Hamsters as a Model of Severe Acute Respiratory Syndrome Coronavirus-2

Rehoming and Other Refinements and Replacement in Procedures Using Golden Hamsters in SARS-CoV-2 Vaccine Research

Effective vaccines are needed to fight the COVID-19 pandemic. Forty golden hamsters were inoculated with two promising vaccine candidates and eighteen animals were used in pilot trials with viral challenge. ELISA assays were performed to determine endpoint serum titres for specific antibodies and virus neutralisation tests were used to evaluate the efficacy of antibodies. All tests with serum from vaccinated hamsters were negative even after booster vaccinations and changes in vaccination protocol. We concluded that antibodies did not have sufficient neutralising properties. Refinements were observed at all steps, and the in vitro method (virus neutralisation test) presented a replacement measure and ultimately lead to a reduction in the total number of animals used in the project. The institutional animal welfare officer and institutional designated veterinarian approved the reuse or rehoming of the surplus animals. Simple socialization procedures were performed and ultimately 19 animals were rehomed, and feedback was collected. Recently, FELASA published recommendations for rehoming of animals used for scientific and educational purposes, with species-specific guidelines, including mice, rats, and rabbits. Based on our positive experience and feedback from adopters, we concluded that the rehoming of rodents, including hamsters, is not only possible, but highly recommended.

Evaluation of a SARS-CoV-2 spike protein ectodomain subunit vaccine with a squalene emulsion adjuvant in rodents and rhesus macaques

COVID-19 vaccines have played an important role in reducing the impact of the current pandemic. Previously, we developed NARUVAX-C19 vaccine based on a recombinant Wuhan spike protein extracellular domain expressed in insect cells and formulated with a squalene emulsion adjuvant (Sepivac SWE™). The current study assessed the immunogenicity, efficacy, and safety of NARUVAX-C19 vaccine in rhesus macaques and hamsters. Macaques immunized intramuscularly with two doses of NARUVAX-C19 vaccine showed no adverse effects and demonstrated cellular immunity as assessed by T cell IFN-γ responses against spike protein, in addition to inducing a humoral response. Serum from immunized animals neutralized the homologous wild-type SARS-CoV-2 virus as well as the Alpha and Delta variants. In hamsters, immunization with NARUVAX-C19 vaccine protected against a heterologous challenge with the Delta virus, as reflected by reduced lung and nasal viral loads and lung pathology in immunized animals. Nevertheless, some NARUVAX-C19 vaccinated animals were still shown to transmit infection to naïve sentinel animals. Overall, NARUVAX-C19 vaccine induced broadly cross-neutralizing antibody and T cell IFN-γ responses in rhesus macaques and provided heterologous protection of hamsters against infection by the Delta virus variant. This data supports the utility of squalene emulsion-based adjuvanted recombinant vaccine in protection against SARS-CoV-2 and supports their continued clinical development.

The impact of primary immunization route on the outcome of infection with SARS-CoV-2 in a hamster model of COVID-19

The COVID-19 pandemic, caused by the SARS-CoV-2 virus, has resulted in over 6.7 million deaths worldwide. COVID-19 vaccines administered parenterally via intramuscular or subcutaneous (SC) routes have reduced the severity of respiratory infections, hospitalization rates, and overall mortality. However, there is a growing interest in developing mucosally delivered vaccines to further enhance the ease and durability of vaccination. This study compared the immune response in hamsters immunized with live SARS-CoV-2 virus via SC or intranasal (IN) routes and assessed the outcome of a subsequent IN SARS-CoV-2 challenge. Results showed that SC-immunized hamsters elicited a dose-dependent neutralizing antibody response but of a significantly lower magnitude than that observed in IN-immunized hamsters. The IN challenge with SARS-CoV-2 in SC-immunized hamsters resulted in body weight loss, increased viral load, and lung pathology than that observed in IN-immunized and IN-challenged counterparts. These results demonstrate that while SC immunization renders some degree of protection, IN immunization induces a stronger immune response and better protection against respiratory SARS-CoV-2 infection. Overall, this study provides evidence that the route of primary immunization plays a critical role in determining the severity of a subsequent respiratory infection caused by SARS-CoV-2. Furthermore, the findings suggest that IN route of immunization may be a more effective option for COVID-19 vaccines than the currently used parenteral routes. Understanding the immune response to SARS-CoV-2 elicited via different immunization routes may help guide more effective and long-lasting vaccination strategies.

