Identification and pathogenicity of a variant porcine epidemic diarrhea virus field strain with reduced virulence

Two New Cardiac Glycosides From Streblus asper

Two undescribed cardiac glycosides, strasperoside K (1) and L (2), together with five known analogs (3-7), were isolated from Streblus asper Lour. Their structures were elucidated on the basis of spectroscopic analysis and chemical methods. The inhibitory activities of isolated compounds against porcine epidemic diarrhea virus (PEDV) and six strains of pathogenic bacteria were evaluated.

Genome Characterization of Mammalian Orthoreovirus and Porcine Epidemic Diarrhea Virus Isolated from the Same Fattening Pig

In 2020, severe diarrhea occurred in four-month-old fattening pigs from nine farms in Shandong Province, China. Fecal samples were collected from diseased pigs and tested by PCR for the presence of mammalian orthoreovirus (MRV), porcine epidemic diarrhea virus (PEDV), porcine deltacoronavirus (PDCoV), porcine rotavirus A (PoRVA), transmissible gastroenteritis virus (TGEV), porcine kobuvirus (PKV), and pseudorabies virus (PRV). The viral RNA of MRV and PEDV was detected in the fecal samples. The genome sequences of MRV and PEDV were successfully amplified from the same fecal sample. Genomic and phylogenetic analysis showed that the MRV isolate named MRV2-SD/2020 belongs to serotype 2 MRV (MRV2) and may originate from the reassortment of human and porcine MRVs. Compared with other MRV2 strains, there were four other unique amino acid mutations (L274I, F302L, V347I, and T440M) in the receptor binding region. For the PEDV isolate named PEDV-SD/2020, the nearly complete genome was amplified from the positive fecal samples. Phylogenetic analysis showed that it was classified into the G2a genotype. Compared with CV777 and other PEDV variant strains, its spike (S) protein exhibited two unique mutations (S663T and L966M). This study first reports the co-infection of PEDV and MRV2 in the pigs and provides a new direction for the prevention and control of the diarrhea diseases.

Porcine epidemic diarrhea virus E protein induces unfolded protein response through activating both PERK and ATF6 rather than IRE1 signaling pathway

Porcine epidemic diarrhea virus (PEDV) small envelope protein (E) plays important roles in virus budding, assembly, and release. Our previous study found that PEDV E protein localizes in the endoplasmic reticulum (ER) to trigger the unfolded protein response (UPR). However, how UPR is directly regulated by PEDV E protein remains elusive. Thus, in this study, we investigated the expression of ER chaperone glucose-regulated protein 78 (GRP78) and activations of the three main UPR signaling pathways to elucidate the underlying mechanisms of UPR triggered by PEDV E protein. The results showed that over-expression of PEDV E protein increased expression of GRP78 and induced stronger phosphorylation of both protein kinase RNA-like ER kinase (PERK) and eukaryotic initiation factor-2α (eIF2α), as well as caused the significant degradation of activating transcription factor 6 (ATF6), in both dose- and time-dependent manners. However, PEDV E protein did not induce UPR through the inositol-requiring enzyme 1 (IRE1) signaling pathway, as revealed by the splicing of XBP1 remaining unaffected and unchanged when PEDV E protein was overexpressed. Taken together, these results demonstrate that PEDV E protein induces UPR through activation of both PERK and ATF6 pathways rather than IRE1 signaling. This study not only provides mechanistic details of UPR induced by the PEDV E protein, but also provides insights into these new biologic functions to help us better understand the interactions between PEDV and host cells.

Efficacy evaluation of a bivalent subunit vaccine against epidemic PEDV heterologous strains with low cross-protection

Variant Porcine epidemic diarrhea virus (PEDV), which causes diarrhea and high mortality in piglets, has become a major pathogen, and co-epidemics of different subtypes of the virus have become a very thorny problem for the clinical prevention and control of PEDV. However, cross-protection between epidemic G2a and G2b subtype strains has not been observed, and there is currently no vaccine against both G2a and G2b strains. In this study, we demonstrate the low cross-protection between G2a and G2b strains with piglet immunization and challenge tests. The trimeric full-length S proteins of G2a and G2b variants were purified and a bivalent subunit vaccine against PEDV G2a/G2b-S was developed. In active and passive immune protection tests, the bivalent subunit vaccine produced high neutralizing antibody titers and S-specific immunoglobulin G (IgG) and IgA titers against both the G2a and G2b strains in piglets and sows. In the attack phase of the viruses, the clinical symptoms and microscopic lesions in the immunized groups were significantly alleviated. Importantly, the PEDV G2a/G2b-S bivalent subunit vaccine conferred effective passive immunity against PEDV G2a and G2b challenges in the form of colostrum-derived antibodies from the immunized sows. In conclusion, our data demonstrate the low cross-protection of PEDV epidemic G2a and G2b strains and show that the G2a/G2b-S bivalent subunit vaccine is protective against both G2a and G2b strains. It is therefore a candidate vaccine for PEDV prevention.

IMPORTANCE

The detection rate of PEDV G2a subtype strains is currently increasing. Although commercial vaccines are available, most vaccines do not exert an ideal protective effect against these strains. Furthermore, there is no definitive research into the cross-protection between G2a and G2b strains, and no bivalent vaccine provides joint protection against both. Therefore, in this study, we investigated the cross-protection between PEDV G2a and G2b strains and designed a candidate bivalent subunit vaccine combining the trimeric S proteins of the G2a and G2b subtypes. We demonstrate that the cross-protection between strains G2a and G2b is poor and that this bivalent subunit vaccine protects piglets from viral attack by inducing both active and passive immunity. This study emphasizes the effectiveness of the PEDV G2a/G2b-S bivalent subunit vaccine and provides a feasible method for the development of efficient PEDV vaccines.

Isolation and characterization of a subtype G2c variant of porcine epidemic diarrhea virus that adapts well to cell culture

Porcine epidemic diarrhea virus (PEDV) causes the third most important disease in the pig industry, after African swine fever and porcine reproductive and respiratory syndrome, and leads to illness or death of the entire litter, causing significant economic losses. In this study, three PEDV strains (HN-1, HN-2, and SC2023) were isolated from swine farms with suspected PEDV infections in Sichuan and Henan provinces. Phylogenetic analysis based on complete S gene sequences showed that all three strains belonged to the G2c subgroup. HN-1 adapted readily to cell culture, grew to a viral titer as high as 2 × 108 TCID50/mL in Vero cells, and caused the formation of large syncytia. We analyzed the amino acid sequence of the HN-1 isolate and found that its S1 subunit contained a three-amino-acid insertion (355KRL358). A seven-amino-acid-deletion (1377FEKVHVQ1383) in the S2 subunit resulted in the partial deletion of the endocytosis signal YxxΦ and the complete deletion of the endoplasmic reticulum retrieval signal (ERRS) KVHVQ in the cytoplasmic tail of the S protein. Consequently, HN-1 is predicted to be less pathogenic than its parent strain, an attribute that facilitates rapid cell-to-cell spread by enhancing syncytium formation. In addition, strain HN-1 was found to have the mutation 884-885SG→RR, which may favor adaptation to cell culture by providing new trypsin cleavage sites. These results suggest that HN-1 is a G2c subtype variant that adapts well to cell culture and can be used to study the adaptive mechanisms of PEDV and develop attenuated vaccines.

