Age-dependent variation in innate immune responses to porcine epidemic diarrhea virus infection in suckling versus weaned pigs

Immunohistochemical detection of the vomiting-inducing monoamine neurotransmitter serotonin and enterochromaffin cells in the intestines of conventional or gnotobiotic (Gn) pigs infected with porcine epidemic diarrhea virus (PEDV) and serum cytokine responses of Gn pigs to acute PEDV infection

Serotonin is a critical monoamine neurotransmitter molecule stored and released from enterochromaffin (EC) cells into the gut submucosa, transmitting the vomiting signal to the brain. We studied one mechanism by which vomiting is induced in pigs infected with porcine epidemic diarrhea virus (PEDV) by characterization of swine EC cells by immunohistochemistry. Conventional or gnotobiotic (Gn) 9-day-old pigs [PEDV-inoculated (n = 12); Mock (n = 14)] were inoculated orally (8.9-9.2 log₁₀ genomic equivalents/pig) with PEDV PC21A strain or mock. This is the first identification of serotonin-positive EC cells in swine by immunohistochemistry and mainly in intestinal crypts, regardless of infection status. They were morphologically triangular-shaped or round cells with or without apical cytoplasmic extensions, respectively. At post-inoculation hour (PIH) 16 or 24, when vomiting was first or frequently observed, respectively, PEDV infection resulted in significantly reduced numbers of serotonin-positive EC cells in duodenum, mid-jejunum, ileum, or colon. However, two of three PEDV-inoculated Gn pigs that did not yet show vomiting at PIH 16 had numbers of serotonin-positive EC cells in duodenum, ileum and colon similar to those in the negative controls. These findings suggest that serotonin release from EC cells (increased serotonin levels) into the gut submucosa might occur early PEDV post-infection to stimulate the vagal afferent neurons, followed by vomiting. Serotonin might be involved in the mechanisms related to vomiting in PEDV-infected piglets. We also found that mid-jejunum was the primary site of acute PEDV infection, and that systemic innate and pro-inflammatory cytokine responses were induced during the acute stage of PEDV infection.

Susceptibility of porcine IPEC-J2 intestinal epithelial cells to infection with porcine deltacoronavirus (PDCoV) and serum cytokine responses of gnotobiotic pigs to acute infection with IPEC-J2 cell culture-passaged PDCoV

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IPEC-J2 cells were susceptible to porcine deltacoronavirus (PDCoV) infection.

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PDCoV antigen was detected in the IPEC-J2 cells showing viral cytopathic effects (CPE).

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Most CPE- and PDCoV antigen-positive IPEC-J2 cells failed to show TUNEL-positive (apoptosis) signals.

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IPEC-J2 cell culture-passaged PDCoV induced systemic innate and pro-inflammatory cytokine responses in gnotobiotic pigs.

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IPEC-J2 cells may be useful to characterize the interactions of enterocytes with PDCoV.

The porcine small intestinal epithelial cell line, IPEC-J2, is useful to characterize the interactions of enterocytes with enteric viruses in vitro. We investigated whether IPEC-J2 cells are susceptible to porcine deltacoronavirus (PDCoV) infection. We conducted quantification of infectious virus or viral RNA, immunofluorescent (IF) staining for the detection of PDCoV antigens, and TUNEL assay in IPEC-J2 cells inoculated with the strain OH-FD22-P8 grown in LLC-PK cells, and supplemented with 10 μg/ml of trypsin in the cell culture medium. Cytopathic effects (CPE) that consisted of enlarged and rounded cells followed by cell shrinkage and detachment, were identified by the 3rd viral passage in the IPEC-J2 cells. PDCoV antigen was detected in the cells showing CPE. By double IF and TUNEL staining, most PDCoV antigen-positive IPEC-J2 cells failed to show TUNEL-positive signals, indicating that PDCoV-infected IPEC-J2 cells may not undergo apoptosis, but rather necrosis, similar to necrotic cell death of infected enterocytes in vivo. There was increased interleukin-6 in PDCoV-infected IPEC-J2 cell culture supernatants at post-inoculation hour (PIH) 48–96, as evaluated by ELISA, concurrent with increased titers of PDCoV at PIH 24–72. The susceptibility of IPEC-J2 cells to PDCoV infection supports their usefulness to characterize the interactions of enterocytes with PDCoV. We also demonstrated that IPEC-J2 cell culture-passaged PDCoV (OH-FD22-P8-I-P4) was enteropathogenic in 10-day-old gnotobiotic pigs, and induced systemic innate and pro-inflammatory cytokine responses during the acute PDCoV infection.

