Project : USDA ARS

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Research Project: Diagnostic and Mitigation Strategies to Control Tuberculosis in Cattle and Wildlife

Location: Infectious Bacterial Diseases Research

2025 Annual Report

Objectives
Objective 1: Develop vaccines that prevent disease or mitigate disease spread with an emphasis on platforms that allow for extended antigen release and remote delivery for livestock and wildlife species. Subobjective 1.A: Assess the potential of a polyanhydride delivery platform to enhance BCG availability and immunogenicity in order to promote protective anti-mycobacterial responses. Subobjective 1.B: Evaluate the immune response of WTD to encapsulated lyophilized BCG delivered in oral vaccine delivery units (VDUs). Objective 2: Improve current diagnostic tests for bovine TB and develop novel, next generation diagnostics which are amenable to remote or continuous disease surveillance and can be incorporated into precision livestock management. Sub-objective 2.A: Assess the sensitivity and specificity of a fluorescence polarization assay (FPA) to detect serum antibodies against synthetic M. bovis antigens. Subobjective 2.B: Develop a battery-free, self-contained sensor for the detection of biological IFN-' in vivo that could be used as a diagnostic platform. Objective 3: To enable the rational-design of intervention strategies, using transcriptomic approaches,define the immunopathogenesis of bovine tuberculosis at the tissue and cellular level by analyzing gene expression of peripheral immune responses and those responses involved in granuloma formation and maintenance. Subobjective 3.A: Characterize the presence of key T cell subsets and transcription factors in granulomas from BCG-vaccinated vs. non-vaccinated animals following experimental infection with M. bovis. Subobjective 3.B: Characterize the gene transcription profiles of Mycobacterium bovis-specific T cells in the periphery following M. bovis infection or vaccination.

Approach
Characterize and compare cytokine and biomarker expression (immune responses) at the cellular level in lungs and lymph nodes of Mycobacterium bovis-infected cattle. Comparing responses between tissues, as well as over time, will aid in understanding the host response to M. bovis within the environment where host and pathogen interact (granuloma). We aim to improve the specificity of diagnostic tests by developing diagnostic reagents from proteins found in M. bovis but not in non-tuberculous mycobacteria, thus avoiding cross-reactivity elicited by environmental mycobacteria that contributes to false positive results on cattle tuberculosis diagnostic tests. Similarly, we aim to identify proteins/genes expressed by M. bovis in vivo that may be considered as potential diagnostic test targets and to use genomics/transcriptomics to characterize genes/gene profiles of M. bovis-infected vs non-infected cattle. These data will aid diagnosis and provide insight into the immunopathogenesis of bovine tuberculosis. In terms of vaccine evaluation, we aim to examine duration of immunity to experimental infection provided by the vaccine M. bovis BCG in white-tailed deer and examine the effects of oral BCG vaccination on deer-to-deer transmission of virulent M. bovis. In cattle, we aim to determine the efficacy of simultaneous administration of parenteral M. bovis BCG and a mucosally delivered bacterial-vectored subunit vaccine against aerosol M. bovis infection in neonatal calves.

