Massive transient damage of the olfactory epithelium associated with infection of sustentacular cells by SARS-CoV-2 in golden Syrian hamsters

Post-COVID-19 Impairment of the Senses of Smell, Taste, Hearing, and Balance

Background: Various symptoms have been associated with COVID-19, but little is known about the impacts of COVID-19 on the sensory system, risk factors, and the duration of symptoms. This study assesses olfactory, gustatory, hearing, and vestibular systems after COVID-19. Methods: This cross-sectional, single-center study involved 50 patients one to six months after COVID-19 and reports their patient records and the extent, onset, and duration of olfactory, gustatory, hearing, and balance disorders using questionnaires during and after COVID-19. Sensory symptoms were objectively studied using the following clinical tests after COVID-19 Sniffin’ Sticks, taste tests, tone/speech audiometry, and video head impulse test. Results: Post-COVID-19-patients were suffering from olfactory and gustatory impairment for up to six months. According to the Dizziness Handicap Inventory, balance disorders were less noticed: Overall, about 40% of the patients during COVID-19 and nearly all patients recovered within six months. After COVID-19, clinical tests revealed that 75% were suffering from hyposomnia/anosmia, and 20% of all patients reported mild hypogeusia for up to six months. Vestibular disorders and hearing impairment rarely/did not occur. Females were significantly more affected by sensory impairments than males. Conclusions: COVID-19 particularly caused olfactory and gustatory impairment; balance disorders were present too; vestibular and auditory symptoms were negligible.

Kampo Medicine Promotes Early Recovery From Coronavirus Disease 2019-Related Olfactory Dysfunction: A Retrospective Observational Study

Background: Olfactory dysfunction is a common symptom in patients with coronavirus disease 2019, and it significantly deteriorates patients’ quality of life. Effective treatments remain unknown.

Purpose: To assess the effect of Japanese traditional (Kampo) medicine on coronavirus disease 2019-related olfactory dysfunction.

Study Design: Retrospective observational study.

Methods: In total, 87 patients aged ≥18 years with coronavirus disease 2019 and severe dysosmia or anosmia (Numeric Rating Scale, ≥7) at isolation facilities in Miyagi Prefecture, Japan, were enrolled from October 2020 to March 2021. Patients were divided into the Kampo group (N = 52) and the control group (N = 35) based on the treatment received. Changes in Numeric Rating Scale scores were evaluated at the first visit and 2 weeks after.

Results: The median reduction in the olfactory dysfunction score at both 1 and 2 weeks after the first visit was significantly greater in the Kampo group (6 and 8, respectively; p = 0.03) than in the control group (3 and 7, respectively; p = 0.04). We defined improvement in olfactory dysfunction as a median reduction in the olfactory dysfunction score of ≥5. Multiple logistic regression analysis demonstrated that only Kampo treatment was significantly associated with improvement in olfactory dysfunction.

Conclusion: This study suggests that Kampo medication promotes early recovery from coronavirus disease 2019-related olfactory dysfunction.

Persistent post-COVID-19 smell loss is associated with inflammatory infiltration and altered olfactory epithelial gene expression

Most human subjects infected by SARS-CoV-2 report an acute alteration in their sense of smell, and more than 25% of COVID patients report lasting olfactory dysfunction. While animal studies and human autopsy tissues have suggested mechanisms underlying acute loss of smell, the pathophysiology that underlies persistent smell loss remains unclear. Here we combine objective measurements of smell loss in patients suffering from post-acute sequelae of SARS-CoV-2 infection (PASC) with single cell sequencing and histology of the olfactory epithelium (OE). This approach reveals that the OE of patients with persistent smell loss harbors a diffuse infiltrate of T cells expressing interferon-gamma; gene expression in sustentacular cells appears to reflect a response to inflammatory signaling, which is accompanied by a reduction in the number of olfactory sensory neurons relative to support cells. These data identify a persistent epithelial inflammatory process associated with PASC, and suggests mechanisms through which this T cell-mediated inflammation alters the sense of smell.

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 tropism from olfactory to respiratory epithelium as the virus evolved. Analyzing each variants revealed that SARS-CoV-2 WA1 or Delta infects a proportion of olfactory neurons in addition to the primary target sustentacular cells. The Delta variant possesses broader cellular invasion capacity into the submucosa, while Omicron displays longer retention in the sinonasal epithelium. The olfactory neuronal infection by WA1 and the subsequent olfactory bulb transport via axon is more pronounced in younger hosts. In addition, the observed viral clearance delay and phagocytic dysfunction in aged olfactory mucosa is accompanied by a decline of phagocytosis related genes. Furthermore, robust basal stem cell activation contributes to neuroepithelial regeneration and restores ACE2 expression post-infection. Together, our study characterized the nasal tropism of SARS-CoV-2 strains, immune clearance, and regeneration post infection. The shifting characteristics of viral infection at the airway portal provides insight into the variability of COVID-19 clinical features and may suggest differing strategies for early local intervention.

International consensus statement on allergy and rhinology: Olfaction

BACKGROUND

The literature regarding clinical olfaction, olfactory loss, and olfactory dysfunction has expanded rapidly over the past two decades, with an exponential rise in the past year. There is substantial variability in the quality of this literature and a need to consolidate and critically review the evidence. It is with that aim that we have gathered experts from around the world to produce this International Consensus on Allergy and Rhinology: Olfaction (ICAR:O).

METHODS

Using previously described methodology, specific topics were developed relating to olfaction. Each topic was assigned a literature review, evidence-based review, or evidence-based review with recommendations format as dictated by available evidence and scope within the ICAR:O document. Following iterative reviews of each topic, the ICAR:O document was integrated and reviewed by all authors for final consensus.

RESULTS

The ICAR:O document reviews nearly 100 separate topics within the realm of olfaction, including diagnosis, epidemiology, disease burden, diagnosis, testing, etiology, treatment, and associated pathologies.

CONCLUSION

This critical review of the existing clinical olfaction literature provides much needed insight and clarity into the evaluation, diagnosis, and treatment of patients with olfactory dysfunction, while also clearly delineating gaps in our knowledge and evidence base that we should investigate further.

Possible Mechanisms Underlying Neurological Post-COVID Symptoms and Neurofeedback as a Potential Therapy

Theoretical considerations related to neurological post-COVID complications have become a serious issue in the COVID pandemic. We propose 3 theoretical hypotheses related to neurological post-COVID complications. First, pathophysiological processes responsible for long-term neurological complications caused by COVID-19 might have 2 phases: (1) Phase of acute Sars-CoV-2 infection linked with the pathogenesis responsible for the onset of COVID-19-related neurological complications and (2) the phase of post-acute Sars-CoV-2 infection linked with the pathogenesis responsible for long-lasting persistence of post-COVID neurological problems and/or exacerbation of another neurological pathologies. Second, post-COVID symptoms can be described and investigated from the perspective of dynamical system theory exploiting its fundamental concepts such as system parameters, attractors and criticality. Thirdly, neurofeedback may represent a promising therapy for neurological post-COVID complications. Based on the current knowledge related to neurofeedback and what is already known about neurological complications linked to acute COVID-19 and post-acute COVID-19 conditions, we propose that neurofeedback modalities, such as functional magnetic resonance-based neurofeedback, quantitative EEG-based neurofeedback, Othmer's method of rewarding individual optimal EEG frequency and heart rate variability-based biofeedback, represent a potential therapy for improvement of post-COVID symptoms.

