Temporal analysis of the interference caused by paratuberculosis vaccination on the tuberculosis diagnostic tests in goats

Vaccination against paratuberculosis (PTB) in goats is a cost-effective control strategy, and is also effective as regards preventing the onset of clinical cases. However, it causes interference in the diagnostic tests used in the control of tuberculosis (TB). A group of 99 goats from a herd with no history of TB or PTB infection was vaccinated against PTB at seven months of age. They then underwent consecutive intradermal tests [single (SIT) and comparative (CIT) intradermal tuberculin tests), interferon-gamma release assays (IGRA) and two serological tests (p22_CE and DR-ELISA) every three months, until the interference disappeared. When using the SIT test, a variable number of positive reactors were observed at 3 months (T3; 32.3%, 95% CI 23.9-42.1), 6 months (T6; 11.5%, 95% CI 6.5-19.4), 9 months (T9; 6.4%, 95% CI 3.0-13.2) and 12 months (T12; 0%, 95% CI 0-4.0) post-vaccination. In contrast, the CIT test had a specificity (Sp) of 100% (95%, CI 96.0-100, regardless of the time post-vaccination. The IGRA also obtained high Sp values throughout the study period. No significant interference in the serological tests was recorded at T3 [p22_CE, Sp = 96% (95% CI 90.1-98.4) and DR-ELISA, Sp = 98% (95% CI 92.9-99.4)], although an increase in antibody titers was observed in the following herd testing events. In conclusion, the use of the SIT test causes the onset of false-positive reactors if applied before 12 months post-vaccination in a TB-free/PTB-vaccinated herd. Nevertheless, the CIT test and IGRA obtained high Sp values under these epidemiological circumstances. The serological tests were also highly specific in the case of PTB-vaccinated goats, although their Sp decreased significantly after several intradermal tests.