Pathological findings. A) Terminal ileum. Equine isolate-infected foal euthanized on day 24 pi. Hyperaemia associated with diffuse and severe thickening of the intestinal mucosa compatible with PE. B) Histologic section of ileum. Equine isolate-infected foal euthanized 24 days pi. L. intracellularis antigen-specific staining with AEC substrate-chromogen and counterstained with Mayer’s hematoxylin. Diffuse hyperplasia of immature enterocytes and severe reduction in the number of goblet cells associated with the diffuse presence of intracellular bacteria in the apical cytoplasm. Scale bar, 100 μm. C–D) IHC staining. Ileal mucosa of porcine isolate-infected pigs euthanized 21 days pi. Diffuse presence of the bacteria in the apical cytoplasm of the hyperplastic enterocytes and in the lamina propria. Scale bar, 200 μm. E–F) IHC staining. Ileal mucosa of equine isolate-infected pigs euthanized 21 days pi. Absence of hyperplastic enterocytes or L. intracellularis antigen associated with diffuse presence of goblet cells in the intestinal epithelium. Scale bar, 200 μm.