Early Detection of Mycobacterium avium subsp. paratuberculosis Infected Cattle: Use of Experimental Johnins and Innovative Interferon-Gamma Test Interpretative Criteria

• Published in: Frontiers in veterinary science Vol. 8; p. 638890
• Main Authors: Corneli, Sara, Di Paolo, Antonella, Vitale, Nicoletta, Torricelli, Martina, Petrucci, Linda, Sebastiani, Carla, Ciullo, Marcella, Curcio, Ludovica, Biagetti, Massimo, Papa, Paola, Costarelli, Silva, Cagiola, Monica, Dondo, Alessandro, Mazzone, Piera
• Format: Journal Article
• Language: English
• Published: Frontiers Media S.A 14.05.2021
• Subjects: bovine paratuberculosis; IFN-γ test; Johne's disease; Johnin PPD; Mycobacterium avium subsp. paratuberculosis; purified protein derivatives; Veterinary Science
• ISSN: 2297-1769; 2297-1769
• DOI: 10.3389/fvets.2021.638890

Paratuberculosis (PTB), also known as Johne's disease, is a chronic proliferative enteritis of ruminants caused by Mycobacterium avium subsp. paratuberculosis (MAP). To date, PTB diagnosis, based on serology, fecal culture, and real-time polymerase chain reaction, has identified animals in advanced stages of infection. To detect MAP infection in animals earlier, the interferon-gamma (IFN-γ) test may be applied. This assay detects cytokines produced by T-lymphocytes of infected subjects after stimulation with purified protein derivatives (PPDs), extracted from Mycobacterium bovis (MB) and from M. avium (MA). The study involved three bovine herds: one PTB-infected herd, one PTB-free herd, and one with an outbreak of bovine tuberculosis. The IFN-γ test was performed on 235 animals, using bovine PPD (PPDB), avian PPD (PPDA), and three experimental PPD Johnins (PPDJs) extracted from a synthetic liquid medium culture of MAP (PPDJ A, B, and C), to assess early MAP detection and avoid false reactions to MB. Furthermore, IFN-γ results were evaluated using 12 interpretative criteria (ICs), based on the differences and ratio between PPD optical density (OD) and IFN-γ basal OD values after lymphocytic stimulation. IC accuracy was expressed as area under the receiver operating characteristic curve. Through a longitudinal study, PPDJs proved to be specific and sensitive in the detection of MAP-infected animals. Among the evaluated ICs, six showed the best performance in terms of accuracy ( p < 0.0001), highlighting PTB subclinical infections. In particular, the two best criteria reached sensitivity values of 100% [confidence interval (CI) 95%, 94.1–100%] with a specificity of 91.8% (CI 95%, 81.9–97.3%) and sensitivity levels of 80.6% (CI 95%, 69.1–89.2%) with a specificity of 100% (CI 95%, 94.1–100%). Thus, the IFN-γ assay proved to be a useful diagnostic tool to identify early subclinical MAP-infected animals, in order to manage infected cattle or those exposed to MAP and to monitor younger calves within a herd. Furthermore, the IFN-γ test can be considered an additional test to avoid the introduction of MAP-infected animals, especially in herds where disease has already been eradicated and preservation of the health status is required to maintain the PTB certification level.