Fig 1. Macroscopical changes and histology of the affected and control lungs.

(A) The lungs of the 3-day-old affected puppy are diffusely edematous and congested with only small visibly aerated area in the dorsal part of the right cranial lung lobe (black arrowheads). (B) In the affected lung of the 3-day-old puppy, the alveoli are small and collapsed in many areas and the alveolar walls are wide. The airspaces contain abundant eosinophilic material (black arrowheads) (Periodic acid Schiff (PAS) stain, 20X, scale bar 100 μm). (C) The morphology of the control lung corresponds to the normal saccular stage of development of 3-day-old puppies (PAS stain, 20X, scale bar 100 μm). (D) In the 28-day-old affected puppy, the lungs are rubbery in texture with multifocal emphysema (black arrowheads). (E) In the affected lung of the 28-day-old puppy, the alveolar septa are wide and contain increased amount of collagenous connective tissue (blue) and there are numerous macrophages and desquamated cells within the alveoli (Masson trichrome stain, 20X, scale bar 100 μm). (F) The morphology of the control lung of a 28-day-old puppy is normal for the alveolar stage of lung development. The alveolar septa are thin with normal amount of collagenous connective tissue (blue) (Masson trichrome stain, 20X, scale bar 100 μm).