1Department of Veterinary Microbiology and Parasitology, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA, USA; 2Department of Veterinary Pathology, College of Veterinary Medicine, Texas A&M University, College Station, TX, USA; 3Department of Veterinary Science, Louisiana State University-Agricultural Experiment Center, Baton Rouge, LA, USA; 4United States Department of Agriculture, Animal Plant Health Inspection Services, Veterinary Services, Riverdale, MD, USA
A current problem confounding the national effort to eradicate brucellosis from the United States is a reservoir of Brucella abortus infected bison (Bison bison) in Yellowstone National Park. This herd is a potential threat to the beef agribusiness surrounding the park since bison to cattle transmission of brucellosis has been documented under both experimental and field conditions. A possible solution to reduce this concern is vaccination of bison with the new cattle brucellosis vaccine, B. abortus strain RB51 (SRB51). This study evaluated the colonization and virulence of SRB51 in a high-risk bison herd of 29 American bison which originated from a brucellosis reactor herd in Strong City, Kansas.
The herd was housed at a bison containment center at Texas A&M University and contained ten adult males, seven calves, and twelve adult females. The adult males and calves were vaccinated with the standard calfhood cattle dose of 1.8×1010 colony forming units (CFUs) of SRB51 subcutaneously while the adult females received the standard adult cattle dose of 1×109 CFU. The vaccination strain was expected to not colonize or cause fetal pathogenesis in bison.
Following vaccination, serologic response was evaluated by western blot analysis which did indicate SRB51 specific antibodies. Additionally, all adult males, all calves, and three non-pregnant adult females were euthanatized at either 13- or 16-wk post-vaccination. Tissue samples were obtained at necropsy for Brucella culture from the liver, spleen, lymph nodes, and reproductive tract. The remaining adult females were in early gestation and were monitored until parturition for signs of fetal pathogenesis. Of these cows, six delivered healthy calves; one delivered a stillborn calf that was Brucella negative; and two failed to produce calves although had been determined pregnant.
From these results, administration of SRB51 to a high-risk, previously exposed bison herd did not appear to cause either prolonged colonization or a high rate of fetal pathogenesis following vaccination in early gestation. This study provided the evidence that SRB51 should be further investigated as a possible Brucella abortus vaccine in American bison. To address this issue, a vaccine efficacy trial is currently under evaluation.