Development of an indirect ELISA for Duck circovirus detection based on prokaryotically expressed antigen

Duck circovirus (DuCV) is an immunosuppressive virus that primarily causes growth retardation and immunosuppression in infected ducks, often leading to secondary infections, thereby posing a serious threat to the global duck industry. Currently, most indirect ELISA assays for DuCV rely on antibodies targeting the Cap structural protein; however, these methods cannot distinguish between antibodies generated by natural infection and those induced by vaccination. In this study, the Rep non-structural protein and truncated Cap structural protein lacking the nuclear localization signal (ΔCap) were successfully expressed using a prokaryotic Escherichia coli expression system. Two indirect ELISA methods were developed using the two proteins as coating antigens, and the method conditions were further optimized. The results demonstrated that both the Rep-ELISA and ΔCap-ELISA exhibited high specificity and sensitivity. When applied to duck serum samples from parts of Shandong Province, the correlation rates between the ELISA and conventional PCR methods were 95.5% and 93.3%, respectively. Furthermore, the positive detection rates in sera from vaccinated ducks were 10% for Rep-ELISA and 91% for ΔCap-ELISA, indicating that the ELISA method established in this study can differentiate between natural infection and vaccine immunization. This study provides a novel serological tool for epidemiological surveillance and vaccine evaluation of DuCV.