Porcine rotavirus C in pigs with gastroenteritis on Thai swine farms, 2011-2016

Swine are economically important food animals, but highly contagious porcine epidemic diarrhea virus (PEDV) and rotavirus can afflict pig herds and contribute significantly to piglet morbidity and mortality. While there have been studies on rotavirus group A (RVA) in Thailand, reports of rotavirus group C (RVC) are limited. Here, we aimed to identify the prevalence of RVC circulating on Thai commercial swine farms. We analyzed 769 feces and intestine mucosal contents of pigs affected with diarrhea between 2011 and 2016 using RT-PCR specific for the PEDV spike (S), rotavirus glycoprotein (G) VP7, and protease-sensitive protein (P) VP4 genes. We found that 6.6% (51/769) of samples tested positive for RVC, of which 11 samples were co-infected with RVA and four samples were co-infected with PEDV. Three samples tested positive for all three viruses. Phylogenetic analysis of the VP7 gene showed that the most frequent RVC genotype was G1, which grouped with the prototypic RVC Cowden strain. While G6 and G9 were also common, G3 was relatively rare. Analysis of the VP4 gene revealed that the most common P type was P[5], followed by P[4], P[7], and P[1]. In all, there were six G/P combinations (G6P[5], G1P[1], G1P[4], G1P[5], G9P[4], and G9P[7]), of which G6P[5] was the most predominant.

Oral Immunization against PEDV with Recombinant Lactobacillus casei Expressing Dendritic Cell-Targeting Peptide Fusing COE Protein of PEDV in Piglets

Porcine epidemic diarrhea (PED) is a highly contagious disease in newborn piglets. In our previous study, a genetically engineered Lactobacillus casei oral vaccine (pPG-COE-DCpep/L393) expressing a dendritic cell (DC)-targeting peptide fused with porcine epidemic diarrhea virus (PEDV) COE antigen was developed. This vaccine induced significant levels of anti-PEDV specific IgG and IgA antibody responses in mice, indicating a potential strategy against PEDV infection. In this study, pPG-COE-DCpep/L393 was used for oral vaccination of newborn piglets against PEDV. We then assessed the immune responses and protection efficacy of pPG-COE-DCpep/L393. An indirect enzyme-linked immunosorbent assay (ELISA) showed that the recombinant Lactobacillus vaccine elicits a specific systemic and mucosal immune response. The T-helper cells mediated by pPG-COE-DCpep/L393 and PEDV infection display a Th1 phenotype. The histopathological results showed that pPG-COE-DCpep/L393 promotes lymphocyte proliferation and effectively protects piglets against PEDV infection. The transforming growth factor-β level indicated that the recombinant Lactobacillus vaccine plays a role in anti-inflammatory responses in mesenteric lymph nodes during PEDV infection. These results show that pPG-COE-DCpep/L393 is a potential vaccine against PEDV infection.

Swine enteric coronavirus disease: A review of 4 years with porcine epidemic diarrhoea virus and porcine deltacoronavirus in the United States and Canada

Swine enteric coronaviruses, including porcine epidemic diarrhoea virus (PEDV) and porcine deltacoronavirus (PDCoV), have emerged and spread throughout the North American swine industry over the last four years. These diseases cause significant losses within the pork industry and within the first year after PEDV introduction, approximately 10% of the US herd died due to the disease. Similar to other enteric coronaviruses, such as transmissible gastroenteritis virus (TGEV), these emerging swine enteric coronavirus diseases (SECD) are age-dependent, with high morbidity and mortality in neonatal pigs. Since the introduction of SECD, research has focused on investigating viral pathogenesis through experimental inoculation, increasing maternal antibody for neonatal protection, understanding transmission risks through feed and transportation, and outlining the importance of biosecurity in preventing SECD introduction and spread. A survey of swine professionals conducted for this review revealed that the majority of respondents (75%) believe SECD can be eradicated and that most herds have been successful at long-term elimination of SECD after exposure (80%). However, unique properties of SECD, such as ineffective immunity through parenteral vaccination and a low oral infectious dose, play a major role in management of SECD. This review serves to describe the current knowledge of SECD and the characteristics of these viruses which provide both opportunities and challenges for long-term disease control and potential eradication from the US swine population.

