ABORTION AND PLACENTITIS IN PREGNANT BISON (BISON-BISON) INDUCED BY THE VACCINE CANDIDATE, BRUCELLA-ABORTUS STRAIN RB51

Objective-To determine the ability of Brucella abortus strain RB51 to induce placentitis and abortion in bison after SC vaccination. Animals -10 pregnant bison cows, 3 to 10 years old and at 3 to 8 months' gesta tion. Procedure-Pregnant bison cows on a Montana ranch were vaccinated SC with 10(9) colony-forming units of B abortus strain RB51. Two COWS , identified prior to the study, were euthanatized and examined 5 week s alter vaccination to obtain optimal histologic samples of placenta. Other cows were euthanatized and examined after abortion, After euthan asia, tissue specimens were collected for histologic and immunohistoch emical evaluation. Tissue and fluid specimens for bacteriologic cultur e were also collected during necropsy. Results-Of 8 cows, 2 aborted at 68 and 107 days after vaccination. Aborting cows had endometritis. St rain RB51 was isolated from reproductive tissues and supramammary lymp h nodes. Fetal lesions were not seen; however, fetal bronchial lymph n odes and amniotic fluid contained strain RB51, Cows examined 5 weeks a fter vaccination had placentitis and endometritis, with numerous bacte ria within trophoblastic epithelial cell that were immunoreactive for strain RB51 antigen, Strain RB51 was isolated from placentomes and num erous lymph nodes. Fetal lesions were not seen 5 weeks after vaccinati on; however, strain RB51 was isolated from numerous lymph nodes and lu ng, allantoic fluid, and rectal swab specimens. Conclusions-The vaccin e candidate B abortus RB51 has tropism for the bison placenta, and can cause placentitis, which induces abortion in pregnant bison. The vac cine dose used was similar to that being tested in cattle, but may not be appropriate for pregnant bison.