COVID-19-Related Anosmia: The Olfactory Pathway Hypothesis and Early Intervention

Abstract

Anosmia is a well-described symptom of Corona Virus Disease 2019 (COVID-19). Several respiratory viruses are able to cause post-viral olfactory dysfunction, suggesting a sensorineural damage. Since the olfactory bulb is considered an immunological organ contributing to prevent the invasion of viruses, it could have a role in host defense. The inflammatory products locally released in COVID-19, leading to a local damage and causing olfactory loss, simultaneously may interfere with the viral spread into the central nervous system. In this context, olfactory receptors could play a role as an alternative way of SARS-CoV-2 entry into cells locally, in the central nervous system, and systemically. Differences in olfactory bulb due to sex and age may contribute to clarify the different susceptibility to infection and understand the role of age in transmission and disease severity. Finally, evaluation of the degree of functional impairment (grading), central/peripheral anosmia (localization), and the temporal course (evolution) may be useful tools to counteract COVID-19.

Updates on Children with Allergic Rhinitis and Asthma during the COVID-19 Outbreak

“…From recent reports, Italian pediatric cases (between 0 and 19 years of age) amounted to 518,057, corresponding to 14.1% of all the affected population, with 22 pediatric deaths. SARS-CoV-2 infection in children is less common, often spreads within family clusters, and manifests with mild and varied symptoms [ 4 , 5 ] such as fever, nasal congestion, cough, dyspnea, myalgia, arthralgia, headache, gastrointestinal, and skin manifestations with the characteristic anosmia and ageusia [ 6 , 7 ]. Rare cases have shown severe respiratory symptoms requiring intensive care or a multisystem inflammatory syndrome (MIS-C) [ 8 ].…”

MOATAI-VIR - an AI algorithm that predicts severe adverse events and molecular features for COVID-19’s complications

“…There is clinical evidence that some individuals infected with SARS-CoV-2 experience a loss of smell and taste(23). Furthermore, it has been found that olfactory receptors may be an alternative SARS-CoV-2 entry into the local host cells, which may lead to its spread into the central nervous system(24).…”

Vitamin A in resistance to and recovery from infection: relevance to SARS-CoV2

“…Interaction of vitamin A with olfactory function SARS-CoV2 causes olfactory and/or gustatory dysfunctions in COVID-19 patients (92)(93)(94)(95) . A recent meta-analysis of eight studies confirmed that patients with COVID-19 had significantly higher risks of developing olfactory and/or gustatory dysfunctions compared with normal subjects (OR of 65•9) or patients with acute respiratory infection without detectable virus (OR of 11•3) (94) .…”

“…The mean time from olfactory loss to recovery onset was reported as 12 d, with complete olfactory recovery in only 51 % of patients (93) . Viral infections are a common cause of olfactory dysfunction (96) , although the pathogenesis of sensory loss after viral infections is not well characterised (92,95) . It is assumed that the nasal epithelium and olfactory bulb could be critical in the pathological development of COVID-19, with mild outcomes of COVID-19 leading to localised effects with mild effects on olfactory function.…”

“…It is assumed that the nasal epithelium and olfactory bulb could be critical in the pathological development of COVID-19, with mild outcomes of COVID-19 leading to localised effects with mild effects on olfactory function. Interestingly, the effects of SARS-CoV2 on chronic olfactory impairment increase with age, affecting up to 50 % of people aged ≥65 years and >80 % of people aged ≥80 years (92) . VA supplementation may play an important role in the regeneration of olfactory receptor neurons, particularly since retinoic acid signalling is involved in neuronal regeneration (97) .…”