Yumeng Yan
When will the sense of taste and smell lost due to the SARS-CoV-2 be restored？
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Part1 According to the survey
According to the results of several questionnaires, fever, cough, and body aches were themost common symptoms in most patients after contracting SARS-CoV-2, and nearly 30% ofrespondents had a brief loss of taste and smell. Afterwards, most of those who recoveredfrom SARS-CoV-2 found that their sense of smell returned within a few weeks (18-21 days),and about 5% had not regained their sense of smell at least up to 6 months after their firstinfection.
In addition, about 96% reported no aftereffects were found, and of the six individuals whogave feedback on the presence of aftereffects, four reported that their sense of taste wasaffected, such as loss of taste and sensitivity, and others reported weakness, sore throat, dryeyes, forgetfulness, or decreased motor skills.
Deeper survey data suggests that 12% of people over the age of 40 will have an olfactorydeficit by 2020. This means that diminished or lost sense of smell will be more likely tooccur in older age groups.
International survey data show that about 41% of patients with SARS-CoV-2 have alteredsense of smell or taste, with the prevalence of olfactory or taste impairment in Chinese, German and French patients at 32%,69% and 49%, respectively.
Among those who already suffer from SARS-CoV-2-induced olfactory loss, perhaps 1 in 20 will never regain their sense of smell. This shows that we must take this problem of olfactoryloss seriously.
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Part2 How SARS-CoV-2 stole
our sense of smell?
As far as the current study is concerned, the altered olfactory and gustatory functions ofpatients are due to neurological invasion by the SARS-CoV-2.
Scientists have confirmed that Angiotensin-Converting Enzyme 2 (ACE2 receptor) may bethe key factor. For neurons in the nose, which do not have the type of receptor used bySARS-CoV-2 to infect cells - ACE2 receptors - and therefore are not normally infected. Incontrast, ACE2 receptors are present in taste bud cells, where people taste food, as well as insalivary glands, and when the virus invades the taste bud cells, it may cause a loss of tastesensation. Or when the virus spreads from the pharyngeal region to the middle ear and affectsthe tympanic cord nerve, it can also lead to taste disorders. The diastolic cells surroundingolfactory sensory neurons in the olfactory epithelium are also filled with ACE2 receptors.These diastolic cells are also called support cells, and the new coronavirus can directly attackthe support cells surrounding olfactory sensory neurons thus causing infection, damage oreven death of these cells.
How do these support cells affect olfactory sensory neurons and cause loss of smell? Wheninfected with SARS-CoV-2, they are in the acute phase of infection, which producesmolecules that activate the inflammatory response against the virus, and these molecules alsoenter the olfactory receptor neurons, thus altering the distribution of genes in them. Thisalteration results in the inability to synthesize proteins in many olfactory sensory neurons. Inthe short term, the protein deficiency prevents neurons from detecting odors and affectsneuronal transmission of odors.
Additional studies suggest that olfactory failure may also be associated with TransmembraneSerine Protease 2 (TMPRSS2). ACE2 primarily expresses the host cell receptor for SARS-CoV-2, and TMPRSS2 expresses surface proteases that mediate the entry of SARS-CoV-2into cells. They are highly expressed in a variety of olfactory epithelial cell types, facilitatingviral entry into the cells and attacking the olfactory system, and leading to inflammation,resulting in impaired olfaction in humans.
It has also been speculated that patients with a genetic variant on chromosome 4 are 11%more likely to lose their sense of smell or taste. People who are highly sensitive to smell ortaste and those with Alzheimer's disease are also more likely to suffer from loss of smell. Inaddition, genetic changes acquired during the evolution of viruses can affect the impact onolfactory tissue. Tiny genes produce mutations thereby increasing the risk of peopledeveloping post-SARS-CoV-2 myxoma, perhaps because it makes the virus more adept atinfecting the supporting cells in the nasal cavity.
(EXPANSION: In addition, a variety offactors including the common cold orinfluenza virus, viral, bacterial orfungal infections of the upperrespiratory tract, head trauma, nasalpolyps, and neurodegenerative diseasessuch as Alzheimer's can reducepeople's ability to smell or even causepermanent loss of the sense of smell.Olfactory failure may also be caused byexposure to toxic chemicals, certaindrugs, or injury to the nose or to areasof the brain that process and interpretodor information. (People with specificvariants in genes associated with odormetabolism are particularly susceptibleto loss of smell due to SARS-CoV-2.)
