Characterization of the gastrointestinal microbiome of the Syrian hamster (Mesocricetus auratus) and comparison to data from mice.

Syrian hamsters (Mesocricetus auratus) have been increasingly used as rodent models in recent years, especially for SARS-CoV-2 since the pandemic. However, the physiology of this animal model is not yet well-understood, even less when considering the digestive tract. Generally, the gastrointestinal microbiome influences the immune system, drug metabolism, and vaccination efficacy. However, a detailed understanding of the gastrointestinal microbiome of hamsters is missing. Therefore, we analyzed 10 healthy 11-week-old RjHan:AURA hamsters fed a pelleted standard diet. Their gastrointestinal content was sampled (i.e., forestomach, glandular stomach, ileum, cecum, and colon) and analyzed using 16S rRNA gene amplicon sequencing. Results displayed a distinct difference in the bacterial community before and after the cecum, possibly due to the available nutrients and digestive functions. Next, we compared hamsters with the literature data of young-adult C57BL/6J mice, another important animal model. We sampled the same gastrointestinal regions and analyzed the differences in the microbiome between both rodents. Surprisingly, we found strong differences in their specific gastrointestinal bacterial communities. For instance, Lactobacillaceae were more abundant in hamsters' forestomach and ileum, while Muribaculaceae dominated in the mouse forestomach and ileum. Similarly, in mouse cecum and colon, Muribaculaceae were dominant, while in hamsters, Lachnospiraceae and Erysipelotrichaceae dominated the bacterial community. Molecular strains of Muribaculaceae in both rodent species displayed some species specificity. This comparison allows a better understanding of the suitability of the Syrian hamster as an animal model, especially regarding its comparability to other rodent models. Thereby, this work contributes to the characterization of the hamster model and allows better experimental planning.

Development of a live attenuated vaccine candidate for equid alphaherpesvirus 1 control: a step towards efficient protection.

Equid alphaherpesvirus 1 (EqAHV1) is a viral pathogen known to cause respiratory disease, neurologic syndromes, and abortion storms in horses. Currently, there are no vaccines that provide complete protection against EqAHV1. Marker vaccines and the differentiation of infected and vaccinated animals (DIVA) strategy are effective for preventing and controlling outbreaks but have not been used for the prevention of EqAHV1 infection. Glycoprotein 2 (gp2), located on the envelope of viruses (EqAHV1), exhibits high antigenicity and functions as a molecular marker for DIVA. In this study, a series of EqAHV1 mutants with deletion of gp2 along with other virulence genes (TK, UL24/TK, gI/gE) were engineered. The mutant viruses were studied in vitro and then in an in vivo experiment using Golden Syrian hamsters to assess the extent of viral attenuation and the immune response elicited by the mutant viruses in comparison to the wild-type (WT) virus. Compared with the WT strain, the YM2019 Δgp2, ΔTK/gp2, and ΔUL24/TK/gp2 strains exhibited reduced growth in RK-13 cells, while the ΔgI/gE/gp2 strain exhibited significantly impaired proliferation. The YM2019 Δgp2 strain induced clinical signs and mortality in hamsters. In contrast, the YM2019 ΔTK/gp2 and ΔUL24/TK/gp2 variants displayed diminished pathogenicity, causing no observable clinical signs or fatalities. Immunization with nasal vaccines containing YM2019 ΔTK/gp2 and ΔUL24/TK/gp2 elicited a robust immune response in hamsters. In particular, compared with the vaccine containing the ΔTK/gp2 strain, the vaccine containing the ΔUL24/TK/gp2 strain demonstrated enhanced immune protection upon challenge with the WT virus. Furthermore, an ELISA for gp2 was established and refined to accurately differentiate between infected and vaccinated animals. These results confirm that the ΔUL24/TK/gp2 strain is a safe and effective live attenuated vaccine candidate for controlling EqAHV1 infection.

Adapting Real-Time Lung Function Measurements for SARS-CoV-2 Infection Studies in Syrian Hamsters.

