Heterogeneous pathological outcomes after experimental pH1N1 influenza infection in ferrets correlate with viral replication and host immune responses in the lung

Vidaña, Beatriz; Martínez, Jorge; Martínez-Orellana, Pamela; García Migura, Lourdes; Montoya, María; Martorell, Jaime; Majó, Natàlia

Cross sections of the cranial, middle and caudal pulmonary lobes of each animal were separately evaluated, and semiquantitative assessments of IAV-associated microscopic lesions in the lungs were performed. The lesional scoring was graded on the basis of lesion severity as follows: grade 0 (no histopathological lesions observed), grade 1 (mild to moderate necrotising bronchiolitis), grade 2 (bronchointerstitial pneumonia characterised by necrotising bronchiolitis and diffuse alveolar damage in adjacent alveoli), and grade 3 (necrotising bronchiolitis and diffuse alveolar damage in the majority of the pulmonary parenchyma). Microscopic lesional scores were assigned for each lobe, and the means of the three lobes were used for the final histopathological score for each animal. Animals with lung lesion scores over 2 that presented with diffuse alveolar damage in at least 2 of the examined lung lobes were considered to have presented with severe lung lesions, and animals with scores below 2 were considered to have developed mild lung lesions.