期刊
FRONTIERS IN VETERINARY SCIENCE
卷 8, 期 -, 页码 -出版社
FRONTIERS MEDIA SA
DOI: 10.3389/fvets.2021.638890
关键词
Mycobacterium avium subsp; paratuberculosis; Johne's disease; bovine paratuberculosis; IFN-gamma test; purified protein derivatives; Johnin PPD; interpretative criteria; cattle
资金
- Italian Ministry of Health [RC IZSUM 011/2008, RC IZSUM 04/2011, RC IZSUM 06/2019]
The IFN-gamma assay proves to be a useful diagnostic tool in identifying early subclinical MAP-infected animals, improving management of infected cattle and monitoring potential cases. It can also help avoid false reactions to MB and is beneficial in maintaining the health status of herds.
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-gamma) 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-gamma 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-gamma results were evaluated using 12 interpretative criteria (ICs), based on the differences and ratio between PPD optical density (OD) and IFN-gamma 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-gamma 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-gamma 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.
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