Thick, corrugated mucosal surface of the ileum

The classic lesion of paratuberculosis is shown. Thickened by the chronic granulomatous inflammatory response to M. paratuberculosis bacteria in the submucosa of the intestine, the ileum becomes dysfunctional. This leads to a protein losing enteropathy. Cows with this degree of pathology typically will have diarrhea and be thin, but they will not have a fever, will be eating well, and in general appear to feel well. A photo of this cow with her calf taken two months before euthanasia is shown in a separate photograph. Other animal species can show this pathology as well, but infected sheep, bison and non-domestic species may not develop this type of pathology. Instead, the infected animal's ilium may appear normal.