Pathogenesis of Olfactory Disorders in COVID-19

Since the outbreak of the SARS-CoV-2 pandemic, olfactory disorders have been reported as a frequent symptom of COVID-19; however, its pathogenesis is still debated. The aim of this review is to summarize the current understanding of the pathogenesis of smell impairment in the course of COVID-19 and to highlight potential avenues for future research on this issue. Several theories have been proposed to explain the pathogenesis of COVID-19-related anosmia, including nasal obstruction and rhinorrhea, oedema of the olfactory cleft mucosa, olfactory epithelial damage either within the olfactory receptor cells or the supporting non-neural cells (either direct or immune-mediated), damage to the olfactory bulb, and impairment of the central olfactory pathways. Although the pathogenesis of COVID-19-related anosmia is still not fully elucidated, it appears to be mainly due to sensorineural damage, with infection of the olfactory epithelium support cells via the ACE1 receptor and disruption of the OE caused by immense inflammatory reaction, and possibly with direct olfactory sensory neurons infection mediated by the NRP-1 receptor. Involvement of the higher olfactory pathways and a conductive component of olfactory disorders, as well as genetic factors, may also be considered.

Fatal Neurodissemination and SARS-CoV-2 Tropism in K18-hACE2 Mice Is Only Partially Dependent on hACE2 Expression

Animal models recapitulating COVID-19 are critical to enhance our understanding of SARS-CoV-2 pathogenesis. Intranasally inoculated transgenic mice expressing human angiotensin-converting enzyme 2 under the cytokeratin 18 promoter (K18-hACE2) represent a lethal model of SARS-CoV-2 infection. We evaluated the clinical and virological dynamics of SARS-CoV-2 using two intranasal doses (10⁴ and 10⁶ PFUs), with a detailed spatiotemporal pathologic analysis of the 10⁶ dose cohort. Despite generally mild-to-moderate pneumonia, clinical decline resulting in euthanasia or death was commonly associated with hypothermia and viral neurodissemination independent of inoculation dose. Neuroinvasion was first observed at 4 days post-infection, initially restricted to the olfactory bulb suggesting axonal transport via the olfactory neuroepithelium as the earliest portal of entry. Absence of viremia suggests neuroinvasion occurs independently of transport across the blood-brain barrier. SARS-CoV-2 tropism was neither restricted to ACE2-expressing cells (e.g., AT1 pneumocytes), nor inclusive of some ACE2-positive cell lineages (e.g., bronchiolar epithelium and brain vasculature). Absence of detectable ACE2 protein expression in neurons but overexpression in neuroepithelium suggest this as the most likely portal of neuroinvasion, with subsequent ACE2 independent lethal neurodissemination. A paucity of epidemiological data and contradicting evidence for neuroinvasion and neurodissemination in humans call into question the translational relevance of this model.

“Anosmia” the mysterious collateral damage of COVID-19

COVID-19 pandemic spreads worldwide, with more than 100 million positive cases and more than 2 million deaths. From the beginning of the COVID-19 pandemic, several otolaryngologists described many cases of a sudden loss of smell (anosmia) associated with the disease with or without additional symptoms. Anosmia is often the first and sometimes the only sign in the asymptomatic carriers of COVID-19. Still, this disorder is underestimated, and it is not life-threatening. However, it significantly decreases the quality of life. This olfactory dysfunction continues in several cases even after the nasopharyngeal swab was negative. The occurrence of anosmia can be used as a screening tool for COVID-19 patients and can be used to identify these patients to accomplish the isolation and tracking procedures. In this review, we highlighted the possible mechanisms of anosmia in COVID-19 patients, major pathologies and features of anosmia, implications of anosmia in early diagnosis of COVID-19, evaluation of the smell function during COVID-19, and management and treatment options of COVID-19 anosmia.

Histopathology and localization of SARS-CoV-2 and its host cell entry receptor ACE2 in tissues from naturally infected US-farmed mink (Neovison vison)

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes respiratory disease in mink similar to human COVID-19. We characterized the pathological findings in 72 mink from US farms with SARS-CoV-2 outbreaks, localized SARS-CoV-2 and its host cellular receptor angiotensin-converting enzyme 2 (ACE2) in mink respiratory tissues, and evaluated the utility of various test methods and specimens for SARS-CoV-2 detection in necropsy tissues. Of SARS-CoV-2-positive animals found dead, 74% had bronchiolitis and diffuse alveolar damage (DAD). Of euthanized SARS-CoV-2-positive animals, 72% had only mild interstitial pneumonia or minimal nonspecific lung changes (congestion, edema, macrophages); similar findings were seen in SARS-CoV-2-negative animals. Suppurative rhinitis, lymphocytic perivascular inflammation in the lungs, and lymphocytic infiltrates in other tissues were common in both SARS-CoV-2-positive and SARS-CoV-2-negative animals. In formalin-fixed paraffin-embedded (FFPE) upper respiratory tract (URT) specimens, conventional reverse transcription-polymerase chain reaction (cRT-PCR) was more sensitive than in situ hybridization (ISH) or immunohistochemistry (IHC) for detection of SARS-CoV-2. FFPE lung specimens yielded less detection of virus than FFPE URT specimens by all test methods. By IHC and ISH, virus localized extensively to epithelial cells in the nasal turbinates, and prominently within intact epithelium; olfactory mucosa was mostly spared. The SARS-CoV-2 receptor ACE2 was extensively detected by IHC within turbinate epithelium, with decreased detection in lower respiratory tract epithelium and alveolar macrophages. This study expands on the knowledge of the pathology and pathogenesis of natural SARS-CoV-2 infection in mink and supports their further investigation as a potential animal model of SARS-CoV-2 infection in humans.

Long-Term Subjective and Objective Assessment of Smell and Taste in COVID-19

Among the first clinical symptoms of the SARS-CoV-2 infection is olfactory−gustatory deficit; this continues for weeks and, in some cases, can be persistent. We prospectively evaluated 162 patients affected by COVID-19 using a visual analogue scale (VAS) for nasal and olfactory−gustatory symptoms. Patients were checked after 7, 14, 21, 28, 90, and 180 days. A total of 118 patients (72.8%) reported an olfactory VAS < 7 at baseline (group B), and 44 (27.2%) reported anosmia (VAS ≥ 7) (group A) and underwent the Brief Smell Identification Test (B-SIT) and Burghart Taste Strips (BTS) to quantify the deficit objectively and repeated the tests to confirm the sense recovery. Group A patients showed B-SIT anosmia and hyposmia in 44.2% and 55.8% of cases, respectively. A total of 88.6% of group A patients reported ageusia with VAS ≥ 7, and BTS confirmed 81.8% of ageusia and 18.2% of hypogeusia. VAS smell recovery was recorded starting from 14 days, with normalization at 28 days. The 28-day B-SIT score showed normosmia in 90.6% of group A patients. The mean time for full recovery (VAS = 0) was shorter in group B (22.9 days) than in group A (31.9 days). Chemosensory deficit is frequently the first symptom in patients with COVID-19, and, in most cases, recovery occurs after four weeks.

