Establishment of a duplex fluorescent quantitative PCR assay for detection of Porcine circovirus type 2 and type 3

To establish a method for simultaneous detection of porcine circovirus type 2 (PCV2) and porcine circovirus type 3 (PCV3), specific primers and TaqMan probes were designed after sequence alignment according to the specific sequences of PCV2 Cap gene and PCV3 Cap gene on GenBank. By optimizing the reaction conditions, a duplex fluorescence quantitative PCR detection method for simultaneous detection of porcine circovirus type 2 and 3 was established, and the specificity, sensitivity, and reproducibility were tested. Specificity test results showed that in addition to the positive test results for PCV2 and PCV3, tests for PRRSV, CSFV, PPV, PRV, PEDV, and TGEV were all negative with no cross-reaction, indicating its good specificity. Sensitivity test results showed that the minimum detection limit for detection of PCV2 and PCV3 can both reach 10 copies.L-1, indicating its high sensitivity. The coefficient of variation within and between groups of this method was less than 2%, indicating its good stability. A total of 181 pork and whole blood samples collected from Zhejiang Province were tested using the detection method established in this article and the standard common fluorescent PCR detection method. The results showed that the positive rate of PCV2 was 50.83% (92/181), the positive rate of PCV3 was 37.57% (68/181), and the co-infection rate of PCV2 and PCV3 was 12.15% (22/181). The above detection results of ordinary fluorescent PCR were 50.28% (91/181), 36.46% (66/181), and the co-infection rate was 11.60% (21/181). The coincidence rates of the two methods for PCV2 and PCV3 can reach 98.91% and 97.06%, and the coincidence rate for PCV2 and PCV3 mixed infection were 95.45%. In summary, the duplex fluorescence quantitative PCR detection method established in this experiment can distinguish PCV2 and PCV3 rapidly, which can be used for pathogen detection and epidemiological investigation.

Effect of Drebrin protein on the proliferation of PEDV in Vero cells

Previous studies have revealed that developmental regulated brain protein (Drebrin) is involved in cell- to-cell communication, nerve transmission, tumor metastasis, spermatogenesis and other life activities, but there are few studies on viruses. The aim of the current research was therefore, to study the function of Drebrin and its effect on the proliferation of porcine epidemic diarrhea virus (PEDV). The Drebrin gene was cloned according to the Drebrin gene sequence (XM_008015438.2) of Chlorocebus sabaeus registered by GenBank, and the phylogenetic tree was constructed to analyze its homology. The results showed that the CDS region of Vero cells Drebrin gene was 2088 bp long, encoding 695 amino acids, and was relatively conserved and had high homology with all species. To investigate the effect of Drebrin on the proliferation of PEDV in Vero cells, the eukaryotic expression vector pcDNA3.1-Drebrin-Flag was constructed. After transfection of Vero cells with different concentrations of pcDNA3.1-Drebrin-Flag, cells were infected with PEDV. Our results showed that overexpression of Drebrin in Vero cells could significantly inhibit the intracellular PEDV mRNA level and N protein expression, reduce the extracellular virus titer and inhibit the proliferation of PEDV. Further study on the interaction between Drebrin and PEDV S proteins by laser confocal technique was also performed. The results showed that Drebrin and S protein were co-located in the cytoplasm, suggesting that the two proteins may interact with each other. This study demonstrated for the first time that Drebrin can inhibit PEDV proliferation in Vero cells, laying a foundation for further research in to Drebrin function and provides a valuable information for anti-PEDV research.

