African swine fever (ASF) is a highly contagious hemorrhagic disease that affects domestic and wild pigs. A recent study reported that both ASF virus (ASFV) genotypes I and II have invaded farm-raised pigs in China, causing chronic infection and morbidity. To develop a duplex fluorescent quantitative PCR method to distinguish the ASFV genotypes I and II in Chinese epidemic strains, the probes and primers were designed based on the B646L sequences of genotypes I and II listed in the GenBank database. After optimizing the system, a duplex fluorescent quantitative PCR method for simultaneous detection of ASFV genotypes I and II B646L genes was successfully established. This method had no cross-reaction with Porcine circovirus type 2 (PCV2), Pseudorabies virus (PRV), or Porcine Parvovirus (PPV), indicating that it has strong specificity. The sensitivity results indicated that the minimum detection limit of ASFV genotypes I and II B646L was 10 copies/Rxn. The inter- and intra-group coefficients of variation were both <3%, indicating that the method was highly reproducible. Therefore, the established duplex fluorescent quantitative PCR assay is important for the differential detection and epidemiological investigation of ASFV.

Pseudorabies virus (PRV) is the pathogen of pseudorabies (PR), which belongs to the alpha herpesvirus subfamily with a double stranded DNA genome encoding approximately 70 proteins. PRV has many non-essential regions for replication, has a strong capacity to accommodate foreign genes, and more areas for genetic modification. PRV is an ideal vaccine vector, and multivalent live virus-vectored vaccines can be developed using the gene-deleted PRV. The immune system continues to be stimulated by the gene-deleted PRVs and maintain a long immunity lasting more than 4 months. Here, we provide a brief overview of the biology of PRV, recombinant PRV construction methodology, the technology platform for efficiently constructing recombinant PRV, and the applications of recombinant PRV in vaccine development. This review summarizes the latest information on PRV usage in vaccine development against swine infectious diseases, and it offers novel perspectives for advancing preventive medicine through vaccinology.

African swine fever is a fatal infectious disease caused by African swine fever virus (ASFV). The high mortality caused by this infectious disease is a significant challenge to the swine industry worldwide. ASFV virulence is related to its ability to antagonize IFN response, yet the mechanism of antagonism is not understood. Recently, a less virulent recombinant virus has emerged that has a EP402R gene deletion within the parental ASFV HLJ/18 (ASFV-ΔEP402R) strain. EP402R gene encodes CD2v. Hence we hypothesized that ASFV uses CD2v protein to evade type I IFN–mediated innate immune response. We found that ASFV-ΔEP402R infection induced higher type I IFN response and increased the expression of IFN-stimulated genes in porcine alveolar macrophages when compared with parental ASFV HLJ/18. Consistent with these results, CD2v overexpression inhibited type I IFN production and IFN-stimulated gene expression. Mechanistically, CD2v, by interacting with the transmembrane domain of stimulator of IFN genes (STING), prevented the transport of STING to the Golgi apparatus, and thereby inhibited the cGMP-AMP synthase–STING signaling pathway. Furthermore, ASFV CD2v disrupted IFNAR1-TYK2 and IFNAR2-JAK1 interactions, and thereby inhibited JAK-STAT activation by IFN-α. In vivo, specific pathogen-free pigs infected with the mutant ASFV-ΔEP402R strain survived better than animals infected with the parental ASFV HLJ/18 strain. Consistent with this finding, IFN-β protein levels in the peripheral blood of ASFV-ΔEP402R–challenged pigs were significantly higher than in the blood of ASFV HLJ/18–challenged pigs. Taken together, our findings suggest a molecular mechanism in which CD2v inhibits cGMP-AMP synthase–STING and IFN signaling pathways to evade the innate immune response rendering ASFV infection fatal in pigs.