Porcine epidemic diarrhea viruses from Vietnam: isolation, characterization, and neutralizing activity

Porcine epidemic diarrhea (PED) is characterized by acute enteritis, watery diarrhea, weight loss, dehydration, and death, with high mortality in neonatal piglets. In this study, 3 virus isolates collected in Vietnam between 2016 and 2017 were propagated successfully in Vero cells at high virus titers. Sequence analysis of the full-length spike (S) gene showed that all 3 isolates belong to genogroup 2b, which is closely related to other prevalent Asian strains. A comparison of the amino acid sequence revealed a 98.19% to 99.13% homology with the Vietnam isolates circulating during 2013–2015, suggesting that field PED viruses (PEDVs) are evolving continuously. Experiments in animals showed that the antisera from guinea pigs immunized with the vaccine strain resulted in higher levels (5 log2) of neutralizing antibodies against the homologous strain and a relatively moderate level of neutralizing antibodies against the field isolates. This finding would be helpful in selecting a PEDV strain for vaccine development.

Newly Characterized Porcine Epidemic Diarrhea Virus GII Subtype Strain

Diarrhea outbreaks in piglets on pig farms are commonly attributed to porcine epidemic diarrhea virus (PEDV) infection. This research analyzed the S gene prevalence variation and recombination patterns in PEDV GII strains. Throughout the previous two years, 172 clinical samples of piglet diarrhea have been collected, from which 24 PEDV isolates have been isolated. Analysis of the evolutionary relationships among all 24 S genes revealed that 21 were most closely related to strains within the GII-a subgroup. The 2 isolates grouped into one clade with the GII-b subgroup. According to the mutation analysis of the amino acids (aa) that encode the S protein, 43 of the common aa in strains of the GII subtype were found to have undergone a change in polarity or charge, and 36 of these aa had a mutation frequency of more than 90%. Three different aa mutation sites were identified as exclusive to GII-a subtype strains. The genomes of three PEDV isolates were sequenced, and the resulting range in genome length was 28,035-28,041 nt. The results of recombination analysis showed that the SD1 isolate is a novel strain recombinant from the foreign S-INDEL strain and a domestic GII subtype strain. Based on the findings, the PEDV GII-a strain has been the most circulating strain in several parts of China during the previous two years. Our study reveals for the first time the unique change of aa mutations in the S protein of the GII-a subtype strain and the new characteristics of the recombination of foreign strains and domestic GII subtype strains, indicating that it is crucial to monitor the epidemic dynamics of PEDV promptly to prevent and control the occurrence of PED effectively.

Porcine Epidemic Diarrhea Virus: An Updated Overview of Virus Epidemiology, Virulence Variation Patterns and Virus-Host Interactions

The porcine epidemic diarrhea virus (PEDV) is a member of the coronavirus family, causing deadly watery diarrhea in newborn piglets. The global pandemic of PEDV, with significant morbidity and mortality, poses a huge threat to the swine industry. The currently developed vaccines and drugs are only effective against the classic GI strains that were prevalent before 2010, while there is no effective control against the GII variant strains that are currently a global pandemic. In this review, we summarize the latest progress in the biology of PEDV, including its transmission and origin, structure and function, evolution, and virus-host interaction, in an attempt to find the potential virulence factors influencing PEDV pathogenesis. We conclude with the mechanism by which PEDV components antagonize the immune responses of the virus, and the role of host factors in virus infection. Essentially, this review serves as a valuable reference for the development of attenuated virus vaccines and the potential of host factors as antiviral targets for the prevention and control of PEDV infection.

Antibody Evaluation and Mutations of Antigenic Epitopes in the Spike Protein of the Porcine Epidemic Diarrhea Virus from Pig Farms with Repeated Intentional Exposure (Feedback)

The feedback strategy, or controlled exposure of pig herd to the porcine epidemic diarrhea virus (PEDV), significantly decreased losses during a severe outbreak in late 2013 in Taiwan. However, some pig farms still suffered from recurrent outbreaks. To evaluate the association between antibody titers and clinical manifestations, sera and colostra were analyzed from one pig farm that employed the feedback strategy. Furthermore, spike (S) gene full sequences from six positive samples of two farms with and without using feedback were compared to investigate the evolution of PEDV variants circulating in pig herds. The results in this study showed that high PEDV antibody titers do not correlate with the high rate of protection from PEDV infection. In addition, repeated feedback generated the emergence of PEDV variants with unique substitutions of N537S and Y561H in the COE domain and S769F in the SS6 epitopes. These mutations indicated the pathogenetic evolution of PEDV strains existing in the cycle of the feedback method. A very strict biosecurity practice to block the routes of pathogen transfer should be followed to achieve successful control of PEDV infections in pig herds.

Isolation, characterization and neutralizing activity of porcine epidemic diarrhea viruses from Vietnam

Porcine epidemic diarrhea (PED) is characterized by acute enteritis, watery diarrhea, weight loss, dehydration, and death with high mortality in neonatal piglets. In this study, 3 virus isolates collected in Vietnam between 2016 and 2017 were successfully propagated in Vero cells at high virus titers. Sequence analysis of the full-length spike (S) gene revealed that all 3 isolates belong to genogroup 2a, which is closely related to other prevalent Asian strains. Amino acid sequence comparisons revealed 98.19% to 99.13% homology with the Vietnam isolates circulating during 2013–2015, suggesting that field PED viruses (PEDVs) evolve continuously. Experiments in animals demonstrated that antisera from guinea pigs immunized with the vaccine strain resulted in higher levels (5 log2) of neutralizing antibody against the homologous strain, and showed a relatively lower level of neutralizing antibody against the field isolates. This finding would be helpful in choosing a PEDV strain for vaccine development.

Molecular Characteristics and Pathogenicity of Porcine Epidemic Diarrhea Virus Isolated in Some Areas of China in 2015-2018

Since 2010, Porcine epidemic diarrhea virus (PEDV) has caused severe diarrhea disease in piglets in China, resulting in large economic losses. To understand the genetic characteristics of the PEDV strains that circulated in some provinces of China between 2015 and 2018, 375 samples of feces and small intestine were collected from pigs and tested. One hundred seventy-seven samples tested positive and the PEDV-positive rate was 47.20%. A phylogenetic tree analysis based on the entire S gene showed that these strains clustered into four subgroups, GI-a, GI-b, GII-a, and GII-b, and that the GII-b strains have become dominant in recent years. Compared with previous strains, these strains have multiple variations in the SP and S1-NTD domains and in the neutralizing epitopes of the S protein. We also successfully isolated and identified a new virulent GII-b strain, GDgh16, which is well-adapted to Vero cells and caused a high mortality rate in piglets in challenge experiments. Our study clarifies the genetic characteristics of the prevalent PEDV strains in parts of China, and suggests that the development of effective novel vaccines is both necessary and urgent.

