Post-viral effects of COVID-19 in the olfactory system and their implications

Orchestration of antiviral responses within the infected central nervous system

Many newly emerging and re-emerging viruses have neuroinvasive potential, underscoring viral encephalitis as a global research priority. Upon entry of the virus into the CNS, severe neurological life-threatening conditions may manifest that are associated with high morbidity and mortality. The currently available therapeutic arsenal against viral encephalitis is rather limited, emphasizing the need to better understand the conditions of local antiviral immunity within the infected CNS. In this review, we discuss new insights into the pathophysiology of viral encephalitis, with a focus on myeloid cells and CD8+ T cells, which critically contribute to protection against viral CNS infection. By illuminating the prerequisites of myeloid and T cell activation, discussing new discoveries regarding their transcriptional signatures, and dissecting the mechanisms of their recruitment to sites of viral replication within the CNS, we aim to further delineate the complexity of antiviral responses within the infected CNS. Moreover, we summarize the current knowledge in the field of virus infection and neurodegeneration and discuss the potential links of some neurotropic viruses with certain pathological hallmarks observed in neurodegeneration.

Evaluating the impact of COVID-19 on vertigo and hearing impairment: A post-recovery analysis

The COVID-19 pandemic, caused by the novel coronavirus SARS-CoV-2, has manifested with respiratory symptoms and a spectrum of extra-pulmonary complications. Emerging evidence suggests potential impacts on the auditory and vestibular systems, but the extent and nature of these effects in recovered individuals remain unclear. This study aimed to investigate the prevalence and severity of vertigo and hearing impairment in individuals who have recovered from COVID-19 and to identify potential risk factors associated with these sensory symptoms. A cohort of 250 recovered COVID-19 patients was assessed. Standardized questionnaires, including the Dizziness Handicap Inventory and the Vertigo Symptom Scale, were used to evaluate vertigo. Hearing assessment was conducted using pure-tone audiometry, speech audiometry, tympanometry, and oto-acoustic emissions testing. Logistic regression analysis was performed to assess the association between COVID-19 severity and the occurrence of sensory symptoms, controlling for confounding variables such as age and comorbidities. Of the participants, 10% reported vertigo, varying severity. Hearing assessments revealed that most participants had normal hearing, with an average speech discrimination score of 94.6. Logistic regression analysis indicated a significant association between severe COVID-19 and an increased likelihood of vertigo (OR 2.11, 95% CI 1.02-4.35, P = .043) and hearing impairment (OR 3.29, 95% CI 1.60-6.78, P = .002). This study suggests a significant association between COVID-19 severity and vertigo and hearing impairment prevalence. The findings underscore the importance of sensory symptom assessment in the post-recovery phase of COVID-19, highlighting the need for comprehensive healthcare approaches to manage long-term sequelae.

Persistent COVID-19 parosmia and olfactory loss post olfactory training: randomized clinical trial comparing central and peripheral-acting therapeutics

PURPOSE

Although COVID-19 anosmia is often transient, patients with persistent olfactory dysfunction (pOD) can experience refractory parosmia and diminished smell. This study evaluated four putative therapies for parosmia in patients with chronic COVID-19 olfactory impairment.

METHODS

After screening nasal endoscopy, 85 patients (49 female, 58%) with pOD and treatment-refractory parosmia were randomized to: (1) ultramicronized palmitoylethanolamide and luteolin + olfactory training (OT) (umPEALUT group, n = 17), (2) alpha-lipoic acid + OT (ALA group, n = 21), (3) umPEALUT + ALA + OT (combination group, n = 28), or 4) olfactory training (OT) alone (control group, n = 23). Olfactory function was assessed at baseline (T0) and 6 months (T1) using a parosmia questionnaire and Sniffin' Sticks test of odor threshold, detection, and identification (TDI). Analyses included one-way ANOVA for numeric data and Chi-Square analyses for nominal data on parosmia.

RESULTS

The umPEALUT group had the largest improvement in TDI scores (21.8 ± 9.4 to 29.7 ± 7.5) followed by the combination group (19.6 ± 6.29 to 27.5 ± 2.7), both p < 0.01. The control and ALA groups had no significant change. Patients in the combination and umPEALUT groups had significantly improved TDI scores compared to ALA and control groups (p < 0.001). Rates of parosmia resolution after 6 months were reported at 96% for combination, 65% for control, 53% for umPEALUT and 29% for ALA (p < 0.001). All treatment regimens were well-tolerated.

CONCLUSIONS

umPEALUT and OT, with or without ALA, was associated with improvement in TDI scores and parosmia, whereas OT alone or OT with ALA were associated with little benefit.

High prevalence of long-term olfactory disorders in healthcare workers after COVID-19: A case-control study

BACKGROUND

More than a year after recovering from COVID-19, a large proportion of individuals, many of whom work in the healthcare sector, still report olfactory dysfunctions. However, olfactory dysfunction was common already before the COVID-19 pandemic, making it necessary to also consider the existing baseline prevalence of olfactory dysfunction. To establish the adjusted prevalence of COVID-19 related olfactory dysfunction, we assessed smell function in healthcare workers who had contracted COVID-19 during the first wave of the pandemic using psychophysical testing.

METHODS

Participants were continuously tested for SARS-CoV-2 IgG antibodies since the beginning of the pandemic. To assess the baseline rate of olfactory dysfunction in the population and to control for the possibility of skewed recruitment of individuals with prior olfactory dysfunction, consistent SARS-CoV-2 IgG naïve individuals were tested as a control group.

RESULTS

Fifteen months after contracting COVID-19, 37% of healthcare workers demonstrated a quantitative reduction in their sense of smell, compared to only 20% of the individuals in the control group. Fifty-one percent of COVID-19-recovered individuals reported qualitative symptoms, compared to only 5% in the control group. In a follow-up study 2.6 years after COVID-19 diagnosis, 24% of all tested recovered individuals still experienced parosmia.

CONCLUSIONS

In summary, 65% of healthcare workers experienced parosmia/hyposmia 15 months after contracting COVID-19. When compared to a control group, the prevalence of olfactory dysfunction in the population increased by 41 percentage points. Parosmia symptoms were still lingering two-and-a half years later in 24% of SARS-CoV-2 infected individuals. Given the amount of time between infection and testing, it is possible that the olfactory problems may not be fully reversible in a plurality of individuals.

Persistent Neurological Deficits in Mouse PASC Reveal Antiviral Drug Limitations

Post-Acute Sequelae of COVID-19 (PASC) encompasses persistent neurological symptoms, including olfactory and autonomic dysfunction. Here, we report chronic neurological dysfunction in mice infected with a virulent mouse-adapted SARS-CoV-2 that does not infect the brain. Long after recovery from nasal infection, we observed loss of tyrosine hydroxylase (TH) expression in olfactory bulb glomeruli and neurotransmitter levels in the substantia nigra (SN) persisted. Vulnerability of dopaminergic neurons in these brain areas was accompanied by increased levels of proinflammatory cytokines and neurobehavioral changes. RNAseq analysis unveiled persistent microglia activation, as found in human neurodegenerative diseases. Early treatment with antivirals (nirmatrelvir and molnupiravir) reduced virus titers and lung inflammation but failed to prevent neurological abnormalities, as observed in patients. Together these results show that chronic deficiencies in neuronal function in SARS-CoV-2-infected mice are not directly linked to ongoing olfactory epithelium dysfunction. Rather, they bear similarity with neurodegenerative disease, the vulnerability of which is exacerbated by chronic inflammation.

Traditional Chinese medicine for post-viral olfactory dysfunction: A systematic review

Background

Post-viral olfactory dysfunction (PVOD) is the common symptoms of long COVID, lacking of effective treatments. Traditional Chinese medicine (TCM) is claimed to be effective in treating olfactory dysfunction, but the evidence has not yet been critically appraised. We conducted a systematic review to evaluate the effectiveness and safety of TCM for PVOD.

Methods

We searched eight databases to identified clinical controlled studies about TCM for PVOD. The Cochrane risk of bias tools and GRADE were used to evaluate the quality of evidence. Risk ratio (RR), mean differences (MD), and 95 % confidence interval (CI), were used for effect estimation and RevMan 5.4.1 was used for data analysis.

Results

Six randomized controlled trials (RCTs) (545 participants), two non-randomized controlled trials (non-RCTs) (112 participants), and one retrospective cohort study (30 participants) were included. The overall quality of included studies was low. Acupuncture (n = 8) and acupoint injection (n = 3) were the mainly used TCM therapies. Five RCTs showed a better effect in TCM group. Four trials used acupuncture, and three trials used acupoint injection. The results of two non-RCTs and one cohort study were not statistically significant. Two trials reported mild to moderate adverse events (pain and brief syncope caused by acupuncture or acupoint injection).

Conclusions

Limited evidence focus on acupuncture and acupoint injection for PVOD and suggests that acupuncture and acupoint injection may be effective in improving PVOD. More well-designed trials should focus on acupuncture to confirm the benefit.

Protocol registration

The protocol of this review was registered at PROSPERO: CRD42022366776.

