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ARS Home » Midwest Area » Ames, Iowa » National Animal Disease Center » Infectious Bacterial Diseases Research » Research » Research Project #432153

Research Project: Pathogenesis and Development of Improved Diagnostic and Control Strategies for Brucellosis in Livestock and Wildlife

Location: Infectious Bacterial Diseases Research

2020 Annual Report

Objective 1: Refine the experimental infection models to characterize pathologic and immunologic responses in elk, swine and bison including use of molecular and/or proteomic and transcriptomic techniques. Subobjective 1.1: Refine the experimental challenge model for elk. Subobjective 1.2: Characterization of immunologic mechanisms related to protection after booster vaccination. Subobjective 1.3: Characterization of immunologic mechanisms related to protection after vaccination of swine and elk with novel new vaccines. Subobjective 1.4: Characterize transcriptomic responses of host and Brucella spp. to in vivo infection. Objective 2: Using the models refined in Objective 1, develop new and/or improved diagnostic and intervention strategies to control Brucella infections in wildlife reservoirs responsible for infecting domestic production animals. Subobjective 2.1: Identify vaccination strategies that are protective for bison, elk, and/or cattle against experimental challenge with Brucella abortus strain 2308. Subobjective 2.2: Characterize efficacy of novel vaccines to protect swine from virulent B. suis. Subobjective 2.3: Development of new brucellosis serologic assays using novel epitope identification strategies.

The long-term goals of this project are to facilitate the completion of brucellosis eradication programs in domestic livestock, and prevent reintroduction of brucellosis into livestock from wildlife reservoirs. Specifically, fundamental knowledge on Brucella pathogenesis will be gained, efficacious vaccination systems will be identified, and sensitive and specific diagnostic tools will be developed to aid eradication programs. Immunogenicity of vaccination strategies in targeted hosts (cattle, bison, elk, and swine), including novel vaccine platforms, will be evaluated in targeted species and efficacy characterized by experimental challenge. In addition, the project will try to improve the standard experimental challenge model for elk to better replicate the clinical effects of brucellosis under field conditions. By simultaneously characterizing the in vivo transcriptome of B. abortus and natural host during infection, we will develop knowledge of molecular mechanisms involved in regulation of host responses to infection, and genes expressed by the pathogen under in vivo conditions. This basic knowledge will identify future targets for development of new vaccines, diagnostics, immunomodulation, and possibly therapeutics. New diagnostics will be developed and analyzed for their ability to detect brucellosis in swine and cattle, and may allow differentiation of which Brucella spp. is associated with infection. The research will help resolve the risk of re-infection of domestic livestock from wildlife reservoirs of brucellosis, protect the financial investment that has been made in the U.S. brucellosis eradication program, and provide public health benefits by reducing the risk of zoonotic infection.

Progress Report
USDA initiated control measures for brucellosis in the 1930s and established an eradication program in the 1950s. In support of these regulatory efforts, billions have been invested at the state and federal levels to achieve eradication of brucellosis from cattle. However, persistence of Brucella in wildlife reservoirs (bison, elk, and feral swine) pose a risk for the reintroduction of disease to domestic livestock. Development of new vaccines and diagnostics that can be applied to domestic livestock and/or wildlife under current field conditions are needed. During the past year, work has been conducted on new vaccine platforms in cattle and elk, performance of diagnostic assays for detection of brucellosis has been characterized, and basic research on genes that may cause attenuation and/or increased immunogenicity of live brucellosis vaccines were identified. Advances in vaccines and diagnostics will be useful for protecting domestic livestock and managing brucellosis in current wildlife reservoirs within the U.S. The overall goal of the project is to facilitate eradication of brucellosis from natural hosts and prevent reintroduction of this disease into livestock in the United States. During the past year, progress was made in evaluating vaccine development in Objective 1 including a study evaluating the immunogenicity of a new vaccination design in elk, developing an in vitro immunologic assay that more accurately measures adaptive immune responses in cattle and bison, and characterizing the immunologic effects of co-administering a live brucellosis vaccine with other modified live vaccines in cattle. In addition, studies were conducted to optimize the performance characteristics of the brucellosis fluorescence polarization assay, a commonly used brucellosis serologic test. Progress was also made in Objective 2 by studies evaluating the efficacy of a new vaccination platform for cattle, and characterizing the efficacy of novel vaccination platforms in bison and elk.

