Hamster model for post-COVID-19 alveolar regeneration offers an opportunity to understand post-acute sequelae of SARS-CoV-2.

COVID-19 survivors often suffer from post-acute sequelae of SARS-CoV-2 infection (PASC). Current evidence suggests dysregulated alveolar regeneration as a possible explanation for respiratory PASC, which deserves further investigation in a suitable animal model. This study investigates morphological, phenotypical and transcriptomic features of alveolar regeneration in SARS-CoV-2 infected Syrian golden hamsters. We demonstrate that CK8+ alveolar differentiation intermediate (ADI) cells occur following SARS-CoV-2-induced diffuse alveolar damage. A subset of ADI cells shows nuclear accumulation of TP53 at 6- and 14-days post infection (dpi), indicating a prolonged arrest in the ADI state. Transcriptome data show high module scores for pathways involved in cell senescence, epithelial-mesenchymal transition, and angiogenesis in cell clusters with high ADI gene expression. Moreover, we show that multipotent CK14+ airway basal cell progenitors migrate out of terminal bronchioles, aiding alveolar regeneration. At 14 dpi, ADI cells, peribronchiolar proliferates, M2-macrophages, and sub-pleural fibrosis are observed, indicating incomplete alveolar restoration. The results demonstrate that the hamster model reliably phenocopies indicators of a dysregulated alveolar regeneration of COVID-19 patients. The results provide important information on a translational COVID-19 model, which is crucial for its application in future research addressing pathomechanisms of PASC and in testing of prophylactic and therapeutic approaches for this syndrome.

SARS-CoV-2 Infection Dysregulates Cilia and Basal Cell Homeostasis in the Respiratory Epithelium of Hamsters.

Similar to many other respiratory viruses, SARS-CoV-2 targets the ciliated cells of the respiratory epithelium and compromises mucociliary clearance, thereby facilitating spread to the lungs and paving the way for secondary infections. A detailed understanding of mechanism involved in ciliary loss and subsequent regeneration is crucial to assess the possible long-term consequences of COVID-19. The aim of this study was to characterize the sequence of histological and ultrastructural changes observed in the ciliated epithelium during and after SARS-CoV-2 infection in the golden Syrian hamster model. We show that acute infection induces a severe, transient loss of cilia, which is, at least in part, caused by cilia internalization. Internalized cilia colocalize with membrane invaginations, facilitating virus entry into the cell. Infection also results in a progressive decline in cells expressing the regulator of ciliogenesis FOXJ1, which persists beyond virus clearance and the termination of inflammatory changes. Ciliary loss triggers the mobilization of p73+ and CK14+ basal cells, which ceases after regeneration of the cilia. Although ciliation is restored after two weeks despite the lack of FOXJ1, an increased frequency of cilia with ultrastructural alterations indicative of secondary ciliary dyskinesia is observed. In summary, the work provides new insights into SARS-CoV-2 pathogenesis and expands our understanding of virally induced damage to defense mechanisms in the conducting airways.

Microgliosis and neuronal proteinopathy in brain persist beyond viral clearance in SARS-CoV-2 hamster model.

BACKGROUND: Neurological symptoms such as cognitive decline and depression contribute substantially to post-COVID-19 syndrome, defined as lasting symptoms several weeks after initial SARS-CoV-2 infection. The pathogenesis is still elusive, which hampers appropriate treatment. Neuroinflammatory responses and neurodegenerative processes may occur in absence of overt neuroinvasion. METHODS: Here we determined whether intranasal SARS-CoV-2 infection in male and female syrian golden hamsters results in persistent brain pathology. Brains 3 (symptomatic) or 14 days (viral clearance) post infection versus mock (n = 10 each) were immunohistochemically analyzed for viral protein, neuroinflammatory response and accumulation of tau, hyperphosphorylated tau and alpha-synuclein protein. FINDINGS: Viral protein in the nasal cavity led to pronounced microglia activation in the olfactory bulb beyond viral clearance. Cortical but not hippocampal neurons accumulated hyperphosphorylated tau and alpha-synuclein, in the absence of overt inflammation and neurodegeneration. Importantly, not all brain regions were affected, which is in line with selective vulnerability. INTERPRETATION: Thus, despite the absence of virus in brain, neurons develop signatures of proteinopathies that may contribute to progressive neuronal dysfunction. Further in depth analysis of this important mechanism is required. FUNDING: Federal Ministry of Health (BMG; ZMV I 1-2520COR501), Federal Ministry of Education and Research (BMBF 01KI1723G), Ministry of Science and Culture of Lower Saxony in Germany (14 - 76103-184 CORONA-15/20), German Research Foundation (DFG; 398066876/GRK 2485/1), Luxemburgish National Research Fund (FNR, Project Reference: 15686728, EU SC1-PHE-CORONAVIRUS-2020 MANCO, no > 101003651).

