Comparison of an improved competitive enzyme-linked immunosorbent assay with the World Organization for Animal Health–prescribed serum neutralization assay for detection of antibody to Equine arteritis virus

Equine arteritis virus (EAV) causes contagious equine viral arteritis, characterized by fever, anorexia, conjunctivitis, nasal discharge, dependent edema, abortion, infrequent death in foals, and establishment of the carrier state in stallions. The World Organization for Animal Health (OIE) defines a horse as seropositive if the serum neutralization (SN) antibody titer is ≥1:4 to EAV. However, determining the SN titer is time-consuming and requires specific laboratory facilities, equipment, and technical expertise to perform. Furthermore, interpretation of the SN titer of some sera can be difficult because of nonspecific cellular cytotoxicity of particular samples. Finally, the problem of interlaboratory variation also exists with SN assays. For these reasons, an alternative serologic test is desirable; however, none of the reported tests have equivalent sensitivity and specificity to the SN to be generally adopted. In an attempt to improve on a previously developed competitive enzyme-linked immunosorbent assay (cELISA) using EAV gp5-specific neutralizing monoclonal antibody (mAb) 4B2, the current study developed a modified protocol substituting the non-neutralizing mAb 17B7 for the neutralizing mAb 4B2; this along with several modifications of the test procedure improved the performance of the test. The relative specificity of the revamped cELISA was 99.8% when evaluated with 2,223 SN-negative sera. The relative sensitivity was 95.5% when evaluated with 246 SN-positive sera. This new cELISA was not affected by the presence of non–EAV-specific cytotoxicity in sera as observed in the SN assay. The results indicate that this new cELISA may be a viable alternative to the SN assay and merit additional validation.