Investigation of three outbreaks of Porcine Epidemic Diarrhea in Germany in 2016 demonstrates age dependent differences in the development of humoral immune response

Porcine epidemic diarrhea (PED) has reemerged in Europe since 2014. Characterized by a rapid onset of diarrhea in pigs of all ages, morbidity can reach up to 100% whereas mortality is variable. The virus strains involved in the recent European outbreaks all cluster together with US strains (S INDEL) that lead to less severe clinical signs. In this study, fattening pigs and suckling piglets (n = 105) on farms with no prior PED history were monitored after an acute outbreak of the disease, caused by an S INDEL strain of PED virus (PEDV). For diagnostic investigations in the affected farms, real time RT-PCR was performed to detect PEDV RNA in individually taken fecal samples, and two commercial ELISA kits, both based on the N protein of PEDV, were used to detect IgG in serum samples of pigs experiencing acute signs of the disease. PEDV RNA could be detected in fecal samples up to 14 days after initial sampling. Comparing both ELISAs by Cohens Kappa showed substantial agreement (κ = 0,771). Antibodies were detectable in all fattening pigs (100%) within 10 days after the occurrence of first clinical signs and remained detectable for about two months at least in 20.6% (farm 1) and 45.7% (farm 2) of the animals, respectively. In contrast, only 18 of 34 (52.9%) suckling piglets seroconverted. Although, PEDV RNA was found in fecal samples of all piglets, 13 piglets did not demonstrate antibodies at any sampling day. PCR to detect PEDV RNA in fecal samples seems to be a reliable diagnostic tool during and after the acute outbreak. In the present study, IgG ELISA kits proved to be a feasible diagnostic tool, but age dependent differences in detection rate and persistence of antibodies need to be considered.

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.

Reduced virulence of a pseudorabies virus isolate from wild boar origin in domestic pigs correlates with hampered visceral spread and age-dependent reduced neuroinvasive capacity

Morbidity and mortality associated with pseudorabies virus (PRV) infection are dependent on the age of the pig and the virulence of the strain. PRV strains circulating in wild boar are considered to be low virulent, but no mechanistic explanation for their reduced virulence is available. Here infection of 2- and 15-week-old domestic pigs with the PRV wild boar strain BEL24043 did not induce clinical symptoms in 15-week-old pigs, but resulted in important neurological and respiratory disease in 2-week-old piglets. A detailed study of the (neuro) pathogenesis and associated cytokine mRNA expression showed that the reduced virulence of the wild boar strain, compared to what was previously reported for the virulent domestic NIA3 strain, is due to a severely hampered spread to visceral organs in pigs of both age categories and to an efficient suppression of viral replication at primary replication sites of 15-week-old pigs and to a lesser extent in those of 2-week-old piglets. The age-dependent difference in induced symptoms seems to be due to an immature development state of the immune and/or nervous system in 2-week-old pigs. An extensive viral replication associated with a robust expression of cytokine-related mRNA was found in the olfactory bulb of 2-week-old piglets, correlating with observed neurological disease. Neuroinvasion also occurred via the trigeminal route in 2-week-old pigs, but viral replication was efficiently suppressed in the trigeminal ganglion in the presence of a moderate induction of cytokine-related mRNA. Viral replication in the peripheral and central nervous system of 15-week-old pigs was limited and efficiently suppressed.

Rapamycin-induced autophagy restricts porcine epidemic diarrhea virus infectivity in porcine intestinal epithelial cells

Porcine epidemic diarrhea virus (PEDV) invades porcine intestinal epithelial cells (IECs) and causes diarrhea and dehydration in pigs. In the present study, we showed a suppression of PEDV infection in porcine jejunum intestinal epithelial cells (IPEC-J2) by an increase in autophagy. Autophagy was activated by rapamycin at a dose that does not affect cell viability and tight junction permeability. The induction of autophagy was examined by LC3I/LC3II conversion. To confirm the autophagic-flux (entire autophagy pathway), autophagolysosomes were examined by an immunofluorescence assay. Pre-treatment with rapamycin significantly restricted not only a 1 h infection but also a longer infection (24 h) with PEDV, while this effect disappeared when autophagy was blocked. Co-localization of PEDV and autophagosomes suggests that PEDV could be a target of autophagy. Moreover, alleviation of PEDV-induced cell death in IPEC-J2 cells pretreated with rapamycin demonstrates a protective effect of rapamycin against PEDV-induced epithelial cell death. Collectively, the present study suggests an early prevention against PEDV infection in IPEC-J2 cells via autophagy that might be an effective strategy for the restriction of PEDV, and opens up the possibility of the use of rapamycin in vivo as an effective prophylactic and prevention treatment.

