The Prevalence and Pathophysiology of Chemical Sense Disorder Caused by the Novel Coronavirus

Distinct olfactory mucosal macrophage populations mediate neuronal maintenance and pathogen defense

The olfactory mucosa is important for both the sense of smell and as a mucosal immune barrier to the upper airway and brain. However, little is known about how the immune system mediates the conflicting goals of neuronal maintenance and inflammation in this tissue. A number of immune cell populations reside within the olfactory mucosa and yet we have little understanding of how these resident olfactory immune cells functionally interact with the chemosensory environment. Identifying these interactions will allow therapeutic manipulations that treat disorders such as post-viral olfactory dysfunction. Macrophages are the most prevalent immune cell type in the uninflamed olfactory mucosa and here, we identify two distinct tissue macrophage populations in murine olfactory mucosa. P2ry12hi macrophages are transcriptionally specialized for neuron interactions, closely associated with olfactory neuron cell bodies, long-term tissue residents, and functionally specialized to phagocytose cells and debris, including olfactory neurons. Conversely, MHC Class IIhi macrophages are transcriptionally dedicated to cytokine production and antigen presentation, localized primarily within the olfactory lamina propria, more rapidly replaced by blood monocytes, and rapidly produce chemokines in response to viral infection. We further show that these macrophage signatures are present in human olfactory biopsies, and P2ry12-like olfactory macrophages are reduced in patients with long-term smell loss following COVID-19. Together, these data show that two olfactory macrophage populations regulate neurons and initiate the immune response, contributing to our understanding of both olfactory immunity and tissue-resident macrophage biology.

Prevalence of skin manifestations in patients with COVID-19: a systematic review and meta-analysis

Background

COVID-19 presents extrapulmonary manifestations that can aid in the diagnosis. Skin manifestations have been reported but their characteristics are not yet clear. Health professionals need information about its prevalence and main characteristics.

Methods

This systematic review followed the PRISMA criteria. The protocol was registered in the PROSPERO (number CRD42020193173). Seven electronic databases and the gray literature were searched independently by two researchers. Observational analytical studies that presented data on the prevalence of skin manifestations in patients aged 19 or older with COVID-19 were included. Prevalence estimates were synthesized through a meta-analysis using random-effects models. Association meta-analysis and comparisons were performed for individual characteristics.

Results

We included 31 studies with 10,934 patients, of which 10,121 tested positive for COVID-19. The general prevalence of skin manifestations was 29% (95% CI: 17.0-43.0; I2: 99%), the most in Africa, with a mean duration between 7 and 9 days and the most frequently affecting feet+hands (75%) and the trunk (71%). Patients with mild/moderate COVID-19 had more of chilblain-like+pernio-like lesions (97%) and inflammatory lesions (86%) than patients with severe or critical COVID-19. Manifestations of vascular origin were only in elderly patients and were significant with the severity of COVID-19 (p = 0).

Conclusion

The global prevalence of skin manifestations is similar to other signs and symptoms of COVID-19. Skin assessment should be considered when investigating and diagnosing COVID-19 in adult and elderly patients.Systematic review registration: PROSPERO, identifier CRD42020193173, https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020193173.

Olfactory immunology: the missing piece in airway and CNS defence

The olfactory mucosa is a component of the nasal airway that mediates the sense of smell. Recent studies point to an important role for the olfactory mucosa as a barrier to both respiratory pathogens and to neuroinvasive pathogens that hijack the olfactory nerve and invade the CNS. In particular, the COVID-19 pandemic has demonstrated that the olfactory mucosa is an integral part of a heterogeneous nasal mucosal barrier critical to upper airway immunity. However, our insufficient knowledge of olfactory mucosal immunity hinders attempts to protect this tissue from infection and other diseases. This Review summarizes the state of olfactory immunology by highlighting the unique immunologically relevant anatomy of the olfactory mucosa, describing what is known of olfactory immune cells, and considering the impact of common infectious diseases and inflammatory disorders at this site. We will offer our perspective on the future of the field and the many unresolved questions pertaining to olfactory immunity.

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.

Olfactory and taste dysfunction in COVID-19-incidence and recovery

Background

Olfactory and taste dysfunctions have been identified as prominent signs of COVID-19 infection. The data on its prevalence, time of onset, and recovery is highly variable.

Objective

The study was aimed at establishing the incidence of and the factors influencing smell and taste disorders in COVID-19-affected patients.

Methodology

Telephonic interviews were used to collect data on the symptoms of COVID-19-positive patients, with an emphasis on smell and taste disorders. Patients have severe disease and a history of illnesses that may affect olfaction or taste, and those unwilling to participate were excluded.

Results

A total of 1488 COVID-19-positive patients were identified. A total of 772 were included and interviewed, and their data were analysed. A total of 242 (31.3%) patients developed symptoms related to smell and/or taste. Anosmia (149) and ageusia (152) were the most common. Younger patients were more commonly affected (p = 0.0016). The presence and degree of smell symptoms and taste symptoms showed a small positive correlation (r = .234, p < .001). A strong relationship was seen with fever (r = .825, p < .001) and a significantly moderate relationship with breathing difficulty. There was no significant difference based on age or sex for the recovery of smell or taste sensations. There was a significant correlation between taste recovery and smell recovery times (p < 0.00001).

Conclusion

Smell and taste disorders, as early clinical symptoms of COVID-19, may have a diagnostic as well as a prognostic value. Treatment protocols for these patients are yet to be defined. A positive association between these symptoms and breathing difficulty was found, and we recommend COVID-19 testing and monitoring of symptoms for all patients with new-onset OTD symptoms. A combination of active enquiry about these symptoms, along with objective testing when the patients present with COVID-19 symptoms may help in better understanding of the pathophysiology and timely initiation of treatment.

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.