The Upper Respiratory Tract of Felids Is Highly Susceptible to SARS-CoV-2 Infection

Characterization of 3D human pulmonary epithelial model morphology and oxygen status under normoxia and hypoxia

Infection generates localized hypoxia in affected tissue, inducing cellular survival responses and modulating inflammatory processes. Consideration of oxygen status as a parameter in in vitro infection research is therefore vital to the generation of physiologically relevant data within the 3R context. In this study, we characterize the culture morphology and oxygenation of liquid-liquid interface (LLI) permanent bronchial epithelial (Calu-3), classical air-liquid interface (cALI) Calu-3, and cALI human primary bronchial epithelial cell (hBEC) models under the normoxic conditions within standard incubators, commonly employed in in vitro work. We compare the normoxic state of these models to their hypoxic state to assess changes in the airway epithelial environment in response to oxygen deprivation, and the extent to which select hypoxia responses can be observed at the molecular level. Additional juxtapositions are drawn between Calu-3 LLI and cALI models and Calu-3 conventional monolayer (CM) and inverted air-liquid interface (iALI) models, due to their relevance for basic and specialized research, respectively. Epithelial complexity was observed to vary amongst the filter-based models, and all models were found to exhibit characteristic extracellular oxygen depletion patterns under normoxia. Importantly, the extracellular oxygen contents of Calu-3 LLI, cALI, and CM models significantly decreased during normoxic incubation. Specific hypoxia responses through stabilization of HIF-1α, HIF-2α, and/or HIF-3α and alteration of ACE2 protein levels differed in response to both culture format and cell type. Therefore, while all models examined provide valuable opportunities for in vitro exploration, variation in their morphological, physiological, and molecular characteristics necessitates careful consideration during experimental design.

SARS-CoV-2 delta variant in African lions (Panthera leo) and humans at Utah's Hogle Zoo, USA, 2021-22

AIMS

We conducted a One Health investigation to assess the source and transmission dynamics of SARS-CoV-2 infection in African lions (Panthera leo) at Utah's Hogle Zoo in Salt Lake City from October 2021 to February 2022.

METHODS AND RESULTS

Following observation of respiratory illness in the lions, zoo staff collected pooled faecal samples and individual nasal swabs from four lions. All specimens tested positive for SARS-CoV-2 by reverse transcription-polymerase chain reaction (RT-PCR). The resulting investigation included: lion observation; RT-PCR testing of lion faeces every 1-7 days; RT-PCR testing of lion respiratory specimens every 2-3 weeks; staff interviews and RT-PCR testing; whole-genome sequencing of viruses from lions and staff; and comparison with existing SARS-CoV-2 human community surveillance sequences. In addition to all five lions, three staff displayed respiratory symptoms. All lions recovered and no hospitalizations or deaths were reported among staff. Three staff reported close contact with the lions in the 10 days before lion illness onset, one of whom developed symptoms and tested positive for SARS-CoV-2 on days 3 and 4, respectively, after lion illness onset. The other two did not report symptoms or test positive. Two staff who did not have close contact with the lions were symptomatic and tested positive on days 5 and 8, respectively, after lion illness onset. We detected SARS-CoV-2 RNA in lion faeces for 33 days and in lion respiratory specimens for 14 weeks after illness onset. The viruses from lions were genetically highly related to those from staff and two contemporaneous surveillance specimens from Salt Lake County; all were delta variants (AY.44).

CONCLUSIONS

We did not determine the sources of these infections, although human-to-lion transmission likely occurred. The observed period of respiratory shedding was longer than in previously documented SARS-CoV-2 infections in large felids, indicating the need to further assess duration and potential implications of shedding.

