ACE2 and COVID-19: Aged ferrets presented higher virus loads and longer shedding in respiratory secretions than young animals did due to higher expression levels of ACE2 and TMPRSS2, receptors of virus entry, in the upper respiratory tract.399 Moreover, the expression of type I interferons, activated T cells, and M1 macrophage response genes was strongly upregulated in aged ferret lungs, which is in agreement with what has been observed in patients with severe COVID-19.400 Overall, compared with young ferrets, aged ferrets more accurately mimicked disease features.