Development and application of a multiplex fluorescent quantitative RT-PCR for detection of Porcine epidemic diarrhea virus, porcine coronavirus and porcine acute diarrhea syndrome coronavirus

To develop a multiplex fluorescent quantitative RT-PCR for the detection of porcine epidemic diarrhea virus (PEDV), porcine deltacoronavirus (PDCoV) and swine acute diarrhea syndrome coronavirus (SADS-CoV), in this study, specific primers/probes were designed based on the conserved regions of M, M and N gene sequences of PEDV, PDCoV and SADS-CoV, respectively. After optimization of the reaction conditions, a multiplex fluorescent quantitative RT-PCR for PEDV, PDCoV and SADS-CoV was established. The results of specificity assay showed that the method was positive for detection of PEDV, PDCoV and SADS-CoV, and negative for detection of porcine transmissible gastroenteritis virus, porcine rotavirus, porcine reproductive and respiratory syndrome virus, porcine pseudorabies virus, porcine circovirus type 2, porcine parvovirus, classical swine fever virus and foot-and-mouth disease virus. The results of sensitivity assay showed that the detection limit of this method for PEDV, PDCoV, and SADS-CoV plasmids standard was 1.0x101 copies/L, and had a good linear relationship with their Ct values in the range of 101 copies/L to 106 copies/L. The results of repeatability assay showed that the coefficients of variation (CVs) of intra- and inter-assay reproducibility ranged from 0.33% to 2.53%, indicating good repeatability and stability. To evaluate the effects of the developed method, 100 clinical samples collected from different parts of Henan province were used for detection of these three viruses and compared with those of single RT-PCR and standard methods. The results of multiplex fluorescent quantitative RT-PCR showed that the positive rates of PEDV, PDCoV and SADS-CoV were 38% (38/100), 14% (14/100) and 5% (5/100), respectively. There was no mixed infection. The coincidence rate with the standard detection methods of PEDV and PDCoV was 100%, and the sensitivity was higher than that of single RT-PCR. In this study, a specific, sensitive and rapid multiplex fluorescent quantitative RTPCR method was established for the first time, which could be used for the differential detection of PEDV, PDCoV and SADS-CoV, and laid a foundation for the differential diagnosis and control of porcine diarrheal diseases.

Natural Evolution of Porcine Epidemic Diarrhea Viruses Isolated from Maternally Immunized Piglets

Simple SummaryDuring the long-term co-evolution of the virus and the host, even closely related vaccines may emerge with incomplete protective immunity due to the mutations or deletions of amino acids at specific antigenic sites. The mutation of PEDV was accelerated by the recombination of different strains and the mutation of the strains adapting to the environment. These mutations either cause immune escape from conventional vaccines or affect the virulence of the virus. Therefore, researching and developing new vaccines with cross-protection through continuous monitoring, isolation and sequencing are important to determine whether their genetic characteristics are changed and to evaluate the protective efficacy of current vaccines. The porcine epidemic diarrhea virus (PEDV) can cause severe piglet diarrhea or death in some herds. Genetic recombination and mutation facilitate the continuous evolution of the virus (PEDV), posing a great challenge for the prevention and control of porcine epidemic diarrhea (PED). Disease materials of piglets with PEDV vaccination failure in some areas of Shanxi, Henan and Hebei provinces of China were collected and examined to understand the prevalence and evolutionary characteristics of PEDV in these areas. Forty-seven suspicious disease materials from different litters on different farms were tested by multiplex PCR and screened by hematoxylin-eosin staining and immunohistochemistry. PEDV showed a positivity rate of 42.6%, infecting the small and large intestine and mesenteric lymph node tissues. The isolated strains infected Vero, PK-15 and Marc-145 multihost cells and exhibited low viral titers in all three cell types, as indicated by their growth kinetic curves. Possible putative recombination events in the isolates were identified by RDP4.0 software. Sequencing and phylogenetic analysis showed that compared with the classical vaccine strain, PEDV SX6 contains new insertion and mutations in the S region and belongs to genotype GIIa. Meanwhile, ORF3 has the complete amino acid sequence with aa80 mutated wild strains, compared to vaccine strains CV777, AJ1102, AJ1102-R and LW/L. These results will contribute to the development of new PEDV vaccines based on prevalent wild strains for the prevention and control of PED in China.

Effects of oral of administration of monoglycide laurate on virus load and inflammation in PEDV infected porcine.