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Rapamycin has an antiviral effect against PEDV infection.

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Rapamycin prevents PEDV-induced cell death.

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Rapamycin-induced autophagy restricted PEDV infection in porcine intestinal epithelial cells.

Porcine epidemic diarrhea virus does not replicate in porcine monocyte-derived dendritic cells, but activates the transcription of type I interferon and chemokine

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PEDV fails to replicate in porcine Mo-DC.

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PEDV does not compromise the viability of porcine Mo-DC.

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PEDV activates the transcription of type I interferon.

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PEDV activates the transcription of IP-10.

Porcine epidemic diarrhea virus (PEDV) belongs to the alphacoronavirus of the Coronaviridae. It is the major etiological agent of the recent outbreaks of piglet diarrhea and death in the US. Limited knowledge is currently available regarding the role of dendritic cells in PEDV infection. Here, we observed that PEDV did not replicate in monocyte-derived dendritic cells as evidenced by the decrease of viral gene transcript copies in infected cells by qRT-PCR and the absence of viral proteins by immunofluorescence staining as well as the absence of virus particles in infected cells by transmission electron microscopy. In addition, PEDV did not compromise cell viability at 48, 72, and 96 h after infection at either a MOI of 2.5 or 5. Interestingly, an increased transcription of type I interferon including interferon-α and β was observed in infected cells compared to mock infected cells. Surprisingly, we did not detect any interferon-β in the supernatants of infected cells. A slight increase in interferon-α protein production in the supernatants of PEDV-infected cells was observed compared to mock infected cells. We also observed a markedly increased transcription of interferon inducible protein −10 (IP-10). Overall, PEDV does not replicate in porcine Mo-DC, but activates the transcription of type I interferon and chemokine IP-10.

Inhibition of NF-κB activity by the porcine epidemic diarrhea virus nonstructural protein 1 for innate immune evasion

Porcine epidemic diarrhea virus emerged in the US is known to suppress the type I interferons response during infection. In the present study using porcine epithelial cells, we showed that PEDV inhibited both NF-κB and proinflammatory cytokines. PEDV blocked the p65 activation in infected cells and suppressed the PRD II-mediated NF-κB activity. Of the total of 22 viral proteins, nine proteins were identified as NF-κB antagonists, and nsp1 was the most potent suppressor of proinflammatory cytokines. Nsp1 interfered the phosphorylation and degradation of IκBα, and thus blocked the p65 activation. Mutational studies demonstrated the essential requirements of the conserved residues of nsp1 for NF-κB suppression. Our study showed that PEDV inhibited NF-κB activity and nsp1 was a potent NF-κB antagonist for suppression of both IFN and early production of pro-inflammatory cytokines.

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PEDV inhibits type I IFNs and NF-κB-mediated pro-inflammatory cytokines.

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PEDV blocks p65 nuclear translocation in virus-infected cells.

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Among 22 viral proteins, nsp1, nsp3, nsp5, nsp7, nsp14, nsp15, nsp16, ORF3, and E are NF-κB antagonists.

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Nsp1 suppresses pro-inflammatory cytokines and p65 activation by blocking IκBα phosphorylation.

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The conserved residues of nsp1 are crucial for NF-κB suppression.

The S2 glycoprotein subunit of porcine epidemic diarrhea virus contains immunodominant neutralizing epitopes

The porcine epidemic diarrhea virus (PEDV) spike (S) protein is the major target of neutralizing antibodies against PEDV. Here immunodominant neutralizing epitopes of PEDV were identified using a panel of S-specific monoclonal antibodies (mAbs). Ten of eleven S-specific mAbs successfully neutralized PEDV infectivity in vitro. Notably, epitope mapping by peptide ELISAs revealed that nine of these mAbs recognized linear neutralizing epitopes located in the N-terminus of the S2 glycoprotein subunit (amino acids [aa] 744-759, 747-774 and/or 756-771). Additionally, one mAb recognized a neutralizing epitope located in the C-terminus of S2 (aa 1371-1377), while only one neutralizing mAb reacted against a region of the S1 glycoprotein subunit (aa 499-600). Notably, mAbs that recognized epitopes within the S2 subunit presented the highest neutralizing activity against PEDV. Together these results indicate that the S2 glycoprotein subunit contains major antigenic determinants and, perhaps, the immunodominant neutralizing epitopes of PEDV.

