Oral SARS-CoV-2 Inoculation Establishes Subclinical Respiratory Infection with Virus Shedding in Golden Syrian Hamsters

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is transmitted largely by respiratory droplets or airborne aerosols.  Despite being frequently found in the immediate environment and faeces of patients, evidence supporting oral acquisition of SARS-CoV-2 is unavailable.  Utilizing Syrian hamster model, we demonstrated that the severity of pneumonia induced by intranasal inhalation of SARS-CoV-2 increased with virus inoculum. SARS-CoV-2 retained its infectivity in vitro in simulated human fed-gastric and fasted-intestinal fluid after two hours. Oral inoculation with the highest intranasal inoculum (10 5 PFU) caused only mild pneumonia in 67% (4/6) of the animals with no clinical symptoms. The lung histopathology and viral load were significantly lower than those infected by the lowest intranasal inoculum (100 PFU). However, 83% oral infection (10/12 hamsters) had similar level of detectable viral shedding from oral swabs and faeces as intranasally infected hamsters. Our findings indicated oral acquisition of SARS-CoV-2 can establish asymptomatic respiratory infection with less efficiency.