Pulmonary function examinations are critical to assess respiratory disease severity in patients. In preclinical rodent models of viral respiratory infections, however, disease is frequently evaluated based on virological, pathological and/or surrogate clinical parameters, which are not directly associated with lung function. To bridge the gap between preclinical and clinical readouts, we aimed to apply unrestrained whole-body plethysmography (WBP) measurements in a SARS-CoV-2 Syrian hamster challenge model. While WBP measurements are frequently used for preclinical research in mice and rats, results from studies in hamsters are still limited. During unrestrained WBP measurements, we obtained highly variable breathing frequency values outside of the normal physiological range for hamsters. Importantly, we observed that animal movements were recorded as breaths during WBP measurements. By limiting animal movement through either mechanical or chemical restraint, we improved the reliability of the lung function readout and obtained breathing frequencies that correlated with clinical signs when comparing two different variants of SARS-CoV-2 post-inoculation. Simultaneously, however, new sources of experimental variation were introduced by the method of restraint, which demands further optimalization of WBP measurements in Syrian hamsters. We concluded that WBP measurements are a valuable refinement either in combination with video recordings or if average values of measurements lasting several hours are analyzed.

Cross-species metabolomic profiling reveals phosphocholine-mediated liver protection from cold and ischemia/reperfusion.

Cold and ischemia/reperfusion (IR)-associated injuries are seemingly inevitable during liver transplantation and hepatectomy. Because Syrian hamsters demonstrate intrinsic tolerance to transplantation-like stimuli, cross-species comparative metabolomic analyses were conducted with hamster, rat, and donor liver samples to seek hepatic cold and IR-adaptive mechanisms. Lower hepatic phosphocholine contents were found in recipients with early graft-dysfunction and with virus-caused cirrhosis or high model for end-stage liver disease scores (≥30). Choline/phosphocholine deficiency in cultured human THLE-2 hepatocytes and animal models weakened hepatocellular cold tolerance and recovery of glutathione and ATP production, which was rescued by phosphocholine supplements. Among the biological processes impacted by choline/phosphocholine deficiency, 3 lipid-related metabolic processes were downregulated, whereas phosphocholine elevated the expression of genes in methylation processes. Consistently, in THLE-2, phosphocholine enhanced the overall RNA m6A methylation, among which the transcript stability of fatty acid desaturase 6 (FADS6) was improved. FADS6 functioned as a key phosphocholine effector in the production of polyunsaturated fatty acids, which may facilitate the hepatocellular recovery of energy and redox homeostasis. Thus, our study reveals the choline-phosphocholine metabolism and its downstream FADS6 functions in hepatic adaptation to cold and IR, which may inspire new strategies to monitor donor liver quality and improve recipient recovery from the liver transplantation process.

Coxsackievirus A7 and Enterovirus A71 Significantly Reduce SARS-CoV-2 Infection in Cell and Animal Models.

In this study, we investigated the features of co-infection with SARS-CoV-2 and the enterovirus vaccine strain LEV8 of coxsackievirus A7 or enterovirus A71 for Vero E6 cells and Syrian hamsters. The investigation of co-infection with SARS-CoV-2 and LEV-8 or EV-A71 in the cell model showed that a competitive inhibitory effect for these viruses was especially significant against SARS-CoV-2. Pre-infection with enteroviruses in the animals caused more than a 100-fold decrease in the levels of SARS-CoV-2 virus replication in the respiratory tract and more rapid clearance of infectious SARS-CoV-2 from the lower respiratory tract. Co-infection with SARS-CoV-2 and LEV-8 or EV-A71 also reduced the severity of clinical manifestations of the SARS-CoV-2 infection in the animals. Additionally, the histological data illustrated that co-infection with strain LEV8 of coxsackievirus A7 decreased the level of pathological changes induced by SARS-CoV-2 in the lungs. Research into the chemokine/cytokine profile demonstrated that the studied enteroviruses efficiently triggered this part of the antiviral immune response, which is associated with the significant inhibition of SARS-CoV-2 infection. These results demonstrate that there is significant viral interference between the studied strain LEV-8 of coxsackievirus A7 or enterovirus A71 and SARS-CoV-2 in vitro and in vivo.

