The histopathologic features in different organs are shown in Fig. 2 . Lung showed diffused alveolar damages including intraalveolar edema, focal intra-alveolar hemorrhage, necrosis of alveolar line cells, focal desquamation of pneumocytes in alveolar spaces, interstitial mononuclear inflammatory cell infiltrates, and extensive hyaline membranes. Trachea showed focal denudation of the epithelium with edema, and mononuclear inflammatory cell infiltrates. Spleen showed depletion of lymphocytes with congestion and organized infarcts. Axillary lymph-node was congested with depletion of lymphocytes. The central nervous system showed extensive edema with focal neuronal necrosis in hippocampus. Diastem between Purkinje cells layer and particle cells layer showed focal augmentation in cerebellum. Liver was congested with edema and focal fatty degeneration. Kidney was congested with edema. Other selected tissues showed no significant histological changes. (Fig. 3I ). As influenza virus is a negative-strand RNA virus, ISH stain with sense and antisense probes detected both virus RNA (with sense probe), mRNA and cRNA(with anti-sense probe). ISH stain showed that the two sets of probes (for hemagglutinin and nucleoprotein) generated similar staining results. In the selected 24 autopsy tissue from 5 organ systems, positive staining of ISH was detected in all samples except Bronchus, stomach and duodenum. In the lung tissue samples, sense probes extensively hybridized in the nuclei of pneumocytes (Fig. 4A) , whereas antisense probes hybridized in both the cytoplasm and nuclei. In all other organs with positive staining, both sense and antisense were present mainly in the cytoplasm of infected cells. In respiratory system, the positive staining was found in epithelial cell of lung ( 