Lung pathology of mice infected with different viral strains. The figure shows lung pathology of C57/BL6 mice at 1 d.p.i. (a) and 3d.p.i. (c and d) and BALB/C at 3 d.p.i. (e) after NC2 infection. In contrast NC8 infected C57/BL6 mice show no (b) and very mild (f) pathological signs at 1 and 3 d.p.i. respectively. Thin arrows – inflammation in interstitial space; thick arrows – hemorrhage in respiratory bronchioles; white arrows – infiltrating cells in lumen of terminal bronchiole; curved arrows – inflammation in peribronchial area; white triangle – pulmonary edema; white cross – damaged epithelium.