Comparative studies between humans and golden Syrian hamsters via thromboelastography.

BACKGROUND: Thromboelastography (TEG) is a widely utilized clinical testing method for real-time monitoring of platelet function and the thrombosis process. Lipid metabolism disorders are crucial risk factors for thrombosis. The lipid metabolism characteristics of hamsters resemble those of humans more closely than mice and rats, and their relatively large blood volume makes them suitable for studying the mechanisms of thrombosis related to plasma lipid mechanisms. Whole blood samples from golden Syrian hamsters and healthy humans were obtained following standard clinical procedures. TEG was employed to evaluate coagulation factor function, fibrinogen (Fib) function, platelet function, and the fibrinolytic system. METHODS: The whole blood from hamster or healthy human was isolated following the clinical procedure, and TEG was employed to evaluate the coagulation factor function, Fib function, platelet function, and fibrinolytic system. Coagulation analysis used ACLTOP750 automatic coagulation analysis pipeline. Blood routine testing used XN-2000 automatic blood analyzer. RESULTS: TEG parameters revealed that hamsters exhibited stronger coagulation factor function than humans (reaction time [R], p = 0.0117), with stronger Fib function (alpha angle, p < 0.0001; K-time [K], p < 0.0001). Platelet function did not differ significantly (maximum amplitude [MA], p = 0.077). Hamsters displayed higher coagulation status than humans (coagulation index [CI], p = 0.0023), and the rate of blood clot dissolution in hamsters differed from that in humans (percentage lysis 30 min after MA, p = 0.02). Coagulation analysis parameters indicated that prothrombin time (PT) and activated partial thromboplastin time (APTT) were faster in hamsters than in humans (PT, p = 0.0014; APTT, p = 0.03), whereas the Fib content was significantly lower in hamsters than in humans (p < 0.0001). No significant difference was observed in thrombin time (p = 0.1949). CONCLUSIONS: In summary, TEG could be used to evaluate thrombosis and bleeding parameters in whole blood samples from hamsters. The platelet function of hamsters closely resembled that of humans, whereas their coagulation function was significantly stronger.

CSF1R inhibitor PLX3397 depletes microglia in Mongolian gerbil Meriones unguiculatus, but not in syrian hamster Mesocricetus auratus.

Microglia are the residential immune cells in the central nervous system. Their roles as innate immune cells and regulators of synaptic remodeling are critical to the development and the maintenance of the brain. Numerous studies have depleted microglia to elucidate their involvement in healthy and pathological conditions. PLX3397, a blocker of colony stimulating factor 1 receptor (CSF1R), is widely used to deplete mouse microglia due to its non-invasiveness and convenience. Recently, other small rodents, including Syrian hamsters (Mesocricetus auratus) and Mongolian gerbils (Meriones unguiculatus), have been recognized as valuable animal models for studying brain functions and diseases. However, whether microglia depletion via PLX3397 is feasible in these species remains unclear. Here, we administered PLX3397 orally via food pellets to hamsters and gerbils. PLX3397 successfully depleted gerbil microglia but had no effect on microglial density in hamsters. Comparative analysis of the CSF1R amino acid sequence in different species hints that amino acid substitutions in the juxtamembrane domain may potentially contribute to the inefficacy of PLX3397 in hamsters.

Slow decrease in temperature produces readthrough transcripts in mammalian hibernation.

