title: Evaluation of the gamma interferon ELISA in sheep subclinically infected with Mycobacterium avium subspecies paratuberculosis using a whole-cell sonicate or a johnin purified-protein derivative.
abstract: The aim of the study reported here was to estimate the sensitivity and specificity of the gamma interferon (IFN-gamma) ELISA for paratuberculosis in sheep using receiver-operating characteristic analysis. Bacteriologic culture of tissues was used to define the reference positive population (n = 33). Two reference negative populations were used: culture-negative sheep from infected flocks (n = 77), and sheep from noninfected flocks (n = 358). We also evaluated the accuracy of 2 Mycobacterium avium subspecies paratuberculosis (MAP) antigen preparations, a whole-cell sonicate (MpS) and a johnin purified-protein derivative (PPDj). The source of the reference negative sheep used in the analysis affected overall accuracy of the IFN-gamma ELISA. The area under the curve was 0.683 (95% confidence interval 0.574-0.787), using culture-negative sheep from infected flocks, was 0.831 (0.764-0.889), using sheep from noninfected flocks for the MpS, and was 0.809 (0.726-0.881) and 0.897 (0.862-0.925) for the PPDj, respectively. Using the MpS, the cut point that classified the most sheep correctly was an optical density reading of 0.20, for sensitivity of 40.7% (19.4-57.6) and specificity of 88.7% (77.0-95.7) or 97.6% (93.04-99.5), depending on the reference negative population used. Using the PPDj, the cut point that classified the most sheep correctly was 0.25 for sensitivity of 66.7% (47.2-82.7) and specificity of 93.5% (85.5-97.9) or 98.3% (96.4-99.4), respectively. The PPDj was more accurate at identifying MAP-infected sheep than was the MpS (P = 0.034).
authors.affiliation: Bacterial Diseases of Livestock Research Unit, National Animal Disease Center, Agricultural Research Service, USDA, Ames, IA 50010, USA. sausterm@nadc.ars.usda.gov
authors.forename: Suelee
authors.initials: S
authors.lastname: Robbe-Austerman
authors.forename: Judith R
authors.initials: JR
authors.lastname: Stabel
authors.forename: Mitchell V
authors.initials: MV
authors.lastname: Palmer
mesh_terms: D000818:Animals; D000942:Antigens, Bacterial / Q000737:chemistry; D019540:Area Under Curve; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods / Q000662:veterinary*; D005767:Gastrointestinal Diseases / Q000175:diagnosis / Q000382:microbiology / Q000473:pathology / Q000662:veterinary; D006651:Histocytochemistry / Q000662:veterinary; D007371:Interferon-gamma / Q000096:biosynthesis* / Q000097:blood; D016927:Mycobacterium avium subsp. paratuberculosis / Q000302:isolation & purification*; D010283:Paratuberculosis / Q000175:diagnosis / Q000382:microbiology* / Q000473:pathology; D012372:ROC Curve; D012680:Sensitivity and Specificity; D012756:Sheep; D012757:Sheep Diseases / Q000175:diagnosis / Q000382:microbiology* / Q000473:pathology
chemical_list: D000942:Antigens, Bacterial; D007371:Interferon-gamma