Potential Mechanisms for COVID-19 Induced Anosmia and Dysgeusia

Emerging roles of the renin-angiotensin system in select oral diseases

OBJECTIVES

The renin-angiotensin system (RAS) plays essential roles in cardiovascular and renal function regulation. Recent studies have shown that the RAS components are widely expressed in oral tissues, but their roles in oral diseases remain underexplored. This review aims to summarize the effects of the RAS in select oral diseases including oral squamous cells carcinoma (OSCC), periodontitis, oral submucous fibrosis (OSF), and ageusia/dysgeusia.

SUBJECTS AND METHODS

Data searches were performed using PubMed, Web of Science and Scopus through July 2024. A narrative overview of current literature was undertaken to synthesize the contexts with elaboration and summary.

RESULTS

In OSCC, ACE/Ang II/AT1R promotes OSCC by inducing angiogenesis, cell proliferation and invasiveness. Conversely, ACE/Ang II/AT2R and ACE2/Ang (1-7)/MasR inhibit OSCC progressions. In periodontitis, ACE/Ang II/AT1R upregulates inflammatory cytokines and promotes osteoclast differentiation factor RANKL, whereas ACE2/Ang (1-7)/MasR exerts opposite effects by preventing inflammation and alveolar bone loss. In OSF, Ang (1-7) counters the profibrotic and proinflammatory action of Ang II. In dysgeusia, Ang II suppresses salt taste responses and enhances sweet taste sensitivities, while Ang (1-7) exhibits opposite effects.

CONCLUSIONS

The RAS cascade plays crucial roles in OSCC, periodontitis, OSF and ageusia/dysgeusia. The imbalanced RAS may aggravate the progression of these diseases.

Potential convergence of olfactory dysfunction in Parkinson's disease and COVID-19: The role of neuroinflammation

Parkinson's disease (PD) is a prevalent neurodegenerative disorder that affects 7-10 million individuals worldwide. A common early symptom of PD is olfactory dysfunction (OD), and more than 90% of PD patients suffer from OD. Recent studies have highlighted a high incidence of OD in patients with SARS-CoV-2 infection. This review investigates the potential convergence of OD in PD and COVID-19, particularly focusing on the mechanisms by which neuroinflammation contributes to OD and neurological events. Starting from our fundamental understanding of the olfactory bulb, we summarize the clinical features of OD and pathological features of the olfactory bulb from clinical cases and autopsy reports in PD patients. We then examine SARS-CoV-2-induced olfactory bulb neuropathology and OD and emphasize the SARS-CoV-2-induced neuroinflammatory cascades potentially leading to PD manifestations. By activating microglia and astrocytes, as well as facilitating the aggregation of α-synuclein, SARS-CoV-2 could contribute to the onset or exacerbation of PD. We also discuss the possible contributions of NF-κB, the NLRP3 inflammasome, and the JAK/STAT, p38 MAPK, TLR4, IL-6/JAK2/STAT3 and cGAS-STING signaling pathways. Although olfactory dysfunction in patients with COVID-19 may be reversible, it is challenging to restore OD in patients with PD. With the emergence of new SARS-CoV-2 variants and the recurrence of infections, we call for continued attention to the intersection between PD and SARS-CoV-2 infection, especially from the perspective of OD.

Prevalence and Prognostic Factors Associated with Early Recovery of Olfactory Dysfunction in COVID-19 Patients

BACKGROUND

The prevalence of smell dysfunction, along with its risk factors, has been evaluated in previous literature; however, little has been established regarding its relation to other factors such as disease severity, history of coronavirus disease-2019 (COVID-19) vaccinations, and medical treatment for COVID-19 infection. These factors may impact the overall recovery of olfaction in COVID-19 patients.

OBJECTIVE

This study investigated the prevalence of early olfactory recovery from COVID-19 infection and its associated factors.

METHODS

This study was a prospective cohort study on 348 COVID-19 patients with a new onset of anosmia or hyposmia. Smell sensation scores on the olfactory self-assessment test were collected at baseline and every week until 6 weeks of follow-up. The primary outcome was the prevalence of early olfactory recovery. The secondary outcomes were analyzing factors associated with early olfactory recovery and the median time to complete recovery of smell loss.

RESULTS

The prevalence of early olfactory recovery was 63.1% (95% CI: 0.58-0.68), and significant associated factors in multivariate analysis included patients without allergic rhinitis (OR 2.22, 95% CI: 1.12-4.40, P = 0.023) and no alteration of taste perception (OR 1.62, 95% CI: 1.02-2.57, P = 0.042). The median time to complete recovery from smell loss was 2 weeks.