Hamsters Expressing Human Angiotensin-Converting Enzyme 2 Develop Severe Disease following Exposure to SARS-CoV-2

The rapid emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has created a global health emergency. While most human disease is mild to moderate, some infections lead to a severe disease characterized by acute respiratory distress, hypoxia, anosmia, ageusia, and, in some instances, neurological involvement. Small-animal models reproducing severe disease, including neurological sequela, are needed to characterize the pathophysiological mechanism(s) of disease and to identify medical countermeasures. Transgenic mice expressing the human angiotensin-converting enzyme 2 (hACE2) viral receptor under the control of the K18 promoter develop severe and lethal respiratory disease subsequent to SARS-CoV-2 intranasal challenge when high viral doses are used. Here, we report on SARS-CoV-2 infection of hamsters engineered to express the hACE2 receptor under the control of the K18 promoter. K18-hACE2 hamsters infected with a relatively low dose of 100 or 1,000 PFU of SARS-CoV-2 developed a severe and lethal disease, with most animals succumbing by day 5 postinfection. Hamsters developed severe lesions and inflammation within the upper and lower respiratory system, including infection of the nasal cavities causing marked destruction of the olfactory epithelium as well as severe bronchopneumonia that extended deep into the alveoli. Additionally, SARS-CoV-2 infection spread to the central nervous system (CNS), including the brain stem and spinal cord. Wild-type (WT) hamsters naturally support SARS-CoV-2 infection, with the primary lesions present in the respiratory tract and nasal cavity. Overall, infection in the K18-hACE2 hamsters is more extensive than that in WT hamsters, with more CNS involvement and a lethal outcome. These findings demonstrate the K18-hACE2 hamster model will be valuable for studying SARS-CoV-2. IMPORTANCE The rapid emergence of SARS-CoV-2 has created a global health emergency. While most human SARS-CoV-2 disease is mild, some people develop severe, life-threatening disease. Small-animal models mimicking the severe aspects of human disease are needed to more clearly understand the pathophysiological processes driving this progression. Here, we studied SARS-CoV-2 infection in hamsters engineered to express the human angiotensin-converting enzyme 2 viral receptor under the control of the K18 promoter. SARS-CoV-2 produces a severe and lethal infection in transgenic hamsters that mirrors the most severe aspects of COVID-19 in humans, including respiratory and neurological injury. In contrast to other animal systems, hamsters manifest disease with levels of input virus more consistent with natural human infection. This system will be useful for the study of SARS-CoV-2 disease and the development of drugs targeting this virus.

Anosmia (smell failure) and dysgeusia (taste distortion) in COVID-19: it is genetic

The COVID-19 pandemic is a very contagious respiratory illness with has affected millions of individuals worldwide. In addition to the well-known symptoms of any respiratory virus, COVID-19 can present with anosmia (failure to smell) and dysgeusia (distortion of the sense of taste). It appears to be a genetic link to the biological mechanisms underlying COVID-19-related anosmia and dysgeusia. Significant locus in the vicinity of the UGT2A1 and UGT2A2 genes are currently considered as the main culprit of the symptoms. However, more studies are needed to delineate a clear pathophysiology.Communicated by Ramaswamy H. Sarma.

COVID-19: Extensive epithelial damage and ciliary dyskinesia in hospitalised patients

Infection with SARS-CoV-2 can cause severe respiratory disease and it is predicted that the COVID-19 pandemic will leave a substantial number of patients with long-term respiratory complications (1).

COVID-19 related olfactory dysfunction

PURPOSE OF REVIEW

This article reviews the literature on COVID-19 related anosmia, focusing on the epidemiology, pathophysiology recovery rates, current available treatment options, and research regarding novel treatments.

RECENT FINDINGS

Loss of sense of smell is one of the most prevalent symptoms reported by patients after COVID-19 infection. Even though there is a high self-reported recovery rate, recent studies have demonstrated that up to 7% of the patients remain anosmic more than 12 months after onset, leaving millions worldwide with severe olfactory dysfunction. Olfactory training remains the first line recommended treatment. Given the paucity of effective medical treatments options researchers are exploring novel therapeutic options.

SUMMARY

Olfactory dysfunction remains a significant and persistent legacy of the COVID-19 pandemic, but heightened awareness may stimulate research that leads to the development of much-needed treatment options.

The UGT2A1/UGT2A2 locus is associated with COVID-19-related loss of smell or taste

Using online surveys, we collected data regarding COVID-19-related loss of smell or taste from 69,841 individuals. We performed a multi-ancestry genome-wide association study and identified a genome-wide significant locus in the vicinity of the UGT2A1 and UGT2A2 genes. Both genes are expressed in the olfactory epithelium and play a role in metabolizing odorants. These findings provide a genetic link to the biological mechanisms underlying COVID-19-related loss of smell or taste.

Potential role of gut microbiota in patients with COVID-19, its relationship with lung axis, central nervous system (CNS) axis, and improvement with probiotic therapy

Coronavirus Disease 2019 (COVID-19) is a pandemic disease caused by a new corona virus. COVID-19 affects different people in different ways. COVID-19 could affect the gastrointestinal system via gut microbiota impairment. Gut microbiota could affect lung health through a relationship between gut and lung microbiota, which is named gut-lung axis. Gut microbiota impairment plays a role in pathogenesis of various pulmonary disease states, so GI diseases were found to be associated with respiratory diseases. Moreover, most infected people will develop mild to moderate gastrointestinal (GI) symptoms such as diarrhea, vomiting, and stomachache, which is caused by impairment in gut microbiota. Therefore, the current study aimed to review potential role of gut microbiota in patients with COVID-19, its relation with lung axis, Central Nervous System (CNS) axis and improvement with probiotic therapy. Also, this review can be a guide for potential role of gut microbiota in patients with COVID-19.

Administration of aerosolized SARS-CoV-2 to K18-hACE2 mice uncouples respiratory infection from fatal neuroinvasion

The development of a tractable small animal model faithfully reproducing human coronavirus disease 2019 pathogenesis would arguably meet a pressing need in biomedical research. Thus far, most investigators have used transgenic mice expressing the human ACE2 in epithelial cells (K18-hACE2 transgenic mice) that are intranasally instilled with a liquid severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) suspension under deep anesthesia. Unfortunately, this experimental approach results in disproportionate high central nervous system infection leading to fatal encephalitis, which is rarely observed in humans and severely limits this model’s usefulness. Here, we describe the use of an inhalation tower system that allows exposure of unanesthetized mice to aerosolized virus under controlled conditions. Aerosol exposure of K18-hACE2 transgenic mice to SARS-CoV-2 resulted in robust viral replication in the respiratory tract, anosmia, and airway obstruction but did not lead to fatal viral neuroinvasion. When compared with intranasal inoculation, aerosol infection resulted in a more pronounced lung pathology including increased immune infiltration, fibrin deposition, and a transcriptional signature comparable to that observed in SARS-CoV-2–infected patients. This model may prove useful for studies of viral transmission, disease pathogenesis (including long-term consequences of SARS-CoV-2 infection), and therapeutic interventions.

