Location: Infectious Bacterial Diseases Research
2017 Annual Report
Objectives
These studies are focused on developing an understanding of how Leptospira and Treponema species interact with their hosts to establish colonization, infection, and clinical disease. A combination of genomic, proteomic and immunological methodologies will be used to analyze how the host responds to infection and how bacteria respond to the host, with the long-term goal of identifying pathways that can be targeted to alter disease outcomes or exploited to induce protective immunity.
Objective 1. Identify and characterize the Leptospira and Treponema sp. circulating in livestock.
Subobjective l.1 - Determine prevalence of leptospires circulating in local bovine herds.
Subobjective l.2 - Characterize clonal isolates of Treponema from bovine digital dermatitis at the phenotypic, genomic and proteomic level.
Objective 2. Develop animal models that will mimic infection, facilitate characterization of interactions between host and pathogen, and allow development of assays that will accurately identify infected individuals.
Subobjective 2.1 - Characterize urinary immunoglobulin from reservoir hosts of leptospirosis.
Subobjective 2.2 - Characterize the cellular immune response of reservoir hosts of leptospirosis.
Subobjective 2.3 - Characterize and refine an ovine model of bovine digital dermatitis.
Objective 3. Characterize spirochete antigens including those that are differentially expressed during infection.
Subobjective 3.1 - Identification and characterization of leptospiral proteins that are expressed in response to mammalian host signals.
Subobjective 3.2 - Characterize host humoral responses to outer membrane protein antigens derived from bacteria associated with digital dermatitis.
Approach
Objective 1: This objective seeks to identify and characterize species of Leptospira and Treponema sp. circulating in livestock. Studies will be conducted to determine the prevalence of leptospires circulating in local bovine herds (Sub-objective 1.1); and to characterize clonal isolates of Treponema from bovine digital dermatitis at the phenotypic, genomic and proteomic levels (Sub-objective 1.2). We expect these studies to determine if serovars of leptospires currently circulating in bovine populations of the Mid-West have changed over the last 20 years and to demonstrate that different phylotypes of Treponema derived from bovine digital dermatitis have unique genomic, proteomic and virulence factors.
Objective 2: Development of animal models that mimic infection will facilitate characterization of interactions between host and pathogen, and allow development of assays that will accurately identify infected individuals. Urinary immunoglobulins from reservoir hosts of leptospirosis will be collected and characterized (Sub-objective 2.1); the cellular immune response of reservoir hosts of leptospirosis will also be characterized (Sub-objective 2.2); and an ovine model of bovine digital dermatitis will be further characterized and refined (Sub-objective 2.3). We will also evaluate immune activation pathways in a reservoir host model of leptospirosis using the inbred Fisher 344 rat. Studies conducted will advance the use of sheep as a ruminant model to understand the pathogenic mechanisms and involvement of treponemes in digital dermatitis.
Objective 3: Characterize spirochete antigens including those that are differentially expressed during infection. Studies will be conducted to identify and characterize leptospiral proteins that are expressed in response to mammalian host signals (Sub-objective 3.1) and to characterize host humoral responses to outer membrane protein antigens derived from bacteria associated with digital dermatitis (Sub-objective 3.2).
Progress Report
Leptospirosis is an insidious disease of cattle that causes reproductive losses and which can also cause clinical disease in humans. Multiple serovars of leptospirosis are present in field infections, and vaccine-induced or immune protection is often serotype specific. During the past year, the project collaborated with scientists at USDA’s Food Safety and Inspection Service to isolate and characterize current Leptospira serovars that are circulating in United States cattle. Microbiologic techniques were paired with diagnostic testing to correlate sensitivity and specificity of serologic tests to cattle infection status. The project also did basic research to refine and improve culture methods for isolation of spirochete bacteria from samples. This work led to enhanced recovery of Leptospira and Treponema isolates from samples. Electron microscopy and biochemical techniques were used to characterize three Treponema spp. associated with digital dermatitis. Urinary antibodies specific to leptospirosis and protein profiles of bacteria in urine were characterized to understand protein expression under in vivo conditions. This work may lead to more sensitive and specific diagnostic tests for detecting infection, particularly in latent infections when no clinical symptoms are present. Laboratory animal models have also been used to characterize immunologic responses and genes/proteins expressed by Leptospira during in vivo infection. Both systemic immunologic responses and local responses at the site of infection were observed and characterized. An animal model for digital dermatitis was developed that will be useful for evaluating new vaccines and treatments.
Accomplishments
1. Current Leptospira serovars circulating in cattle. It has been more than 25 years since a comprehensive analysis was performed on Leptospira serovars infecting cattle in the U.S. Culture and characterization of circulating serovars is important as immune protection is serovar specific, and commercial vaccines are formulated based on serovars expected to be circulating in the cattle population. In a collaborative study, ARS scientists in Ames, Iowa, cultured more than 600 bovine urine samples resulting in the recovery of 23 Leptospira isolates. Microbiologic and molecular studies establishing the serovar and characterizing biochemical properties of the isolates are continuing. This study will allow comparison of current circulating isolates to the previous study from almost 3 decades ago. This work will be of benefit to commercial vaccine companies, producers, and scientists by providing knowledge on what serovars are circulating in cattle, thereby preventing economic losses by allowing selection of more efficacious vaccines.
Review Publications
Nally, J.E., Bayles, D.O., Hornsby, R.L., Arent, Z., Gilmore, C., Regan, S., McDevitt, A.D., Yearsley, J., Fanning, S., McMahon, B.J. 2016. Emerging infectious disease implications of invasive mammalian species: the greater white-toothed shrew (Crocidura russula) is associated with a novel serovar of pathogenic Leptospira in Ireland. PLOS Neglected Tropical Diseases. 10(12):e0005174.
Nally, J.E., Bayles, D.O., Hurley, D., Fanning, S., McMahon, B.J., Arent, Z. 2016. Complete genome sequence of Leptospira alstonii serovar room 22, strain GWTS#1. Genome Announcements. pii: e01230-16. doi: 10.1128/genomeA.01230-16.
Schuller, S., Arent, Z., Gilmore, C., Nally, J.E. 2015. Prevalence of antileptospiral serum antibodies in dogs in Ireland. Veterinary Record. 177(5):126. doi: 10.1136/vr.102916.
Wilson-Welder, J.H., Frank, A.T., Hornsby, R.L., Olsen, S.C., Alt, D.P. 2016. Interaction of bovine peripheral blood polymorphonuclear cells and Leptospira species; innate responses in the natural bovine reservoir host. Frontiers in Microbiology. 7:1110.
Wilson-Welder, J.H., Alt, D.P., Nally, J.E. 2015. Digital dermatitis in cattle: current bacterial and immunological findings. Animals. 5:114-1135. doi: 10.3390/ani5040400.
Scanlan, E., Ardill, L., Whelan, M., Shortt, C., Nally, J.E., Bourke, B., O'Croinin, T. 2017. Relaxation of DNA supercoiling leads to increased invasion of epithelial cells and protein secretion by Campylobacter jejuni. Molecular Microbiology. 104(1):92-104. doi: 10.1111/mmi.13614.
