Variation in time and magnitude of immune response and viremia in experimental challenges with Porcine circovirus 2b

Field Evaluation of a Ready-to-Use Porcine Circovirus Type 2 and Mycoplasma hyopneumoniae Vaccine in Naturally Infected Farms in Taiwan

Porcine circovirus type 2 (PCV2) and Mycoplasma hyopneumoniae (MHP) are both important and common pathogens in the pig industry. Both pathogens are major contributors to the porcine respiratory disease complex and serve to potentiate other bacterial infections such as Actinobacillus pleuropneumonia. This study aims to evaluate the efficacy of a ready-to-use bivalent PCV2 and MHP vaccine in the field under naturally PCV2-infected farms against existing monovalent options. We evaluated PCV2 viremia, PCV2 antibodies, and lung lesion scores in slaughtered pigs in our study across four farms in Taiwan. Our results found that in two out of four farms, the piglets vaccinated with Porcilis® PCV M Hyo had superior whole-life PCV2 viremia reduction compared to the existing vaccination program on farms. In the lung lesion scoring, the Porcilis® PCV M Hyo group had significantly lower Actinobacillus pleuropneumonia-type lesions in pigs than in the competitor group in two out of three farms evaluated. In this field trial, Porcilis® PCV M Hyo proved to be efficacious in protecting piglets against both PCV2 viremia and the impact of MHP secondary infection, in the context of a reduction in viremia and reduced APP-like lesions found at slaughter.

The Evaluation of a Porcine Circovirus Type 2 (PCV2) Intradermal Vaccine Against a PCV2 Field Strain

Background/Objectives: Porcine circovirus type 2 (PCV2) has a major impact on swine productivity. Vaccines are used to aid in control and mitigate production losses. We investigated the protection provided by an intradermal PCV2 vaccine against a field strain in Taiwan. Methods: We conducted a safety and efficacy study. In the safety study, four Specific Pathogen Free (SPF) piglets were enrolled in the study. One was selected as the control and left unvaccinated, one was selected to be intradermally vaccinated with five times the standard dose (1 mL, Porcilis® PCV ID), and the other two were vaccinated with two times the standard dose (0.4 mL, Porcilis® PCV ID). All animals were observed for 3 weeks for adverse events post-vaccination. In the efficacy study, twelve SPF pigs negative for the PCV2 antibody were randomly divided into two groups. The first group of six pigs was vaccinated (Porcilis PCV ID, 0.2 mL) intradermally at 3 weeks of age. The second group of six pigs was sham vaccinated with 0.2 mL of normal saline. At 7 weeks of age, all pigs were challenged with the PCV2 strain CYC08 (1 × 105 TCID50/mL) by nasal and intramuscular injection. Clinical monitoring of body temperature and mortality was conducted daily. At 11 weeks of age, all animals were sacrificed for histopathological analysis. Results: No adverse events were reported in the safety study. In the efficacy study, the vaccinated animals had statistically improved results in the following areas post-challenge: body temperature rise, viremia, virus shedding, mortality, tissue histopathological and microscopic scores. Conclusions: The study results support that a one-dose PCV2 vaccine administered intradermally with a needle-free injector is safe and provides protection when challenged with a field PCV2 strain.

Host-genetic-based outcome of co-infection by PCV2b and PRRSV in pigs

Replication of porcine circovirus type 2 (PCV2), an important worldwide swine pathogen, has been demonstrated to be influenced by host genotype. Specifically, a missense DNA polymorphism (SYNGR2 p.Arg63Cys) within the SYNGR2 gene was demonstrated to contribute to variation in PCV2b viral load and subsequent immune response following infection. PCV2 is known to induce immunosuppression leading to an increase in susceptibility to subsequent infections with other viral pathogens such as porcine reproductive and respiratory syndrome virus (PRRSV). In order to assess the role of SYNGR2 p.Arg63Cys in co-infections, pigs homozygous for the favorable SYNGR2 p.63Cys (N = 30) and unfavorable SYNGR2 p.63Arg (N = 29) alleles were infected with PCV2b followed a week later by a challenge with PRRSV. A lower PCV2b viremia (P < 0.001) and PCV2-specific IgM antibodies (P < 0.005) were observed in SYNGR2 p.63Cys compared to SYNGR2 p.63Arg genotypes. No significant differences in PRRSV viremia and specific IgG antibodies were observed between SYNGR2 genotypes. Lung histology score, an indicator of disease severity, was lower in the pigs with SYNGR2 p.63Cys genotypes (P < 0.05). Variation in the lung histology scores within SYNGR2 genotypes suggests that additional factors, environmental and/or genetic, could be involved in disease severity.