SARS-CoV-2 Psychiatric Sequelae: A Review of Neuroendocrine Mechanisms and Therapeutic Strategies

From the earliest days of the coronavirus disease 2019 (COVID-19) pandemic, there have been reports of significant neurological and psychological symptoms following Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection. This narrative review is designed to examine the potential psychoneuroendocrine pathogenic mechanisms by which SARS-CoV-2 elicits psychiatric sequelae as well as to posit potential pharmacologic strategies to address and reverse these pathologies. Following a brief overview of neurological and psychological sequelae from previous viral pandemics, we address mechanisms by which SARS-CoV-2 could enter or otherwise elicit changes in the CNS. We then examine the hypothesis that COVID-19-induced psychiatric disorders result from challenges to the neuroendocrine system, in particular the hypothalamic-pituitary-adrenal stress axis and monoamine synthesis, physiological mechanisms that are only further enhanced by the pandemic-induced social environment of fear, isolation, and socioeconomic pressure. Finally, we evaluate several FDA-approved therapeutics in the context of COVID-19-induced psychoneuroendocrine disorders.

Recovery of anosmia in hamsters infected with SARS-CoV-2 is correlated with repair of the olfactory epithelium

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is responsible for a pandemic affecting billions of people worldwide. Apart from the extreme global economic impact, the pandemic will likely have a lasting impact through long-term sequelae not yet fully understood. Fully understanding the mechanisms driving the various symptoms and sequelae of SARS-CoV-2 infection will allow for the eventual development of therapeutics to prevent or treat such life-altering symptoms. In this study, we developed a behavioral test of anosmia in SARS-CoV-2-infected hamsters. We find a moderately strong correlation between the level of anosmia and the score of histological damage within the olfactory epithelium. We also find a moderately strong correlation between the level of anosmia and the thickness of the olfactory epithelium, previously demonstrated to be severely damaged upon infection. Thus, this food-searching behavioral test can act as a simple and effective screening method in a hamster model for various therapeutics for SARS-CoV-2-related anosmia.

Increased small particle aerosol transmission of B.1.1.7 compared with SARS-CoV-2 lineage A in vivo

The major transmission route for SARS-CoV-2 is airborne. However, previous studies could not elucidate the contribution between large droplets and aerosol transmission of SARS-CoV-2 and its variants. Here, we designed and validated an optimized transmission caging setup, which allows for the assessment of aerosol transmission efficiency at various distances. At a distance of 2 m, only particles of <5 μm traversed between cages. Using this setup, we investigated the relative efficiency of aerosol transmission between the SARS-CoV-2 Alpha variant (B.1.1.7) and lineage A in Syrian hamsters. Aerosol transmission of both variants was confirmed in all sentinels after 24 h of exposure as demonstrated by respiratory virus shedding and seroconversion. Productive transmission also occurred after 1 h of exposure, highlighting the efficiency of this transmission route. Interestingly, after donors were infected with a mix of both variants, the Alpha variant outcompeted the lineage A variant in an airborne transmission chain. Overall, these data indicate that a lower infectious dose of the Alpha variant, compared to lineage A, could be sufficient for successful transmission. This highlights the continuous need to assess emerging variants and the development for pre-emptive transmission mitigation strategies.

Smell deficits in COVID-19 and possible links with Parkinson's disease

Olfactory impairment is a common symptom in Coronavirus Disease 2019 (COVID-19), the disease caused by Severe Acute Respiratory Syndrome—Coronavirus 2 (SARS-CoV-2) infection. While other viruses, such as influenza viruses, may affect the ability to smell, loss of olfactory function is often smoother and associated to various degrees of nasal symptoms. In COVID-19, smell loss may appear also in absence of other symptoms, frequently with a sudden onset. However, despite great clinical interest in COVID-19 olfactory alterations, very little is known concerning the mechanisms underlying these phenomena. Moreover, olfactory dysfunction is observed in neurological conditions like Parkinson's disease (PD) and can precede motor onset by many years, suggesting that viral infections, like COVID-19, and regional inflammatory responses may trigger defective protein aggregation and subsequent neurodegeneration, potentially linking COVID-19 olfactory impairment to neurodegeneration. In the following chapter, we report the neurobiological and neuropathological underpinnings of olfactory impairments encountered in COVID-19 and discuss the implications of these findings in the context of neurodegenerative disorders, with particular regard to PD and alpha-synuclein pathology.

Immune responses in the injured olfactory and gustatory systems: a role in olfactory receptor neuron and taste bud regeneration?

Sensory cells that specialize in transducing olfactory and gustatory stimuli are renewed throughout life and can regenerate after injury unlike their counterparts in the mammalian retina and auditory epithelium. This uncommon capacity for regeneration offers an opportunity to understand mechanisms that promote the recovery of sensory function after taste and smell loss. Immune responses appear to influence degeneration and later regeneration of olfactory sensory neurons and taste receptor cells. Here we review surgical, chemical, and inflammatory injury models and evidence that immune responses promote or deter chemosensory cell regeneration. Macrophage and neutrophil responses to chemosensory receptor injury have been the most widely studied without consensus on their net effects on regeneration. We discuss possible technical and biological reasons for the discrepancy, such as the difference between peripheral and central structures, and suggest directions for progress in understanding immune regulation of chemosensory regeneration. Our mechanistic understanding of immune-chemosensory cell interactions must be expanded before therapies can be developed for recovering the sensation of taste and smell after head injury from traumatic nerve damage and infection. Chemosensory loss leads to decreased quality of life, depression, nutritional challenges, and exposure to environmental dangers highlighting the need for further studies in this area.

Störungen des Riech- und Schmeckvermögens bei COVID-19

Der Verlust des Riechvermögens ist eines der Symptome, die von Patienten mit COVID-19 mit am häufigsten angegeben werden. Obwohl die Spontanheilungsrate hoch ist, haben neuere Studien gezeigt, dass bis zu 7 % der Patienten mehr als zwölf Monate nach Beginn der Infektion anosmisch bleiben, sodass weltweit Millionen von Menschen unter schweren Riechstörungen leiden. Riechtraining ist nach wie vor die erste empfohlene Behandlungsform. Angesichts weiterhin fehlender zugelassener medikamentöser Behandlungsmöglichkeiten werden neue therapeutische Optionen erforscht.

Dieser Artikel gibt einen Überblick über den aktuellen Stand der Wissenschaft zu COVID-19-bedingten Riechstörungen, wobei der Schwerpunkt auf der Epidemiologie, der Pathophysiologie, den Heilungsraten, den derzeit verfügbaren Behandlungsmöglichkeiten und der Forschung zu neuen Behandlungsmethoden liegt.

Zitierweise: Klimek L, Hagemann J, Döge J, Freudelsperger L, Cuevas M, Klimek F, Hummel T. Olfactory and gustatory disorders in COVID-19. Allergo J Int 2022;31:243-50

https://doi.org/10.1007/s40629-022-00216-7

Animal Models of COVID-19 II. Comparative Immunology

Developing strong animal models is essential for furthering our understanding of how the immune system functions in response to Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection. The alarming speed at which SARS-CoV-2 has spread, and the high mortality rate of severe Coronavirus Disease 2019 (COVID-19), has required both basic science and clinical research to move at an unprecedented pace. Models previously developed to study the immune response against SARS-CoV have been rapidly deployed to now study SARS-CoV-2. To date, both small and large animal models are remarkably consistent when infected with SARS-CoV-2; however, certain models have proven more useful when answering specific immunological questions than others. Small animal models, such as Syrian hamsters, ferrets, and mice carrying the hACE2 transgene, appear to reliably recapitulate the initial cytokine surge seen in COVID-19 as well as show significant innate and adaptive cell infiltration in to the lung early in infection. Additionally, these models develop strong antibody responses to the virus, are protected from reinfection, and genetically modified versions exist that can be used to ask specific immunological questions. Large animal models such as rhesus and cynomologus macaques and African green monkeys are critical to understanding how the immune system responds to SARS-CoV-2 infection because they are considered to be the most similar to humans. These models are considered the gold standard for assessing vaccine efficacy and protection, and recapitulate the initial cytokine surge, immune cell infiltration into the lung, certain aspects of thrombosis, and the antibody and T-cell response to the virus. In this review, we discuss both small and large animal model studies previously used in SARS-CoV-2 research that may be useful in elucidating the immunological contributions to hallmark syndromes observed with COVID-19.