Summary of European guidelines on infection control and prevention during COVID-19 pandemic.

OBJECTIVES: The current COVID-19 pandemic highlighted the need for a review of guidelines on infection control and prevention to ensure safe delivery of dental care. However, it is not clear to what extent the rapidly published European guidelines reflect the current evidence and thus provide homogeneous recommendations. MATERIAL & METHODS: Guidelines from all European Union countries, Scotland, Switzerland and United Kingdom were retrieved. Information on triage, mouth rinse, personal protective equipment (PPE) for aerosol free/ generating procedures (non-AGP/AGP) and treatment of potentially infectious patients were summarized and compared with recommendations from international organizations (WHO, ECDC, CDC). RESULTS: All included countries (30/30) published COVID-19 guidelines in 2020. All countries recommended triage and to postpone non-urgent treatment of potentially infectious patients. Hydrogen peroxide (1%-1.5%) was the most frequently recommended antiseptic mouth rinse to reduce viral load (24/30). PPE for non-AGP treatments included mainly surgical masks (21/30) or FFP2/FFP3/N95 masks (16/30), whereas FFP2/FFP3 masks (25/30) and face shields (24/30) were recommended for AGP by the vast majority of guidelines. For high-risk/COVID positive patients, most countries recommended maximum protection and treatment in specialized dental clinics (22/30). CONCLUSION: There was general agreement among recommendations for triage, mouth rinse, and PPE during AGP and treatment of potentially infectious patients. In contrast, recommendations on PPE for non-AGP treatment varied considerably among the European countries possibly due to limited scientific evidence regarding transmission risk during non-AGP treatments.

Dental care during COVID-19 pandemic: Follow-up survey of experts' opinion.

OBJECTIVES: The purpose of the present survey is to give an update of European experts' opinion on infection control and prevention in dentistry during second wave of pandemic. The secondary aim was to analyze how experts' opinion changed in the light of the new scientific evidence since the first wave. MATERIAL & METHODS: An anonymous online 14-item questionnaire was sent to a total of 27 leading academic experts in Oral (and Maxillofacial) Surgery from different European countries, who had completed a previous survey in April-May 2020. The questionnaire covered the topics of dental setting safety, personal protective equipment (PPE), and patient-related measures to minimize transmission risk. Data collection took place in November-February 2020/21. RESULTS: 26 experts participated in the follow-up survey. The overall transmission risk in dental settings was scored significantly lower compared to the initial survey (p < .05), though the risk associated with aerosol-generating procedures (AGP) was still considered to be high. Maximum PPE was less frequently recommended for non-AGP (p < .05), whereas the majority of experts still recommended FFP2/FFP3 masks (80.8%), face shields or goggles (88.5%), gowns (61.5%), and caps (57.7%) for AGP. Most of the experts also found mouth rinse relevant (73.1%) and reported to be using it prior to treatment (76.9%). No uniform opinion was found regarding the relevance of COVID-19 testing of staff and patients. CONCLUSION: With the continuation of dental care provision, transmission risk has been scored lower compared to the first wave of pandemic. However, high risk is still assumed for AGP, and maximum PPE remained advised for the respective treatments.

COVID-19: Review of European recommendations and experts' opinion on dental care. Summary and consensus statements of group 5. The 6th EAO Consensus Conference 2021.

OBJECTIVES: The present work reports the EAO workshop group 5 and consensus plenary discussions and statements based on two reviews summarising European guidelines and experts' opinion on infection control and prevention (ICP) in dentistry during the pandemic. MATERIAL: Two manuscripts were presented at the 6th EAO Consensus Conference. The first study compared the most recent national guidelines/recommendations of European countries. The second paper was an experts' opinion-based survey on application of ICP regulation during the second wave. The outcome of COVID-19 group discussion was presented to all participants of the consensus to come to an agreement about the consensus statements and clinical recommendation. RESULTS: The dynamic of the pandemic had an impact on rapidly published and frequently updated national guidelines in Europe. As guidelines were not based on solid evidence, they were supplemented by experts' opinion on ICP in dentistry. The dental care should be guaranteed during the pandemic; however, in case of suspected or confirmed COVID-19 disease, the treatment should be postponed if possible. Remote triage and patient-related measures (i.e., social distancing, hand hygiene and mask wearing) were recommended to be the most efficient to reduce SARS-CoV-2 transmission. The type of personal protective equipment for dental staff should be adequate to the procedure and infection risk. CONCLUSIONS: Adequate infection control protocols have to be followed by healthcare professionals and patients to minimise the spreading of COVID-19. We foresee the importance of continuously updating the national dental guidelines, considering the evolution of the pandemic and new scientific evidence becoming available.

