Effects of an inactivated porcine circovirus type 2 (PCV2) vaccine on PCV2 virus shedding in semen from experimentally infected boars

Comparative Efficacy of Chimeric Porcine Circovirus (PCV) Vaccines against Experimental Heterologous PCV2d Challenges

The objective of this study was to evaluate the efficacy of two multivalent commercial porcine circovirus (PCV) vaccines against heterologous PCV2d challenges. A total of 24 crossbred male pigs aged 26 days selected from a specific pathogen-free herd were randomly divided into four groups (six pigs per group) and assigned as follows: negative control (unvaccinated/sham-challenge), vaccinated with chimeric PCV1-2a vaccine (PCV1-2a/PCV2d-challenge), vaccinated with chimeric PCV1-2a-2b vaccine (PCV1-2a-2b/PCV2d-challenge) and positive control (unvaccinated/PCV2d-challenge). At 21 days after vaccination, the pigs were intranasally and intramuscularly inoculated with either sham or field isolates of PCV2d (PCV2d/149/TH/2020). After being challenged, blood samples were obtained weekly and analyzed for levels of PCV2d viremia, neutralizing antibodies, and IgG against PCV2. At 30 days post-challenge (DPC), the pigs were euthanized and then subjected to pathological evaluations and molecular analysis. The results indicated that pigs in the PCV1-2a-2b/PCV2d-challenge and the PCV1-2a/PCV2d-challenge groups possessed significantly greater levels of PCV2d-neutralizing antibody titer when compared with the positive control group. Moreover, pigs in the PCV1-2a-2b/PCV2d-challenge group exhibited a lower degree of severity in terms of gross lesion scores and lower levels of PCV2 viremia when compared with the positive control group. This study demonstrated that vaccinating pigs with either the PCV1-2a or PCV1-2a-2b chimeric vaccines elicits a potent immune response against PCV2d infection and reduces viremia after PCV2d inoculation in pigs.

Live attenuated Salmonella enterica serovar Choleraesuis vector delivering a virus-like particles induces a protective immune response against porcine circovirus type 2 in mice

The virus-like particles (VLPs) of porcine circovirus type 2 (PCV2) is an attractive vaccine candidate that retains the natural conformation of the virion but lacks the viral genome to replicate, thus balancing safety and immunogenicity. However, the assembly of VLPs requires cumbersome subsequent processes, hindering the development of related vaccines. In addition, as a subunit antigen, VLPs are defective in inducing cellular and mucosal immune responses. In this study, the capsid (Cap) protein of PCV2 was synthesized and self-assembled into VLPs in the recombinant attenuated S. Choleraesuis vector, rSC0016(pS-Cap). Furthermore, rSC0016(pS-Cap) induced a Cap-specific Th1-dominant immune response, mucosal immune responses, and neutralizing antibodies against PCV2. Finally, the virus genome copies in mice immunized with the rSC0016(pS-Cap) were significantly lower than those of the empty vector control group after challenge with PCV2. In conclusion, our study demonstrates the potential of using S. Choleraesuis vectors to delivery VLPs, providing new ideas for the development of PCV2 vaccines.

Evaluation of a Virus-like Nanoparticle Porcine Circovirus Type-2 (PCV2) Capsid Protein Fused with the Pig Immunoglobulin Fc Fragment as a Novel Vaccine Candidate against PCV2 in Mice

Porcine circovirus Type 2 (PCV2) is a primary etiological pathogen of post-weaning multi-systemic wasting syndrome (PMWS). The capsid protein of PCV2 is the crucial immunogenic protein which can induce antibody generation and immune responses. However, there is still a lack of efficient PCV2 vaccines with high immunogenicity. In the current study, we developed a novel engineered PCV2 capsid (∆1-41aa)-pFc fusion protein (PCFP), which comprised a truncated capsid protein of PCV2 and a porcine IgG Fc fragment, fused to the capsid protein of PCV2 at the C-terminus. We found that this novel fusion protein could auto-assemble into virus-like nanoparticles with an estimated mean diameter of 22.6 nm, characterized by transmission electron microscopy. Immunization of BALB/c mice with this fusion protein significantly increased the production levels of anti-PCV2-capsid protein antibody in serum. Besides, the virus-like nanoparticles, PCFP was demonstrated to induce efficient cellular immune responses in mice, as evident by the high specific T cell reactivity to the PCFP fusion protein and the high production of the immune cytokines IFN-γ and IL-10 in an ex vivo re-stimulation system. Collectively, these findings demonstrate that the PCV2 truncated capsid subunit Fc-fusion protein can induce both cellular and humoral immune responses, and it displays great application potential.

