Porcine circovirus type 2 (PCV2) belongs to the genus Circovirus and family Circovirus, is one of the smallest DNA viruses with a diameter of 16–18 nm (Guo et al., 2022). This disease is prevalent worldwide, causing huge economic losses to the global pig farming industry (Bandrick et al., 2022; Meng, 2013). PCV2 is considered a pathogenic pathogen of porcine circovirus disease (PCVD), porcine circovirus associated disease (PCVAD), including postweaning multisystemic wasting syndrome (PMWS), porcine dermatitis and nephropathy syndrome (PDNS), porcine proliferative and necrotizing pneumonia, porcine respiratory disease complex (PRDC), granulomatous enteritis, porcine respiratory disease complex, reproductive failure, and acute pulmonary edema (Bandrick et al., 2022; Chen et al., 2023; Park et al., 2023). Although PCV2 mainly infects pigs, it has also been found to exist in some animals other than pigs, including ruminants (such as cattle and goat), rodents (such as house mice and black rat), carnivores (such as dogs, minks, foxes), and insects (such as flies, mosquitoes, and ticks) (Maity et al., 2023; Zhai et al., 2019). Epidemiological investigations have shown that PCV2 is widely prevalent in pig farms, and it is often co-infected with other pig pathogens such as porcine reproductive and respiratory syndrome virus (PRRSV), pseudorabies virus (PRV), classical swine fever virus (CSFV), and porcine epidemic diarrhea virus (PEDV) (Chen et al., 2019; Tang et al., 2022). PCV2 can induce immune suppression in pigs by regulating innate immune responses, leading to increased susceptibility to other infectious pathogens and poor immune response to vaccination, making pigs more susceptible to secondary or concurrent viral or bacterial infections (Eclercy et al., 2020; Renzhammer et al., 2023; Wang et al., 2021; Yang et al., 2023). Therefore, effective prevention and control of PCV2 is of great significance to the healthy development of the breeding industry.

At present, PCV2 has detected about 11 open reading frames (ORFs), among which ORF2 encodes a 27.8 kDa structural capsid (Cap) protein which is the main antigen that stimulates the host to produce a protective immune response (Hamel et al., 1998; Park et al., 2023). The PCV2 Cap protein is the main immunogenic molecule that can self-assemble to form viral-like particles (VLPs). The recombinant Cap protein has been successfully in various expression systems such as Baculovirus Expression Vector System, E. coli expression system and Nicotiana benthamiana expression system, and the expressed protein can effectively protect piglets (Luo et al., 2021; Wu et al., 2022; Xi et al., 2016). At least 8 genotypes have been identified in PCV2, from PCV2a to PCV2h, with the main genotypes being PCV2a, PCV2b, and PCV2d (Kang et al., 2022). The genotype was transformed in the process of PCV2 epidemic. The global epidemic strain slowly transitioned from PCV2a to PCV2b before the first batch of commercial vaccines was introduced in 2006. This genotype change greatly enhances the toxicity of the virus. Subsequently, PCV2 underwent a second genotype transformation that the main epidemic strain PCV2b transitioning to PCV2d (Bandrick et al., 2022; Franzo and Segalés, 2018; Guo et al., 2022; Harmon et al., 2015). PCV2d has the potential to overcome the protective immunity conferred by existing vaccines (Huan et al., 2018; Kim and Hahn, 2021; Maity et al., 2023).

The main method of PCV2 prevention and control is vaccination. The efficacy of vaccines is mainly evaluated through animal immunity protective test. However, these experiments require numerous animals, longer duration and have highly variable deviations (Sun et al., 2022; Zhao et al., 2013). Using a sandwich enzyme-linked immunosorbent assay (ELISA) based on mAb can distinguish the influenza B antigens in inactivated trivalent and quadrivalent vaccines (Verma et al., 2017). Therefore, measuring the content of effective proteins in vaccines to evaluate vaccine efficacy is an excellent alternative to traditional methods, which can greatly accelerate the development speed and testing time of vaccines, laying the foundation for the development of new vaccines to cope with the rapid mutation of PCV2. The ELISA detection method can be used to detect specific antigens, which has the characteristics of simplicity, accuracy, stable results, and no need for complex instruments (Le et al., 2003; Lim and Cardosa, 2019; Wang et al., 2018). It is an ideal method for vaccine quality control.

We screened and identified the mAb that has a specific response to PCV2 Cap. Subsequently, we developed a double antibody sandwich ELISA (DAS-ELISA) method based on this monoclonal antibody to evaluate the efficacy of E. coli-expressed recombinant subunit vaccine, baculovirus expression recombinant subunit vaccine and PCV2 inactivated vaccine that widely used on the market. The accuracy of this method was verified by measuring the levels of antibody production in mice after immunization with the vaccine. This ELISA method will assist in the detection and quantitative analysis of PCV2 Cap in the production process and final vaccine products. This method has the advantages of simple operation, good sensitivity, high specificity, and wide application. It can simultaneously measure multiple samples, detect the effective antigen Cap protein content of various types of PCV2 vaccines, shorten vaccine testing time, and save costs.