To investigate the effect of monoglyceryl laurate (GML) against PEDV in vivo, the clinical signs, pathological changes, tissue viral load and cytokine levels of piglets were compared in different GML treatment groups and PEDV infected group. The diets of experimental groups were supplemented with different doses of GML (5g for A1, 10g for A2, 20g for A3) on day 1, 2, and 3 after PEDV challenge, and the virus challenge group (group C) and blank group (group B) were set as control. The results showed that compared with group C, groups As could reduce the mortality rate of piglets, among which the protection rates of groups A2 and A3 could reach 100%. The trend of weight loss of piglets was effectively slowed down and growth performance recovered in GML treated groups. GML reduced the pathological damage of intestinal tract and the viral load in intestine and mesenteric lymph nodes. The levels of IL-8 and TNF-α in the blood of group As were inhibited by GML in a dose-dependent manner when compared with group C. Our study suggests that GML has potential anti-PEDV effects in vivo.

Investigation of variants in genetics and virulence of Porcine Epidemic Diarrhea Virus after serial passage on Vero cells.

Porcine epidemic diarrhea virus (PEDV) is a highly contagious intestinal virus. However, the current PEDV vaccine, which is produced from classical strain G1, offers low protection against recently emerged strain G2. This study aims to develop a better vaccine strain by propagating the PS6 strain, a G2b subgroup originating from Vietnam, on Vero cells until the 100th passage. As the virus was propagated, its titer increased, and its harvest time decreased. Analysis of the nucleotide and amino acid variation of the PS6 strain showed that the P100PS6 had 11, 4, and 2 amino acid variations in the 0 domain, B domain, and ORF3 protein, respectively, compared to the P7PS6 strain. Notably, the ORF3 gene was truncated due to a 16-nucleotide deletion mutation, resulting in a stop codon. The PS6 strain's virulence was evaluated in 5-day-old piglets, with P7PS6 and P100PS6 chosen for comparison. The results showed that P100PS6-inoculated piglets exhibited mild clinical symptoms and histopathological lesions, with a 100% survival rate. In contrast, P7PS6-inoculated piglets showed rapid and typical clinical symptoms of PEDV infection, and the survival rate was 0%. Additionally, the antibodies (IgG and IgA) produced from inoculated piglets with P100PS6 bound to both the P7PS6 and P100PS6 antigens. This finding suggested that the P100PS6 strain was attenuated and could be used to develop a live-attenuated vaccine against highly pathogenic and prevalent G2b-PEDV strains.

Development of Effective PEDV Vaccine Candidates Based on Viral Culture and Protease Activity.

Porcine epidemic diarrhea (PED) is a highly contagious disease that has been reported annually in several Asian countries, causing significant economic losses to the swine livestock industry. Although vaccines against the porcine epidemic diarrhea virus (PEDV) are available, their efficacy remains questionable due to limitations such as viral genome mutation and insufficient intestinal mucosal immunity. Therefore, the development of a safe and effective vaccine is necessary. In this study, a virulent Korean strain of PEDV, CKT-7, was isolated from a piglet with severe diarrhea, and six different conditions were employed for serial passage of the strain in a cell culture system to generate effective live attenuated vaccine (LAV) candidates. The characteristics of these strains were analyzed in vitro and in vivo, and the CKT-7 N strain was identified as the most effective vaccine candidate, with a viral titer peak of 8.67 ± 0.29 log10TCID50/mL, and no mortality or diarrhea symptoms were observed in five-day-old piglets. These results indicate that LAV candidates can be generated through serial passage with different culture conditions and provide valuable insights into the development of a highly effective LAV against PEDV.

Current State of Molecular and Serological Methods for Detection of Porcine Epidemic Diarrhea Virus.