Potential pharmacologic treatments for COVID-19 smell and taste loss: A comprehensive review

The acute loss of taste and smell following COVID-19 are hallmark symptoms that affect 20-85% of patients. However, the pathophysiology and potential treatments of COVID-19 smell and taste loss are not fully understood. We searched the literature to review the potential pathologic pathways and treatment options for COVID-19 smell and taste loss. The interaction of novel coronavirus with ACE-2 receptors expressed on sustentacular cells and taste buds results in direct damage to the olfactory and gustatory systems. Also, the invasion of the virus to the olfactory neurons and consequent local inflammation are other proposed mechanisms. Therefore, COVID-19 patients with smell or taste loss may benefit from neuroprotective, anti-inflammatory, or depolarizing agents. Based on the current evidence, phosphodiesterase inhibitors, insulin, and corticosteroids can be promising for the management of COVID-19 smell and taste loss. This review provided crucial information for treating COVID-19-related smell and/or taste loss, urging to perform large clinical trials to find optimum treatment options.

Anosmia in COVID-19: Underlying Mechanisms and Assessment of an Olfactory Route to Brain Infection

In recent months it has emerged that the novel coronavirus-responsible for the COVID-19 pandemic-causes reduction of smell and taste in a large fraction of patients. The chemosensory deficits are often the earliest, and sometimes the only signs in otherwise asymptomatic carriers of the SARS-CoV-2 virus. The reasons for the surprisingly early and specific chemosensory dysfunction in COVID-19 are now beginning to be elucidated. In this hypothesis review, we discuss implications of the recent finding that the prevalence of smell and taste dysfunction in COVID-19 patients differs between populations, possibly because of differences in the spike protein of different virus strains or because of differences in the host proteins that enable virus entry, thus modifying infectivity. We review recent progress in defining underlying cellular and molecular mechanisms of the virus-induced anosmia, with a focus on the emerging crucial role of sustentacular cells in the olfactory epithelium. We critically examine the current evidence whether and how the SARS-CoV-2 virus can follow a route from the olfactory epithelium in the nose to the brain to achieve brain infection, and we discuss the prospects for using the smell and taste dysfunctions seen in COVID-19 as an early and rapid diagnostic screening tool.

Animal models for SARS-CoV-2 infection and pathology

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the etiology of coronavirus disease 2019 (COVID-19) pandemic. Current variants including Alpha, Beta, Gamma, Delta, and Lambda increase the capacity of infection and transmission of SARS-CoV-2, which might disable the in-used therapies and vaccines. The COVID-19 has now put an enormous strain on health care system all over the world. Therefore, the development of animal models that can capture characteristics and immune responses observed in COVID-19 patients is urgently needed. Appropriate models could accelerate the testing of therapeutic drugs and vaccines against SARS-CoV-2. In this review, we aim to summarize the current animal models for SARS-CoV-2 infection, including mice, hamsters, nonhuman primates, and ferrets, and discuss the details of transmission, pathology, and immunology induced by SARS-CoV-2 in these animal models. We hope this could throw light to the increased usefulness in fundamental studies of COVID-19 and the preclinical analysis of vaccines and therapeutic agents.

Global prevalence of persistent neuromuscular symptoms and the possible pathomechanisms in COVID-19 recovered individuals: A systematic review and meta-analysis

This study was conducted to determine the prevalence of prolonged neuromuscular symptoms, including fatigue, anosmia, headache, myalgia, and joint pain in COVID-19 survivors hospitalized with mild, moderate, or severe infections worldwide. The search was conducted up to January 30th, 2021 using three databases (PubMed, Scopus, and Web of Science) to identify potentially eligible studies. Data on study characteristics, follow-up characteristics, and severity of COVID-19 during hospitalization were collected in accordance with PRISMA guidelines. The Newcastle-Ottawa scale was used to assess the quality of relevant articles. The estimated prevalence of specific prolonged neuromuscular symptoms and the association between COVID-19 severity and occurrence of prolonged neuromuscular symptoms was analyzed wherever appropriate. Database search yielded 4,050 articles and 22 articles were included for meta-analysis. The estimated prevalence of prolonged fatigue was recorded in 21.2% (95%CI: 11.9%- 34.8%) of 3,730 COVID-19 survivors. Persistent anosmia was recorded in 239 of 2,600 COVID-19 survivors (9.7%, 95%CI: 6.1%-15.2%). In 84 out of 2,412 COVID-19 survivors (8.9%, 95%CI: 3.2%-22.6%), prolonged headache was observed. A total of 53 out of 1,125 COVID-19 patients (5.6%, 95%CI: 2.1%-14.2%) complained of persistent myalgia even after being discharged from the hospital. The prevalence of prolonged joint pain was in 15.4% (95%CI: 8.2%-27.2%) of subjects. Due to data scarcity on COVID-19 severity and prolonged neuromuscular symptoms, association analysis could not be conducted. Widespread concern regarding long-term impacts of COVID-19 was raised after several studies reported prolonged symptoms in COVID-19 survivors. Numerous theories have been proposed to address this concern; however, as the research on this pandemic is still ongoing, no explanation is definitive yet. Therefore, follow-up studies in COVID-19 survivors after recovery from COVID-19 are warranted to determine the pathogenesis of prolonged symptoms. PROSPERO registration: CRD42021242332.

[Understanding and caring for patients with smelly wounds]

Sudden loss of smell is a very common symptom that can be observed in two-thirds of patients with Covid-19, and may be the only symptom of this disease. A study has demonstrated that 80% of infected patients have sudden loss of smell without nasal obstruction. This suggests that anomalies of the olfactory epithelium are a key element of pathogenesis and local involvement. Management of odor disorders related to Covid-19 is still being debated. Share of experience of the ear, nose and throat team at the University Hospital of Nancy (54).

Influenza viruses and coronaviruses: Knowns, unknowns, and common research challenges

The development of safe and effective vaccines in a record time after the emergence of the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is a remarkable achievement, partly based on the experience gained from multiple viral outbreaks in the past decades. However, the Coronavirus Disease 2019 (COVID-19) crisis also revealed weaknesses in the global pandemic response and large gaps that remain in our knowledge of the biology of coronaviruses (CoVs) and influenza viruses, the 2 major respiratory viruses with pandemic potential. Here, we review current knowns and unknowns of influenza viruses and CoVs, and we highlight common research challenges they pose in 3 areas: the mechanisms of viral emergence and adaptation to humans, the physiological and molecular determinants of disease severity, and the development of control strategies. We outline multidisciplinary approaches and technological innovations that need to be harnessed in order to improve preparedeness to the next pandemic.

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.

