Comparison of Severe Acute Respiratory Syndrome Coronavirus 2 Spike Protein Binding to ACE2 Receptors from Human, Pets, Farm Animals, and Putative Intermediate Hosts

SARS-CoV-2 envelope protein-derived extracellular vesicles act as potential media for viral spillover

Extracellular vesicles (EVs) are shown to be a novel viral transmission model capable of increasing a virus's tropism. According to our earlier research, cells infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) or transfected with envelope protein plasmids generate a novel type of EVs that are micrometer-sized and able to encase virus particles. Here, we showed the capacity of these EVs to invade various animals both in vitro and in vivo independent of the angiotensin-converting enzyme 2 receptor. First, via macropinocytosis, intact EVs produced from Vero E6 (monkey) cells were able to enter cells from a variety of animals, including cats, dogs, bats, hamsters, and minks, and vice versa. Second, when given to zebrafish with cutaneous wounds, the EVs showed favorable stability in aqueous environments and entered the fish. Moreover, infection of wild-type (WT) mice with heterogeneous EVs carrying SARS-CoV-2 particles led to a strong cytokine response and a notable amount of lung damage. Conversely, free viral particles did not infect WT mice. These results highlight the variety of processes behind viral transmission and cross-species evolution by indicating that EVs may be possible vehicles for SARS-CoV-2 spillover and raising risk concerns over EVs' potential for viral gene transfer.

Sero-epidemiological investigation and cross-neutralization activity against SARS-CoV-2 variants in cats and dogs, Thailand

Epidemiological data on SARS-CoV-2 infection in companion animals have been thoroughly investigated in many countries. However, information on the neutralizing cross-reactivity against SARS-CoV-2 variants in companion animals is still limited. Here, we explored the neutralizing antibodies against SARS-CoV-2 in cats and dogs between May 2020 and December 2021 during the first wave (a Wuhan-Hu-1-dominant period) and the fourth wave (a Delta-dominant period) of the Thailand COVID-19 outbreak. Archival plasma samples of 1,304 cats and 1,795 dogs (total = 3,099) submitted for diagnosis and health checks were collected at the Prasu-Arthorn Veterinary Teaching Hospital, Faculty of Veterinary Science, Mahidol University, Nakhon Pathom. A microneutralization test was used to detect neutralizing antibodies against the ancestral Wuhan-Hu-1 and the Delta variants. A plasma sample with neutralizing titers ≥10 was considered positive. Our results showed relatively low seroprevalence with seropositive samples detected in 8 out of 3,099 individuals (0.26, 95% CI 0.11-0.51%). Among these cases, SARS-CoV-2 neutralizing antibodies from both the ancestral Wuhan-Hu-1 and the Delta variants were found in three out of eight cases in two cats (n = 2) and one dog (n = 1). Furthermore, neutralizing antibodies specific to only the ancestral Wuhan-Hu-1 variant were exclusively found in one cat (n = 1), while antibodies against only the Delta variant were detected in four dogs (n = 4). Additionally, the neutralizing cross-activities against SARS-CoV-2 variants (Alpha, Beta, and Omicron BA.2) were observed in the seropositive cats with limited capacity to neutralize the Omicron BA.2 variant. In summary, the seropositivity among cats and dogs in households with an unknown COVID-19 status was relatively low in Thailand. Moreover, the neutralizing antibodies against SARS-CoV-2 found in the seropositive cats and dogs had limited or no ability to neutralize the Omicron BA.2 variant. Thus, monitoring SARS-CoV-2 infection and sero-surveillance, particularly in cats, is imperative for tracking virus susceptibility to the emergence of new SARS-CoV-2 variants.

Pseudotyped virus infection of multiplexed ACE2 libraries reveals SARS-CoV-2 variant shifts in receptor usage

Pairwise compatibility between virus and host proteins can dictate the outcome of infection. During transmission, both inter- and intraspecies variabilities in receptor protein sequences can impact cell susceptibility. Many viruses possess mutable viral entry proteins and the patterns of host compatibility can shift as the viral protein sequence changes. This combinatorial sequence space between virus and host is poorly understood, as traditional experimental approaches lack the throughput to simultaneously test all possible combinations of protein sequences. Here, we created a pseudotyped virus infection assay where a multiplexed target-cell library of host receptor variants can be assayed simultaneously using a DNA barcode sequencing readout. We applied this assay to test a panel of 30 ACE2 orthologs or human sequence mutants for infectability by the original SARS-CoV-2 spike protein or the Alpha, Beta, Gamma, Delta, and Omicron BA1 variant spikes. We compared these results to an analysis of the structural shifts that occurred for each variant spike's interface with human ACE2. Mutated residues were directly involved in the largest shifts, although there were also widespread indirect effects altering interface structure. The N501Y substitution in spike conferred a large structural shift for interaction with ACE2, which was partially recreated by indirect distal substitutions in Delta, which does not harbor N501Y. The structural shifts from N501Y greatly influenced the set of animal orthologs the variant spike was capable of interacting with. Out of the thirteen non-human orthologs, ten exhibited unique patterns of variant-specific compatibility, demonstrating that spike sequence changes during human transmission can toggle ACE2 compatibility and potential susceptibility of other animal species, and cumulatively increase overall compatibilities as new variants emerge. These experiments provide a blueprint for similar large-scale assessments of protein compatibility during entry by diverse viruses. This dataset demonstrates the complex compatibility relationships that occur between variable interacting host and virus proteins.

Zoonosis and zooanthroponosis of emerging respiratory viruses

Lung infections in Influenza-Like Illness (ILI) are triggered by a variety of respiratory viruses. All human pandemics have been caused by the members of two major virus families, namely Orthomyxoviridae (influenza A viruses (IAVs); subtypes H1N1, H2N2, and H3N2) and Coronaviridae (severe acute respiratory syndrome coronavirus 2, SARS-CoV-2). These viruses acquired some adaptive changes in a known intermediate host including domestic birds (IAVs) or unknown intermediate host (SARS-CoV-2) following transmission from their natural reservoirs (e.g. migratory birds or bats, respectively). Verily, these acquired adaptive substitutions facilitated crossing species barriers by these viruses to infect humans in a phenomenon that is known as zoonosis. Besides, these adaptive substitutions aided the variant strain to transmit horizontally to other contact non-human animal species including pets and wild animals (zooanthroponosis). Herein we discuss the main zoonotic and reverse-zoonosis events that occurred during the last two pandemics of influenza A/H1N1 and SARS-CoV-2. We also highlight the impact of interspecies transmission of these pandemic viruses on virus evolution and possible prophylactic and therapeutic interventions. Based on information available and presented in this review article, it is important to close monitoring viral zoonosis and viral reverse zoonosis of pandemic strains within a One-Health and One-World approach to mitigate their unforeseen risks, such as virus evolution and resistance to limited prophylactic and therapeutic interventions.

Two-Stage Recognition Mechanism of the SARS-CoV-2 Receptor-Binding Domain to Angiotensin-Converting Enzyme-2 (ACE2)

The SARS-CoV-2 virus, commonly known as COVID-19, occurred in 2019. It is a highly contagious illness with effects ranging from mild symptoms to severe illness. It is also one of the best-known pathogens since more than 200,000 scientific papers occurred in the last few years. With the publication of the SARS-CoV-2 (SARS-CoV-2-CTD) spike (S) protein in a complex with human ACE2 (hACE2) (PDB (6LZG)), the molecular analysis of one of the most crucial steps on the infection pathway was possible. The aim of this manuscript is to simulate the most widely spread mutants of SARS-CoV-2, namely Alpha, Beta, Gamma, Delta, Omicron, and the first recognized variant (natural wild type). With the wide search of the hypersurface of the potential energy performed using the UNRES force field, the intermediate state of the ACE2-RBD complex was found. R403, K/N/T417, L455, F486, Y489, F495, Y501, and Y505 played a crucial role in the protein recognition mechanism. The intermediate state cannot be very stable since it will prevent the infection cascade.

