Comparison of bison and elk susceptibility to experimental challenge with Brucella abortus strain 2308.

Introduction: Brucellosis is endemic in bison and elk in Yellowstone National Park and surrounding areas.

Methods: A comparative study was conducted using data from naive (n = 82 and 67, respectively) and Brucella abortus strain RB51 (RB51) vaccinated (n-99 and 29, respectively) bison and elk experimentally challenged with virulent B. abortus strain during pregnancy.

Results: The incidence of abortion, fetal infection, uterine or mammary infection, or infection in maternal tissues after experimental challenge was greater (p < 0.05) in naïve and vaccinated bison when compared to similar groups in elk. Vaccinated bison had lower (p < 0.002) abortion rates and recovery of Brucella from fetal or uterine/mammary tissues when compared to naïve bison. Vaccinated elk had reduced (p < 0.01) rates of maternal infection, but rates of abortion and fetal or uterine/mammary infection did not differ (p > 0.05) from naïve elk. Naïve and vaccinated bison had greater (p < 0.05) Brucella colonization in placentomes, and parotid and supramammary lymphatic tissues when compared to elk. In elk or bison that aborted, mean colonization in placentome tissues were typically more than 5 logs higher than in animals that did not abort.

Discussion: The results of our study suggest differences in disease pathogenesis between these two wildlife reservoirs of B. abortus.