Neurological complications and infection mechanism of SARS-COV-2

Currently, SARS-CoV-2 has caused a global pandemic and threatened many lives. Although SARS-CoV-2 mainly causes respiratory diseases, growing data indicate that SARS-CoV-2 can also invade the central nervous system (CNS) and peripheral nervous system (PNS) causing multiple neurological diseases, such as encephalitis, encephalopathy, Guillain-Barré syndrome, meningitis, and skeletal muscular symptoms. Despite the increasing incidences of clinical neurological complications of SARS-CoV-2, the precise neuroinvasion mechanisms of SARS-CoV-2 have not been fully established. In this review, we primarily describe the clinical neurological complications associated with SARS-CoV-2 and discuss the potential mechanisms through which SARS-CoV-2 invades the brain based on the current evidence. Finally, we summarize the experimental models were used to study SARS-CoV-2 neuroinvasion. These data form the basis for studies on the significance of SARS-CoV-2 infection in the brain.

COVID-19 Anosmia: High Prevalence, Plural Neuropathogenic Mechanisms, and Scarce Neurotropism of SARS-CoV-2?

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative pathogen of coronavirus disease 2019 (COVID-19). It is known as a respiratory virus, but SARS-CoV-2 appears equally, or even more, infectious for the olfactory epithelium (OE) than for the respiratory epithelium in the nasal cavity. In light of the small area of the OE relative to the respiratory epithelium, the high prevalence of olfactory dysfunctions (ODs) in COVID-19 has been bewildering and has attracted much attention. This review aims to first examine the cytological and molecular biological characteristics of the OE, especially the microvillous apical surfaces of sustentacular cells and the abundant SARS-CoV-2 receptor molecules thereof, that may underlie the high susceptibility of this neuroepithelium to SARS-CoV-2 infection and damages. The possibility of SARS-CoV-2 neurotropism, or the lack of it, is then analyzed with regard to the expression of the receptor (angiotensin-converting enzyme 2) or priming protease (transmembrane serine protease 2), and cellular targets of infection. Neuropathology of COVID-19 in the OE, olfactory bulb, and other related neural structures are also reviewed. Toward the end, we present our perspectives regarding possible mechanisms of SARS-CoV-2 neuropathogenesis and ODs, in the absence of substantial viral infection of neurons. Plausible causes for persistent ODs in some COVID-19 convalescents are also examined.

COVID-19 induces neuroinflammation and loss of hippocampal neurogenesis

Infection with the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is associated with onset of neurological and psychiatric symptoms during and after the acute phase of illness 1-4 . Acute SARS-CoV-2 disease (COVID-19) presents with deficits of memory, attention, movement coordination, and mood. The mechanisms of these central nervous system symptoms remain largely unknown.In an established hamster model of intranasal infection with SARS-CoV-2 5 , and patients deceased from COVID-19, we report a lack of viral neuroinvasion despite aberrant BBB permeability, microglial activation, and brain expression of interleukin (IL)-1β and IL-6, especially within the hippocampus and the inferior olivary nucleus of the medulla, when compared with non-COVID control hamsters and humans who died from other infections, cardiovascular disease, uremia or trauma. In the hippocampus dentate gyrus of both COVID-19 hamsters and humans, fewer cells expressed doublecortin, a marker of neuroblasts and immature neurons.Despite absence of viral neurotropism, we find SARS-CoV-2-induced inflammation, and hypoxia in humans, affect brain regions essential for fine motor function, learning, memory, and emotional responses, and result in loss of adult hippocampal neurogenesis. Neuroinflammation could affect cognition and behaviour via disruption of brain vasculature integrity, neurotransmission, and neurogenesis, acute effects that may persist in COVID-19 survivors with long-COVID symptoms.

The D614G Virus Mutation Enhances Anosmia in COVID-19 Patients: Evidence from a Systematic Review and Meta-analysis of Studies from South Asia

The prevalence of chemosensory dysfunction in patients with COVID-19 varies greatly between populations. It is unclear whether such differences are due to factors at the level of the human host, or at the level of the coronavirus, or both. At the host level, the entry proteins which allow virus binding and entry have variants with distinct properties, and the frequency of such variants differs between ethnicities. At the level of the virus, the D614G mutation enhances virus entry to the host cell. Since the two virus strains (D614 and G614) coexisted in the first six months of the pandemic in most populations, it has been difficult to distinguish between contributions of the virus and contributions of the host for anosmia. To answer this question, we conducted a systematic review and meta-analysis of studies in South Asian populations when either the D614 or the G614 virus was dominant. We show that populations infected predominantly with the G614 virus had a much higher prevalence of anosmia (pooled prevalence of 31.8%) compared with the same ethnic populations infected mostly with the D614 virus strain (pooled anosmia prevalence of 5.3%). We conclude that the D614G mutation is a major contributing factor that increases the prevalence of anosmia in COVID-19, and that this enhanced effect on olfaction constitutes a previously unrecognized phenotype of the D614G mutation. The new virus strains that have additional mutations on the background of the D614G mutation can be expected to cause a similarly increased prevalence of chemosensory dysfunctions.

Hamster organotypic modeling of SARS-CoV-2 lung and brainstem infection

SARS-CoV-2 has caused a global pandemic of COVID-19 since its emergence in December 2019. The infection causes a severe acute respiratory syndrome and may also spread to central nervous system leading to neurological sequelae. We have developed and characterized two new organotypic cultures from hamster brainstem and lung tissues that offer a unique opportunity to study the early steps of viral infection and screening antivirals. These models are not dedicated to investigate how the virus reaches the brain. However, they allow validating the early tropism of the virus in the lungs and demonstrating that SARS-CoV-2 could infect the brainstem and the cerebellum, mainly by targeting granular neurons. Viral infection induces specific interferon and innate immune responses with patterns specific to each organ, along with cell death by apoptosis, necroptosis, and pyroptosis. Overall, our data illustrate the potential of rapid modeling of complex tissue-level interactions during infection by a newly emerged virus.

Natural and Experimental SARS-CoV-2 Infection in Domestic and Wild Animals

SARS-CoV-2 is the etiological agent responsible for the ongoing COVID-19 pandemic, which continues to spread with devastating effects on global health and socioeconomics. The susceptibility of domestic and wild animal species to infection is a critical facet of SARS-CoV-2 ecology, since reverse zoonotic spillover events resulting in SARS-CoV-2 outbreaks in animal populations could result in the establishment of new virus reservoirs. Adaptive mutations in the virus to new animal species could also complicate ongoing mitigation strategies to combat SARS-CoV-2. In addition, animal species susceptible to SARS-CoV-2 infection are essential as standardized preclinical models for the development and efficacy testing of vaccines and therapeutics. In this review, we summarize the current findings regarding the susceptibility of different domestic and wild animal species to experimental SARS-CoV-2 infection and provide detailed descriptions of the clinical disease and transmissibility in these animals. In addition, we outline the documented natural infections in animals that have occurred at the human-animal interface. A comprehensive understanding of animal susceptibility to SARS-CoV-2 is crucial to inform public health, veterinary, and agricultural systems, and to guide environmental policies.