Risk assessment of SARS-CoV-2 replicating and evolving in animals

The retransmissions of SARS-CoV-2 from several mammals - primarily mink and white-tailed deer - to humans have raised concerns for the emergence of a new animal-derived SARS-CoV-2 variant to worsen the pandemic. Here, we discuss animal species that are susceptible to natural or experimental infection with SARS-CoV-2 and can transmit the virus to mates or humans. We describe cutting-edge techniques to assess the impact of a mutation in the viral spike (S) protein on its receptor and on antibody binding. Our review of spike sequences of animal-derived viruses identified nine unique amino acid exchanges in the receptor-binding domain (RBD) that are not present in any variant of concern (VOC). These mutations are present in SARS-CoV-2 found in companion animals such as dogs and cats, and they exhibit a higher frequency in SARS-CoV-2 found in mink and white-tailed deer, suggesting that sustained transmissions may contribute to maintaining novel mutations. Four of these exchanges, such as Leu452Met, could undermine acquired immune protection in humans while maintaining high affinity for the human angiotensin-converting enzyme 2 (ACE2) receptor. Finally, we discuss important avenues of future research into animal-derived viruses with public health risks.

Transmission of severe acute respiratory syndrome coronavirus 2 from humans to animals: is there a risk of novel reservoirs?

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a zoonotic virus able to infect humans and multiple nonhuman animal species. Most natural infections in companion, captive zoo, livestock, and wildlife species have been related to a reverse transmission, raising concern about potential generation of animal reservoirs due to human-animal interactions. To date, American mink and white-tailed deer are the only species that led to extensive intraspecies transmission of SARS-CoV-2 after reverse zoonosis, leading to an efficient spread of the virus and subsequent animal-to-human transmission. Viral host adaptations increase the probability of new SARS-CoV-2 variants' emergence that could cause a major global health impact. Therefore, applying the One Health approach is crucial to prevent and overcome future threats for human, animal, and environmental fields.

Susceptibility of bovine to SARS-CoV-2 variants of concern: insights from ACE2, AXL, and NRP1 receptors

The possibilities of cross-species transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) between humans and important livestock species are not yet known. Herein, we used the structural and genetic alignment and surface potential analysis of the amino acid (aa) in angiotensin-converting enzyme 2 (ACE2), tyrosine kinase receptor UFO (AXL), and neuropilin 1 (NRP1) in different species with substantial public health importance. The residues interfacing with the N-terminal domain (NTD) or receptor-binding domain (RBD) of S were aligned to screen the critical aa sites that determined the susceptibility of the SARS-CoV-2 to the host. We found that AXL and NRP1 proteins might be used as the receptors of SARS-CoV-2 in bovines. However, ACE2 protein may not be considered to be involved in the cross-species transmission of SARS-CoV-2 VOCs in cattle because the key residues of the ACE2-S-binding interface were different from those in known susceptible species. This study indicated that emerging SARS-CoV-2 variants potentially expand species tropism to bovines through AXL and NRP1 proteins.

Demonstration of SARS-CoV-2 Exposure in Korean Native Cattle and Korean Native Black Goats in Korea

The COVID-19 pandemic is caused by the zoonotic SARS-CoV-2 virus. A wide range of animals that interact with humans have been investigated to identify potential infections. As the extent of infection became more apparent, extensive animal monitoring became necessary to assess their susceptibility. This study analyzed nasal swabs and blood samples collected from randomly selected Korean native cattle and Korean native black goats. The tests conducted included real-time qPCR to detect SARS-CoV-2 antigens, an ELISA to detect antibodies, and a plaque reduction neutralization test (PRNT) to determine the presence of neutralizing antibodies. Among the 1798 animals tested (consisting of 1174 Korean native cattle and 624 Korean native black goats), SARS-CoV-2 viral RNA was detected in one Korean native cattle and one Korean native black goat. ELISA testing revealed positive results for antibodies in 54 Korean native cattle (4.60%) and 16 Korean native black goats (2.56%), while PRNTs yielded positive results in 51 Korean native cattle (4.34%) and 14 Korean native black goats (2.24%). The presence of SARS-CoV-2 antigens and/or antibodies was identified in animals on farms where farmworkers were already infected. It is challenging to completely rule out the possibility of reverse zoonotic transmission from humans to livestock in Korea, although the transmission is not to the same extent as it is in highly susceptible animal species like minks, cats, and dogs. This is due to the limited geographical area and the dense, intensive farming practices implemented in these regions. In conclusion, continuous viral circulation between humans and animals is inevitable, necessitating ongoing animal monitoring to ensure public health and safety.

Cell type dependent stability and virulence of a recombinant SARS-CoV-2, and engineering of a propagation deficient RNA replicon to analyze virus RNA synthesis

Engineering of reverse genetics systems for newly emerged viruses allows viral genome manipulation, being an essential tool for the study of virus life cycle, virus-host interactions and pathogenesis, as well as for the development of effective antiviral strategies. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an emergent human coronavirus that has caused the coronavirus disease (COVID-19) pandemic. The engineering of a full-length infectious cDNA clone and a fluorescent replicon of SARS-CoV-2 Wuhan-Hu-1, using a bacterial artificial chromosome, is reported. Viral growth and genetic stability in eleven cell lines were analyzed, showing that both VeroE6 cells overexpressing transmembrane serin protease 2 (TMPRSS2) and human lung derived cells resulted in the optimization of a cell system to preserve SARS-CoV-2 genetic stability. The recombinant SARS-CoV-2 virus and a point mutant expressing the D614G spike protein variant were virulent in a mouse model. The RNA replicon was propagation-defective, allowing its use in BSL-2 conditions to analyze viral RNA synthesis. The SARS-CoV-2 reverse genetics systems developed constitute a useful tool for studying the molecular biology of the virus, the development of genetically defined vaccines and to establish systems for antiviral compounds screening.

Delineating the Structure-Dynamics-Binding Differences among BA.1, BA.4/5, and BF.7 SARS-CoV-2 Variants through Atomistic Simulations: Correlation with Structural and Epidemiological Features

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an RNA virus possessing a spike (S) protein that facilitates the entry of the virus into human cells. The emergence of highly transmissible and fit SARS-CoV-2 variants has been driven by the positive selection of mutations within the S-protein. Notable among these variants are alpha, beta, gamma, delta, and omicron (BA.1), with the latter contributing to significant global health challenges and impacting populations worldwide. Recently, a novel subvariant of BA.1, named BF.7, has surfaced, purportedly exhibiting elevated transmissibility and infectivity rates. In order to comprehend and compare the transmissibility and disease progression characteristics of distinct SARS-CoV-2 variants, we performed an extensive comparative analysis utilizing all-atom molecular dynamics (MD) simulations (in triplicate) to investigate the structural, dynamic, and binding features of BA.1, BA.4/5, and BF.7. Our simulation findings, energetic analysis, and assessment of physicochemical properties collectively illuminate the dominance of the BA.1 variant over the others, a trend that is further substantiated by the sustained global prevalence of BA.1 relative to BA.4/5 and BF.7. Additionally, our simulation results align well with the reported cryoelectron microscopy (cryo-EM) structural data and epidemiological characteristics obtained from the Global Initiative on Sharing All Influenza Data (GISAID). This study presents a comprehensive comparative elucidation of the critical structural, dynamic, and binding attributes of these variants, providing insights into the predominance of BA.1 and its propensity to continuously generate numerous novel subvariants.