Isolation and evolutionary analyses of porcine epidemic diarrhea virus in Asia

Porcine epidemic diarrhea virus (PEDV) is a leading cause of diarrhea in pigs worldwide. Virus isolation and genetic evolutionary analysis allow investigations into the prevalence of epidemic strains and provide data for the clinical diagnosis and vaccine development. In this study, we investigated the genetic characteristics of PEDV circulation in Asia through virus isolation and comparative genomics analysis. APEDV strain designated HB2018 was isolated from a pig in a farm experiencing a diarrhea outbreak. The complete genome sequence of HB2018 was 28,138 bp in length. Phylogenetic analysis of HB2018 and 207 PEDVs in Asia showed that most PEDV strains circulating in Asia after 2010 belong to genotype GII, particularly GII-a. The PEDV vaccine strain CV777 belonged to GI, and thus, unmatched genotypes between CV777 and GII-a variants might partially explain incomplete protection by the CV777-derived vaccine against PEDV variants in China. In addition, we found the S protein of variant strains contained numerous mutations compared to the S protein of CV777, and these mutations occurred in the N-terminal domain of the S protein. These mutations may influence the antigenicity, pathogenicity, and neutralization properties of the variant strains.

Emergence and evolution of highly pathogenic porcine epidemic diarrhea virus by natural recombination of a low pathogenic vaccine isolate and a highly pathogenic strain in the spike gene

Outbreaks of a new variant of porcine epidemic diarrhea virus (PEDV) at the end of 2010 have raised interest in the mutation and recombination of PEDV. A PEDV strain (CN/Liaoning25/2018) isolated from a clinical outbreak of piglet diarrhea contained a 49-bp deletion in the ORF3 gene. This deletion is considered a genetic characteristic of low pathogenic attenuated vaccine strains. However, CN/Liaoning25/2018 was highly pathogenic. Complete genome sequencing, identity analysis, phylogenetic tree construction, and recombination analysis showed that this virus was a recombinant strain containing the Spike (S) gene from the highly pathogenic CN/GDZQ/2014 strain and the remaining genomic regions from the low pathogenic vaccine isolate SQ2014. Histopathology and immunohistochemistry results confirmed that this strain was highly pathogenic and indicated that intestinal epithelial cell vacuolation was positively correlated with the intensity and density of PEDV antigens. A new natural recombination model for PEDV was identified. Our results suggest that new highly pathogenic recombinant strains in the field may be generated by recombination between low pathogenic attenuated live PEDV vaccines and pathogenic circulating PEDV strains. Our findings also highlight that the 49-bp deletion of the ORF3 gene in low pathogenic attenuated vaccine strains will no longer be a reliable standard to differentiate the classical vaccine attenuated from the field strains.

Development of a droplet digital PCR for detection and quantification of porcine epidemic diarrhea virus

Porcine epidemic diarrhea, a disease caused by porcine epidemic diarrhea virus (PEDV), results in large economic losses to the global swine industry. To manage this disease effectively, it is essential to detect PEDV early and accurately. We developed a sensitive and accurate droplet digital PCR (ddPCR) assay to detect PEDV. The optimal primer-to-probe concentration and melting temperature were identified as 300:200 nM and 59.2°C, respectively. The specificity of the ddPCR assay was confirmed by negative test results for common swine pathogens. The detection limit for the ddPCR was 0.26 copies/μL, which is a 5.7-fold increase in sensitivity compared to that of real-time PCR (rtPCR). Both ddPCR and rtPCR assays exhibited good linearity, although ddPCR provided higher sensitivity for clinical detection compared to that of rtPCR. Our ddPCR methodology provides a promising tool for evaluating the PEDV viral load when used for clinical testing, particularly for detecting samples with low-copy viral loads.

A flagellin-adjuvanted inactivated porcine epidemic diarrhea virus (PEDV) vaccine provides enhanced immune protection against PEDV challenge in piglets

Since late 2010, outbreaks of porcine epidemic diarrhea (PED) have been reported in the swine industry in China. A variant PEDV strain that differs from strain CV777 causes prevalent PEDV infections which commercial vaccines based on CV777 cannot provide complete protection. In this study, we designed a new vaccine based on the epidemic PEDV strain AH2012/12, adjuvanted with flagellin, a mucosal adjuvant that induces mucosal and systemic production of IgA. Three groups of pregnant sows were immunized twice, with a 14-day interval, with PEDV adjuvanted with flagellin, PEDV alone, or PBS before farrowing, and newborn piglets from each group were selected and challenged with PEDV. Immunization with this vaccine elicited high levels of IgG, IgA, and neutralizing antibodies in the serum and colostrum of sows, and newborn piglets were protected against PEDV while suckling. This study should guide the prevention and control strategies for PEDV infection, thereby reducing the losses associated with this virus.

Establishment and application of a multiplex RT-PCR to differentiate wild-type and vaccine strains of porcine epidemic diarrhea virus

Due to outbreaks of porcine epidemic diarrhea (PED) and the wide use of attenuated live vaccine, both wild-type and vaccine strains (CV777) are believed to circulate in Chinese pig farms. Thus, identification of different PEDV strains is of epidemiological importance. In this study, a multiplex RT-PCR method was established based on the sequence features of spike (S) gene and ORF3 gene of PEDVs. The method could identify PEDV variant strains, classical wild-type strains and classical vaccine strains. The limit of detection of the RT-PCR was 1.51 × 10⁴ copies/uL for plasmids and 1 × 10^1.7 TCID₅₀/100 u L for PEDV, respectively. There were no cross-detections among three different PEDVs and no false detections among six swine pathogens. This assay was used to test 940 samples from China of which 303 samples were PEDV positive, and 289, 5, 10 were positive for variant, classical wild, classical vaccine, respectively. One sample was positive for both variant and classical vaccine PEDV. The variant PEDVs could be detected in samples from 13 provinces, while classical PEDVs were detected from nine provinces, supporting the prevalence of variant PEDV in China. In summary, this multiplex RT-PCR was a useful tool for the clinical detection and epidemiological survey of PEDV.

