Passive immunity to porcine epidemic diarrhea virus following immunization of pregnant gilts with a recombinant orf virus vector expressing the spike protein

Identification of an Immunodominant B-Cell Epitope in African Swine Fever Virus p30 Protein and Evidence of p30 Antibody-Mediated Antibody Dependent Cellular Cytotoxicity

African Swine Fever Virus (ASFV) is a large dsDNA virus that encodes at least 150 proteins. The complexity of ASFV and lack of knowledge of effector immune functions and protective antigens have hindered the development of safe and effective ASF vaccines. In this study, we constructed four Orf virus recombinant vectors expressing individual ASFV genes B602L, -CP204L, E184L, and -I73R (ORFVΔ121-ASFV-B602L, -CP204L, -E184L, and -I73R). All recombinant viruses expressed the heterologous ASFV proteins in vitro. We then evaluated the immunogenicity of the recombinants by immunizing four-week-old piglets. In two independent animal studies, we observed high antibody titers against ASFV p30, encoded by CP204L gene. Using Pepscan ELISA, we identified a linear B-cell epitope of 12 amino acids in length (Peptide 15) located in an exposed loop region of p30 as an immunodominant ASFV epitope. Additionally, antibodies elicited against ASFV p30 presented antibody-dependent cellular cytotoxicity (ADCC) activity. These results underscore the role of p30 on antibody responses elicited against ASFV and highlight an important functional epitope that contributes to p30-specific antibody responses.

Swine influenza A virus: challenges and novel vaccine strategies

Swine Influenza A Virus (IAV-S) imposes a significant impact on the pork industry and has been deemed a significant threat to global public health due to its zoonotic potential. The most effective method of preventing IAV-S is vaccination. While there are tremendous efforts to control and prevent IAV-S in vulnerable swine populations, there are considerable challenges in developing a broadly protective vaccine against IAV-S. These challenges include the consistent diversification of IAV-S, increasing the strength and breadth of adaptive immune responses elicited by vaccination, interfering maternal antibody responses, and the induction of vaccine-associated enhanced respiratory disease after vaccination. Current vaccination strategies are often not updated frequently enough to address the continuously evolving nature of IAV-S, fail to induce broadly cross-reactive responses, are susceptible to interference, may enhance respiratory disease, and can be expensive to produce. Here, we review the challenges and current status of universal IAV-S vaccine research. We also detail the current standard of licensed vaccines and their limitations in the field. Finally, we review recently described novel vaccines and vaccine platforms that may improve upon current methods of IAV-S control.

Immunogenicity of chimeric hemagglutinins delivered by an orf virus vector platform against swine influenza virus

Orf virus (ORFV) is a large DNA virus that can harbor and efficiently deliver viral antigens in swine. Here we used ORFV as a vector platform to deliver chimeric hemagglutinins (HA) of Influenza A virus of swine (IAV-S). Vaccine development against IAV-S faces limitations posed by strain-specific immunity and the antigenic diversity of the IAV-S strains circulating in the field. A promising alternative aiming at re-directing immune responses on conserved epitopes of the stalk segment of the hemagglutinin (HA2) has recently emerged. Sequential immunization with chimeric HAs comprising the same stalk but distinct exotic head domains can potentially induce cross-reactive immune responses against conserved epitopes of the HA2 while breaking the immunodominance of the head domain (HA1). Here, we generated two recombinant ORFVs expressing chimeric HAs encoding the stalk region of a contemporary H1N1 IAV-S strain and exotic heads derived from either H6 or H8 subtypes, ORFVΔ121cH6/1 and ORFVΔ121cH8/1, respectively. The resulting recombinant viruses were able to express the heterologous protein in vitro. Further, the immunogenicity and cross-protection of these vaccine candidates were assessed in swine after sequential intramuscular immunization with OV-cH6/1 and OV-cH8/1, and subsequent challenge with divergent IAV-S strains. Humoral responses showed that vaccinated piglets presented increasing IgG responses in sera. Additionally, cross-reactive IgG and IgA antibody responses elicited by immunization were detected in sera and bronchoalveolar lavage (BAL), respectively, by ELISA against different viral clades and a diverse range of contemporary H1N1 IAV-S strains, indicating induction of humoral and mucosal immunity in vaccinated animals. Importantly, viral shedding was reduced in nasal swabs from vaccinated piglets after intranasal challenge with either Oh07 (gamma clade) or Ca09 (npdm clade) IAV-S strains. These results demonstrated the efficiency of ORFV-based vectors in delivering chimeric IAV-S HA-based vaccine candidates and underline the potential use of chimeric-HAs for prevention and control of influenza in swine.

