Epidemiology and vaccine of porcine epidemic diarrhea virus in China: a mini-review

Poly(A)-Binding Protein Cytoplasmic 1 Inhibits Porcine Epidemic Diarrhea Virus Replication by Interacting with Nucleocapsid Protein

Porcine epidemic diarrhea virus (PEDV) is the etiological agent of porcine epidemic diarrhea (PED) characterized by vomit, watery diarrhea, dehydration and high mortality. Outbreaks of highly pathogenic variant strains of PEDV have resulted in extreme economic losses to the swine industry all over the world. The study of host–virus interaction can help to better understand the viral pathogenicity. Many studies have shown that poly(A)-binding proteins are involved in the replication process of various viruses. Here, we found that the infection of PEDV downregulated the expression of poly(A)-binding protein cytoplasmic 1 (PABPC1) at the later infection stage in Vero cells. The overexpression of PABPC1 inhibited the proliferation of PEDV at transcription and translation level, and siRNA-mediated depletion of PABPC1 promoted the replication of PEDV. Furthermore, mass spectrometry analysis and immunoprecipitation assay confirmed that PABPC1 interacted with the nucleocapsid (N) protein of PEDV. Confocal microscopy revealed the co-localizations of PABPC1 with N protein in the cytoplasm. Taken together, these results demonstrate the antiviral effect of PABPC1 against PEDV replication by interacting with N protein, which increases understanding of the interaction between PEDV and host.

TRIM56 overexpression restricts porcine epidemic diarrhoea virus replication in Marc-145 cells by enhancing TLR3-TRAF3-mediated IFN-β antiviral response

Infection with the porcine epidemic diarrhoea virus (PEDV) causes severe enteric disease in suckling piglets, causing massive economic losses in the swine industry worldwide. Tripartite motif-containing 56 (TRIM56) has been shown to augment type I IFN response, but whether it affects PEDV replication remains uncharacterized. Here we investigated the role of TRIM56 in Marc-145 cells during PEDV infection. We found that TRIM56 expression was upregulated in cells infected with PEDV. Overexpression of TRIM56 effectively reduced PEDV replication, while knockdown of TRIM56 resulted in increased viral replication. TRIM56 overexpression significantly increased the phosphorylation of IRF3 and NF-κB P65, and enhanced the IFN-β antiviral response, while silencing TRIM56 did not affect IRF3 activation. TRIM56 overexpression increased the protein level of TRAF3, the component of the TLR3 pathway, thereby significantly activating downstream IRF3 and NF-κB signalling. We demonstrated that TRIM56 overexpression inhibited PEDV replication and upregulated expression of IFN-β, IFN-stimulated genes (ISGs) and chemokines in a dose-dependent manner. Moreover, truncations of the RING domain, N-terminal domain or C-terminal portion on TRIM56 were unable to induce IFN-β expression and failed to restrict PEDV replication. Together, our results suggested that TRIM56 was upregulated in Marc-145 cells in response to PEDV infection. Overexpression of TRIM56 inhibited PEDV replication by positively regulating the TLR3-mediated antiviral signalling pathway. These findings provide evidence that TRIM56 plays a positive role in the innate immune response during PEDV infection.

Strategy of Developing Oral Vaccine Candidates Against Co-infection of Porcine Diarrhea Viruses Based on a Lactobacillus Delivery System

The number of co-infections with multiple porcine diarrhea viruses has increased in recent years. Inducing mucosal immunity through oral immunization is an effective approach for controlling these pathogens. To generate a multi-pathogen vaccine against viral co-infection, we employed the Lactobacillus vector platform, which was previously used to generate potent candidate vaccines against various diseases. Two strategies were used to test the protective efficiency of recombinant Lactobacillus against multiple diarrhea viruses. First, we used a mixture of recombinant Lactobacillus separately expressing antigens of transmissible gastroenteritis virus (TGEV), porcine epidemic diarrhea virus (PEDV), and porcine rotavirus (PoRV). Next, we used a recombinant Lactobacillus expressing an antigen fusion protein of the above viruses. Twenty-four newborn piglets were divided into three groups and orally immunized with a mixture of recombinant Lactobacillus, recombinant Lactobacillus expressing the antigen fusion protein, or sterile phosphate-buffered saline daily for seven consecutive days after birth. After immunization, the piglets were randomly selected from each group for oral administration of PEDV, and these piglets were then cohabited with piglets without PEDV infection for 7 days. The protective effect against PEDV was evaluated based on clinical symptoms, viral shedding, and intestinal pathological damage. Piglets immunized with recombinant Lactobacillus showed specific mucosal and humoral immune responses to the three viruses and were protected against severe diarrhea and intestinal pathology. Our results highlight the potential of an oral multi-pathogen vaccine based on Lactobacillus to prevent transmission and limit the severity of viral co-infection.

Inactivated Pseudomonas PE(ΔIII) exotoxin fused to neutralizing epitopes of PEDV S proteins produces a specific immune response in mice

Porcine epidemic diarrhea (PED) caused by the porcine epidemic diarrhea virus (PEDV), is a severe infectious and devastating swine disease that leads to serious economic losses in the swine industry worldwide. An increased number of PED cases caused by variant PEDV have been reported in many countries since 2010. S protein is the main immunogenic protein containing some B-cell epitopes that can induce neutralizing antibodies of PEDV. In this study, the construction, expression and purification of Pseudomonas aeruginosa exotoxin A (PE) without domain III (PEΔIII) as a vector was performed for the delivery of PEDV S-A or S-B. PE(ΔIII) PEDV S-A and PE(ΔIII) PEDV S-B recombinant proteins were confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analysis. The immunogenicity of PEDV S-A and PEDV S-B subunit vaccines were evaluated in mice. The results showed that PEDV-S-B vaccine could not only induce specific humoral and Th1 type-dominant cellular immune responses, but also stimulate PEDV-specific mucosal immune responses in mice. PEDV-S-B subunit vaccine is a novel candidate mucosal vaccine against PEDV infection.

Immunogenicity of Recombinant-Deficient Lactobacillus casei with Complementary Plasmid Expressing Alanine Racemase Gene and Core Neutralizing Epitope Antigen against Porcine Epidemic Diarrhea Virus

Porcine epidemic diarrhea (PED), which is caused by the porcine epidemic diarrhea virus (PEDV), has occurred worldwide and poses a serious threat to the pig industry. Intestine is the main function site of PEDV; therefore, it is important to develop an oral mucosal immunity vaccine against this virus infection. Most traditional plasmid delivery vectors use antibiotic genes as a selective marker, easily leading to antibiotic accumulation and gene contamination. In this study, to explore whether the alanine racemase gene (Alr) could be used as a screening marker and develop an efficient oral vaccine against PEDV infection, a recombinant strain was constructed using Lactobacillus casei with Alr deletion (L. casei ΔAlr W56) to deliver the Alr gene and a core-neutralizing epitope (COE) antigen. This recombinant bacterium efficiently induced secretory immunoglobulin A (SIgA)-based mucosal and immunoglobulin G (IgG)-based humoral immune responses via oral vaccination in mice. Compared to the other strains, the recombinant bacteria were able to grow without the addition of D-alanine, revealing that Alr in the plasmid could function normally in defective bacteria. This oral mucosal vaccine would provide a useful strategy to substitute the application of antibiotics in the future and induce efficient immune responses against PEDV infection.

EGR1 Suppresses Porcine Epidemic Diarrhea Virus Replication by Regulating IRAV To Degrade Viral Nucleocapsid Protein

Porcine epidemic diarrhea virus (PEDV) is a globally distributed alphacoronavirus that has reemerged lately, resulting in large economic losses. During viral infection, type I interferon (IFN-I) plays a vital role in the antiviral innate immunity. However, PEDV has evolved strategies to limit IFN-I production. To suppress virus replication, the host must activate IFN-stimulated genes and some host restriction factors to circumvent viral replication. This study observed that PEDV infection induced early growth response gene 1 (EGR1) expression in PEDV-permissive cells. EGR1 overexpression remarkably suppressed PEDV replication. In contrast, depletion of EGR1 led to a significant increase in viral replication. EGR1 suppressed PEDV replication by directly binding to the IFN-regulated antiviral (IRAV) promoter and upregulating IRAV expression. A detailed analysis revealed that IRAV interacts and colocalizes with the PEDV nucleocapsid (N) protein, inducing N protein degradation via the E3 ubiquitin ligase MARCH8 to catalyze N protein ubiquitination. Knockdown of endogenous MARCH8 significantly reversed IRAV-mediated N protein degradation. The collective findings demonstrate a new mechanism of EGR1-mediated viral restriction, in which EGR1 upregulates the expression of IRAV to degrade PEDV N protein through MARCH8. IMPORTANCE PEDV is a highly contagious enteric coronavirus that has rapidly emerged worldwide and has caused severe economic losses. No currently available drugs or vaccines can effectively control PEDV. PEDV has evolved many strategies to limit IFN-I production. We identified EGR1 as a novel host restriction factor and demonstrated that EGR1 suppresses PEDV replication by directly binding to the IRAV promoter and upregulating the expression of IRAV, which interacts with and degrades the PEDV N protein via the E3 ubiquitin ligase MARCH8 to catalyze nucleocapsid protein ubiquitination, which adds another layer of complexity to the innate antiviral immunity of this newly identified restriction factor. A better understanding of the innate immune response to PEDV infection will aid the development of novel therapeutic targets and more effective vaccines against virus infection.

