Location: Infectious Bacterial Diseases Research2017 Annual Report
Objective 1: Identify MAP antigens including protein to protein interactions using proteomic and genomic tools to better understand their function in pathogenesis of Johne’s disease and develop improved diagnostic tools. Subobjective 1.1: Define pathogenic mechanisms of MAP through bacterial community interactions as well as protein interactions with the host. Subobjective 1.2: Detection reagents for Johne’s Disease. Objective 2: Characterize host immunity and pathogenesis of disease using immunophenotypic and cell signaling markers in response to asymptomatic and clinical MAP infection, as well as vaccination. Subobjective 2.1: Characterize patterns of Th17-mediated immune responses to natural infection in cattle in asymptomatic and clinical stages. Subobjective 2.2. Characterize key differences in host immunity upon vaccination compared to infection. Subobjective 2.3: Assess B cell mediated immunity to natural infection in cattle in asymptomatic and clinical stages using maturation and activation markers for B cell subsets. Subobjective 2.4: Characterize the impact of infection on the phenotypes of antigenpresenting cells in target tissues of infected cattle. Objective 3: Investigate genetic variability among MAP isolates of livestock using whole genome sequencing to develop improved epidemiological tools and evaluate the genetic basis of virulence. Subobjective 3.1: Identify the genotypes of MAP present in U.S. dairies using whole genome sequencing. Subobjective 3.2: Identify and characterize virulent strains of MAP.
Within Objective 1 the function of MAP proteins as antigens will be identified using genomic and proteomic tools to better understand their role(s) in pathogenesis of Johne’s Disease and to develop improved diagnostic tools. In Objective 2, tools such as cellular phenotype and secretion of cytokines involved in cell signaling will be measured to characterize host immune responses in asymptomatic and clinical stages of infection, as well after vaccination, to gain knowledge as to correlates involved in controlling the disease. Genetic variability of MAP isolates of livestock will be investigated using whole genome sequencing under Objective 3. This will lead to improved epidemiological tools in the field and understanding of MAP genes involved in virulence. The 3 major objectives outlined within this project plan will work in an interactive manner to provide us with tools to control this disease.
Mycobacterium avium paratuberculosis (MAP), the causative agent of Johne’s Disease, is a chronic progressive enteric disease characterized clinically by chronic or intermittent diarrhea, emaciation, and death. The disease has a worldwide distribution with 70% of US dairy herds currently infected. Dairies infected with Johne’s disease have significant economic losses due to reduced milk production and premature culling. Because the host immune responses to MAP is complex, the project is characterizing host-pathogen interactions to develop new diagnostic and vaccination tools. During the past year, a calf study was conducted using a novel vaccine containing recombinant proteins. The recent study found a dose-dependent impact on vaccine efficacy with higher vaccine dosages demonstrating earlier and more robust immunologic responses. In a separate study, tissues from naturally infected and non-infected cattle were used to demonstrate an association between stage of infection and macrophage populations and phenotypes. In collaborative research, new candidate diagnostic antigens for Johne’s disease were identified using a Mycobacterium tuberculosis protein array. This work will facilitate development of more sensitive and specific diagnostic tests and more effective vaccines to control MAP. Better diagnostics and vaccines will provide intervention tools for veterinarians, herd owners, and diagnosticians to identify and prevent infection, and reduce the economic losses associated with Johne’s disease in infected dairy herds.
1. Identification of new diagnostic antigens. Paratuberculosis is a chronic intestinal disease of ruminants caused by Mycobacterium avium subsp. paratuberculosis (MAP). Because of the increasing prevalence of MAP, new diagnostic tests are needed to identify subclinical infections. ARS researchers in Ames, Iowa, demonstrated that a specific combination of MAP antigens resulted in more sensitive and specific diagnosis of Johne’s infection. Cows with Johne’s disease had strong responses to the combined antigens. The antigens are currently being further evaluated using other assay formats. It is anticipated that diagnostic tests using these antigens will be more sensitive and specific than currently available diagnostics for Johne’s disease. Development of better diagnostic tests for Johne’s disease will improve the ability to detect MAP infection and provide economic benefits to dairy producers.
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