Molecular characteristics and pathogenic assessment of porcine epidemic diarrhoea virus isolates from the 2018 endemic outbreaks on Jeju Island, South Korea

Since the 2013–2014 incursion of the virulent G2b porcine epidemic diarrhoea virus (PEDV) pandemic strains in South Korea, frequent moderate‐scale regional outbreaks have recurred. In particular, areas of Jeju Island with extensive swine production have faced repeated epidemics since the re‐emergence in 2014. The current study reports the complete genome sequences and molecular characterization of the representative PEDV strains responsible for the 2018 endemic outbreaks on Jeju Island. All isolates were determined to belong genetically to the highly pathogenic pandemic G2b group. Full‐length genome sizes of four isolates differed from that of the G2b epidemic field strain due to insertion or deletion (DEL) mutations in the non‐structural protein (nsp)‐ or spike (S) protein‐coding regions. The 2018 Jeju isolates shared 96.7%–98.7% and 98.5%–99.4% identity at the S gene and whole‐genome levels, respectively, compared to global G2b PEDV strains. Genetic and phylogenetic analyses indicated that the 2018 isolates were closest to the 2014 G2b re‐emergent Jeju strains, but appeared to have undergone substantial rapid independent evolution. Among the isolates, a notable nsp3 DEL variant strain, KOR/KNU‐1807/2018, was isolated and propagated by continuous passages in Vero cells, and displayed typical PEDV‐induced syncytia formation. Genomic sequencing identified a unique 8‐nt DEL in the extreme C‐terminal region of the S gene at the 4th passage (KNU‐1807‐P4) compared to its original sample. This DEL resulted in the premature termination of S by nine amino acid residues (EVFEKVHVQ), which contained a KxHxx motif that is a potential endoplasmic reticulum retrieval signal. In vivo animal studies showed that variant strain KNU‐1807 had decreased virulence in suckling piglets. These results advance our knowledge regarding the genetic variation and pathogenicity of the G2b PEDV endemic strains prevalent in Jeju swine herds in South Korea.

A Single V672F Substitution in the Spike Protein of Field-Isolated PEDV Promotes Cell⁻Cell Fusion and Replication in VeroE6 Cells

While porcine epidemic diarrhea virus (PEDV) infects and replicates in enterocytes lining villi of neonatal piglets with high efficiency, naturally isolated variants typically grow poorly in established cell lines, unless adapted by multiple passages. Cells infected with most cell-adapted PEDVs usually displayed large syncytia, a process triggered by the spike protein (S). To identify amino acids responsible for S-mediated syncytium formation, we constructed and characterized chimeric S proteins of the cell-adapted variant, YN144, in which the receptor binding domain (RBD) and S1/S2 cleavage site were replaced with those of a poorly culturable field isolate (G2). We demonstrated that the RBD, not the S1/S2 cleavage site, is critical for syncytium formation mediated by chimeric S proteins. Further mutational analyses revealed that a single mutation at the amino acid residue position 672 (V672F) could enable the chimeric S with the entire RBD derived from the G2 strain to trigger large syncytia. Moreover, recombinant PEDV viruses bearing S of the G2 strain with the single V672F substitution could induce extensive syncytium formation and replicate efficiently in VeroE6 cells stably expressing porcine aminopeptidase N (VeroE6-APN). Interestingly, we also demonstrated that while the V672F mutation is critical for the syncytium formation in VeroE6-APN cells, it exerts a minimal effect in Huh-7 cells, thereby suggesting the difference in receptor preference of PEDV among host cells.

Genetic evolution analysis and pathogenicity assessment of porcine epidemic diarrhea virus strains circulating in part of China during 2011-2017

In recent years, the outbreaks of porcine epidemic diarrhea (PED) caused by the highly virulent porcine epidemic diarrhea virus (PEDV) variants occurred frequently in China, resulting in severe economic impacts to the pork industry. In this study, we selected and analyzed the genetic evolution of 15 PEDV representative strains that were identified in fecal samples of diarrheic piglets in 10 provinces and cities during 2011-2017. The phylogenetic analysis indicated that all the 15 PEDV isolates clustered into G2 genotype associated with the current circulating strains. Compared with the genome of the prototype strain CV777, these strains had 103-120 amino acid mutations in their S proteins, most of which were in the N terminal domain of S1 (S1-NTD). We also found 37 common mutations in all these 15 strains, although these strains shared 96.9-99.7% nucleotide homology and 96.3-99.8% amino acid homology in the S protein compared with the other original pandemic strains. Computational analysis showed that these mutations may lead to remarkable changes in the conformational structure and asparagine (N)-linked glycosylation sites of S1-NTD, which may be associated with the altered pathogenicity of these variant PEDV strains. We evaluated the pathogenicity of the PEDV strain FJzz1 in piglets through oral and intramuscular infection routes. Compared with oral infection, intramuscular infection could also cause typical clinical signs but with a slightly delayed onset, confirming that the variant PEDV isolate FJzz1 was highly pathogenic to suckling piglets. In conclusion, we analyzed the genetic variation and pathogenicity of the emerging PEDV isolates of China, indicating that G2 variant PEDV strains as the main prevalent strains that may mutate continually. This study shows the necessity of monitoring the molecular epidemiology and the etiological characteristics of the epidemic PEDV isolates, which may help better control the PED outbreaks.

Deletion of both the Tyrosine-Based Endocytosis Signal and the Endoplasmic Reticulum Retrieval Signal in the Cytoplasmic Tail of Spike Protein Attenuates Porcine Epidemic Diarrhea Virus in Pigs

Porcine epidemic diarrhea virus (PEDV) causes high mortality in neonatal piglets. The PEDV spike (S) protein contains two intracellular sorting motifs, YxxΦ (tyrosine-based motif YEVF or YEAF) and KVHVQ at the cytoplasmic tail, yet their functions have not been fully elucidated. Some Vero cell-adapted and/or attenuated PEDV variants contain ablations in these two motifs. We hypothesized that these motifs contribute to viral pathogenicity. By transiently expressing PEDV S proteins with mutations in the motifs, we confirmed that the motif KVHVQ is involved in retention of the S proteins in the endoplasmic reticulum (ER)-Golgi intermediate compartment (ERGIC). In addition, we showed that the YxxΦ motif triggers endocytosis of S proteins. These two motifs synergistically regulate the level of S expressed on the cell surface. To investigate their role in viral pathogenicity, we generated three recombinant PEDVs by introducing deletions or a mutation in the two motifs of the infectious clone of PEDV PC22A strain (icPC22A): (i) icΔ10aa (ΔYxxΦEKVHVQ), (ii) icΔ5aa (ΔKVHVQ), and (iii) icYA (Y1378A, to an inactivated motif, AEVF). Infection of Vero cells with icΔ10aa resulted in larger syncytia and more virions, with reduced numbers of S protein projections on the surface compared with icPC22A. Furthermore, we orally inoculated five groups of 5-day-old gnotobiotic piglets with the three mutants, icPC22A, or a mock treatment. Mutant icΔ10aa caused less severe diarrhea rate and significantly milder intestinal lesions than icPC22A, icΔ5aa, and icYA. These data suggest that the deletion of both motifs can reduce the virulence of PEDV in piglets.IMPORTANCE Many coronaviruses (CoVs) possess conserved motifs YxxΦ and/or KxHxx/KKxx in the cytoplasmic tail of the S protein. The KxHxx/KKxx motif has been identified as the ER retrieval signal, but the function of the YxxΦ motif in the intracellular sorting of CoV S proteins remains controversial. In this study, we showed that the YxxΦ of PEDV S protein is an endocytosis signal. Furthermore, using reverse genetics technology, we evaluated its role in PEDV pathogenicity in neonatal piglets. Our results explain one attenuation mechanism of Vero cell-adapted PEDV variants lacking functional YxxΦ and KVHVQ motifs. Knowledge from this study may aid in the design of efficacious live attenuated vaccines against PEDV, as well as other CoVs bearing the same motif in their S protein.

