Animals naturally infected with SBV (n = 15) show pore-associated axonal damage and demyelination. Astrogliosis and deposition of hemosiderin and calcium is also shown.

<p><b>A)</b> Bielschowsky’s silver impregnation indicating axonal loss within a pore in the temporal lobe (black asterisks). The remaining white matter surrounding the pore shows a light brown staining of Bielschowsky’s silver impregnation indicating further axonal loss. In contrast, the non-affected white matter with normal axonal density is characterized by a dark brown staining (white asterisk) within the same tissue section (animal no 14; bar, 5000 µm). <b>B)</b> Pore associated demyelination (black asterisk) as shown by myelin basic protein immunohistochemistry in the temporal lobe of a neonatal sheep. The degree of severity of myelin loss varied from mild (arrow), moderate (closed circle) to severe (triangular). Note region of intact myelin basic protein expression consists of a dark brown immunoreaction (arrow head; animal no 5, bar, 1000 µm). <b>C)</b> Prominent immunoreactive processes of astrocytes are found especially in association with the vessel walls (GFAP staining, animal no 14; bar, 20 µm). <b>D)</b> Deposition of von Kossa positive, extracellular, coarsely granular material (mineralization), presumably due to tissue loss and necrosis (sheep lamb, animal no 12; bar, 20 µm). <b>E)</b> Deposition of Prussian blue, extracellular, coarsely granular material (iron) next to a pore, interpreted as hemosiderin is presumably a sequel of old hemorrhages (arrows; animal no 4; bar, 20 µm). <b>F)</b> Summarized presentation of axonal damage, demyelination, astrogliosis, mineralization and hemosiderosis. Axonal and myelin loss were present only in close proximity to por- or hydranencephaly, whereas mineralization, hemosiderosis and astrogliosis were found in brain regions exhibiting malformations or inflammation. Individual numbers within depicted cell types indicate the percentages of affected animals in the respective region of the brain.</p>