Accumulating evidence suggests that various cellular stresses interfere with the end processing of mRNA synthesis and lead to the production of abnormally long transcripts, known as readthrough transcripts (RTTs), which extend beyond the termination sites. Small mammalian hibernators repeatedly enter a state referred to as deep torpor (DT), where the metabolic rate, respiration rate, and core body temperature become extremely low, which produces various types of cellular stresses and therefore induces RTTs. However, the types of stresses and processes around the DT that cause RTTs are unclear. In the present study, we showed that RTTs are produced from different gene loci in the livers of Syrian hamsters under DT and summer-like conditions. Moreover, in vitro analysis using hamster primary hepatocytes revealed that DT-specific RTTs are induced by a slow decline in temperature, as seen in body temperature in the entrance phase of DT, but not by rapid cold treatment or hypoxia. In addition, it was observed that RTTs were not elongated under a significantly cold temperature (4 °C). These results indicate that DT-specific RTTs are produced during the entrance phase of torpor by a slow decrease in body temperature.

Establishment and application of a surrogate model for human Ebola virus disease in BSL-2 laboratory.

The Ebola virus (EBOV) is a member of the Orthoebolavirus genus, Filoviridae family, which causes severe hemorrhagic diseases in humans and non-human primates (NHPs), with a case fatality rate of up to 90%. The development of countermeasures against EBOV has been hindered by the lack of ideal animal models, as EBOV requires handling in biosafety level (BSL)-4 facilities. Therefore, accessible and convenient animal models are urgently needed to promote prophylactic and therapeutic approaches against EBOV. In this study, a recombinant vesicular stomatitis virus expressing Ebola virus glycoprotein (VSV-EBOV/GP) was constructed and applied as a surrogate virus, establishing a lethal infection in hamsters. Following infection with VSV-EBOV/GP, 3-week-old female Syrian hamsters exhibited disease signs such as weight loss, multi-organ failure, severe uveitis, high viral loads, and developed severe systemic diseases similar to those observed in human EBOV patients. All animals succumbed at 2-3 days post-infection (dpi). Histopathological changes indicated that VSV-EBOV/GP targeted liver cells, suggesting that the tissue tropism of VSV-EBOV/GP was comparable to wild-type EBOV (WT EBOV). Notably, the pathogenicity of the VSV-EBOV/GP was found to be species-specific, age-related, gender-associated, and challenge route-dependent. Subsequently, equine anti-EBOV immunoglobulins and a subunit vaccine were validated using this model. Overall, this surrogate model represents a safe, effective, and economical tool for rapid preclinical evaluation of medical countermeasures against EBOV under BSL-2 conditions, which would accelerate technological advances and breakthroughs in confronting Ebola virus disease.

Host and viral determinants of airborne transmission of SARS-CoV-2 in the Syrian hamster.

It remains poorly understood how SARS-CoV-2 infection influences the physiological host factors important for aerosol transmission. We assessed breathing pattern, exhaled droplets, and infectious virus after infection with Alpha and Delta variants of concern (VOC) in the Syrian hamster. Both VOCs displayed a confined window of detectable airborne virus (24-48 hr), shorter than compared to oropharyngeal swabs. The loss of airborne shedding was linked to airway constriction resulting in a decrease of fine aerosols (1-10 µm) produced, which are suspected to be the major driver of airborne transmission. Male sex was associated with increased viral replication and virus shedding in the air. Next, we compared the transmission efficiency of both variants and found no significant differences. Transmission efficiency varied mostly among donors, 0-100% (including a superspreading event), and aerosol transmission over multiple chain links was representative of natural heterogeneity of exposure dose and downstream viral kinetics. Co-infection with VOCs only occurred when both viruses were shed by the same donor during an increased exposure timeframe (24-48 hr). This highlights that assessment of host and virus factors resulting in a differential exhaled particle profile is critical for understanding airborne transmission.

Coxsackievirus B3 HFMD animal models in Syrian hamster and rhesus monkey.

