Classification of lesions observed in natural cases of paratuberculosis in goats.

Sixty-eight adult goats with clinical or sub-clinical paratuberculosis, from naturally infected flocks, were subjected post mortem to a pathological examination that focused on the intestinal lymphoid tissue. The lesions were divided into four categories. Focal lesions, found in 16 goats, consisted of small granulomata in the ileocaecal Peyer's patches or related lamina propria. Diffuse multibacillary lesions (34 goats) consisted of a granulomatous enteritis, affecting different intestinal sites. Numerous macrophages containing many mycobacteria were present, resulting in macroscopical changes in the normal gut morphology; in the ileum of nine of the 34 animals, however, these changes were confined to the apex of the villi and the intestinal wall was not thickened. In diffuse lymphocytic lesions (10 goats), the lymphocyte was the main inflammatory cell, with some macrophages (containing few if any mycobacteria). In diffuse mixed lesions (eight goats) the infiltrate consisted of numerous lymphocytes and macrophages, with small numbers of mycobacteria. The three types of diffuse lesion were often associated with necrosis in the lymph vessels of the mucosa, mesentery and lymph nodes, and with greater thickening of the jejunum than of the ileum. Mycobacterium avium subspecies paratuberculosis was cultured from 69% of goats with diffuse lesions and from 44.4% of those with focal lesions.