Long-term effects of SARS-CoV-2 infection in patients with and without chemosensory disorders at disease onset: a psychophysical and magnetic resonance imaging exploratory study

A preserved sense of smell and taste allows us to understand many environmental "messages" and results in meaningfully improvements to quality of life. With the COVID-19 pandemic, it became clear how important these senses are for social and nutritional status and catapulted this niche chemosensory research area towards widespread interest. In the current exploratory work, we assessed two groups of post-COVID-19 patients who reported having had (Group 1) or not (Group 2) a smell/taste impairment at the disease onset. The aim was to compare them using validated smell and taste tests as well as with brain magnetic resonance imaging volumetric analysis. Normative data were used for smell scores comparison and a pool of healthy subjects, recruited before the pandemic, served as controls for taste scores. The majority of patients in both groups showed an olfactory impairment, which was more severe in Group 1 (median UPSIT scores: 24.5 Group 1 vs 31.0 Group 2, p = 0.008), particularly among women (p = 0.014). No significant differences emerged comparing taste scores between Group 1 and Group 2, but dysgeusia was only present in Group 1 patients. However, for taste scores, a significant difference was found between Group 1 and controls (p = 0.005). No MRI anatomical abnormalities emerged in any patients while brain volumetric analysis suggested a significant difference among groups for the right caudate nucleus (p = 0.028), although this was not retained following Benjamini-Hochberg correction. This exploratory study could add new information in COVID-19 chemosensory long-lasting impairment and address future investigations on the post-COVID-19 patients' research.

Understanding the olfactory role in post-COVID cognitive and neuropsychiatric manifestations

Introduction

Olfactory dysfunction (OD) is frequent after SARS-CoV-2 infection. The aim of this study was to examine if long-term OD is common in post-COVID condition, and the relationship between olfaction, cognition, neuropsychiatric symptoms, and disease duration in these patients.

Methods

This study included 121 participants with post-COVID condition and 51 healthy controls (HC). A comprehensive neuropsychological and neuropsychiatric assessment was conducted, encompassing various domains, including general cognition, processing speed, verbal fluency, attention, verbal memory, visual memory, visuoconstructive ability, visuospatial ability, abstraction, executive functions, anxious-depressive symptoms, general health perception, fatigue level, sleep quality, and olfaction. Statistical analyses were carried out to understand the relationship of OD with cognition, and its role as moderator variable.

Results

In total, 25% of the post-covid patients had a reduced smell capacity, while only 9.3% of HC presented OD. Post-COVID patients had statistically significantly worse cognitive performance and clinical status than HC. Verbal fluency (AUC = 0.85, p < 0.001), and attention (AUC = 0.82, p < 0.001) were the variables that best discriminate between groups. OD seemed to be a moderator between fatigue and cognition, and between disease duration and attention (β = -0.04; p = 0.014).

Discussion

The study highlights marked cognitive and neuropsychiatric sequelae in individuals post-COVID relative to HC. Olfactory impairment exhibits correlations with both cognitive performance and general health. Olfaction emerges as a potential prognostic marker owing to its moderating influence on disease severity indicators.

Type 2 and Non-type 2 Inflammation in the Upper Airways: Cellular and Molecular Alterations in Olfactory Neuroepithelium Cell Populations

PURPOSE OF REVIEW

Neurogenesis occurring in the olfactory epithelium is critical to continuously replace olfactory neurons to maintain olfactory function, but is impaired during chronic type 2 and non-type 2 inflammation of the upper airways. In this review, we describe the neurobiology of olfaction and the olfactory alterations in chronic rhinosinusitis with nasal polyps (type 2 inflammation) and post-viral acute rhinosinusitis (non-type 2 inflammation), highlighting the role of immune response attenuating olfactory neurogenesis as a possibly mechanism for the loss of smell in these diseases.

RECENT FINDINGS

Several studies have provided relevant insights into the role of basal stem cells as direct participants in the progression of chronic inflammation identifying a functional switch away from a neuro-regenerative phenotype to one contributing to immune defense, a process that induces a deficient replacement of olfactory neurons. The interaction between olfactory stem cells and immune system might critically underlie ongoing loss of smell in type 2 and non-type 2 inflammatory upper airway diseases. In this review, we describe the neurobiology of olfaction and the olfactory alterations in type 2 and non-type 2 inflammatory upper airway diseases, highlighting the role of immune response attenuating olfactory neurogenesis, as a possibly mechanism for the lack of loss of smell recovery.

Brain temperature and free water increases after mild COVID-19 infection

The pathophysiology underlying the post-acute sequelae of COVID-19 remains understudied and poorly understood, particularly in healthy adults with a history of mild infection. Chronic neuroinflammation may underlie these enduring symptoms, but studying neuroinflammatory phenomena in vivo is challenging, especially without a comparable pre-COVID-19 dataset. In this study, we present a unique dataset of 10 otherwise healthy individuals scanned before and after experiencing mild COVID-19. Two emerging MR-based methods were used to map pre- to post-COVID-19 brain temperature and free water changes. Post-COVID-19 brain temperature and free water increases, which are indirect biomarkers of neuroinflammation, were found in structures functionally associated with olfactory, cognitive, and memory processing. The largest pre- to post-COVID brain temperature increase was observed in the left olfactory tubercle (p = 0.007, 95% CI [0.48, 3.01]), with a mean increase of 1.75 °C. Notably, the olfactory tubercle is also the region of the primary olfactory cortex where participants with chronic olfactory dysfunction showed the most pronounced increases as compared to those without lingering olfactory dysfunction (adjusted pFDR = 0.0189, 95% CI [1.42, 5.27]). These preliminary insights suggest a potential link between neuroinflammation and chronic cognitive and olfactory dysfunction following mild COVID-19, although further investigations are needed to improve our understanding of what underlies these phenomena.

Evolution of nasal and olfactory infection characteristics of SARS-CoV-2 variants

SARS-CoV-2 infection of the upper airway and the subsequent immune response are early, critical factors in COVID-19 pathogenesis. By studying infection of human biopsies in vitro and in a hamster model in vivo, we demonstrated a transition in nasal tropism from olfactory to respiratory epithelium as the virus evolved. Analyzing each variant revealed that SARS-CoV-2 WA1 or Delta infect a proportion of olfactory neurons in addition to the primary target sustentacular cells. The Delta variant possessed broader cellular invasion capacity into the submucosa, while Omicron displayed enhanced nasal respiratory infection and longer retention in the sinonasal epithelium. The olfactory neuronal infection by WA1 and the subsequent olfactory bulb transport via axon were more pronounced in younger hosts. In addition, the observed viral clearance delay and phagocytic dysfunction in aged olfactory mucosa were accompanied by a decline of phagocytosis-related genes. Further, robust basal stem cell activation contributed to neuroepithelial regeneration and restored ACE2 expression postinfection. Together, our study characterized the nasal tropism of SARS-CoV-2 strains, immune clearance, and regeneration after infection. The shifting characteristics of viral infection at the airway portal provide insight into the variability of COVID-19 clinical features, particularly long COVID, and may suggest differing strategies for early local intervention.

Proteomic and transcriptomic profiling of brainstem, cerebellum and olfactory tissues in early- and late-phase COVID-19

Neurological symptoms, including cognitive impairment and fatigue, can occur in both the acute infection phase of coronavirus disease 2019 (COVID-19) and at later stages, yet the mechanisms that contribute to this remain unclear. Here we profiled single-nucleus transcriptomes and proteomes of brainstem tissue from deceased individuals at various stages of COVID-19. We detected an inflammatory type I interferon response in acute COVID-19 cases, which resolves in the late disease phase. Integrating single-nucleus RNA sequencing and spatial transcriptomics, we could localize two patterns of reaction to severe systemic inflammation, one neuronal with a direct focus on cranial nerve nuclei and a separate diffuse pattern affecting the whole brainstem. The latter reflects a bystander effect of the respiratory infection that spreads throughout the vascular unit and alters the transcriptional state of mainly oligodendrocytes, microglia and astrocytes, while alterations of the brainstem nuclei could reflect the connection of the immune system and the central nervous system via, for example, the vagus nerve. Our results indicate that even without persistence of severe acute respiratory syndrome coronavirus 2 in the central nervous system, local immune reactions are prevailing, potentially causing functional disturbances that contribute to neurological complications of COVID-19.

Global fungal-host interactome mapping identifies host targets of candidalysin

Candidalysin, a cytolytic peptide toxin secreted by the human fungal pathogen Candida albicans, is critical for fungal pathogenesis. Yet, its intracellular targets have not been extensively mapped. Here, we performed a high-throughput enhanced yeast two-hybrid (HT-eY2H) screen to map the interactome of all eight Ece1 peptides with their direct human protein targets and identified a list of potential interacting proteins, some of which were shared between the peptides. CCNH, a regulatory subunit of the CDK-activating kinase (CAK) complex involved in DNA damage repair, was identified as one of the host targets of candidalysin. Mechanistic studies revealed that candidalysin triggers a significantly increased double-strand DNA breaks (DSBs), as evidenced by the formation of γ-H2AX foci and colocalization of CCNH and γ-H2AX. Importantly, candidalysin binds directly to CCNH to activate CAK to inhibit DNA damage repair pathway. Loss of CCNH alleviates DSBs formation under candidalysin treatment. Depletion of candidalysin-encoding gene fails to induce DSBs and stimulates CCNH upregulation in a murine model of oropharyngeal candidiasis. Collectively, our study reveals that a secreted fungal toxin acts to hijack the canonical DNA damage repair pathway by targeting CCNH and to promote fungal infection.

