Several approaches have been described to sensitize mice to infection with these virus strains, including transduction with adenovirus encoding human ACE2 (hACE2) (Ad5-hACE2) (10), providing hACE2 transgenically (e.g., K18-hACE2 Tg mice) (11, 12) and mutating the virus so that it can use mouse ACE2 to enter cells (13, 14). Here, ACE2 is linked to infection.