Location: Infectious Bacterial Diseases Research
2017 Annual Report
Objectives
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.
Approach
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 use 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 including studies evaluating the efficacy of a ballistic vaccine in bison and characterization of immunologic responses to new vaccine candidates. Work was also completed to improve the brucellosis challenge model for elk. Although our laboratory has obtained high levels of abortions in non-vaccinated cattle and bison after experimental challenge, previous studies have resulted in very few abortions when elk receive an experimental challenge in accordance with the standard challenge model. In the current experiment the effect of challenge dose and time of gestation was evaluated in an effort to increase infection and clinical effects (abortions). Work was also completed on development of new diagnostics including use of a unique molecular approach for antigen discovery and evaluation of synthetic antigens. In addition, preliminary data on gene expression after infection by both the host and Brucella were also obtained.
Accomplishments
1. Long duration antibiotic not effective against brucellosis in goats. Whole herd treatment of infected goats with a long lasting antibiotic could be an effective treatment for reducing infection, clinical effects and disease transmission to humans. ARS scientists in Ames, Iowa treated goats with a commercial antibiotic after experimental infection with Brucella melitensis and found that infection and abortion rates were not decreased. Although this antibiotic is expected to remain efficacious for 21 days after treatment, our study indicates that it would not provide economic or epidemiologic benefits under field conditions. This work eliminates a possible therapeutic approach for managing brucellosis in areas of high disease prevalence but is of value as it resolves a question regarding an intervention strategy.
2. Brucella bacteria have long-term viability under in vivo conditions. The gold standard for clinical diagnosis is microbiologic recovery of live bacteria from samples. ARS scientists in Ames, Iowa recovered Brucella RNA from tissues of goats at approximately 9 months after experimental infection when all examined tissues were culture negative for recovery of bacteria. The presence of RNA in tissue indicates that live bacteria are still present and allows characterization of gene expression/utilization during latent infections in vivo. This work provides new insights into mechanisms used by Brucella to survive in vivo but also highlights the difficulty in determining the infection status of an animal host but provides intriguing scientific data for understanding the pathogenesis of brucellosis.
3. Synthetic antigens are immunoreactive. The majority of serologic tests for brucellosis are based on detecting antibodies against the O side-chain of the lipopolysaccharide. In a collaborative project, ARS scientists in Ames, Iowa characterized the serologic responses of infected livestock and wildlife using a synthetic antigen. Antibodies from infected animals had high levels of binding to the synthetic antigen. This work provides data on the performance of a new immunoreactive antigen that may be produced more efficiently than antigens currently used for serologic tests.
4. Characterization of inactivation procedures for Brucella. The Select Agent program has increased emphasis on validation of methods for inactivation of biothreat agents. In a series of experiments, ARS scientists in Ames, Iowa characterized and validated a number of inactivation methods. This work may impact public health as experiments suggested that current recommendations for heating milk may not be sufficient to inactive live Brucella. This work benefits scientists working with Brucella by providing validated procedures that improve safety and prevent possible exposures due to inadequate inactivation methods.
Review Publications
Pederson, K., Bauer, N., Gidlewski, T., Olsen, S.C., Arenas, A., Henry, A., Sibley, T., Nolte, D. 2017. Identification of Brucella spp. in feral swine (Sus scrofa) at abattoirs in Texas, USA. Zoonoses and Public Health. doi: 10.1111/zph.12359.
Olsen, S.C., Wilson-Welder, J.H., Nol, P., Rhyan, J., Srirangathan, N. 2017. Immunogenicity and efficacy of a rough Brucella suis vaccine delivered orally or parenterally to feral swine. International Journal of Vaccine Research. 2(1): 6.