Progress Report
Over 100 years ago, in 1917, USDA initiated a bovine tuberculosis (bTB) eradication program that is still in place today. Although significant progress has been made, eradication has proved elusive. Obstacles to eradication include, 1) lack of rapid and accurate diagnostic tests to detect animals infected with Mycobacterium bovis; the cause of tuberculosis in animals, and 2) infected wildlife acting as a source of infection for cattle. Research activities of ARS scientists in Ames, Iowa, provide direct support for the USDA bTB eradication program, specifically, through development of more sensitive diagnostics, efficacious vaccines, and improved animal disease models to enhance the capability to detect, prevent and control bTB. Improved disease detection and/or disease prevention will benefit cattle producers by reducing production losses and costs associated with replacing infected animals. In support of Objective 1, and in collaboration with other USDA scientists at Ft. Collins, Colorado, ARS scientists in Ames, Iowa, published two manuscripts describing the use of an edible form of the human TB vaccine to provide immunity to wild deer. White-tailed deer in Michigan are a source of infection for cattle and vaccination of wild deer has been proposed as one tool to decrease deer-to-cattle disease transmission. Specifically, the publications describe the immune response to these edible bait vaccines in a study using captive deer in Ames, Iowa, as well as a pilot project that deployed vaccine baits at specific farms in Michigan demonstrating the feasibility of vaccinating wild deer against tuberculosis. To date, over 85 cattle herds in Michigan have contracted tuberculosis from white-tailed deer and 2-3 herds are infected every year. A vaccine for wild deer will benefit cattle producers by decreasing deer-to-cattle transmission and aid in ensuring a safe food supply for consumers. Current diagnostic tests for bTB are time-consuming and lack the accuracy necessary to identify all infected animals within a herd. Removal of all infected animals will decrease the need for more drastic methods such as whole herd depopulation. In support of Objective 2, banked serum samples from Mycobacterium bovis infected cattle were identified and analyzed using the fluorescent polarization assay (FPA), a novel means of tuberculosis diagnosis in cattle, which is more rapid than current tests and has proven useful with other diseases of cattle such as brucellosis; however, the accuracy of the FPA for tuberculosis was observed to be unsatisfactory. To continue investigation of the FPA, new proprietary reagents will need to be created by the developer of the FPA. Development of novel vaccines and diagnostic tests will require increased knowledge of the disease process in cattle. In support of Objective 3, ARS scientists in Ames, Iowa, continue to analyze tissue and blood samples from tuberculous cattle for gene expression of key immune system genes at both the tissue level and at the level of the blood. In tissue, several key immune factors were identified and described in publications. Data for gene expression in blood continues to be analyzed. Identification of key immune system genes will enhance vaccine and diagnostic test development, thereby expediting tuberculosis eradication.

Accomplishments
1. Demonstrated the susceptibility of bison to infection with the COVID virus. The role of animals in the COVID-19 pandemic, as well as the true range of susceptible animal hosts remains unclear. Previous work by ARS scientists in Ames, Iowa, demonstrated the lack of susceptibility of agricultural animals such as cattle and swine to infection with the COVID virus. However, ARS scientists in Ames, Iowa, also demonstrated the susceptibility of wildlife such as white-tailed deer. It was shown that deer were easily infected and spread disease to other deer. Extending our research on the susceptibility of various animal species to the COVID virus, bison were evaluated for their susceptibility to infection with the COVID virus. Bison on public lands are considered wildlife, while farmed bison are an important and growing agricultural commodity. ARS scientists in Ames, Iowa, demonstrated that bison are more susceptible to infection than cattle or swine, develop antibodies against the virus unlike cattle or swine, and virus persists in tissues up to 21 days, which was not seen in cattle or swine. However, bison do not shed significant amounts of virus and are therefore, unlikely to transmit disease to other animals or humans. This information is critical to understand the role various wildlife and agricultural species play in the epidemiology of COVID. Therefore, bison producers do not need to be concerned about economic losses due to COVID or the risk of bison becoming an animal reservoir of the COVID virus.

2. Demonstrated the inability of COVID infected deer to transmit virus to sheep. As white-tailed deer are the only known wildlife reservoir of the COVID virus in North American it is important to understand the potential of virus spread from deer to other species such as livestock. Cattle and swine were not susceptible to experimental infection with the COVID virus, while sheep were shown to be susceptible to experimental infection, but did not develop clinical signs of disease. In the western United States sheep are often grazed in areas also occupied by wildlife such as deer. ARS scientists in Ames, Iowa, demonstrated that although deer are easily infected and shed virus in nasal and oral secretions, in a natural infection setting, sheep are resistant to infection, even when there is close direct contact between sheep and deer. Therefore, sheep producers do not need to be concerned about economic losses due to COVID, even in areas where sheep are grazed on ranges where deer are also found.

3. Elucidated the disease process of bTB in cattle. To better understand the host immune response at the tissue level, ARS scientists in Ames, Iowa, analyzed tissues from Mycobacterium bovis infected cattle to identify the role of various immune cells as the disease progresses. This work demonstrated the early stages of bTB and factors which promote and sustain disease. Understanding the host response, especially at the earliest stages of disease will aid in development of improved diagnostic assays that will benefit producers by identifying infected animals early in infection before disease spreads throughout a herd. This knowledge will also aid in development of effective vaccines to prevent disease introduction, thereby benefitting cattle producers.

U.S. DEPARTMENT OF AGRICULTURE

Infectious Bacterial Diseases Research: Ames, IA