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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

2019 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 1930’s and established an eradication program in the 1950’s. In support of these regulatory efforts, billions have been invested at the state and federal level to achieve eradication of brucellosis from cattle. However, persistence of Brucella in wildlife reservoirs (bison, elk, and feral swine) pose a risk for 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 vaccines for livestock and wildlife hosts, new diagnostics to detect brucellosis, and basic research to understand mechanisms that Brucella uses to establish and maintain infection. 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 vaccine development in Objective 1 including a study evaluating a novel vaccine delivery in cattle. The novel vaccine delivery in cattle induces a robust recall response on booster vaccination that mimics responses to live vaccine. Progress was also made in Objective 2 by studies evaluating the efficacy of a mucosal vaccine in elk and booster vaccination of bison. In addition, immunologic studies have characterized cellular subtypes responding to vaccination in cattle, identified a technique that allows differentiation of responding antigen-specific cells in cattle and bison, and characterized humoral and cellular responses in cattle persistently infected with RB51. Validation of inactivation procedures for preparation of DNA and RNA from samples obtained from Brucella-infected animals was also completed.

1. Efficacy of Brucella vaccination in elk. The prevalence of brucellosis in free-ranging elk in the Greater Yellowstone Area (area surrounding Yellowstone National Park) has been epidemiologically linked to infections in cattle herds. In an effort to identify an efficacious vaccine in elk, scientists in Ames, Iowa, collaborated with Colorado State University and the Animal Plant Health Inspection Service to assess the efficacy of a new mucosal brucellosis vaccine. Pregnant elk cows were experimentally challenged with virulent Brucella abortus in the third trimester. There was no difference in abortion rates between control and vaccination treatments. Data indicates that the mucosal vaccine did not protect elk against brucellosis. As an efficacious brucellosis vaccine has not yet been identified in elk, intervention strategies to address brucellosis in free ranging elk are lacking. This data will be of interest to regulatory personnel addressing brucellosis in free-ranging elk and scientists working to develop brucellosis vaccines.

2. RB51 shedding in milk. Over the past two years, people in at least 3 states have been infected with the Brucella abortus RB51 vaccine strain after consumption of unpasteurized milk. In an effort to understand why some calfhood-vaccinated cattle stay persistently infected and shed RB51 in milk as adults, scientists in Ames, Iowa, collaborated with the Centers for Disease Control and Prevention and the Animal and Plant Health Inspection Service to characterize immunologic responses in the peripheral blood and milk of these cattle. Cattle shedding RB51 in milk have high antibody responses in both milk and serum, with the antibody subtype predominantly being IgG1. A cellular immune response was not detected in the peripheral blood of animals shedding RB51. An ELISA assay developed in our lab can detect cattle shedding RB51 in milk. This work has provided a diagnostic assay for detecting cattle shedding RB51 in milk, and provided immunologic insights into why these cattle stay persistently infected with the vaccine strain. Due to the widespread use of RB51 vaccination in cattle, this work is critical to minimize the public health impact associated with human infection.

3. A novel Brucella vaccination in cattle. Live-modified Brucella vaccines are more immunogenic and protective as compared with killed or subunit 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. In an effort to develop a safer, yet efficacious vaccine, scientists in Ames, Iowa, vaccinated cattle with a biodegradable polymer containing killed Brucella antigen and determined its immunogenicity. After booster vaccination cellular and humoral immune responses in animals vaccinated with the polymer vaccine were similar to responses to a live vaccine. This work provided a new vaccination platform that may lead to improved brucellosis vaccines. This data will be of interest to investigators developing vaccines to animals against brucellosis or other pathogens.

Review Publications
Boggiatto, P.M., Vrentas, C.E., Fitzsimmons, D.J., Bayles, D.O., Alt, D.P., Olsen, S.C. 2018. Coincidence cloning recovery of Brucella melitensis RNA from goat tissues: advancing the in vivo analysis of pathogen gene expression in brucellosis. BioMed Central (BMC) Molecular Biology. 19:10.
Register, K.B., Olsen, S.C., Sacco, R.E., Ridpath, J., Falkenberg, S., Briggs, R., Kanipe, C., Madison, R. 2018. Relative virulence in bison and cattle of bison-associated genotypes of Mycoplasma bovis. Veterinary Microbiology. 222:55-63.