Innate Immune Evasion of Porcine Epidemic Diarrhea Virus through Degradation of F-box and WD repeat domain-containing 7 protein via Ubiquitin-proteasome Pathway

Porcine epidemic diarrhea virus (PEDV) causes a porcine disease associated with swine epidemic diarrhea. Different antagonistic strategies have been identified, and the mechanism by which PEDV infection impairs the production of interferon (IFN) and delays the activation of the IFN response to escape host innate immunity has been determined, but the pathogenic mechanisms of PEDV infection remain enigmatic. Our preliminary results revealed that endogenous F-box and WD repeat domain-containing 7 (FBXW7), the substrate recognition component of the SCF-type E3 ubiquitin ligase, is downregulated in PEDV-infected Vero E6 cells, according to the results from an isobaric tags for relative and absolute quantification (iTRAQ) analysis. Overexpression of FBXW7 in target cells makes them more resistant to PEDV infection, whereas ablation of FBXW7 expression by small interfering RNA (siRNA) significantly promotes PEDV infection. In addition, FBXW7 was verified as an innate antiviral factor capable of enhancing the expression of RIG-I and TBK1, and it was found to induce interferon-stimulated genes (ISGs), which led to an elevated antiviral state of the host cells. Moreover, we revealed that PEDV nonstructural protein 2 (nsp2) interacts with FBXW7 and targets FBXW7 for degradation through the K48-linked ubiquitin-proteasome pathway. Consistent with the results proven in vitro, FBXW7 reduction was also confirmed in different intestinal tissues from PEDV-infected specific-pathogen-free (SPF) pigs. Taken together, the data indicated that PEDV has evolved with a distinct antagonistic strategy to circumvent the host antiviral response by targeting the ubiquitin-proteasome-mediated degradation of FBXW7. Our findings provide novel insights into PEDV infection and pathogenesis. IMPORTANCE To counteract the host antiviral defenses, most viruses, including coronaviruses, have evolved with diverse strategies to dampen host IFN-mediated antiviral response, wither by interfering with or evading specific host regulators at multiple steps of this response. In this study, a novel antagonistic strategy was revealed showing that PEDV infection could circumvent the host innate response by targeted degradation of endogenous FBXW7 in target cells, a process that was verified to be a positive modulator for the host innate immune system. Degradation of FBXW7 hampers host innate antiviral activation and facilitates PEDV replication. Our findings reveal a new mechanism exploited by PEDV to suppress the host antiviral response.

Coronavirus Porcine Epidemic Diarrhea Virus Nucleocapsid Protein Interacts with p53 To Induce Cell Cycle Arrest in S-Phase and Promotes Viral Replication

Subversion of the host cell cycle to facilitate viral replication is a common feature of coronavirus infections. Coronavirus nucleocapsid (N) protein can modulate the host cell cycle, but the mechanistic details remain largely unknown. Here, we investigated the effects of manipulation of porcine epidemic diarrhea virus (PEDV) N protein on the cell cycle and the influence on viral replication. Results indicated that PEDV N induced Vero E6 cell cycle arrest at S-phase, which promoted viral replication (P < 0.05). S-phase arrest was dependent on the N protein nuclear localization signal S⁷¹NWHFYYLGTGPHADLRYRT⁹⁰ and the interaction between N protein and p53. In the nucleus, the binding of N protein to p53 maintained consistently high-level expression of p53, which activated the p53-DREAM pathway. The key domain of the N protein interacting with p53 was revealed to be S¹⁷¹RGNSQNRGNNQGRGASQNRGGNN¹⁹⁴ (N^S171-N194), in which G¹⁸³RG¹⁸⁵ are core residues. N^S171-N194 and G¹⁸³RG¹⁸⁵ were essential for N-induced S-phase arrest. Moreover, small molecular drugs targeting the N^S171-N194 domain of the PEDV N protein were screened through molecular docking. Hyperoside could antagonize N protein-induced S-phase arrest by interfering with interaction between N protein and p53 and inhibit viral replication (P < 0.05). The above-described experiments were also validated in porcine intestinal cells, and data were in line with results in Vero E6 cells. Therefore, these results reveal the PEDV N protein interacts with p53 to activate the p53-DREAM pathway, and subsequently induces S-phase arrest to create a favorable environment for virus replication. These findings provide new insight into the PEDV-host interaction and the design of novel antiviral strategies against PEDV. IMPORTANCE Many viruses subvert the host cell cycle to create a cellular environment that promotes viral growth. PEDV, an emerging and reemerging coronavirus, has led to substantial economic loss in the global swine industry. Our study is the first to demonstrate that PEDV N-induced cell cycle arrest during the S-phase promotes viral replication. We identified a novel mechanism of PEDV N-induced S-phase arrest, where the binding of PEDV N protein to p53 maintains consistently high levels of p53 expression in the nucleus to mediate S-phase arrest by activating the p53-DREAM pathway. Furthermore, a small molecular compound, hyperoside, targeted the PEDV N protein, interfering with the interaction between the N protein and p53 and, importantly, inhibited PEDV replication by antagonizing cell cycle arrest. This study reveals a new mechanism of PEDV-host interaction and also provides a novel antiviral strategy for PEDV. These data provide a foundation for further research into coronavirus-host interactions.

A persistent epidemic of porcine epidemic diarrhoea virus infection by serological survey of commercial pig farms in northern Vietnam

Background

Porcine epidemic diarrhoea (PED) is a highly contagious infectious disease with negative economic impacts on the swine industry. PED outbreaks were reported from 2009 to 2015, but sporadic infection has been observed until now in Vietnam. However, the seroprevalence of PEDV infection has not yet been reported for commercial pig farms in Vietnam. The aim of this study was to assess the seroprevalence of PEDV infection in Vietnamese pig farms to reveal the endemic status of PEDV in northern Vietnam.

Results

A serological survey of PEDV infection was carried out using indirect ELISA in commercial pig farms in Hai Duong, Hung Yen and Thai Binh provinces in northern Vietnam in 2019. Twenty sera were randomly collected from each of 10 commercial pig farms, from each province; none of the farms had vaccinated for PEDV. Serological evidence of natural PEDV infection, expressed as a high antibody titre, was observed in the pig farms in all 3 provinces. The OD values were significantly higher (p < 0.001) for pig sera from Thai Binh than from Hai Duong and Hung Yen. No significant differences (p > 0.05) were detected for seropositivity to PEDV based on locality, age, pig breed and farm size.

Conclusions

This study indicates serological evidence of natural PEDV infection with high antibody titre in commercial pig farms. PEDV infection was widespread among the pig population in these 3 provinces and that good management and strict biosecurity are needed at these pig farms.

The New Porcine Epidemic Diarrhea Virus Outbreak May Mean That Existing Commercial Vaccines Are Not Enough to Fully Protect Against the Epidemic Strains

Background: On October 30, 2020, piglets and sows in the farrowing house of a pig farm in Jiangxi showed clinical symptoms such as anorexia, watery diarrhea, and vomiting. Epidemiological test, clinical necropsy, and RT-PCR test were carried out on the pig farm for diagnosis. After comprehensive considerations, the disease was judged as porcine epidemic diarrhea virus infection.

Results: Thereafter, a series of comprehensive prevention and control measures such as emergency vaccination with autogenous vaccines were adopted. Half a month after inoculation with autogenous vaccines for the farm, the mortality rate of newborn piglets in the farrowing house began to decline, and production gradually returned to being stable. The second-generation sequencing analysis and phylogenetic analysis showed that the porcine epidemic diarrhea virus (PEDV) sequence obtained from the stool and small intestine samples of the diseased pigs on the farm was 97.8% homologous to the vaccine strain. At the same time, antibody testing found that the vaccinated pigs on the pig farm had satisfactory immune response.

Conclusion: This case indicated that the PEDV outbreak on the pig farm might aggravate owing to the strain being mutated and could escape the immune protection of the existing vaccine. This case has accumulated technical data for the clinical prevention and control of porcine epidemic diarrhea.

