Submitted to: American Journal of Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 13, 2000
Publication Date: N/A
Interpretive Summary: Brucella abortus is a disease of cattle that causes abortion and associated economic losses in infected herds. The persistence of a small number of cattle herds with brucellosis, and the Brucella abortus infections in bison and elk in Yellowstone National Park pose a risk to the completion of the Brucellosis Eradication Program for cattle. Development of an dosage of strain RB51 that is efficacious in preventing brucellosis in adult cattle which would allow regulatory personnel to safely booster immunity in Brucella-infected or exposed herds is needed. Booster vaccination with strain RB51 would reduce economic losses due to brucellosis in cattle and would expedite regulatory efforts to remove Brucella-infected individuals. In this study we evaluated a reduced dosage of strain RB51 with proven safety in pregnant cattle, for its ability to protect cattle against challenge with a virulent strain of Brucella abortus during pregnancy. Our data suggests that this dosage is efficacious in preventing abortions or Brucella-infections in cattle. This data will be of benefit to personnel in state and federal regulatory agencies for preventing transmission of brucellosis and for expediting elimination of brucellosis from infected cattle herds. This study will also be of benefit to the cattlemen in the states of Montana, Wyoming, and Idaho which may be at risk for transmission of brucellosis from wildlife vectors. Development of adult brucellosis vaccination regimens will help prevent transmission of brucellosis and assist in the completion of the Brucellosis Eradication Program.
Technical Abstract: The purpose of the study reported here was to evaluate the efficacy of a reduced dosage of Brucella abortus strain RB51 (SRB51) in adult cattle. Hereford heifers were vaccinated SC at 18 months of age with SRB51 dosages of 3 x 10**9 colony-forming units (CFU) once, 1 x 10**9 CFU once, or 1 x 10**9 CFU twice. Additional heifers were vaccinated SC once with 0.15 M NaCl (saline). Cattle vaccinated with 3 x 10**9 CFU of SRB51 had the greatest antibody responses and cell-mediated responses to SRB51 after vaccination. Strain RB51 was recovered at 6 weeks after vaccination from superficial cervical lymph nodes of 5 of 6 heifers vaccinated once with 3 x 10**9 CFU, from 6 of 6 heifers vaccinated once with 1 x 10**9 CFU, but only from 1 of 6 heifers vaccinated twice with 1 x 10**9 CFU of SRB51. Heifers were naturally bred and intraconjunctivally challenged in midgestation with 1 x 10**7 CFU of B. abortus strain 2308 (S2308). Tissues obtained for bacteriologic evaluation at necropsy after abortion or 1 week prior to parturition. Four of 6 saline-inoculated heifers aborted 5 to 9 weeks after experimental challenge and S2308 was recovered from tissues from all saline-inoculated heifers. In comparison, S2308 or SRB51 were not recovered from tissues obtained at necropsy from heifers vaccinated with any of the SRB51 dosage regimens evaluated in this study. This study demonstrates that vaccination immediately prior to breeding with a reduced dosage of SRB51 protects adult cattle against abortion or infection caused by exposure to virulent B. abortus during the subsequent pregnancy.