Determination of Decisional Cut-Off Values for the Optimal Diagnosis of Bovine Tuberculosis With a Modified IFNγ Assay (Bovigam®) in a Low Prevalence Area in France

Vet Microbiol. 2011 Jul 5;151(1-2):60-7. doi: 10.1016/j.vetmic.2011.02.026. Epub 2011 Feb 24.

Abstract

The Bovigam(®) gamma interferon (IFNγ) assay was used to complement official skin-test screening in a low bovine tuberculosis (bTB) prevalence region in France. The aim of our work was to determine decisional cut-off values for protein purified derivatives (PPD) and ESAT6-CFP10 antigens (R) in order to optimize the efficacy of the modified Bovigam(®) test, in this low-prevalence area, for optimal classification of infected or non-infected herds following positive skin tests. The sensitivity of the IFNγ assay relative to post-mortem bTB-positive animals (Se(r)) was studied in 60 cattle from 20 bTB-infected herds. Its absolute specificity (Sp) was studied in 492 cattle from 25 bTB-free herds from a bTB-free zone. Its operational specificity (relative to the positive skin test) (Sp(r)) was also studied in 547 skin-test positive cattle from 172 bTB-free herds from an infected zone. Using normalized interpretations for individual (PPD or R) results, the cut-off values at 0.02 for PPD and 0.01 for R were obtained with a view to employ them in low prevalence areas with no previously observed non-specific reactions to SITT. Concerning its use after positive skin tests, cut-off values were set at 0.05 for PPD and at 0.03 for R. The choice of an interpretation method considering positive results with PPD and/or R (PPDUR), justified in a high risk context, provided a test Se(r) of 93% [84-98] and Sp(r) of 71.8% [67.9-75.6]. Analysis of positive results with PPD and R (PPDUR), ideal for low-risk contexts, provided a test Sp(r) of 94.3% [92.0-96.1] and Se(r) of 77% [64-87]. Thus, adapting the criteria to the region's infection status and to the conditions for its application is essential for the appropriate use of the IFNγ assay.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Antigens, Bacterial / analysis
  • Bacterial Proteins / analysis
  • Cattle / immunology
  • Cattle / microbiology*
  • France / epidemiology
  • Interferon-gamma / analysis*
  • Molecular Diagnostic Techniques / methods
  • Molecular Diagnostic Techniques / veterinary
  • Molecular Sequence Data
  • Prevalence
  • Sensitivity and Specificity
  • Skin Tests / methods
  • Skin Tests / veterinary*
  • Tuberculosis, Bovine / diagnosis*
  • Tuberculosis, Bovine / epidemiology
  • Tuberculosis, Bovine / immunology

Substances

  • Antigens, Bacterial
  • Bacterial Proteins
  • CFP-10 protein, Mycobacterium bovis
  • Interferon-gamma