CONCLUSION

The present study found that the prevalence of early olfactory recovery within 2 weeks was 63.1%. The median time to olfactory recovery was also 2 weeks. Patients without allergic rhinitis and taste alteration had a significantly better chance of early recovery of olfactory function.

Viral Pneumonia: From Influenza to COVID-19

Respiratory viruses are increasingly recognized as a cause of community-acquired pneumonia (CAP). The implementation of new diagnostic technologies has facilitated their identification, especially in vulnerable population such as immunocompromised and elderly patients and those with severe cases of pneumonia. In terms of severity and outcomes, viral pneumonia caused by influenza viruses appears similar to that caused by non-influenza viruses. Although several respiratory viruses may cause CAP, antiviral therapy is available only in cases of CAP caused by influenza virus or respiratory syncytial virus. Currently, evidence-based supportive care is key to managing severe viral pneumonia. We discuss the evidence surrounding epidemiology, diagnosis, management, treatment, and prevention of viral pneumonia.

Oral manifestations associated with Novel Coronavirus Disease - 2019 (COVID-19): A questionnaire based hypothetical study

Background: Since the Coronavirus disease 2019 (COVID-19) outbreak in 2019, the virus has evolved drastically, presenting with sets of mutations that influence its properties, including transmissibility and antigenicity. The oral mucosa is postulated as probable portal entry and several oral manifestations have been identified, which places dental professionals in a position to recognize probable COVID-19 patients depending on oral signs and symptoms in the initial phases of the disease itself. As co-existing with COVID-19 seems to be a new reality, greater understanding is required regarding early oral signs and symptoms which can be predictors for timely intervention and prevention of complications in COVID-19 patients. The objective of the study is to identify the distinguishing oral signs and symptoms among COVID-19 patients and to establish possible correlation between severity of COVID-19 infection and oral symptoms. Methods: This study recruited 179 ambulatory, non-hospitalized COVID-19 patients from the Kingdom of Saudi Arabia's Eastern Province's designated hotels for COVID-19 and home isolated patients from the same region using a convenience sample method. Data was collected by qualified and experienced investigators, including two physicians and three dentists, using a validated comprehensive questionnaire through telephonic interviews with the participants. The X 2 was used to assess the categorical variables, and odd's ratio was calculated to determine the strength of the association between general symptoms and oral manifestations. Results: Oral and nasopharyngeal lesions or conditions like loss of smell and taste, xerostomia, sore throat, and burning sensation were predictors of COVID-19-related systemic symptoms such as cough, fatigue, fever, and nasal congestion were identified to be statistically significant (p<0.05). Conclusions: The study reveals the occurrence of olfactory or taste dysfunction, dry mouth, sore throat, and burning sensation along with COVID-19 generic symptoms, should be considered as suggestive yet not conclusive indicators of COVID-19.

Angina Bullosa Haemorrhagica in COVID 19: A Diagnostic Conundrum. Case Report and Review of Literature

Oral manifestations of COVID-19 are amongst the most obscure and ill-reported. Of these, angina bullosa haemorrhagica is amongst the rarest. Only 2 cases of angina bullosa haemorrhagica in COVID-19 patients have been reported in literature. Angina bullosa haemorrhagica (ABH) is an enigmatic, abstruse condition represented by sudden onset of painful subepithelial, mucosal blood-filled vesicles and bullae in the oral cavity. It is not attributed to any systemic conditions, blood dyscracias or other well-known dermatological pathologies. The occurrence of these lesions in patients of COVID-19 suggests that the underlying pathology of the latter may predispose to ABH and thus help in shedding some light onto the pathogenesis of this obscure disease. Herein we present 2 cases of ABH in patients of COVID-19 within a few weeks of the resolution of the latter. Both patients reported that they had never had this condition before and that this was the first presentation of the symptom. A review of literature shows that the etiopathogenesis of ABH is ambiguous at best and that the pathology underlying the oral manifestation of COVID-19 may well be applicable to ABH as well. Various mechanisms have been proposed to cause oral manifestations in COVID-19 patients. These include imbalance in the RAS pathway causing mucosal disruption, immune dysregulation, deranged cellular immune mechanism and disruption of local immune mechanisms. Since ABH has been reported in COVID 19, it is plausible that some of the mechanisms underlying the pathogenesis of oral manifestations may explain the pathogenesis of ABH.