A retrospective study of SARS-CoV-2 seroprevalence in dogs and cats in the Community of Madrid, Spain

To date, susceptibility to SARS-CoV-2 infection in domestic animals including cats and dogs has been described. However, it is important to carry out passive surveillance of these animals to be aware of any changes in the outcomes of the disease in these species that may occur. In this study, we have performed a retrospective study in which we analyzed sera (n = 1,640) from random animals: dogs (n = 1,381) and cats (n = 259) belonging to both homes (n = 1,533) and animal protection centers (n = 107) in the Community of Madrid, Spain. Neutralizing antibodies were evaluated between November 2021 and May 2022 using a surrogate ELISA kit to determine the seroprevalence. Based on the results obtained, a few animals (both cats and dogs) presented neutralizing antibodies to SARS-CoV-2 (2.3%), all of them from private owners. However, the seroprevalence in cats (4.6%) resulted to be almost twice as much as in dogs (1.9%) which reinforces that cats' susceptibility to the infection seems higher than in the case of dogs, maybe due to the lower ACE2 expression of the dogs in the respiratory tract. These findings also confirm that the probability of infection is considerably higher in domestic animals in close contact with infected owners, compared to animals living in animal shelters whose contact with humans is markedly lower.

First serological evidence of SARS-CoV-2 natural infection in small ruminants : Brief report

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) emerged in late December 2019 and spread worldwide, quickly becoming a pandemic. This zoonotic coronavirus shows a broad host range, including wildlife and domestic animals. Small ruminants are shown to be susceptible to SARS-CoV-2 but, to date, no natural infection has been reported. Herein, we performed a survey for SARS-CoV-2 among sheep and goats in the Campania region of Italy using an indirect multispecies ELISA. Next, positive sera were submitted to virus serum neutralization for the quantification of specific neutralizing antibodies. Out of 612 sheep and goats, 23 were found ELISA positive (3.75%) and 1 of them showed 1:20 neutralizing antibodies titer. No significant difference was found between the two species, as well as between male and female, geographical location and age. Our findings demonstrate that natural infection can occur in flocks in a field situation. Moreover, low susceptibility to SARS-CoV-2 is reported for sheep and goats, nevertheless, the continuous mutations of this virus open new scenarios on viral host range and tropism, highlighting the importance of investigating animal species that could represent ongoing or future possible hosts.

Identification of host receptors for viral entry and beyond: a perspective from the spike of SARS-CoV-2

Identification of the interaction between the host membrane receptor and viral receptor-binding domain (RBD) represents a crucial step for understanding viral pathophysiology and for developing drugs against pathogenic viruses. While all membrane receptors and carbohydrate chains could potentially be used as receptors for viruses, prioritized searches focus typically on membrane receptors that are known to have been used by the relatives of the pathogenic virus, e.g., ACE2 used as a receptor for SARS-CoV is a prioritized candidate receptor for SARS-CoV-2. An ideal receptor protein from a viral perspective is one that is highly expressed in epithelial cell surface of mammalian respiratory or digestive tracts, strongly conserved in evolution so many mammalian species can serve as potential hosts, and functionally important so that its expression cannot be readily downregulated by the host in response to the infection. Experimental confirmation of host receptors includes (1) infection studies with cell cultures/tissues/organs with or without candidate receptor expression, (2) experimental determination of protein structure of the complex between the putative viral RDB and the candidate host receptor, and (3) experiments with mutant candidate receptor or homologues of the candidate receptor in other species. Successful identification of the host receptor opens the door for mechanism-based development of candidate drugs and vaccines and facilitates the inference of what other animal species are vulnerable to the viral pathogen. I illustrate these approaches with research on identification of the receptor and co-factors for SARS-CoV-2.

Future trajectory of SARS-CoV-2: Constant spillover back and forth between humans and animals

SARS-CoV-2, known as severe acute respiratory syndrome coronavirus 2, is causing a massive global public health dilemma. In particular, the outbreak of the Omicron variants of SARS-CoV-2 in several countries has aroused the great attention of the World Health Organization (WHO). As of February 1st, 2023, the WHO had counted 671,016,135 confirmed cases and 6,835,595 deaths worldwide. Despite effective vaccines and drug treatments, there is currently no way to completely and directly eliminate SARS-CoV-2. Moreover, frequent cases of SARS-CoV-2 infection in animals have also been reported. In this review, we suggest that SARS-CoV-2, as a zoonotic virus, may be frequently transmitted between animals and humans in the future, which provides a reference and warning for rational prevention and control of COVID-19.

Cervids ACE2 Residues that Bind the Spike Protein can Provide Susceptibility to SARS-CoV-2

The susceptibility of the white-tailed deer (WTD; Odocoileus virginianus) to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has highlighted cervids as coronavirus reservoirs. This study aimed to evaluate the angiotensin-converting enzyme 2 (ACE2) residues which bind the spike protein of SARS-CoV-2 from 16 cervids to predict their potential susceptibility to SARS-CoV-2 infection. Eleven out of 16 species presented identical ACE2 key residues to WTD ACE2. Four cervids presented K31N, a variant associated with low SARS-CoV-2 susceptibility. Large herding of cervids with ACE2 key residues identical to that of the WTD can result in extensive reservoirs of SARS-CoV-2. Cervids as potential reservoirs could favor SARS-CoV-2 adaptation and the emergence of new coronavirus strains.

Susceptibility of domestic and companion animals to SARS-CoV-2: a comprehensive review

The ongoing coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has caused a large global outbreak. The reports of domestic animals' infection with SARS-CoV-2 raise concerns about the virus's longer-lasting spread, the establishment of a new host reservoir, or even the evolution of a new virus, as seen with COVID-19. In this review, we focus on the susceptibility of domestic animals, especially companion animals, towards SARS-CoV-2 in light of existing studies of natural infection, experimental infection, and serological surveys. Susceptibility of domestic and companion animals to SARS-CoV-2 infection.

Identification of a novel linear B-cell epitope in porcine deltacoronavirus nucleocapsid protein

Porcine deltacoronavirus (PDCoV) is an emerging swine enteropathogenic coronavirus that caused diarrhea and/or vomiting in neonatal piglets worldwide. Coronaviruses nucleocapsid (N) protein is the most conserved structural protein for viral replication and possesses good antigenicity. In this study, three monoclonal antibodies (mAbs), 3B4, 4D3, and 4E3 identified as subclass IgG2aκ were prepared using the lymphocytic hybridoma technology against PDCoV N protein. Furthermore, the B-cell epitope recognized by mAb 4D3 was mapped by dozens of overlapping truncated recombinant proteins based on the western blotting. The polypeptide ²⁸QFRGNGVPLNSAIKPVE⁴⁴ (EP-4D3) in the N-terminal of PDCoV N protein was identified as the minimal linear epitope for binding mAb 4D3. And the EP-4D3 epitope's amino acid sequence homology study revealed that PDCoV strains are substantially conserved, with the exception of the Alanine⁴³ substitution Valine⁴³ in the China lineage, the Early China lineage, and the Thailand, Vietnam, and Laos lineage. The epitope sequences shared high similarity (94.1%) with porcine coronavirus HKU15-155 (PorCoV HKU15), Asian leopard cats coronavirus (ALCCoV), sparrow coronavirus HKU17 (SpCoV HKU17), and sparrow deltacoronavirus. In contrast, the epitope sequences shared a very low homology (11.8 to 29.4%) with other porcine CoVs (PEDV, TGEV, PRCV, SADS-CoV, PHEV). Overall, the study will enrich the biological function of PDCoV N protein and provide foundational data for further development of diagnostic applications. KEY POINTS: • Three monoclonal antibodies against PDCoV N protein were prepared. • Discovery of a novel B-cell liner epitope (²⁸QFRGNGVPLNSAIKPVE⁴⁴) of PDCoV N protein. • The epitope EP-4D3 was conserved among PDCoV strains.