Effects of the COVID-19 pandemic on the incidence of central precocious puberty; a narrative review

Central precocious puberty (CPP) is the premature activation of the hypothalamus-pituitary-gonadal axis, resulting in the early development of secondary sexual characteristics. CPP classically occurs before the age of 8 years in girls and 9 years in boys. The aetiology of this precocious onset of puberty is governed by complex mechanistic interactions between genetic and environmental factors. The rates of CPP have been documented to have been rising before the COVID-19 pandemic; despite this, the incidence of CPP has increased exponentially since the start of the pandemic. There are multiple theories potentially explaining this change in incidence of CPP over COVID-19. These include the direct effect of SARS-coV-2 infection, increasing body mass index of adolescents over sequential lockdowns, changes in sleep patterns, increased use of electronic devices and levels of stress, and additionally potential earlier detection of signs of CPP by parents and carers. Whilst there is evidence from observational cohorts, case studies and animal models for each of these factors, it is difficult to definitively prove which has had the greatest impact due to the mainly retrospective nature of the human research that has been conducted. Moreover, studies set in diverse settings with varying population make comparison complex. Additionally, each country responded differently to the COVID-19 pandemic and the lockdowns varied between locations, hence the effect of lockdown was not equal or universal. Despite this, similar trends have been identified, with various lifestyle changes that occurred over the pandemic being potentially influential factors on the development of CPP.

A Comprehensive Review of COVID-19-Related Olfactory Deficiency: Unraveling Associations with Neurocognitive Disorders and Magnetic Resonance Imaging Findings

Olfactory dysfunction (OD) is one of the most common symptoms in COVID-19 patients and can impact patients' lives significantly. The aim of this review was to investigate the multifaceted impact of COVID-19 on the olfactory system and to provide an overview of magnetic resonance (MRI) findings and neurocognitive disorders in patients with COVID-19-related OD. Extensive searches were conducted across PubMed, Scopus, and Google Scholar until 5 December 2023. The included articles were 12 observational studies and 1 case report that assess structural changes in olfactory structures, highlighted through MRI, and 10 studies correlating the loss of smell with neurocognitive disorders or mood disorders in COVID-19 patients. MRI findings consistently indicate volumetric abnormalities, altered signal intensity of olfactory bulbs (OBs), and anomalies in the olfactory cortex among COVID-19 patients with persistent OD. The correlation between OD and neurocognitive deficits reveals associations with cognitive impairment, memory deficits, and persistent depressive symptoms. Treatment approaches, including olfactory training and pharmacological interventions, are discussed, emphasizing the need for sustained therapeutic interventions. This review points out several limitations in the current literature while exploring the intricate effects of COVID-19 on OD and its connection to cognitive deficits and mood disorders. The lack of objective olfactory measurements in some studies and potential validity issues in self-reports emphasize the need for cautious interpretation. Our research highlights the critical need for extensive studies with larger samples, proper controls, and objective measurements to deepen our understanding of COVID-19's long-term effects on neurological and olfactory dysfunctions.

Olfactory immune response to SARS-CoV-2

Numerous pathogens can infect the olfactory tract, yet the pandemic caused by SARS-CoV-2 has strongly emphasized the importance of the olfactory mucosa as an immune barrier. Situated in the nasal passages, the olfactory mucosa is directly exposed to the environment to sense airborne odorants; however, this also means it can serve as a direct route of entry from the outside world into the brain. As a result, olfactotropic infections can have serious consequences, including dysfunction of the olfactory system, CNS invasion, dissemination to the lower respiratory tract, and transmission between individuals. Recent research has shown that a distinctive immune response is needed to protect this neuronal and mucosal tissue. A better understanding of innate, adaptive, and structural immune barriers in the olfactory mucosa is needed to develop effective therapeutics and vaccines against olfactotropic microbes such as SARS-CoV-2. Here, we summarize the ramifications of SARS-CoV-2 infection of the olfactory mucosa, review the subsequent immune response, and discuss important areas of future research for olfactory immunity to infectious disease.

Prevalence and Trajectories of Post-COVID-19 Neurological Manifestations: A Systematic Review and Meta-Analysis

INTRODUCTION

The aim of this systematic review and meta-analysis was to evaluate the prevalence of thirteen neurological manifestations in people affected by COVID-19 during the acute phase and at 3, 6, 9 and 12-month follow-up time points.

METHODS

The study protocol was registered with PROSPERO (CRD42022325505). MEDLINE (PubMed), Embase, and the Cochrane Library were used as information sources. Eligible studies included original articles of cohort studies, case-control studies, cross-sectional studies, and case series with ≥5 subjects that reported the prevalence and type of neurological manifestations, with a minimum follow-up of 3 months after the acute phase of COVID-19 disease. Two independent reviewers screened studies from January 1, 2020, to June 16, 2022. The following manifestations were assessed: neuromuscular disorders, encephalopathy/altered mental status/delirium, movement disorders, dysautonomia, cerebrovascular disorders, cognitive impairment/dementia, sleep disorders, seizures, syncope/transient loss of consciousness, fatigue, gait disturbances, anosmia/hyposmia, and headache. The pooled prevalence and their 95% confidence intervals were calculated at the six pre-specified times.

RESULTS

126 of 6,565 screened studies fulfilled the eligibility criteria, accounting for 1,542,300 subjects with COVID-19 disease. Of these, four studies only reported data on neurological conditions other than the 13 selected. The neurological disorders with the highest pooled prevalence estimates (per 100 subjects) during the acute phase of COVID-19 were anosmia/hyposmia, fatigue, headache, encephalopathy, cognitive impairment, and cerebrovascular disease. At 3-month follow-up, the pooled prevalence of fatigue, cognitive impairment, and sleep disorders was still 20% and higher. At six- and 9-month follow-up, there was a tendency for fatigue, cognitive impairment, sleep disorders, anosmia/hyposmia, and headache to further increase in prevalence. At 12-month follow-up, prevalence estimates decreased but remained high for some disorders, such as fatigue and anosmia/hyposmia. Other neurological disorders had a more fluctuating occurrence.

DISCUSSION

Neurological manifestations were prevalent during the acute phase of COVID-19 and over the 1-year follow-up period, with the highest overall prevalence estimates for fatigue, cognitive impairment, sleep disorders, anosmia/hyposmia, and headache. There was a downward trend over time, suggesting that neurological manifestations in the early post-COVID-19 phase may be long-lasting but not permanent. However, especially for the 12-month follow-up time point, more robust data are needed to confirm this trend.

Role of Microglia, Decreased Neurogenesis and Oligodendrocyte Depletion in Long COVID-Mediated Brain Impairments

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the cause of a recent worldwide coronavirus disease-2019 (COVID-19) pandemic. SARS-CoV-2 primarily causes an acute respiratory infection but can progress into significant neurological complications in some. Moreover, patients with severe acute COVID-19 could develop debilitating long-term sequela. Long-COVID is characterized by chronic symptoms that persist months after the initial infection. Common complaints are fatigue, myalgias, depression, anxiety, and "brain fog," or cognitive and memory impairments. A recent study demonstrated that a mild COVID-19 respiratory infection could generate elevated proinflammatory cytokines and chemokines in the cerebral spinal fluid. This commentary discusses findings from this study, demonstrating that even a mild respiratory SARS-CoV-2 infection can cause considerable neuroinflammation with microglial and macrophage reactivity. Such changes could also be gleaned by measuring chemokines and cytokines in the circulating blood. Moreover, neuroinflammation caused by mild SARS-CoV-2 infection can also impair hippocampal neurogenesis, deplete oligodendrocytes, and decrease myelinated axons. All these changes likely contribute to cognitive deficits in long-COVID syndrome. Therefore, strategies capable of restraining neuroinflammation, maintaining better hippocampal neurogenesis, and preserving oligodendrocyte lineage differentiation and maturation may prevent or reduce the incidence of long-COVID after SARS-CoV-2 respiratory infection.

Mechanism and treatment of olfactory dysfunction caused by coronavirus disease 2019

Coronavirus disease 2019 (COVID-19) is an infectious disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Since the start of the pandemic, olfactory dysfunction (OD) has been reported as a common symptom of COVID-19. In some asymptomatic carriers, OD is often the first and even the only symptom. At the same time, persistent OD is also a long-term sequela seen after COVID-19 that can have a serious impact on the quality of life of patients. However, the pathogenesis of post-COVID-19 OD is still unclear, and there is no specific treatment for its patients. The aim of this paper was to review the research on OD caused by SARS-CoV-2 infection and to summarize the mechanism of action, the pathogenesis, and current treatments.