Isolation and Identification of a Recombinant Porcine Epidemic Diarrhea Virus With a Novel Insertion in S1 Domain

Porcine epidemic diarrhea virus (PEDV) is the major pathogen that causes diarrhea and high mortality in newborn piglets with devastating impact to the pig industry. Recombination and mutation are the main driving forces of viral evolution and genetic diversity of PEDV. In 2016, an outbreak of diarrhea in piglets occurred in an intensive pig farm in Central China. A novel PEDV isolate (called HNAY) was successfully isolated from clinical samples. Sequence analysis and alignment showed that HNAY possessed 21-nucleotide (nt) insertion in its S1 gene, which has never been reported in other PEDV isolates. Moreover, the sequence of the insertion was identical with the sequence fragment in PEDV N gene. Notably, the HNAY strain exhibited two unique mutations (T500A and L521Y) in the neutralizing epitopes of the S1 protein that were different from those of other PEDV variant strains and CV777-based vaccine strains. Additionally, PEDV HNAY might be derived from a natural recombination between two Chinese variant PEDV strains. Animal experiments demonstrated that HNAY displayed higher pathogenicity compared with two other clinical isolates. This study lays the foundation for better understanding of the genetic evolution and molecular pathogenesis of PEDV.

Establishment of stable Vero cell lines expressing TMPRSS2 and MSPL: A useful tool for propagating porcine epidemic diarrhea virus in the absence of exogenous trypsin

Porcine epidemic diarrhea virus (PEDV) is the causative agent of porcine epidemic diarrhea, causing substantial economic losses to the swine industry worldwide. However, the development of PEDV vaccine is hampered by its low propagation titer in vitro, due to difficulty in adapting to the cells and complex culture conditions, even in the presence of trypsin. Furthermore, the frequent variation, recombination, and evolution of PEDV resulted in reemergence and vaccination failure. In this study, we established the Vero/TMPRSS2 and Vero/MSPL cell lines, constitutively expressing type II transmembrane serine protease TMPRSS2 and MSPL, in order to increase the stability and titer of PEDV culture and isolation in vitro. Our study revealed that the Vero/TMPRSS2, especially Vero/MSPL cell lines, can effectively facilitate the titer and multicycle replication of cell-adapted PEDV in the absence of exogenous trypsin, by cleaving and activating PEDV S protein. Furthermore, our results also highlighted that Vero/TMPRSS2 and Vero/MSPL cells can significantly enhance the isolation of PEDV from the clinical tissue samples as well as promote viral infection and replication by cell-cell fusion. The successful construction of the Vero/TMPRSS2 and Vero/MSPL cell lines provides a useful approach for the isolation and propagation of PEDV, simplification of virus culture, and large-scale production of industrial vaccine, and the cell lines are also an important system to research PEDV S protein cleaved by host protease.

Clinical and molecular aspects of veterinary coronaviruses

Coronaviruses are a large group of RNA viruses that infect a wide range of animal species. The replication strategy of coronaviruses involves recombination and mutation events that lead to the possibility of cross-species transmission. The high plasticity of the viral receptor due to a continuous modification of the host species habitat may be the cause of cross-species transmission that can turn into a threat to other species including the human population. The successive emergence of highly pathogenic coronaviruses such as the Severe Acute Respiratory Syndrome (SARS) in 2003, the Middle East Respiratory Syndrome Coronavirus in 2012, and the recent SARS-CoV-2 has incentivized a number of studies on the molecular basis of the coronavirus and its pathogenesis. The high degree of interrelatedness between humans and wild and domestic animals and the modification of animal habitats by human urbanization, has favored new viral spreads. Hence, knowledge on the main clinical signs of coronavirus infection in the different hosts and the distinctive molecular characteristics of each coronavirus is essential to prevent the emergence of new coronavirus diseases. The coronavirus infections routinely studied in veterinary medicine must be properly recognized and diagnosed not only to prevent animal disease but also to promote public health.

Epigallocatechin-3-Gallate, the Main Polyphenol in Green Tea, Inhibits Porcine Epidemic Diarrhea Virus In Vitro

There are currently no licensed drugs against porcine epidemic diarrhea virus (PEDV), but vaccines are available. We identified a natural molecule, epigallocatechin-3-gallate (EGCG), the main polyphenol in green tea, which is effective against infection with PEDV. We used a variety of methods to test its effects on PEDV in Vero cells. Our experiments show that EGCG can effectively inhibit PEDV infections (with HLJBY and CV777 strains) at different time points in the infection using western blot analysis. We found that EGCG inhibited PEDV infection in a dose-dependent manner 24 h after the infection commenced using western blotting, plaque formation assays, immunofluorescence assays (IFAs), and quantitative reverse-transcriptase PCR (qRT-PCR). We discovered that EGCG treatment of Vero cells decreased PEDV attachment and entry into them by the same method analysis. Western blotting also showed that PEDV replication was inhibited by EGCG treatment. Whereas EGCG treatment was found to inhibit PEDV assembly, it had no effect on PEDV release. In summary, EGCG acts against PEDV infection by inhibiting PEDV attachment, entry, replication, and assembly.

PEDV Infection Generates Conformation-Specific Antibodies That Can Be Effectively Detected by a Cell-Based ELISA

Porcine epidemic diarrhea virus (PEDV) is a coronavirus that causes serious and highly contagious enteric disease in swine worldwide. In this study, we constructed a recombinant baculovirus (S-Bac) expressing full-length spike protein of the virulent epidemic genotype 2b (G2b) PEDV strain for serological studies of infected pigs. We found that most spike-specific antibodies produced upon PEDV infection in pigs are conformation-specific and they could be detected on S-Bac-infected insect cells by immunofluorescent assay, but they were insensitive to Western blot analysis, the typical method for antiserum analysis. These results indicated that spike conformation is crucial for serum recognition. Since it is difficult to purify trimeric spike membrane protein for conventional enzyme-linked immunosorbent assay (ELISA), we used S-Bac to generate a novel cell-based ELISA for convenient PEDV detection. We analyzed 100 pig serum samples, and our cell-based ELISA exhibited a sensitivity of 100%, a specificity of 97%, and almost perfect agreement [Cohen’s kappa coefficient value (κ) = 0.98] with immunocytochemical staining results. Our cell-based ELISA rapidly presented antigen for proper detection of conformation-specific antibodies, making PEDV detection more convenient, and it will be useful for detecting many viral diseases in the future.

Transcriptome analysis reveals modulation of the STAT family in PEDV-infected IPEC-J2 cells

BACKGROUND

Porcine epidemic diarrhea virus (PEDV) is a causative agent of serious viral enteric disease in suckling pigs. Such diseases cause considerable economic losses in the global swine industry. Enhancing our knowledge of PEDV-induced transcriptomic responses in host cells is imperative to understanding the molecular mechanisms involved in the immune response. Here, we analyzed the transcriptomic profile of intestinal porcine epithelial cell line J2 (IPEC-J2) after infection with a classical strain of PEDV to explore the host response.

RESULTS

In total, 854 genes were significantly differentially expressed after PEDV infection, including 716 upregulated and 138 downregulated genes. Functional annotation analysis revealed that the differentially expressed genes were mainly enriched in the influenza A, TNF signaling, inflammatory response, cytokine receptor interaction, and other immune-related pathways. Next, the putative promoter regions of the 854 differentially expressed genes were examined for the presence of transcription factor binding sites using the MEME tool. As a result, 504 sequences (59.02%) were identified as possessing at least one binding site of signal transducer and activator of transcription (STAT), and five STAT transcription factors were significantly induced by PEDV infection. Furthermore, we revealed the regulatory network induced by STAT members in the process of PEDV infection.

CONCLUSION

Our transcriptomic analysis described the host genetic response to PEDV infection in detail in IPEC-J2 cells, and suggested that STAT transcription factors may serve as key regulators in the response to PEDV infection. These results further our understanding of the pathogenesis of PEDV.

Several lineages of porcine epidemic diarrhea virus in Colombia during the 2014 and 2016 epidemic

Porcine epidemic diarrhea virus (PEDV) is a significant global, enteric coronavirus in pigs and was first reported in Colombia in 2014. However, the epidemiology, genetic and antigenic characteristics of the virus have yet to be investigated. In this study, we investigated the dissemination of PEDV by testing 536 samples by RT-PCR over a 33-month period. The 35.8% of positive samples (n = 192) was significantly different (p < .01) between months over time, with a higher number of positives samples occurring at the beginning of the epidemic and during the second epidemic wave within the main pork producing region. The complete PEDV genomes were generated for 21 strains, which shared a high nucleotide and amino acid sequence identity, except for the spike (S) gene. Recombinant regions were identified within the Colombian strains and between Colombian and Asian PEDV strains. Phylogenetic analysis of the 21 Colombian strains demonstrated the presence of 7 lineages that shared common ancestors with PEDV strains from the United States. Moreover, the antigenic analysis demonstrated residue differences in the neutralizing epitopes in the spike and nucleocapsid proteins. Our results illustrated the simultaneous introduction of the two PEDV genotypes (GIIa American pandemic and S-INDEL) into the Colombian swine industry during the 2014 PEDV epidemic and enhanced our understanding of the epidemiology and molecular diversity of PEDV in Colombia.