Advances in SARS-CoV-2 receptor-binding domain-based COVID-19 vaccines

INTRODUCTION

The Coronavirus Disease 2019 (COVID-19) pandemic has caused devastating human and economic costs. Vaccination is an important step in controlling the pandemic. Severe acute respiratory coronavirus-2 (SARS-CoV-2), the causative agent of COVID-19, infects cells by binding a cellular receptor through the receptor-binding domain (RBD) within the S1 subunit of the spike (S) protein. Viral entry and membrane fusion are mediated by the S2 subunit.

AREAS COVERED

SARS-CoV-2 S protein, particularly RBD, serves as an important target for vaccines. Here we review the structure and function of SARS-CoV-2 S protein and its RBD, summarize current COVID-19 vaccines targeting the RBD, and outline potential strategies for improving RBD-based vaccines. Overall, this review provides important information that will facilitate rational design and development of safer and more effective COVID-19 vaccines.

EXPERT OPINION

The S protein of SARS-CoV-2 harbors numerous mutations, mostly in the RBD, resulting in multiple variant strains. Although many COVID-19 vaccines targeting the RBD of original virus strain (and previous variants) can prevent infection of these strains, their ability against recent dominant variants, particularly Omicron and its offspring, is significantly reduced. Collective efforts are needed to develop effective broad-spectrum vaccines to control current and future variants that have pandemic potential.

A one-year extensive molecular survey on SARS-CoV-2 in companion animals of Turkey shows a lack of evidence for viral circulation in pet dogs and cats

Current evidence have now demonstrated that SARS-CoV-2 infects a wide array of mammalian animals; however, the full range of hosts and the viral circulation in companion animals remains to be clarified. In this context, as no such evidenced cases have been reported from Turkey, we aimed to screen for SARS-CoV-2 nucleic acid in housed dogs and cats clinically evaluated for respiratory symptoms and reared in different locations of Samsun province in the black sea region of Turkey from July 2020 to July 2021. Nasal swabs were collected from a total of 415 pets (65 cats and 350 dogs) aged between 1 and 9 years old. All the specimens were tested for SARS-CoV-2 RNA presence by real-time RT-PCR targeting two genomic regions of SARS-CoV-2, but none showed positive results. Our findings suggest that SARS-CoV-2 does not circulate in local pets and is not responsible for respiratory symptoms. However, further comprehensive molecular and serological surveys are required to have a better picture of the zoonotic, reverse zoonotic and pathogenic consequences of the ongoing COVID-19 pandemic in Turkey.

ACE2 decoy receptor generated by high-throughput saturation mutagenesis efficiently neutralizes SARS-CoV-2 and its prevalent variants

The recent global pandemic was a spillover from the SARS-CoV-2 virus. Viral entry involves the receptor binding domain (RBD) of the viral spike protein interacting with the protease domain (PD) of the cellular receptor, ACE2. We hereby present a comprehensive mutational landscape of the effects of ACE2-PD point mutations on RBD-ACE2 binding using a saturation mutagenesis approach based on microarray-based oligo synthesis and a single-cell screening assay. We observed that changes in glycosylation sites and directly interacting sites of ACE2-PD significantly influenced ACE2-RBD binding. We further engineered an ACE2 decoy receptor with critical point mutations, D30I, L79W, T92N, N322V, and K475F, named C4-1. C4-1 shows a 200-fold increase in neutralization for the SARS-CoV-2 D614G pseudotyped virus compared to wild-type soluble ACE2 and a sevenfold increase in binding affinity to wild-type spike compared to the C-terminal Ig-Fc fused wild-type soluble ACE2. Moreover, C4-1 efficiently neutralized prevalent variants, especially the omicron variant (EC50=16 ng/mL), and rescued monoclonal antibodies, vaccine, and convalescent sera neutralization from viral immune-escaping. We hope to next investigate translating the therapeutic potential of C4-1 for the treatment of SARS-CoV-2.

Tracing the origin of Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2): A systematic review and narrative synthesis

The aim of the study was to trace and understand the origin of Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) through various available literatures and accessible databases. Although the world enters the third year of the coronavirus disease 2019 pandemic, health and socioeconomic impacts continue to mount, the origin and mechanisms of spill-over of the SARS-CoV-2 into humans remain elusive. Therefore, a systematic review of the literature was performed that showcased the integrated information obtained through manual searches, digital databases (PubMed, CINAHL, and MEDLINE) searches, and searches from legitimate publications (1966-2022), followed by meta-analysis. Our systematic analysis data proposed three postulated hypotheses concerning the origin of the SARS-CoV-2, which include zoonotic origin (Z), laboratory origin (L), and obscure origin (O). Despite the fact that the zoonotic origin for SARS-CoV-2 has not been conclusively identified to date, our data suggest a zoonotic origin, in contrast to some alternative concepts, including the probability of a laboratory incident or leak. Our data exhibit that zoonotic origin (Z) has higher evidence-based support as compared to laboratory origin (L). Importantly, based on all the studies included, we generated the forest plot with 95% confidence intervals (CIs) of the risk ratio estimates. Our meta-analysis further supports the zoonotic origin of SARS/SARS-CoV-2 in the included studies.

Variants of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) and Vaccine Effectiveness

The incidence and death toll due to SARS-CoV-2 infection varied time-to-time; and depended on several factors, including severity (viral load), immune status, age, gender, vaccination status, and presence of comorbidities. The RNA genome of SARS-CoV-2 has mutated and produced several variants, which were classified by the SARS-CoV-2 Interagency Group (SIG) into four major categories. The first category; “Variant Being Monitored (VBM)”, consists of Alpha (B.1.1.7), Beta (B.1.351), Gamma (P.1), Delta (B.1.617.2), Epsilon (B.1.427, B.1.429), Eta (B.1.525), Iota (B.1.526), Kappa (B.1.617.1), Mu (B.1.621), and Zeta (P.2); the second category; “Variants of Concern” consists of Omicron (B.1.1.529). The third and fourth categories include “Variants of Interest (VOI)”, and “Variants of High Consequence (VOHC)”, respectively, and contain no variants classified currently under these categories. The surge in VBM and VOC poses a significant threat to public health globally as they exhibit altered virulence, transmissibility, diagnostic or therapeutic escape, and the ability to evade the host immune response. Studies have shown that certain mutations increase the infectivity and pathogenicity of the virus as demonstrated in the case of SARS-CoV-2, the Omicron variant. It is reported that the Omicron variant has >60 mutations with at least 30 mutations in the Spike protein (“S” protein) and 15 mutations in the receptor-binding domain (RBD), resulting in rapid attachment to target cells and immune evasion. The spread of VBM and VOCs has affected the actual protective efficacy of the first-generation vaccines (ChAdOx1, Ad26.COV2.S, NVX-CoV2373, BNT162b2). Currently, the data on the effectiveness of existing vaccines against newer variants of SARS-CoV-2 are very scanty; hence additional studies are immediately warranted. To this end, recent studies have initiated investigations to elucidate the structural features of crucial proteins of SARS-CoV-2 variants and their involvement in pathogenesis. In addition, intense research is in progress to develop better preventive and therapeutic strategies to halt the spread of COVID-19 caused by variants. This review summarizes the structure and life cycle of SARS-CoV-2, provides background information on several variants of SARS-CoV-2 and mutations associated with these variants, and reviews recent studies on the safety and efficacy of major vaccines/vaccine candidates approved against SARS-CoV-2, and its variants.

