ACE2 and respiratory tract infectious disorder: While mouse adapted SARS-CoV-2 viruses and genetic modifications for expression of hACE2 in mouse respiratory epithelial cells allow for infection by SARS-CoV-2, these appear to develop highly diverse pathologies after infection, depending on the levels and cell type–specific expression of humanized ACE2 (hACE2).20 In natural disease models, animals with endogenous ACE2 compatible with S may develop respiratory infection but often have subclinical disease.