Thumbnail of Immunohistochemical staining for equine influenza A virus (brown stain) in sections of respiratory tissue from English foxhounds involved in 2002 respiratory disease outbreak, United Kingdom. A) Case 1, showing focal staining of an apparently necrotic bronchiole in an area of pneumonia; magnification x100. B) Case 2, showing a large amount of staining throughout the epithelium and inflammatory cells present in the brush border; magnification x200; hematoxylin counterstain.