Porcine epidemic diarrhea virus (PEDV), a member of the Coronaviridae family, is the etiological agent of an acute and devastating enteric disease that causes moderate-to-high mortality in suckling piglets. The accurate and early detection of PEDV infection is essential for the prevention and control of the spread of the disease. Many molecular assays have been developed for the detection of PEDV, including reverse-transcription polymerase chain reaction (RT-PCR), real-time RT-PCR (qRT-PCR) and loop-mediated isothermal amplification assays. Additionally, several serological methods have been developed and are widely used for the detection of antibodies against PEDV. Some of them, such as the immunochromatography assay, can generate results very quickly and in field conditions. Molecular assays detect viral RNA in clinical samples rapidly, and with high sensitivity and specificity. Serological assays can determine prior immune exposure to PEDV, can be used to monitor the efficacy of vaccination strategies and may help to predict the duration of immunity in piglets. However, they are less sensitive than nucleic acid-based detection methods. Sanger and next-generation sequencing (NGS) allow the analysis of PEDV cDNA or RNA sequences, and thus, provide highly specific results. Furthermore, NGS based on nonspecific DNA cleavage in clustered regularly interspaced short palindromic repeats (CRISPR)-Cas systems promise major advances in the diagnosis of PEDV infection. The objective of this paper was to summarize the current serological and molecular PEDV assays, highlight their diagnostic performance and emphasize the advantages and drawbacks of the application of individual tests.

Interaction between target peptide and complementary peptide by bimolecular fluorescence complementary technology

[Objective] Using the bimolecular fluorescence complementation (BiFC) technology, the present experiment aimed to study the interaction relationship and localization of the target peptide and the complementary peptide based on the porcine epidemic diarrhea virus (PEDV) S protein receptor binding site peptide in living cells, so as to provide the foundation and theoretical support for the further use of the peptide in the detection of porcine epidemic diarrhea virus. [Method] The target peptide was designed according to the physical and chemical characteristics of the target protein, such as the amino acid composition, the type of charge, the ability to form intennolecular hydrogen bonds, the strength of polarity, and hydrophobicity;According to the amino acid composition of the target protein, a complementary peptide that interacted with it in theory was designed, and the target peptide and complementary peptide were predicted and analyzed by using bioinfonnatics tools;The target peptide and complementary peptide were inserted into the pBiFC-VC155 and pBiFC-VN173 vector, which was double digested by the EcoRI/XhoI and NotI/SalI, respectively, verified by enzyme digestion and sequencing, and then transfected into Vero cells to study the interaction between the target peptide and the complementary peptide, and the precise localization of BiFC complex in cells. [Result] Bioinfonnatics analysis showed that the target peptide and complementary peptide had hydrophilic and hydrophobic domains, respectively, and the hydrophilic domains were both positively and negatively charged, which could generate electrostatic attraction. The results of enzyme digestion and sequencing showed that the pBiFC-VC155-target peptide and pBiFC-VNI73-complementary peptide plasmids were successfully constructed;Cell transfection experiments showed that the target peptide and complementary peptide could form BiFC complexes in Vcro cells after co-transfection of recombinant plasmids, indicating that they could interact with each other;Indirect immuttolluorescence assay confirmed that the BiFC complex was mainly distributed in the nucleus. [Conclusion] It was confirmed that the peptide designed based on the PEW/ S protein receptor binding site can interact with each other in living cells, demonstrating the feasibility of the peptide for detection.

Improved virus inhibition by microencapsulated monoclonal antibody against porcine epidemic diarrhea virus

Porcine epidemic diarrhea virus (PEDV) has been affecting the swine industry, especially in suckling pigs in with a high mortality rate. Among all the strategies to overcome PEDV, boosting mucosal immunity in pig intestine via oral administration appears to be more efficient than other routes. However, there are biological obstacles such as acidic environment that could damage biologics, a product from organisms often used for PEDV treatment. The plant-derived 2C10 monoclonal antibody (mAb) from Nicotiana benthamiana produced by transient expression was revealed as one of the potential candidates against PEDV through oral delivery. Herein, we demonstrated the calcium-alginate microencapsulation system to protect the 2C10 mAb from the harsh condition in the stomach and to be released the 2C10 mAb when arriving in the intestine. The pH-responsive encapsulated 2C10 mAb microbeads were constructed from the calcium-alginate system. The microbeads were well-tolerated under the acidic environment of simulated gastric fluid (SGF) and were digested under the alkaline condition of simulated intestinal fluid (SIF). The encapsulated 2C10 mAb in the SPF-treated microbeads exhibited high virus neutralization efficiency in Vero cells when compared to the unencapsulated 2C10 mAb treated by SPF that cannot neutralize the virus. For these reasons, calcium-alginate microencapsulation system is an attractive platform to be considered as a candidate for the next generation of oral vaccine development.