Vasculitis and Neutrophil Extracellular Traps in Lungs of Golden Syrian Hamsters With SARS-CoV-2.

Neutrophil extracellular traps (NETs) have been identified as one pathogenetic trigger in severe COVID-19 cases and therefore well-described animal models to understand the influence of NETs in COVID-19 pathogenesis are needed. SARS-CoV-2 infection causes infection and interstitial pneumonia of varying severity in humans and COVID-19 models. Pulmonary as well as peripheral vascular lesions represent a severe, sometimes fatal, disease complication of unknown pathogenesis in COVID-19 patients. Furthermore, neutrophil extracellular traps (NETs), which are known to contribute to vessel inflammation or endothelial damage, have also been shown as potential driver of COVID-19 in humans. Though most studies in animal models describe the pulmonary lesions characterized by interstitial inflammation, type II pneumocyte hyperplasia, edema, fibrin formation and infiltration of macrophages and neutrophils, detailed pathological description of vascular lesions or NETs in COVID-19 animal models are lacking so far. Here we report different types of pulmonary vascular lesions in the golden Syrian hamster model of COVID-19. Vascular lesions included endothelialitis and vasculitis at 3 and 6 days post infection (dpi), and were almost nearly resolved at 14 dpi. Importantly, virus antigen was present in pulmonary lesions, but lacking in vascular alterations. In good correlation to these data, NETs were detected in the lungs of infected animals at 3 and 6 dpi. Hence, the Syrian hamster seems to represent a useful model to further investigate the role of vascular lesions and NETs in COVID-19 pathogenesis.

Dental care during COVID-19 pandemic: Survey of experts' opinion.

OBJECTIVES: The current COVID-19 outbreak in conjunction with the need to provide safe dental treatments and the limited knowledge on the efficacy of protective measures has posed dentists into a challenging situation. Therefore, the present article aimed at collecting experiences and recommendations of frontline clinical experts on critical aspects of dental treatment provision during pandemic. MATERIAL & METHODS: From a total of 32 European countries, one leading academic expert in Oral and Maxillofacial Surgery or Oral Surgery per country was asked to participate in an anonymous online 10-item survey on COVID-19 covering the topics of safety of dental settings, personal protective equipment (PPE), and patient-related measures to reduce transmission risk. Data collection took place from April 12th to May 22nd, 2020. RESULTS: A total of 27 experts from different European countries completed the survey. The transmission risk of SARS-CoV-2 in dental settings for aerosol-generating procedures was considered high by all experts except two. For aerosol-free and aerosol-generating procedures, more than 80% of the experts recommended face protection and caps for every single treatment. For aerosol-generating procedures, additional measures (FFP2/FFP3 masks and gowns) were suggested by the vast majority of the experts. To reduce transmission risk, all experts recommended limiting aerosol-generating procedures and reducing the number of patients in waiting areas as well as hand hygiene for the patients. CONCLUSION: The limitation of aerosol-generating procedures along with the usage of adequate personal protection equipment was considered to be crucial to protect dental healthcare providers and patients, thus reducing the transmission risk of COVID-19.

Recommendations for Dental Care during COVID-19 Pandemic.

Dental clinics were suspected to be a hotspot for nosocomial transmission of coronavirus disease 19 (COVID-19), yet there has been no clear recommendation about emergency dental care and appropriate personal protective equipment during pandemics. In this paper, we aim to summarize recommendations for (i) patient risk assessment, (ii) patient triage, and (iii) measures to prevent infection of health professionals and nosocomial transmission in dental clinics. The available evidence was collected by performing searches on PubMed, Embase, and Cochrane databases. We reviewed papers on COVID-19, severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), influenza, and related respiratory viral diseases. Legal and ethical frameworks, as well as international (e.g., World Health Organization (WHO)) and national (e.g., public health institutes, dental associations) guidelines were screened to summarize recommendations related to dental emergency care. To assess the patient risk, a questionnaire was developed to classify patients at unknown, high, and very high risk. Patient triage recommendations were summarized in a flow chart that graded the emergency level of treatments (i.e., urgent, as soon as possible, and postpone). Measures to prevent disease transmission based on current evidence were grouped for dental health professionals, dental clinics, and patients. The present recommendations may support health professionals implement preventative measures during the pandemic.