The transcriptome of the parapoxvirus Orf virus reveals novel promoters for heterologous gene expression by poxvirus vectors

Orf virus (ORFV) has been used as a vaccine delivery vector for multiple animal species. Several strategies are being used to improve the immunogenicity and efficacy of ORFV vectors, including the use of poxviral promoter(s) with strong early and late activity capable of driving the expression of the heterologous genes for a prolonged time and eliciting a potent immune response. Here, we used RNA-sequencing (RNA-Seq) approach to analyze the transcriptome of ORFV during infection in primary ovine cells. Based on the transcriptional profile of individual ORFV genes, we identified ORFV promoters with strong early and late activity and have shown that they can be used to express heterologous genes in ORFV vectors. Our results show that the intergenic regulatory sequence containing core promoter sequences present upstream of ORF112 (p112) and ORF116 (p116) lead to markedly higher transgene expression than conventional poxviral promoters. Thus, these promoters are valuable alternatives to express transgenes in poxviral vectors.

An Orf-Virus (ORFV)-Based Vector Expressing a Consensus H1 Hemagglutinin Provides Protection against Diverse Swine Influenza Viruses

Influenza A viruses (IAV-S) belonging to the H1 subtype are endemic in swine worldwide. Antigenic drift and antigenic shift lead to a substantial antigenic diversity in circulating IAV-S strains. As a result, the most commonly used vaccines based on whole inactivated viruses (WIVs) provide low protection against divergent H1 strains due to the mismatch between the vaccine virus strain and the circulating one. Here, a consensus coding sequence of the full-length of HA from H1 subtype was generated in silico after alignment of the sequences from IAV-S isolates obtained from public databases and was delivered to pigs using the Orf virus (ORFV) vector platform. The immunogenicity and protective efficacy of the resulting ORFVΔ121conH1 recombinant virus were evaluated against divergent IAV-S strains in piglets. Virus shedding after intranasal/intratracheal challenge with two IAV-S strains was assessed by real-time RT-PCR and virus titration. Viral genome copies and infectious virus load were reduced in nasal secretions of immunized animals. Flow cytometry analysis showed that the frequency of T helper/memory cells, as well as cytotoxic T lymphocytes (CTLs), were significantly higher in the peripheral blood mononuclear cells (PBMCs) of the vaccinated groups compared to unvaccinated animals when they were challenged with a pandemic strain of IAV H1N1 (CA/09). Interestingly, the percentage of T cells was higher in the bronchoalveolar lavage of vaccinated animals in relation to unvaccinated animals in the groups challenged with a H1N1 from the gamma clade (OH/07). In summary, delivery of the consensus HA from the H1 IAV-S subtype by the parapoxvirus ORFV vector decreased shedding of infectious virus and viral load of IAV-S in nasal secretions and induced cellular protective immunity against divergent influenza viruses in swine.

The immunogenicity of plant-based COE-GCN4pII protein in pigs against the highly virulent porcine epidemic diarrhea virus strain from genotype 2

Porcine epidemic diarrhea virus (PEDV) is a serious infectious causative agent in swine, especially in neonatal piglets. PEDV genotype 2 (G2) strains, particularly G2a, were the primary causes of porcine epidemic diarrhea (PED) outbreaks in Vietnam. Here, we produced a plant-based CO-26K-equivalent epitope (COE) variant from a Vietnamese highly virulent PEDV strain belonging to genotype 2a (COE/G2a) and evaluated the protective efficacy of COE/G2a-GCN4pII protein (COE/G2a-pII) in piglets against the highly virulent PEDV G2a strain following passive immunity. The 5-day-old piglets had high levels of PEDV-specific IgG antibodies, COE-IgA specific antibodies, neutralizing antibodies, and IFN-γ responses. After virulent challenge experiments, all of these piglets survived and had normal clinical symptoms, no watery diarrhea in feces, and an increase in their body weight, while all of the negative control piglets died. These results suggest that the COE/G2a-pII protein produced in plants can be developed as a promising vaccine candidate to protect piglets against PEDV G2a infection in Vietnam.