Olfactory dysfunction in SARS-CoV-2 infection: Focus on odorant specificity and chronic persistence

Background

Smell dysfunction has been recognized as an early symptom of SARS-CoV-2 infection, often occurring before the onset of core symptoms of the respiratory tract, fever or muscle pain. In most cases, olfactory dysfunction is accompanied by reduced sense of taste, is partial (microsmia) and seems to normalize after several weeks, however, especially in cases of virus-induced complete smell loss (anosmia), there are indications of persisting deficits even 2 months after recovery from the acute disease, pointing towards the possibility of chronic or even permanent smell reduction for a significant part of the patient population. To date, we have no knowledge on the specificity of anosmia towards specific odorants or chemicals and about the longer-term timeline of its persistence or reversal.

Methods

In this longitudinal study, 70 participants from a community in Lower Austria that had been tested positive for either IgG or IgM SARS-CoV-2 titers in June 2020 and a healthy control cohort (N = 348) underwent smell testing with a 12-item Cross-Cultural Smell Identification Test (CC-SIT), based upon items from the University of Pennsylvania Smell Identification Test (UPSIT). The test was performed in October 2020, i.e. 4 months after initial diagnosis via antibody testing. Results were analyzed using statistical tests for contingency for each smell individually in order to detect whether reacquisition of smell is dependent on specific odorant types.

Results

For all odorants tested, except the odor “smoke”, even 4 months or more after acute SARS-CoV-2 infection, participants with a positive antibody titer had a reduced sense of smell when compared to the control group. On average, while the control cohort detected a set of 12 different smells with 88.0% accuracy, the antibody-positive group detected 80.0% of tested odorants. A reduction of accuracy of detection by 9.1% in the antibody-positive cohort was detected. Recovery of the ability to smell was particularly delayed for three odorants: strawberry (encoded by the aldehyde ethylmethylphenylglycidate), lemon (encoded by citronellal, a monoterpenoid aldehyde), and soap (alkali metal salts of the fatty acids plus odorous additives) exhibit a sensitivity of detection of an infection with SARS-CoV-2 of 31.0%, 41.0% and 40.0%, respectively.

Conclusion

Four months or more after acute infection, smell performance of SARS-CoV-2 positive patients with mild or no symptoms is not fully recovered, whereby the ability to detect certain odors (strawberry, lemon and soap) is particularly affected, suggesting the possibility that these sensitivity to these smells may not only be lagging behind but may be more permanently affected.

The Microvillar and Solitary Chemosensory Cells as the Novel Targets of Infection of SARS-CoV-2 in Syrian Golden Hamsters

Patients infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019, suffer from respiratory and non-respiratory symptoms. Among these symptoms, the loss of smell has attracted considerable attention. The objectives of this study were to determine which cells are infected, what happens in the olfactory system after viral infection, and how these pathologic changes contribute to olfactory loss. For this purpose, Syrian golden hamsters were used. First, we verified the olfactory structures in the nasal cavity of Syrian golden hamsters, namely the main olfactory epithelium, the vomeronasal organ, and their cellular components. Second, we found angiotensin-converting enzyme 2 expression, a receptor protein of SARS-CoV-2, in both structures and infections of supporting, microvillar, and solitary chemosensory cells. Third, we observed pathological changes in the infected epithelium, including reduced thickness of the mucus layer, detached epithelia, indistinct layers of epithelia, infiltration of inflammatory cells, and apoptotic cells in the overall layers. We concluded that a structurally and functionally altered microenvironment influences olfactory function. We observed the regeneration of the damaged epithelium, and found multilayers of basal cells, indicating that they were activated and proliferating to reconstitute the injured epithelium.

Similar patterns of [18F]-FDG brain PET hypometabolism in paediatric and adult patients with long COVID: a paediatric case series

PURPOSE

Several weeks after COVID-19 infection, some children report the persistence or recurrence of functional complaints. This clinical presentation has been referred as "long COVID" in the adult population, and an [¹⁸F]-FDG brain PET hypometabolic pattern has recently been suggested as a biomarker. Herein, we present a retrospective analysis of 7 paediatric patients with suspected long COVID who were explored by [¹⁸F]-FDG brain PET exam. Metabolic brain findings were confronted to those obtained in adult patients with long COVID, in comparison to their respective age-matched control groups.

METHODS

Review of clinical examination and whole-brain voxel-based analysis of [¹⁸F]-FDG PET metabolism of the 7 children in comparison to 21 paediatric controls, 35 adult patients with long COVID and 44 healthy adult subjects.

RESULTS

Despite lower initial severity at the acute stage of the infection, paediatric patients demonstrated on average 5 months later a similar brain hypometabolic pattern as that found in adult long COVID patients, involving bilateral medial temporal lobes, brainstem and cerebellum (p-voxel < 0.001, p-cluster < 0.05 FWE-corrected), and also the right olfactory gyrus after small volume correction (p-voxel = 0.010 FWE-corrected), with partial PET recovery in two children at follow-up.

CONCLUSION

These results provide arguments in favour of possible long COVID in children, with a similar functional brain involvement to those found in adults, regardless of age and initial severity.

Activation of the trigeminal system as a likely target of SARS-CoV-2 may contribute to anosmia in COVID-19

Clinical publications show consistently that headache is a common symptom in the coronavirus disease of 2019 (COVID-19). Several studies specifically investigated headache symptomatology and associated features in patients with COVID-19. The headache is frequently debilitating with manifold characters including migraine-like characteristics. Studies suggested that COVID-19 patients with headache vs. those without headache are more likely to have anosmia. We present a pathophysiological hypothesis which may explain this phenomenon, discuss current hypotheses about how the coronavirus SARS-CoV-2 enters the central nervous system and suggest that activation of the trigeminal nerve may contribute to both headache and anosmia in COVID-19.

SARS-CoV-2 disease severity and transmission efficiency is increased for airborne compared to fomite exposure in Syrian hamsters

Transmission of SARS-CoV-2 is driven by contact, fomite, and airborne transmission. The relative contribution of different transmission routes remains subject to debate. Here, we show Syrian hamsters are susceptible to SARS-CoV-2 infection through intranasal, aerosol and fomite exposure. Different routes of exposure present with distinct disease manifestations. Intranasal and aerosol inoculation causes severe respiratory pathology, higher virus loads and increased weight loss. In contrast, fomite exposure leads to milder disease manifestation characterized by an anti-inflammatory immune state and delayed shedding pattern. Whereas the overall magnitude of respiratory virus shedding is not linked to disease severity, the onset of shedding is. Early shedding is linked to an increase in disease severity. Airborne transmission is more efficient than fomite transmission and dependent on the direction of the airflow. Carefully characterized SARS-CoV-2 transmission models will be crucial to assess potential changes in transmission and pathogenic potential in the light of the ongoing SARS-CoV-2 evolution.

Increased aerosol transmission for B.1.1.7 (alpha variant) over lineage A variant of SARS-CoV-2

Airborne transmission, a term combining both large droplet and aerosol transmission, is thought to be the main transmission route of SARS-CoV-2. Here we investigated the relative efficiency of aerosol transmission of two variants of SARS-CoV-2, B.1.1.7 (alpha) and lineage A, in the Syrian hamster. A novel transmission caging setup was designed and validated, which allowed the assessment of transmission efficiency at various distances. At 2 meters distance, only particles <5 µm traversed between cages. In this setup, aerosol transmission was confirmed in 8 out of 8 (N = 4 for each variant) sentinels after 24 hours of exposure as demonstrated by respiratory shedding and seroconversion. Successful transmission occurred even when exposure time was limited to one hour, highlighting the efficiency of this transmission route. Interestingly, the B.1.1.7 variant outcompeted the lineage A variant in an airborne transmission chain after mixed infection of donors. Combined, this data indicates that the infectious dose of B.1.1.7 required for successful transmission may be lower than that of lineage A virus. The experimental proof for true aerosol transmission and the increase in the aerosol transmission potential of B.1.1.7 underscore the continuous need for assessment of novel variants and the development or preemptive transmission mitigation strategies.

