Development of a capsid protein-based ELISA for the detection of PCV2 antibodies in swine serum

Porcine circovirus type 2 (PCV2) is the major causative agent of postweaning multisystemic wasting syndrome which leads to significant economic losses in the global swine industry. In China, there is a widespread dissemination of PCV2 infection in the pig population. Serological diagnosis of the disease is considered as an effective control measure. Here, we developed a capsid protein (Cap)-based enzyme-linked immunosorbent assay (Cap-ELISA) for the detection of PCV2 antibodies in swine serum using a nuclear localization signal-truncated capsid protein produced in Escherichia coli. The Cap protein was expressed as water-soluble and purified using nickel-nitrilotriacetic acid (Ni-NTA) chromatography. After the optimization of the working conditions of the Cap-ELISA using chessboard titrations, a total of 649 serum samples were tested using the Cap-ELISA and a commercial ELISA kit. The diagnostic sensitivity (DSN), diagnostic specificity (DSP) and accuracy of the Cap-ELISA were determined to be 96.7%, 94.1% and 99.5%, respectively. Cross-reactivity analysis indicated that the Cap-ELISA was PCV2-specific and possessed no cross-reactions with antibodies against other common swine pathogens including porcine circovirus type 1 (PCV1), porcine reproductive and respiratory syndrome virus (PRRSV), classical swine fever virus (CSFV), porcine parvovirus (PPV), foot and mouth disease virus (FMDV), porcine epidemic diarrhea virus (PEDV) and pseudorabies virus (PRV). Repeatability of the experiment showed that Cap-ELISA was highly repeatable with the intra- and inter-plate coefficients of variation less than 10%. Hence, the Cap-ELISA has the potential for the swine industry to monitor PCV2 epidemiology and to evaluate PCV2 vaccine efficacy.