COVID‐19 and olfactory dysfunction: A possible associative approach towards neurodegenerative diseases

Abstract

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the agent of novel coronavirus 2019 (COVID-19), has kept the globe in disquiets due to its severe life-threatening conditions. The most common symptoms of COVID-19 are fever, sore throat, and shortness of breath. According to the anecdotal reports from the health care workers, it has been suggested that the virus could reach the brain and can cause anosmia, hyposmia, hypogeusia, and hypopsia. Once the SARS-CoV-2 has entered the central nervous system (CNS), it can either exit in an inactive form in the tissues or may lead to neuroinflammation. Here, we aim to discuss the chronic infection of the olfactory bulb region of the brain by SARS-CoV-2 and how this could affect the nearby residing neurons in the host. We further review the probable cellular mechanism and activation of the microglia 1 phenotype possibly leading to various neurodegenerative disorders. In conclusion, SARS-CoV-2 might probably infect the olfactory bulb neuron enervating the nasal epithelium accessing the CNS and might cause neurodegenerative diseases in the future.

Severe Acute Respiratory Syndrome Coronavirus 2 Impact on the Central Nervous System: Are Astrocytes and Microglia Main Players or Merely Bystanders?

“…As commented in the previous sections, microglial cells are highly heterogenic and have a plethora of functions in the healthy CNS that are likely to be affected by the SARS-CoV-2 entrance to the brain, or by the cytokine storm originated in the periphery. This line of reasoning allowed some authors to propose that SARS-CoV-2-induced proinflammatory microglial phenotype might contribute to the development of neurodegenerative disorders (Alam et al, 2020;Mahalaxmi et al, 2020). Furthermore, the proinflammatory priming of microglia achieved by the direct SARS-CoV-2 infection, or by the peripheral cytokine storm, could contribute to the development of neuropsychiatric symptoms or to exacerbate previous clinical or even subclinical signs and symptoms of neurodegenerative diseases.…”

Persistence of COVID-19 Symptoms after Recovery in Mexican Population

“…It has also been described that symptoms such as dyspnea, anosmia, have appeared in survivors of severe acute respiratory syndrome (SARS-CoV) in 2003, where the individuals presented persistent functional disability, after discharge, it stands out that they were young patients, it is even mentioned that cases were registered, that they presented debilitating symptoms after one year of apparent recovery, and the possibility that these sequelae, were neurological, caused by infection or inflammation in the central nervous system, is discussed in other research [ 45 ]. Anosmia is an important symptom, because it could be indicate of intranasal inoculation of SARS-CoV-2 into the olfactory neural circuitry causing a neuroinvasion that could result in chronic neurodegenerative disease [ 46 , 47 , 48 ]. However, it’s necessary to make research in this area to uncover the mechanism of SARS-CoV-2 infection via olfactory bulb and its implications in neurodegenerative diseases the long term [ 48 ].…”

“…Anosmia is an important symptom, because it could be indicate of intranasal inoculation of SARS-CoV-2 into the olfactory neural circuitry causing a neuroinvasion that could result in chronic neurodegenerative disease [ 46 , 47 , 48 ]. However, it’s necessary to make research in this area to uncover the mechanism of SARS-CoV-2 infection via olfactory bulb and its implications in neurodegenerative diseases the long term [ 48 ].…”

Utility of Olfactory test as screening tool for COVID-19: A pilot study

“…In our study, although, the COVID-19 asymptomatic patient group was not presenting symptoms associated with congestion or nasal blockage but still the traits of loss of smell were noticed in the respondents indicating the importance of mechanisms other than congestion in pathoetiology of COVID-19 associated anosmia [6,11]. Moreover, the variable response of asymptomatic patient to the different types of odors can be attributed to the level of virus induced dysfunctions leading to neuronal damage due to COVID-19 infection which is not completely known yet but a recent study has pointed towards this [12] This type of tests if developed and validated in larger set of population will have many advantages. It will enable us do rapid and wider testing to identify at risk individuals as well localities.…”