There is a vital need for authentic COVID-19 animal models to enable the pre-clinical evaluation of candidate vaccines and therapeutics. Here we report a dose titration study of SARS-CoV-2 in the ferret model. After a high (5 × 106 pfu) and medium (5 × 104 pfu) dose of virus is delivered, intranasally, viral RNA shedding in the upper respiratory tract (URT) is observed in 6/6 animals, however, only 1/6 ferrets show similar signs after low dose (5 × 102 pfu) challenge. Following sequential culls pathological signs of mild multifocal bronchopneumonia in approximately 5–15% of the lung is seen on day 3, in high and medium dosed groups. Ferrets re-challenged, after virus shedding ceased, are fully protected from acute lung pathology. The endpoints of URT viral RNA replication & distinct lung pathology are observed most consistently in the high dose group. This ferret model of SARS-CoV-2 infection presents a mild clinical disease.

A novel coronavirus, SARS-CoV-2, has been identified as the causative agent of the current COVID-19 pandemic. Animal models, and in particular non-human primates, are essential to understand the pathogenesis of emerging diseases and to assess the safety and efficacy of novel vaccines and therapeutics. Here, we show that SARS-CoV-2 replicates in the upper and lower respiratory tract and causes pulmonary lesions in both rhesus and cynomolgus macaques. Immune responses against SARS-CoV-2 are also similar in both species and equivalent to those reported in milder infections and convalescent human patients. This finding is reiterated by our transcriptional analysis of respiratory samples revealing the global response to infection. We describe a new method for lung histopathology scoring that will provide a metric to enable clearer decision making for this key endpoint. In contrast to prior publications, in which rhesus are accepted to be the preferred study species, we provide convincing evidence that both macaque species authentically represent mild to moderate forms of COVID-19 observed in the majority of the human population and both species should be used to evaluate the safety and efficacy of interventions against SARS-CoV-2. Importantly, accessing cynomolgus macaques will greatly alleviate the pressures on current rhesus stocks.

41In December 2019 an outbreak of coronavirus disease emerged in 42 Wuhan, China. The causative agent was subsequently identified and named severe 43 acute respiratory syndrome coronavirus 2 (SARS-CoV-2) which rapidly spread 44 worldwide causing a pandemic. Currently there are no licensed vaccines or 45 therapeutics available against SARS-CoV-2 but numerous candidate vaccines are in 46 development and repurposed drugs are being tested in the clinic. There is a vital need 47 for authentic COVID-19 animal models to further our understanding of pathogenesis 48 and viral spread in addition to pre-clinical evaluation of candidate interventions. 49 50Here we report a dose titration study of SARS-CoV-2 to determine the most suitable 51 infectious dose to use in the ferret model. We show that a high (5x10 6 pfu) and medium 52 (5x10 4 pfu) dose of SARS-CoV-2 induces consistent upper respiratory tract (URT) viral 53 RNA shedding in both groups of six challenged animals, whilst a low dose (5x10 2 pfu) 54 resulted in only one of six displaying signs of URT viral RNA replication. The URT 55 shedding lasted up to 21 days in the high dose animals with intermittent positive signal 56 from day 14. Sequential culls revealed distinct pathological signs of mild multifocal 57 bronchopneumonia in approximately 5-15% of the lung, observed on day 3 in high and 58 medium dosed animals, with presence of mild broncho-interstitial pneumonia on day 59 7 onwards. No obvious elevated temperature or signs of coughing or dyspnoea were 60 observed although animals did present with a consistent post-viral fatigue lasting from 61 day 9-14 in the medium and high dose groups. After virus shedding ceased, re-62 challenged ferrets were shown to be fully protected from acute lung pathology. The 63Page 4 of 39 endpoints of URT viral RNA replication in addition to distinct lung pathology and post 64 viral fatigue were observed most consistently in the high dose group. This ferret model 65 of SARS-CoV-2 infection presents a mild clinical disease (as displayed by 80% of 66 patients infected with SARS-CoV-2). In addition, intermittent viral shedding on days 67 14-21 parallel observations reported in a minority of clinical cases. 68 69 70 71 Word count: 327 72 Introduction 73 74 Coronaviruses are positive sense, single stranded RNA viruses belonging to the family 75 Coronaviridae 1 . These viruses can infect a range of animals, including humans and 76 usually cause a mild respiratory infection, much like the common cold. Two highly 77 pathogenic coronaviruses have emerged in the human population in the last 20 years; 78 severe acute respiratory syndrome (SARS) CoV and middle eastern respiratory 79 syndrome (MERS) CoV. SARS-CoV infected approximately 8,000 people worldwide with 80 a case fatality rate (CFR) of 10%, while MERS-CoV has infected approximately 2,500 81 people with a CFR of 36% 2 .82 83 In December 2019 several pneumonia cases of unknown cause emerged in Wuhan, 84 Hubei, China. Deep sequencing analysis from lower respiratory tract samples from ...

The global pandemic of coronavirus disease (COVID-19) caused by infection with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has led to an international thrust to study pathogenesis and evaluate interventions. Experimental infection of hamsters and the resulting respiratory disease is one of the preferred animal models since clinical signs of disease and virus shedding are similar to more severe cases of human COVID-19. The main route of challenge has been direct inoculation of the virus via the intranasal route. To resemble the natural infection, we designed a bespoke natural transmission cage system to assess whether recipient animals housed in physically separate adjacent cages could become infected from a challenged donor animal in a central cage, with equal airflow across the two side cages. To optimise viral shedding in the donor animals, a low and moderate challenge dose were compared after direct intranasal challenge, but similar viral shedding responses were observed and no discernible difference in kinetics. The results from our natural transmission set-up demonstrate that most recipient hamsters are infected within the system developed, with variation in the kinetics and levels of disease between individual animals. Common clinical outputs used for the assessment in directly-challenged hamsters, such as weight loss, are less obvious in hamsters who become infected from naturally acquiring the infection. The results demonstrate the utility of a natural transmission model for further work on assessing the differences between virus strains and evaluating interventions using a challenge system which more closely resembles human infection.

The mutation profile of the SARS-CoV-2 Omicron variant poses a concern for naturally acquired and vaccine-induced immunity. We investigated the ability of prior infection with an early SARS-CoV-2, 99.99% identical to Wuhan-Hu-1, to protect against disease caused by the Omicron variant. We established that infection with Omicron in naive Syrian hamsters resulted in a less severe disease than a comparable dose of prototype SARS-CoV-2 (Australia/VIC01/2020), with fewer clinical signs and less weight loss. We present data to show that these clinical observations were almost absent in convalescent hamsters challenged with the same dose of Omicron 50 days after an initial infection with Australia/VIC01/2020. The data provide evidence for immunity raised against prototype SARS-CoV-2 being protective against Omicron in the Syrian hamster model. Further investigation is required to conclusively determine whether Omicron is less pathogenic in Syrian hamsters and whether this is predictive of pathogenicity in humans.