Isolation and characterization of a new porcine epidemic diarrhea virus variant that occurred in Korea in 2014

Outbreaks of porcine epidemic diarrhea (PED) have resulted in significant economic losses in the swine industry, and another PED outbreak occurred in 2014 in Korea. Isolating and culturing PED virus (PEDV) allow investigations into its pathogenesis and the development of vaccines and diagnostic assays. In this study, we successfully isolated two PEDV isolates (QIAP1401 and QIAP1402) from naturally infected piglets at Jeju-do, Korea. Viral propagation was confirmed in Vero cells based on cytopathic effect, immunofluorescence assay, reverse transcription-polymerase chain reaction, and electron microscopic analyses. The QIAP401 isolate propagated well in Vero cells for 70 passages, with titers of 10^6.5 to 10^7.0 50% tissue culture infectious dose/mL, which increased gradually with passaging. The nucleotide and amino acid sequences of the QIAP1401 isolate were determined and compared with those of other PEDV isolates. The QIAP1401 isolate was determined to be closely related to the USA/Minnesota271/2014 strain (> 99.9% nucleotide similarity) that was isolated in the USA in 2014. Phylogenetic analysis based on several PEDV genes suggested that a new PEDV variant is circulating in the Korean swine industry, with 93.08% similarity to the SM98 strain isolated in 1998. In addition, the QIAP1401 strain showed strong virulence in 3-day-old piglets and 11-week-old growing pigs.

The Accessory Protein ORF3 Contributes to Porcine Epidemic Diarrhea Virus Replication by Direct Binding to the Spike Protein

The porcine epidemic diarrhea virus (PEDV) is an important swine pathogen responsible for severe watery diarrhea, particularly in neonatal piglets. Despite extensive studies performed to elucidate the function of several viral proteins, the contribution of an accessory protein ORF3 in PEDV replication is still largely unknown. Here, we constructed expression plasmids as well as recombinant PEDV carrying myc-tagged ORF3 to assess their expression and subcellular localization in both transfected and infected cells. In PEDV-infected cells, ORF3 was predominantly localized in the cytoplasm, partially in the endoplasmic reticulum (ER) and the Golgi apparatus (Golgi). Interestingly, ORF3 with the N-terminal Flag tag was also detected on the cell surface concomitant with the spike (S) protein as determined by flow cytometry and confocal microscopy. ORF3 and S proteins were also co-localized at perinuclear compartments and in the vesicle-like structures in transfected and infected cells. We also demonstrated that both full-length and naturally truncated ORF3 proteins could interact with the S protein but with different binding affinity, which correlate with the ability of the protein to regulate virus replication in cell culture. Collectively, our results underscore the unprecedented role of the ORF3, which involves the interaction of ORF3 with S and, possibly, other structural protein during PEDV replication.

Different intestinal tropism of the G2b Taiwan porcine epidemic diarrhea virus-Pintung 52 strain in conventional 7-day-old piglets

The group 2b (G2b) porcine epidemic diarrhea virus (PEDV) that emerged in 2013 has since caused devastating diseases and economic loss. The full-length genome of the G2b Taiwan PEDV-Pintung 52 (PEDV-PT) strain and its intestinal tropism by evaluating the pathological changes in the original PEDV-PT infected field piglet and orally inoculation of either 10, 10³, or 10⁵ 50% tissue culture infective dose/mL (TCID₅₀/mL) of the plaque-purified PEDV-PT-Passage 5 (P5) in 7-day-old conventional piglets were analyzed. Phylogenetic analysis of the full-length genome indicated that the G2b Taiwan PEDV-PT strain was closely related to the North American G2b PEDV strains. Some pathological features of the G2b Taiwan PEDV-PT infection, including the absence of lesions and antigen signal in the crypt epithelial cells of the jejunum and ileum and in the villus enterocytes of the duodenum and colon, were different from those of infections by the North American G2b PEDV strains. This difference in the intestinal tropism of the G2b Taiwan PEDV-PT strain highlights the importance of studying the pathogenicities of different PEDV variants. Moreover, similar distributions of PEDV antigens and lesions in the G2b Taiwan PEDV-PT infected field piglet and its plaque-purified isolate, PEDV-PT-P5, inoculated piglets indicating that the plaque-purified PEDV-PT-P5 viral stock could facilitate the preclinical evaluation of vaccines and other interventions aimed at preventing the G2b PEDV infection.

Isolation and characterization of Chinese porcine epidemic diarrhea virus with novel mutations and deletions in the S gene

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We successfully isolated two novel PEDV strains, PEDV-LA1 and PEDV-LY4-98 in China.

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The two novel PEDV isolates shared higher identities with United States strains than with South Korean strains.

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Three unique amino acid substitutions were identified in the S1 N terminal domain of the PEDV-LY4-98 strain.

Porcine epidemic diarrhea (PEDV) has raised growing concerns in the pig-breeding industry because it has caused significant economic losses. To better understand the molecular epidemiology and genetic diversity of PEDV field isolates, in this study, the complete spike (S) and ORF3 genes of 17 PEDV variants in Zhejiang, China during 2014 to 2017, were characterized and analyzed. Phylogenetic analysis based on the S gene and ORF3 gene of these 17 novel PEDV strains and PEDV reference strains indicated that all the PEDV strains fell into two groups designated G1 and G2. Notably, the strains identified in 2014–2015 were in G2, while the other five strains identified from 2016 to 2017 were in G1. Sequencing and phylogenetic analyses showed that recently prevalent Chinese PEDV field strains shared higher identities with United States strains than with South Korean strains. Compared with classical vaccine strains, a series of deletions and frequently occurring mutations were observed in the receptor binding domains of our PEDV strains. Besides, we successfully isolated and reported the genetic characterization two novel PEDV strains, PEDV-LA1 and PEDV-LY4-98, found on the Chinese mainland, which had significant variations in the S gene. Meanwhile, the virulence of the new mutants may be changed, the PEDV-LY4-98 strain, which has multiple mutations in the signal peptide-encoding fragment of the S gene showed delayed cytopathic effects and smaller plaque size compared with strain PEDV-LA1, which lacks these mutations. Three unique amino acid substitutions (L7, G8, and V9) were identified in the SP-encoding fragment of the S1 N-terminal domain of the PEDV-LY4-98 S protein compared with the S proteins of all the previous PEDV strains. The animal experiment revealed that these two novel strains were high pathogenic to neonatal pigs. Whether these amino acids substitutions and the N-glycosylation site substitutions influence the antigenicity and pathogenicity of PEDV remains to be investigated. Meanwhile, amino acid substitutions in the neutralizing epitopes may have conferred the capacity for immune evasion in these PEDV field strains. This study improves our understanding of ongoing PEDV outbreaks in China, and it will guide further efforts to develop effective measures to control this virus.