The Latest Cellular and Molecular Mechanisms of COVID-19 on Non-Lung Organs

Understanding the transmission pathways of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) will aid in developing effective therapies directed at the virus’s life cycle or its side effects. While severe respiratory distress is the most common symptom of a coronavirus 2019 (COVID-19) infection, the virus is also known to cause damage to almost every major organ and system in the body. However, it is not obvious whether pathological changes in extra-respiratory organs are caused by direct infection, indirect, or combination of these effects. In this narrative review, we first elaborate on the characteristics of SARS-CoV-2, followed by the mechanisms of this virus on various organs such as brain, eye, and olfactory nerve and different systems such as the endocrine and gastrointestinal systems.

SARS-CoV-2 infection and multi-organ system damage: A review

The SARS-CoV-2 infection causes COVID-19, which has affected approximately six hundred million people globally as of August 2022. Organs and cells harboring angiotensin-converting enzyme 2 (ACE2) surface receptors are the primary targets of the virus. However, once it enters the body through the respiratory system, the virus can spread hematogenously to infect other body organs. Therefore, COVID-19 affects many organs, causing severe and long-term complications, even after the disease has ended, thus worsening the quality of life. Although it is known that the respiratory system is most affected by the SARS-CoV-2 infection, many organs/systems are affected in the short and long term. Since the COVID-19 disease simultaneously affects many organs, redesigning diagnostic and therapy policies to fit the damaged organs is strongly recommended. Even though the pathophysiology of many problems the infection causes is unknown, the frequency of COVID-19 cases rises with age and the existence of preexisting symptoms. This study aims to update our knowledge of SARS-CoV-2 infection and multi-organ dysfunction interaction based on clinical and theoretical evidence. For this purpose, the study comprehensively elucidates the most recent studies on the effects of SARS-CoV-2 infection on multiple organs and systems, including respiratory, cardiovascular, gastrointestinal, renal, nervous, endocrine, reproductive, immune, and parts of the integumentary system. Understanding the range of atypical COVID-19 symptoms could improve disease surveillance, limit transmission, and avoid additional multi-organ-system problems.

Effects of COVID-19 on Synaptic and Neuronal Degeneration

Neurons are the basic building blocks of the human body's neurological system. Atrophy is defined by the disintegration of the connections between cells that enable them to communicate. Peripheral neuropathy and demyelinating disorders, as well as cerebrovascular illnesses and central nervous system (CNS) inflammatory diseases, have all been linked to brain damage, including Parkinson's disease (PD). It turns out that these diseases have a direct impact on brain atrophy. However, it may take some time after the onset of one of these diseases for this atrophy to be clearly diagnosed. With the emergence of the Coronavirus disease 2019 (COVID-19) pandemic, there were several clinical observations of COVID-19 patients. Among those observations is that the virus can cause any of the diseases that can lead to brain atrophy. Here we shed light on the research that tracked the relationship of these diseases to the COVID-19 virus. The importance of this review is that it is the first to link the relationship between the Coronavirus and diseases that cause brain atrophy. It also indicates the indirect role of the virus in dystrophy.

Eating Habits and Body Weight Changes Induced by Variation in Smell and Taste in Patients with Previous SARS-CoV-2 Infection

Olfactory and gustatory dysfunction are recognized as common symptoms in patients with COVID-19, with a prevalence ranging, respectively, between 41-61% and 38.2-49%. This review focused on relating the variations in dietary habits with the reduction/loss of smell and/or taste in patients who contracted the COVID-19 infection. Primarily, we reviewed the main pathological mechanisms involved in COVID 19-induced anosmia/dysosmia and ageusia/dysgeusia. Then, we explored and summarized the behavioural changes in food intake and body weight during the COVID-19 pandemic in relation to sensory impairment and the underlying mechanisms. Most studies on this topic argue that the altered chemosensory perception (taste and smell) mainly induces reduced appetite, leading to a faster fullness sensation during the consumption of a meal and, therefore, to a decrease in body weight. On the other hand, a reduced perception of the food's sensory properties may trigger compensatory responses that lead some individuals to increase food intake with a different effect on body weight. Regarding body weight, most studies evaluated malnutrition in patients hospitalized for COVID-19; more studies are warranted to investigate nutritional status specifically in non-hospitalized patients with olfactory and gustatory dysfunctions caused by COVID-19 infection.

