Abstract

Estimates for the seroprevalence of brucellosis in bison (Bison bison) in Yellowstone National Park, or elk (Cervus elaphus) on feedgrounds in the Greater Yellowstone Area, are between 40 and 50%. In a similar manner, in Michigan the prevalence of tuberculosis in white-tailed deer (Odocoileus virginianus) in some areas is as high as 10–15%. The high prevalence of these diseases in wildlife reservoirs is of concern due to the possibility of transmission of these pathogens to domestic livestock in which they have almost been eradicated by regulatory programs. Long-term protection against intracellular pathogens such as Brucella spp. or Mycobacterium bovis, is predominantly through cell-mediated immunity. In a series of studies conducted at the National Animal Disease Center, immunologic responses of bison, elk, white-tailed deer, cattle, and reindeer (Rangifer tarandus tarandus) were evaluated after vaccination with brucellosis or tuberculosis vaccines or following experimental infection with virulent strains of B. abortus or M. bovis. Bison and cattle have robust immunologic responses to brucellosis vaccines with strong humoral and cell-mediated responses, although the temporal interferon-γ (IFN-γ) responses differed. In a similar manner, white-tailed deer develop robust humoral and cell-mediated responses following vaccination with M. bovis bacille Calmette-Guerin (BCG) or infection with a virulent strain of M. bovis. In comparison, elk and reindeer develop strong humoral responses following vaccination with BCG or brucellosis vaccines, but measurements of cellular immunity suggest very poor responses that are transient and associated with low levels of IFN-γ production. Our data suggests that immunologic responses may markedly vary between species. We hypothesize that these immunologic responses explain differences in susceptibility to infection and vaccine efficacy and may reflect evolutionary selection against natural pathogens. Our findings may have implications for management decisions on programs to control or eliminate intracellular pathogens within captive or free-ranging populations.