Pigmented paratuberculosis granulomata in the liver of sheep

Abstract

Pigmented paratuberculosis granulomata in the liver of a sheep affected with Johne’s disease are described. The granulomata were visible on the surface of the liver, irregular in shape, patchily distributed in the parenchyma and contained yellowish-orange pigment. Microscopically, the granuloma was composed of epithelioid cells containing small poorly basophilic granules (H&E), and surrounded by a tiny fibrous capsule. Intestinal lesions were widespread from the ileum to the rectum and included thickening, corrugation and staining of the mucosa with a yellowish-orange pigment. Histologically, epithelioid cells containing pigment granules infiltrated the enteric mucosa and submucosa. The mesenteric lymph nodes were swollen and contained white irregular spots, which were visualized microscopically as aggregates of epithelioid cells. Clumps of short, slender acid-fast bacilli were isolated in pure culture on Herrold’s egg-yolk agar medium from various lesions including the granulomata. The organism was identified as Mycobacterium avium subsp. paratuberculosis on the basis of slow growth and strict mycobactin dependence. The nature of the yellowish-orange pigment was not identified but it was possibly produced by the Mycobacterium spp.