Early-stage findings in an experimental calf model infected with Argentinean isolates of Mycobacterium avium subsp. paratuberculosis

Abstract

Mycobacterium avium subsp. paratuberculosis (MAP) is an important pathogen that causes granulomatous enteritisknown as Johne?s disease or paratuberculosis (PTB). In this study an experimental model of calves infected withArgentinean isolates of MAP for 180 days was used to provide more data of the early PTB stages. Calves werechallenged by oral route with MAP strain IS900-RFLPA (MA; n = 3), MAP strain IS900-RFLPC (MC; n = 2) or mockinfected (MI; n = 2), and response to infection was evaluated through peripheral cytokine expression, MAP tissuedistribution and histopathological early-stage findings. Specific and varied levels of IFN-γ were only detected at80 days post-infection in infected calves. These data indicate that specific IFN-γ is not a useful indicator for earlydetection of MAP infection in our calf model. At 110 days post-infection, TNF-α expression was higher than IL-10in 4 of the 5 infected animals and a significant decrease of TNF-α expression was detected in infected vs. noninfected calves. All calves challenged were identified as infected by mesenteric lymph node tissue culture andreal time IS900 PCR. In addition, for lymph nodes samples, the agreement between these techniques was almostperfect (κ = 0.86). Colonization of tissues and levels of tissue infection varied between individuals. Evidence ofearly MAP dissemination to extraintestinal tissues such as the liver was detected by culture in one animal (MAPstrain IS900-RFLPA). In both groups microgranulomatous lesions were observed predominantly in the lymph nodes,with giant cells present only in the MA group. In summary, the findings described herein may indicate that localMAP strains induced specific immune responses with particularities that could suggest differences in their biological behavior. Further studies should be carried out in order to obtain an in-depth understanding of the influence of MAP strains in host-pathogen interactions and the outcome of disease.