Treatment of COVID-19 olfactory dysfunction with olfactory training, palmitoylethanolamide with luteolin, or combined therapy: a blinded controlled multicenter randomized trial

PURPOSE

Few evidence-based therapies are available for chronic olfactory dysfunction after COVID-19. This study investigated the relative efficacy of olfactory training alone, co-ultramicronized palmitoylethanolamide with luteolin (um-PEA-LUT, an anti-neuroinflammatory supplement) alone, or combined therapy for treating chronic olfactory dysfunction from COVID-19.

METHODS

This double-blinded controlled, placebo-controlled multicenter randomized clinical trial was conducted in 202 patients with persistent COVID-19 olfactory dysfunction of > 6 month duration. After a screening nasal endoscopy, patients were randomized to: (1) olfactory training and placebo; (2) once daily um-PEA-LUT alone; (3) twice daily um-PEA-LUT alone; or (4) combination of once daily um-PEA-LUT with olfactory training. Olfactory testing (Sniffin' Sticks odor identification test) was performed at baseline and at 1, 2, and 3 months. The primary outcome was recovery of over three points on olfactory testing, with outcomes compared at T0, T1, T2 and T3 across groups. Statistical analyses included one-way ANOVA for numeric data and chi-square for nominal data.

RESULTS

All patients completed the study, and there were no adverse events. At 90 days, odor identification scores improved by > 3 points in 89.2% of patients receiving combined therapy vs. 36.8% receiving olfactory training with placebo, 40% receiving twice daily um-PEA-LUT alone, and 41.6% receiving once daily um-PEA-LUT alone (p < 0.00001). Patients receiving treatment with um-PEA-LUT alone demonstrated subclinical improvement (< 3 point odor identification improvement) more often than patients receiving olfactory training with placebo (p < 0.0001.) CONCLUSIONS: Olfactory training plus once daily um-PEA-LUT resulted in greater olfactory recovery than either therapy alone in patients with long-term olfactory function due to COVID-19.

TRIAL REGISTRATION

20112020PGFN on clinicaltrials.gov.

LEVEL OF EVIDENCE

1b (Individual Randomized Clinical Trial).

Olfactory disorders in childhood: A comparative study of olfaction in children with adenoid hyperplasia versus a control group and the postoperative effects of adenoidectomy with respect to olfactory ability

PURPOSE

Hyposmia in childhood is poorly characterized. The "U-Sniff Test", validated for children with anosmia, can be used to objectify olfactory impairment but has not been used to distinguish between hyposmia and normosmia. Therefore, we investigated children with enlarged adenoids with respect to hyposmia, its correlation with adenoid size, and the sensitivity of questionnaires to predict olfactory impairment.

METHODS

In a prospective comparison, olfaction was assessed by "U-Sniff Test" (score 0-12; <8 hyposmia) in 41 children (5-18 years) with adenoid hyperplasia and compared with 196 children without any respiratory affection (control) after exclusion of previous SARS-Cov2-infection from December 2020 to December 2021. ENT-related complaints were collected using a self-designed questionnaire. We were able to include 13 children in a follow-up examination to compare preoperative performance in the "U-Sniff Test" with postoperative outcome after adenoidectomy.

STATISTICS

chi-square-test (p < 0.05), odds-ratio, Spearman's rho, ROC-, cluster analysis.

RESULTS

Severe hyposmia was present in 36.6% of children with adenoid-hyperplasia compared to 3.1% of the control-group. Adenoid-children scored significantly more often between 8 and 10 points (58.5%) than the control (31.6%; p < 0.01). Adenoid size and olfactory performance correlate significantly (r: 0.83; CI -0.89 … -0.72). Hyposmia in the adenoid group is characterized predominately by loss of the odors banana, butter and rose. None of children with hyposmia or parents reported impaired olfactory performance. Postoperatively, olfactory function improved significantly in 85% of cases (p 0.01, SD ± 1.71, Δ3.54points).

CONCLUSION

Questionnaires are insufficient to detect hyposmia in this cohort. In contrast, the "U-Sniff Test" detects even reduced olfactory performance without reaching the cut-off value, which represents the majority of test results in the adenoid group. Therefore, we recommend the classification of moderate hyposmia (8-10 points) to be included for our study population.

Complications of COVID-19 on the Central Nervous System: Mechanisms and Potential Treatment for Easing Long COVID

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) invades human cells by binding to the angiotensin-converting-enzyme-2 (ACE-2) using a spike protein and leads to Coronavirus disease-2019 (COVID-19). COVID-19 primarily causes a respiratory infection that can lead to severe systemic inflammation. It is also common for some patients to develop significant neurological and psychiatric symptoms. The spread of SARS-CoV-2 to the CNS likely occurs through several pathways. Once spread in the CNS, many acute symptoms emerge, and such infections could also transpire into severe neurological complications, including encephalitis or ischemic stroke. After recovery from the acute infection, a significant percentage of patients develop "long COVID," a condition in which several symptoms of COVID-19 persist for prolonged periods. This review aims to discuss acute and chronic neurological problems after SARS-CoV-2 infection. The potential mechanisms by which SARS-CoV-2 enters the CNS and causes neuroinflammation, neuropathological changes observed in post-mortem brains of COVID-19 patients, and cognitive and mood problems in COVID-19 survivors are discussed in the initial part. The later part of the review deliberates the causes of long COVID, approaches for noninvasive tracking of neuroinflammation in long COVID patients, and the potential therapeutic strategies that could ease enduring CNS symptoms observed in long COVID.

Chemosensory Dysfunction 3-Months After COVID-19, Medications and Factors Associated with Complete Recovery

OBJECTIVES

To examine the longitudinal prevalence and recovery of olfactory, gustatory, and oral chemesthetic deficits in a sizable cohort of SARS-CoV-2 infected persons using quantitative testing. To determine whether demographic and clinical factors, mainly the medications used after the COVID-19 diagnosis, influence the test measures.

METHODS

Prospective cohort in a hospital with primary, secondary, tertiary, and quaternary care. Patients with confirmed COVID-19 were tested during the acute infection phase (within 15 days of initial symptom, n = 187) and one (n = 113) and 3 months later (n = 73). The University of Pennsylvania Smell Identification Test, the Global Gustatory Test, and a novel test for chemesthesis were administered at all visits.

RESULTS

During the acute phase, 93% were anosmic or microsmic and 29.4% were hypogeusic. No one was ageusic. A deficit in oral chemesthesis was present in 13.4%. By 3 months, taste and chemesthesis had largely recovered, however, some degree of olfactory dysfunction remained in 54.8%. Remarkably, patients who had been treated with anticoagulants tended to have more olfactory improvement. Recovery was greater in men than in women, but was unrelated to disease severity, smoking behavior, or the use of various medications prior to, or during, COVID-19 infection.

CONCLUSIONS

When using quantitative testing, olfactory disturbances were found in nearly all SARS-CoV-2 infected patients during the acute infection phase. Taste or chemesthetic deficits were low. Olfactory impairment persisted to some degree in over half of the patients at the 3-month follow-up evaluation, being more common in women and less common in those who had been treated earlier with anticoagulants.

LEVEL OF EVIDENCE

3.

Anosmia predicts memory impairment in post-COVID-19 syndrome: results of a neuropsychological cohort study

Recovered COVID-19 patients frequently suffer of cognitive disorders. Several etiopathogenetic mechanisms have been considered for the brain complications in COVID-19 but results are uncertain. Amongst them, an olfactory route to SARS-CoV-2 brain infection might explain cognitive and memory disturbances in post-COVID-19 patients, given the cooccurrence of anosmia and possible underlying limbic involvement. The aims of the study are to investigate cognition of patients with post-COVID-19 syndrome, and to find clinical factors predicting cognitive and memory impairments. 18 patients with post-COVID-19 syndrome underwent neuropsychological assessment and evaluation of clinical parameters. Stepwise regression analysis was used between clinical parameters as factors and cognitive global scores as dependent variables. Since only anosmia predicted memory performances, repeated measures ANOVA of memory scores was conducted between anosmic and non-anosmic patients. We found lack of association between clinical parameters and cognitive performances. Only anosmia was a good predictor for memory performances, with anosmic subjects showing a temporo-mesial amnesic profile. Our study shows novel findings of causal association between transient anosmia during COVID-19 and memory disorders with temporo-mesial dysfunction, probably sharing a common pathophysiological mechanism, and suggesting a possible SARS-CoV 2 infection of the limbic brain via the olfactory route. In contrast to previous studies, cognitive dysfunctions were not associated with respiratory distress, comorbidity, and depression.