Ex vivo challenge models for infectious diseases

Traditionally, molecular mechanisms of pathogenesis for infectious agents were studied in cell culture or animal models but have limitations on the extent to which the resulting data reflect natural infection in humans. The COVID-19 pandemic has highlighted the urgent need to rapidly develop laboratory models that enable the study of host-pathogen interactions, particularly the relative efficacy of preventive measures. Recently, human and animal ex vivo tissue challenge models have emerged as a promising avenue to study immune responses, screen potential therapies and triage vaccine candidates. This approach offers the opportunity to closely approximate human disease from the perspective of pathology and immune response. It has advantages compared to animal models which are expensive, lengthy and often require containment facilities. Herein, we summarize some recent advances in the development of ex vivo tissue challenge models for COVID-19, HIV-1 and other pathogens. We focus on the contribution of these models to enhancing knowledge of host-pathogen interactions, immune modulation, and their value in testing therapeutic agents. We further highlight the advantages and limitations of using ex vivo challenge models and briefly summarize how the use of organoids provides a useful advancement over current approaches. Collectively, these developments have enormous potential for the study of infectious diseases.

Mortality associated with SARS-CoV-2 in nondomestic felids

Between September and November 2021, 5 snow leopards (Panthera uncia) and 1 lion (Panthera leo) were naturally infected with severe acute respiratory coronavirus 2 (SARS-CoV-2) and developed progressive respiratory disease that resulted in death. Severe acute respiratory syndrome coronavirus 2 sequencing identified the delta variant in all cases sequenced, which was the predominant human variant at that time. The time between initial clinical signs and death ranged from 3 to 45 days. Gross lesions in all 6 cats included nasal turbinate hyperemia with purulent discharge and marked pulmonary edema. Ulcerative tracheitis and bronchitis were noted in 4 cases. Histologically, there was necrotizing and ulcerative rhinotracheitis and bronchitis with fibrinocellular exudates and fibrinosuppurative to pyogranulomatous bronchopneumonia. The 4 cats that survived longer than 8 days had fungal abscesses. Concurrent bacteria were noted in 4 cases, including those with more acute disease courses. Severe acute respiratory syndrome coronavirus 2 was detected by in situ hybridization using probes against SARS-CoV-2 spike and nucleocapsid genes and by immunohistochemistry. Viral nucleic acid and protein were variably localized to mucosal and glandular epithelial cells, pneumocytes, macrophages, and fibrinocellular debris. Based on established criteria, SARS-CoV-2 was considered a contributing cause of death in all 6 cats. While mild clinical infections are more common, these findings suggest that some SARS-CoV-2 variants may cause more severe disease and that snow leopards may be more severely affected than other felids.

Susceptibility and transmissibility of SARS-CoV-2 variants in transgenic mice expressing the cat angiotensin-converting enzyme 2 (ACE-2) receptor

The emergence of SARS-CoV-2 in 2019 and its rapid spread throughout the world has caused the largest pandemic of our modern era. The zoonotic origin of this pathogen highlights the importance of the One Health concept and the need for a coordinated response to this kind of threats. Since its emergence, the virus has caused >7 million deaths worldwide. However, the animal source for human outbreaks remains unknown. The ability of the virus to jump between hosts is facilitated by the presence of the virus receptor, the highly conserved angiotensin-converting enzyme 2 (ACE2), found in various mammals. Positivity for SARS-CoV-2 has been reported in various species, including domestic animals and livestock, but their potential role in bridging viral transmission to humans is still unknown. Additionally, the virus has evolved over the pandemic, resulting in variants with different impacts on human health. Therefore, suitable animal models are crucial to evaluate the susceptibility of different mammalian species to this pathogen and the adaptability of different variants. In this work, we established a transgenic mouse model that expresses the feline ACE2 protein receptor (cACE2) under the human cytokeratin 18 (K18) gene promoter's control, enabling high expression in epithelial cells, which the virus targets. Using this model, we assessed the susceptibility, pathogenicity, and transmission of SARS-CoV-2 variants. Our results show that the sole expression of the cACE2 receptor in these mice makes them susceptible to SARS-CoV-2 variants from the initial pandemic wave but does not enhance susceptibility to omicron variants. Furthermore, we demonstrated efficient contact transmission of SARS-CoV-2 between transgenic mice that express either the feline or the human ACE2 receptor.

