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
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.
Dukkipati, V. S. R., Ridler, A. L., Thompson, K. G., Buddle, B. M., Hedgespeth, B. A., Price-Carter, M., Begg, D. J., Whittington, R. J., Gicquel, B., & Murray, A. (2016). 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. Veterinary Microbiology, 195, 136–143. doi:10.1016/j.vetmic.2016.09.018