Schematic drawing to show the topographical distribution of IAV antigen in chickens infected with H7N1 HPAIV at 2, 3 and 4 dpi. A. Schematic view of a chicken's brain showing the rostro-caudal levels depicted in the coronal diagrams below. The diagram on the left shows the brain regions evaluated in each section and on sections c, d, e, and f, the neural nuclei where viral antigen was found bilaterally and symmetrically are represented and labelled. The severity of viral antigen immunostaining in cells of the central nervous system (neurons, endothelial cells and microglia) is represented using different density of dots, as follows: null, scarce, slight, moderate and severe. The intensity of viral antigen staining of the ependymal cells is scored using different colours as follows: null (no colour), scarce (yellow), slight (green), moderate (blue), intense (red). (Illustration modified and reproduced with permission from Ref. ).