Detection of S. suis serotype 2 by immunohistochemistry. Piglets were intranasally inoculated with S. suis T15 (non-virulent) or S10 (virulent) strains, and tissues were collected at 1 and 3 days post-inoculation (dpi). A: Bacteria present at 1 dpi in the bronchiole (arrowhead) and alveolar lumen of a piglet inoculated with T15. B: Bacteria present at 1 dpi in the epithelial surface of bronchioles (arrowhead) and alveoli of a piglet inoculated with S10. C: Presence of bacteria at 3 dpi in neutrophils in the mucus of the cribriform plate of ethmoid of a piglet inoculated with T15 (arrowhead). D: Bacteria next to the cartilage of the cribriform plate of ethmoid (CT) at 3 dpi, from a piglet inoculated with S10 (arrowhead).