US variant porcine epidemic diarrhea virus: histological lesions and genetic characterization

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

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

Isolation and Identification of Porcine Epidemic Diarrhea Virus and Its Effect on Host Natural Immune Response

Porcine epidemic diarrhea (PED) is a highly infectious intestinal disease caused by porcine epidemic diarrhea virus (PEDV). A PEDV strain was isolated from the piglet intestinal tract in Vero cells in Jiangsu Province, designated as the JS-A strain. PEDV was identified as the isolated virus by cytopathology, immunofluorescence assay, western blotting, transmission electron microscopy, and sequence analysis. The full-length genome of the JS-A isolate and the S gene were systematically analyzed, indicating that PEDV JS-A belongs to the G2a subtype, which is closely related to the prevalent PEDV in many countries and different from many current vaccines. Animal regression tests showed that piglets that are orally infected with the virus continue to develop diarrhea with yellowish and unpleasant odors. Further, piglets showed reduced food consumption and weight loss in the challenged group, while there were no abnormalities in the control group. In addition, Toll-like receptors (TLRs), RIG-I, and the downstream medium gene in the intestinal mucosa of newborn pigs infected with PEDV JS-A strain were studied. The neonatal Fc receptor (FcRn) was the only IgG transport receptor and protected IgG from degradation. Therefore, PEDV JS-A infection might inhibit FcRn expression by down-regulating TLRs and downstream signaling molecules. Taken together, isolation of the JS-A variant contributes to evolutionary analysis of the diarrhea virus. Further, the experimental infection model lays a foundation for further research related to vaccine development and the antiviral natural immune response of infected piglets, which helps us to better understand PEDV pathogenesis and immune mechanism.

Differential gene modulation of pattern-recognition receptor TLR and RIG-I-like and downstream mediators on intestinal mucosa of pigs infected with PEDV non S-INDEL and PEDV S-INDEL strains

Porcine epidemic diarrhea virus (PEDV) strains can be divided into non-S-INDEL and S-INDEL strains. PEDV pathogenesis is strain-specific, and studies in neonatal pigs have demonstrated that the PEDV non-S-INDEL strains are more pathogenic than the PEDV S-INDEL strains. RNA viruses, including PEDV, can interact with a large number of pattern recognition receptors (PRRs) in the intestinal mucosa, including toll-like receptors (TLRs) and RIG-I-like receptors (RLRs). We investigated the differential gene modulation of TLRs, RIG-I, and downstream mediators on the intestinal mucosa of neonatal pigs infected with PEDV S-INDEL and non-S-INDEL strains. Ten five-day-old piglets were inoculated orally with 10 ml of 10⁴ TCDI₅₀/ml of either PEDV non-S-INDEL or S-INDEL strains. PEDV S-INDEL infection induced pro-inflammatory cytokines through the non-canonical NF-κB signaling pathway by activating RIG-I. In contrast, PEDV non-S-INDEL infection suppressed the induction of pro-inflammatory cytokines and type 1 interferon production by down-regulation of TLRs and downstream signaling molecules.

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Differential gene modulation of TLR and RIG-I-like receptors and downstream mediators.

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PEDV S-INDEL induces pro-inflammatory cytokines through non-canonical NF-κB signaling pathway.

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PEDV S-INDEL pro-inflammatory cytokines activation is RIG-I dependent.

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PEDV non-S-INDEL suppresses the induction of pro-inflammatory cytokines and type 1 interferon.

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PEDV non-S-INDEL effect is mediated by down-regulation of TLRs and its downstream-signaling molecules.

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PEDV S-INDEL and PEDV non-S-INDEL cause differential modulation on innate immune response pathways.

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Differential modulation could be translated into differences in pathogenesis and clinical outcomes.

Short communication: antiviral activity of porcine IFN-λ3 against porcine epidemic diarrhea virus in vitro

A new family of IFNs called type III IFN or IFN-λ has been described, and shown to induce antiviral activity against several viruses in the cell culture. In this study, the molecular cloning, expression, and antiporcine epidemic diarrhea virus (PEDV) activity of porcine IFN-λ3 (poIFN-λ3) were reported. The full-length poIFN-λ3 cDNA sequence encoded 196 amino acids with a 23 amino acid signal peptide. Sequence alignments showed that poIFN-λ3 had an amino acid sequence similarity to Ovis aries (78.1 %), Bos taurus (76.0 %), Tupaia belangeri (71.3 %), Equus caballus (69.9 %), and Homo sapiens (69.9 %). The phylogenetic analysis based on the genomic sequences indicated that poIFN-λ3 is located in the same branch as B. taurus and O. aries IFN-λ3. The poIFN-λ3 without a signal anchor sequence was efficiently expressed in Escherichia coli, and the purified recombinant poIFN-λ3 exhibited significant antiviral effects against PEDV in a dose- and time-dependent manner. This inhibitory effect of poIFN-λ3 on PEDV was observed under three different treatment conditions. The highest inhibition of PEDV was observed in Vero E6 cell cultures pretreated with poIFN-λ3 (prior to PEDV infection). In addition, poIFN-λ3 was able to induce the expression of IFN-stimulated genes, including ISG15, OAS1, and Mx1 in Vero E6 cells. These data demonstrate that poIFN-λ3 has antiviral activity against PEDV and may serve as a useful biotherapeutic candidate to inhibit PEDV or other viruses in swine.