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Validation and evaluation of VapA ‐specific IgG and IgG subclass enzyme‐linked immunosorbent assays ( ELISA s) to identify foals with R hodococcus equi pneumonia
Author(s) -
Sanz M. G.,
Oliveira A. F.,
Loynachan A.,
Page A.,
Svansson V.,
Giguère S.,
Horohov D. W.
Publication year - 2016
Publication title -
equine veterinary journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.82
H-Index - 87
eISSN - 2042-3306
pISSN - 0425-1644
DOI - 10.1111/evj.12363
Subject(s) - rhodococcus equi , antibody , immunoglobulin g , foal , pneumonia , immunology , medicine , subclass , virology , virulence , microbiology and biotechnology , biology , biochemistry , gene , genetics
Summary Reasons for performing study R hodococcus equi ( Rhodococcus hoagii/Prescottella equi ) is a common cause of foal pneumonia, but its diagnosis remains a challenge for equine veterinarians. While the VapA ‐specific (virulence‐associated protein A) immunoglobulin G ( IgG ) enzyme‐linked immunosorbent assay ( ELISA ) has low sensitivity and specificity for detecting pneumonic foals, little is known about VapA ‐specific IgG subclasses. Objectives To evaluate the performance of VapA ‐specific ELISA for IgG and its subclasses IgGa , IgGb and IgG ( T ) in the early diagnosis of pneumonia caused by R . equi . Study design Assay validation followed by assessment of diagnostic performance using archived samples from animals of known status. Methods Serum samples from exposed (n = 125) and nonexposed adult horses (n = 10) and from experimentally challenged and naturally infected foals were used for ELISA validation. Post mortem and tissue culture records of the last 24 years from the Institute for Experimental Pathology at the University of I celand in K eldur, I celand laboratory were evaluated to confirm the absence of R. equi cases in I celand. The diagnostic performance of VapA ‐specific IgG and its subclasses was evaluated using banked serum samples from pneumonic (n = 21) and healthy foals (n = 80). To evaluate each IgG assay, a cut‐off value was selected based on receiver operating characteristic curve analysis and used to calculate sensitivity and specificity. The intra‐ and interassay coefficients of variation were calculated for each ELISA . Results Using sera from I celand, where R . equi infection has not been reported, the VapA ‐specific IgG ELISA differentiated exposed from nonexposed horses. When used to identify infected foals, VapA ‐specific IgG , IgGa and IgGb had no diagnostic value. In contrast, IgG ( T ) had high sensitivity and specificity. Conclusions Horses from I celand are not exposed to VapA + R . equi and can serve as negative controls. VapA ‐specific IgG subclasses, with the exception of IgG ( T ), are poor predictors of disease. Further investigation on the use of IgG ( T ) as a diagnostic tool in field conditions is needed.