[Opportunities and risks of the use of genetic resistances to infectious diseases in pigs - an overview]

Demands for health, performance and welfare in pigs, as well as the desire for consumer protection and reduced antibiotic use, require optimal measures in advance of disease development. This includes, in principle, the use of genetically more resistant lines and breeding animals, whose existence has been proven for a wide range of pathogen-host interactions. In addition, attempts are being made to identify the gene variants responsible for disease resistance in order to force the selection of suitable populations, also using modern biotechnical technics. The present work is intended to provide an overview of the research status achieved in this context and to highlight opportunities and risks for the future.The evaluation of the international literature shows that genetic disease resistance exist in many areas of swine diseases. However, polygenic inheritance, lack of animal models and the influence of environmental factors during evaluation render their implementation in practical breeding programs demanding. This is where modern molecular genetic methods, such as Gene Editing, come into play. Both approaches possess their pros and cons, which are discussed in this paper. The most important infectious diseases in pigs, including general diseases and epizootics, diseases of the respiratory and digestive tract and diseases of the immune system are taken into account.

Genomic Analysis of IgG Antibody Response to Common Pathogens in Commercial Sows in Health-Challenged Herds

Losses due to infectious diseases are one of the main factors affecting productivity in the swine industry, motivating the investigation of disease resilience-related traits for genetic selection. However, these traits are not expected to be expressed in the nucleus herds, where selection is performed. One alternative is to use information from the commercial level to identify and select nucleus animals genetically superior for coping with pathogen challenges. In this study, we analyzed the genetic basis of antibody (Ab) response to common infectious pathogens in health-challenged commercial swine herds as potential indicator traits for disease resilience, including Ab response to influenza A virus of swine (IAV), Mycoplasma hyopneumoniae (MH), porcine circovirus (PCV2), and Actinobacillus pleuropneumoniae (APP; different serotypes). Ab response was measured in blood at entry into gilt rearing, post-acclimation (∼40 days after entering the commercial herd), and parities 1 and 2. Heritability estimates for Ab response to IAV, MH, and PCV2 ranged from 0 to 0.76. Ab response to APP ranged from 0 to 0.40. The genetic correlation (r _G ) of Ab response to IAV with MH, PCV2, PRRSV, and APP_mean (average Ab responses for all serotypes of APP) were positive (>0.29) at entry. APP_mean was negatively correlated with PCV2 and MH at entry and parity 2 but positively correlated with MH at post-acclimation and parity 1. Genomic regions associated with Ab response to different APP serotypes were identified on 13 chromosomes. The region on chromosome 14 (2 Mb) was associated with several serotypes of APP, explaining up to 4.3% of the genetic variance of Ab to APP7 at entry. In general, genomic prediction accuracies for Ab response were low to moderate, except average Ab response to all infectious pathogens evaluated. These results suggest that genetic selection of Ab response in commercial sows is possible, but with variable success depending on the trait and the time-point of collection. Future work is needed to determine genetic correlations of Ab response with disease resilience, reproductive performance, and other production traits.

Genome-wide association analysis for porcine reproductive and respiratory syndrome virus susceptibility traits in two genetic populations of pigs1

Porcine reproductive and respiratory syndrome virus (PRRSV) is an economically important pathogen that continues to threaten swine industry sustainability. The complexity and high genetic diversity of PRRSV has prevented vaccines from conferring adequate protection against disease outbreaks. Genome-wide association analyses of PRRSV experimentally infected pigs representing two genetic lines (n = 174 to 176) revealed two major genomic regions accounting for ~1.2% of the genetic variation in PRRSV-specific antibody level in serum or lung. The major region for serum antibody was mapped to SSC7 near the SLAII complex, which has also been implicated in susceptibility to other swine viral pathogens. Haplotype substitution analysis uncovered potential DQB1 haplotypes associated with divergent effects. A novel major region for lung antibody was mapped to the proximal end of SSC17 with the top SNP overlapping two genes, PRAG1 and LONRF1. Sequencing LONRF1 uncovered polymorphisms within the coding region that may play a role in regulating PRRSV-specific antibody production in lung tissue following PRRSV infection. These data implicate novel host genomic regions (SSC17) that influence PRRSV-specific immune response as well as a common region (SSC7) potentially involved in susceptibility to multiple viral pathogens.

