The histopathologic diagnosis of subclinical Johne's disease in North American Bison (Bison bison)

The morphologic changes of subclinical Johne's disease in North American Bi son (Bison bison) are characterized by microgranulomas composed of epitheli oid macrophages and individual multinucleate giant cells of Langhans'-type occasionally containing individual cytoplasmic acid-fast bacilli compatible with Mycobacterium avium paratuberculosis. The microgranulomas are best vi sualized in the mesenteric lymph nodes of infected subclinical animals. Mac rophages that can be confused with infection-associated Epithelioid macroph ages in the mesenteric lymph nodes are pigment-carrying cells from the inte stinal tract. Mesenteric lymph node biopsy may be a useful diagnostic tool for detection of mild subclinical infection in individual ruminants from he rds of unknown infection status. The biopsy may also be useful for Johne's disease surveillance during test-and-cull programs. (C) 2000 Elsevier Scien ce B.V. All rights reserved.