Development of a recombinant pB602L-based indirect ELISA assay for detecting antibodies against African swine fever virus in pigs

African swine fever (ASF), caused by the African swine fever virus (ASFV), is a devastating disease of domestic and wild pigs. There is no effective vaccine, and the control of the disease relies mainly on surveillance and early detection of infected pigs. Previously, serological assays, such as ELISA, have been developed mainly based on recombinant structural viral proteins of ASFV, including p72, p54, and p30. However, the antibodies against these proteins do not provide efficient protection against ASFV infection in pigs. Therefore, new serological assays that can be applied for clinical diagnosis and evaluating serological immune response in vaccinated pigs are still required. In this study, we expressed and purified a recombinant pB602L protein. The purified pB602L protein was then used as an antigen to develop an indirect ELISA assay. This assay has no cross-reaction with the anti-sera against the 15 most common pig pathogens in China, such as classical swine fever virus, pseudorabies virus, and porcine parvovirus. This assay and a commercial ELISA kit were then used to detect 60 field pig serum samples, including an unknown number of anti-ASFV sera. The coincidence of the two assays was 95%. Furthermore, the pB602L-based ELISA was employed to test the antibody responses to the seven-gene-deleted ASFV strain HLJ/18-7GD in pigs. The results showed that the antibody levels in all vaccinated pigs, starting from the 10th day post-inoculation, have increased continuously during the observation period of 45 days. Our results indicate that this pB602L-based indirect ELISA assay can be employed potentially in the field of ASFV diagnosis.