Coxsackievirus B3 (CVB3) is the pathogen causing hand, foot and mouth disease (HFMD), which manifests across a spectrum of clinical severity from mild to severe. However, CVB3-infected mouse models mainly demonstrate viral myocarditis and pancreatitis, failing to replicate human HFMD symptoms. Although several enteroviruses have been evaluated in Syrian hamsters and rhesus monkeys, there is no comprehensive data on CVB3. In this study, we have first tested the susceptibility of Syrian hamsters to CVB3 infection via different routes. The results showed that Syrian hamsters were successfully infected with CVB3 by intraperitoneal injection or nasal drip, leading to nasopharyngeal colonization, acute severe pathological injury, and typical HFMD symptoms. Notably, the nasal drip group exhibited a longer viral excretion cycle and more severe pathological damage. In the subsequent study, rhesus monkeys infected with CVB3 through nasal drips also presented signs of HFMD symptoms, viral excretion, serum antibody conversion, viral nucleic acids and antigens, and the specific organ damages, particularly in the heart. Surprisingly, there were no significant differences in myocardial enzyme levels, and the clinical symptoms resembled those often associated with common, mild infections. In summary, the study successfully developed severe Syrian hamsters and mild rhesus monkey models for CVB3-induced HFMD. These models could serve as a basis for understanding the disease pathogenesis, conducting pre-trial prevention and evaluation, and implementing post-exposure intervention.

Bivalent VSV Vectors Mediate Rapid and Potent Protection from Andes Virus Challenge in Hamsters.

Orthohantaviruses may cause hemorrhagic fever with renal syndrome or hantavirus cardiopulmonary syndrome. Andes virus (ANDV) is the only orthohantavirus associated with human-human transmission. Therefore, emergency vaccination would be a valuable public health measure to combat ANDV-derived infection clusters. Here, we utilized a promising vesicular stomatitis virus (VSV)-based vaccine to advance the approach for emergency applications. We compared monovalent and bivalent VSV vectors containing the Ebola virus (EBOV), glycoprotein (GP), and ANDV glycoprotein precursor (GPC) for protective efficacy in pre-, peri- and post-exposure immunization by the intraperitoneal and intranasal routes. Inclusion of the EBOV GP was based on its favorable immune cell targeting and the strong innate responses elicited by the VSV-EBOV vaccine. Our data indicates no difference of ANDV GPC expressing VSV vectors in pre-exposure immunization independent of route, but a potential benefit of the bivalent VSVs following peri- and post-exposure intraperitoneal vaccination.

Prototype and BA.5 protein nanoparticle vaccines protect against Omicron BA.5 variant in Syrian hamsters.

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants with greater transmissibility or immune evasion properties has jeopardized the existing vaccine and antibody-based countermeasures. Here, we evaluated the efficacy of boosting pre-immune hamsters with protein nanoparticle vaccines (Novavax, Inc.) containing recombinant Prototype (Wuhan-1) or BA.5 S proteins against a challenge with the Omicron BA.5 variant of SARS-CoV-2. Serum antibody binding and neutralization titers were quantified before challenge, and viral loads were measured 3 days after challenge. Boosting with Prototype or BA.5 vaccine induced similar antibody binding responses against ancestral Wuhan-1 or BA.5 S proteins, and neutralizing activity of Omicron BA.1 and BA.5 variants. One and three months after vaccine boosting, hamsters were challenged with the Omicron BA.5 variant. Prototype and BA.5 vaccine-boosted hamsters had reduced viral infection in the nasal washes, nasal turbinates, and lungs compared to unvaccinated animals. Although no significant differences in virus load were detected between the Prototype and BA.5 vaccine-boosted animals, fewer breakthrough infections were detected in the BA.5-vaccinated hamsters. Thus, immunity induced by Prototype or BA.5 S protein nanoparticle vaccine boosting can protect against the Omicron BA.5 variant in the Syrian hamster model. IMPORTANCE: As SARS-CoV-2 continues to evolve, there may be a need to update the vaccines to match the newly emerging variants. Here, we compared the protective efficacy of the updated BA.5 and the original Wuhan-1 COVID-19 vaccine against a challenge with the BA.5 Omicron variant of SARS-CoV-2 in hamsters. Both vaccines induced similar levels of neutralizing antibodies against multiple variants of SARS-CoV-2. One and three months after the final immunization, hamsters were challenged with BA.5. No differences in protection against the BA.5 variant virus were observed between the two vaccines, although fewer breakthrough infections were detected in the BA.5-vaccinated hamsters. Together, our data show that both protein nanoparticle vaccines are effective against the BA.5 variant of SARS-CoV-2 but given the increased number of breakthrough infections and continued evolution, it is important to update the COVID-19 vaccine for long-term protection.