Efficacy of Palmitoylethanolamide and Luteolin Association on Post-Covid Olfactory Dysfunction: A Systematic Review and Meta-Analysis of Clinical Studies

Post-Covid Olfactory Dysfunction (PCOD) is characterized by olfactory abnormalities, hyposmia, and anosmia, which are among the most often enduring symptoms in individuals who have recovered from SARS-CoV-2 infection. This disorder has been reported to persist in subsets of patients well after 12 months following infection, significantly affecting their quality of life. Despite the high prevalence of PCOD among patients who suffered from SARS-CoV-2 infection, specific therapeutic strategies are still limited. Among these, emerging evidence seems to indicate the administration of CoUltraPEALut, a combination of micronized Palmitoylethanolamide (PEA), an endogenous fatty acid amide, and Luteolin, a natural antioxidant flavonoid, as a viable therapy, especially when given as an adjuvant to olfactory training. Based on the above, a systematic review and a meta-analysis of the literature were conducted, with the aim of evaluating the efficacy of CoUltraPEALut as an addition to olfactory training (OT), in treating PCOD symptoms. Pubmed (MEDLINE), Embase (OVID), and Web of Science scientific databases were screened from the inception until 31 May 2023, and a total of 407 articles were recovered; only five of these studies (441 total patients between treated and control groups) were included in the systematic review. CoUltraPEALut demonstrated significant efficacy in the overall recovery of the olfactory function, compared to the conventional therapy, suggesting that it could represent a possible future adjuvant treatment for PCOD.

Olfactory Dysfunction following COVID-19 and the Potential Benefits of Olfactory Training

COVID-19 is associated with a common symptom of olfactory dysfunction, which may persist even after the infection is resolved. Olfactory training (OT) has emerged as the most effective intervention for post-viral olfactory dysfunction. OT involves daily exposure of the olfactory system to various odors. The current study aims to explore olfactory dysfunction following COVID-19 and the potential benefits of olfactory training.

METHODS

This is a cross-sectional study conducted among adults aged 18-60 living in Alahssa, Saudi Arabia. An online questionnaire containing an informed consent form and a survey to collect demographic data, vaccination status, level of loss of smell and taste, and the level of awareness about olfactory training (OT) was distributed among all participants who agreed to participate in this study.

RESULTS

The study included 524 participants and presented their baseline characteristics, including age, gender, COVID-19 infection status, and complaints. Most patients were female (66.0%), and 46.2% had previously been infected with COVID-19. About 54.8% of participants reported chemosensory dysfunction, while 286 had olfactory dysfunction. Of those, 29.8% had anosmia, 16.8% had hyposmia, and 8.0% had parosmia. Results suggest that being fully or partially vaccinated may offer some protection against olfactory dysfunction compared to being unvaccinated. Adherence to olfactory training was associated with improvement in the sense of smell.

CONCLUSIONS

The study highlights the importance of awareness and adherence to olfactory training, which may improve the sense of smell in individuals with chemosensory dysfunction. The findings of this study can inform public health policies and interventions aimed at reducing the burden of olfactory dysfunction associated with COVID-19 vaccination.

Feasibility of diffusion-tensor and correlated diffusion imaging for studying white-matter microstructural abnormalities: Application in COVID-19

There has been growing attention on the effect of COVID-19 on white-matter microstructure, especially among those that self-isolated after being infected. There is also immense scientific interest and potential clinical utility to evaluate the sensitivity of single-shell diffusion magnetic resonance imaging (MRI) methods for detecting such effects. In this work, the performances of three single-shell-compatible diffusion MRI modeling methods are compared for detecting the effect of COVID-19, including diffusion-tensor imaging, diffusion-tensor decomposition of orthogonal moments and correlated diffusion imaging. Imaging was performed on self-isolated patients at the study initiation and 3-month follow-up, along with age- and sex-matched controls. We demonstrate through simulations and experimental data that correlated diffusion imaging is associated with far greater sensitivity, being the only one of the three single-shell methods to demonstrate COVID-19-related brain effects. Results suggest less restricted diffusion in the frontal lobe in COVID-19 patients, but also more restricted diffusion in the cerebellar white matter, in agreement with several existing studies highlighting the vulnerability of the cerebellum to COVID-19 infection. These results, taken together with the simulation results, suggest that a significant proportion of COVID-19 related white-matter microstructural pathology manifests as a change in tissue diffusivity. Interestingly, different b-values also confer different sensitivities to the effects. No significant difference was observed in patients at the 3-month follow-up, likely due to the limited size of the follow-up cohort. To summarize, correlated diffusion imaging is shown to be a viable single-shell diffusion analysis approach that allows us to uncover opposing patterns of diffusion changes in the frontal and cerebellar regions of COVID-19 patients, suggesting the two regions react differently to viral infection.

Subjectively intense odor does not affect dream emotions during rapid eye movement sleep

Dreams experienced during rapid eye movement (REM) sleep have emotional features. Intervention methods for dream affectivity have recently garnered interest; we previously demonstrated that negative dreams were induced during REM sleep by exposure to favorable or familiar odors. However, the underlying mechanisms behind this phenomenon remain unclear. Thus, to address this gap, we investigated whether more intense odors could induce negative dreams, as odors tend to be perceived as more intense when they are preferred or familiar. Contrary to our hypothesis, the results of our study indicated that subjective intense odors did not induce negative dreams. We initially anticipated stronger odors to have a greater impact on dream emotionality, as they stimulate the brain more intensely. Notably, during arousal, weak odors tended to evoke a more potent olfactory response, while strong odors tended to produce a weaker response. To investigate whether this difference influenced the effects on dreams, we compared the respiratory activities of the strongly and weakly perceived odor groups; however, no significant differences were observed. Our findings suggest that subjectively perceived strong odors are unlikely to affect dream emotionality and may be processed differently than favorable or familiar odors.

Alzheimer's early detection in post-acute COVID-19 syndrome: a systematic review and expert consensus on preclinical assessments

Introduction

The risk of developing Alzheimer's disease (AD) in older adults increasingly is being discussed in the literature on Post-Acute COVID-19 Syndrome (PACS). Remote digital Assessments for Preclinical AD (RAPAs) are becoming more important in screening for early AD, and should always be available for PACS patients, especially for patients at risk of AD. This systematic review examines the potential for using RAPA to identify impairments in PACS patients, scrutinizes the supporting evidence, and describes the recommendations of experts regarding their use.

Methods

We conducted a thorough search using the PubMed and Embase databases. Systematic reviews (with or without meta-analysis), narrative reviews, and observational studies that assessed patients with PACS on specific RAPAs were included. The RAPAs that were identified looked for impairments in olfactory, eye-tracking, graphical, speech and language, central auditory, or spatial navigation abilities. The recommendations' final grades were determined by evaluating the strength of the evidence and by having a consensus discussion about the results of the Delphi rounds among an international Delphi consensus panel called IMPACT, sponsored by the French National Research Agency. The consensus panel included 11 international experts from France, Switzerland, and Canada.

Results

Based on the available evidence, olfaction is the most long-lasting impairment found in PACS patients. However, while olfaction is the most prevalent impairment, expert consensus statements recommend that AD olfactory screening should not be used on patients with a history of PACS at this point in time. Experts recommend that olfactory screenings can only be recommended once those under study have reported full recovery. This is particularly important for the deployment of the olfactory identification subdimension. The expert assessment that more long-term studies are needed after a period of full recovery, suggests that this consensus statement requires an update in a few years.

Conclusion

Based on available evidence, olfaction could be long-lasting in PACS patients. However, according to expert consensus statements, AD olfactory screening is not recommended for patients with a history of PACS until complete recovery has been confirmed in the literature, particularly for the identification sub-dimension. This consensus statement may require an update in a few years.

Omega-3 Fatty Acid Supplementation for the Treatment of Persistent COVID-Related Olfactory Dysfunction

OBJECTIVE

To evaluate the efficacy of omega-3 fatty acid (O3FA) supplementation in the treatment of COVID-related olfactory dysfunction (OD).

METHODS

Patients with laboratory-confirmed or clinically-suspected COVID-19 infection and new-onset OD from August 2020 to November 2021 were prospectively recruited. Patients with quantitative OD, defined as a brief smell identification test (BSIT) score of 9 or less, were eligible for study inclusion. The experimental group received 2 g of O3FA supplementation, while the control group received an identical placebo to be taken daily for 6 weeks. The primary outcome was a change in BSIT score between the initial and 6-week follow-up tests.

RESULTS

One hundred and seventeen patients were included in the analysis, including 57 patients in the O3FA group and 60 in the placebo group. O3FA group patients demonstrated a mean BSIT improvement of 1.12 ± 1.99 compared to 0.68 ± 1.86 in the placebo group (p = 0.221). Seventy-seven patients, 42 within the O3FA group and 35 in the placebo group, completed a follow-up BSIT survey at an average of 717.8 days from study onset. At long-term follow-up, there was an average BSIT score improvement of 1.72 within the O3FA group compared to 1.76 within the placebo group (p = 0.948).

CONCLUSION

Among patients with persistent COVID-related OD, our study showed no clear evidence of relative short-term or long-term olfactory recovery among patients receiving high doses of O3FA supplementation.

The functional and structural changes in the hippocampus of COVID-19 patients

Since the hippocampus is predominantly susceptible to injuries caused by COVID-19, there are increasing data indicating the likelihood of post-infection memory loss and quickening neurodegenerative disorders, such as Alzheimer's disease. This is due to the fact that the hippocampus has imperative functions in spatial and episodic memory as well as learning. COVID-19 activates microglia in the hippocampus and induces a CNS cytokine storm, leading to loss of hippocampal neurogenesis. The functional and structural changes in the hippocampus of COVID-19 patients can explain neuronal degeneration and reduced neurogenesis in the human hippocampus. This will open a window to explain memory and cognitive dysfunctions in "long COVID" through the resultant loss of hippocampal neurogenesis.

