The comparative evaluation of immunohistochemical and acid fast staining with histopathological changes in naturally occurring paratuberculosis in sheep

Histopathological changes and degrees of positivity by Ziehl–Neelsen (ZN) and avidin–biotin complex peroxidase (ABC) techniques were studied in 29 adult sheep grossly or clinically suspected to have paratuberculosis. Of these, 16 (55.1%) had microscopic lesions associated with paratuberculosis, which were classified into 4 categories. Focal–multifocal lesions (6.9%) consisted of small granulomas in the lamina propria of the ileum especially in the ileocecal Peyer’s patches and also in the mesenteric lymph nodes. Diffuse multibacillary lesions (31%) characterized by a diffuse granulomatous enteritis with epithelioid macrophages infiltration as main inflammatory cells that arranged in mosaic-like appearance, filled with numerous acid fast bacilli in ZN, and highly positive in ABC. Diffuse paucibacillary (lymphocytic) lesions (6.9%) composed of lymphocytes as main inflammatory infiltrate with some epithelioid macrophages or giant cells containing few if any mycobacteria. Diffuse intermediate (mixed) lesions (10.3%) characterized by a diffuse granulomatous enteritis with infiltration of large numbers of lymphocytes and also epithelioid macrophages with varying degrees of positivity in ZN and ABC. In the diffuse lesions, other lesions such as granulomatous or lymphocytic lymphangitis, lymphangiectasis, intravascular aggregates of epithelioid macrophages, lymphocytic infiltration around the myenteric nerve ganglia, severe granulomatous arteritis, atherosclerotic-like lesions and vascular thrombosis especially in the capsule of mesenteric lymph nodes, and serosal layer of intestine were observed. We could not find any necrotic or calcified lesion in the intestinal tissues of affected sheep but we found a few small foci in the mesenteric lymph nodes of two cases. High numbers of multinucleated langhans giant cells were seen only in mesenteric lymph node of one affected sheep. In conclusion, the present study showed four categories of lesions in which multinucleated giant cells, necrosis, and calcification were uncommon particularly in the intestine. Both immunohistochemistry (IHC) and ZN methods can detect IHC with more positivity in almost all the sheep with diffuse lesions; more cases with focal and paucibacillary forms were positive by IHC than by ZN. The importance of sampling the ileum (especially ileocecal valve), jejunum, and mesenteric lymph nodes to find microscopic lesions of paratuberculosis in sheep is emphasized.