Evaluation of transmission of Brucella abortus strain 19 in bison by intravaginal, intrauterine, and intraconjunctival inoculation.

Bovine brucellosis, caused by the bacterium Brucella abortus, is endemic in bison (Bison bison) and elk (Cervus elaphus nelsoni) populations in the area of Yellowstone National Park, USA. Two strategies have been proposed to reduce the risk of transmission of disease in bison: remote vaccination with the vaccine RB51, and the use of immunocontraception of bison to decrease shedding of organisms from infected females. The frequent occurrence of venereal transmission in bison would complicate either of these strategies, requiring vaccination of males as well as females, and rendering immunocontraception less effective in reducing transmission of B. abortus. To address the question of venereal transmission, we inoculated each of 18 bison cows with 4.5 × 10(8) colony-forming units of B. abortus strain 19, as a surrogate of field strain, by three routes: intraconjunctival (IC), intravaginal (VI), and intracervical/intrauterine (AI). Bison semen was mixed with strain 19 inoculum for the latter route. Bison were monitored by serology and culture for 12 wk, at which time they were euthanized and specimens collected for culture. All IC-inoculated animals seroconverted on multiple tests and one was culture positive at 12 wk postexposure. Seven of eight VI bison developed suspect or positive serologic tests and four were positive at one or more time points. Weak transient serologic responses (suspect) were seen in four of five AI bison. Results showed that IC inoculation with strain 19 was a suitable surrogate for field strain to demonstrate exposure to the B. abortus. The seroconversion of four of eight VI bison indicated exposure of the immune system to the agent and the need for further studies on venereal transmission in bison.