Multiple Types of Taste Disorders among Patients with COVID-19

Objective Based on the increasing incidence of smell and taste dysfunction among coronavirus disease 2019 (COVID-19) patients, such issues have been considered an early symptom of infection. However, few studies have investigated the type of taste components that are most frequently affected in COVID-19 patients. This study investigated the difference in frequencies of the types of taste component disorders among hospitalized COVID-19 patients. Methods In this retrospective, single-center, observational study, patients' background characteristics, clinical course, laboratory and radiological findings, and details on taste and/or smell disorders were collected and analyzed from medical records. Patients A total of 227 COVID-19 patients were enrolled, among whom 92 (40.5%) complained of taste disorders. Results Multiple types of taste disorders (hypogeusia/ageusia and hypersensitivity, or hypersensitivity and changing tastes) were reported in 10 patients. In particular, 23 patients reported hypersensitivity to at least 1 type of taste, and 2 patients complained of a bitter taste on consuming sweet foods. Impairment of all taste components was found in 48 patients (52.2%). The most frequent taste disorder was salty taste disorder (81 patients, 89.0%). Hypersensitivity to salty taste was most frequently observed (19 patients, 20.9%). Conclusion Patients with COVID-19 develop multiple types of taste disorders, among which salty taste disorder was the most frequent, with many patients developing hypersensitivity to salty taste. As smell and taste are subjective senses, further studies with the combined use of objective examinations will be required to confirm the findings.

COVID-19 Induced Taste Dysfunction and Recovery: Association with Smell Dysfunction and Oral Health Behaviour

Background and Objectives: Disruption to taste and smell are common symptoms of COVID-19 infection. The current literature overlooks taste symptoms and tends to focus on the sense of smell. Persisting cases (>28 days) of taste dysfunction are increasingly recognised as a major future healthcare challenge. This study focuses on the severity and recovery of COVID-19 induced taste loss and association with olfactory symptoms, lifestyle and oral health factors. Materials and Methods: This study was a cross-sectional survey comparing 182 rapid taste recovery participants (≤28 days) with 47 participants with prolonged taste recovery >28 days. Analyses of taste loss in association with smell loss, age, sex, illness severity, diet, BMI, vitamin-D supplementation, antidepressants, alcohol use, smoking, brushing frequency, flossing, missing teeth, appliances and number of dental restorations were conducted. Differences in the severity of the loss of sour, sweet, salt, bitter and umami tastes were explored. Results: Both the severity and the duration of taste and smell loss were closely correlated (p < 0.001). Salt taste was significantly less affected than all other taste qualities (p < 0.001). Persisting taste loss was associated with older age (mean ± 95% CI = 31.73 ± 1.23 years vs. 36.66 ± 3.59 years, p < 0.001) and reduced likelihood of using floss (odds ratio ± 95% CI = 2.22 (1.15−4.25), p = 0.047). Conclusions: Smell and taste loss in COVID-19 are closely related, although a minority of individuals can experience taste or smell dysfunction in the absence of the other. The taste of salt may be less severely affected than other taste qualities and future work exploring this finding objectively is indicated. The association of flossing with rapid taste recovery adds to the growing evidence of a link between good periodontal health and favourable COVID-19 outcomes.

COVID-19 and neurological sequelae: Vitamin D as a possible neuroprotective and/or neuroreparative agent

SARS-CoV-2, the etiological agent of the current COVID-19 pandemic, belongs to a broad family of coronaviruses that also affect humans. SARS-CoV-2 infection usually leads to bilateral atypical pneumonia with significant impairment of respiratory function. However, the infectious capacity of SARS-CoV-2 is not limited to the respiratory system, but may also affect other vital organs such as the brain. The central nervous system is vulnerable to cell damage via direct invasion or indirect virus-related effects leading to a neuroinflammatory response, processes possibly associated with a decrease in the activity of angiotensin II converting enzyme (ACE2), the canonical cell-surface receptor for SARS-CoV-2. This enzyme regulates neuroprotective and neuroimmunomodulatory functions and can neutralize both inflammation and oxidative stress generated at the cellular level. Furthermore, there is evidence of an association between vitamin D deficiency and predisposition to the development of severe forms of COVID-19, with its possible neurological and neuropsychiatric sequelae: vitamin D has the ability to down-modulate the effects of neuroinflammatory cytokines, among other anti-inflammatory/immunomodulatory effects, thus attenuating harmful consequences of COVID-19. This review critically analyzes current evidence supporting the notion that vitamin D may act as a neuroprotective and neuroreparative agent against the neurological sequelae of COVID-19.