Cognitive and functional connectivity impairment in post-COVID-19 olfactory dysfunction

OBJECTIVES

To explore the neuropsychological profile and the integrity of the olfactory network in patients with COVID-19-related persistent olfactory dysfunction (OD).

METHODS

Patients with persistent COVID-19-related OD underwent olfactory assessment with Sniffin' Sticks and neuropsychological evaluation. Additionally, both patients and a control group underwent brain MRI, including T1-weighted and resting-state functional MRI (rs-fMRI) sequences on a 3 T scanner. Morphometrical properties were evaluated in olfaction-associated regions; the rs-fMRI data were analysed using graph theory at the whole-brain level and within a standard parcellation of the olfactory functional network. All the MR-derived quantities were compared between the two groups and their correlation with clinical scores in patients were explored.

RESULTS

We included 23 patients (mean age 37 ± 14 years, 12 females) with persistent (mean duration 11 ± 5 months, range 2-19 months) COVID-19-related OD (mean score 23.63 ± 5.32/48, hyposmia cut-off: 30.75) and 26 sex- and age-matched healthy controls. Applying population-derived cut-off values, the two cognitive domains mainly impaired were visuospatial memory and executive functions (17 % and 13 % of patients). Brain MRI did not show gross morphological abnormalities. The lateral orbital cortex, hippocampus, and amygdala volumes exhibited a reduction trend in patients, not significant after the correction for multiple comparisons. The olfactory bulb volumes did not differ between patients and controls. Graph analysis of the functional olfactory network showed altered global and local properties in the patients' group (n = 19, 4 excluded due to artifacts) compared to controls. Specifically, we detected a reduction in the global modularity coefficient, positively correlated with hyposmia severity, and an increase of the degree and strength of the right thalamus functional connections, negatively correlated with short-term verbal memory scores.

DISCUSSION

Patients with persistent COVID-19-related OD showed an altered olfactory network connectivity correlated with hyposmia severity and neuropsychological performance. No significant morphological alterations were found in patients compared with controls.

The Roles of Transient Receptor Potential Vanilloid 1 and 4 in Olfactory Regeneration

Olfactory disorders, which are closely related to cognitive deterioration, can be caused by several factors, including infections, such as COVID-19; aging; and environmental chemicals. Injured olfactory receptor neurons (ORNs) regenerate after birth, but it is unclear which receptors and sensors are involved in ORN regeneration. Recently, there has been great focus on the involvement of transient receptor potential vanilloid (TRPV) channels, which are nociceptors expressed on sensory nerves during the healing of damaged tissues. The localization of TRPV in the olfactory nervous system has been reported in the past, but its function there are unclear. Here, we investigated how TRPV1 and TRPV4 channels are involved in ORN regeneration. TRPV1 knockout (KO), TRPV4 KO, and wild-type (WT) mice were used to model methimazole-induced olfactory dysfunction. The regeneration of ORNs was evaluated using olfactory behavior, histologic examination, and measurement of growth factors. Both TRPV1 and TRPV4 were found to be expressed in the olfactory epithelium (OE). TRPV1, in particular, existed near ORN axons. TRPV4 was marginally expressed in the basal layer of the OE. The proliferation of ORN progenitor cells was reduced in TRPV1 KO mice, which delayed ORN regeneration and the improvement of olfactory behavior. Postinjury OE thickness improved faster in TRPV4 KO mice than WT mice but without acceleration of ORN maturation. The nerve growth factor and transforming growth factor ß levels in TRPV1 KO mice were similar to those in WT mice, and the transforming growth factor ß level was higher than TRPV4 KO mice. TRPV1 was involved in stimulating the proliferation of progenitor cells. TRPV4 modulated their proliferation and maturation. ORN regeneration was regulated by the interaction between TRPV1 and TRPV4. However, in this study, TRPV4 involvement was limited compared with TRPV1. To our knowledge, this is the first study to demonstrate the involvement of TRPV1 and TRPV4 in OE regeneration.

Prevalence of taste and smell dysfunction in mild and asymptomatic COVID-19 patients during Omicron prevalent period in Shanghai, China: a cross-sectional survey study

OBJECTIVES

COVID-19, which is caused by SARS-CoV-2, is a severe threat to human health and the economy globally. This study aimed to investigate the prevalence of taste and/or smell dysfunction and associated risk factors in mild and asymptomatic patients with Omicron infection in Shanghai, China.DesignThis was a questionnaire-based cross-sectional study.

SETTING

COVID-19 patients at the makeshift hospital in the Shanghai World Expo Exhibition and Convention Centre were recruited from March to April 2022.

PARTICIPANTS

In total, 686 COVID-19-infected patients who were defined as mild or asymptomatic cases according to the diagnostic criteria of New Coronavirus Pneumonia Prevention and Control Programme ninth edition (National Health Commission of China, 2022) were enrolled.

MEASURES

Data to investigate taste and smell loss and to characterise other symptoms were collected by the modified Chemotherapy-induced Taste Alteration Scale and Sino-Nasal Outcome Test-22 questionnaires. The risk factors for the severity of taste/smell dysfunction were analysed by binary logistic regression models.

RESULTS

379 males (379/686, 55.2%) and 307 females (307/686, 44.8%) completed the questionnaires to record recent changes in taste and smell ability. A total of 302 patients (44%) had chemosensory dysfunction with Omicron infection, of which 22.7% (156/686) suffered from both taste and smell dysfunction. In addition, cough (60.2%), expectoration (40.5%), fever (33.2%) and sore throat (32.5%) were common symptoms during Omicron infection. The quality-of-life-related indicators were negatively associated with participants' self-reported taste and smell dysfunction.

CONCLUSIONS

The prevalence of taste or/and smell dysfunction in patients with Omicron infections was 44%. Individuals with chemosensory dysfunction had significantly higher rates of various upper respiratory influenza-like symptoms, xerostomia and bad breath. Moreover, smell dysfunction was a risk factor for the prevalence of taste dysfunction in patients with Omicron infection.

TRIAL REGISTRATION NUMBER

ChiCTR 2200059097.

Proteomic and phosphoproteomic characteristics of the cortex, hippocampus, thalamus, lung, and kidney in COVID-19-infected female K18-hACE2 mice

BACKGROUND

Neurological damage caused by coronavirus disease 2019 (COVID-19) has attracted increasing attention. Recently, through autopsies of patients with COVID-19, the direct identification of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in their central nervous system (CNS) has been reported, indicating that SARS-CoV-2 might directly attack the CNS. The need to prevent COVID-19-induced severe injuries and potential sequelae is urgent, requiring the elucidation of large-scale molecular mechanisms in vivo.

METHODS

In this study, we performed liquid chromatography-mass spectrometry-based proteomic and phosphoproteomic analyses of the cortex, hippocampus, thalamus, lungs, and kidneys of SARS-CoV-2-infected K18-hACE2 female mice. We then performed comprehensive bioinformatic analyses, including differential analyses, functional enrichment, and kinase prediction, to identify key molecules involved in COVID-19.

FINDINGS

We found that the cortex had higher viral loads than did the lungs, and the kidneys did not have SARS-COV-2. After SARS-CoV-2 infection, RIG-I-associated virus recognition, antigen processing and presentation, and complement and coagulation cascades were activated to different degrees in all five organs, especially the lungs. The infected cortex exhibited disorders of multiple organelles and biological processes, including dysregulated spliceosome, ribosome, peroxisome, proteasome, endosome, and mitochondrial oxidative respiratory chain. The hippocampus and thalamus had fewer disorders than did the cortex; however, hyperphosphorylation of Mapt/Tau, which may contribute to neurodegenerative diseases, such as Alzheimer's disease, was found in all three brain regions. Moreover, SARS-CoV-2-induced elevation of human angiotensin-converting enzyme 2 (hACE2) was observed in the lungs and kidneys, but not in the three brain regions. Although the virus was not detected, the kidneys expressed high levels of hACE2 and exhibited obvious functional dysregulation after infection. This indicates that SARS-CoV-2 can cause tissue infections or damage via complicated routes. Thus, the treatment of COVID-19 requires a multipronged approach.

INTERPRETATION

This study provides observations and in vivo datasets for COVID-19-associated proteomic and phosphoproteomic alterations in multiple organs, especially cerebral tissues, of K18-hACE2 mice. In mature drug databases, the differentially expressed proteins and predicted kinases in this study can be used as baits to identify candidate therapeutic drugs for COVID-19. This study can serve as a solid resource for the scientific community. The data in this manuscript will serve as a starting point for future research on COVID-19-associated encephalopathy.

FUNDING

This study was supported by grants from the Chinese Academy of Medical Sciences Innovation Fund for Medical Sciences, the National Natural Science Foundation of China, and the Natural Science Foundation of Beijing.