Protective Efficacy of an Orf Virus-Vector Encoding the Hemagglutinin and the Nucleoprotein of Influenza A Virus in Swine

Swine influenza is a highly contagious respiratory disease of pigs caused by influenza A viruses (IAV-S). IAV-S causes significant economic losses to the swine industry and poses challenges to public health given its zoonotic potential. Thus effective IAV-S vaccines are needed and highly desirable and would benefit both animal and human health. Here, we developed two recombinant orf viruses, expressing the hemagglutinin (HA) gene (OV-HA) or the HA and the nucleoprotein (NP) genes of IAV-S (OV-HA-NP). The immunogenicity and protective efficacy of these two recombinant viruses were evaluated in pigs. Both OV-HA and OV-HA-NP recombinants elicited robust virus neutralizing antibody response in pigs, with higher levels of neutralizing antibodies (NA) being detected in OV-HA-NP-immunized animals pre-challenge infection. Although both recombinant viruses elicited IAV-S-specific T-cell responses, the frequency of IAV-S-specific proliferating CD8+ T cells upon re-stimulation was higher in OV-HA-NP-immunized animals than in the OV-HA group. Importantly, IgG1/IgG2 isotype ELISAs revealed that immunization with OV-HA induced Th2-biased immune responses, whereas immunization with OV-HA-NP virus resulted in a Th1-biased immune response. While pigs immunized with either OV-HA or OV-HA-NP were protected when compared to non-immunized controls, immunization with OV-HA-NP resulted in incremental protection against challenge infection as evidenced by a reduced secondary antibody response (NA and HI antibodies) following IAV-S challenge and reduced virus shedding in nasal secretions (lower viral RNA loads and frequency of animals shedding viral RNA and infectious virus), when compared to animals in the OV-HA group. Interestingly, broader cross neutralization activity was also observed in serum of OV-HA-NP-immunized animals against a panel of contemporary IAV-S isolates representing the major genetic clades circulating in swine. This study demonstrates the potential of ORFV-based vector for control of swine influenza virus in swine.

Immunomodulatory Strategies for Parapoxvirus: Current Status and Future Approaches for the Development of Vaccines against Orf Virus Infection

Orf virus (ORFV), the prototype species of the parapoxvirus genus, is the causative agent of contagious ecthyma, an extremely devastating skin disease of sheep, goats, and humans that causes enormous economic losses in livestock production. ORFV is known for its ability to repeatedly infect both previously infected and vaccinated sheep due to several immunomodulatory genes encoded by the virus that temporarily suppress host immunity. Therefore, the development of novel, safe and effective vaccines against ORFV infection is an important priority. Although, the commercially licensed live-attenuated vaccines have provided partial protection against ORFV infections, the attenuated viruses have been associated with major safety concerns. In addition to safety issues, the persistent reinfection of vaccinated animals warrants the need to investigate several factors that may affect vaccine efficacy. Perhaps, the reason for the failure of the vaccine is due to the long-term adaptation of the virus in tissue culture. In recent years, the development of vaccines against ORFV infection has achieved great success due to technological advances in recombinant DNA technologies, which have opened a pathway for the development of vaccine candidates that elicit robust immunity. In this review, we present current knowledge on immune responses elicited by ORFV, with particular attention to the effects of the viral immunomodulators on the host immune system. We also discuss the implications of strain variation for the development of rational vaccines. Finally, the review will also aim to demonstrate future strategies for the development of safe and efficient vaccines against ORFV infections.

Orf virus ORFV112, ORFV117 and ORFV127 contribute to ORFV IA82 virulence in sheep