The Roles of Apoptosis in Swine Response to Viral Infection and Pathogenesis of Swine Enteropathogenic Coronaviruses

Apoptosis is a tightly regulated mechanism of cell death that plays important roles in various biological processes including biological evolution, multiple system development, anticancer, and viral infections. Swine enteropathogenic coronaviruses invade and damage villous epithelial cells of the small intestine causing severe diarrhea with high mortality rate in suckling piglets. Transmissible gastroenteritis virus (TGEV), Porcine epidemic diarrhea virus (PEDV), Porcine deltacoronavirus (PDCoV), and Swine acute diarrhea syndrome coronavirus (SADS-CoV) are on the top list of commonly-seen swine coronaviruses with a feature of diarrhea, resulting in significant economic losses to the swine industry worldwide. Apoptosis has been shown to be involved in the pathogenesis process of animal virus infectious diseases. Understanding the roles of apoptosis in host responses against swine enteropathogenic coronaviruses infection contribute to disease prevention and control. Here we summarize the recent findings that focus on the apoptosis during swine coronaviruses infection, in particular, TGEV, PEDV, PDCoV, and SADS-CoV.

Aloe extract inhibits porcine epidemic diarrhea virus in vitro and in vivo

Porcine epidemic diarrhea virus (PEDV) causes severe diarrhoea and high mortality in neonatal suckling piglets, leading to significant economic losses to the swine industry. Currently there are no adequate control strategies against circulating PEDV variants, making an urgent need to exploit effect antiviral therapies to compensate for vaccines. Here, we report that Aloe extract can hamper completely the proliferation of PEDV at a non-cytotoxic concentration of 16 mg/mL determined by CCK-8 assay in Vero and IPEC-J2 cells in vitro. Furthermore, time course analysis indicated the extract exerted its inhibition at the late stage of the viral life cycle. Moreover, we also confirmed that the extract can inactivated PEDV directly but did not act on the viral genome and S1 protein. Importantly, the extract at a relatively safety concentration of 100 mg/kg of body weight, which was confirmed in mice, could reduce virus load and pathological change in intestinal tract of pigs and protect newborn piglets from lethal challenge with highly pathogenic PEDV variant GDS01 infection, indicating that Aloe extract efficiently inhibited PEDV infection in vivo. Collectively, our findings suggest that the aqueous extract from the Aloe could inhibit PEDV replication in vitro and in vivo and might be a good target for drug development against PEDV.

Rapid differentiation of PEDV wild-type strains and classical attenuated vaccine strains by fluorescent probe-based reverse transcription recombinase polymerase amplification assay

Background

Porcine epidemic diarrhea virus (PEDV), an intestinal coronavirus that causes acute diarrhea and high mortality in suckling piglets, can result in high economic losses in the swine industry. In recent years, despite the use of China’s current vaccine immunization strategy, multiple types of PEDV strains were still found in immunized swine herds. Our research aims to explore a new rapid differentiation method to distinguish the different types of PEDV strains and assess the safety evaluation of classical attenuated vaccine strains in swine herds.

Results

In the study, a differential one-step quantitative real-time fluorescent reverse transcription recombinase polymerase amplification (real-time RT-RPA) method based on the PEDV universal real-time RT-RPA assay was established according to the ORF1 deletion sequences of three classical attenuated vaccine strains (PEDV attenuated vaccine KC189944, attenuated CV777 and DR13) and five Vero cell-adapted isolates (JS2008, SDM, SQ2014, SC1402, HLJBY), which could effectively differentiate PEDV classical attenuated vaccine strains from wild-type strains (PEDV classical wild strains and variant strains). The detection limits of PEDV RNA in the both PEDV real-time RT-RPA assays were 300 copies within 20 min at 39 °C, and the detection limits of classical attenuated vaccine strain CV777, Vero-cell-adapted isolate JS2008, and PEDV wild-type strain DX were 10^0.5 TCID₅₀/100 μL, 10^1.1 TCID₅₀/100 μL, and 10^1.2 TCID₅₀/100 μL, respectively. Both assays were highly specific for PEDV, showing no cross-reactivity with other enteral viruses.

Conclusion

This RPA method we developed is simple, time-effective, and safe and provides a reliable technical tool for the differential diagnosis and clinical epidemic surveillance of PEDV classical attenuated vaccine strains and wild-type strains.

Genome-wide analysis of long noncoding RNA profiles in Vero cells infected with porcine epidemic diarrhea virus

Porcine epidemic diarrhea (PED) is an acute enteric disease caused by porcine epidemic diarrhea virus (PEDV). In China, variant PEDV causes severe watery diarrhea, vomiting, and dehydration in piglets, leading to very high morbidity and mortality. However, the pathogenesis of PEDV is still not fully understood. In our study, we analyzed the long noncoding RNA (lncRNA) and mRNA expression profiles of PEDV GDgh16 in infected Vero cells at 60 h postinfection. A total of 61,790 annotated mRNAs, 14,247 annotated lncRNAs and 1290 novel lncRNAs were identified. A total of 227 annotated lncRNAs and 13 novel lncRNAs were significantly and differentially expressed after viral infection. The Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) databases were used to identify genes adjacent to the lncRNAs, and it was found that these lncRNAs were enriched in pathways related to immune and antiviral responses. Next, we selected candidate lncRNAs and their predicted target genes for study. RT-qPCR demonstrated that these lncRNAs and genes were differentially expressed after PEDV infection. Our study investigated the function of lncRNAs involved in PEDV infection, providing new insight into the pathogenic mechanisms of PEDV.

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.

Rapid and efficient detection methods of pathogenic swine enteric coronaviruses

Abstract

Porcine enteric coronaviruses (CoVs) cause highly contagious enteric diarrhea in suckling piglets. These COV infections are characterized by clinical signs of vomiting, watery diarrhea, dehydration, and high morbidity and mortality, resulting in significant economic losses and tremendous threats to the pig farming industry worldwide. Because the clinical manifestations of pigs infected by different CoVs are similar, it is difficult to differentiate between the specific pathogens. Effective high-throughput detection methods are powerful tools used in the prevention and control of diseases. The immune system of piglets is not well developed, so serological methods to detect antibodies against these viruses are not suitable for rapid and early detection. This paper reviews various PCR-based methods used for the rapid and efficient detection of these pathogenic CoVs in swine intestines.

Key points

Swine enteric coronaviruses (CoVs) emerged and reemerged in past years.

Enteric CoVs infect pigs at all ages with high mortality rate in suckling pigs.

Rapid and efficient detection methods are needed and critical for diagnosis.

Cold Exposure-Induced Up-Regulation of Hsp70 Positively Regulates PEDV mRNA Synthesis and Protein Expression In Vitro

Porcine epidemic diarrhea (PED) is a highly contagious, intestinal infectious disease caused by porcine epidemic diarrhea virus (PEDV). PEDV as an emerging and re-emerging epizootic virus of swine causes substantial economic losses to the pig industry in China and other countries. In China, the occurrence of PED shows significant seasonal variations, usually outbreak during the winter season. The epidemic characteristics of PED may be highly correlated with the changes of ambient temperature. However, molecular mechanism on the seasonal occurrence of PED still remains unclear. It has been widely observed that low ambient temperature up-regulates the expression of host heat shock protein 70 (Hsp70). Here, we showed that nucleotide and protein levels of Hsp70 were up-regulated in the intestinal of cold exposed pig and cold exposed Vero E6 cells. We found that overexpression of Hsp70 could increase PEDV mRNA synthesis and protein expression in Vero E6 and IPEC-J2 cells, while the siRNAs mediated knockdown of Hsp70 and VER155008 mediated inhibition of Hsp70 resulted in inhibition of viral mRNA synthesis and protein expression in Vero E6 cells. These data suggested that Hsp70 positively regulated PEDV mRNA synthesis and protein expression, which being helpful for understanding the seasonality of PED epidemics and development of novel antiviral therapies in the future.