A tetravalent bispecific antibody outperforms the combination of its parental antibodies and neutralizes diverse SARS-CoV-2 variants

The devastating impact of COVID-19 on global health shows the need to increase our pandemic preparedness. Recombinant therapeutic antibodies were successfully used to treat and protect at-risk patients from COVID-19. However, the currently circulating Omicron subvariants of SARS-CoV-2 are largely resistant to therapeutic antibodies, and novel approaches to generate broadly neutralizing antibodies are urgently needed. Here, we describe a tetravalent bispecific antibody, A7A9 TVB, which actively neutralized many SARS-CoV-2 variants of concern, including early Omicron subvariants. Interestingly, A7A9 TVB neutralized more variants at lower concentration as compared to the combination of its parental monoclonal antibodies, A7K and A9L. A7A9 also reduced the viral load of authentic Omicron BA.1 virus in infected pseudostratified primary human nasal epithelial cells. Overall, A7A9 displayed the characteristics of a potent broadly neutralizing antibody, which may be suitable for prophylactic and therapeutic applications in the clinics, thus highlighting the usefulness of an effective antibody-designing approach.

Mortality associated with SARS-CoV-2 in nondomestic felids

Between September and November 2021, 5 snow leopards ( Panthera uncia) and 1 lion ( Panthera leo) were naturally infected with severe acute respiratory coronavirus 2 (SARS-CoV-2) and developed progressive respiratory disease that resulted in death. Severe acute respiratory syndrome coronavirus 2 sequencing identified the delta variant in all cases sequenced, which was the predominant human variant at that time. The time between initial clinical signs and death ranged from 3 to 45 days. Gross lesions in all 6 cats included nasal turbinate hyperemia with purulent discharge and marked pulmonary edema. Ulcerative tracheitis and bronchitis were noted in 4 cases. Histologically, there was necrotizing and ulcerative rhinotracheitis and bronchitis with fibrinocellular exudates and fibrinosuppurative to pyogranulomatous bronchopneumonia. The 4 cats that survived longer than 8 days had fungal abscesses. Concurrent bacteria were noted in 4 cases, including those with more acute disease courses. Severe acute respiratory syndrome coronavirus 2 was detected by in situ hybridization using probes against SARS-CoV-2 spike and nucleocapsid genes and by immunohistochemistry. Viral nucleic acid and protein were variably localized to mucosal and glandular epithelial cells, pneumocytes, macrophages, and fibrinocellular debris. Based on established criteria, SARS-CoV-2 was considered a contributing cause of death in all 6 cats. While mild clinical infections are more common, these findings suggest that some SARS-CoV-2 variants may cause more severe disease and that snow leopards may be more severely affected than other felids.

Establishment of sheep nasal mucosa explant model and its application in antiviral research

The nasal mucosa is the first barrier to pathogen invasion through the respiratory tract. Few studies have focused on nasal resistance to invasion by respiratory pathogens due to the lack of models related to the nasal mucosa. Hence, it is necessary to construct a nasal mucosal model to study host-pathogen interactions. We established a long-term in vitro sheep nasal mucosa explant model (NMEM), which exhibited typical epithelial cilia and epithelial proliferation ability within 11 days. Moreover, to evaluate whether the NMEM was suited for in vitro pathogenic study, we used pseudorabies virus (PRV) and showed that it successfully infected and produced severe lesions in the NMEM, particularly interferon (IFN)-stimulated gene product 15 (ISG15). IFN decreased significantly after the PRV infection. Similarly, we used this NMEM model to screen several antiviral substances, such as probiotics and drugs. A previous study showed that nasal commensal bacteria, particularly Bacillus subtilis, had high antiviral activity. Then, we used the NMEM to evaluate six sheep-derived B. subtilis strains and demonstrated that it significantly induced the production of IFN and expression of ISG15. The sheep-derived B. subtilis was pretreated with the sheep NMEM before the PRV infection to evaluate the antiviral effect. The results showed that NSV2 significantly inhibited infection by PRV and reduced the viral load (p < 0.05). Furthermore, NSV2 may inhibit PRV replication by enhancing ISGylation of cells. In conclusion, we established a reliable in vitro culture model of sheep NMEM, and applied it in antiviral research.