The parapoxvirus orf virus (ORFV) encodes several immunomodulatory proteins (IMPs) that modulate host innate and pro-inflammatory responses to infection. Using the ORFV IA82 strain as the parental virus, recombinant viruses with individual deletions in the genes encoding the IMPs chemokine binding protein (CBP; ORFV112), inhibitor of granulocyte-monocyte colony-stimulating factor and IL-2 (GIF, ORFV117) and interleukin 10 homologue (vIL-10; ORFV127) were generated and characterized in vitro and in vivo. The replication properties of the individual gene deletion viruses in cell culture was not affected comparing with the parental virus. To investigate the effect of the individual gene deletions in ORFV infection and pathogenesis, groups of four lambs were inoculated with each virus and were monitored thereafter. Lambs inoculated with either recombinant or with the parental ORFV developed characteristic lesions of contagious ecthyma. The onset, nature and severity of the lesions in the oral commissure were similar in all inoculated groups from the onset (3 days post-inoculation [pi]) to the peak of clinical lesions (days 11-13 pi). Nonetheless, from days 11-13 pi onwards, the oral lesions in lambs inoculated with the recombinant viruses regressed faster than the lesions produced by the parental virus. Similarly, the amount of virus shed in the lesions were equivalent among lambs of all groups up to day 15 pi, yet they were significantly higher in the parental virus group from day 16-21 pi. In conclusion, individual deletion of these IMP genes from the ORFV genome resulted in slight reduction in virulence in vivo, as evidenced by a reduction in the duration of the clinical disease and virus shedding.

NF-κB as an Important Factor in Optimizing Poxvirus-Based Vaccines against Viral Infections

Poxviruses are large dsDNA viruses that are regarded as good candidates for vaccine vectors. Because the members of the Poxviridae family encode numerous immunomodulatory proteins in their genomes, it is necessary to carry out certain modifications in poxviral candidates for vaccine vectors to improve the vaccine. Currently, several poxvirus-based vaccines targeted at viral infections are under development. One of the important aspects of the influence of poxviruses on the immune system is that they encode a large array of inhibitors of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), which is the key element of both innate and adaptive immunity. Importantly, the NF-κB transcription factor induces the mechanisms associated with adaptive immunological memory involving the activation of effector and memory T cells upon vaccination. Since poxviruses encode various NF-κB inhibitor proteins, before the use of poxviral vaccine vectors, modifications that influence NF-κB activation and consequently affect the immunogenicity of the vaccine should be carried out. This review focuses on NF-κB as an essential factor in the optimization of poxviral vaccines against viral infections.

Efficacy of Porcine Epidemic Diarrhea Vaccines: A Systematic Review and Meta-Analysis

Porcine epidemic diarrhea (PED) is a devastating disease that causes considerable economic damage to the global pig industry. Although the causative agent, the porcine epidemic diarrhea virus (PEDV), was identified about a half century ago, there is still much debate on the preventive measures against the disease, especially regarding the PED vaccine. Recent reports on PEDV variants make the vaccination for PEDV more confusing. Therefore, we systematically reviewed published articles on PED and vaccines against the disease and performed a meta-analysis of vaccine efficacy based on the clinical signs, fecal score and survival rates. A total of 299 articles on the efficacy of PED vaccines were found online, and 21 articles were selected that fulfilled all the criteria. A meta-analysis was performed on the 21 articles based on the fecal scores and survival rates. This analysis showed the efficacy of PED vaccines, and no significant differences in the efficacy depending on vaccine type (killed vs. live) or administration route (intramuscular vs. oral) were found. The results from our study suggest that any vaccination against PED is a useful strategy to control the disease regardless of the type of vaccine and administration route.

Porcine epidemic diarrhea virus: Molecular mechanisms of attenuation and vaccines

Porcine epidemic diarrhea virus (PEDV) causes an emerging and re-emerging coronavirus disease characterized by vomiting, acute diarrhea, dehydration, and up to 100% mortality in neonatal suckling piglets, leading to huge economic losses in the global swine industry. Vaccination remains the most promising and effective way to prevent and control PEDV. However, effective vaccines for PEDV are still under development. Understanding the genomic structure and function of PEDV and the influence of the viral components on innate immunity is essential for developing effective vaccines. In the current review, we systematically describe the recent developments in vaccine against PEDV and the roles of structural proteins, non-structural proteins and accessory proteins of PEDV in affecting viral virulence and regulating innate immunity, which will provide insight into the rational design of effective and safe vaccines for PEDV or other coronaviruses.

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Advances in vaccines of PEDV, such as inactivated and attenuated live vaccines, subunit vaccines, and nucleic acid vaccines.

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The application of reverse genetics in the development of live attenuated PEDV vaccines.

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The roles of PEDV proteins in affecting viral virulence and regulating innate immunity.