Porcine Epidemic Diarrhoea Virus Induces Cell-cycle Arrest through the DNA Damage-signalling Pathway

Introduction

Porcine epidemic diarrhoea virus (PEDV) infection causes watery diarrhoea, vomiting, anorexia, and weight loss, especially among neonatal piglets, inflicting on them morbidity and mortality potentially reaching 90%–100%. Despite it being known that certain mammalian cell phases are arrested by PEDV, the mechanisms have not been elucidated, and PEDV pathogenesis is poorly understood. This study determined the effect of an epidemic PEDV strain on cell cycle progression.

Material and Methods

We observed the effect of the PEDV SHpd/2012 strain on an infected Vero cell cycle through flow cytometry and Western blot, investigating the interrelationships of cell-cycle arrest, the DNA damage–signalling pathway caused by PEDV and the phosphorylation levels of the key molecules Chk.2 and H2A.X involved upstream and downstream in this pathway.

Results

PEDV induced Vero cell-cycle arrest at the G1/G0 phase. The phosphorylation levels of Chk.2 and H2A.X increased with the prolongation of PEDV infection, and no significant cell-cycle arrest was observed after treatment with ATM or Chk.2 inhibitors. The proliferation of PEDV was also inhibited by treatment with ATM or Chk.2 inhibitors.

Conclusion

PEDV-induced cell-cycle arrest is associated with activation of DNA damage–signalling pathways. Our findings elucidate the molecular basis of PEDV replication and provide evidence to support further evaluation of PEDV pathogenesis.

Attenuated porcine-derived type 2 bovine viral diarrhea virus as vector stably expressing viral gene

Infectious bovine viral diarrhea virus (BVDV) cDNA clones have been used for the expression of classical swine fever virus (CSFV) genes for immune prevention and control. However, can it be used for the expression of an allogenetic fragment? To answer this question, a BVDV chimeric virus expressing the spike (S) antigen fragment of porcine epidemic diarrhea virus (PEDV) was constructed. Antigen S_499-602 was inserted into pig-derived BVDV-2 infectious cDNA clone pASH28 in tandem by overlapping PCR, located between the seventh and eighth amino acids at the N-terminus of the capsid (C) protein of BVDV. Indirect immunofluorescence assay confirmed that the chimeric virus vASH-dS312 containing double S_499-602 sequences was successfully assembled, which could react with the monoclonal antibody (MAb) against BVDV E2 and PEDV S proteins. Further western blot analysis confirmed that the exogenous S_499-602 double protein could be stably expressed. Next, the chimeric virus vASH-dS312 was administered to BALB/C mice either orally or by intramuscular injection. The immunized mice were healthy and showed no signs of toxicity. IgG against BVDV and PEDV antibodies could be detected in the mice administered vASH-dS312 by intramuscular injection, which had neutralization activity against BVDV and PEDV. Thus, this study reported a new insertion site in the BVDV infectious cDNA clone that could successfully express an allogenetic antigen.

Porcine Coronaviruses

Transmissible gastroenteritis virus (TGEV), porcine epidemic diarrhoea virus (PEDV), and porcine deltacoronavirus (PDCoV) are enteropathogenic coronaviruses (CoVs) of swine. TGEV appearance in 1946 preceded identification of PEDV (1971) and PDCoV (2009) that are considered as emerging CoVs. A spike deletion mutant of TGEV associated with respiratory tract infection in piglets appeared in 1984 in pigs in Belgium and was designated porcine respiratory coronavirus (PRCV). PRCV is considered non-pathogenic because the infection is very mild or subclinical. Since PRCV emergence and rapid spread, most pigs have become immune to both PRCV and TGEV, which has significantly reduced the clinical and economic importance of TGEV. In contrast, PDCoV and PEDV are currently expanding their geographic distribution, and there are reports on the circulation of TGEV-PEDV recombinants that cause a disease clinically indistinguishable from that associated with the parent viruses. TGEV, PEDV and PDCoV cause acute gastroenteritis in pigs (most severe in neonatal piglets) and matches in their clinical signs and pathogenesis. Necrosis of the infected intestinal epithelial cells causes villous atrophy and malabsorptive diarrhoea. Profuse diarrhoea frequently combined with vomiting results in dehydration, which can lead to the death of piglets. Strong immune responses following natural infection protect against subsequent homologous challenge; however, these viruses display no cross-protection. Adoption of advance biosecurity measures and effective vaccines control and prevent the occurrence of diseases due to these porcine-associated CoVs. Recombination and reversion to virulence are the risks associated with generally highly effective attenuated vaccines necessitating further research on alternative vaccines to ensure their safe application in the field.

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.

Prevalence and phylogenetic analysis of porcine diarrhea associated viruses in southern China from 2012 to 2018

Background

In China, large-scale outbreaks of severe diarrhea caused by viruses have occurred in pigs since late 2010. To investigate the prevalence and genetic evolution of diarrhea-associated viruses responsible for the outbreaks, a total of 2987 field diarrheal samples collected from 168 pig farms in five provinces in Southern China during 2012–2018 were tested.

Results

Porcine epidemic diarrhea virus (PEDV) was most frequently detected virus with prevalence rates between 50.21 and 62.10% in samples, and 96.43% (162/168) in premises, respectively. Porcine deltacoronavirus (PDCoV) was the second prevalent virus with prevalence rates ranging from 19.62 to 29.19% in samples, and 70.24% (118/168) in premises, respectively. Both transmissible gastroenteritis virus (TGEV) and porcine rotavirus (PoRV) were detected at low prevalence rates of < 3% in samples and 10.12% in premises. In this study, we identified a newly emerged swine acute diarrhea syndrome coronavirus (SADS-CoV) in diarrheal samples of piglets from Fujian province in Southern China, and the prevalence rate of SADS-CoV was 10.29% (7/68). Co-infections of these diarrhea-associated viruses were common. The most frequent co-infection was PEDV with PDCoV, with an average detection rate of 12.72% (380/2987, ranging from 8.26–17.33%). Phylogenetic analysis revealed that PEDVs circulating in Southern China during the last 7 years were clustered with the variant strains of PEDV in genotype IIa. The most frequent mutations were present in the collagenase equivalent (COE) and epitope regions of the spike gene of the PEDVs currently circulating in the field. Genetic relationships of PDCoVs were closely related with Chinese strains, other than those present in the USA, South Korea, Thailand and Lao’s public.

Conclusions

The findings of this study indicated that variant PEDV, PDCoV, and SADS-CoV were leading etiologic agents of porcine diarrhea, and either mono-infections or co-infections of pathogenic enteric CoVs were common in pigs in Southern China during 2012–2018. Thus, significant attention should be paid in order to effectively prevent and control porcine viral diarrhea.

A molecular epidemiological investigation of PEDV in China: Characterization of co-infection and genetic diversity of S1-based genes

Porcine epidemic diarrhoea virus (PEDV) is an emerging and re‐emerging epizootic virus of swine that causes substantial economic losses to the pig industry in China and other countries. The variations in the virus, and its co‐infections with other enteric viruses, have contributed to the poor control of PEDV infection. In the current study, a broad epidemiological investigation of PEDV was carried out in 22 provinces or municipalities of China during 2015–2018. The enteric viruses causing co‐infection with PEDV and the genetic diversity of the PEDV S1 gene were also analysed. The results indicated that, of the 543 diarrhoea samples, 66.85% (363/543) were positive for PEDV, and co‐infection rates of PEDV with 13 enteric viruses ranged from 3.58% (13/363) to 81.55% (296/363). Among these enteric viruses, the signs of diarrhoea induced by PEDV were potentially associated with co‐infections with porcine enterovirus 9/10 (PEV) and torque teno sus virus 2 (TTSuV‐2) (p < .05). The 147 PEDV strains identified in our study belong to Chinese pandemic strains and exhibited genetic diversity. The virulence‐determining S1 proteins of PEDV pandemic strains were undergoing amino acid mutations, in which S58_S58insQGVN–N135dup–D158_I159del‐like mutations were common patterns (97.28%, 143/147). When compared with 2011–2014 PEDV strains, the amino acid mutations of PEDV pandemic strains were mainly located in the N‐terminal domain of S1 (S1‐NTD), and 21 novel mutations occurred in 2017 and 2018. Furthermore, protein homology modelling showed that the mutations in pattern of insertion and deletion mutations of the S1 protein of PEDV pandemic strains may have caused structural changes on the surface of the S1 protein. These data provide a better understanding of the co‐infection and genetic evolution of PEDV in China.

Isolation and characterization of a variant subgroup GII-a porcine epidemic diarrhea virus strain in China

Background

Highly virulent variants of porcine epidemic diarrhea virus (PEDV) have been closely associated with recent outbreaks of porcine epidemic diarrhea (PED) in China, which have resulted in severe economic losses to the pork industry.

