Exceptionally high susceptibility of Golden Syrian hamsters to SARS-CoV-2 infection supports recent findings of zoonotic transmission between pet hamsters and humans

Golden Syrian hamsters (Mesocricetus auratus) have been established as a small animal model for human infections with Severe Acute Coronavirus 2 (SARS-CoV-2) and the associated human disease, Coronavirus Disease 19 (COVID-19), and are widely being used in various fields of research. Millions of Syrian hamsters are being kept as pets in very close contact to humans worldwide. To determine the minimal infectious dose for this species, and to define the optimal infection dose for further studies, we inoculated hamsters with SARS-CoV-2 doses ranging from 1*103 TCID50 to 1*10-5 TCID50, and monitored the body weight, clinical behavior, and virus shedding daily for up to 10 days. We found that an infection dose of 1*10-2 TCID50 was sufficient to induce clinical disease and virus shedding in infected hamsters, while even a dose of 1*10-4 TCID50 (equivalent of 0.7 RNA copies per infection dose) was sufficient to induce a subclinical SARS-CoV-2 infection without detectable shedding. A 2-3 day delay in the onset of virus shedding in the groups infected with doses below 1*10-1 TCID50 occurred, but viral loads detected in the tissue samples reached comparable levels in all infected groups. All uninfected control animals remained negative. This astonishing susceptibility of Golden Syrian hamsters to extremely low infection doses is relevant for the assessment of a transmission risk regarding pet Syrian hamsters.