Figure 5.

Histopathology and IHC. (a–f) H&E staining of respiratory organs. (a) Unaffected lung tissue of a negative control animal. (b) Unaffected nasal conchae of a negative control animal. (c) Unaffected trachea section of a negative control animal. (d) Severe interstitial pneumonia of a lung on DPI 4. (e) Severe inflammation of nasal conchae. Note the degenerated epithelial layer (arrow) and the mononuclear cell infiltration (arrowhead). (f) Trachea with loss of ciliated epithelium and influx of inflammatory cells in submucosa (arrowhead). (g–i) IHC staining against the nucleoprotein of SARS-CoV-2. (g) Staining of alveolar and bronchiolar epithelial cells (DPI 2). (h) Staining of nasal respiratory epithelium and desquamated epithelial cells (DPI 2). (i) Staining of tracheal epithelial cells (DPI 2). (j) Extent of lung histopathology in juvenile and adult hamsters graded from 0 (no changes) to 4 (≥70% of left lung surface is affected). (k) Cumulative severity of lung histopathology in juvenile and adult hamsters. (l) SARS-CoV-2 viral nucleoprotein expression in juvenile and adult lung tissue (IHC) graded from 0 (no staining) to 4 (extensive staining) throughout the whole tissue. (j–l) Symbols represent individual values and lines represent averages of N = 2 and N = 8 hamsters per group on days post-infection (DPI) 0-10 and DPI 21, respectively. For statistical analysis, a Poisson (k) or a linear (j,l) regression model was used to compare differences in the progression of histopathological lesions/scores in time between adult and juvenile hamsters in time. The Nagelkerke (k) or adjusted (j,l) R-squared value for the regression models is shown in the respective graphs. Differences with p values ≤ 0.05 were considered significant. Significance code: *—p ≤ 0.05; ns—not significant.