Development of immortalized feline respiratory epithelial cells in an air-liquid-interface culture system for feline herpesvirus-1 study

Feline herpesvirus-1 (FHV-1) is responsible for approximately 50% of diagnosed viral upper respiratory tract disease in cats. The virus infects and replicates in the epithelial cells located in upper respiratory tract. Commercial vaccines do not protect cats from the infection itself or development of latency. Previously, our lab developed a cell culture model using primary feline respiratory epithelial cells (pFRECs) to study respiratory innate immunity to FHV-1 and FHV-1 deletion mutants. However, the numbers of pFRECs that can be obtained per cat is limited. To improve the usage of respiratory epithelial 3D cultures in FHV-1 research, the present study immortalized feline respiratory epithelial cells (iFRECs) and characterized them morphologically and immunologically and evaluated the response to FHV-1 infection. Immortalization was achieved by transduction with Lenti-SV40T and Lenti-HPV E6/E7. Immortalized FRECs could be successfully subcultured for >20 passages, with positive gene expression of SV40T and HPV E6/E7. Immortalized FRECs expressed similar innate immunity-associated genes compared to pFRECs, including genes of Toll-like receptors (TLR1-9), interferon induced genes (OAS1, OAS3, IFI44, IFITM1, IFIT1), chemokines (CCL2, CCL3, CXCL8), pro-inflammatory and regulatory cytokines (IL-6, IL-4, IL-5, IL-12, and IL-18), and antimicrobials (DEFβ10, DEFβ4B). Finally, FHV-1 inoculation resulted in characteristic cytopathic effects starting at 24 hpi, with more than 80% cells detached and lysed by 72 hpi. Overall FHV-1 growth kinetics in iFRECs resembled the kinetics observed in pFRECs. In conclusion, we demonstrated that iFRECs are a useful tool to study feline respiratory disease including but not limited to FHV-1.

SARS-CoV-2 Infection in Captive Hippos (Hippopotamus amphibius), Belgium

Two adult female hippos in Zoo Antwerp who were naturally infected with SARS-CoV-2 showed nasal discharge for a few days. Virus was detected by immunocytochemistry and PCR in nasal swab samples and by PCR in faeces and pool water. Serology was also positive. No treatment was necessary.

An Overview of Epithelial-to-Mesenchymal Transition and Mesenchymal-to-Epithelial Transition in Canine Tumors: How Far Have We Come?

Historically, pre-clinical and clinical studies in human medicine have provided new insights, pushing forward the contemporary knowledge. The new results represented a motivation for investigators in specific fields of veterinary medicine, who addressed the same research topics from different perspectives in studies based on experimental and spontaneous animal disease models. The study of different pheno-genotypic contexts contributes to the confirmation of translational models of pathologic mechanisms. This review provides an overview of EMT and MET processes in both human and canine species. While human medicine rapidly advances, having a large amount of information available, veterinary medicine is not at the same level. This situation should provide motivation for the veterinary medicine research field, to apply the knowledge on humans to research in pets. By merging the knowledge of these two disciplines, better and faster results can be achieved, thus improving human and canine health.