Molecular surveillance revealed no SARS-CoV-2 spillovers to raccoons (Procyon lotor) in four German federal states

Raccoons (Procyon lotor), which are closely related to the family Mustelidae, might be susceptible to natural infection by SARS-CoV-2. This assumption is based on experimental evidence that confirmed the vulnerability of farmed fur-carnivore species, including Procyon lotor to SARS-CoV-2. To date, there are no reports of natural SARS-CoV-2 infections of raccoons in Germany. Here, we use RT-PCR to analyze 820 samples from raccoons hunted in Germany with a focus on 4 German federal states (Saxony-Anhalt, Thuringia, Hesse, North Rhine-Westphalia). Lung tissues were homogenized and processed for RNA extraction and RT-qPCR for detecting SARS-CoV-2 was performed. No viral RNA was detected in any samples (0/820). Next, we compared raccoons and human ACE-2 residues that are known to serve for binding with SARS-CoV-2 receptor binding domain (RBD). Interestingly, we found only 60% identity on amino acid level, which may have contributed to the absence of SARS-CoV-2 infections in raccoons. In conclusion, the chance of raccoons being intermediate reservoir hosts for SARS-CoV-2 seems to be very low.

Variations in Cell Surface ACE2 Levels Alter Direct Binding of SARS-CoV-2 Spike Protein and Viral Infectivity: Implications for Measuring Spike Protein Interactions with Animal ACE2 Orthologs

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of coronavirus disease 2019 (COVID-19), the most severe pandemic in a century. The virus gains access to host cells when the viral spike protein (S-protein) binds to the host cell surface receptor angiotensin-converting enzyme 2 (ACE2). Studies have attempted to understand SARS-CoV-2 S-protein interactions with vertebrate orthologs of ACE2 by expressing ACE2 orthologs in mammalian cells and measuring viral infection or S-protein binding. Often, these cells only transiently express ACE2 proteins, and the levels of ACE2 at the cell surface are not quantified. Here, we describe a cell-based assay that uses stably transfected cells expressing ACE2 proteins in a bicistronic vector with an easy-to-quantify reporter protein, Thy1.1. We found that both the binding of the S-protein receptor-binding domain (RBD) and infection with a SARS-CoV-2 pseudovirus are proportional to the amount of human ACE2 expressed at the cell surface, which can be inferred by quantifying the level of Thy1.1. We also compared different ACE2 orthologs, which were expressed in stably transfected cells expressing equivalent levels of Thy1.1. When ranked for either viral infectivity or RBD binding, mouse ACE2 had a weak to undetectable affinity for S-protein, while human ACE2 had the highest level detected, and feline ACE2 had an intermediate phenotype. The generation of stably transfected cells whose ACE2 level can be normalized for cross-ortholog comparisons allows us to create a reusable cellular library useful for measuring emerging SARS-CoV-2 variants' abilities to potentially infect different animals. IMPORTANCE SARS-CoV-2 is a zoonotic virus responsible for the worst global pandemic in a century. An understanding of how the virus can infect other vertebrate species is important for controlling viral spread and understanding the natural history of the virus. Here, we describe a method to generate cells stably expressing different orthologs of ACE2, the receptor for SARS-CoV-2, on the surface of a human cell line. We find that both the binding of the viral spike protein receptor-binding domain (RBD) and infection of cells with a SARS-CoV-2 pseudovirus are proportional to the ACE2 levels at the cell surface. This method will allow the creation of a library of stably transfected cells expressing similar levels of different vertebrate ACE2 orthologs, which can be used repeatedly for identifying vertebrate species that may be susceptible to infection with SARS-CoV-2 and its many variants.

Susceptibility of Domestic Goat (Capra aegagrus hircus) to Experimental Infection with Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) B.1.351/Beta Variant

A wide range of animal species are susceptible to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Natural and/or experimental infections have been reported in pet, zoo, farmed and wild animals. Interestingly, some SARS-CoV-2 variants, such as B.1.1.7/Alpha, B.1.351/Beta, and B.1.1.529/Omicron, were demonstrated to infect some animal species not susceptible to classical viral variants. The present study aimed to elucidate if goats (Capra aegagrus hircus) are susceptible to the B.1.351/Beta variant. First, an in silico approach was used to predict the affinity between the receptor-binding domain of the spike protein of SARS-CoV-2 B.1.351/Beta variant and angiotensin-converting enzyme 2 from goats. Moreover, we performed an experimental inoculation with this variant in domestic goat and showed evidence of infection. SARS-CoV-2 was detected in nasal swabs and tissues by RT-qPCR and/or immunohistochemistry, and seroneutralisation was confirmed via ELISA and live virus neutralisation assays. However, the viral amount and tissue distribution suggest a low susceptibility of goats to the B.1.351/Beta variant. Therefore, although monitoring livestock is advisable, it is unlikely that goats play a role as SARS-CoV-2 reservoir species, and they are not useful surrogates to study SARS-CoV-2 infection in farmed animals.

Cytokine storm and neuropathological alterations in patients with neurological manifestations of COVID-19

The COVID-19 pandemic is caused by the severe acute respiratory syndrome coronavirus (SARS-CoV-2), a respiratory pathogen with neuroinvasive potential. Neurological COVID-19 manifestations include loss of smell and taste, headache, dizziness, stroke, and potentially fatal encephalitis. Several studies found elevated proinflammatory cytokines such as TNF-α, IFN-γ, IL-6 IL-8, IL-10 IL-16, IL-17A, and IL-18 in severely and critically ill COVID-19 patients, which may persist even after apparent recovery from infection. Biomarker studies on CSF and plasma and serum from COVID-19 patients have also shown a high level of IL-6, intrathecal IgG, neurofilament light chain (NFL), glial fibrillary acidic protein (GFAP), and tau protein. Emerging evidence on the matter has established the concept of COVID-19 associated neuroinflammation, in the context of COVID-19 associated cytokine storm. While the short-term implications of this condition are extensively documented, its long-term implications are yet to be understood. The association of the aforementioned cytokines with the pathogenesis of neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, Huntington disease, and amyotrophic lateral sclerosis, may increase COVID-19 patients' risk to develop neurodegenerative diseases. Analysis of proinflammatory cytokines and CSF biomarkers in patients with COVID-19 can contribute to the early detection of the disease's exacerbation, monitoring the neurological implications of the disease and devising risk scales, and identifying treatment targets.

SARS-CoV-2 origins: zoonotic Rhinolophus vs contemporary models

The question of the origin of coronavirus spread like wildfire ever since it wreaked havoc among humankind, and ever since the scientific community has worked tirelessly to trace the history of the virus. In this review, we have tried to compile relevant literature pertaining to the different theories of origin of SARS-CoV-2, hopefully without any bias, and we strongly support the zoonotic origin of the infamous SARS-CoV-2 in bats and its transfer to human beings through the most probable evolutionary hosts, pangolins and minks. We also support the contemporary 'Circulation Model' that simply mirrors the concept of evolution to explain the origin of the virus which, the authors believe, is the most rational school of thought. The most recent variant of SARS-CoV-2, Omicron, has been taken as an example to clarify the concept. We recommend the community to refer to this model for further understanding and delving deep into this mystery of the origin of SARS-CoV-2.

Cell and Animal Models for SARS-CoV-2 Research

During the last two years following the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, development of potent antiviral drugs and vaccines has been a global health priority. In this context, the understanding of virus pathophysiology, the identification of associated therapeutic targets, and the screening of potential effective compounds have been indispensable advancements. It was therefore of primary importance to develop experimental models that recapitulate the aspects of the human disease in the best way possible. This article reviews the information concerning available SARS-CoV-2 preclinical models during that time, including cell-based approaches and animal models. We discuss their evolution, their advantages, and drawbacks, as well as their relevance to drug effectiveness evaluation.