Animal Models for the Study of SARS-CoV-2-Induced Respiratory Disease and Pathology

Emergence of the betacoronavirus SARS-CoV-2 has resulted in a historic pandemic, with millions of deaths worldwide. An unprecedented effort has been made by the medical, scientific, and public health communities to rapidly develop and implement vaccines and therapeutics to prevent and reduce hospitalizations and deaths. Although SARS-CoV-2 infection can lead to disease in many organ systems, the respiratory system is its main target, with pneumonia and acute respiratory distress syndrome as the hallmark features of severe disease. The large number of patients who have contracted COVID-19 infections since 2019 has permitted a detailed characterization of the clinical and pathologic features of the disease in humans. However, continued progress in the development of effective preventatives and therapies requires a deeper understanding of the pathogenesis of infection. Studies using animal models are necessary to complement in vitro findings and human clinical data. Multiple animal species have been evaluated as potential models for studying the respiratory disease caused by SARSCoV-2 infection. Knowing the similarities and differences between animal and human responses to infection is critical for effective translation of animal data into human medicine. This review provides a detailed summary of the respiratory disease and associated pathology induced by SARS-CoV-2 infection in humans and compares them with the disease that develops in 3 commonly used models: NHP, hamsters, and mice. The effective use of animals to study SARS-CoV-2-induced respiratory disease will enhance our understanding of SARS-CoV-2 pathogenesis, allow the development of novel preventatives and therapeutics, and aid in the preparation for the next emerging virus with pandemic potential.

Severe Acute Respiratory Syndrome Coronavirus-2 Delta Variant Study In Vitro and Vivo

At the end of 2019, an outbreak of a new severe acute respiratory syndrome caused by a coronavirus occurred in Wuhan, China, after which the virus spread around the world. Here, we have described the adaptive capacity and pathogenesis of the SARS-CoV-2 Delta variant, which is widespread in Armenia, in vitro and vivo on Syrian hamsters. We have studied the changes in the SARS-CoV-2genome using viral RNA sequencing during virus adaptation in vitro and in vivo. Our findings revealed that SARS-CoV-2 in Syrian hamsters causes a short-term pulmonary form of the disease, the first symptoms appear within 48 h after infection, reach 5-7 days after infection, and begin to disappear by 7-9 days after infection. The virus induces pathogenesis in the blood and bone marrow, which generally corresponds to the manifestation of the inflammatory process. The pulmonary form of the disease passes faster than changes in blood cells and bone marrow. Our data show that hamster organs do not undergo significant pathological changes in the Delta variant of SARS-CoV-2 infection.

Volume-Associated Clinical and Histopathological Effects of Intranasal Instillation in Syrian Hamsters: Considerations for Infection and Therapeutic Studies

Syrian hamsters are a key animal model of SARS-CoV-2 and other respiratory viruses and are useful for the evaluation of associated medical countermeasures. Delivery of an infectious agent or intervention to the respiratory tract mirrors natural routes of exposure and allows for the evaluation of clinically relevant therapeutic administration. The data to support instillation or inoculation volumes are important both for optimal experimental design and to minimize or avoid effects of diluent alone, which may compromise both data interpretation and animal welfare. Here we investigate four intranasal (IN) instillation volumes in hamsters (50, 100, 200, or 400 µL). The animals were monitored daily, and a subset were serially euthanized at one of four pre-determined time-points (1, 3, 7, and 14 days post-instillation). Weight, temperature, oxygen saturation, CBC, radiographs, and respiratory tissue histopathology were assessed to determine changes associated with instillation volume alone. With all the delivery volumes, we found no notable differences between instilled and non-instilled controls in all of the parameters assessed, except for histopathology. In the animals instilled with 200 or 400 µL, inflammation associated with foreign material was detected in the lower respiratory tract indicating that higher volumes may result in aspiration of nasal and/or oropharyngeal material in a subset of animals, resulting in IN instillation-associated histopathology.