Duplex Taq man qPCR for detecting porcine epidemic diarrhea and transmissible gastroenteritis viruses and epidemic study in Fujian

Objective: A Taq Man probe-based duplex real-time PCR for rapid detection of porcine epidemic diarrhea virus(PEDV) and transmissible gastroenteritis virus(TGEV) was developed. A study was conducted using the methodology to analyze the related 2019-2021 epidemic occurred in Fujian. Method: Specific primers and probes labeled with FAM and VIC were designed to amplify the N gene of PEDV and the S gene of TGEV, respectively. A reaction system for the assay was established, optimized, and tested for sensitivity, specificity, and repeatability. The assay was used for the viral detection on297 suspected clinic specimens collected from 2019 to 2021 for an epidemiology study. Result: The newly developed duplex qPCR methodology showed a sensitivity of 10 copies.L-1 on PEDV and TGEV, which was 100 times higher than that of regular PCR. There were no cross reactions with other common viruses. The inter-and intra-assays had variations on Ct values below 1%. On the 297 specimens, the infection rate of PEDV was 88.89%, that of TGEV 1.01%, and that of both PEDV and TGEV 3.37%. Conclusion: The established duplex qPCR had high sensitivity, specificity, repeatability, and reproducibility for detecting PEDV and TGEV. The 2019-2021 epidemic involving the viruses appeared to be mostly PEDV with low incidents of mixed TGEV and PEDV/TGEV infection.

Recombinant human adenovirus type 5 based vaccine candidates against GIIa- and GIIb-genotype porcine epidemic diarrhea virus induce robust humoral and cellular response in mice.

Porcine epidemic diarrhea virus (PEDV) is a porcine enteropathogenic coronavirus causing severe watery diarrhea, vomiting, dehydration, and death in piglets. However, most commercial vaccines are developed based on the GI genotype strains, and have poor immune protection against the currently dominant GII genotype strains. Therefore, four novel replication-deficient human adenovirus 5-vectored vaccines expressing codon-optimized forms of the GIIa and GIIb strain spike and S1 glycoproteins were constructed, and their immunogenicity was evaluated in mice by intramuscular (IM) injection. All the recombinant adenoviruses generated robust immune responses, and the immunogenicity of recombinant adenoviruses against the GIIa strain was stronger than that of recombinant adenoviruses against the GIIb strain. Moreover, Ad-XT-tPA-Sopt-vaccinated mice elicited optimal immune effects. In contrast, mice immunized with Ad-XT-tPA-Sopt by oral gavage did not induce strong immune responses. Overall, IM administration of Ad-XT-tPA-Sopt is a promising strategy against PEDV, and this study provides useful information for developing viral vector-based vaccines.

Molecular and Structural Evolution of Porcine Epidemic Diarrhea Virus.

To analyze the evolutionary characteristics of the highly contagious porcine epidemic diarrhea virus (PEDV) at the molecular and structural levels, we analyzed the complete genomes of 647 strains retrieved from the GenBank database. The results showed that the spike (S) gene exhibited larger dS (synonymous substitutions per synonymous site) values than other PEDV genes. In the selective pressure analysis, eight amino acid (aa) sites of the S protein showed strong signals of positive selection, and seven of them were located on the surface of the S protein (S1 domain), suggesting a high selection pressure of S protein. Topologically, the S gene is more representative of the evolutionary relationship at the genome-wide level than are other genes. Structurally, the evolutionary pattern is highly S1 domain-related. The haplotype networks of the S gene showed that the strains are obviously clustered geographically in the lineages corresponding to genotypes GI and GII. The alignment analysis on representative strains of the main haplotypes revealed three distinguishable nucleic acid sites among those strains, suggesting a putative evolutionary mechanism in PEDV. These findings provide several new fundamental insights into the evolution of PEDV and guidance for developing effective prevention countermeasures against PEDV.

