Validation and evaluation of VapA-specific IgG and IgG subclass enzyme-linked immunosorbent assays (ELISAs) to identify foals with Rhodococcus equi pneumonia.

MG Sanz, AF Oliviera, A Loynachan, A Page, V Svansson, S Giguère and DW Horohov


Current methods of diagnosis of Rhodococcus pneumonia include PCR from a tracheobronchial aspirate or imaging techniques to detect bronchopneumonia. Detection of infection prior to clinical signs and allowing differentiation of cases that are mild enough to resolve without treatment is a challenge. ELISAs have previously been investigated but were problematic due to interference with maternally derived antibodies and antibodies produced as a result of environmental exposure. This study investigated an ELISA detecting a specific virulence associated protein (VapA) for subclasses of IgG. This test is in current use but its performance characteristics are not known. Serum samples were collected from both exposed and non-exposed adult horses to validate the ELISA and samples from pneumonic and healthy foals were used to assess the diagnostic performance of the ELISA. The VapA-specific IgG (T) subclass was found to have both high sensitivity and specificity for the detection of infected foals and significantly outperformed the other subclasses of VapA-specific IgG.

The bottom line: The VapA specific IgG(T) shows potential to be used as a means of identifying infected foals although the test still requires assessment under field conditions.


Photo: Rhodococcus foal

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