Combining two serological assays optimises sensitivity and specificity for the identification of Streptococcus equi subsp. equi exposure

Abstract

The detection of anti-Streptococcus equi antibodies in the blood serum of horses can assist with the identification of apparently healthy persistently infected carriers and the prevention of strangles outbreaks. The aim of the current study was to use genome sequencing data to develop an indirect enzyme linked immunosorbent assay (iELISA) that targets two S. equi-specific protein fragments. The sensitivity and specificity of the antigen A and antigen C iELISAs were compared to an SeM-based iELISA marketed by IDvet - diagnostic Vétérinaire (IDvet). Individually, each assay compromised specificity in order to achieve sufficient sensitivity (SeM iELISA had a sensitivity of 89.9%, but a specificity of only 77.0%) or sensitivity to achieve high specificity. However, combining the results of the antigen A and antigen C iELISAs permitted optimisation of both sensitivity (93.3%) and specificity (99.3%), providing a robust assay for the identification of horses exposed to S. equi.

Comparison of Immunologic Responses Following Intranasal and Oral Administration of a USDA-Approved, Live-Attenuated Streptococcus equi Vaccine

“…antigens (antigens A and C) was compared to the SeM iELISA. This combined antigen A and antigen C iELISA increased sensitivity and specificity from 89.8% and 77.0%, respectively, to 93.3% and 99.3%, respectively (Robinson et al 2013).…”

Cloning, expression and characterization of SeM protein of Streptococcus equi subsp. equi and evaluation of its use as antigen in an indirect ELISA

“…Since immunologically mediated protection against strangles resides in antibodies (Galan et al, 1986;Sheoran et al, 1997), ELISA is well suited to evaluate the immunity herd status for S. equi and for Strangles diagnosis (Robinson et al, 2013).…”

“…ELISA was subjected to Receiver Operating Characteristic analysis (Greiner, 2000), where this analysis has been successfully used for interpretation of ELISA results (Fosgate et al, 2007), including the Strangles diagnostics (Robinson et al, 2013). The rationale for the optimal ROC curve is that one wants the highest true-positive rate (sensitivity) for the lowest false positive rate (1-specificity).…”

“…Thus, its use should be together with bacterial culture (Timoney, 2004). Since antibodies against the pathogen rise during the infection (Timoney, 2004;Robinson et al, 2013), ELISA (Enzyme Linked Immuno Sorbent Assay) is a Strangles diagnostic alternative. The use of ELISA for indirect diagnosis of the disease has become a subject of interest for researchers who wish to use the test as an auxiliary tool of equine adenitis control.…”

Vaccination with a live multi-gene deletion strain protects horses against virulent challenge with Streptococcus equi

“…The Equilis StrepE strain produces SeM and SEQ2190 surface proteins that are used in serological assays for the detection of horses that have been exposed to S. equi [6]. Therefore, horses vaccinated with Equilis StrepE are likely to test positive using this serological assay, requiring them to be examined further to determine if they present an infectious risk to naïve horses before they can be moved to other premises [7].…”