Angiotensin II Type I Receptor (AT1R): The Gate towards COVID-19-Associated Diseases

The binding of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike glycoprotein to its cellular receptor, the angiotensin-converting enzyme 2 (ACE2), causes its downregulation, which subsequently leads to the dysregulation of the renin-angiotensin system (RAS) in favor of the ACE-angiotensin II (Ang II)-angiotensin II type I receptor (AT1R) axis. AT1R has a major role in RAS by being involved in several physiological events including blood pressure control and electrolyte balance. Following SARS-CoV-2 infection, pathogenic episodes generated by the vasoconstriction, proinflammatory, profibrotic, and prooxidative consequences of the Ang II-AT1R axis activation are accompanied by a hyperinflammatory state (cytokine storm) and an acute respiratory distress syndrome (ARDS). AT1R, a member of the G protein-coupled receptor (GPCR) family, modulates Ang II deleterious effects through the activation of multiple downstream signaling pathways, among which are MAP kinases (ERK 1/2, JNK, p38MAPK), receptor tyrosine kinases (PDGF, EGFR, insulin receptor), and nonreceptor tyrosine kinases (Src, JAK/STAT, focal adhesion kinase (FAK)), and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. COVID-19 is well known for generating respiratory symptoms, but because ACE2 is expressed in various body tissues, several extrapulmonary pathologies are also manifested, including neurologic disorders, vasculature and myocardial complications, kidney injury, gastrointestinal symptoms, hepatic injury, hyperglycemia, and dermatologic complications. Therefore, the development of drugs based on RAS blockers, such as angiotensin II receptor blockers (ARBs), that inhibit the damaging axis of the RAS cascade may become one of the most promising approaches for the treatment of COVID-19 in the near future. We herein review the general features of AT1R, with a special focus on the receptor-mediated activation of the different downstream signaling pathways leading to specific cellular responses. In addition, we provide the latest insights into the roles of AT1R in COVID-19 outcomes in different systems of the human body, as well as the role of ARBs as tentative pharmacological agents to treat COVID-19.

Severe Infections Due to Respiratory Viruses

Severe viral infections may result in severe illnesses capable of causing acute respiratory failure that could progress rapidly to acute respiratory distress syndrome (ARDS), related to worse outcomes, especially in individuals with a higher risk of infection, including the elderly and those with comorbidities such as asthma, diabetes mellitus and chronic respiratory or cardiovascular disease. In addition, in cases of severe viral pneumonia, co-infection with bacteria such as Streptococcus pneumoniae and Staphylococcus aureus is related to worse outcomes. Respiratory viruses like influenza, rhinovirus, parainfluenza, adenovirus, metapneumovirus, respiratory syncytial virus, and coronavirus have increasingly been detected. This trend has become more prevalent, especially in critically ill patients, due to the availability and implementation of molecular assays in clinical practice. Respiratory viruses have been diagnosed as a frequent cause of severe pneumonia, including cases of community-acquired pneumonia, hospital-acquired pneumonia, and ventilator-associated pneumonia. In this review, we will discuss the epidemiology, diagnosis, clinical characteristics, management, and prognosis of patients with severe infections due to respiratory viruses, with a focus on influenza viruses, non-influenza viruses, and coronaviruses.

Relationship between Recovery from COVID-19-Induced Smell Loss and General and Oral Health Factors

Background and Objectives: Loss of smell is one of the strongest predictors of coronavirus disease 2019 (COVID-19) and can persist long after other symptoms have resolved. “Long” cases (>28 days) of smell dysfunction present future challenges to medical and dental professionals, as there is a lack of evidence on the causes and any exacerbating or relieving factors. This study aimed to explore the persistence of COVID-19-induced smell loss and association with physical, lifestyle and oral health factors. Materials and Methods: This study was a cross-sectional survey of 235 participants. Recovery of smell was explored, comparing rapid recovery (≤28 days) with prolonged recovery (>28 days). Associative factors included age, sex, illness severity, diet, BMI, vitamin D supplementation, antidepressants, alcohol use, smoking, brushing frequency, flossing, missing teeth, appliances and number of dental restorations. Results: Smell loss showed 87% resolution within 30 days. Prolonged smell loss was significantly associated with older age (mean ± 95%, CI = 31.53 ± 1.36 years for rapid recovery vs. mean ± 95%, CI = 36.0 ± 3 years for prolonged recovery, p = 0.003) and increased self-reported illness severity (mean ± 95%, CI = 4.39 ± 0.27 for rapid recovery vs. 5.01 ± 0.54 for prolonged recovery, p = 0.016). Fisher’s exact test revealed flossing was associated with rapid recovery, with flossers comprising 75% of the rapid-recovery group, compared to 56% in the prolonged-recovery group (odds ratio ± 95%, CI = 2.26 (1.23–4.15), p = 0.01). All other factors were not significantly associated (p > 0.05). Conclusions: Increased age and illness severity were associated with prolonged smell recovery. Use of floss was the only modifiable factor associated with rapid recovery of smell loss. As 87% of cases resolve within 30 days, future studies may benefit from targeted recruitment of individuals experiencing prolonged sense loss. This would increase statistical confidence when declaring no association with the other factors assessed, avoiding type II errors.

