Safety of Brucella abortus strain RB51 in bull elk

Some of the elk (Cervus elaphus nelsoni) of the Greater Yellowstone Area (W yoming, Idaho, Montana; USA) are infected with Brucella abortus, the bacter ium that causes bovine brucellosis. Brucella abortus strain RB51 vaccine is being considered as a means to control B. abortus induced abortions in cow elk. However, the most probable vaccination strategies for use in free-ran ging elk might also result in some bull elk being inoculated, thus, it is i mportant to insure that the vaccine is safe in these animals. In the winter of 1995, 10 free-ranging bull elk calves were captured, tested for B. abor tus antibodies, and intramuscularly inoculated with 1.0 x 10(9) colony form ing units (CFU) of B. abortus strain RB51. Blood was collected for hemocult ure and serology every 2 wk after inoculation for 14 wk. Beginning 4 mo pos tinoculation and continuing until 10 mo postinoculation elk were serially e uthanized, necropsied, and tissues collected for culture and histopathology . These elk cleared the organism from the blood within 6 wk and from all ti ssues within 10 mo. No lesions attributable to B. abortus were found grossl y and only minimal to mild lymphoplasmacytic epididymitis was found in a fe w elk on histologic examination. In a separate study, six adult bull elk fr om Wind Cave National Park (South Dakota, USA) were taken to a ranch near C arrington (North Dakota, USA). Three were orally inoculated with approximat ely 1.0 x 10(10) CFU of RB51 and three were inoculated with corn syrup and saline. Ninety days post-inoculation semen was examined and cultured from t hese bulls. Strain RB51 was not cultured from their semen at that time. The re were no palpable abnormalities in the genital tract and all elk produced viable sperm. Although they contain small sample sizes, these studies sugg est that B. abortus strain RB51 is safe in bull elk.