Positive-strand RNA viruses-a Keystone Symposia report

Positive-strand RNA viruses have been the cause of several recent outbreaks and epidemics, including the Zika virus epidemic in 2015, the SARS outbreak in 2003, and the ongoing SARS-CoV-2 pandemic. On June 18-22, 2022, researchers focusing on positive-strand RNA viruses met for the Keystone Symposium "Positive-Strand RNA Viruses" to share the latest research in molecular and cell biology, virology, immunology, vaccinology, and antiviral drug development. This report presents concise summaries of the scientific discussions at the symposium.

Human Nasal Epithelium Damage as the Probable Mechanism Involved in the Development of Post-COVID-19 Parosmia

Purpose

Since the beginning of the COVID-19 pandemic, understanding the physiopathological mechanisms of its manifestations has been crucial to understand the disease and its implications. As the disease evolved, post-infection complications have arisen such as olfactory dysfunctions including parosmia in which odourants are perceived in a distorted or an unpleasant way.

Methods

In this article, we attempt to clarify these mechanisms and the role of human nasal epithelium in the development of post-COVID-19 parosmia.

Results

The mechanisms by which SARS-CoV-2 generates olfactory dysfunction have not been elucidated, and multiple theories have been proposed pointing to the sustentacular cells of the olfactory epithelium as the main probable target of the virus.

Conclusion

Establishing the main physiopathological mechanism of post-COVID-19 parosmia will set a path for further investigations and determine treatment and preventive options for patients who have been reported to be extensively affected in multiple aspects of their lives such as eating habits and mental health.

Association between olfactory dysfunction and mood disturbances with objective and subjective cognitive deficits in long-COVID

Background and purpose

The coronavirus disease 2019 (COVID-19) has been associated with olfactory dysfunction. The persistent symptoms of anosmia or hyposmia were associated in previous studies with the development of memory impairment and mood disturbances. We aimed to investigate the association between the chronicity of reported olfactory dysfunction and subjective and objective cognitive performance in long-COVID patients and to explore whether their emotional symptoms are related to their cognition.

Methods

One hundred twenty-eight long-COVID participants were recruited. Reported symptomatology, subjective memory complaints, anxiety and depression symptomatology, and trait-anxiety were assessed. Subjective memory complaints and mood disturbances were compared among groups of participants with olfactory dysfunction as an acute (AOD), persistent (POD), or nonexistent (NOD) symptom. Seventy-six of the volunteers also participated in a face-to-face session to assess their objective performance on tests of general cognitive function and verbal declarative memory. Objective cognitive performance and mood disturbances were compared among the AOD, POD, and NOD groups.

Results

The subjective memory complaints and the anxiety and depression symptoms were similar among the groups, but the score in general cognitive function was lower in the participants with symptoms of acute olfactory dysfunction than in those with no olfactory symptoms at any time. Participants' memory complaints were positively related to their emotional symptoms. The relationship between depressive symptomatology and memory complaints interacted with the olfactory dysfunction, as it only occurred in the participants without symptoms of olfactory dysfunction. Depressive symptomatology and acute olfactory symptoms were negatively associated with general cognitive function and delayed memory performance. The months elapsed from diagnosis to assessment also predicted delayed memory performance. Anxious symptomatology was negatively associated with the immediate ability to recall verbal information in participants who did not present olfactory dysfunction in the acute phase of the infection.

Conclusion

Olfactory dysfunction in the acute phase of the infection by COVID-19 is related to cognitive deficits in objective tests, and mood disturbances are associated with self-reported and objective memory. These findings may contribute to further understanding the neuropsychological and emotional aspects of long-COVID.

Coronaviruses: Troubling Crown of the Animal Kingdom

The existence of coronaviruses has been known for many years. These viruses cause significant disease that primarily seems to affect agricultural species. Human coronavirus disease due to the 2002 outbreak of Severe Acute Respiratory Syndrome and the 2012 outbreak of Middle East Respiratory Syndrome made headlines; however, these outbreaks were controlled, and public concern quickly faded. This complacency ended in late 2019 when alarms were raised about a mysterious virus responsible for numerous illnesses and deaths in China. As we now know, this novel disease called Coronavirus Disease 2019 (COVID-19) was caused by Severe acute respiratory syndrome-related-coronavirus-2 (SARS-CoV-2) and rapidly became a worldwide pandemic. Luckily, decades of research into animal coronaviruses hastened our understanding of the genetics, structure, transmission, and pathogenesis of these viruses. Coronaviruses infect a wide range of wild and domestic animals, with significant economic impact in several agricultural species. Their large genome, low dependency on host cellular proteins, and frequent recombination allow coronaviruses to successfully cross species barriers and adapt to different hosts including humans. The study of the animal diseases provides an understanding of the virus biology and pathogenesis and has assisted in the rapid development of the SARS-CoV-2 vaccines. Here, we briefly review the classification, origin, etiology, transmission mechanisms, pathogenesis, clinical signs, diagnosis, treatment, and prevention strategies, including available vaccines, for coronaviruses that affect domestic, farm, laboratory, and wild animal species. We also briefly describe the coronaviruses that affect humans. Expanding our knowledge of this complex group of viruses will better prepare us to design strategies to prevent and/or minimize the impact of future coronavirus outbreaks.

Therapeutic options of post-COVID-19 related olfactory dysfunction: a systematic review and meta-analysis

BACKGROUND

Olfactory dysfunction is a typical post-COVID-19 presentation, affecting patients' quality of life. There are currently multiple treatment options in this group of patients such as oral and intranasal corticosteroids, olfactory training, oral vitamin-mineral supplementation, amongst others. This meta-analysis aims to consolidate existing evidence for current therapies in patients with persistent olfactory dysfunction related to COVID-19 infection and evaluate the possible role of corticosteroid add-on therapy in olfactory training.

METHODOLOGY

A systematic review and meta-analysis to study current treatments/interventions for olfactory dysfunction in post-COVID-19 infection were conducted. Data were pooled for the meta-analysis. The outcomes include subjective or objective olfactory assessment major and minor adverse reactions.

RESULTS

Eleven studies (1414 participants) were included in this review, with six studies (916 participants) then assessed for the meta-analysis. Combined treatment of intranasal corticosteroid (INCS) with olfactory training (OT) has no benefit over OT monotherapy from both a VAS score improvement and identification component of Sniffin' Sticks test standpoint. In addition, there were no differences in improvement of TDI score between combined oral corticosteroid (OCS) with OT therapy compared to OT alone. Olfactory function was, however, significantly improved after OT.

CONCLUSION

There were no significant differences in the improvement of olfactory scores in combination INCS+OT or OCS+OT therapies compared to OT monotherapy. However, there is improvement in olfactory function after OT.

European Working Group on SARS-CoV-2: Current Understanding, Unknowns, and Recommendations on the Neurological Complications of COVID-19

The emergence of COVID-19 was rapidly followed by infection and the deaths of millions of people across the globe. With much of the research and scientific advancement rightly focused on reducing the burden of severe and critical acute COVID-19 infection, the long-term effects endured by those who survived the acute infection has been previously overlooked. Now, an appreciation for the post-COVID-19 condition, including its neurological manifestations, is growing, although there remain many unknowns regarding the aetiology and risk factors of the condition, as well as how to effectively diagnose and treat it. Here, drawing upon the experiences and expertise of the clinicians and academics of the European working group on COVID-19, we have reviewed the current literature to provide a comprehensive overview of the neurological sequalae of the post-COVID-19 condition. In this review, we provide a summary of the neurological symptoms associated with the post-COVID-19 condition, before discussing the possible mechanisms which may underly and manifest these symptoms. Following this, we explore the risk factors for developing neurological symptoms as a result of COVID-19 and the post-COVID-19 condition, as well as how COVID-19 infection may itself be a risk factor for the development of neurological disease in the future. Lastly, we evaluate how the post-COVID condition could be accurately diagnosed and effectively treated, including examples of the current guidelines, clinical outcomes and tools that have been developed to aid in this process, as well as addressing the protection provided by COVID-19 vaccines against post-COVID-19 condition. Overall, this review provides a comprehensive overview of the neurological sequalae of the post-COVID-19 condition.

Neurological Manifestations of Long COVID: A Single-Center One-Year Experience

PURPOSE

We report our single-center experience on the neurological manifestations of long COVID.

PATIENTS AND METHODS

This is a retrospective observational study. All consecutive patients referred to the neurological long COVID outpatient clinic of our institute from January 21 2021 to December 9 2021 underwent a general neurological objective examination. Treatments and investigations (brain MRI, neuropsychological evaluation, or others) were prescribed on an individual basis as per standard clinical practice. A follow-up visit was performed when appropriate. Descriptive statistics were presented as absolute and relative frequencies for categorical variables and as means, median, and ranges for continuous variables.