Gastrointestinal manifestations and possible mechanisms of COVID-19 in different periods

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, has become a pandemic worldwide. Although COVID-19 mainly affects the respiratory system, gastrointestinal (GI) manifestations have been frequently reported in such cases, even as initial symptoms. There have been several studies on different GI manifestations in patients with mild and severe disease or in remission. In this review article we summarized different GI manifestations of COVID-19 at various disease stages and the possible mechanisms based on published literatures, as well as the significance of GI manifestations in systemic inflammatory injury.

The Nutrition-COVID-19 Interplay: a Review

Purpose of Review

Nutritional status is affected by the COVID-19 pandemic, directly or indirectly. Even with the recent rollout of the coronavirus disease 2019 (COVID-19) vaccines and availability of medicines such as remdesivir, and monoclonal antibodies, host nutritional status is pivotal in the fight against the acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and outcomes. The purpose of this review is to discuss the effects of COVID-19-related lockdown on lifestyle behaviors, and the nutritional consequences, and the direct sequelae of the infection on nutrition including potential nutritional interventions.

Recent Findings

The COVID-19-related lockdown imposed radical changes in lifestyle behaviors with considerable short-term and long-term health and nutritional consequences including weight gain and obesity and increased cardiometabolic risk, consistently linked to worsened prognosis. The extent of the impact was dependent on food insecurity, overall stress and disordered eating, physical inactivity, and exposure to COVID-19-related nutrition information sources. COVID-19 could directly induce inflammatory responses and poor nutrient intake and absorption leading to undernutrition with micronutrient deficiencies, which impairs immune system function with subsequent amplified risk of infection and disease severity. Nutrition interventions through nutrition support, dietary supplementation, and home remedies such as use of zinc, selenium, vitamin D, and omega-3 fatty acids showed the most significant promise to mitigate the course of COVID-19 infection and improve survival rates.

Summary

The nutrition-COVID-19 relationship and related dietary changes mimic a vicious cycle of the double burden of malnutrition, both obesity and undernutrition with micronutrient deficiencies, which promote infection, disease progression, and potential death.

Dysautonomia and Implications for Anosmia in Long COVID-19 Disease

Long COVID-19 patients often reported anosmia as one of the predominant persisting symptoms. Recent findings have shown that anosmia is associated with neurological dysregulations. However, the involvement of the autonomic nervous system (ANS), which can aggregate all the long COVID-19 neurological symptoms, including anosmia, has not received much attention in the literature. Dysautonomia is characterized by the failure of the activities of components in the ANS. Long COVID-19 anosmia fatigue could result from damage to olfactory sensory neurons, leading to an augmentation in the resistance to cerebrospinal fluid outflow by the cribriform plate, and further causing congestion of the glymphatic system with subsequent toxic build-up in the brain. Studies have shown that anosmia was an important neurologic symptom described in long COVID-19 in association with potential COVID-19 neurotropism. SARS-CoV-2 can either travel via peripheral blood vessels causing endothelial dysfunction, triggering coagulation cascade and multiple organ dysfunction, or reach the systemic circulation and take a different route to the blood–brain barrier, damaging the blood–brain barrier and leading to neuroinflammation and neuronal excitotoxicity. SARS-CoV-2 entry via the olfactory epithelium and the increase in the expression of TMPRSS2 with ACE2 facilitates SARS-CoV-2 neurotropism and then dysautonomia in long COVID-19 patients. Due to this effect, patients with anosmia persisting 3 months after COVID-19 diagnosis showed extensive destruction of the olfactory epithelium. Persistent anosmia observed among long COVID-19 patients may be involved by a cascade of effects generated by dysautonomia leading to ACE2 antibodies enhancing a persistent immune activation.

Dysgeusia: A review in the context of COVID-19

Background

Taste disorders in general, and dysgeusia in particular, are relatively common disorders that may be a sign of a more complex acute or chronic medical condition. During the COVID-19 pandemic, taste disorders have found their way into the realm of general as well as specialty dentistry, with significance in screening for patients who potentially may have the virus.

Types of Studies Reviewed

The authors searched electronic databases (PubMed, Embase, Web of Science, Google Scholar) for studies focused on dysgeusia, ageusia, and other taste disorders and their relationship to local and systemic causes.

