Lungs were inflated and stored in 10% neutral-buffered formalin. Three lung sections were placed into cassettes per lung section (right cranial, left cranial, left caudal, and right middle lobe) until they were trimmed, paraffin-embedded, and sectioned. Sections were mounted on glass slides and stained with hematoxylin and eosin for microscopic evaluation at Experimental Pathology Laboratories, Inc. by a veterinary pathologist. Sections were examined for the presence of abnormal findings including supprative and necrosupprative inflammation; epithelial hyperplasia and cytokaryomegaly; and fibrinous and exudative changes. Changes were graded with a standardized scale of 0-5, with 0 classified as ''not present'', 1 as ''minimal'', 2 as ''slight/mild'', 3 as ''moderate'', 4 as ''moderately severe'', and 5 as ''severe/high.'' For each ferret, a composite score for pathological changes was generated based on the locations in the respiratory tract (alveoli, bronchioli, bronchi) for statistical evaluation.