Tracking the Origin and Deciphering the Phylogenetic Relationship of Porcine Epidemic Diarrhea Virus in Ecuador

In 2010, new Chinese strains of porcine epidemic diarrhea virus (PEDV), clinically more severe than the classical strains, emerged. These strains were spread to United States in 2013 through an intercontinental transmission from China with further spreading across the world, evidencing the emergent nature of these strains. In the present study, an analysis of PEDV field sequences from Ecuador was conducted by comparing all the PEDV S gene sequences available in the GenBank database. Phylogenetic comparisons and Bayesian phylogeographic inference based on complete S gene sequences were also conducted to track the origin and putative route of PEDV. The sequence from the PED-outbreak in Ecuador was grouped into the clade II of PEDV genogroup 2a together with other sequences of isolates from Mexico, Canada, and United States. The phylogeographic study revealed the emergence of the Chinese PEDV strains, followed by spreading to US in 2013, from US to Korea, and later the introduction of PEDV to Canada, Mexico, and Ecuador directly from the US. The sources of imports of live swine in Ecuador in 2014 were mainly from Chile and US. Thus, this movement of pigs is suggested as the main way for introducing PEDV to Ecuador.

Poly (d,l-lactide-co-glycolide) nanoparticle-entrapped vaccine induces a protective immune response against porcine epidemic diarrhea virus infection in piglets

Porcine epidemic diarrhea (PED) causes 80-100% mortality in neonatal piglets, and its causative agent, the porcine epidemic diarrhea virus (PEDV), poses an important threat to the swine industry worldwide. In this study, we prepared biodegradable poly (d,l-lactide-co-glycolide) (PLGA) nanoparticle-entrapped PEDV killed vaccine antigens (KAg) (PLGA-KAg). Late-term pregnant sows were intranasally inoculated with PLGA-KAg, and the mortality resulting from challenge with highly virulent PEDV was investigated in their passively immunized suckling piglets. PEDV-specific IgG and IgA antibody titers were enhanced in pregnant sows immunized with PLGA-KAg relative to the titers in sows inoculated with KAg. Similar results were seen in the passively immunized suckling piglets of these sows. Improved lymphocyte proliferation responses and IFN-γ levels were induced in pregnant sows immunized with PLGA-KAg compared with those vaccinated with KAg or with Montanide™ ISA 201 VG emulsified killed PEDV vaccine (201-KAg). Importantly, there was less piglet mortality in the group vaccinated with PLGA-KAg than in the groups vaccinated with KAg or 201-KAg. These results demonstrate that PLGA-KAg is a promising candidate vaccine that can provide protective immunity against PEDV infection in suckling piglets.

Discovery of a novel swine enteric alphacoronavirus (SeACoV) in southern China

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A novel swine enteric alphacoronavirus (tentatively named SeACoV) was isolated from diarrheic piglets in southern China.

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SeACoV is likely antigenetically distinct from PEDV, TGEV and PDCoV.

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Genomic and phylogenetic analysis showed that SeACoV might have originated from the bat coronavirus HKU2.

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The extreme amino-terminal domain of SeACoV spike glycoprotein had an extremely high variability compared to that of HKU2.

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Experimental infection study showed that SeACoV is infectious and pathogenic in newborn piglets.

Outbreaks of diarrhea in newborn piglets without detection of transmissible gastroenteritis virus (TGEV), porcine epidemic diarrhea virus (PEDV) and porcine deltacoronavirus (PDCoV), have been recorded in a pig farm in southern China since February 2017. Isolation and propagation of the pathogen in cell culture resulted in discovery of a novel swine enteric alphacoronavirus (tentatively named SeACoV) related to the bat coronavirus HKU2 identified in the same region a decade ago. Specific fluorescence signal was detected in Vero cells infected with SeACoV by using a positive sow serum collected in the same farm, but not by using TGEV-, PEDV- or PDCoV-specific antibody. Electron microscopy observation demonstrated that the virus particle with surface projections was 100–120 nm in diameter. Complete genomic sequencing and analyses of SeACoV indicated that the extreme amino-terminal domain of the SeACoV spike (S) glycoprotein structurally similar to the domain 0 of the alphacoronavirus NL63, whereas the rest part of S structurally resembles domains B to D of the betacoronavirus. The SeACoV-S domain 0 associated with enteric tropism had an extremely high variability, harboring 75-amino-acid (aa) substitutions and a 2-aa insertion, compared to that of HKU2, which is likely responsible for the extended host range or cross-species transmission. The isolated virus was infectious in pigs when inoculated orally into 3-day-old newborn piglets, leading to clinical signs of diarrhea and fecal virus shedding. These results confirmed that it is a novel swine enteric coronavirus representing the fifth porcine coronavirus.

Genetic and pathogenic characterization of a novel reassortant mammalian orthoreovirus 3 (MRV3) from a diarrheic piglet and seroepidemiological survey of MRV3 in diarrheic pigs from east China

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A novel reassortant mammalian orthoreovirus 3 (MRV3), designated MRV-ZJ2013, was isolated from diarrheic piglets.

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Genomic and phylogenetic analysis shows that MRV-ZJ2013 may have originated from reassortments among mink, bat, and pig MRVs.

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Experimental infection study showed that MRV-ZJ2013 had low, if any, pathogenesis in newborn piglets.

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A seroepidemiological survey of MRV3 revealed a high seroprevalence (77%) from diarrheic pigs of different ages in east China.

Mammalian orthoreoviruses (MRVs), which cause gastrointestinal and respiratory illness, have been isolated from a wide variety of mammalian species including bats, minks, pigs and humans. Here we report the isolation and genetic and pathogenic characterization of a novel MRV type 3 (MRV3), named MRV-ZJ2013, from the diarrheic feces of piglets in Zhejiang province, China. Genomic and phylogenetic analysis shows that MRV-ZJ2013 may have originated from reassortments among mink, bat, and pig MRVs, suggesting the hypothesis that interspecies transmission has occurred in pig herds. Neonatal piglets infected with MRV-ZJ2013 displayed mild clinical signs such as poor appetite and soft feces, but vomiting and diarrhea were not observed. Fecal virus shedding was detected only in three out of six piglets, each for one- or two-day post-infection. In contrast, piglets inoculated with a virulent porcine epidemic diarrhea virus (PEDV) strain as the control group had severe signs characterized by acute vomiting and watery diarrhea. These findings suggest that the virulence of MRV-ZJ2013, if any, was likely not significant compared to that of PEDV. A seroepidemiological survey of MRV by means of an indirect enzyme-linked immune-sorbent assay (ELISA) based on a recombinant MRV3 capsid protein sigma1 as antigen revealed a high seroprevalence (77%) in 1037 samples from diarrheic pigs of different ages from 24 herds in seven provinces of east China between 2015 and 2016, indicating that MRV3 is endemic in pig herds in China, and may contribute collectively to enteric disease along with other porcine pathogens.

