Is TB Testing Associated With Increased Blood Interferon-Gamma Levels?

Area of Science:

• Veterinary Immunology
• Infectious Disease Epidemiology

Background:

• The Republic of Ireland exhibits low Johne's disease (JD) prevalence, potentially due to smaller herd sizes, grass-based systems, and extensive bovine tuberculosis (bTB) testing.
• Interferon-gamma (IFN-γ) is crucial for protection against JD, and its response to bTB testing is hypothesized to influence disease progression.

Purpose of the Study:

• To investigate the association between bTB testing and systemic IFN-γ production.
• To assess the impact of bTB testing on Mycobacterium avium subspecies paratuberculosis (MAP) antibody response.

Main Methods:

• 265 cows were enrolled, with blood samples collected pre- and post-bTB testing (72 hours for IFN-γ, 10 days for MAP antibodies).
• Avian and bovine purified protein derivative (PPD) were administered as part of the compulsory annual bTB test.
• IFN-γ levels and MAP antibody responses were measured to evaluate changes after PPD administration.

Main Results:

• A significant increase in MAP antibody response was observed post-bTB testing compared to pre-testing levels (p < 0.001).
• IFN-γ production also showed a significant increase at the post-bTB test time point (p < 0.001) compared to baseline readings.
• These findings suggest a potential beneficial effect of bTB testing in managing JD.

Conclusions:

• The bTB testing protocol, involving PPD administration, significantly enhances both IFN-γ and MAP antibody responses in cattle.
• This immune stimulation may play a role in limiting the clinical progression of Johne's disease in the Irish cattle population.
• Further research is warranted to confirm the direct impact of bTB testing on JD control strategies.