Methods

In the current study, the variant PEDV strain HM2017 was isolated and purified and a viral growth curve was constructed according to the median tissue culture infective dose (TCID50). HM2017 were amplify with RT-PCR and analyzed by phylogeny analysis. Animal pathogenicity experiment was carried to evaluate the HM2017 clinical assessment.

Results

Genome-based phylogenetic analysis revealed that PEDV strain HM2017 was clustered into the variant subgroup GII-a that is currently circulating in pig populations in China. The highest median tissue culture infectious dose of strain HM2017 after 15 passages in Vero cells was 1.33 × 10⁷ viral particles/mL. Strain HM2017 was highly virulent to suckling piglets, which exhibited clinical symptoms at 12 h post-infection (hpi) (i.e., weight loss at 12–84 hpi, increased body temperatures at 24–48 hpi, high viral loads in the jejunum and ileum, and 100% mortality by 84 hpi).

Conclusion

The present study reports a variant subgroup GII-a PEDV HM2017 strain in China and characterize its pathogenicity. PEDV strain HM2017 of subgroup GII-a presents a promising vaccine candidate for the control of PED outbreaks in China.

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A variant subgroup GII-a PEDV strain HM2017 was successfully isolated in China.

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PEDV strain HM2017 appeared to be highly virulent in suckling piglets.

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PEDV strain HM2017 was well adapted to Vero cells, as evidenced by the rapid growth.

Attenuation of a virulent swine acute diarrhea syndrome coronavirus strain via cell culture passage

Swine acute diarrhea syndrome coronavirus (SADS-CoV) is a newly identified enteric alphacoronavirus that causes fatal diarrhea in newborn piglets in China. Here, we propagated a virulent strain SADS-CoV/CN/GDWT/2017 in Vero cells for up to 83 passages. Four strains of SADS-CoV/GDWT-P7, -P18, -P48 and -P83 were isolated and characterized. Sequence alignments showed that these four novel strains exhibited 16 nucleotide mutations and resultant 10 amino acid substitutions in open reading frame 1a/1b, spike, NS3a, envelope, membrane and nucleocapsid proteins. Furthermore, a 58-bp deletion in NS7a/7b was found in P48 and P83 strains, which led to the loss of NS7b and 38 amino acid changes of NS7a. Pig infection studies showed that the P7 strain caused typical watery diarrhea, while the P83 strain induced none-to-mild, delayed and transient diarrhea. This is the first report on cell adaption of a virulent SADS-CoV strain, which gives information on the potential virulence determinants of SADS-CoV.

Rapid manipulation of the porcine epidemic diarrhea virus genome by CRISPR/Cas9 technology

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A reverse genetics system for highly virulent PEDV strain AJ1102 was established.

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A recombinant PEDV was generated using CRISPR/Cas9 technology.

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Recombinant PEDV can be created within one week using this strategy.

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Provides an efficient platform for PEDV genome manipulation and vaccine development.

Porcine epidemic diarrhea virus (PEDV) is a highly pathogenic enteric coronavirus causing lethal watery diarrhea in suckling piglets. Reverse genetics is a valuable tool to study the functions of viral genes and to generate vaccine candidates. In this study, a full-length infectious cDNA clone of the highly virulent PEDV strain AJ1102 was assembled in a bacterial artificial chromosome (BAC). The rescued virus (rAJ1102) exhibited similar proliferation characteristics in vitro to the wildtype AJ1102. Using CRISPR/Cas9 technology, a recombinant virus rAJ1102-ΔORF3-EGFP in which the ORF3 gene was replaced with an EGFP gene, was successfully generated, and its proliferation characteristics were compared with the parental rAJ1102. Importantly, it just took one week to construct the recombinant PEDV rAJ1102-ΔORF3-EGFP using this method, providing a more efficient platform for PEDV genome manipulation, which could also be applied to other RNA viruses.

Characterization and pathogenicity of Vero cell-attenuated porcine epidemic diarrhea virus CT strain

Background

Porcine epidemic diarrhea virus (PEDV) has caused enormous economic losses to the global pig industry. Currently available PEDV vaccine strains have limited protective effects against PEDV variant strains.

Methods

In this study, the highly virulent epidemic virus strain CT was serially passaged in Vero cells for up to 120 generations (P120). Characterization of the different passages revealed that compared with P10 and P64, P120 had a higher viral titer and more obvious cytopathic effects, thereby demonstrating better cell adaptability.

Results

Pathogenicity experiments using P120 in piglets revealed significant reductions in clinical symptoms, histopathological lesions, and intestinal PEDV antigen distribution; the piglet survival rate in the P120 group was 100%. Furthermore, whole-genome sequencing identified 13 amino acid changes in P120, which might be responsible for the attenuated virulence of P120.

Conclusions

Thus, an attenuated strain was obtained via cell passaging and that this strain could be used in preparing attenuated vaccines.

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.

Integrin αvβ3 enhances replication of porcine epidemic diarrhea virus on Vero E6 and porcine intestinal epithelial cells

The entry mechanism of porcine epidemic diarrhea virus (PEDV) remains unclear, especially the virus receptor. Our previous study revealed a potential correlation between integrin αvβ3 and PEDV infection. In the current study, the effect of overexpression, silencing, antibody inhibition, and co-expression with porcine aminopeptidase N (pAPN) of integrin αvβ3 on PEDV infection was investigated and analyzed in African green monkey Vero E6 cells and porcine intestinal epithelial cells (IECs) using the classical strain CV777 and variant strain HM2017 of PEDV. Integrin αvβ3 significantly enhanced the replication of the classical and variant strains of PEDV in Vero E6 cells and IECs. The integrin αv and β3 subunits were both involved in the enhancement of PEDV infection, the Arg-Gly-Asp peptides targeting integrin αvβ3 significantly inhibited replication of PEDV in Vero E6 cells, and co-expression of integrin αvβ3 with pAPN significantly enhanced replication of PEDV in Vero E6 and BHK-21 cells. These results demonstrate that integrin αvβ3 enhances PEDV replication in Vero E6 cells and IECs. These data provide novel insights into the entry mechanism of PEDV.

Specific recombinant proteins of porcine epidemic diarrhea virus are immunogenic, revealing their potential use as diagnostic markers

Given the highly contagious and acute nature of porcine epidemic diarrhea (PED), especially in piglets, there is an urgent need for the development of rapid and sensitive diagnostic assays. The diagnostic potentials of specific porcine epidemic diarrhea virus (PEDV) accessory and nonstructural proteins, if any, have not yet been investigated. In order to determine and compare which of the viral proteins may be useful as diagnostic antigens, whole virus (WV) particles and a panel of structural and nonstructural PEDV proteins [spike subunit 1 (S1), the C-terminal part of ORF3 (ORF3C), envelope (E), nonstructural protein 1 (Nsp1), Nsp2, Ac (acidic domain of Nsp3), and ADRP (ADP-ribose-1-monophosphatase domain of Nsp3), expressed individually in bacterial and/or mammalian cells] were tested for reactivity with sera from PEDV-infected pigs by ELISA and/or western blot analysis. According to western blots, serum antibody interactions with the S1 protein were relatively more sensitive and specific than ORF3C, E and Ac. Furthermore, a total of 851 serum samples from diarrheal pigs of different ages were analyzed by ELISA, with most showing immune-reactivity towards the WV, S1, ORF3C, and E proteins. The earliest IgG antibody response was observed in the one-week-old piglets, with similar antibody ontogeny and patterns of seroconversion for S1, ORF3C, E, and WV antigens. In addition, the pattern of neutralizing antibody was more similar to that of IgA in weaning piglets after PEDV infection. Collectively, these data provide more reliable information on the host immune response to different viral proteins, which will be useful for development of novel serological assays and for design of vaccines that better stimulate protective immunity.

Global Mapping of H3K4 Trimethylation (H3K4me3) and Transcriptome Analysis Reveal Genes Involved in the Response to Epidemic Diarrhea Virus Infections in Pigs

Porcine epidemic diarrhea virus (PEDV) is currently detected as the main pathogen causing severe diarrhea in pig farms. The phenotypic alterations induced by pathogenic infections are usually tightly linked with marked changes in epigenetic modification and gene expression. We performed global mapping of H3K4 trimethylation (H3K4me3) and transcriptomic analyses in the jejunum of PEDV-infected and healthy piglets using chromatin immunoprecipitation sequencing and RNA-seq techniques. A total of 1885 H3K4me3 peaks that are associated with 1723 genes were characterized. Moreover, 290 differentially expressed genes were identified, including 104 up-regulated and 186 down-regulated genes. Several antiviral genes including 2'-5'-oligoadenylate synthetase 1 (OAS1), 2'-5'-oligoadenylate synthetase 2 (OAS2), ephrin B2 (EFNB2), and CDC28 protein kinase regulatory subunit 1B (CKS1B) with higher H3K4me3 enrichment and expression levels in PEDV-infected samples suggested the potential roles of H3K4me3 deposition in promoting their expressions. Transcription factor annotation analysis highlighted the potential roles of two transcription factors interferon regulatory factor 8 (IRF8) and Kruppel like factor 4 (KLF4) in modulating the differential expression of genes involved in PEDV infection. The results provided novel insights into PEDV infection from the transcriptomic and epigenetic layers and revealed previously unknown and intriguing elements potentially involved in the host responses.