Nursery pig growth performance and tissue accretion modulation due to porcine epidemic diarrhea virus or porcine deltacoronavirus challenge

Porcine epidemic diarrhea virus (PEDV) and porcine deltacoronavirus (PDCoV) are both members of the family Coronaviridae which induce clinical signs of diarrhea, dehydration, and in some circumstances, mortality. Most research has been focused on isolation, genome sequencing, pathogenicity, and virulence of these viruses, but there is little information on long-term growth performance and tissue accretion of pigs inoculated with PEDV or PDCoV. Therefore, our objective was to determine the effect of PEDV or PDCoV infection on growth performance and tissue accretion over 42 d following inoculation. A total of 75 Choice Genetics Large White Pureline barrows and gilts (BW = 10.81 ± 0.81 kg) at approximately 2 wk post-wean and naïve for PEDV and PDCoV were selected. Pigs were allotted based on BW and sex, stratified across 3 treatments with 8 pens per treatment. Treatments were: 1) Control (n = 8); 2) PEDV inoculated (n = 8); and 3) PDCoV inoculated (n = 8). On day post inoculation (dpi) 2, 5, 7, and 14 pigs were euthanized for tissue collection and analyses from these tissues are discussed elsewhere. Pen feed intake and BW were recorded on dpi 2, 5, 7, and weekly thereafter until dpi 42. On 1 designated pig per pen, initial and final body composition was determined using dual-energy X-ray absorptiometry (DXA) and tissue accretion rates were calculated over 6 wk test period. Peak PEDV infection was noted at 3 dpi compared with 4 dpi for PDCoV pigs as determined by fecal swab quantitative real-time PCR (RT-PCR). Control pigs remained negative for PEDV and PDCoV throughout the experiment. Overall, Control and PDCoV pigs did not differ in ADG, ADFI or G:F (P > 0.05). Compared to Control and PDCoV pigs, the overall 42 d ADFI was reduced in the challenged PEDV pigs (P < 0.05) by 19 and 27%, respectively. PEDV did not significantly reduce the overall ADG or G:F compared with Control and PDCoV pigs; however, the biggest reduction in ADG and ADFI for PEDV pigs was within 14 dpi compared to the Control pigs (P < 0.05). Whole body tissue accretion was altered due to PED, with fat, lean, protein, and bone mineral accretion reductions by 24, 20, 21, and 42%, respectively (P < 0.05) compared with Control pigs. Overall, nursery pig performance was greatly impacted by PEDV challenge. Surprisingly, the PDCoV challenge did not negatively influence nursery pig performance. This study provides further insight into the longitudinal impact swine enteric coronaviruses have on growing pigs.

Protein Malnutrition Modifies Innate Immunity and Gene Expression by Intestinal Epithelial Cells and Human Rotavirus Infection in Neonatal Gnotobiotic Pigs

Malnutrition and rotavirus infection, prevalent in developing countries, individually and in combination, affect the health of millions of children, compromising their immunity and increasing the rates of death from infectious diseases. However, the interactions between the two and their combined effects on immune and intestinal functions are poorly understood. We have established the first human infant microbiota-transplanted neonatal pig model of childhood malnutrition that reproduced the impaired immune, intestinal, and other physiological functions seen in malnourished children. This model can be used to evaluate relevant dietary and other health-promoting interventions. Our findings provide an explanation of why adequate nutrition alone may lack efficacy in malnourished children.