Evaluation of genotype quality parameters for SowPro90, a new genotyping array for swine1

Understanding early predictors of sow fertility has the potential to improve genomic predictions. A custom SNP array (SowPro90 produced by Affymetrix) was developed to include genetic variants overlapping quantitative trait loci for age at puberty, one of the earliest indicators of sow fertility, as well as variants related to innate and adaptive immunity. The polymorphisms included in the custom genotyping array were identified using multiple genomic approaches including deep genomic and transcriptomic sequencing and genome-wide associations. Animals from research and commercial populations (n = 2,586) were genotyped for 103,476 SNPs included in SowPro90. To assess the quality of data generated, genotype concordance was evaluated between the SowPro90 and Porcine SNP60 BeadArray using a subset of common SNP (n = 44,708) and animals (n = 277). The mean genotype concordance rate per SNP was 98.4%. Differences in distribution of data quality were observed between the platforms indicating the need for platform specific thresholds for quality parameters. The optimal thresholds for SowPro90 (≥97% SNP and ≥93% sample call rate) were obtained by analyzing the data quality distribution and genotype concordance per SNP across platforms. At ≥97% SNP call rate, there were 42,151 SNPs (94.3%) retained with a mean genotype concordance of 98.6% across platforms. Similarly, ≥94% SNPs and ≥85% sample call rates were established as thresholds for Porcine SNP60 BeadArray. At ≥94% SNPs call rate, there were 41,043 SNPs (91.8%) retained with a mean genotype concordance of 98.6% across platforms. Final evaluation of SowPro90 array content (n = 103,476) at ≥97% SNPs and ≥93% sample call rates allowed retention of 89,040 SNPs (86%) for downstream analysis. The findings and strategy for quality control could be helpful in identifying consistent, high-quality genotypes for genomic evaluations, especially when integrating genotype data from different platforms.

Synaptogyrin-2 influences replication of Porcine circovirus 2

Porcine circovirus 2 (PCV2) is a circular single-stranded DNA virus responsible for a group of diseases collectively known as PCV2 Associated Diseases (PCVAD). Variation in the incidence and severity of PCVAD exists between pigs suggesting a host genetic component involved in pathogenesis. A large-scale genome-wide association study of experimentally infected pigs (n = 974), provided evidence of a host genetic role in PCV2 viremia, immune response and growth during challenge. Host genotype explained 64% of the phenotypic variation for overall viral load, with two major Quantitative Trait Loci (QTL) identified on chromosome 7 (SSC7) near the swine leukocyte antigen complex class II locus and on the proximal end of chromosome 12 (SSC12). The SNP having the strongest association, ALGA0110477 (SSC12), explained 9.3% of the genetic and 6.2% of the phenotypic variance for viral load. Dissection of the SSC12 QTL based on gene annotation, genomic and RNA-sequencing, suggested that a missense mutation in the SYNGR2 (SYNGR2 p.Arg63Cys) gene is potentially responsible for the variation in viremia. This polymorphism, located within a protein domain conserved across mammals, results in an amino acid variant SYNGR2 p.63Cys only observed in swine. PCV2 titer in PK15 cells decreased when the expression of SYNGR2 was silenced by specific-siRNA, indicating a role of SYNGR2 in viral replication. Additionally, a PK15 edited clone generated by CRISPR-Cas9, carrying a partial deletion of the second exon that harbors a key domain and the SYNGR2 p.Arg63Cys, was associated with a lower viral titer compared to wildtype PK15 cells (>24 hpi) and supernatant (>48hpi)(P < 0.05). Identification of a non-conservative substitution in this key domain of SYNGR2 suggests that the SYNGR2 p.Arg63Cys variant may underlie the observed genetic effect on viral load.

Analysis of swine leukocyte antigen class I gene profiles and porcine endogenous retrovirus viremia level in a transgenic porcine herd inbred for xenotransplantation research

Molecular characterization of swine leukocyte antigen (SLA) genes is important for elucidating the immune responses between swine-donor and human-recipient in xenotransplantation. Examination of associations between alleles of SLA class I genes, type of pig genetic modification, porcine endogenous retrovirus (PERV) viral titer, and PERV subtypes may shed light on the nature of xenograft acceptance or rejection and the safety of xenotransplantation. No significant difference in PERV gag RNA level between transgenic and non-transgenic pigs was noted; likewise, the type of applied transgene had no impact on PERV viremia. SLA-1 gene profile type may correspond with PERV level in blood and thereby influence infectiveness. Screening of pigs should provide selection of animals with low PERV expression and exclusion of specimens with PERV-C in the genome due to possible recombination between A and C subtypes, which may lead to autoinfection. Presence of PERV-C integrated in the genome was detected in 31.25% of specimens, but statistically significant increased viremia in specimens with PERV-C was not observed. There is a need for multidirectional molecular characterization (SLA typing, viremia estimation, and PERV subtype screening) of animals intended for xenotransplantation research in the interest of xeno-recipient safety.

