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

ABSTRACT Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a highly transmissible respiratory pathogen whose main transmission route is respiratory droplets and/or aerosols. The development of an animal model and exposure system that recapitulates airborne transmission of SARS-CoV-2 is integral to understanding the dynamics of SARS-CoV-2 spread in individuals and populations. Here, we designed, built, and characterized a hamster transmission caging and exposure system that allows for efficient SARS-CoV-2 airborne transmission from an infected index animal to naïve recipients under unidirectional airflow, without contribution from direct contact transmission. We hypothesized that a 1:1 or 1:4 ratio of infected index to naïve recipient hamsters would have comparable virological and clinical measurements after 8 h of exposure. Air concentrations and pulmonary deposited doses of SARS-CoV-2 in index and naïve hamsters, respectively, were statistically similar in both groups. Daily nasal viral RNA levels, terminal (day 5) lung viral RNA and infectious virus, and fecal viral RNA levels were statistically similar among 1:1 and 1:4 naïve animals. However, virological measurements in the 1:4 naïve animals were more variable than those in the 1:1 naïve animals, possibly due to hamster piling behavior creating uneven SARS-CoV-2 exposure during the grouped 1:4 airborne exposure. This resulted in slight, but not statistically significant, changes in daily body weights between the 1:1 and 1:4 naïve groups. Our report describes a multi-chamber caging and exposure system that allowed for efficient SARS-CoV-2 airborne transmission in single and grouped hamsters, regardless of ratio. This system can be used to better define transmission dynamics and test transmission-blocking therapeutic strategies against SARS-CoV-2 between individuals and among groups. 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.