As the SARS-CoV-2 epidemic develops further, scientists are conducting further in-depthresearch into the causes of the loss of smell due to SARS-CoV-2.
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Part3 Current status
From the original strain at the beginning to the currently circulating Omicron variant, the rateof developing olfactory and gustatory disturbances has decreased from about 70% to 17%.The Omicron mutant strain is highly infectious and has multiple new mutations on itsstinging proteins that may make it less likely to enter the nasal mucosal barrier and thusthreaten the supporting cells in the nose, thus easily breaking through at the first respiratorytissues it encounters, such as the human throat, making sore throat the first noticeablesymptom of the new crown infection today.
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Part4 Can the sense of smell
be restored?
The slow recovery of smell, and the loss of smell associated with SARS-CoV-2 may last forseveral months, is due to the time needed for olfactory neurons to regenerate from the stemcell supply in the nasal lining.
According to research studies, most patients will regain their sense of smell or taste, and onlya very small percentage of patients will experience long-term loss of smell or taste. In thissmall percentage of patients, the study indicates that recovery is lower in women than in menand that the presence of nasal congestion or more severe symptoms can lead to a slowrecovery.Abnormal function of some classes of immune cells such as Centrosome and Tcells may also affect the recovery of smell. These T cells produce inflammation and thusprevent full recovery in people with long-term olfactory problems after post-SARS-CoV-2pneumonia.
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Part5
How to bring back the sense of smell?
Currently, researchers say many of the treatments being investigated are aimed at promotingneuronal regeneration and calming inflammation. Scientists are investigating a number oftherapies that promote cell regeneration, and some studies are testing whether injections ofplatelet-rich plasma, vitamin A, can help restore olfactory neurons. In addition, someelectrical stimulation of the sense of smell, or training, show that this is helpful in post-viralolfactory loss, in post-traumatic olfactory loss, and possibly also in ageing.
Scientists have also found that omega-3 fatty acids can help restore the sense of smell inthose who have lost it after undergoing surgery with instruments through the nose. An anti-nodular inflammatory drug known as a JAKinhibitor - an enzyme that targets the Janusfamily of kinases to prevent communication through pro-inflammatory signaling molecules -could help calm the immune response to the nose and is now considered to have considerablepotential.
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Part6 Beware
For some patients after the infection blindly take drugs, experts have made recommendations.Do not take a variety of cold medicines together, it is best to read the instructions carefullywhen taking the medicine to check whether the active ingredients, especially acetaminophen,are repeated; also do not eat cold medicines containing acetaminophen ingredients, but alsotake antipyretics; the same effect such as antipyretics only take one kind of medicine, it is notrecommended to alternate acetaminophen and ibuprofen.
For some specific susceptible people who suffer from new crown sequelae such as loss ofsense of smell, early intervention and treatment are required. Some active olfactory trainingcan be done in the early stage, do not wait until after full recovery, which makes the recoveryof smell more likely.
Because diminished or lost sense of smell will be more likely to appear in older people,therefore for some middle-aged and elderly people, they should actively pay attention to theirhealth status, seek help from their neighbors, and get appropriate treatment at an early stage.
If some people have underlying diseases and other related diseases, they should try to avoidinfection or secondary infection. People should be fully aware of the seriousness of thesequelae of the new crown and avoid taking it lightly, which may pose a threat to their health.
Wish you a speedy recovery and good health!
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Reference
Persistent post–COVID-19 smell loss is associated with immune cell infiltration andaltered gene expression in olfactory epitheliumhttps://www.science.org/doi/10.1126/scitranslmed.add0484
How to bring back the sense of smell
https://www.nature.com/articles/d41586-022-01628-9
The science behind COVID’s assault on smell
https://www.nature.com/articles/d41586-022-01627-w
How COVID-19 stole our sense of smell
https://cen.acs.org/articles/100/i34/COVID-19-stole-sense-smell.html
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