Malnutrition affects millions of children in developing countries, compromising immunity and contributing to increased rates of death from infectious diseases. Rotavirus is a major etiological agent of childhood diarrhea in developing countries, where malnutrition is prevalent. However, the interactions between the two and their combined effects on immune and intestinal functions are poorly understood. In this study, we used neonatal gnotobiotic (Gn) pigs transplanted with the fecal microbiota of a healthy 2-month-old infant (HIFM) and fed protein-deficient or -sufficient bovine milk diets. Protein deficiency induced hypoproteinemia, hypoalbuminemia, hypoglycemia, stunting, and generalized edema in Gn pigs, as observed in protein-malnourished children. Irrespective of the diet, human rotavirus (HRV) infection early, at HIFM posttransplantation day 3 (PTD3), resulted in adverse health effects and higher mortality rates (45 to 75%) than later HRV infection (PTD10). Protein malnutrition exacerbated HRV infection and affected the morphology and function of the small intestinal epithelial barrier. In pigs infected with HRV at PTD10, there was a uniform decrease in the function and/or frequencies of natural killer cells, plasmacytoid dendritic cells, and CD103⁺ and apoptotic mononuclear cells and altered gene expression profiles of intestinal epithelial cells (chromogranin A, mucin 2, proliferating cell nuclear antigen, SRY-Box 9, and villin). Thus, we have established the first HIFM-transplanted neonatal pig model that recapitulates major aspects of protein malnutrition in children and can be used to evaluate physiologically relevant interventions. Our findings provide an explanation of why nutrient-rich diets alone may lack efficacy in malnourished children.

IMPORTANCE Malnutrition and rotavirus infection, prevalent in developing countries, individually and in combination, affect the health of millions of children, compromising their immunity and increasing the rates of death from infectious diseases. However, the interactions between the two and their combined effects on immune and intestinal functions are poorly understood. We have established the first human infant microbiota-transplanted neonatal pig model of childhood malnutrition that reproduced the impaired immune, intestinal, and other physiological functions seen in malnourished children. This model can be used to evaluate relevant dietary and other health-promoting interventions. Our findings provide an explanation of why adequate nutrition alone may lack efficacy in malnourished children.

Glycyrrhizin inhibits porcine epidemic diarrhea virus infection and attenuates the proinflammatory responses by inhibition of high mobility group box-1 protein

Porcine epidemic diarrhea (PED), caused by porcine epidemic diarrhea virus (PEDV) infection, leads to significant economic losses in the swine industry worldwide. In our studies, we found that glycyrrhizin, the major component of licorice root extracts, could moderately inhibit PEDV infection in Vero cells, when analyzed by western blot, qRT-PCR and a plaque formation assay. We also revealed that glycyrrhizin inhibited the entry and replication of PEDV. In addition, we demonstrated that glycyrrhizin decreased the mRNA levels of proinflammatory cytokines. Since glycyrrhizin is a competitive inhibitor of high mobility group box-1 (HMGB1), we confirmed that TLR4 and RAGE (£ associated with PEDV pathogenesis during the infection in Vero cells. In summary, our studies provide a molecular basis for developing novel therapeutic methods to control PEDV infection, based on glycyrrhizin and its derivatives.

Comparative Proteome Analysis of Porcine Jejunum Tissues in Response to a Virulent Strain of Porcine Epidemic Diarrhea Virus and Its Attenuated Strain

Porcine epidemic diarrhea virus (PEDV), a predominant cause of acute enteric infection, leads to severe dehydrating diarrhea and mortality in piglets all over the world. A virulent PEDV YN13 strain, isolated in our laboratory, was attenuated to yield an attenuated PEDV strain YN144. To better understand the pathogenesis mechanism and the virus-host interaction during infection with both PEDV YN13 and YN144 strains, a comparative proteomic analysis was carried out to investigate the proteomic changes produced in the primary target organ, using isobaric tags for relative and absolute quantitation (iTRAQ) labeling, followed by liquid chromatography tandem-mass spectrometry (LC-MS/MS). A total of 269 and 301 differently expressed proteins (DEPs) were identified in the jejunum tissues of the piglets inoculated with YN13 and YN144, respectively. Bioinformatics analysis revealed that these proteins were involved in stress responses, signal transduction, and the immune system. All of these involved interferon-stimulated genes (ISGs) which were up-regulated in jejunums by both of the PEDV-infected groups. Based on the comparative analysis, we proposed that different changes induced by YN13 and YN144 in heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1), eukaryotic initiation factor 4G1 (eIF4G1), and some members in the heat shock protein (HSP) family, may be responsible for differences in their pathogenicity.