Recovery From COVID-19-Related Olfactory Disorders and Quality of Life: Insights From an Observational Online Study

Although olfactory disorders (OD) are among the most significant symptoms of COVID-19, recovery time from COVID-19-related OD and their consequences on the quality of life remain poorly documented. We investigated the characteristics and behavioral consequences of COVID-19-related OD using a large-scale study involving 3111 French respondents (78% women) to an online questionnaire over a period of 9 months covering different epidemic waves (from 8 April 2020 to 13 January 2021). In the patients who subjectively recovered from COVID-19-related OD (N = 609), recovery occurred on average after 16 days and most of the time within 1 month ("normal" recovery range); 49 subjectively recovered in 1-2.5 months, and several cases took up to 6.5 months. Among the patients with ongoing OD (N = 2502), 974 were outside the "normal" recovery range (persistent OD) and reported OD for 1-10 months. Developing a persistent OD was more likely with increasing age and in women and was more often associated with parosmia and phantosmia. The deleterious impact of COVID-19-related OD on the quality of life was significantly aggravated by OD duration and was more pronounced in women. Because persistent OD is not infrequent after COVID-19, has deleterious consequences on the quality of life, and receives few solutions from the health practitioners, it would be beneficial to implement screening and treatment programs to minimize the long-term behavioral consequences of COVID-19-related OD.

Olfactory and gustatory dysfunctions in SARS-CoV-2 infection: A systematic review

BACKGROUND

Among Coronavirus Disease 2019 (COVID-19) manifestations, Olfactory (OD) and Gustatory (GD) Dysfunctions (OGD) have drawn considerable attention, becoming a sort of hallmark of the disease. Many have speculated on the pathogenesis and clinical characteristics of these disturbances; however, no definite answers have been produced on the topic. With this systematic review, we aimed to collect all the available evidence regarding the prevalence of OGD, the timing of their onset and their resolution, their rate of recovery and their role as diagnostic and prognostic tools for Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection.

METHODS

A systematic review comprising all the observational studies that reported the prevalence and/or the longitudinal trajectories of OGD in COVID-19 patients, as self-reported by patients or measured through objective psychophysical tests.

RESULTS

After the selection process, 155 studies were included, with a total of 70,920 patients and 105,291 not-infected individuals. Prevalence reports were extremely variable across studies, with wide ranges for OD (0%-98%) and GD (0-89%) prevalence. OGD occurred early during the disease course and only rarely preceded other symptoms; out of 30 studies with a follow-up time of at least 20 days, only in 5 studies OGD fully resolved in more than 90% of patients. OGD had low sensitivity and high specificity for SARS-CoV-2 infection; accuracy of OD and GD for infection identification was higher than 80% in 10 out of 33 studies and in 8 out of 22 studies considered, respectively. 28 out of 30 studies that studied the association between OGD and disease severity found how OGD were associated with lower rates of severe pneumonia, hospitalization and mortality.

CONCLUSIONS

OGD seem to be highly prevalent in SARS-CoV-2 infection. They occur early, concomitantly with other symptoms and often persist after recovery, in some cases for months; whether a full recovery eventually occurs in all cases is not clear yet. OGD are good predictors of SARS-CoV-2 infection and are associated with a milder disease course.

Increased aerosol transmission for B.1.1.7 (alpha variant) over lineage A variant of SARS-CoV-2

Airborne transmission, a term combining both large droplet and aerosol transmission, is thought to be the main transmission route of SARS-CoV-2. Here we investigated the relative efficiency of aerosol transmission of two variants of SARS-CoV-2, B.1.1.7 (alpha) and lineage A, in the Syrian hamster. A novel transmission caging setup was designed and validated, which allowed the assessment of transmission efficiency at various distances. At 2 meters distance, only particles <5 µm traversed between cages. In this setup, aerosol transmission was confirmed in 8 out of 8 (N = 4 for each variant) sentinels after 24 hours of exposure as demonstrated by respiratory shedding and seroconversion. Successful transmission occurred even when exposure time was limited to one hour, highlighting the efficiency of this transmission route. Interestingly, the B.1.1.7 variant outcompeted the lineage A variant in an airborne transmission chain after mixed infection of donors. Combined, this data indicates that the infectious dose of B.1.1.7 required for successful transmission may be lower than that of lineage A virus. The experimental proof for true aerosol transmission and the increase in the aerosol transmission potential of B.1.1.7 underscore the continuous need for assessment of novel variants and the development or preemptive transmission mitigation strategies.

Age-dependent appearance of SARS-CoV-2 entry sites in mouse chemosensory systems reflects COVID-19 anosmia-ageusia symptoms

COVID-19 pandemic has given rise to a collective scientific effort to study its viral causing agent SARS-CoV-2. Research is focusing in particular on its infection mechanisms and on the associated-disease symptoms. Interestingly, this environmental pathogen directly affects the human chemosensory systems leading to anosmia and ageusia. Evidence for the presence of the cellular entry sites of the virus, the ACE2/TMPRSS2 proteins, has been reported in non-chemosensory cells in the rodent’s nose and mouth, missing a direct correlation between the symptoms reported in patients and the observed direct viral infection in human sensory cells. Here, mapping the gene and protein expression of ACE2/TMPRSS2 in the mouse olfactory and gustatory cells, we precisely identify the virus target cells to be of basal and sensory origin and reveal the age-dependent appearance of viral entry-sites. Our results propose an alternative interpretation of the human viral-induced sensory symptoms and give investigative perspectives on animal models.

Brechbühl et al characterise the gene and protein expression of ACE2/TMPRSS2 in the mouse olfactory and gustatory cells, which reveals that SARS-CoV-2 target cells are of basal and sensory origin. They also demonstrate an age-dependent appearance of viral entry-sites, which could inform the use of mouse models in the investigation of SARS-CoV-2 effects on olfaction.

Animal Transmission of SARS-CoV-2 and the Welfare of Animals during the COVID-19 Pandemic

The accelerated pace of research into Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) necessitates periodic summaries of current research. The present paper reviews virus susceptibilities in species with frequent human contact, and factors that are best predictors of virus susceptibility. Species reviewed were those in contact with humans through entertainment, pet, or agricultural trades, and for whom reports (either anecdotal or published) exist regarding the SARS-CoV-2 virus and/or the resulting disease state COVID-19. Available literature was searched using an artificial intelligence (AI)-assisted engine, as well as via common databases, such as Web of Science and Medline. The present review focuses on susceptibility and transmissibility of SARS-CoV-2, and polymorphisms in transmembrane protease serine 2 (TMPRSS2) and angiotensin-converting enzyme 2 (ACE2) that contribute to species differences. Dogs and pigs appear to have low susceptibility, while ferrets, mink, some hamster species, cats, and nonhuman primates (particularly Old World species) have high susceptibility. Precautions may therefore be warranted in interactions with such species, and more selectivity practiced when choosing appropriate species to serve as models for research.