Submitted to: Journal of Veterinary Diagnostic Investigation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/6/1997
Publication Date: N/A
Interpretive Summary: Brucella abortus is a disease of cattle that causes abortion and associated economic losses in infected herds. For the first time in more than 40 years, a new calfhood vaccine to prevent cattle brucellosis was approved in March, 1996 by the Animal Plant and Health Service (APHIS). This vaccine, B. abortus strain RB51 (SRB51), will not interfere with detection of infected cattle as it does not cause positive responses on brucellosis serologic surveillance tests. The only test available for monitoring immunologic responses following SRB51 vaccination is a dot blot assay developed by ARS scientists. This study characterized the dot blot assay for its ability to identify non-vaccinated (specificity) and SRB51-vaccinat ensitivity) cattle. This study demonstrated that this assay will accurately identify animals vaccinated with SRB51 and is therefore the eonly assay available to monitor immune responses in SRB51-vaccinated herds Veterinarians, regulatory personnel, and cattlemen will be able to use this assay to evaluate if successful vaccination against brucellosis has occurred within a herd of cattle. This will assist APHIS in the Brucellosis Eradication Program by providing a test that identifies animals that have been protected against brucellosis infection by SRB51 vaccination.
Technical Abstract: B. abortus strain RB51 (SRB51) was recently approved as an official brucellosis calfhood vaccine for cattle by the Animal and Plant Health Inspection Service branch of the United States Department of Agriculture. Currently available serologic surveillance tests for B. abortus do not detect seroconversion of cattle following SRB51 vaccination. The purpose of this study was to evaluate a dot-blot assay using (gamma)-irradiated SRB51 bacteria for its specificity and sensitivity to detect antibody responses of SRB51-vaccinated cattle. Dot-blot titers of cattle vaccinated with approximately 1 x 10(10) CFU of SRB51 were similar to those of cattle vaccinated with similar numbers of B. abortus strain 19 (S19), and greater (P<0.05) than titers of non-vaccinated cattle. In the first 12 weeks after vaccination, the dot-blot assay had a 100% specificity for titers of 80 or less and a 53% sensitivity for titers of 160 or greater. Sensitivity of the dot-blot assay peaked at 4 weeks after vaccination. Dot-blot response of cattle vaccinated with 1 x 10(9) CFU of SRB51 did not differ (P>0.05) from titers of non-vaccinated cattle. Following intraconjunctival challenge with B. abortus strain 2308, titers on the dot-blot assay did not differ (P>0.05) between S19-, SRB51-, and non-vaccinated cattle.