Spatiotemporal analysis of SARS-CoV-2 infection reveals an expansive wave of monocyte-derived macrophages associated with vascular damage and virus clearance in hamster lungs.

IMPORTANCE: We present the first study of the 3D kinetics of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and the early host response in a large lung volume using a combination of tissue imaging and transcriptomics. This approach allowed us to make a number of important findings: Spatially restricted antiviral response is shown, including the formation of monocytic macrophage clusters and upregulation of the major histocompatibility complex II in infected epithelial cells. The monocyte-derived macrophages are linked to SARS-CoV-2 clearance, and the appearance of these cells is associated with post-infection endothelial damage; thus, we shed light on the role of these cells in infected tissue. An early onset of tissue repair occurring simultaneously with inflammatory and necrotizing processes provides the basis for longer-term alterations in the lungs.

Characterization of humoral responses to Nipah virus infection in the Syrian Hamster model of disease.

Nipah virus (NiV) is a highly pathogenic paramyxovirus. The Syrian hamster model recapitulates key features of human NiV disease and is a critical tool for evaluating antivirals and vaccines. Here we describe longitudinal humoral immune responses in NiV-infected Syrian hamsters. Samples were obtained 1-28 days after infection and analyzed by ELISA, neutralization, and Fc-mediated effector function assays. NiV infection elicited robust antibody responses against the nucleoprotein and attachment glycoprotein. Levels of neutralizing antibodies were modest and only detectable in surviving animals. Fc-mediated effector functions were mostly observed in nucleoprotein-targeting antibodies. Antibody levels and activities positively correlated with challenge dose.

Cardiomyopathy Does Not Exacerbate the Severity of Pneumonia Caused by a SARS-CoV-2 Delta Variant in the J2N-k Hamster Model.

Cardiovascular disease is one of many risk factors that have been linked to increased severity or mortality in coronavirus disease 2019 (COVID-19) patients; however, the exact role of SARS-CoV-2 in the pathogenesis of cardiac inflammatory injury has not been established. A previous study reported that SARS-CoV-2 causes more severe disease with cardiomyopathy in a J2N-k animal model. Here, we investigated the sensitivity of J2N-k hamsters, as a cardiomyopathy animal model, to a delta strain of SARS-CoV-2 compared to J2N-n control animals. We found that J2N-k hamsters were less susceptible to this delta strain than J2N-n animals, and we found no evidence that cardiomyopathy is a risk factor in this animal model. Since the previous study reported that SARS-CoV-2 causes more severe disease with cardiomyopathy in the same animal model, further analysis of the relationship between cardiomyopathy and SARS-CoV-2 infection is needed.

[Clinical symptoms and signs in hamsters during experimental infection with the SARS-CoV-2 virus (Coronaviridae: Betacoronavirus)].