Complete genome sequence of a novel S-insertion variant of porcine epidemic diarrhea virus from South Korea

Porcine epidemic diarrhea virus (PEDV) is an emerging and re-emerging viral pathogen of pigs that is causing significant economic concerns in the global pork industry. The virulent G2b PEDV subgroup, which was responsible for the 2013–2014 pandemics on the American and Asian continents, hit Jeju Island in 2014, which had been PEDV-free since 2004. This study presents molecular characterization of a novel PEDV variant with a 5-amino acid (aa) insertion (DTHPE) in the spike (S) gene (an S-insertion) that was identified in diarrheic piglets from Jeju Island. The genome of the PEDV strain KOR/KNU-1601/2016 was sequenced and analyzed to characterize the S-insertion variant circulating on Jeju Island. The full-length genome sequence of KNU-1601 is 28,053 nucleotides (nt) in length, which is 24 nt and 15 nt longer than the genome sequences of G1 classical and G2 epidemic field strains, respectively. KNU-1601 shares 99.5–99.6% nucleotide sequence identity at the genome level and 98.0–98.6% amino acid sequence identity at the S gene level with other global G2b PEDV strains. Genetic and phylogenetic analyses indicated that the KNU-1601 variant is most closely related to the G2b field isolates but appears to undergo continuous evolution in the field. These data advance our understanding of the genetic diversity and evolutionary characteristics of the PEDV field strains circulating in South Korea.

Characterization of Chinese Porcine Epidemic Diarrhea Virus with Novel Insertions and Deletions in Genome

Outbreaks of porcine epidemic diarrhoea virus (PEDV) have caused great economic losses to the global pig industry. PEDV strains with variants in the spike (S) gene have been reported in several countries. To better understand the molecular epidemiology and genetic diversity of PEDV field isolates, in this study, we characterised the complete genome sequence of a novel PEDV variant JSCZ1601 from a outbreak in China in 2016. The PEDV isolate was 28,033 nucleotides (nt) in length without the polyadenylated sequences. Phylogenetic analysis based on the full-length genome sequence of JSCZ1601 grouped it with the pandemic variants determined post-2010 into group 2 (G2). However, the S gene of JSCZ1601 formed a new subgroup separated from the subgroups containing the other G2 strains. Comparative analysis of the amino acids encoded by the S genes revealed the N-terminal of the deduced JSCZ1601 S protein had a novel two-amino-acid deletion (N58 and S59) compared with all identified genogroups. Further, compared with the reference strains, a 'G' insertion was detected in the 5' terminal of the 5'UTR of the JSCZ1601. The animal experiment revealed that this strain was high pathogenic to neonatal pigs. Taken together, a PEDV strain with the new molecular characterizations and phylogenies was found in mainland China. It is necessary to strengthen the monitoring of PEDV variations.

Attenuation of an original US porcine epidemic diarrhea virus strain PC22A via serial cell culture passage

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An original US PEDV strain PC22A was attenuated via Vero cell culture passages.

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Attenuated PEDV PC22A strain elicited protective immunity in pigs.

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Genomic changes of PEDV PC22A at high passage levels were identified.

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Various molecular changes are related to PEDV attenuation in pigs.

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PEDV PC22A at high passage levels can be live, attenuated vaccine candidates.

Although porcine epidemic diarrhea (PED) has caused huge economic losses in the pork industry worldwide, an effective live, attenuated vaccine is lacking. In this study, an original US, highly virulent PED virus (PEDV) strain PC22A was serially passaged in Vero CCL81 and Vero BI cells. The virus growth kinetics in cell culture, virulence in neonatal pigs and the whole genomic sequences of selected passages were examined. Increased virus titers and sizes of syncytia were observed at the 65th passage level (P65) and P120, respectively. Based on the severity of clinical signs, histopathological lesions and the distribution of PEDV antigens in the gut, the virulence of P100 and above, but not P95C13 (CCL81), was markedly reduced in 4-day-old, caesarian-derived, colostrum-deprived piglets. Subsequently, the attenuation of P120 and P160 was confirmed in 4-day-old, conventional suckling piglets. Compared with P120, P160 replicated less efficiently in the intestine of pigs and induced a lower rate of protection after challenge. Sequence analysis revealed that the virulent viruses [P3 and P95C13 (CCL81)] had one, one, sixteen (including an early termination of nine amino acids) and two amino acid differences in non-structure protein 1 (nsp1), nsp4, spike and membrane proteins, respectively, from the fully attenuated P160. However, the overall pattern of attenuation-related genetic changes in PC22A differed from those of the other four pairs of PEDV wild type strains and their attenuated derivatives. These results suggest that PEDV attenuation can occur through multiple molecular mechanisms. The knowledge provides insights into potential molecular mechanisms of PEDV attenuation.

Characterization of a pathogenic full-length cDNA clone of a virulent porcine epidemic diarrhea virus strain AH2012/12 in China

Since 2010, outbreaks of variant porcine epidemic diarrhea virus (PEDV) have swept across the world causing substantial economic losses. The development of new, more effective vaccines has been hampered by difficulties in isolating strains and viral genome manipulation. In the present study, we successfully isolated a highly pathogenic field strain AH2012/12, from a pig farm reporting severe diarrhea in China. Phylogenetic analysis revealed that the new isolate belongs to group G2, which represents epidemic and pandemic field strains. Furthermore, we constructed an infectious cDNA clone of the newly isolated strain, rAH2012/12, and the rescued virus displayed phenotypic properties identical to the parental virus in vitro. In vivo experiments demonstrated that the rescued virus displayed similar pathogenicity to the parental isolate, causing high mortality rates in suckling pigs. This study provided a strong basis for the development of live attenuated vaccines and for research into the pathogenic mechanisms of this virus.

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We successfully isolated one epidemic PEDV strain AH2012/12 with high virulent in newborn pigs.

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We firstly generated the infectious cDNA clone of the virulent PEDV strain AH2012/12 in China.

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The rescued virus has similar biological characteristics with the parent virus in vitro and vivo.

