title: Clinical evaluation of a peptide-ELISA based upon N-terminal B-cell epitope of the VapA protein for diagnosis of Rhodococcus equi pneumonia in foals.
abstract: A total of 227 field samples from naturally exposed foals aged between 3 weeks and 6 months were used in an evaluation of a peptide-based enzyme-linked immunosorbent assay (ELISA) for diagnosis of Rhodococcus equi infection. A biotinylated peptide derived from the virulence-associated protein A (VapA) of R. equi, a horse pathogen, was synthesized and designated as PN11-14. The peptide corresponds to the N-terminal B-cell epitope TSLNLQKDEPNGRASDTAGQ of the VapA protein. Based upon a serum immunoglobulin (Ig)G titre of 512 as a positive cut-off value for the R. equi infection, the ELISA provided the overall sensitivity of 47.62%, specificity of 69.67% and an accuracy of 59.47% with a positive predictive value of 57.47% for true R. equi pneumonia. The assay was improved by detecting VapA-specific IgGb antibodies against N-terminal B-cell epitope of the VapA protein rather than IgG antibodies. The VapA-IgGb ELISA showed the overall sensitivity of 70.47%, specificity of 72.13% and accuracy of 71.36% with a positive predictive value of 68.52%. Diagnosis of R. equi disease in 6-week-old foals showed that the VapA-IgGb ELISA provided an increasing trend (P=0.0572) in sensitivity of 82.4% in comparison with the VapA-IgG ELISA which showed the sensitivity of 58.8%. However, differences in specificity of both tests were statistically insignificant (P=0.357) as analysed by the McNemar test. These results indicated that detection of VapA-specific IgGb antibodies may be a better predictor of R. equi disease in foals.
authors.affiliation: Infectious Diseases Laboratories, Institute of Medical and Veterinary Science, Adelaide, SA 5000, Australia.
authors.forename: T
authors.initials: T
authors.lastname: Phumoonna
authors.forename: G
authors.initials: G
authors.lastname: Muscatello
authors.forename: C
authors.initials: C
authors.lastname: Chicken
authors.forename: J R
authors.initials: JR
authors.lastname: Gilkerson
authors.forename: G F
authors.initials: GF
authors.lastname: Browning
authors.forename: M D
authors.initials: MD
authors.lastname: Barton
authors.forename: M W
authors.initials: MW
authors.lastname: Heuzenroeder
mesh_terms: D000193:Actinomycetales Infections / Q000175:diagnosis / Q000662:veterinary*; D000818:Animals; D000831:Animals, Newborn; D000907:Antibodies, Bacterial / Q000032:analysis; D001426:Bacterial Proteins / Q000276:immunology; D004797:Enzyme-Linked Immunosorbent Assay / Q000662:veterinary*; D018985:Epitopes, B-Lymphocyte / Q000276:immunology; D006734:Horse Diseases / Q000097:blood / Q000175:diagnosis* / Q000382:microbiology; D006736:Horses; D007074:Immunoglobulin G; D018410:Pneumonia, Bacterial / Q000175:diagnosis / Q000662:veterinary*; D011237:Predictive Value of Tests; D016929:Rhodococcus equi / Q000276:immunology* / Q000302:isolation & purification; D012680:Sensitivity and Specificity
chemical_list: D000907:Antibodies, Bacterial; D001426:Bacterial Proteins; D018985:Epitopes, B-Lymphocyte; D007074:Immunoglobulin G