INTRODUCTION: At the beginning of December 2019, humanity has faced a new problem caused by coronavirus. In Hubei province of central China, epidemic events associated with severe primary viral pneumonia in humans began to develop. The isolated etiological agent was identified as a representative of Coronaviridae family. The global pandemic associated with the new coronavirus infection, acute respiratory syndrome type 2 (Severe acute respiratory syndrome 2, SARS-CoV-2), has become a challenge for humanity. OBJECTIVE: In our work, we assessed the replicative ability and pathogenesis of the SARS-CoV-2 virus in hamsters. MATERIALS AND METHODS: Syrian hamsters (n=16) randomly divided into two groups were used in experiment. The first group was infected intranasally with the SARS-CoV-2 virus, strain SARS-CoV-2/human/KAZ/KZ_Almaty/2020 deposited in GenBank under number MZ379258.1. The second group remained as a control group. Clinical manifestations of the disease in hamsters were observed within 14 days. Samples were collected on days 3, 5, 7, 9, 12, and 14 postinfection. The obtained samples were tested for viral isolation in cell culture, histological examination and analysis of viral RNA by RT-PCR. RESULTS: SARS-CoV-2 virus isolates showed efficient replication in the lungs of hamsters, causing pathological lung lesions in animals infected intranasally. Clinical manifestations of the disease in hamsters infected with this virus were characterized by a decrease in temperature and body weight, wetness and ruffled fur, and frequent stroking of the nasal planum. High virus titers were observed following the virus isolation in cell cultures from nasal, oral swabs and lungs of animals infected intranasally. Pathological autopsy demonstrated pathological changes in the lungs. Moreover, transmission by airborne droplets has been established when a healthy hamster was kept together with animals infected using the intranasal method. CONCLUSION: In conclusion, our study showed that the Syrian hamster model is a useful tool for studying the SARS-CoV-2 pathogenesis, as well as testing vaccine candidates against acute respiratory syndrome type 2.

Spontaneous recurrence of a summer-like diel rhythm in the body temperature of the Syrian hamster after hibernation.

Mammalian hibernation is a survival strategy characterized by metabolic suppression and drastically lowering body temperature (Tb), used during harsh seasons with food shortages and cold. The Syrian hamster commences hibernation in response to a short photoperiod and cold but spontaneously concludes hibernation after several months without environmental cues. Little is known about the changes in diel rhythms during hibernation. Using long-term and high-resolution Tb data, we analysed the diel Tb rhythm time-course changes in Syrian hamsters raised under summer-like conditions (long photoperiod (LP) and warm; LP-warm) and transferred to winter-like conditions (short photoperiod (SP) and cold; SP-cold). The diel Tb rhythm was undetectable during the hibernation period (HIBP), reappearing after the HIBP. The phase of this returning rhythm reverted to the LP entrainment phase characteristics despite the ambient SP and then re-entrained to the ambient SP as if the hamsters were transferred from the LP-warm to SP-cold conditions. The diel Tb rhythm reverted from the SP- to LP-type in a hibernation-dependent manner. Under constant dark and cold conditions, the circadian Tb rhythm recovered without photic stimuli following the HIBP. These findings suggest that hibernation involves a program that anticipates the ambient photoperiod when animals emerge from hibernation.

Design and validation of an exposure system for efficient inter-animal SARS-CoV-2 airborne transmission in Syrian hamsters.

IMPORTANCE: The main route of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission is airborne. However, there are few experimental systems that can assess the airborne transmission dynamics of SARS-CoV-2 in vivo. Here, we designed, built, and characterized a hamster transmission caging and exposure system that allows for efficient SARS-CoV-2 airborne transmission in Syrian hamsters without contributions from fomite or direct contact transmission. We successfully measured SARS-CoV-2 viral RNA in aerosols and demonstrated that SARS-CoV-2 is transmitted efficiently at either a 1:1 or 1:4 infected index to naïve recipient hamster ratio. This is meaningful as a 1:4 infected index to naïve hamster ratio would allow for simultaneous comparisons of various interventions in naïve animals to determine their susceptibility to infection by aerosol transmission of SARS-CoV-2. Our SARS-CoV-2 exposure system allows for testing viral airborne transmission dynamics and transmission-blocking therapeutic strategies against SARS-CoV-2 in Syrian hamsters.

Human-to-Human Transmission of Andes Virus Modeled in Syrian Hamsters.

Several occurrences of human-to-human transmission of Andes virus, an etiological agent of hantavirus cardiopulmonary syndrome, are documented. Syrian hamsters consistently model human hantavirus cardiopulmonary syndrome, yet neither transmission nor shedding has been investigated. We demonstrate horizontal virus transmission and show that Andes virus is shed efficiently from both inoculated and contact-infected hamsters.