Pathology and immunohistochemistry of influenza A H1N1 2009 pandemic virus in naturally infected pigs

Swine influenza (SI) is an acute, highly contagious, respiratory disease caused by Influenza A virus infection. Present study describes pathology and tissue distribution of the virus in pigs naturally infected with Influenza A 2009 H1N1 pandemic virus. Unusual clinical signs such as fever, lethargy, anorexia, nasal discharge and occasional coughing were noticed in pigs raised in the farm located in Uttar Pradesh, India. At necropsy, lung revealed red, consolidations and depressions corresponding to individual lobules in the cranial, middle and accessory lobes. Lymphocyte infiltration in epithelial lining and lamina propria of small bronchi and bronchioles extending to peribronchial and peribronchiolar regions, epithelial degeneration and necrosis were the main microscopical findings. Infection with pandemic influenza A/Sw/UP-India/IVRI01/2009 H1N1 virus was confirmed by reverse transcriptase polymerase chain reaction (RT- PCR) and virus distribution in the tissue was localized by immunohistochemistry (IHC). This investigation showed that the natural infection with pandemic influenza A/Sw/UP-India/IVRI01/2009 H1N1 virus could induce lung lesions similar to lesions produced by other swine adapted influenza A virus subtypes in experimentally or naturally infected swine.