Results

The authors found pertinent literature explaining the normal physiology of taste sensation, proposals for suggested new tastes, presence of gustatory receptors in remote tissues of the body, and etiology and pathophysiology of taste disorders, in addition to the valuable knowledge gained about gustatory disorders in the context of COVID-19. Along with olfactory disorders, taste disorders are one of the earliest suggestive symptoms of COVID-19 infection.

Conclusions

Gustatory disorders are the result of local or systemic etiology or both. Newer taste sensations, such as calcium and fat tastes, have been discovered, as well as taste receptors that are remote from the oropharyngeal area. Literature published during the COVID-19 pandemic to date reinforces the significance of early detection of potential patients with COVID-19 by means of screening for recent-onset taste disorders.

Practical Implications

Timely screening and identification of potential gustatory disorders are paramount for the dental care practitioner to aid in the early diagnosis of COVID-19 and other serious systemic disorders.

The taste of the pandemic-contemporary review on the current state of research on gustation in coronavirus disease 2019 (COVID-19)

Subjectively perceived impairment of taste is a common and distinct symptom of coronavirus disease 2019 (COVID-19). Large meta-analyses identified this symptom in approximately 50% of cases. However, this high prevalence is not supported by blinded and validated psychophysical gustatory testing, which showed a much lower prevalence in up to 26% of patients. This discrepancy may be due to misinterpretation of impaired retronasal olfaction as gustatory dysfunction. In addition, we hypothesized that COVID-19-associated hyposmia is involved in the decrease of gustatory function, as found for hyposmia of different origin. This indirect mechanism would be based on the central-nervous mutual amplification between the chemical senses, which fails in COVID-19-associated olfactory loss. However, further research is necessary on how severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) may directly impair the gustatory pathway as well as its subjective perception.

Possible Use of Phytochemicals for Recovery from COVID-19-Induced Anosmia and Ageusia

The year 2020 became the year of the outbreak of coronavirus, SARS-CoV-2, which escalated into a worldwide pandemic and continued into 2021. One of the unique symptoms of the SARS-CoV-2 disease, COVID-19, is the loss of chemical senses, i.e., smell and taste. Smell training is one of the methods used in facilitating recovery of the olfactory sense, and it uses essential oils of lemon, rose, clove, and eucalyptus. These essential oils were not selected based on their chemical constituents. Although scientific studies have shown that they improve recovery, there may be better combinations for facilitating recovery. Many phytochemicals have bioactive properties with anti-inflammatory and anti-viral effects. In this review, we describe the chemical compounds with anti- inflammatory and anti-viral effects, and we list the plants that contain these chemical compounds. We expand the review from terpenes to the less volatile flavonoids in order to propose a combination of essential oils and diets that can be used to develop a new taste training method, as there has been no taste training so far. Finally, we discuss the possible use of these in clinical settings.

Therapeutic supplementation with zinc in the management of COVID-19-related diarrhea and ageusia/dysgeusia: mechanisms and clues for a personalized dosage regimen

Zinc supplementation is indicated for diarrhea and taste disorders, which are both features of COVID-19. Nevertheless, this strategy has not been tested for the treatment of these secondary complications in the current pandemic. Through an updated review, a practical appraisal was considered as a means of providing a medical nexus of therapeutic zinc regimens as an adjunct in the management of COVID-19–related diarrhea and ageusia/dysgeusia. While diarrhea and taste disorders are consequences of COVID-19, zinc supplementation is useful for non–COVID-19 patients with these clinical problems. The overwhelming evidence for supplementing with zinc in diarrhea and pneumonia is associated with the treatment of children, while for taste disorders the use of supplementing with zinc is more examined in adults. Whereas COVID-19 is more prevalent in adults, precautions should be exercised not to translate the zinc dosage used for children with diarrhea and taste disorders into the current pandemic. Therapeutic doses of zinc used for adults (∼50–150 mg/day of elemental zinc) could be included in the treatment strategies for COVID-19, but this proposal should be examined through randomized studies.

Pathophysiological relationship between COVID-19 and olfactory dysfunction: A systematic review

Introduction

SARS-CoV-2 is the pathogen of COVID-19. The virus is composed of the spike, membrane and envelope. On physiological smell, odoriferous substances bind to proteins secreted by sustentacular cells in order to be processed by olfactory receptor neurons. Olfactory disorder is one of the main manifestations of COVID-19, however, research is still required to clarify the mechanism involved in SARS-CoV-2 induced anosmia.

Objective

This article aims to analyze current scientific evidence intended to elucidate the pathophysiological relationship between COVID-19 and the cause of olfactory disorders.

