Compellingly high SARS-CoV-2 susceptibility of Golden Syrian hamsters suggests multiple zoonotic infections of pet hamsters during the COVID-19 pandemic

Golden Syrian hamsters (Mesocricetus auratus) are used as a research model for severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2). Millions of Golden Syrian hamsters are also kept as pets in close contact to humans. To determine the minimum infective dose (MID) for assessing the zoonotic transmission risk, and to define the optimal infection dose for experimental studies, we orotracheally inoculated hamsters with SARS-CoV-2 doses from 1*10⁵ to 1*10⁻⁴ tissue culture infectious dose 50 (TCID₅₀). Body weight and virus shedding were monitored daily. 1*10⁻³ TCID₅₀ was defined as the MID, and this was still sufficient to induce virus shedding at levels up to 10^2.75 TCID₅₀/ml, equaling the estimated MID for humans. Virological and histological data revealed 1*10² TCID₅₀ as the optimal dose for experimental infections. This compellingly high susceptibility resulting in productive infections in Golden Syrian hamsters needs to be considered also as a source of SARS-CoV-2 infections in humans.