Vertical Transmission of PCV2b to Fetuses in Sows Intramuscularly Infected with PCV2b

Protective humoral immunity in guinea pigs induced by PCV2 virus-like particles displaying the B cell linear epitope (228QQITDA233) of PPV1

Although PCV2 infections generally cause mild disease in pigs, concurrent co-infections with other pathogens can damage the immune system and cause more severe diseases, collectively termed porcine circovirus associated diseases (PCVAD). Involvement of porcine parvovirus (PPV, a common cause of reproductive failure in naïve dams) in PCVAD caused by PCV2, has been reported. As this co-infection can be difficult to eliminate, there is a critical need to develop an effective vaccine to protect against PPV or synergistic effects of PCV2 and PPV under field conditions. In this study, we designed chimeric PCV2 virus-like particles (cVLPs) displaying a B-cell epitope derived from PPV1 structural protein around the surface of the 2-fold axes of PCV2 VLPs, based on 3D-structure analysis of the PCV2 capsid. The cVLPs were successfully prepared, verified by transmission electron microscopy and chromatography, with robust antibody titers against PCV2 and PPV1 produced in mice and guinea pigs. In addition, in guinea pigs challenged with 10⁶ TCID₅₀ PCV2, cVLPs conferred more effective immune protection (based on viral load) than a commercial PCV2 vaccine. Finally, antibody responses and immune protection against PPV were also evaluated. In guinea pigs vaccinated with cVLPs, although PPV antibodies detected by a hemagglutination inhibition (HI) assay appeared later after vaccination in the PCV2 cVLPs group than in the commercial PPV vaccine group, there were fewer PPV genomic DNA copies in the PCV2 cVLPs group than in a PBS group. In conclusion, guinea pigs vaccinated with cVLPs developed effective protective immunity against PCV2 challenge, with some protective immunity against PPV. This study provided valuable research data to pursue molecular design of chimeric epitopes PCV2 VLPs.

Inhibition of Abl or Src tyrosine kinase decreased porcine circovirus type 2 production in PK15 cells

Porcine circovirus type 2 (PCV2) causes huge economic losses in the global swine industry and has a complex and poorly understood virus-host interaction mechanism. We reported that the C-terminal of the capsid protein of all PCV2 isolates shared a strictly conserved PXXP motif that may interact with SH3 domain-containing tyrosine kinases; however, its roles in PCV2 cell entry and replication remain unknown. In this study, we determined that mRNA levels of two SH3 domain-containing tyrosine kinases family (Abl and Src) had distinct profiles (wild-type and PXXP-mutated) during PCV2 infections of PK15 cells. Therefore, we hypothesized that activities of tyrosine kinases (Abl and Fyn) in PK15 cells may be hijacked by PCV2 via its PXXP motif of the Cap, to favor virus replication. Specific inhibitors PP2 of Lck/Fyn and STI-571 of Abl family kinases decreased viral production through suppression of DNA and Cap synthesis at the replication stage. However, based on indirect immunofluorescence assay (IFA), entry of PCV2 virus-like particles (VLPs) into PK15 cells was not altered. Elucidating mechanisms of PCV2-host interactions should provide new insights for development of new compounds to prevent or reduce PCV2 infections.

Discovery of fur seal feces-associated circular DNA virus in swine feces in Japan

Fur seal feces-associated circular ssDNA virus (FSfaCV) was discovered in a pig for the first time in Japan using a next-generation sequencer with duplex-specific nuclease. Full genome of the virus showed approximately 92% similarity to FSfaCVs from New Zealand fur seals. Furthermore, we investigated the prevalence of the ssDNA virus in 85 piglets in Japan, and 65 piglets were positive (76%) for the virus.