Investigating SARS-CoV-2 Susceptibility in Animal Species: A Scoping Review

In the early stages of response to the SARS-CoV-2 pandemic, it was imperative for researchers to rapidly determine what animal species may be susceptible to the virus, under low knowledge and high uncertainty conditions. In this scoping review, the animal species being evaluated for SARS-CoV-2 susceptibility, the methods used to evaluate susceptibility, and comparing the evaluations between different studies were conducted. Using the PRISMA-ScR methodology, publications and reports from peer-reviewed and gray literature sources were collected from databases, Google Scholar, the World Organization for Animal Health (OIE), snowballing, and recommendations from experts. Inclusion and relevance criteria were applied, and information was subsequently extracted, categorized, summarized, and analyzed. Ninety seven sources (publications and reports) were identified which investigated 649 animal species from eight different classes: Mammalia, Aves, Actinopterygii, Reptilia, Amphibia, Insecta, Chondrichthyes, and Coelacanthimorpha. Sources used four different methods to evaluate susceptibility, in silico, in vitro, in vivo, and epidemiological analysis. Along with the different methods, how each source described "susceptibility" and evaluated the susceptibility of different animal species to SARS-CoV-2 varied, with conflicting susceptibility evaluations evident between different sources. Early in the pandemic, in silico methods were used the most to predict animal species susceptibility to SARS-CoV-2 and helped guide more costly and intensive studies using in vivo or epidemiological analyses. However, the limitations of all methods must be recognized, and evaluations made by in silico and in vitro should be re-evaluated when more information becomes available, such as demonstrated susceptibility through in vivo and epidemiological analysis.

Noninvasive Mapping of Angiotensin Converting Enzyme-2 in Pigeons Using Micro Positron Emission Tomography

The ACE2 receptor, as the potential entrance site of SARS-CoV-2-affected cells, plays a crucial role in spreading infection. The DX600 peptide is a competitive inhibitor of ACE2. We previously constructed the ⁶⁸Ga-labeled DOTA-DX600 (also known as ⁶⁸Ga-HZ20) peptide and confirmed its ACE2 binding ability both in vitro and in vivo. In this research, we aimed to investigate the noninvasive mapping of ACE2 expression in fowl using ⁶⁸Ga-HZ20 micro-PET. We chose pigeons as an animal model and first studied the administration method of ⁶⁸Ga-HZ20 by direct site injection or intravenous injection. Then, the dynamic micro-PET scan of ⁶⁸Ga-HZ20 was conducted at 0–40 min. Additionally, ¹⁸F-FDG was used for comparison. Finally, the pigeons were sacrificed, and the main organs were collected for further immunoPET and IHC staining. Micro PET/CT imaging results showed that ⁶⁸Ga-HZ20 uptake was distributed from the heart at the preliminary injection to the kidneys, liver, stomach, and lungs over time, where the highest uptake was observed in the kidneys (SUV_max = 6.95, 20 min) and lung (SUV_max = 1.11, 20 min). Immunohistochemical experiments were carried out on its main organs. Compared to the SUVmax data, the IHC results showed that ACE2 was highly expressed in both kidneys and intestines, and the optimal imaging time was determined to be 20 min after injection through correlation analysis. These results indicated that ⁶⁸Ga-HZ20 is a potential target molecule for SARS-CoV-2 in fowl, which is worthy of promotion and further study.

Recent developments in SARS-CoV-2 vaccines: A systematic review of the current studies

Designing and manufacturing efficient vaccines against coronavirus disease 2019 (COVID-19) is a major objective. In this systematic review, we aimed to evaluate the most important vaccines under construction worldwide, their efficiencies and clinical results in healthy individuals and in those with specific underlying diseases. We conducted a comprehensive search in PubMed, Scopus, EMBASE, and Web of Sciences by 1 December 2021 to identify published research studies. The inclusion criteria were publications that evaluated the immune responses and safety of COVID-19 vaccines in healthy individuals and in those with pre-existing diseases. We also searched the VAERS database to estimate the incidence of adverse events of special interest (AESI) post COVID-19 vaccination. Almost all investigated vaccines were well tolerated and developed good levels of both humoural and cellular responses. A protective and efficient humoural immune response develops after the second or third dose of vaccine and a longer interval (about 28 days) between the first and second injections of vaccine could induce higher antibody responses. The vaccines were less immunogenic in immunocompromised patients, particularly those with haematological malignancies. In addition, we found that venous and arterial thrombotic events, Bell's palsy, and myocarditis/pericarditis were the most common AESI. The results showed the potency of the SARS-CoV-2 vaccines to protect subjects against disease. The provision of further effective and safe vaccines is necessary in order to reach a high coverage of immunisation programs across the globe and to provide protection against infection itself.

Emerging viruses: Cross-species transmission of Coronaviruses, Filoviruses, Henipaviruses and Rotaviruses from bats

Emerging infectious diseases, especially if caused by bat-borne viruses, significantly affect public health and the global economy. There is an urgent need to understand the mechanism of interspecies transmission, particularly to humans. Viral genetics; host factors, including polymorphisms in the receptors; and ecological, environmental, and population dynamics are major parameters to consider. Here, we describe the taxonomy, geographic distribution, and unique traits of bats associated with their importance as virus reservoirs. Then, we summarize the origin, intermediate hosts, and the current understanding of interspecies transmission of Middle East respiratory syndrome coronavirus (MERS-CoV), severe acute respiratory syndrome coronavirus (SARS-CoV), SARS-CoV-2, Nipah, Hendra, Ebola, Marburg virus, and rotaviruses. Finally, the molecular interactions of viral surface proteins with host cell receptors are examined, and a comparison of these interactions in humans, intermediate hosts, and bats is conducted. This uncovers adaptive mutations in virus spike protein that facilitate cross-species transmission and risk factors associated with the emergence of novel viruses from bats.

COVID-19: A Veterinary and One Health Perspective

Interface with animals has been responsible for the occurrence of a major proportion of human diseases for the past several decades. Recent outbreaks of respiratory, haemorrhagic, encephalitic, arthropod-borne and other viral diseases have underlined the role of animals in the transmission of pathogens to humans. The on-going coronavirus disease-2019 (COVID-19) pandemic is one among them and is thought to have originated from bats and jumped to humans through an intermediate animal host. Indeed, the aetiology, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), can infect and cause disease in cats, ferrets and minks, as well as be transmitted from one animal to another. The seriousness of the pandemic along with the zoonotic origin of the virus has been a red alert on the critical need for collaboration and cooperation among human and animal health professionals, as well as stakeholders from various other disciplines that study planetary health parameters and the well-being of the biosphere. It is therefore imminent that One Health principles are applied across the board for human infectious diseases so that we can be better prepared for future zoonotic disease outbreaks and pandemics.