A heterologous 'prime-boost' anti-PEDV immunization for pregnant sows protects neonatal piglets through lactogenic immunity against PEDV

Abstract

Porcine epidemic diarrhoea virus (PEDV) causes severe diarrhoea in neonatal suckling piglets with a high mortality. Maternal vaccines that can induce lactogenic immunity to protect suckling piglets via colostrums and milk are pivotal for the prevention and control of PEDV infection in neonatal suckling piglets. In this study, a group of pregnant sows were first orally immunized with coated PEDV‐loaded microspheres and boosted with killed PEDV vaccines (heterologous prime‐boost). It has been detected that the levels of PEDV‐specific antibodies (IgG and IgA) in their sera and milks were higher than other negative groups (P < 0·001 or P < 0·05). Furthermore, it has been proved by the neutralization assay that the induced antibodies could significantly inhibit virus infection as compared to other negative groups (P < 0·01 or P < 0·05). Importantly, after PEDV challenge, more than 90% of the suckling piglets delivered by the sows in the heterologous prime‐boost group were completely protected. Overall, the results show that ‘heterologous prime‐boost’ form is an efficient and effective way to provide protection for suckling piglets against PEDV through lactogenic immunity.

Significance and Impact of the Study

As a widespread swine pathogen, PEDV affects the swine industry enormously. It causes enteritis in swine of all ages and is often fatal in neonatal piglets. Our data show that pregnant sows were immunized with ‘coated PEDV‐loaded microspheres + killed PEDV vaccines’ (heterologous prime‐boost immunization) could protect more than 90% suckling piglets delivered by the sows against the virus. These findings provide a new model of developing safe and effective immunizations for newborn animals against established and emerging enteric infections.

Recombinant Chimeric Transmissible Gastroenteritis Virus (TGEV) - Porcine Epidemic Diarrhea Virus (PEDV) Virus Provides Protection against Virulent PEDV

Porcine epidemic diarrhea virus (PEDV) is an enteric coronavirus causing high morbidity and mortality in porcine herds worldwide. Although both inactivated and live attenuated vaccines have been extensively used, the emergence of highly virulent strains and the recurrent outbreaks even in vaccinated farms highlight the need of effective vaccines. Engineering of genetically defined live attenuated vaccines is a rational approach for novel vaccine development. In this line, we engineered an attenuated virus based on the transmissible gastroenteritis virus (TGEV) genome, expressing a chimeric spike protein from a virulent United States (US) PEDV strain. This virus (rTGEV-RS-SPEDV) was attenuated in highly-sensitive five-day-old piglets, as infected animals did not lose weight and none of them died. In addition, the virus caused very minor tissue damage compared with a virulent virus. The rTGEV-RS-SPEDV vaccine candidate was also attenuated in three-week-old animals that were used to evaluate the protection conferred by this virus, compared with the protection induced by infection with a virulent PEDV US strain (PEDV-NVSL). The rTGEV-RS-SPEDV virus protected against challenge with a virulent PEDV strain, reducing challenge virus titers in jejunum and leading to undetectable challenge virus RNA levels in feces. The rTGEV-RS-SPEDV virus induced a humoral immune response specific for PEDV, including neutralizing antibodies. Altogether, the data indicated that rTGEV-RS-SPEDV is a promising vaccine candidate against virulent PEDV infection.

A TaqMan probe-based real-time PCR to differentiate porcine epidemic diarrhea virus virulent strains from attenuated vaccine strains

Porcine epidemic diarrhea virus (PEDV) is an important pathogen causing severe watery diarrhea, vomiting, dehydration, and death in sucking piglets. Attenuated vaccines have been used widely in sows in order to protect piglets through passive lactogenic immunity. Rapid and sensitive detection methods for differentiating attenuated vaccine strains from virulent ones are essential and practical in PEDV prevention and control. Based on the deletion mutation in ORF3 gene sequence, a TaqMan probe-based real-time quantitative PCR (TaqMan qPCR) was developed to distinguish PEDV virulent strains from attenuated vaccine ones in this study. The TaqMan qPCR could specifically detect PEDV virulent strain but not attenuated vaccine strain and other viruses. At least 37 DNA copies and PEDV of 0.995 TCID₅₀ could be detected by TaqMan qPCR. The reproducibility was evaluated using various dilution of plasmids carrying PEDV ORF3 gene and virulent PEDV, and the inter-assay coefficient of variation (CV) was less than 0.44%. The TaqMan qPCR was further applied to detect 38 samples including intestines and their contents, fecal swabs, and mesenteric lymph nodes. Meanwhile, indirect immunofluorescence assay (IFA) was employed to detect PEDV-specific antigen. PEDV positive rates were 31.58% (12/38) and 26.32% (10/38) by TaqMan PCR and IFA, respectively, which suggested that the former was more sensitive than the latter. The TaqMan qPCR based on PEDV ORF3 gene could be a valuable tool in diagnose of porcine epidemic diarrhea and in molecular epidemiological study of the virulent PEDV.

Porcine epidemic diarrhea virus infections induce apoptosis in Vero cells via a reactive oxygen species (ROS)/p53, but not p38 MAPK and SAPK/JNK signalling pathways

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p53 is activated, translocated to nucleus and involved in PEDV-induced apoptosis.

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ROS are accumulated during PEDV infection and involved in PEDV-induced apoptosis.

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ROS are the upper stream of p53 in PEDV infection.

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This is the first report that PEDV induce Vero cells apoptosis via ROS/p53 signal pathway.

Porcine epidemic diarrhea virus (PEDV) is a member of Coronavirus, which causes severe watery diarrhea in piglets with high morbidity and mortality. ROS and p53 play key roles in regulating many kinds of cell process during viral infection, however, the exact function in PEDV-induced apoptosis remains unclear. In this study, the pro-apoptotic effect of PEDV was examined in Vero cells and we observed that PEDV infection increased MDM2 and CBP, promoted p53 phosphorylation at serine 20 and, promoted p53 nuclear translocation, leading to p53 activation in Vero cells. Treatment with the p53 inhibitor PFT-α could significantly inhibit PEDV-induced apoptosis. We also observed PEDV infection induced time-dependent ROS accumulation. Treatment with antioxidants, such as pyrrolidine dithiocarbamate (PDTC) or N-acetylcysteine (NAC), significantly inhibited PEDV-induced apoptosis.

Moreover, further inhibition tests were established to prove that p53 was regulated by ROS in PEDV-induced apoptosis. In addition, we also found that p38 MAPK and SAPK/JNK were activated in PEDV-infected Vero cells. However, treatment with the p38 MAPK inhibitor SB203580, and the SAPK/JNK inhibitor SP600125 reversed PEDV-induced apoptosis. Taken together, the results of this study demonstrate that activated p53 and accumulated ROS participated in PEDV-induced apoptosis and p53 could be regulated by ROS during PEDV infection. Activated p38 MAPK and SAPK/JNK exerted no influence on PEDV-induced apoptosis. These findings provide new insights into the function of p53 and ROS in the interaction of PEDV with Vero cells.

The serological response in dogs inoculated with canine distemper virus vaccine at the acupuncture point governing vessel-14: A randomized controlled trial

The improvement of immunity to vaccination has historically focused on manipulation of antigen presentation rather than the host. Immune modulation by stimulating specific acupuncture points along the Meridian System has been practiced in Traditional Chinese Medicine. The purpose of this study was to quantitatively determine whether acupoint vaccination, in which vaccine is administered at an acupuncture point in dogs, has the potential to enhance the immune response. A randomized controlled trial was conducted to compare the effectiveness of acupoint vaccination versus a conventional method, based on humoral immune response in dogs given Canine Distemper Vaccine (CDV). One hundred client-owned dogs were admitted to the study with following characteristics: (1) passed a routine physical exam, (2) aged between 1 and 10 years old, (3) had no history of chronic disease, and (4) were not on immunomodulating medications. Dogs were randomly assigned to either the Acupuncture group inoculated at the acupoint Governing Vessel (GV)-14, or to the Control group inoculated conventionally at a non-acupuncture site. Mean changes from Day0 to Day14 of the response to CDV vaccination, measured by serum neutralization (SN) titers with log-transformation for reducing outlier effects, were compared between groups. No significant difference was found between groups in age, weight, or sex (all p >0.2). Both groups had significant increases of CDV SN titer post-vaccination (p < 0.001). The mean increase in Acupuncture group (0.72; SD = 0.79) was significantly greater than that of the Control group (0.36; SD = 0.67); p = 0.019. Inference on percentage of change in raw SN titer data further revealed that the effects in the Acupuncture group was significantly greater than the Control group (242% vs. 83%; p = 0.02). This study demonstrated that Acupoint vaccination at GV-14 resulted in a significantly elevated humoral immune response to CDV vaccine compared to Controls, which suggests the potential of acupoint vaccination to enhance the immune response.