Humoral immune responses in piglets experimentally infected with a field strain of porcine epidemic diarrhea virus

Porcine epidemic diarrhea virus (PEDV) causes severe clinical diarrhea in neonatal piglets, with reported mortality rates between 70-100%. The humoral immunity, especially the local intestinal IgA responses, plays an important role in the immune protection against PEDV infection. In this study, we evaluated the isotype antibody responses against the PEDV nucleocapsid (N) protein and the spike (S) protein subunits 1 (S1) and 2 (S2) in the serum and intestine of piglets. We also determined its serum neutralizing activity against the PEDV field strain HBMC2012 in 21-day-old piglets. Enzyme-linked immunosorbent assays (ELISA) revealed that the production of IgM against the N protein and S1 subunit was higher compared to the S2 subunit. The anti-S2 IgA antibodies were higher than the anti-N protein and anti-S1 IgA at 3 days post-infection (dpi). The specific IgA responses to the S2 subunit were higher than the responses observed in S1. The specific IgG responses against S1 and S2 subunits exceeded those of N protein. The serum neutralizing activities against PEDV were relatively low with a tendency to decline over time. No isotype-specific antibodies were found in the intestinal contents from infected pigs, except the one with weak IgA responses against N protein at 28 dpi. Immunohistochemical staining showed that a few IgM, IgA, and IgG antibody-secreting cells were mainly located in the mucosa of the duodenum and ileum of PEDV-infected pigs at 3 dpi. This study suggests poor systemic and intestinal isotype-specific antibody responses, especially those of IgA, and weak serum neutralizing activities against the field PEDV strain in piglets.

Intramuscular Immunization with Chemokine-Adjuvanted Inactive Porcine Epidemic Diarrhea Virus Induces Substantial Protection in Pigs

Intramuscular (IM) immunization is generally considered incapable of generating a protective mucosal immune response. In the swine industry, attempts to develop a safe and protective vaccine for controlling porcine epidemic diarrhea (PED) via an IM route of administration have been unsuccessful. In the present study, porcine chemokine ligand proteins CCL25, 27, and 28 were constructed and stably expressed in the mammalian expression system. IM co-administration of inactivated PEDV (iPEDV) particles with different CC chemokines and Freund’s adjuvants resulted in recruiting CCR9+ and/or CCR10+ inflammatory cells to the injection site, thereby inducing superior systemic PEDV specific IgG, fecal IgA, and viral neutralizing antibodies in pigs. Moreover, pigs immunized with iPEDV in combination with CCL25 and CCL28 elicited substantial protection against a virulent PEDV challenge. We show that the porcine CC chemokines could be novel adjuvants for developing IM vaccines for modulating mucosal immune responses against mucosal transmissible pathogens in pigs.

Host Factors Affecting Generation of Immunity Against Porcine Epidemic Diarrhea Virus in Pregnant and Lactating Swine and Passive Protection of Neonates

Porcine epidemic diarrhea virus (PEDV) is a highly virulent re-emerging enteric coronavirus that causes acute diarrhea, dehydration, and up to 100% mortality in neonatal suckling piglets. Despite this, a safe and effective PEDV vaccine against highly virulent strains is unavailable, making PEDV prevention and control challenging. Lactogenic immunity induced via the gut-mammary gland-secretory IgA (sIgA) axis, remains the most promising and effective way to protect suckling piglets from PEDV. Therefore, a successful PEDV vaccine must induce protective maternal IgA antibodies that passively transfer into colostrum and milk. Identifying variables that influence lymphocyte migration and IgA secretion during gestation and lactation is imperative for designing maternal immunization strategies that generate the highest amount of lactogenic immune protection against PEDV in suckling piglets. Because pregnancy-associated immune alterations influence viral pathogenesis and adaptive immune responses in many different species, a better understanding of host immune responses to PEDV in pregnant swine may translate into improved maternal immunization strategies against enteric pathogens for multiple species. In this review, we discuss the role of host factors during pregnancy on antiviral immunity and their implications for generating protective lactogenic immunity in suckling neonates.

