Experimental infection of New Zealand Merino sheep with a suspension of Mycobacterium avium subspecies paratuberculosis (Map) strain Telford: Kinetics of the immune response, histopathology and Map culture

• Published in: Veterinary microbiology 2016-11, Vol.195, p.136-143
• Main Authors: Dukkipati, Venkata S.R., Ridler, Anne L., Thompson, Keith G., Buddle, Bryce M., Hedgespeth, Barry A., Price-Carter, Marian, Begg, Douglas J., Whittington, Richard J., Gicquel, Brigitte, Murray, Alan
• Format: Article
• Language: English
• Subjects: Animal diseases; Animals; Antibodies; Bacilli; Bacteriological Techniques; Body Weight; Experimental infection; Faecal cultures; Histopathology; IFN-γ responses; Immune response; Immune responses; Interferon; Interferon-gamma - blood; Johne’s disease; Kinetics; Lesions; Liver; Lymph nodes; Male; Merino; Mycobacterium avium; Mycobacterium avium subsp. paratuberculosis; Mycobacterium avium subspecies paratuberculosis; OJD; Ovis aries; Paratuberculosis; Paratuberculosis - immunology; Paratuberculosis - microbiology; Paratuberculosis - pathology; Pathogenesis; Sheep; Sheep Diseases - microbiology; Tissue culture; Tissue cultures; Tissues; γ-Interferon
• ISSN: 0378-1135; 1873-2542
• DOI: 10.1016/j.vetmic.2016.09.018

•New Zealand Merino lambs were experimentally infected with a pure culture of Mycobacterium avium subspecies paratuberculosis (Map) strain Telford.•Immune responses and Map shedding were monitored for 63 weeks post-challenge.•Sheep were euthanized at 63 weeks for histopathology and tissue cultures.•Challenge was highly effective in establishing Johne’s disease in NZ Merino lambs. A long-term study was undertaken to monitor immune responses, faecal cultures and clinical disease in sheep experimentally infected with Mycobacterium avium subspecies paratuberculosis (Map) strain Telford. New Zealand Merino lambs (N=56) were challenged with three oral doses of Map suspension. The lambs were weighed and faecal and blood samples obtained at different time-points. At 63 weeks post-challenge, surviving sheep were euthanised and samples of liver, ileo-caecal valve and mesenteric lymph node were collected for histopathology and Map culture. High IFN-γ and antibody responses were evident as early as 8 weeks post-C1 which persisted until the end of the trial. Approximately 92% of the sheep shed Map in faeces at 36 weeks post-challenge, with the prevalence decreasing to around 40% at the end of the trial. Thirteen sheep progressively lost weight and were euthanised between weeks 32 and 58 post-challenge. Nearly 58% of surviving sheep exhibited histo-pathological lesions in at least one of the three tissues sampled, while 42% showed acid-fast bacilli in at least one tissue. A positive Map culture in at least one tissue was obtained from approximately 85% of sheep. These results indicate that the three doses of Map challenge were highly effective in establishing Johne’s disease in NZ Merino lambs.