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. 2011:2011:565787.
doi: 10.1155/2011/565787. Epub 2011 Dec 20.

Pathological Findings and Distribution of Pandemic Influenza A (H1N1) 2009 Virus in Lungs from Naturally Infected Fattening Pigs in Norway

Mette Valheim  1 , Hans Gamlem, Britt Gjerset, Anna Germundsson, Bjørn Lium
Affiliations

Pathological Findings and Distribution of Pandemic Influenza A (H1N1) 2009 Virus in Lungs from Naturally Infected Fattening Pigs in Norway

Mette Valheim et al. Influenza Res Treat. 2011.

Abstract

The Norwegian pig population was considered free from influenza A virus infections until the first case of porcine pandemic influenza A (H1N1) 2009 virus infection in October 2009. Human to pig transmission of virus was suspected. Unusual lung lesions were observed in fattening pigs, with red, lobular, multifocal to coalescing consolidation, most frequently in the cranial, middle, and accessory lobes. The main histopathological findings were epithelial degeneration and necrosis, lymphocyte infiltration in the epithelial lining and lamina propria of small bronchi and bronchioles, and peribronchial and peribronchiolar lymphocyte infiltrations. Infection with pandemic influenza A (H1N1) 2009 virus was confirmed by real-time RT-PCR and immunohistochemical detection of influenza A virus nucleoprotein in the lesions. This investigation shows that natural infection with the pandemic influenza A (H1N1) 2009 virus induces lung lesions similar to lesions described in experimental studies and natural infections with other swine-adapted subtypes of influenza A viruses.

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Figures

Figure 1
Figure 1
(Lung) Dorsal view. Dark red, multifocal atelectasis or mild consolidation (large arrows) primarily in cranial and middle lobes, but also in caudal lobes. The tracheobronchial lymph nodes were slightly enlarged (small arrows).
Figure 2
Figure 2
(Lung) Cranial and middle lobe. Lobular, multifocal dark red atelectasis or mild consolidation (large arrows) alternating with pink, emphysematous lobules (small arrows).
Figure 3
Figure 3
(Lung) Acute phase. Moderate infiltration of lymphocytes in the lamina propria (LP) in a bronchiole and peribronchiolar (PB) and perivascular (PV) lymphocyte infiltration. HE, 10x.
Figure 4
Figure 4
(Lung) Convalescence phase. Prominent peribronchial lymphoid hyperplasia with multiple large lymphoid follicles (arrows) that sometimes seemed to compress the lumina of small bronchi (BL) and bronchioles. HE, 10x.
Figure 5
Figure 5
Abundant influenza A virus nucleoprotein was detected in epithelial nuclei (large arrows) and in luminal cellular debris (CD) in bronchioles and small bronchi and in the nuclei (small arrows) in pneumocytes lining the alveolar septa. Immunohistochemistry AEC, counterstain hematoxylin, 20x.
Figure 6
Figure 6
(Lung) Sparse influenza A virus nucleoprotein was detected in few nuclei (large arrows) in bronchial and bronchiolar epithelial cells and in few nuclei (small arrow) in pneumocytes in the parenchyma. Immunohistochemistry AEC, counterstain hematoxylin, 20x.
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