuals infected with SARS-CoV-2, which has been reported throughout the world since the beginning of the pandemic. Until recently, there has been uncertainty as to whether the virus plays a direct role in anosmia. According to one hypothesis generally accepted until now, it was assumed that a transient edema of the olfactory clefts inhibited airflow transporting odor molecules to the olfactory neurons (the familiar sensation of a blocked nose experienced during a common cold).
In a recent study, scientists shed light on the mechanisms involved in COVID-19-related anosmia. The study was conducted with COVID-19 patients and supplemented with tests on an animal model. This study unexpectedly demonstrates that nasopharyngeal swabs may test negative by standard RT-qPCR even if the virus is still present at the back of the nasal cavities, in the olfactory epithelium. In light of this discovery, SARS-CoV-2 diagnosis by nasal brushing may be envisaged in addition to nasopharyngeal swabbing for the PCR test in patients experiencing loss of smell.
This work also sheds light on the mechanism of COVID-19-related smell loss by revealing a series of chronological steps:
1) Cilia carried by sensory neurons are lost post-viral infection. These cilia enable the sensory neurons to receive odor molecules;
2) Virus present in sensory neurons;
3) Disruption of the olfactory epithelium (sensory organ) integrity linked to apoptosis (i.e. cell death). The epithelium is organized into regular lamellae, which are destructured by coronavirus infection;
4) Virus dissemination to the olfactory bulb, which is the first cerebral relay station in the olfactory system;
5) Inflammation and viral RNA present in several regions of the brain.
This study demonstrates that loss of smell is also caused by deterioration of the sensory organ at the back of the nasal cavities. "We observed that SARS-CoV-2 infects not only the sensory neurons, but also the olfactory nerve and the olfactory nerve centers in the brain," comments a co-author of the study.
"Another key finding from this study emerged from an observation of animal models, which revealed that once the virus enters the olfactory bulb, it spreads to other nerve structures, where it induces a major inflammatory response," explains another co-author of the study. Infection of the olfactory neurons may therefore provide a gateway to the brain and explain why some patients develop various psychological clinical signs (anxiety disorders, depression) or those of a neurological nature (cognitive decline, susceptibility to developing a neurodegenerative disease), for which further studies are necessary.
Another co-author of the study concludes: "According to our results, loss of smell in COVID-19 may persists for several months in some patients and this persistence of clinical signs may be attributed to the persistence of the virus and inflammation in the olfactory mucosa." These observations should be used to adapt the diagnosis and management of long-term COVID-19 signs.
https://www.pasteur.fr/en/home/press-area/press-documents/covid-19-discovery-mechanisms-short-and-long-term-anosmia
https://stm.sciencemag.org/content/early/2021/04/30/scitranslmed.abf8396
The mechanisms of short- and long-term anosmia following SARS-CoV-2 infection
- 1,451 views
- Added
Edited
Latest News
Complete vascularization of…
By newseditor
Posted 28 Mar
Immune cells identified as…
By newseditor
Posted 28 Mar
TB blood test which could d…
By newseditor
Posted 27 Mar
Propionate supplementation…
By newseditor
Posted 27 Mar
Role of human Kallistatin i…
By newseditor
Posted 26 Mar
Other Top Stories
First successful treatment of mycobacterial lung infection with bac…
Read more
Biomaterial improves islet transplants for treatment of type 1 diab…
Read more
How deep brain stimulation treats Parkinson's disease symptoms
Read more
Plasma membrane phospholipid plays a key role in epithelial cell ad…
Read more
Stopping nervous system tumor growth in mice with an epilepsy drug
Read more
Protocols
Spatial proteomics in neuro…
By newseditor
Posted 28 Mar
All-optical presynaptic pla…
By newseditor
Posted 23 Mar
Epigenomic tomography for p…
By newseditor
Posted 20 Mar
A mouse DRG genetic toolkit…
By newseditor
Posted 17 Mar
An optogenetic method for t…
By newseditor
Posted 13 Mar
Publications
A microfluidic platform int…
By newseditor
Posted 28 Mar
Salmonella manipulates macr…
By newseditor
Posted 28 Mar
BHLHE40/41 regulate microgl…
By newseditor
Posted 28 Mar
Balancing neuronal activity…
By newseditor
Posted 28 Mar
OSBP-mediated PI(4)P-choles…
By newseditor
Posted 28 Mar
Presentations
Hydrogels in Drug Delivery
By newseditor
Posted 12 Apr
Lipids
By newseditor
Posted 31 Dec
Cell biology of carbohydrat…
By newseditor
Posted 29 Nov
RNA interference (RNAi)
By newseditor
Posted 23 Oct
RNA structure and functions
By newseditor
Posted 19 Oct
Posters
A chemical biology/modular…
By newseditor
Posted 22 Aug
Single-molecule covalent ma…
By newseditor
Posted 04 Jul
ASCO-2020-HEALTH SERVICES R…
By newseditor
Posted 23 Mar
ASCO-2020-HEAD AND NECK CANCER
By newseditor
Posted 23 Mar
ASCO-2020-GENITOURINARY CAN…
By newseditor
Posted 23 Mar