Methods

Pubmed, Embase, Scopus and ScienceDirect were used to compose this article. The research was conducted on November 24th, 2020. Original articles with experimental studies in human, animal and in vitro, short communications, viewpoint, published in the English language and between 2019 and 2020 were included, all related to the pathophysiological relationship between olfactory disorders and COVID-19 infection.

Results

Both human cell receptors ACE2 and TMPRSS2 are essential for the SARS-CoV-2 entrance. These receptors are mostly present in the olfactory epithelium cells, therefore, the main hypothesis is that anosmia is caused due to damage to non-neuronal cells which, thereafter, affects the normal olfactory metabolism. Furthermore, magnetic resonance imaging studies exhibit a relationship between a reduction on the neuronal epithelium and the olfactory bulb atrophy. Damage to non-neuronal cells explains the average recovery lasting a few weeks. This injury can be exacerbated by an aggressive immune response, which leads to damage to neuronal cells and stem cells inducing a persistent anosmia. Conductive anosmia is not sufficient to explain most cases of COVID-19 induced anosmia.

Conclusion

Olfactory disorders such as anosmia and hyposmia can be caused by COVID-19, the main mechanism is associated with olfactory epithelium damage, targeting predominantly non-neuronal cells. However, neuronal cells can also be affected, worsening the condition of olfactory loss.

"Mask up to keep it up": Preliminary evidence of the association between erectile dysfunction and COVID-19

Background

Erectile dysfunction (ED), as the hallmark of endothelial dysfunction, could be a short‐ or long‐term complication of COVID‐19. Additionally, being ED a clinical marker and predictor of non‐communicable chronic diseases, particularly cardiovascular, subjects with ED could potentially have a higher risk of contracting COVID‐19.

Objectives

To investigate the prevalence of ED among subjects with a reported diagnosis of COVID‐19 and to measure the association of COVID‐19 and ED.

Materials and methods

We reviewed data from the Sex@COVID online survey (performed between April 7 and May 4, 2020, in Italy) to retrieve a sample of Italian male sexually active subjects with reported SARS‐CoV‐2 infection. A matching sample of COVID‐19‐negative male sexually active subjects was also retrieved using propensity score matching in a 3:1 ratio. The survey used different standardized psychometric tools to measure effects of lockdown and social distancing on the intrapsychic, relational, and sexual health of Italian subjects.

Results

One hundred subjects were included in the analysis (25 COVID‐positive; 75 COVID‐negative). The prevalence of ED, measured with the Sexual Health Inventory for Men, was significantly higher in the COVID+ group (28% vs. 9.33%; p = 0.027). Logistic regression models confirmed a significant effect of COVID‐19 on the development of ED, independently of other variables affecting erectile function, such as psychological status, age, and BMI [OR 5.66, 95% CI: 1.50–24.01]. Likewise, subjects with ED were more likely to have COVID‐19, once corrected for age and BMI [OR 5.27, 95% CI: 1.49–20.09].

Discussion and conclusion

On top of well‐described pathophysiological mechanisms, there is preliminary evidence in a real‐life population of ED as a risk factor of developing COVID‐19 and possibly occurring as a consequence of COVID‐19. Universal vaccination against the COVID‐19 and the personal protective equipment could possibly have the added benefit of preventing sexual dysfunctions.

Microglia Fighting for Neurological and Mental Health: On the Central Nervous System Frontline of COVID-19 Pandemic

Coronavirus disease 2019 (COVID-19) is marked by cardio-respiratory alterations, with increasing reports also indicating neurological and psychiatric symptoms in infected individuals. During COVID-19 pathology, the central nervous system (CNS) is possibly affected by direct severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) invasion, exaggerated systemic inflammatory responses, or hypoxia. Psychosocial stress imposed by the pandemic further affects the CNS of COVID-19 patients, but also the non-infected population, potentially contributing to the emergence or exacerbation of various neurological or mental health disorders. Microglia are central players of the CNS homeostasis maintenance and inflammatory response that exert their crucial functions in coordination with other CNS cells. During homeostatic challenges to the brain parenchyma, microglia modify their density, morphology, and molecular signature, resulting in the adjustment of their functions. In this review, we discuss how microglia may be involved in the neuroprotective and neurotoxic responses against CNS insults deriving from COVID-19. We examine how these responses may explain, at least partially, the neurological and psychiatric manifestations reported in COVID-19 patients and the general population. Furthermore, we consider how microglia might contribute to increased CNS vulnerability in certain groups, such as aged individuals and people with pre-existing conditions.