1. Performance of a diagnostic test. The fluorescence polarization assay (FPA) is a highly sensitive and specific test that is commonly used for brucellosis surveillance under field conditions. The assay measures optical differences in rotational velocity to detect brucellosis antibodies. Although designed for use in cattle the test is also used for surveillance in elk, swine, and bison using the negative control cattle sera included in the kit. In an effort to determine if species differences may influence FPA responses, sera from non-infected cattle, swine, bison, and elk were used by ARS scientists in Ames, Iowa, as background sera against panels of sera from control, vaccinated, and Brucella-infected animals. Data demonstrated that FPA responses were influenced by the species of background sera leading to some sera incorrectly interpreted as positive for brucellosis. The study also showed that elk develop antibody responses faster after infection than cattle and bison, the FPA has low sensitivity and specificity in swine, and cattle persistently infected with the Brucella abortus strain RB51 vaccine remain seronegative on the FPA. This work will be of interest to regulatory personnel in states with brucellosis-infected wildlife and livestock producers.

2. Immunologic interaction between vaccines in cattle. It is a common practice under field conditions to simultaneously administer multiple vaccines to calves at one time. However, live attenuated vaccines, such as brucellosis and bovine viral diarrhea (BVD) vaccines, may have suppressive influences on immunologic responses leading to reduced efficacy by vaccines. Therefore, ARS scientists in Ames, Iowa, determined the immunologic effects of co-administration of a live attenuated brucellosis vaccine, Brucella abortus strain RB51, with a modified live bovine viral diarrhea vaccine in calves. After monitoring for six months after inoculation, data indicated no negative interactions on adaptive immunologic responses. This work will be of interest to producers and regulatory personnel working to develop effective vaccine strategies to prevent brucellosis and BVD.

3. Characterization of immunologic responses. Protection against intracellular pathogens such as Brucella requires development of adaptive immunity involving T cells. Current in vitro testing to understand these cellular immune responses does not always correlate with protection observed after experimental infection or under field conditions. In an effort to develop improved immunologic tests ARS scientists, in Ames, Iowa, developed a new immunologic assay that more accurately characterizes function of T cells after vaccination. This assay also allows more sensitive detection of the production of immune signaling molecules (cytokines), and enhanced knowledge of how the immune system responds to vaccination. This work will be of interest to producers, veterinarians, and academic scientists working to understand immunologic responses to vaccination and working to develop effective intervention strategies.

Review Publications
Boggiatto, P.M., Olsen, S.C. 2019. Tulathromycin treatment does not affect bacterial dissemination or clearance of Brucella melitensis 16M following experimental infection of goats. PLoS One. 14(12):e0226242.
Bricker, B.J., Goonesekere, N., Bayles, D.O., Alt, D.P., Olsen, S.C., Vrentas, C.E. 2020. Genome report-a genome sequence analysis of the RB51 strain of Brucella abortus in the context of its vaccine properties. G3, Genes/Genomes/Genetics. 10(4):1175-1181.
Vrentas, C.E., Boggiatto, P.M., Olsen, S.C., Leppla, S.H., Moayeri, M. 2020. Characterization of the NLRP1 inflammasome response in bovine species. Innate Immunity. 26(4):301-311.
Boggiatto, P.M., Schaut, R.G., Kanipe, C., Kelly, S.M., Narasimhan, B., Jones, D.E., Olsen, S.C. 2019. Sustained antigen release, polyanhydride-based vaccine platform for immunixation against bovine brucellosis. Heliyon. 5(8).