Molecular Characterization of the ORF3 and S1 Genes of Porcine Epidemic Diarrhea Virus Non S-INDEL Strains in Seven Regions of China, 2015

In an effort to trace the evolution of porcine epidemic diarrhea virus (PEDV), S1 and ORF3 genes of viruses identified in 41 pig farms from seven regions (North, Northeast, Northwest, Central, East, South West, and South, respectively) of China in 2015 were sequenced and analyzed. Sequence analysis revealed that the 41 ORF3 genes and 29 S1 genes identified in our study exhibited nucleotide homologies of 98.2%–100% and 96.6%–100%, respectively; these two genes exhibited low nucleotide sequence similarities with classical CV777 strain and early Chinese strain LZC. Phylogenetic analysis indicated that the identified PEDV strains belonged to global non S-INDEL strains, and exhibited genetic diversity; S1 gene of the HLJ2015/DP1-1 strain harbored an unique deletion of 12 nucleotides (A¹¹³⁰CAACTCCACTG¹¹⁴¹); while the Chinese PEDV S-INDEL reference strains included two types of the “CV777” S-INDEL as well as the “US” S-INDEL, and all co-circulated with Chinese non S-INDEL strains. Of 29 identified S1 genes, the SS2 epitope (Y⁷⁴⁸SNIGVCK⁷⁵⁵) was highly conserved, while the SS6 epitope (L⁷⁶⁴QDGQVKI⁷⁷¹) and pAPN receptor-binding region (aa 490–615) exhibited amino substitutions. Nine possible recombination events were identified between the 29 identifed S1 genes and the 3 S1 reference genes from early Chinese PEDV strains. The complete S genes of selected Chinese PEDV field strains (2011–2015) showed 5.18%–6.07% nucleotide divergence, which is far higher than the divergence observed in early Chinese PEDV strains (3.1%) (P<0.05). Our data provide evidence that PEDV non S-INDEL strains with genetic diversities and potential recombination circulate in seven regions of China in 2015; Chinese PEDV S-INDEL strains exhibit genetic diversity and co-circulate with non S-INDEL strains.

Evolution, antigenicity and pathogenicity of global porcine epidemic diarrhea virus strains

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Evolution of global PEDV strains.

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Cross-reactivity between PEDV and other coronaviruses and antigenic variations among different PEDV strains.

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Pathologic features of different PEDV strains.

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Considerations for vaccine strain selection: PEDV virulence attenuation and in vivo cross-protection among PEDV variants.

Emerging and re-emerging coronaviruses cause morbidity and mortality in human and animal populations, resulting in serious public and animal health threats and economic losses. The ongoing outbreak of a highly contagious and deadly porcine epidemic diarrhea virus (PEDV) in Asia, the Americas and Europe is one example. Genomic sequence analyses of PEDV variants have revealed important insights into the evolution of PEDV. However, the antigenic variations among different PEDV strains are less explored, although they may contribute to the failure of PEDV vaccines in Asian countries. In addition, the evolution of PEDV results in variants with distinct genetic features and virulence differences; thus PEDV can serve as a model to explore the molecular mechanisms of coronavirus evolution and pathogenesis. In this article, we review the evolution, antigenic relationships and pathologic features of PEDV strains. This information and review of researches will aid in the development of strategies for control and prevention of PED.

Porcine epidemic diarrhea virus: An overview of current virological and serological diagnostic methods

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Molecular assays such as rRT-PCR are the method of choice for PEDV diagnosis.

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Multiplex rRT-PCR allow simultaneous testing for PEDV, TGEV and PDCoV.

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Serological assays provide valuable information on previous exposure to PEDV and population immunity.

Porcine epidemic diarrhea virus (PEDV) is the causative agent of an acute, highly contagious, and severe enteric disease that leads to high mortality rates in suckling piglets. Therefore, accurate diagnosis of PEDV infection is critical for the implementation of control measures for the virus. Many diagnostic tests have been recently developed and are currently available for the detection of PEDV, its proteins or nucleic acid, including virus isolation, immunofluorescence (IF) or immunohistochemistry (IHC), polymerase chain reaction (PCR) and isothermal amplification assays. Additionally, several serological assays have been developed and are currently used for the detection of antibodies against PEDV. Molecular assays such as real-time reverse transcriptase-PCR (rRT-PCR) became the methods of choice for the diagnosis of PEDV infection, providing sensitive, specific and rapid detection of the virus RNA in clinical samples. Whereas serological assays have been widely used to monitor prior exposure to the virus and to evaluate the efficacy of novel vaccine candidates or vaccination strategies. Here we discuss the properties of current PEDV diagnostic assays and prospects for improving diagnostic strategies in the future.

Collection and review of updated scientific epidemiological data on porcine epidemic diarrhoea

Porcine epidemic diarrhoea (PED) is a non-zoonotic viral disease of pigs caused by a coronavirus and characterised by watery diarrhoea and weight loss. PED is not notifiable to the EU or World Organisation for Animal Health listed but it is notifiable at the national level in Finland, France, Ireland and Sweden. PED case reports from seven countries and PED surveillance and monitoring activities in thirteen countries were reported. This information was combined with an extensive literature review to provide an update on global PED occurrence, circulating strains and impact in 2014-2015. PED confirmed cases have been reported in North America, South America, Asia and Europe. PED virus (PEDV) sequences originating from EU pig herds indicate that the strains currently in circulation share nearly 100% sequence identity and have greater than 99% sequence identity with the reference INDEL (insertion/deletion) strain USA/OH851/2014. In 2014-2015, greater genetic variability has been reported in strains circulating in Asia compared with EU Member States and a non-INDEL strain has been detected in the Ukraine in 2014. Data on impact confirms that mortality is higher in suckling piglets and diarrhoea is observed in all age groups. The reported impact is in agreement with that reported in EFSA AHAW Panel (2014) indicating that the impact of recently reported PED outbreaks in Asia and the USA seems to be more severe than that described in EU countries, although the impact of different PEDV strains is difficult to compare between one country and another, as impact is dependent not only on pathogenicity but also on factors such as biosecurity, herd size, farm management, sanitary status or herd immune status.

Porcine epidemic diarrhea virus: An emerging and re-emerging epizootic swine virus

The enteric disease of swine recognized in the early 1970s in Europe was initially described as “epidemic viral diarrhea” and is now termed “porcine epidemic diarrhea (PED)”. The coronavirus referred to as PED virus (PEDV) was determined to be the etiologic agent of this disease in the late 1970s. Since then the disease has been reported in Europe and Asia, but the most severe outbreaks have occurred predominantly in Asian swine-producing countries. Most recently, PED first emerged in early 2013 in the United States that caused high morbidity and mortality associated with PED, remarkably affecting US pig production, and spread further to Canada and Mexico. Soon thereafter, large-scale PED epidemics recurred through the pork industry in South Korea, Japan, and Taiwan. These recent outbreaks and global re-emergence of PED require urgent attention and deeper understanding of PEDV biology and pathogenic mechanisms. This paper highlights the current knowledge of molecular epidemiology, diagnosis, and pathogenesis of PEDV, as well as prevention and control measures against PEDV infection. More information about the virus and the disease is still necessary for the development of effective vaccines and control strategies. It is hoped that this review will stimulate further basic and applied studies and encourage collaboration among producers, researchers, and swine veterinarians to provide answers that improve our understanding of PEDV and PED in an effort to eliminate this economically significant viral disease, which emerged or re-emerged worldwide.