Epidemiology and Genetic Diversity of PCV2 Reveals That PCV2e Is an Emerging Genotype in Southern China: A Preliminary Study

Porcine circovirus-associated disease (PCVAD), caused by porcine circovirus type 2 (PCV2), has ravaged the pig industry, causing huge economic loss. At present, PCV2b and PCV2d are highly prevalent genotypes worldwide, while in China, in addition to PCV2b and PCV2d, a newly emerged PCV2e genotype detected in the Fujian province has attracted attention, indicating that PCV2 genotypes in China are more abundant. A preliminary study was conducted to better understand the genetic diversity and prevalence of PCV2 genotypes in southern China. We collected 79 random lung samples from pigs with respiratory signs, from 2018 to 2021. We found a PCV2-positivity rate of 29.1%, and frequent co-infections of PCV2 with PCV3, Streptococcus suis (S. suis), and other porcine pathogens. All PCV2-positive samples were sequenced and subjected to whole-genome analysis. Phylogenetic analysis, based on the PCV2 ORF2 gene and complete genomes, found that PCV2 strains identified in this study belonged to genotypes PCV2a (1), PCV2b (6), PCV2d (10), and PCV2e (6). Importantly, PCV2e was identified for the first time in some provinces, including Guangdong and Jiangxi. Additionally, we found two positively selected sites in the ORF2 region, located on the previously reported antigenic epitopes. Moreover, codon 63, one of the positively selected sites, has different types of amino acids in different genotypes. In conclusion, this study shows that PCV2e is an emerging genotype circulating in southern China, which warrants urgent, specific surveillance to aid the development of prevention and control strategies in China.

Theoretical Investigation of the Coronavirus SARS-CoV-2 (COVID-19) Infection Mechanism and Selectivity

The SARS-CoV-2 virus, commonly known as COVID-19, first occurred in December 2019 in Wuhan, Hubei Province, China. Since then, it has become a tremendous threat to human health. With a pandemic threat, it is in the significant interest of the scientific world to establish its method of infection. In this manuscript, we combine knowledge of the infection mechanism with theoretical methods to answer the question of the virus’s selectivity. We proposed a two-stage infection mechanism. In the first step, the virus interacts with the ACE2 receptor, with the “proper strength”. When the interaction is too strong, the virus will remain in an “improper position”; if the interaction is too weak, the virus will “run away” from the cell. We also indicated three residues (positions 30, 31, and 353) located on the ACE2 protein-binding interface, which seems to be crucial for successful infection. Our results indicate that these residues are necessary for the initiation of the infection process.

Therapeutic and prophylactic effect of flavonoids in post-COVID-19 therapy

The high incidence of post-covid symptoms in humans confirms the need for effective treatment. Due to long-term complications across several disciplines, special treatment programs emerge for affected patients, emphasizing multidisciplinary care. For these reasons, we decided to look at current knowledge about possible long-term complications of COVID-19 disease and then present the effect of flavonoids, which could help alleviate or eliminate complications in humans after overcoming the COVID-19 infection. Based on articles published from 2003 to 2021, we summarize the flavonoids-based molecular mechanisms associated with the post-COVID-19 syndrome and simultaneously provide a complex view regarding their prophylactic and therapeutic potential. Review clearly sorts out the outcome of post-COVID-19 syndrome according particular body systems. The conclusion is that flavonoids play an important role in prevention of many diseases. We suggest that flavonoids as critical nutritional supplements, are suitable for the alleviation and shortening of the period associated with the post-COVID-19 syndrome. The most promising flavonoid with noteworthy therapeutic and prophylactic effect appears to be quercetin.

Experimental and natural infections of severe acute respiratory syndrome-related coronavirus 2 in pets and wild and farm animals

The severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) has spread globally and has led to extremely high mortality rates. In addition to infecting humans, this virus also has infected animals. Experimental studies and natural infections showed that dogs have a low susceptibility to SARS-CoV-2 infection, whereas domesticated cats and other animals in the family Felidae, such as lions, tigers, snow leopards, and cougars, have a high susceptibility to viral infections. In addition, wild white-tailed deer, gorillas, and otters have been found to be infected by SARS-CoV-2. Furry farm animals, such as minks, have a high susceptibility to SARS-CoV-2 infection. The virus appears to spread among minks and generate several new mutations, resulting in increased viral virulence. Furthermore, livestock animals, such as cattle, sheep, and pigs, were found to have low susceptibility to the virus, whereas chicken, ducks, turkeys, quail, and geese did not show susceptibility to SARS-CoV-2 infection. This knowledge can provide insights for the development of SARS-CoV-2 mitigation strategies in animals and humans. Therefore, this review focuses on experimental (both replication and transmission) in vitro, ex vivo, and in vivo studies of SARS-CoV-2 infections in pets and in wild and farm animals, and to provide details on the mechanism associated with natural infection.

Why All the Fury over Furin?

Analysis of the SARS-CoV-2 sequence revealed a multibasic furin cleavage site at the S1/S2 boundary of the spike protein distinguishing this virus from SARS-CoV. Furin, the best-characterized member of the mammalian proprotein convertases, is an ubiquitously expressed single pass type 1 transmembrane protein. Cleavage of SARS-CoV-2 spike protein by furin promotes viral entry into lung cells. While furin knockout is embryonically lethal, its knockout in differentiated somatic cells is not, thus furin provides an exciting therapeutic target for viral pathogens including SARS-CoV-2 and bacterial infections. Several peptide-based and small-molecule inhibitors of furin have been recently reported, and select cocrystal structures have been solved, paving the way for further optimization and selection of clinical candidates. This perspective highlights furin structure, substrates, recent inhibitors, and crystal structures with emphasis on furin's role in SARS-CoV-2 infection, where the current data strongly suggest its inhibition as a promising therapeutic intervention for SARS-CoV-2.

Structural Bases of Zoonotic and Zooanthroponotic Transmission of SARS-CoV-2

The emergence of multiple variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) highlights the importance of possible animal-to-human (zoonotic) and human-to-animal (zooanthroponotic) transmission and potential spread within animal species. A range of animal species have been verified for SARS-CoV-2 susceptibility, either in vitro or in vivo. However, the molecular bases of such a broad host spectrum for the SARS-CoV-2 remains elusive. Here, we structurally and genetically analysed the interaction between the spike protein, with a particular focus on receptor binding domains (RBDs), of SARS-CoV-2 and its receptor angiotensin-converting enzyme 2 (ACE2) for all conceivably susceptible groups of animals to gauge the structural bases of the SARS-CoV-2 host spectrum. We describe our findings in the context of existing animal infection-based models to provide a foundation on the possible virus persistence in animals and their implications in the future eradication of COVID-19.

Diversity of Coronaviruses with Particular Attention to the Interspecies Transmission of SARS-CoV-2

Simple Summary

Coronaviruses are a broad group of viruses that may infect a wide range of animals, including humans. Despite the fact that each coronavirus has a limited host range, frequent interspecies transmission of coronaviruses across diverse hosts has resulted in a complex ecology. The recently discovered SARS-CoV-2 virus is the clearest evidence of the danger of a global pandemic spreading. Natural infection with SARS-CoV-2 has been reported in a variety of domestic and wild animals, which may complicate the virus’s epidemiology and influence its development. In this review, we discussed the potential determinants of SARS-CoV-2 interspecies transmission. Additionally, despite the efforts that have been made to control this pandemic and to implement the One Health policy, several problems, such as the role of animals in SARS-CoV-2 evolution and the dynamics of interspecies transmission, are still unanswered.

Abstract

In December 2019, the outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was reported in China with serious impacts on global health and economy that is still ongoing. Although interspecies transmission of coronaviruses is common and well documented, each coronavirus has a narrowly restricted host range. Coronaviruses utilize different receptors to mediate membrane fusion and replication in the cell cytoplasm. The interplay between the receptor-binding domain (RBD) of coronaviruses and their coevolution are determinants for host susceptibility. The recently emerged SARS-CoV-2 caused the coronavirus disease 2019 (COVID-19) pandemic and has also been reported in domestic and wild animals, raising the question about the responsibility of animals in virus evolution. Additionally, the COVID-19 pandemic might also substantially have an impact on animal production for a long time. In the present review, we discussed the diversity of coronaviruses in animals and thus the diversity of their receptors. Moreover, the determinants of the susceptibility of SARS-CoV-2 in several animals, with special reference to the current evidence of SARS-CoV-2 in animals, were highlighted. Finally, we shed light on the urgent demand for the implementation of the One Health concept as a collaborative global approach to mitigate the threat for both humans and animals.