Coronavirus Porcine Epidemic Diarrhea Virus Utilizes Chemokine Interleukin-8 to Facilitate Viral Replication by Regulating Ca2+ Flux.

Chemokine production by epithelial cells is crucial for neutrophil recruitment to sites of inflammation during viral infection. However, the effect of chemokine on epithelia and how chemokine is involved in coronavirus infection remains to be fully understood. Here, we identified an inducible chemokine interleukin-8 (CXCL8/IL-8), which could promote coronavirus porcine epidemic diarrhea virus (PEDV) infection in African green monkey kidney epithelial cells (Vero) and Lilly Laboratories cell-porcine kidney 1 epithelial cells (LLC-PK1). IL-8 deletion restrained cytosolic calcium (Ca2+), whereas IL-8 stimulation improved cytosolic Ca2+. The consumption of Ca2+ restricted PEDV infection. PEDV internalization and budding were obvious reductions when cytosolic Ca2+ was abolished in the presence of Ca2+ chelators. Further study revealed that the upregulated cytosolic Ca2+ redistributes intracellular Ca2+. Finally, we identified that G protein-coupled receptor (GPCR)-phospholipase C (PLC)-inositol trisphosphate receptor (IP3R)-store-operated Ca2+ (SOC) signaling was crucial for enhancive cytosolic Ca2+ and PEDV infection. To our knowledge, this study is the first to uncover the function of chemokine IL-8 during coronavirus PEDV infection in epithelia. PEDV induces IL-8 expression to elevate cytosolic Ca2+, promoting its infection. Our findings reveal a novel role of IL-8 in PEDV infection and suggest that targeting IL-8 could be a new approach to controlling PEDV infection. IMPORTANCE Coronavirus porcine epidemic diarrhea virus (PEDV) is a highly contagious enteric coronavirus that caused severe economic losses worldwide, and more effort is needed to develop economical and efficient vaccines to control or eliminate this disease. The chemokine interleukin-8 (CXCL8/IL-8) is indispensable for the activation and trafficking of inflammatory mediators and tumor progression and metastasis. This study evaluated the effect of IL-8 on PEDV infection in epithelia. We found that IL-8 expression improved cytosolic Ca2+ in epithelia, facilitating PEDV rapid internalization and egress. G protein-coupled receptor (GPCR)-phospholipase C (PLC)-inositol trisphosphate receptor (IP3R)-SOC signaling was activated by IL-8, releasing the intracellular Ca2+ stores from endoplasmic reticulum (ER). These findings provide a better understanding of the role of IL-8 in PEDV-induced immune responses, which will help develop small-molecule drugs for coronavirus cure.

A therapeutic chimeric IgG/IgA expressed by CHO cells for oral treatment of PED in piglets.

Immunoglobulin A (IgA) of sows is critically important for assessing piglets' protective capacity against porcine epidemic diarrhea virus (PEDV). Here, we report a therapeutic chimeric anti-PEDV IgG/IgA expressed by Chinese hamster ovary (CHO) cells for oral treatment of PED. The chimeric anti-PEDV IgG/IgA was produced by the CHO cell lines, in which the heavy chain was constructed by combining the VH, Cγ1 and hinge regions of PEDV IgG mAb 8A3, and the Cα2 and Cα3 domains of a Mus musculus immunoglobulin alpha chain. The chimeric anti-PEDV IgG/IgA could neutralize the strains of CV777 (G1), P014 (G2) and HN1303 (G2) in vitro effectively, showing broad-spectrum neutralization activity. The in vivo challenge experiments demonstrated that chimeric anti-PEDV IgG/IgA (9C4) produced in the CHO cell supernatant could alleviate clinical diarrhea symptoms of the PEDV infection in piglets. In general, our study showed that chimeric anti-PEDV IgG/IgA produced from CHO cell line supernatants effectively alleviates PEDV infection in piglets, which also gives the foundation for the construction of fully functional secretory IgA by the J chain introduction to maximize the antibody therapeutic effect.

Development of Duplex LAMP Technique for Detection of Porcine Epidemic Diarrhea Virus (PEDV) and Porcine Circovirus Type 2 (PCV 2).