Rift Valley Fever Virus Non-Structural Protein S Is Associated with Nuclear Translocation of Active Caspase-3 and Inclusion Body Formation

Rift Valley fever phlebovirus (RVFV) causes Rift Valley fever (RVF), an emerging zoonotic disease that causes abortion storms and high mortality rates in young ruminants as well as severe or even lethal complications in a subset of human patients. This study investigates the pathomechanism of intranuclear inclusion body formation in severe RVF in a mouse model. Liver samples from immunocompetent mice infected with virulent RVFV 35/74, and immunodeficient knockout mice that lack interferon type I receptor expression and were infected with attenuated RVFV MP12 were compared to livers from uninfected controls using histopathology and immunohistochemistry for RVFV nucleoprotein, non-structural protein S (NSs) and pro-apoptotic active caspase-3. Histopathology of the livers showed virus-induced, severe hepatic necrosis in both mouse strains. However, immunohistochemistry and immunofluorescence revealed eosinophilic, comma-shaped, intranuclear inclusions and an intranuclear (co-)localization of RVFV NSs and active caspase-3 only in 35/74-infected immunocompetent mice, but not in MP12-infected immunodeficient mice. These results suggest that intranuclear accumulation of RVFV 35/74 NSs is involved in nuclear translocation of active caspase-3, and that nuclear NSs and active caspase-3 are involved in the formation of the light microscopically visible inclusion bodies.

Elevated angiotensin-converting enzyme 2 (ACE2) expression in cats with hypertrophic cardiomyopathy

Angiotensin-converting enzyme 2 (ACE2) is an enzyme within the renin-angiotensin-aldosterone system that plays a role in regulating blood pressure. However, it is also a cellular receptor for infection with SARS coronaviruses. Although most cats develop subclinical or mild disease following infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) acquired from human patients, a previous study has suggested hypertrophic cardiomyopathy (HCM) is a potential risk factor for the development of severe disease in the cat. Herein we investigate the ACE2 protein expression in the lung, heart, and kidney from a small subset of cats with (n = 10) and without HCM (n = 10) by immunohistochemistry. The abundance and intensity of ACE2 expression is slightly elevated in alveoli (p = 0.09; 0.07, respectively) and bronchioles (p = 0.095; 0.37, respectively). However, statistically elevated abundance and intensity of ACE-2 expression was only evident in the heart of cats with HCM (p = 0.032; p = 0.011, respectively). Further investigation did not demonstrate a statistical correlation between the ACE2 expression in the heart in relation to the heart weight to body weight ratio, and the ventricular wall ratio. Current findings suggest an overexpression of ACE2 in HCM cases but follow up study is warranted to understand the pathophysiological process.

Persistent Infection of a Canine Histiocytic Sarcoma Cell Line with Attenuated Canine Distemper Virus Expressing Vasostatin or Granulocyte-Macrophage Colony-Stimulating Factor

Canine histiocytic sarcoma (HS) represents a neoplasia with poor prognosis. Due to the high metastatic rate of HS, there is urgency to improve treatment options and to prevent tumor metastases. Canine distemper virus (CDV) is a single-stranded negative-sense RNA (ssRNA (-)) virus with potentially oncolytic properties. Moreover, vasostatin and granulocyte-macrophage colony-stimulating factor (GM-CSF) are attractive molecules in cancer therapy research because of their anti-angiogenetic properties and potential modulation of the tumor microenvironment. In the present study, an in vitro characterization of two genetically engineered viruses based on the CDV strain Onderstepoort (CDV-Ond), CDV-Ondneon-vasostatin and CDV-Ondneon-GM-CSF was performed. Canine histiocytic sarcoma cells (DH82 cells) were persistently infected with CDV-Ond, CDV-Ondneon, CDV-Ondneon-vasostatin and CDV-Ondneon-GM-CSF and characterized on a molecular and protein level regarding their vasostatin and GM-CSF production. Interestingly, DH82 cells persistently infected with CDV-Ondneon-vasostatin showed a significantly increased number of vasostatin mRNA transcripts. Similarly, DH82 cells persistently infected with CDV-Ondneon-GM-CSF displayed an increased number of GM-CSF mRNA transcripts mirrored on the protein level as confirmed by immunofluorescence and Western blot. In summary, modified CDV-Ond strains expressed GM-CSF and vasostatin, rendering them promising candidates for the improvement of oncolytic virotherapies, which should be further detailed in future in vivo studies.