Genomic regions associated with host response to porcine reproductive and respiratory syndrome vaccination and co-infection in nursery pigs

BACKGROUND

The WUR1000125 (WUR) single nucleotide polymorphism (SNP) can be used as a genetic marker for host response to porcine reproductive and respiratory syndrome (PRRS), PRRS vaccination, and co-infection with porcine circovirus type 2b (PCV2b). Objectives of this study were to identify genomic regions other than WUR associated with host response to PRRS vaccination and PRRSV/PCV2b co-infection and regions with a different effect on host response to co-infection, depending on previous vaccination for PRRS.

METHODS

Commercial crossbred nursery pigs were pre-selected for WUR genotype (n = 171 AA and 198 AB pigs) where B is the dominant and favorable allele. Half of the pigs were vaccinated for PRRS and 4 weeks later, all pigs were co-infected with PRRS virus and PCV2b. Average daily gain (ADG) and viral load (VL) were quantified post vaccination (Post Vx) and post co-infection (Post Co-X). Single-SNP genome-wide association analyses were then conducted to identify genomic regions associated with response to vaccination and co-infection.

RESULTS

Multiple SNPs near the major histocompatibility complex were significantly associated with PCV2b VL (-log ₁₀ P ≥ 5.5), regardless of prior vaccination for PRRS. Several SNPs were also significantly associated with ADG Post Vx and Post Co-X. SNPs with a different effect on ADG, depending on prior vaccination for PRRS, were identified Post Vx (-log ₁₀ P = 5.6) and Post Co-X (-log ₁₀ P = 5.5). No SNPs were significantly associated with vaccination VL (-log₁₀ P ≤ 4.7) or PRRS VL (-log₁₀ P ≤ 4.3). Genes near SNPs associated with vaccination VL, PRRS VL, and PCV2b VL were enriched (P ≤ 0.01) for immune-related pathways and genes near SNPs associated with ADG were enriched for metabolism pathways (P ≤ 0.04). SNPs associated with vaccination VL, PRRS VL, and PCV2b VL showed overrepresentation of health QTL identified in previous studies and SNPs associated with ADG Post Vx of Non-Vx pigs showed overrepresentation of growth QTL.

CONCLUSIONS

Multiple genomic regions were associated with PCV2b VL and ADG Post Vx and Post Co-X. Different SNPs were associated with ADG, depending on previous vaccination for PRRS. Results of functional annotation analyses and novel approaches of using previously-reported QTL support the identified regions.

Genetic and genomic basis of antibody response to porcine reproductive and respiratory syndrome (PRRS) in gilts and sows

Background

Our recent research showed that antibody response to porcine reproductive and respiratory syndrome (PRRS), measured as sample-to-positive (S/P) ratio, is highly heritable and has a high genetic correlation with reproductive performance during a PRRS outbreak. Two major quantitative trait loci (QTL) on Sus scrofa chromosome 7 (SSC7; QTL_MHC and QTL₁₃₀) accounted for ~40 % of the genetic variance for S/P. Objectives of this study were to estimate genetic parameters for PRRS S/P in gilts during acclimation, identify regions associated with S/P, and evaluate the accuracy of genomic prediction of S/P across populations with different prevalences of PRRS and using different single nucleotide polymorphism (SNP) sets.

Methods

Phenotypes and high-density SNP genotypes of female pigs from two datasets were used. The outbreak dataset included 607 animals from one multiplier herd, whereas the gilt acclimation (GA) dataset included data on 2364 replacement gilts from seven breeding companies placed on health-challenged farms. Genomic prediction was evaluated using GA for training and validation, and using GA for training and outbreak for validation. Predictions were based on SNPs across the genome (SNP_All), SNPs in one (SNP_MHC and SNP₁₃₀) or both (SNP_SSC7) QTL, or SNPs outside the QTL (SNP_Rest).

Results

Heritability of S/P in the GA dataset increased with the proportion of PRRS-positive animals in the herd (from 0.28 to 0.47). Genomic prediction accuracies ranged from low to moderate. Average accuracies were highest when using only the 269 SNPs in both QTL regions (SNP_SSC7, with accuracies of 0.39 and 0.31 for outbreak and GA validation datasets, respectively. Average accuracies for SNP_ALL, SNP_MHC, SNP₁₃₀, and SNP_Rest were, respectively, 0.26, 0.39, 0.21, and 0.05 for the outbreak, and 0.28, 0.25, 0.22, and 0.12, for the GA validation datasets.