Animal models for COVID-19: advances, gaps and perspectives

COVID-19, caused by SARS-CoV-2, is the most consequential pandemic of this century. Since the outbreak in late 2019, animal models have been playing crucial roles in aiding the rapid development of vaccines/drugs for prevention and therapy, as well as understanding the pathogenesis of SARS-CoV-2 infection and immune responses of hosts. However, the current animal models have some deficits and there is an urgent need for novel models to evaluate the virulence of variants of concerns (VOC), antibody-dependent enhancement (ADE), and various comorbidities of COVID-19. This review summarizes the clinical features of COVID-19 in different populations, and the characteristics of the major animal models of SARS-CoV-2, including those naturally susceptible animals, such as non-human primates, Syrian hamster, ferret, minks, poultry, livestock, and mouse models sensitized by genetically modified, AAV/adenoviral transduced, mouse-adapted strain of SARS-CoV-2, and by engraftment of human tissues or cells. Since understanding the host receptors and proteases is essential for designing advanced genetically modified animal models, successful studies on receptors and proteases are also reviewed. Several improved alternatives for future mouse models are proposed, including the reselection of alternative receptor genes or multiple gene combinations, the use of transgenic or knock-in method, and different strains for establishing the next generation of genetically modified mice.

Natural and genetically-modified animal models to investigate pulmonary and extrapulmonary manifestations of COVID-19

Coronavirus disease-19 (COVID-19), a pandemic caused by Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2), is a primarily respiratory tract disease. Suitable animal models for COVID-19 are required to study various aspects of pathogenesis, drug discovery, effective and safe vaccine development. Several laboratory animals including, non-human primates, hamsters, ferrets, transgenic mice, and zebrafish, have been used and proven their significance experimentally. Currently available animal models of SARS-CoV-2 can be broadly classified into two categories 1) natural animal models 2) genetically-modified that exhibit different degrees of susceptibility of SARS-CoV-2, tissue damage in respiratory and other organ systems. Not all the available animal models mimic COVID-19-like phenotype completely. Therefore, understanding various aspects of COVID-19 requires different animal models. In this review article, we provide an update on the immune response and clinical manifestations observed in naturally occurring and genetically-modified animals of COVID-19. We then review the transmission, viral replication, lung pathology, immunological aspects, and extrapulmonary phenotypes observed in various animal models. In the end, we put forth our perspective on the anticipated uses, disadvantages, and limitations of each type of animal model.

An intra-cytoplasmic route for SARS-CoV-2 transmission unveiled by Helium-ion microscopy

SARS-CoV-2 virions enter the host cells by docking their spike glycoproteins to the membrane-bound Angiotensin Converting Enzyme 2. After intracellular assembly, the newly formed virions are released from the infected cells to propagate the infection, using the extra-cytoplasmic ACE2 docking mechanism. However, the molecular events underpinning SARS-CoV-2 transmission between host cells are not fully understood. Here, we report the findings of a scanning Helium-ion microscopy study performed on Vero E6 cells infected with mNeonGreen-expressing SARS-CoV-2. Our data reveal, with unprecedented resolution, the presence of: (1) long tunneling nanotubes that connect two or more host cells over submillimeter distances; (2) large scale multiple cell fusion events (syncytia); and (3) abundant extracellular vesicles of various sizes. Taken together, these ultrastructural features describe a novel intra-cytoplasmic connection among SARS-CoV-2 infected cells that may act as an alternative route of viral transmission, disengaged from the well-known extra-cytoplasmic ACE2 docking mechanism. Such route may explain the elusiveness of SARS-CoV-2 to survive from the immune surveillance of the infected host.