The effect of porcine circovirus type 2 (PCV2) vaccination of male piglets on sperm quality at the age of puberty

The objective of the study was to investigate the effect of porcine circovirus type 2 (PCV2) vaccination in piglets on sperm quality of young boars. A total of 136 sows were divided in four groups of 34 animals each (17 vaccinated with Circovac®, Merial and 17 unvaccinated in each group). A total of 1 200 piglets were selected, half of which were vaccinated against PCV2 on the 21st day (Porcilis® PCV, MSD) and the other half was left unvaccinated. Four groups of 300 pigs each were formed as follows: PS group (vaccinated sows + piglets), S group (vaccinated sows + unvaccinated piglets), P group (unvaccinated sows + vaccinated piglets), C group (unvaccinated sows + piglets). Furthermore, 80 boars (20 piglets per group) were selected and slaughtered at the age of 5.5 months and weight of 95 ± 5.5 kg and their epididymal sperm was collected and evaluated for motility and kinetics, concentration and morphology. Additionally, 10 pigs from each group were used for blood sampling and serological testing for PCV2 IgM and IgG antibodies at the age of 21, 70, 110 and 150 days. The IgG and IgM patterns suggested that the piglets were coming into contact with PCV2 early in life. The S group demonstrated significantly lower curvilinear velocity (VCL, μm/s), amplitude of lateral head displacement (ALH, μm) and significantly higher head abnormalities (%) compared to other groups (P< 0.05). In conclusion, vaccinated young boars showed some improved epididymal sperm kinetic indices and head morphology.

Porcine circovirus type 2 and its associated diseases in Korea

This review describes the characterization of porcine circovirus type 2 (PCV2), the field situation of porcine circovirus-associated disease (PCVAD) and the PCV2 vaccine in Korea. PCVAD has been considered the most devastating disease in Korean livestock history since its first outbreak in 1999. Postweaning multisystemic wasting syndrome (PMWS) and porcine respiratory disease complex (PRDC) are the most common clinical forms of PCVAD. Interestingly, only PCV2b strains have been isolated from pigs with PMWS since 2005, but only PCV2a strains were isolated from pigs with PMWS in 2000 to 2001. Clinically, PMWS is divided into two stages: early and late. Early PMWS primarily occurs in pigs between 4 and 8 weeks of age. This form is a typical presentation of PMWS and is characterized clinically by wasting, decreased weight gain, enlarged lymph nodes, and dyspnea. Late PMWS primarily occurs in pigs between 8 and 12 weeks of age. The main clinical manifestation is diarrhea, which is often accompanied by salmonellosis coinfection. In recent years, the PCVAD disease pattern has slightly changed. The occurrence of PMWS has decreased while PRDC cases are increasing in frequency.

Efficacy and future prospects of commercially available and experimental vaccines against porcine circovirus type 2 (PCV2)

Porcine circovirus type 2 (PCV2) is the causative agent of an economically significant collection of disease syndromes in pigs, now known as porcine circovirus associated diseases (PCVADs) in the United States or porcine circovirus diseases (PCVDs) in Europe. Inactivated and subunit vaccines based on PCV2a genotype are commercially available and have been shown to be effective at decreasing mortality and increasing growth parameters in commercial swine herds. Since 2003, there has been a drastic global shift in the predominant prevalence of PCV2b genotype in swine populations, concurrently in most but not all cases with increased severity of clinical disease. Although the current commercial vaccines based on PCV2a do confer cross-protection against PCV2b, novel experimental vaccines based on PCV2b genotype such as modified live-attenuated vaccines are being developed and may provide a superior protection and reduce vaccine costs. In this review, we discuss the current understanding of the impact of PCV2 infection on the host immune response, review the efficacy of the currently available commercial PCV2 vaccines in experimental and field conditions, and provide insight into novel experimental approaches that are useful in the development of next generation vaccines against PCV2.