Development of a recombinant N-Gp5c fusion protein-based ELISA for detection of antibodies to porcine reproductive and respiratory syndrome virus.

The recent dramatic increase in reported cases of porcine reproductive and respiratory syndrome (PRRS) in pig farms is a potential threat to the global swine industry, and thus, detecting PRRS virus (PRRSV) in pig herds is essential to help control the spread of PRRS. IDEXX HerdChek™ PRRS, a commercially available indirect enzyme-linked immunosorbent assay (iELISA), is the industry standard for detection of antibodies against PRRSV. In the present study, an effective iELISA for detection of PRRSV antibodies was developed using a recombinant fusion protein N-Gp5c (rN5c, a combination of the nucleocapsid protein and the C-terminal 78 aa of Gp5) produced in Escherichia coli. This assay was validated by comparison with an immunofluorescent assay and IDEXX-ELISA. The diagnostic specificity, sensitivity, and accuracy of the rN5c-iELISA method were 94.8, 95.6, and 95.1%, respectively. Cross-reactivity assays demonstrated that iELISA was PRRSV-specific. Repeatability tests revealed that the coefficients of variation of positive sera within and between runs were less than 13 and 22%, respectively. The rN5c-iELISA is simpler to produce and perform, time-saving, and suitable for large scale surveys of PRRSV infection at lower cost.