RESULTS

One hundred and three patients were visited (mean age 50.5 ±36 years, 62 females). The average time from acute COVID-19 infection to the first visit to our outpatient clinic was 243 days. Most patients presented with a mild form of acute COVID-19, with only 24 cases requiring hospitalization. The neurological symptoms mostly (n=70/103, 68%) started during the acute phase (before a negative swab for SARS-CoV-2). The most frequent acute manifestations reported, which lately became persistent, were fatigue (n=58/103, 56%), olfactory/taste dysfunction (n=58/103, 56%), headache (n=47/103, 46%), cognitive disorders (n=46/103, 45%), sleep disorders (n=30/103, 29%), sensitivity alterations (n=29/103, 28%), and dizziness (n=7/103, 7%). Tremor was also reported (n=8/103, 7%). Neuropsychological evaluation was performed in 30 patients and revealed alterations in executive functions (n=6/30, 20%), memory (n=11/30, 37%), with pathological depressive (n=9/30, 30%) and anxiety (n=8/30, 27%) scores. Brain MRIs have been performed in 41 cases, revealing nonspecific abnormal findings only in 4 cases. Thirty-six patients underwent a follow-up, where a general improvement was observed but rarely (n=2/36) a complete recovery.

CONCLUSION

The majority of patients presenting persistent neurological symptoms (most frequently fatigue, cognitive disorders, and olfactory dysfunctions) developed a previous mild form of COVID-19. Further studies are required to develop therapeutic strategies.

Olfactory dysfunction: A plausible source of COVID-19-induced neuropsychiatric symptoms

Olfactory dysfunction and neuropsychiatric symptoms are commonly reported by patients of coronavirus disease 2019 (COVID-19), a respiratory infection caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Evidence from recent research suggests linkages between altered or loss of smell and neuropsychiatric symptoms after infection with the coronavirus. Systemic inflammation and ischemic injury are believed to be the major cause of COVID-19-related CNS manifestation. Yet, some evidence suggest a neurotropic property of SARS-CoV-2. This mini-review article summarizes the neural correlates of olfaction and discusses the potential of trans-neuronal transmission of SARS-CoV-2 or its particles within the olfactory connections in the brain. The impact of the dysfunction in the olfactory network on the neuropsychiatric symptoms associated with COVID-19 will also be discussed.

Pathophysiology of SARS-CoV-2 Infection of Nasal Respiratory and Olfactory Epithelia and Its Clinical Impact

PURPOSE OF REVIEW

While the predominant cause for morbidity and mortality with SARS-CoV-2 infection is the lower respiratory tract manifestations of the disease, the effects of SARS-CoV-2 infection on the sinonasal tract have also come to the forefront especially with the increased recognition of olfactory symptom. This review presents a comprehensive summary of the mechanisms of action of the SARS-CoV-2 virus, sinonasal pathophysiology of COVID-19, and the correlation with the clinical and epidemiological impact on olfactory dysfunction.

RECENT FINDINGS

ACE2 and TMPRSS2 receptors are key players in the mechanism of infection of SARS-CoV-2. They are present within both the nasal respiratory as well as olfactory epithelia. There are however differences in susceptibility between different groups of individuals, as well as between the different SARS-CoV-2 variants. The sinonasal cavity is an important route for SARS-CoV-2 infection. While the mechanism of infection of SARS-CoV-2 in nasal respiratory and olfactory epithelia is similar, there exist small but significant differences in the susceptibility of these epithelia and consequently clinical manifestations of the disease. Understanding the differences and nuances in sinonasal pathophysiology in COVID-19 would allow the clinician to predict and counsel patients suffering from COVID-19. Future research into molecular pathways and cytokine responses at different stages of infection and different variants of SARS-CoV-2 would evaluate the individual clinical phenotype, prognosis, and possibly response to vaccines and therapeutics.

Olfactory dysfunction in COVID-19: new insights into the underlying mechanisms

The mechanisms of olfactory dysfunction in COVID-19 are still unclear. In this review, we examine potential mechanisms that may explain why the sense of smell is lost or altered. Among the current hypotheses, the most plausible is that death of infected support cells in the olfactory epithelium causes, besides altered composition of the mucus, retraction of the cilia on olfactory receptor neurons, possibly because of the lack of support cell-derived glucose in the mucus, which powers olfactory signal transduction within the cilia. This mechanism is consistent with the rapid loss of smell with COVID-19, and its rapid recovery after the regeneration of support cells. Host immune responses that cause downregulation of genes involved in olfactory signal transduction occur too late to trigger anosmia, but may contribute to the duration of the olfactory dysfunction.

SARS-CoV-2 infection of sustentacular cells disrupts olfactory signaling pathways

Loss of olfactory function has been commonly reported in SARS-CoV-2 infections. Recovery from anosmia is not well understood. Previous studies showed that sustentacular cells, and occasionally olfactory sensory neurons (OSNs) in the olfactory epithelium (OE), are infected in SARS-CoV-2-infected patients and experimental animals. Here, we show that SARS-CoV-2 infection of sustentacular cells induces inflammation characterized by infiltration of myeloid cells to the olfactory epithelium and variably increased expression of proinflammatory cytokines. We observed widespread damage to, and loss of cilia on, OSNs, accompanied by downregulation of olfactory receptors and signal transduction molecules involved in olfaction. A consequence of OSN dysfunction was a reduction in the number of neurons in the olfactory bulb expressing tyrosine hydroxylase, consistent with reduced synaptic input. Resolution of the infection, inflammation, and olfactory dysfunction occurred over 3-4 weeks following infection in most but not all animals. We also observed similar patterns of OE infection and anosmia/hyposmia in mice infected with other human coronaviruses such as SARS-CoV and MERS-CoV. Together, these results define the downstream effects of sustentacular cell infection and provide insight into olfactory dysfunction in COVID-19-associated anosmia.

Olfactory Training Impacts Olfactory Dysfunction Induced by COVID-19: A Pilot Study

INTRODUCTION

Olfactory dysfunction is one of the main symptoms of COVID-19 and may last beyond resolution of the infection. The most promising intervention for post-viral olfactory dysfunction is olfactory training (OT), which involves exposing the olfactory system to a range of odors daily. This approach is thought of promoting the regeneration of olfactory receptor cells, but its effectiveness in patients with post-COVID-19 olfactory dysfunction has yet to be confirmed.

METHODS

This double-blind randomized pilot study compared the effectiveness of OT versus placebo in the treatment of post-COVID-19 olfactory dysfunction. Twenty-five participants were recruited in each group. OT protocol consisted of sniffing 4 scents (rose, orange, clove, and eucalyptus) for 5 min twice daily for 12 weeks. Olfactory function was assessed before and after the training using (1) a validated odor identification test (UPSIT-40) and (2) a 10-point visual analog scale; we further assessed the presence of (3) parosmia.

RESULTS

While we did not observe any effect of OT on olfactory test scores, we observed a significant improvement of subjective olfactory function in the intervention group, while no such effect was observed in the placebo group. Finally, the frequency of parosmia was significantly lower in the intervention group.

CONCLUSIONS

This study highlights an increase in subjective but not objective olfactory function when performing OT for 12 weeks. Further, parosmia seems to be positively affected by OT. These results may serve as a starting point for larger scale studies to assess the efficacy of OT for treatment of post-COVID-19 olfactory dysfunction.

Anosmia in COVID-19 could be associated with long-term deficits in the consolidation of procedural and verbal declarative memories

Background and purpose

Long-COVID describes the long-term effects of the coronavirus disease 2019 (COVID-19). In long-COVID patients, neuropsychological alterations are frequently reported symptoms. Research points to medial temporal lobe dysfunction and its association with anosmia in long-COVID patients. This study aims to investigate the acquisition and consolidation of declarative and procedural memory in long-COVID patients and to explore whether anosmia is related to these dissociated memory functions.

Methods

Forty-two long-COVID participants and 30 controls (C) were recruited. The sample of long-COVID patients was divided into two groups based on the presence or absence of anosmia, group A and group NA, respectively. Objective performance in verbal declarative memory (Paired-Associate Learning, PAL), procedural memory (Mirror Tracing Test, MTT), general cognitive function (Montreal Cognitive Assessment scale), psychomotor speed, and incidental learning (Digit Symbol Substitution Test) were assessed and compared among the A, NA, and C groups. Long-term retention of PAL and MTT were assessed 24 h after acquisition.

Results

Lower scores in general cognition, psychomotor speed, and sustained attention were found in A and NA compared with C. However, incidental learning, both cue-guided and free-recalled, was diminished in group A compared with C, with no differences with group NA. General cognition and incidental learning were related to declarative memory function exclusively in long-COVID groups. Long-COVID groups presented lower long-term retention of verbal declarative memory than controls in recall tests but no differences in recognition tests. No group differences were found in the acquisition of procedural memory. However, long-term retention of this memory was worse in group A as compared to the NA and C groups, respectively, when errors and time of execution were considered.

Conclusion

Findings support that consolidation of both procedural and declarative memories is more affected than the acquisition of these memories in long-COVID patients, who are also more vulnerable to deficits in delayed recall than in recognition of declarative memories. Deficits in the consolidation of procedural memory and immediate recall of declarative information are especially relevant in long-COVID participants with anosmia. This indicates that anosmia in COVID-19 could be associated with a long-term dysfunction of the limbic system.