Increased frequency of porcine epidemic diarrhea virus shedding and lesions in suckling pigs compared to nursery pigs and protective immunity in nursery pigs after homologous re-challenge

Porcine epidemic diarrhea virus (PEDV) causes enteric disease in pigs and spreads rapidly after entering naïve pig populations. The objectives were to (1) compare the disease course following inoculation with PEDV isolate US/Colorado/2013 in naïve 10 day and 8 week-old pigs, and (2) contrast the naïve response to homologous challenge in 8 week-old pigs. Pigs were randomly assigned into group 1 (n = 40, no PEDV exposure), group 2 (n = 43, PEDV inoculation at 10 days of age) and group 3 (n = 48, PEDV inoculation at 8 weeks of age). Thirty-three group 2 pigs received a homologous challenge at 8 weeks of age. Following primary or secondary inoculation, 3–10 pigs were euthanized at days post-inoculation (dpi) 1, 2, 3, 7 or 14. Clinical signs were more pronounced in 10 day-old pigs compared to 8 week-old pigs at dpi 2 and 3, a higher number of 10 day-old pigs shed PEDV RNA in feces compared to 8 week-old pigs. Typical severe atrophic enteritis of PEDV infection was observed at dpi 3 in both age groups, and at dpi 4 and 14 fecal shedding patterns were also similar. While both age groups had seroconverted to PEDV by dpi 14, IgG levels were higher in 8 week-old pigs. PEDV IgA antibodies were detected in feces of approximately 50% of the pigs at dpi 44. In homologous challenged pigs, no clinical signs or lesions were found, and PEDV fecal shedding was restricted to less than 10% of the pigs indicating the existence of homologous protection 44 days after initial PEDV exposure.

Quantifying the effect of lactogenic antibody on porcine epidemic diarrhea virus infection in neonatal piglets

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The objective of this experiment was to assess the role of lactogenic immunity in protecting piglets against the effects of PEDV by quantifying virus shedding in feces and piglet growth, thermoregulation, and survival in the presence (PEDV exposed sows) or absence (PEDV negative sows) of PEDV antibody in colostrum and milk.

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The presence of lactogenic antibody markedly affected the outcome of PEDV infection in neonates, including less PEDV shedding in feces, better thermostability (p = 0.0001), higher rate of growth, and higher rate of survivability.

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Therefore, maintenance of sufficient levels of lactogenic immunity will be the cornerstone for the prevention of PED in endemically-infected herds.

The contribution of lactogenic antibody to the protection of piglets against porcine epidemic diarrhea virus (PEDV) was evaluated. Pregnant multiparous sows and their litters were allocated to one of 3 treatment groups: Group 1–6 serum antibody-negative sows and a subset (n = 11) of their piglets. Group 2–8 serum antibody-positive sows and their 91 piglets. Piglets were orally inoculated with PEDV at 4 (Group 1) or 2 (Group 2) days of age. Group 3–2 PEDV serum antibody-negative sows and 22 piglets, provided a baseline for piglet survivability and growth rate. Piglets were monitored daily for clinical signs, body weight, and body temperature through day post-inoculation (DPI) 12 (Groups 2 and 3) or 14 (Group 1). Serum and mammary secretions were tested for PEDV IgG, IgA, and virus-neutralizing antibody. Feces were tested by PEDV real-time, reverse transcriptase PCR (rRT-PCR). Piglets on sows without (Group 1) or with (Group 2) anti-PEDV antibody showed significantly different responses to PEDV infection in virus shedding (p < 0.05), thermoregulation (p < 0.05), growth rate (p < 0.05), and survivability (p < 0.0001). Specifically, Group 1 piglets shed more virus on DPIs 1 to 5, were hypothermic at all sampling points except DPIs 9, 11, and 12, gained weight more slowly, and exhibited lower survivability than Group 2 piglets. Within Group 2 litters, significant differences were found in virus shedding (p < 0.05), and body temperature (p < 0.05), but not in piglet survival rate. The number of sows and litters in Group 2 was insufficient to derive the relationship between specific levels of lactogenic antibody (FFN, IgA, and IgG) and the amelioration of clinical effects. However, when combined with previous PEDV literature, it can be concluded that the optimal protection to piglets will be provided by dams able to deliver sufficient lactogenic immunity, both humoral and cellular, to their offspring.

