Roadmap for the development of diagnostic test for bTB

What are we trying to achieve and why? What is the problem we are trying to solve?

To establish how the host is responding and what it is responding to at different stages of infection.

What are the scientific and technological challenges
(knowledge gaps needing to be addressed)?

• Indistinguishable exposure and infection: current tests generate immunoreactivity but do not distinguish exposure from infection; consequently, a proportion of reacting cattle may have cleared infection. This requires empirical study.
• Interaction with macrophages: M. bovis infects macrophages which are an important contributor to the immune response so establishing how the bacterium interacts with macrophages is central to identifying the protective mechanisms and how the bacteria evades them.
• To enhance the killing of infected immune cells.
• Variability in animal resistance: compelling evidence that animals vary in their resistance to M. bovis infection; there is heritable and exploitable variation in how animals respond to M. bovis exposure.
• Genotypic variations of M. bovis: M. bovis populations can be genotyped into various lineages and clones globally. These genotypes may have epidemiologically relevant phenotypes at the clone level. This remains to be demonstrated empirically.

What approaches could/should be taken to address the research question?

Relatively high risk and low risk cattle sires can be identified via quantitative genetics and the TB risk that follows in their daughters. Consider in vitro or in vivo experiments to investigate how these extreme phenotypes handle the pathogen.
TB phenotypes, such as susceptibility and/or transmissibility may be expressed via structural genetic variation or via epigenetics.
M. bovis and macrophage gene expression (transcriptome/RNA sequence data) in different in vivo environments (macrophages from naïve and immune hosts)
Compare response where macrophages are infected with different M. bovis strains, BCG and M. tuberculosis looking at gene responses of the macrophage and the bacterium.
Compare response where neutrophils (and subsets including regulatory neutrophils) are infected with different M. bovis strains, BCG and M. tuberculosis looking at gene responses of the macrophage and the bacterium

Comparison of the macrophage-bacteria response following clearance (is infection ever cleared or just walled off?), in latency (this may involve comparative studies involving different breeds or species) and in active infections.
Comparison of the response to different strains of M. bovis Incubation period in species other than cattle
Role of co-infections in disease progression.
Relationship between granuloma characteristics and the number of organisms present.
Establishing the role of γδT cells and granulocytes in granulomas.
Consider other important cell types such as different neutrophil subsets in the evolution of the disease

What else needs to be done before we can solve this need?

Existing knowledge including successes and failures