An enhanced immunochromatographic strip test using colloidal gold nanoparticles labled dual type N proteins for detection of antibodies to porcine reproductive and respiratory syndrome virus.

Porcine reproductive and respiratory syndrome (PRRS) has been proposed to be one of the most important infectious diseases causing serious economic loss in swine industry worldwide. Due to its increasing genetic diversity, a rapid and accurate diagnosis is critical in PRRS control. The immunochromatographic strip test (ICST) has been recognized as a type of immunoassay with speed and convenience. In this study, the on-site diagnostic method with immunochromatographic assay was developed for detection of PRRSV-specific antibodies based on colloidal gold nanoparticles-labeled dual-type nucleocapsid (N) proteins encoded by open reading frame (ORF) 7, and evaluated using 991 field samples from pig farms and 66 serum samples from experimentally PRRSV-inoculated pigs. Based on true PRRSV-specific antibody-positive or -negative sera determined by indirect-immunofluorescent-antibody (IFA) assay and IgM enzyme-linked-immunosorbent assay (ELISA), the specificity and sensitivity of ICST were 97.5 and 91.1%, respectively, which were similar to those of commercial ELISA (IDEXX PRRS X3 Ab ELISA). More importantly, this strip test was completed within only 15 minutes and can detect PRRSV-specific antibody at earlier stage (3-7 days) of infection than ELISA. These results demonstrated that current ICST has great potential for on-farm diagnostic method with excellent diagnostic performance in a quick and more convenient manner.