Conclusions

Moderate genomic prediction accuracies can be obtained for PRRS antibody response using SNPs located within two major QTL on SSC7, while the rest of the genome showed limited predictive ability. Results were obtained using data from multiple genetic sources and farms, which further strengthens these findings. Further research is needed to validate the use of S/P ratio as an indicator trait for reproductive performance during PRRS outbreaks.

Electronic supplementary material

The online version of this article (doi:10.1186/s12711-016-0230-0) contains supplementary material, which is available to authorized users.

Oral application of freeze-dried yeast particles expressing the PCV2b Cap protein on their surface induce protection to subsequent PCV2b challenge in vivo

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PCV2 is the underlying cause for an economically devastating disease of pigs.

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Vaccine construct was PCV2b Cap protein expressed on the surface of yeast.

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Oral vaccination of freeze-dried yeast-Cap did not induce negative side effects.

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Application protected pigs from subsequent PCV2b challenge.

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Vaccination reduced pro-inflammatory but increased antiviral cytokine expression.

Porcine circovirus type 2 (PCV2) is now endemic in every major pig producing country, causing PCV-associated disease (PCVAD), linked with large scale economic losses. Current vaccination strategies are based on the capsid protein of the virus and are reasonably successful in preventing PCVAD but fail to induce sterile immunity. Additionally, vaccinating whole herds is expensive and time consuming. In the present study a “proof of concept” vaccine trial was employed to test the effectiveness of powdered freeze-dried recombinant Saccharomyces cerevisiae yeast stably expressing the capsid protein of PCV2b on its surface as an orally applied vaccine. PCV2-free pigs were given 3 doses of vaccine or left un-vaccinated before challenge with a defined PCV2b strain. Rectal temperatures were measured and serum and faeces samples were collected weekly. At the end of the study, pigs were euthanized, tissue samples taken and tested for PCV2b load by qPCR and immunohistochemistry. The peak of viraemia in sera and faeces of unvaccinated pigs was higher than that of vaccinated pigs. Additionally more sIgA was found in faeces of vaccinated pigs than unvaccinated. Vaccination was associated with lower serum concentrations of TNFα and IL-1β but higher concentrations of IFNα and IFNγ in comparison to the unvaccinated animals. At the end of the trial, a higher viral load was found in several lymphatic tissues and the ileum of unvaccinated pigs in comparison to vaccinated pigs. The difference between groups was especially apparent in the ileum. The results presented here demonstrate a possible use for recombinant S. cerevisiae expressing viral proteins as an oral vaccine against PCV2. A powdered freeze-dried recombinant S. cerevisiae used as an oral vaccine could be mixed with feed and may offer a cheap and less labour intensive alternative to inoculation with the additional advantage that no cooling chain would be required for vaccine transport and storage.

A commercial PCV2a-based vaccine is effective in protection from experimental challenge of PCV2 mutant with two amino acids elongation in capsid protein

Current commercial PCV2 vaccines are almost based on PCV2a and have been shown to be effective in reducing PCV2a and PCV2b viremia and PCV2-associated lesions and diseases. The recent emergence of novel mutant PCV2 (mPCV2) strains and linkage of mPCV2 with cases of porcine circovirus associated disease (PCVAD) in pig herds have raised concerns over emergence of vaccine-escape mutants and reduced efficacy of PCV2a-based vaccines. The aim of this study was to determine the ability of a commercial PCV2a-based vaccine developed by our laboratory to protect conventional pigs against experimental challenge with mPCV2 at 9 weeks of age. Twenty 4-week-old pigs free of PCV2 infection were randomly divided into four treatment groups with 5 pigs each. Two groups were unvaccinated as positive and negative controls. Another two groups were vaccinated with the commercial PCV2a-based vaccine (PCV2-LG strain, China) at 4 weeks of age and identical booster immunization was conducted 3 weeks post primary immunization. At 9 weeks of age, all pigs except the negative control were challenged with a mutant PCV2b/YJ (mPCV2b/YJ) with two amino acids elongation in capsid protein. The experiment was terminated 28 days after challenge. Under the conditions of this study, vaccinated pigs were protected against PCV2 viremia and lesions whereas unvaccinated pigs were not. Moreover, mPCV2b/YJ infection was demonstrated in positive control and almost all had macroscopic or microscopic lesions consistent with PCVAD while negative control did not develop PCVAD. This study indicates that mPCV2b/YJ infection alone can trigger PCVAD development and that the commercial vaccine (PCV2-LG) is still effective in protecting conventional pigs against the emerging mPCV2b/YJ strain in China.