Vaccination of white-tailed deer with Mycobacterium bovis bacille Calmette-Guerin : efficacy, immunology, and molecular detection
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Wildlife reservoirs of Mycobacterium bovis are believed to play very important roles in the epidemiology of bovine tuberculosis in many countries throughout the world. In the United States, a free-ranging white-tailed deer (Odocoileus virginianus) population in northeastern Michigan serves as such a reservoir. Although changes in management have decreased prevalence of the disease, additional tools, such as vaccination, are needed to achieve eradication of bovine tuberculosis from Michigan deer. In this project, the efficacy of oral and parenteral Mycobacterium bovis bacille Calmette-Guerin Danish strain 1331 (BCG) was evaluated for its ability to protect white-tailed deer against disease caused by M. bovis infection. In addition, cellular and humoral immune responses in deer to BCG vaccination and M. bovis challenge were examined, and molecular detection techniques were developed to monitor shedding of BCG and M. bovis in vaccinated and infected animals. Results indicate that white-tailed deer vaccinated with BCG both orally and parenterally were protected from development of severe disease after experimental infection with virulent M. bovis when compared to unvaccinated deer. Antibody responses to M. bovis antigens by the deer in this study were evaluated over time using multiantigen (multiantigen print immunoassay, rapid test, and immunoblot to whole-cell sonicate) and single antigen tests (lipoarabinomannan [LAM] ELISA and immunoblot to MPB83). Multiantigen tests detected minimal to no antibody responses in vaccinated deer after challenge, whereas antibody responses were more readily detectable by these tests in unvaccinated deer with more advanced disease. The ELISA results indicated an overall decrease in detectable antibodies produced against LAM-enriched mycobacterial antigen in vaccinated animals as compared to unvaccinated animals after challenge. Few trends could be determined from the immunoblot results. Cellular immunity was measured via interferon gamma production and lymphocyte proliferation in response to mycobacterial antigens. Findings in regards to cellular immunity were inconclusive. Molecular techniques developed to detect M. tuberculosis complex in cervid feces, nasal and pharyngeal swabs, soil, feed, and hay produced data indicating that deer shed M. bovis and BCG only intermittently at 1-3 months after vaccination and 1-4 months after M. bovis challenge. The findings from these studies strongly support further research that could lead to the eventual use of BCG in wild white-tailed deer herds affected by bovine tuberculosis. The data also encourage the improvement and potential use of antibody-based assays, such as the multiantigen tests and the LAM-ELISA as ante-mortem tools to assess disease progression in white-tailed deer in both experimental and field vaccine trials. Finally, further improvements in the molecular detection of M. bovis could enable more effective monitoring of shedding of M. bovis by deer in both experimental and free-ranging environments.