Gross

• Changes often slight.
• Dehydration a feature.
• Evidence of vomiting or fetid diarrhoea.
• Jejunum and ileum dilated and oedematous with petechial haemorrhages ('rose-red' appearance) on the serosal and mucosal surfaces.
• Mesenteric lymph nodes may be oedematous and haemorrhagic.

Histopathology



Intestinal effects

• Lesions usually present in jejunum and ileum; sometimes also duodenum and colon.
• Mild to total destruction of epithelial lining, with dilatation of crypts.
• Crypts often filled with cellular debris.
• In early cases, transient intranuclear inclusion bodies may be seen.

Lymphoid tissue and bone marrow effects

• In lymphoid tissues lymphocytic depletion and reticulo-endothelial cell hyperplasia are regularly seen; mesenteric lymph nodes, Peyer's patches and spleen are particularly affected, and in younger animals also the thymus.
• In bone marrow, there is a general depression in myeloid activity with marked reduction in neutrophils and depletion of reticulum cell meshwork.

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