Porcine epidemic diarrhea virus (PEDV) and porcine circovirus type 2 (PCV2) are both important global pathogenic viruses which have a significant impact on the swine industry. In this study, a duplex loop-mediated isothermal amplification (duplex LAMP) method was developed in combination with lateral flow dipstick (LFD) for simultaneous detection of PEDV and PCV2 using specific sets of primers and probes designed based on the conserved regions of a spike gene (KF272920) and an ORF gene (EF493839), respectively. The limit of detection (LOD) values of the duplex LAMP-LFD for the detection of PEDV and PCV2 were 0.1 ng/µL and 0.246 ng/µL, respectively. The LOD of duplex LAMP-LFD was 10-times more sensitive than conventional PCR and RT-PCR-agarose gel-electrophoresis (PCR-AGE and RT-PCR-AGE). No cross-reaction to each other and to other pathogenic viruses that can infect pigs were observed according to analytical specificity tests. The duplex LAMP-LFD method for the simultaneous detection of PEDV and PCV2 co-infection could be completed within approximately 1.5 h, and only a simple heating block was required for isothermal amplification. The preliminary validation using 50 swine clinical samples with positive and negative PEDV and/or PCV2 revealed that the sensitivity, specificity, and accuracy of duplex LAMP-LFD were all 100% in comparison to conventional PCR and RT-PCR. Hence, this study suggests that duplex LAMP-LFD is a promising tool for the early detection and initial screening of PEDV and PCV2, which could be beneficial for prevention, planning, and epidemiological surveys of these diseases.

Porcine epidemic diarrhea virus (PEDV) ORF3 protein inhibits cellular type I interferon signaling through down-regulating proteins expression in RLRs-mediated pathway.

Porcine epidemic diarrhea virus (PEDV) is an entero-pathogenic coronavirus, which belongs to the genus Alphacoronavirus in the family Coronaviridae, causing lethal watery diarrhea in piglets. Previous studies have shown that PEDV has developed an antagonistic mechanism by which it evades the antiviral activities of interferon (IFN), such as the sole accessory protein open reading frame 3 (ORF3) being found to inhibit IFN-ß promoter activities, but how this mechanism used by PEDV ORF3 inhibits activation of the type I signaling pathway remains not fully understood. Thus, in this present study, we showed that PEDV ORF3 inhibited both polyinosine-polycytidylic acid (poly(I:C))- and IFNα2b-stimulated transcription of IFN-ß and interferon-stimulated genes (ISGs) mRNAs. The expression levels of antiviral proteins in the retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs)-mediated pathway was down-regulated in cells with over-expression of PEDV ORF3 protein, but global protein translation remained unchanged and the association of ORF3 with RLRs-related antiviral proteins was not detected, implying that ORF3 only specifically suppressed the expression of these signaling molecules. At the same time, we also found that the PEDV ORF3 protein inhibited interferon regulatory factor 3 (IRF3) phosphorylation and poly(I:C)-induced nuclear translocation of IRF3, which further supported the evidence that type I IFN production was abrogated by PEDV ORF3 through interfering with RLRs signaling. Furthermore, PEDV ORF3 counteracted transcription of IFN-ß and ISGs mRNAs, which were triggered by over-expression of signal proteins in the RLRs-mediated pathway. However, to our surprise, PEDV ORF3 initially induced, but subsequently reduced the transcription of IFN-ß and ISGs mRNAs to normal levels. Additionally, mRNA transcriptional levels of signaling molecules located at IFN-ß upstream were not inhibited, but elevated by PEDV ORF3 protein. Collectively, these results demonstrate that inhibition of type I interferon signaling by PEDV ORF3 can be realized through down-regulating the expression of signal molecules in the RLRs-mediated pathway, but not via inhibiting their mRNAs transcription. This study points to a new mechanism evolved by PEDV through blockage of the RLRs-mediated pathway by ORF3 protein to circumvent the host's antiviral immunity.

Accurate and ultrasensitive detection for PEDV based on photoelectrochemical sensing coupling loop-mediated isothermal amplification.

