Figure 2.

High pathogenicity avian influenza virus H5N1 in bush dogs. (a) Liver, H&E. Acute, random focal hepatocellular necrosis, comprised of karyorrhectic debris and fibrin exudation with rare neutrophils and histiocytes. (b) IHC shows viral antigen in hepatocytes (thick brown arrow) on the periphery of the lesion, and in cellular debris. (c) Brain, cerebral cortex (CC), H&E. Vasculitis with segmental multifocal infiltration of a venule wall with neutrophils and histiocytes, is shown (thin black arrows). Multifocal to locally extensive necrosis and inflammation extends from the meninges into the adjacent neuropil (black circle). (d) IHC demonstrates antigen in vascular endothelial (black arrow) and arachnoid epithelial cells (blue arrow). (e) Lung, H&E. The bronchiolar lumen (B) is filled with degenerate and viable neutrophils, macrophages, eosinophilic material and shed epithelial cells, and the lamina propria and submucosa of the bronchiolar wall is diffusely mildly infiltrated by lymphocytes, histiocytes and fewer neutrophils. Adjacent alveolar spaces are collapsed and alveolar septae are congested and mildly expanded by neutrophils and macrophages. (f) IHC labelling is present in bronchiolar epithelial cells (black arrows) and within shed epithelial cells and macrophages in the lumen. (g) Adrenal gland, H&E. A subacute focal severe necrotizing vasculitis is seen with expansion of the vascular wall with neutrophils, pyknotic cellular debris and fewer mononuclear cells (black arrowheads), with subacute multifocal severe necrosis and inflammation of the adjacent epithelial cells in the acini of the adrenal medulla and cortex. (h) IHC highlights viral antigen in the acinar epithelial cells (black arrows).