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Front. Vet. Sci. | doi: 10.3389/fvets.2018.00229

Evaluation of the performance of the IDvet IFN-gamma test for diagnosis of bovine tuberculosis in Spain

 Maria Luisa de la Cruz1, Adam J. Branscum2, Jesus Nacar3, Enrique Pages4,  Pilar Pozo1, 5,  Andres M. Perez6, Anna Grau3, Jose Luis Saez7, Lucia de Juan1, 8, Rosa Diaz4, Olga Minguez3 and  Julio Alvarez1, 6, 8*
  • 1VISAVET Health Surveillance Centre (UCM), Spain
  • 2Oregon State University, United States
  • 3Junta de Castilla y Leon, Spain
  • 4Comunidad de Madrid, Spain
  • 5MAEVA SERVET S.L., Spain
  • 6University of Minnesota Twin Cities, United States
  • 7Ministerio de Agricultura y Pesca, Alimentacion y Medio Ambiente, Spain
  • 8Departamento de Sanidad Animal, Universidad Complutense de Madrid, Spain

In Spain, the national bovine tuberculosis (bTB) eradication program is based on yearly skin testing of every ≥6 weeks old animal using the single or comparative tuberculin test and parallel use of the interferon-gamma (IFN-γ) assay as an ancillary diagnostic test in infected herds. There are several versions of the latter. Recently, a new commercial IDvet IFN-γ assay has been authorized for use in the program, but there is limited scientific evidence about its performance in different epidemiological settings. Therefore, two studies to evaluate the performance of the IDvet assay were conducted. In study 1, a concordance analysis between the new IDvet and the Bovigam IFN-γ assay in use in Spain for over 10 years was conducted. In study 2, results from the IDvet assay when applied in tandem with a single intradermal tuberculin (SIT) test were used to evaluate the concordance between both tests and to estimate their sensitivity (Se) and specificity (Sp) using a Bayesian latent-class model. Field data from cattle herds located in Madrid and Castilla y Leon (Spain) were collected. For study 1, herd selection was based on a high expected prevalence of reactors to the IFN-γ assay, while herds were selected at random to estimate Se and Sp of the new IDvet assay in study 2. Agreement between the results obtained with both kits for IFN-γ assay was poor (Kappa= 0.20), and a receiver operating characteristic (ROC) analysis indicated a low Se of the new IDvet relative to the Bovigam in a heavily bTB infected population. The Bayesian latent-class analysis estimated the Se of the IDvet assay to be 36.7% [95% probability posterior interval (PPI) 14.7%-78.8%] with estimated Sp close to 100% when the cut-off recommended by the manufacturer (35) was applied. At the alternative cut-off values of 16 and 4, the estimated Se of the IDvet assay increased to 49.0% (PPI: 24.8-94.1%) and 56.0% (PPI: 30.8-96.3%), respectively, while maintaining a high specificity. The results suggest that the new IDvet assay may have lower sensitivity than the Bovigam for diagnosis of bTB in cattle herds in Spain, and that adjusting its cut-off might be considered.

Keywords: bovine tuberculosis, Cattle, diagnosis, Interferon-gamma, Bayesian modeling

Received: 06 Feb 2018; Accepted: 04 Sep 2018.

Edited by:

Salome Dürr, Universität Bern, Switzerland

Reviewed by:

Andrew W. Byrne, Agri-Food and Biosciences Institute (AFBI), United Kingdom
Ferran Jori, Centre de coopération internationale en recherche agronomique pour le développement (CIRAD), France  

Copyright: © 2018 de la Cruz, Branscum, Nacar, Pages, Pozo, Perez, Grau, Saez, de Juan, Diaz, Minguez and Alvarez. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: DVM, PhD. Julio Alvarez, VISAVET Health Surveillance Centre (UCM), Madrid, Spain, jalvarez@umn.edu