Evaluation of the Efficacy of a Recombinant Adenovirus Expressing the Spike Protein of Porcine Epidemic Diarrhea Virus in Pigs

In recent years, many studies have shown that recombinant adenovirus live vector-based vaccines are a promising novel vaccine candidate against virus infection. Therefore, in this study, a new type of recombinant adenovirus expressing the spike (S) protein of porcine epidemic diarrhea virus (PEDV), rAd-PEDV-S, was generated, and its characteristics were determined. Then, its efficacy as a vaccine candidate was evaluated in 4-week-old pigs. The results showed that the S protein could be well expressed at a high level in rAd-PEDV-S-infected cells and that the viral titers could reach 10¹¹ PFU/mL. Further animal experimental results showed that rAd-PEDV-S elicited a significant PEDV-specific humoral immune response after vaccination (P < 0.05). In addition, rAd-PEDV-S provided partial protection for pigs against the highly virulent PEDV challenge. The results presented in this study indicate that the adenovirus vector can be used as a vaccine delivery vector for the development of a PEDV vaccine and is a promising novel vaccine candidate for future prevention and control of porcine epidemic diarrhea (PED), but its efficacy still needs to be improved in the future.

Effect of intervention practices to control the porcine epidemic diarrhea (PED) outbreak during the first epidemic year (2013-2014) on time to absence of clinical signs and the number of dead piglets per sow in Japan

Porcine epidemic diarrhea (PED) is an emerging and/or re-emerging disease of pigs in several countries, with high morbidity and mortality in suckling piglets. Farms affected with PED perform various intervention practices to control and/or eliminate the PED virus. The objectives of the present study were to assess the effect of biosecurity measures and intervention practices to control PED on time to absence of clinical signs (TAC) and number of dead suckling piglets during TAC. A questionnaire was administered to 120-PED affected farms located across Japan between 2013, when the first case was reported in Japan, and 2014. Farms were asked to provide information on farm characteristics and internal or external biosecurity measures during PED outbreak, as well as on intervention practices to control PED. The TAC was defined as the number of days from the date that clinical PED signs appeared to the date that clinical PED signs disappeared. The number of dead piglets per sow (DP/S) was calculated as the number of dead suckling piglets during TAC divided by the sow inventory. Regarding the effect of biosecurity measures during PED outbreak on TAC and DP/S, longer TAC was observed in Actinobacillus pleuropneumoniae-positive farms and farms outsourcing pig transport to the slaughterhouse (p <  0.05). In addition, farms with divided truck entrances had lower DP/S than those without divided entrances (p <  0.05).Regarding the effect of intervention practices to control PED on TAC and DP/S, farms that performed feedback at 2 weeks or later after PED outbreak had longer TAC and higher DP/S than other farms (p <  0.05). Farms that fixed the hours staff worked in farrowing barn had lower DP/S than the other farms (p <  0.05). In conclusion, variables associated with long TAC were Actinobacillus pleuropneumoniae -positive farms, farms outsourcing pig transport to the slaughterhouse, and farms performing feedback at 2 week or later after PED outbreak. Additionally, those associated with high DP/S were farms without divided entrances, farms without a fixed hours worked in the barn, and farms that performed feedback at 2 week or later after PED outbreak.

Display of Porcine Epidemic Diarrhea Virus Spike Protein on Baculovirus to Improve Immunogenicity and Protective Efficacy

A new variant of the porcine epidemic diarrhea virus (PEDV) is an emerging swine disease, killing considerable numbers of neonatal piglets in North America and Asia in recent years. To generate immunogens mimicking the complex spike (S) protein folding with proper posttranslational modification to mount a robust immune response against the highly virulent PEDV, two baculoviruses displaying the full-length S protein (S-Bac) and the S1 protein (S1-Bac) of the virulent Taiwan genotype 2b (G2b) PEDV Pintung 52 (PEDV-PT) strain were constructed. Intramuscular immunizations of mice and piglets with the S-Bac and S1-Bac demonstrated significantly higher levels of systemic anti-PEDV S-specific IgG, as compared with control group. Our results also showed that piglets in the S-Bac group elicited superior PEDV-specific neutralizing antibodies than those of the S1-Bac and control groups. The highly virulent PEDV-PT strain challenge experiment showed that piglets immunized with S-Bac and S1-Bac showed milder clinical symptoms with significantly less fecal viral shedding as compared with non-immunized control piglets. More importantly, piglets immunized with the S-Bac exhibited no to mild clinical signs, with a delayed, minimal viral shedding. Our results demonstrated that the S-Bac could serve as a safe, easy to manipulate, and effective vaccine candidate against the PEDV infection.