A long-term study in Merino sheep experimentally infected with Mycobacterium avium subsp. paratuberculosis: clinical disease, faecal culture and immunological studies

• Published in: Veterinary microbiology Vol. 104; no. 3; pp. 165 - 178
• Main Authors: Stewart, D.J., Vaughan, J.A., Stiles, P.L., Noske, P.J., Tizard, M.L.V., Prowse, S.J., Michalski, W.P., Butler, K.L., Jones, S.L.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 09.12.2004; Elsevier Science
• Subjects: Absorbed ELISA; Animals; Antibodies, Bacterial - blood; Biological and medical sciences; Bovine Johne's disease; Cattle; Cattle Diseases - microbiology; Enzyme-Linked Immunosorbent Assay - veterinary; Feces - microbiology; Fundamental and applied biological sciences. Psychology; Immunity, Cellular; Interferon-gamma - biosynthesis; Interferon-gamma - blood; Interferon-γ; Johne's disease; Longitudinal Studies; Male; Microbiology; Mycobacterium avium paratuberculosis; Mycobacterium avium subsp. paratuberculosis; Mycobacterium avium subsp. paratuberculosis - immunology; Mycobacterium avium subsp. paratuberculosis - pathogenicity; Ovine Johne's disease; Paratuberculosis - microbiology; Sheep; Sheep Diseases - microbiology; Bovine Johne's disease; Mycobacterium avium subsp. paratuberculosis; Interferon-γ; Johne's disease; Ovine Johne's disease; Sheep; Absorbed ELISA; Interferon- γ; Microbiology; Paratuberculosis; Mycobacterium avium; Mycobacterial infection; Infection; Vertebrata; Experimental disease; Mammalia; Mycobacteriales; Bacteriosis; Mycobacteriaceae; Bacteria; Actinomycetes; Artiodactyla; Veterinary; Ungulata
• ISSN: 0378-1135; 1873-2542
• DOI: 10.1016/j.vetmic.2004.09.007

Two longitudinal experiments involving Merino sheep challenged with either bovine or ovine strains of Mycobacterium avium subsp. paratuberculosis ( Map) have been conducted over a period of 54 and 35 months, respectively. Blood samples for the interferon-γ test, the absorbed ELISA and faecal samples for bacteriological culture were taken pre-challenge and monthly post-challenge. Infections were induced with either a bovine or ovine strain of Map in separate experiments with infections being more easily established, in terms of faecal bacterial shedding and clinical disease when the challenge inoculum was prepared from gut mucosal tissue than cultured bacteria. The patterns of response for shedding and clinical disease were similar. Cell-mediated immune responses were proportionally elevated by at least an order of magnitude in all sheep dosed with either a bovine or ovine strain of Map. Conversely, antibody responses were only elevated in a relatively small proportion of infected sheep. Neither of the clinically affected tissue challenged sheep developed an antibody response despite the presence of persistent shedding and the development and decline in cell-mediated immunity. The results indicated that for sheep the interferon-γ test may be useful for determining if a flock has been exposed to ovine Johne's disease.