Development of an in vitro model for animal species susceptibility to SARS-CoV-2 replication based on expression of ACE2 and TMPRSS2 in avian cells

The SARS-CoV-2 (SARS-CoV-2) virus has caused a worldwide pandemic because of the virus's ability to transmit efficiently human-to-human. A key determinant of infection is the attachment of the viral spike protein to the host receptor angiotensin-converting enzyme 2 (ACE2). Because of the presumed zoonotic origin of SARS-CoV-2, there is no practical way to assess the susceptibility of every species to SARS-CoV-2 by direct challenge studies. In an effort to have a better predictive model of animal host susceptibility to SARS-CoV-2, we expressed the ACE2 and/or transmembrane serine protease 2 (TMPRSS2) genes from humans and other animal species in the avian fibroblast cell line, DF1, that is not permissive to infection. We demonstrated that expression of both human ACE2 and TMPRSS2 genes is necessary to support SARS-CoV-2 infection and replication in DF1 and a non-permissive sub-lineage of MDCK cells. Titers of SARS-CoV-2 in these cell lines were comparable to those observed in control Vero cells. To further test the model, we developed seven additional transgenic cell lines expressing the ACE2 and TMPRSS2 derived from Felis catus (cat), Equus caballus (horse), Sus domesticus (pig), Capra hircus (goat), Mesocricetus auratus (Golden hamster), Myotis lucifugus (Little Brown bat) and Hipposideros armiger (Great Roundleaf bat) in DF1 cells. Results demonstrate permissive replication of SARS-CoV-2 in cat, Golden hamster, and goat species, but not pig or horse, which correlated with the results of reported challenge studies. Cells expressing genes from either bat species tested demonstrated temporal replication of SARS-CoV-2 that peaked early and was not sustained. The development of this cell culture model allows for more efficient testing of the potential susceptibility of many different animal species for SARS-CoV-2 and emerging variant viruses.

SARS-CoV-2 Serological and Biomolecular Analyses among Companion Animals in Campania Region (2020–2021)

The first reports of SARS-CoV-2 among domestic and wild animals, together with the rapid emergence of new variants, have created serious concerns regarding a possible spillback from animal hosts, which could accelerate the evolution of new viral strains. The present study aimed to investigate the prevalence and the transmission of SARS-CoV-2 among both owned and stray pets. A total of 182 dogs and 313 cats were tested for SARS-CoV-2. Specimens collected among owned and stray pets were subjected to RT-PCR and serological examinations. No viral RNA was detected, while anti-N antibodies were observed in six animals (1.3%), one dog (0.8%) and five cats (1.7%). Animals’ background revealed that owned cats, living with owners with COVID-19, showed significantly different prevalence compared to stray ones (p = 0.0067), while no difference was found among dogs. Among the seropositive pets, three owned cats also showed moderate neutralizing antibody titers. Pets and other species are susceptible to SARS-CoV-2 infection because of the spike affinity towards their ACE2 cellular receptor. Nevertheless, the risk of retransmission remains unclear since pet-to-human transmission has never been described. Due to the virus’ high mutation rate, new reservoirs cannot be excluded; thus, it is reasonable to test pets, mostly if living in households affected by COVID-19.

[Review of new evidence about the possible vertical transmission of coronavirus disease-2019]

OBJECTIVE

To conduct a systematic review of original peer-reviewed studies, containing data on the identification of SARS-CoV-2 in clinical samples of amniotic fluid, placenta or membranes, umbilical cord blood, and human milk, from women with a clinically or confirmed diagnosis of COVID-19. These studies should have been published after the guide for the management of patients with COVID-19 from World Health Organization guide (available in March 13, 2020).

RESULTS

Seventeen studies were included, in which 143 clinical samples were identified (38 of amniotic fluid; 34 of placentas or membranes; 39 from umbilical cord blood and 32 from human milk). Among the 143 samples, nine were positive for SARS-CoV-2 RNA (one amniotic fluid sample obtained before rupturing the membranes; six samples of placenta or membranes, although authors indicate the possibility of contamination by maternal blood in three of these, and two samples of human milk).

CONCLUSIONS

Following our search criteria, we found no studies that demonstrate the detection of SARS-CoV-2, in conjunction with viral isolation and the evaluation of the infective capacity of viral particles, in clinical samples of amniotic fluid, placenta or membranes, umbilical cord blood and human milk, from women with a confirmed or clinical diagnosis of COVID-19. However, vertical transmission cannot be ruled out, larger studies are required that ideally locate in situ RNA and protein of SARS-CoV-2, as well as isolation that demonstrate the infective capacity of the viral particles.

One Health: EAACI Position Paper on coronaviruses at the human-animal interface, with a specific focus on comparative and zoonotic aspects of SARS-CoV-2

The latest outbreak of a coronavirus disease in 2019 (COVID‐19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2), evolved into a worldwide pandemic with massive effects on health, quality of life, and economy. Given the short period of time since the outbreak, there are several knowledge gaps on the comparative and zoonotic aspects of this new virus. Within the One Health concept, the current EAACI position paper dwells into the current knowledge on SARS‐CoV‐2’s receptors, symptoms, transmission routes for human and animals living in close vicinity to each other, usefulness of animal models to study this disease and management options to avoid intra‐ and interspecies transmission. Similar pandemics might appear unexpectedly and more frequently in the near future due to climate change, consumption of exotic foods and drinks, globe‐trotter travel possibilities, the growing world population, the decreasing production space, declining room for wildlife and free‐ranging animals, and the changed lifestyle including living very close to animals. Therefore, both the society and the health authorities need to be aware and well prepared for similar future situations, and research needs to focus on prevention and fast development of treatment options (medications, vaccines).

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.

Seroprevalence of SARS-CoV-2 (COVID-19) exposure in pet cats and dogs in Minnesota, USA

The COVID-19 pandemic caused by the coronavirus SARS-CoV-2 is continuing to spread globally. SARS-CoV-2 infections of feline and canine species have also been reported. However, it is not entirely clear to what extent natural SARS-CoV-2 infection of pet dogs and cats is in households. We have developed enzyme-linked immunosorbent assays (ELISAs) using recombinant SARS-CoV-2 nucleocapsid (N) protein and the receptor-binding-domain (RBD) of the spike protein, and the SARS-CoV-2 spike-pseudotyped vesicular stomatitis virus (VSV)-based neutralization assay to screen serum samples of 239 pet cats and 510 pet dogs in Minnesota in the early phase of the COVID-19 pandemic from mid-April to early June 2020 for evidence of SARS-CoV-2 exposures. A cutoff value was used to identify the seropositive samples in each experiment. The average seroprevalence of N- and RBD-specific antibodies in pet cats were 8% and 3%, respectively. Among nineteen (19) N-seropositive cat sera, fifteen (15) exhibited neutralizing activity and seven (7) were also RBD-seropositive. The N-based ELISA is also specific and does not cross react with antigens of common feline coronaviruses. In contrast, SARS-CoV-2 antibodies were detected at a very low percentage in pet dogs (~ 1%) and were limited to IgG antibodies against SARS-CoV-2 N protein with no neutralizing activities. Our results demonstrate that SARS-CoV-2 seropositive rates are higher in pet cats than in pet dogs in MN early in the pandemic and that SARS-CoV-2 N-specific IgG antibodies can detect SARS-CoV-2 infections in companion animals with higher levels of specificity and sensitivity than RBD-specific IgG antibodies in ELISA-based assays.