Isolation and identification of a variant subtype G 2b porcine epidemic diarrhea virus and S gene sequence characteristic

Porcine epidemic diarrhea (PED) which is caused by porcine epidemic diarrhea virus (PEDV), is an intestinal communicable disease. In recent years, though pigs have been immunized with the vaccines in pig farms, PED still broke out and caused severe economic losses to the swine industry in the northeast China. In this study, the sample was positive for PEDV variant strains via the nano-nest PCR. The strain was successfully isolated from positive samples and was serially passaged in Vero-E6 cells. In addition, the strain was identified via electron microscopy observation, indirect immunofluorescence assay and infection experiment in newborn piglets and named PEDV CH/JLDH/2016 strain (Accession No. MF346935). Phylogenetic analysis of the S gene showed that the CH/JLDH/2016 strain was clustered into G2b subgroup. Comparing with the CV777 vaccine strain, amino acid sequence analysis of CH/JLDH/2016 strain showed that 15 nucleotides were inserted and 9 were absent in S gene, whose amino acid sequence it educed insertions of 5 amino acids(⁵⁸NQGX⁶¹ and ¹⁴⁵N) and absences of 3 amino acids(¹⁶⁴RD¹⁶⁵ and ¹²⁰⁴Y). Our strain, in the SS2 epitope have no amino acid, variant while in SS6 epitope, Y changed into S in 776th amino acid. The results indicated that PEDV G2b variant strains have been emerged in Jilin province. The identification of new types of PEDV variant strains would stimulate the development of effective vaccines for the prevention and control of PED. The novel vaccines that based on these newly identified PEDV variant strains may contribute to the control of PED outbreaks in China.

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The isolated variant PEDV from Dehui, China, was distributed into the G2b subgroup.

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The differences of strains help to explain why PEDV vaccines have no protection in most piglets in China.

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Our variant PEDV with the absence of Y in the 776^th aa was from G2b subgroup while others were from G1a subgroup.

Construction of a Recombinant Lactococcus lactis Strain Expressing a Variant Porcine Epidemic Diarrhea Virus S1 Gene and Its Immunogenicity Analysis in Mice

Porcine epidemic diarrhea caused by porcine epidemic diarrhea virus (PEDV) is a highly contagious disease in newborn piglets. The spike (S) protein is the surface glycoprotein of PEDV, which can induce specific neutralization antibodies and is a candidate antigen for vaccination attempts. In our study, the S1 region of PEDV strain CH/JLDH/2016 spike gene was inserted into the Lactococcus lactis expression vector, pNZ8149, resulting in recombinant plasmid pNZ8149-S1, and the immunogenicity of recombinant L. lactis pNZ8149-S1/NZ3900 was evaluated in mice. After immunization, significantly higher levels of anti-PEDV serum IgG antibodies and mucosal sIgA antibodies were detected in mice orally administered with pNZ8149-S1/NZ3900, compared with control groups pNZ8149/NZ3900, NZ3900, and phosphate buffered saline (p < 0.01). Lymphocyte proliferation assay results showed that the recombinant L. lactis pNZ8149-S1/NZ3900 significantly stimulated the proliferation of splenic lymphocytes (p < 0.01). In addition, the recombinant L. lactis vaccine could induce high levels of IL-4 and IFN-γ in immunized mice (p < 0.01). The results of our study suggest that the recombinant L. lactis pNZ8149-S1/NZ3900 can provide a promising vaccine strategy against PEDV infection.

Biological characterization and pathogenicity of a newly isolated Chinese highly virulent genotype GIIa porcine epidemic diarrhea virus strain

Since 2010, continual outbreaks of highly virulent variants of porcine epidemic diarrhea virus (PEDV) belonging to genotype GII have led to serious economic losses for the Chinese swine industry. To better understand the biological characteristics and pathogenicity of the current prevalent Chinese PEDV field strains, in this study, a highly virulent Chinese genotype GIIa PEDV strain, CH/HBXT/2018, was isolated and serially propagated using Vero cells. Sequencing and phylogenetic analysis showed that strain CH/HBXT/2018 contained novel insertion and deletion mutations in the S gene region relative to the classical strain and belonged to the genotype GIIa, similar to other recently isolated PEDV strains from China and the United States. Pig infection studies indicated that the CH/HBXT/2018 strain was highly virulent in suckling piglets, and the median pig diarrhea dose (PDD₅₀) was 8.63 log₁₀PDD₅₀/3 mL at 7 days postinfection (DPI). The results of the present study are important for future PEDV challenge studies and the development of new PEDV vaccines based on prevalent field strains for the prevention and control of PED in China.

Identification of Neutralizing Monoclonal Antibodies Targeting Novel Conformational Epitopes of the Porcine Epidemic Diarrhoea Virus Spike Protein

Since 2010, newly identified variants of porcine epidemic diarrhoea virus (PEDV) have caused high mortality in neonatal piglets which has devastated the swine industry. The spike (S) glycoprotein of PEDV contains multiple neutralizing epitopes and is a major target for PEDV neutralization and vaccine development. To understand the antigenicity of the new PEDV variant, we characterized the neutralizing epitopes of a new genotype 2b PEDV isolate from Taiwan, PEDV Pintung 52 (PEDV-PT), by the generation of neutralizing monoclonal antibodies (NmAbs). Two NmAbs, P4B-1, and E10E-1–10 that recognized the ectodomain of the full-length recombinant PEDV S protein and exhibited neutralizing ability against the PEDV-PT virus were selected. Recombinant truncated S proteins were used to identify the target sequences for the NmAbs and P4B-1 was shown to recognize the C-terminus of CO-26K equivalent epitope (COE) at amino acids (a.a.) 575–639 of the PEDV S. Interestingly, E10E-1–10 could recognize a novel neutralizing epitope at a.a. 435–485 within the S1^A domain of the PEDV S protein, whose importance and function are yet to be determined. Moreover, both NmAbs could not bind to linearized S proteins, indicating that only conformational epitopes are recognized. This data could improve our understanding of the antigenic structures of the PEDV S protein and facilitate future development of novel epitope-based vaccines.

Epidemiology of porcine epidemic diarrhea virus among Chinese pig populations: A meta-analysis

BACKGROUND

Porcine epidemic diarrhea results from infection with porcine epidemic diarrhea virus (PEDV). It is an acute and highly contagious enteric disease in swine characterized by watery diarrhea and vomiting. Here, we performed a systematic review and meta-analysis in order to assess the prevalence of PEDV infection in pig populations from mainland China.

METHODS

We conducted a literature search on the prevalence of PEDV infection in pigs between Jan 1, 1988 and Aug 20, 2018 in English and Chinese databases, including PubMed, Google scholar, Cochrane library, Clinical Trials, VIP, CNKI and WanFang database. Selections were made based on the title and the abstract of paper, and duplicated literature was excluded along with other host studies, and data incomplete literature according to the exclusion criteria we formulated. Finally, we extracted the number of swine with PEDV infection from the obtained studies and provided information that permitted us to estimate the prevalence of PEDV infection in pigs in mainland China.

RESULTS

A total of 45 studies (including data from 15,990 pigs) met our evaluation criteria. In China, the overall estimated prevalence of PEDV infection in pigs was 44% (7113/15,990), while the estimated prevalence of PEDV infection in pigs from northern China was 37% (793/2136), lower than those in other regions of China. The prevalence of PEDV infection was associated with sampling season, category of pigs and clinical signs (diarrhea) in pigs. However, the prevalence of PEDV among pigs in China was not significantly associated with the effect of detected target genes, nor was it associated with date of study publication.

CONCLUSION

Our findings suggest that PEDV infection is common among pigs in China. It is therefore necessary to carry out further research and monitor the prevalence of PEDV infection. Furthermore, powerful and effective regulatory measures should be taken in order to prevent the transmission and spread of PEDV among pig populations.