Abstract
A major drawback of current whole-cell vaccines for Mycobacterium avium subsp. paratuberculosis is the interference with diagnostic tests for bovine tuberculosis (TB) and paratuberculosis. The current study was designed to explore the effects of immunization with a heat-killed whole-cell vaccine (Mycopar) on diagnostic test performance and to characterize host immune responses to vaccination over a 12-month period. Neonatal dairy calves were assigned to treatment groups consisting of (i) controls, not vaccinated (n = 5), and (ii) vaccinates, vaccinated with Mycopar vaccine (n = 5). The results from this study demonstrated a rapid initiation of M. avium subsp. paratuberculosis-specific gamma interferon (IFN-γ) in vaccinated calves by 7 days, with robust responses throughout the study. Vaccinated calves also had responses to M. bovis purified protein derivative tuberculin (BoPPD) but minimal reactivity to ESAT-6/CFP-10, an M. bovis recombinant fusion protein. The levels of antigen-specific interleukin-4 (IL-4) and IL-10 were markedly decreased in vaccinated calves between days 7 and 90 of the study but thereafter were similar to the levels in controls. Vaccinated calves began to seroconvert at 4 months, with 4/5 calves having detectable M. avium subsp. paratuberculosis antibody by 6 months. The responses in test platforms for bovine TB were negligible in the vaccinate group, as only one calf had a response, which was in the suspect range of the comparative cervical skin test. Serum antibody responses to M. bovis antigens ESAT-6, CFP-10, and MPB83 were negative on the Vet TB STAT-PAK, DPP VetTB, and DPP BovidTB tests. These results suggest that the Mycopar vaccine will interfere with diagnostic tools for paratuberculosis but result in low interference with the comparative cervical skin test and emerging serologic tests for M. bovis.