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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

2021 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
This will be the final report for project 5030-32000-224-00D terminating November 11, 2021. Research will continue under a bridging (or new) project. USDA initiated control measures for brucellosis in the 1930s and established an eradication program in the 1950’s. In support of these regulatory efforts, billions of dollars 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. During the 5 years of the project, an enhanced understanding of the immune responses of cattle, bison and elk to brucellosis vaccination was gained. The efficacy of vaccination strategies was demonstrated in cattle and bison. The effects of combining brucellosis vaccination with other standard cattle vaccines and the immunogenicity and efficacy of new vaccine platforms was determined. Additional data on the unique immunologic responses of elk to vaccination was gained that was beneficial in understanding the lack of efficacy of current brucellosis vaccines in this species. The project characterized the pathophysiology of brucellosis in elk and demonstrated elk have similar infection rates as bison and cattle after experimental infection, but lower rates of abortion. The project compared sensitivity and specificity of brucellosis diagnostic tests in cattle, bison, swine, and elk. The project developed a novel in vitro assay which enhances characterization of T cell responses after vaccination or infection. In Brucella-infected goats, the project demonstrated that long-term antibiotic treatment is not effective in eliminating infection, and that culture-negative goats retain evidence of latent infection for long periods of time (months). Shedding of RB51 in milk of cattle after vaccination was characterized due to its public health importance and scientists demonstrated reduced cellular immunity in persistently infected animals. The project also determined optimal methods for collecting samples for evaluation of gene expression and published validated inactivation protocols to meet Select Agent regulations. Efforts of project scientists supported the National Brucellosis Eradication program and resulted in the development of new tools and strategies that could be used by regulatory personnel to address brucellosis issues in domestic livestock and wildlife hosts.

1. Bottlenecks of Brucella infection. Brucella populations must overcome natural mucosal barriers and innate immunity to establish in vivo infection in tissues of cattle or other hosts. To understand how Brucella populations are limited during infection, and identify genes critical for establishing infection, ARS scientists in Ames, Iowa, infected cattle with a pool of transposon deletion B. abortus strains. Recovery of Brucella strains from tissues after infection were characterized and compared to the composition of strains within the challenge inoculum. Our data demonstrate that the composition of Brucella populations in tissues after infection are limited by mucosal barriers and innate immunity. This work offers unique insights into Brucella genes required to establish infection in host tissues that may be useful for developing new vaccines and/or diagnostics. This work will be of interest to regulatory personnel and researchers working to address brucellosis infections in domestic livestock and wildlife.

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, interactions between live attenuated vaccines, such as brucellosis RB51 and bovine viral diarrhea (BVD) vaccines, may have suppressive influences on immunologic responses leading to reduced efficacy Therefore, ARS scientists in Ames, Iowa, evaluated the short-term and long-term effects of simultaneous administration of RB51 and BVD vaccines and found evidence of enhanced interferon gamma production, a key component of cellular immunity. This work provides insight into possible benefits, rather than detrimental effects, of RB51 vaccination in cattle. This work will be of interest to producers, regulatory personnel and researchers working to prevent infectious disease in domestic livestock.

3. A novel Brucella vaccination in bison. Modified-live Brucella vaccines are more immunogenic and protective as compared killed or subunits vaccines. However, live brucellosis vaccines pose a risk as they can cause abortions in pregnant animals, can be infectious to humans, and their use in wildlife species can be limited due to environmental concerns. Therefore, ARS scientists in Ames, Iowa, evaluated the immunogenicity and efficacy of a new killed brucellosis vaccine in bison that can be delivered remotely. The new vaccine demonstrated efficacy in reducing abortions in bison after experimental infection but was not as efficacious as the current B. abortus RB51 vaccine. This work provided a new vaccination platform that may lead to improved brucellosis vaccines. This data is of interest to producers, regulatory personnel, and researchers working on vaccines against brucellosis or other pathogens.

Review Publications
Olsen, S.C., Boggiatto, P.M., Kanipe, C. 2020. Immune responses and clinical effects of experimental challenge of elk with Brucella abortus strain 2308. Veterinary Immunology and Immunopathology. 227.
Olsen, S.C., Crawford, L., Fuentes, A., Kostovic, M., Boggiatto, P.M. 2020. Influence of species of negative control sera on results of a brucellosis fluorescence polarization assay . Journal of Veterinary Diagnostic Investigation. 33:67-72.
Boggiatto, P.M., Schaut, R.G., Olsen, S.C. 2020. Enhancing the detection of Brucella-specific CD4+ T cell responses in cattle via in vitro antigenic expansion and restimulation. Frontiers in Immunology. 11:1944.
Pierce, .F., Brown, V.R., Olsen, S.C., Boggiatto, P.M., Pedersen, K., Miller, R.S. Speidel, S.E., Smyser, T.J. 2020. Loci associated with antibody response in feral swine (Sus scrofa)infected with Brucella suis. Frontiers in Veterinary Science. 7.
Fiebig, A., Vrentas, C.E., Le,T, Huebner, M., Boggiatto, P.M., Olsen, S.C., Crosson, S. 2021. Quantification of Brucella abortus population structure in a natural host. Proceedings of the National Academy of Sciences(PNAS). 118.