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

Roy, Álvaro, Infantes-Lorenzo, José Antonio, Blázquez, Juan Carlos, Venteo, Ángel, Mayoral, Francisco José, Domínguez, Mercedes, Moreno, Inmaculada, Romero, Beatriz, de Juan, Lucía, Grau, Anna, Domínguez, Lucas, Bezos, Javier
Preventive veterinary medicine 2018 v.156 pp. 68-75
antibodies, cost effectiveness, diagnostic techniques, goats, herds, immunologic techniques, interferon-gamma, paratuberculosis, tuberculin, tuberculosis, vaccination
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.