Figure 4: SARS-CoV-2 infection of Syrian hamsters results in broncho-interstitial pneumonia.

Syrian hamsters were infected intranasally with 500 ID₅₀ (10³ TCID₅₀) of SARS-CoV-2. Lungs were fixed in 10% formalin, cut and stained with Hematoxylin and Eosin (HE) to examine pulmonary pathology at 3, 5 and 10dpi. (A-C), 3dpi. (A) Inflammation initiates within interstitial spaces in and around terminal airways with a minimal cellular exudate into the airway spaces (100x, size bar is 50um). (B) Bronchiolar epithelial necrosis with influx of neutrophils into the mucosa and airway lumen (400x, size bar is 20um). (C) Attenuation of the tracheal mucosa with loss of apical cilia accompanied with an influx of moderate numbers of degenerate and non-degenerate neutrophils (400x, size bar is 20um). (D-F), 5dpi. (D) Locally extensive inflammation is noted (100x, size bar is 50um). (E) Progressive bronchiolitis with degenerate and non-degenerate neutrophils and exudate within the lumen and prominent epithelial syncytial cells (arrows; 400x, size bar is 20um). (F) Alveolar spaces contain macrophages and neutrophils. Alveolar septa are thickened and expanded by fibrin, edema fluid and infiltrating leukocytes and are lined by prominent type II pneumocytes (arrowhead) and rare syncytial cells (arrow; 400x, size bar is 20um). (G-I), 10dpi. (G) Resolving inflammation is largely limited to bronchioles and the adjacent alveolar spaces (100x, size bar is 50um) (H) Alveolar septa are thickened by collagen with lymphocytes and lined by numerous plump type II pneumocytes that surround low numbers of foamy alveolar macrophages (400x, size bar is 20um). (I) Multifocal pleural fibrosis is evident with mild subpleural inflammation (200x, size bar is 20um).