Transgenic mice expressing the human angiotensin I–converting enzyme (ACE2) receptor driven by the cytokeratin-18 gene promoter, K18-hACE2, an additional model for the SARS-CoV-2 infection, were also tested here for changes in group activity following the i.n. infection with a lethal dose of 2000 pfu of SARS-CoV-2 (Figure 3). Here, ACE2 is linked to infection.