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.

Investigations on SARS-CoV-2 Susceptibility of Domestic and Wild Animals Using Primary Cell Culture Models Derived from the Upper and Lower Respiratory Tract

Several animal species are susceptible to SARS-CoV-2 infection, as documented by case reports and serological and in vivo infection studies. However, the susceptibility of many animal species remains unknown. Furthermore, the expression patterns of SARS-CoV-2 entry factors, such as the receptor angiotensin-converting enzyme 2 (ACE2), as well as transmembrane protease serine subtype 2 (TMPRSS2) and cathepsin L (CTSL), cellular proteases involved in SARS-CoV-2 spike protein activation, are largely unexplored in most species. Here, we generated primary cell cultures from the respiratory tract of domestic and wildlife animals to assess their susceptibility to SARS-CoV-2 infection. Additionally, the presence of ACE2, TMPRSS2 and CTSL within respiratory tract compartments was investigated in a range of animals, some with unknown susceptibility to SARS-CoV-2. Productive viral replication was observed in the nasal mucosa explants and precision-cut lung slices from dogs and hamsters, whereas culture models from ferrets and multiple ungulate species were non-permissive to infection. Overall, whereas TMPRSS2 and CTSL were equally expressed in the respiratory tract, the expression levels of ACE2 were more variable, suggesting that a restricted availability of ACE2 may contribute to reduced susceptibility. Summarized, the experimental infection of primary respiratory tract cell cultures, as well as an analysis of entry-factor distribution, enable screening for SARS-CoV-2 animal reservoirs.

The Omicron variant is highly resistant against antibody-mediated neutralization: Implications for control of the COVID-19 pandemic

The rapid spread of the SARS-CoV-2 Omicron variant suggests that the virus might become globally dominant. Further, the high number of mutations in the viral spike protein raised concerns that the virus might evade antibodies induced by infection or vaccination. Here, we report that the Omicron spike was resistant against most therapeutic antibodies but remained susceptible to inhibition by sotrovimab. Similarly, the Omicron spike evaded neutralization by antibodies from convalescent patients or individuals vaccinated with the BioNTech-Pfizer vaccine (BNT162b2) with 12- to 44-fold higher efficiency than the spike of the Delta variant. Neutralization of the Omicron spike by antibodies induced upon heterologous ChAdOx1 (Astra Zeneca-Oxford)/BNT162b2 vaccination or vaccination with three doses of BNT162b2 was more efficient, but the Omicron spike still evaded neutralization more efficiently than the Delta spike. These findings indicate that most therapeutic antibodies will be ineffective against the Omicron variant and that double immunization with BNT162b2 might not adequately protect against severe disease induced by this variant.

The Swine IFN System in Viral Infections: Major Advances and Translational Prospects

Interferons (IFNs) are a family of cytokines that play a pivotal role in orchestrating the innate immune response during viral infections, thus representing the first line of defense in the host. After binding to their respective receptors, they are able to elicit a plethora of biological activities, by initiating signaling cascades which lead to the transcription of genes involved in antiviral, anti-inflammatory, immunomodulatory and antitumoral effector mechanisms. In hindsight, it is not surprising that viruses have evolved multiple IFN escape strategies toward efficient replication in the host. Hence, in order to achieve insight into preventive and treatment strategies, it is essential to explore the mechanisms underlying the IFN response to viral infections and the constraints thereof. Accordingly, this review is focused on three RNA and three DNA viruses of major importance in the swine farming sector, aiming to provide essential data as to how the IFN system modulates the antiviral immune response, and is affected by diverse, virus-driven, immune escape mechanisms.