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African swine fever (ASF), the highly lethal swine infectious disease caused by the African swine fever virus (ASFV), is a great threat to the swine industry. There is no effective vaccine or diagnostic method to prevent and control this disease currently. The p30 protein of ASFV is an important target for serological diagnosis, expressed in the early stage of viral replication and has high immunogenicity and sequence conservatism. Here, the CP204L gene was cloned into the expression vector pET-30a (+), and the soluble p30 protein was successfully expressed in the E. coli prokaryotic expression system and then labeled with horseradish peroxidase (HRP) to be the enzyme-labeled antigen. Using the purified recombinant p30 protein, a double-antigen sandwich ELISA for ASFV antibody detection was developed. This method exhibits excellent specificity, sensitivity and reproducibility in clinical sample detection with lower cost and shorter production cycles. Taken together, this study provides technical support for antibody detection for ASFV.

Background The aim of this study is to compare double‐antigen sandwich enzyme‐linked immunosorbent assay (ELISA) and indirect ELISA in the diagnosis of hepatitis C virus（HCV）infection. Methods and materials A total of 176 samples from the Tumor Hospital Affiliated to Xin Jiang Medical University were utilized to comparison. All serum samples were tested using double‐antigen sandwich ELISA and indirect ELISA. Cohen's kappa statistics were used to assess the agreement between the two assays, and multivariate analysis was used to evaluate risk factors for the discordance between the double‐antigen ELISA and indirect ELISA. Results The positivities of indirect ELISA (Beijing Wantai), double‐antigen sandwich ELISA (Beijing Wantai), and indirect ELISA (Beijing Jinhao) were 74.43%, 68.75%, and 73.30%, respectively. The agreement between the indirect ELISA (Beijing Wantai) and double‐antigen sandwich ELISA (Beijing Wantai) was high (κ = 0.829;P, Compare doubl‐antigen sandwich enzyme‐linked immunosorbent assay (ELISA) and indirect ELISA in the diagnosis of hepatitis C virus (HCV) infection.

A fusion protein SBP-Cap∆41, consisting of Cap∆41 (without 41 amino acids at the N-terminus) protein of porcine circovirus 2 (PCV2) and a streptavidin binding peptide (SBP), was constructed. This fusion protein binds to HRP-labeled streptavidin (HRP-SA) through high affinity between SBP and SA, forming an HRP-streptavidin bound antigen (Hsb-Ag) with both immunoreactivity and enzymatic activity, which can be used in a double-antigen sandwich ELISA for detection of PCV2 antibodies. Comparison of the characteristics of the HSb-Cap∆41 and chemical conjugates of the recombinant Cap∆41 protein showed that the HSb-Cap∆41 based double-antigen sandwich ELISA (HBDS-ELISA) had higher specificity and sensitivity. Use of the HBDS-ELISA detected PCV2-IgG in 9 injected pigs as early as 10 days p.i., 3 days earlier than both a double-antigen sandwich ELISA (DS-ELISA) based on a chemically conjugated antigen, and a commercial indirect ELISA kit. Electronic supplementary material The online version of this article (doi:10.1186/s13568-017-0473-3) contains supplementary material, which is available to authorized users.