Porcine epidemic diarrhea (PED) is a serious disease requiring a simple and accurate detection method. Accordingly, this study developed a novel, ultrasensitive photoelectrochemical (PEC) sensing platform using the loop-mediated isothermal amplification (LAMP) technique (LAMP-PEC). An amino (-NH2)-modified LAMP product is obtained by amplification of the PED virus gene with specially designed primers. The generated NH2-modified LAMP product is assembled on the surface of an electrode by forming imine linkages between aldehyde and amino groups based on the Schiff base reaction. A stable photocurrent is provided by a CdIn2S4 photoactive material, which possesses high photoelectric conversion efficiency. Amplified DNA assembled on the electrode surface increases steric hindrance and hinders electrons from moving from the electrode to electron acceptors, which decreases the photocurrent. This strategy can detect PEDV with a low detection limit of 0.3 fg µL-1 and a wide linear range of 1 × 10-3-1 × 102 pg/µL. The sensing platform has excellent specificity and sensitivity and can be used for the quantitative detection of many other pathogens with the assistance of LAMP.

An ultrasensitive electrochemical sensor for detecting porcine epidemic diarrhea virus based on a Prussian blue-reduced graphene oxide modified glassy carbon electrode.

This study developed a novel, ultrasensitive sandwich-type electrochemical immunosensor for detecting the porcine epidemic diarrhea virus (PEDV). By electrochemical co-deposition of graphene and Prussian blue, a Prussian blue-reduced graphene oxide-modified glassy carbon electrode was made, further modified with PEDV-monoclonal antibodies (mAbs) to create a new PEDV immunosensor using the double antibody sandwich technique. The electrochemical characteristics of several modified electrodes were investigated using cyclic voltammetry (CV). We optimized the pH levels and scan rate. Additionally, we examined specificity, reproducibility, repeatability, accuracy, and stability. The study indicates that the immunosensor has good performance in the concentration range of 1 × 101.88 to 1 × 105.38 TCID50/mL of PEDV, with a detection limit of 1 × 101.93 TCID50/mL at a signal-to-noise ratio of 3σ. The composite membranes produced via co-deposition of graphene and Prussian blue effectively increased electron transport to the glassy carbon electrode, boosted response signals, and increased the sensitivity, specificity, and stability of the immunosensor. The immunosensor could accurately detect PEDV, with results comparable to real-time quantitative PCR. This technique was applied to PEDV detection and served as a model for developing additional immunosensors for detecting hazardous chemicals and pathogenic microbes.

Construction and immunogenicity of a trypsin-independent porcine epidemic diarrhea virus variant.

Porcine epidemic diarrhea virus (PEDV) is a re-emerging enteropathogenic coronavirus that causes high mortality in neonatal piglets. The addition of trypsin plays a crucial role in the propagation of PEDV, but also increases the complexity of vaccine production and increases its cost. Previous studies have suggested that the S2' site and Y976/977 of the PEDV spike (S) protein might be the determinants of PEDV trypsin independence. In this study, to achieve a recombinant trypsin-independent PEDV strain, we used trypsin-dependent genotype 2 (G2) PEDV variant AJ1102 to generate three recombinant PEDVs with mutations in S (S2' site R894G and/or Y976H). The three recombinant PEDVs were still trypsin dependent, suggesting that the S2' site R894 and Y976 of AJ1102 S are not key sites for PEDV trypsin dependence. Therefore, we used AJ1102 and the classical trypsin-independent genotype 1 (G1) PEDV strain JS2008 to generate a recombinant PEDV carrying a chimeric S protein, and successfully obtained trypsin-independent PEDV strain rAJ1102-S2'JS2008, in which the S2 (amino acids 894-1386) domain was replaced with the corresponding JS2008 sequence. Importantly, immunization with rAJ1102-S2'JS2008 induced neutralizing antibodies against both AJ1102 and JS2008. Collectively, these results suggest that rAJ1102-S2'JS2008 is a novel vaccine candidate with significant advantages, including no trypsin requirement for viral propagation to high titers and the potential provision of protection for pigs against G1 and G2 PEDV infections.