Mycobacterial Species and Diseases

Mycobacterial Species and Diseases

• Mycobacteria are important human and animal pathogens, rod-shaped, aerobic, and non-motile.
• Key characteristics include large amounts of cell wall lipid (mycolic acids) that retain the Ziehl-Neelsen stain.
• Some species are fast-growing, while others are slow-growing.
• Some, like M. leprae, require host cells to grow.
• Mycobacteria have a common ancestor, and their evolution has included adaptations to various niches.
• Important mycobacterial species in veterinary medicine include M. bovis (bovine tuberculosis), M. avium paratuberculosis (Johne's disease), M. avium complex (TB in birds and pigs), M. microti (TB in cats).
• M. tuberculosis complex (MTBC) includes M. tuberculosis, M. bovis, M. microti, M. africanum, and M. canetti, as well as the vaccine strain BCG.

Johne's Disease

• Chronic wasting disease of ruminants, caused by M. avium paratuberculosis (MAP).
• Symptoms include severe diarrhea and weight loss.
• Typically, infection occurs in early life (days of birth) with a long subclinical period that can last 2-4 years.
• Triggers, often related to calving or co-infection, can transition animals into the clinical stage.
• Characterized by chronic granulomatous inflammation, particularly in the ileum of the small intestine.
• Evidence suggests potential human link with Crohn's disease.
• "Supershedder" cattle can be a significant source of environmental contamination.

Bovine Tuberculosis

• Caused by M. bovis.
• Similar pathology and immunology to human TB, high genetic similarity.
• Important zoonotic pathogen, historically responsible for human TB cases prior to milk pasteurization.
• Incidence in UK cattle herds has increased since the 1980s, despite control measures.
• Leading to substantial economic losses to farming.
• Affects primarily cattle, but also presents in other animals.

Pathogenesis of Mycobacterial Infections

• Survival and growth inside macrophages (like macrophages and dendritic cells) is a key virulence characteristic.
• Immune responses are central to controlling infection, particularly IFNγ mediated macrophage activation.
• Granuloma formation is a key component of the host response, which can either contain or allow bacteria to evade immune systems.
• The tough, hydrophobic cell wall of these bacteria is a primary defense mechanism against the host immune system.

Diagnostic and Detection Techniques

• Variety of diagnostic methods exist for Johne's and bovine TB.
• These include detection of the pathogen or measurement of immune responses.
• Diagnostic techniques for MAP often focus on faeces, blood testing, and the intermittent nature of pathogen shedding.
• Bovine tuberculosis is diagnosed and managed through skin testing with PPD and IFNy secretion measurement.

Vaccination

• Currently, no licensed vaccines exist for either Johne's or bovine TB in cattle.
• Partially effective vaccines exist (e.g., BCG), but these may interfere with existing diagnostic techniques.
• Development of diagnostic tests compatible with the use of these alternative vaccines can improve infection management.

Explore the key characteristics and significance of various mycobacterial species that affect both human and animal health. This quiz covers important pathogens like M. tuberculosis, M. bovis, and M. avium paratuberculosis, including their roles in diseases such as tuberculosis and Johne's disease. Test your knowledge on their features and adaptations.