Efficient priming of CD4 T cells by Langerin-expressing dendritic cells targeted with porcine epidemic diarrhea virus spike protein domains in pigs

Porcine epidemic diarrhea virus (PEDV) first emerged in the United States in 2013 causing high mortality and morbidity in neonatal piglets with immense economic losses to the swine industry. PEDV is an alpha-coronavirus replicating primarily in porcine intestinal cells. PEDV vaccines are available in Asia and Europe, and conditionally-licensed vaccines recently became available in the United States but the efficacies of these vaccines in eliminating PEDV from swine populations are questionable. In this study, the immunogenicity of a subunit vaccine based on the spike protein of PEDV, which was directly targeted to porcine dendritic cells (DCs) expressing Langerin, was assessed. The PEDV S antigen was delivered to the dendritic cells through a single-chain antibody specific to Langerin and the targeted cells were stimulated with cholera toxin adjuvant. This approach, known as "dendritic cell targeting," greatly improved PEDV S antigen-specific T cell interferon-γ responses in the CD4^posCD8^pos T cell compartment in pigs as early as 7days upon transdermal administration. When the vaccine protein was targeted to Langerin^pos DCs systemically through intramuscular vaccination, it induced higher serum IgG and IgA responses in pigs, though these responses require a booster dose, and the magnitude of T cell responses were lower as compared to transdermal vaccination. We conclude that PEDV spike protein domains targeting Langerin-expressing dendritic cells significantly increased CD4 T cell immune responses in pigs. The results indicate that the immunogenicity of protein subunit vaccines can be greatly enhanced by direct targeting of the vaccine antigens to desirable dendritic cell subsets in pigs.

Escherichia coli Nissle 1917 protects gnotobiotic pigs against human rotavirus by modulating pDC and NK-cell responses

Lactobacillus rhamnosus GG (LGG), a gram-positive lactic acid bacterium, is one of the most widely used probiotics; while fewer gram-negative probiotics including Escherichia coli Nissle 1917 (EcN) are characterized. A mechanistic understanding of their individual and interactive effects on human rotavirus (HRV) and immunity is lacking. In this study, noncolonized, EcN-, LGG-, and EcN + LGG-colonized neonatal gnotobiotic (Gn) pigs were challenged with HRV. EcN colonization is associated with a greater protection against HRV, and induces the highest frequencies of plasmacytoid dendritic cells (pDCs), significantly increased NK-cell function and decreased frequencies of apoptotic and TLR4⁺ mononuclear cells (MNCs). Consistent with the highest NK-cell activity, splenic CD172⁺ MNCs (DC enriched fraction) of EcN-colonized pigs produced the highest levels of IL-12 in vitro. LGG colonization has little effect on the above parameters, which are intermediate in EcN + LGG-colonized pigs, suggesting that probiotics modulate each other's effects. Additionally, in vitro EcN-treated splenic or intestinal MNCs produce higher levels of innate, immunoregulatory and immunostimulatory cytokines, IFN-α, IL-12, and IL-10, compared to MNCs of pigs treated with LGG. These results indicate that the EcN-mediated greater protection against HRV is associated with potent stimulation of the innate immune system and activation of the DC-IL-12-NK immune axis.

Virulence factors in porcine coronaviruses and vaccine design

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Engineered live attenuated vaccines may improve the control porcine CoVs infection.

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Porcine CoVs affect many host-cell pathways modulating pathogenesis.

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CoV genes acting as virulence factors should be modified for virus attenuation.

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To use attenuated CoVs as vaccine candidates several safety guards should be included.

Porcine enteric coronaviruses (CoVs) cause severe disease in the porcine herds worldwide, leading to important economic losses. Despite the knowledge of these viruses since the 1970s, vaccination strategies have not been implemented, leading to continuous re-emergence of novel virulent strains. Live attenuated vaccines historically have been the most efficient. We consider that the new trend is the development of recombinant vaccines by using reverse genetics systems to engineer attenuated viruses, which could be used as effective and safe modified live vaccine candidates. To this end, host cell signaling pathways influencing porcine CoV virulence should be identified. Similarly, the identity of viral proteins involved in the modulation of host cell pathways influencing CoV pathogenesis should be analyzed. With this information, and using reverse genetics systems, it is possible to design viruses with modifications in the viral proteins acting as virulence factors, which may lead to attenuated viruses and, therefore, vaccine candidates. In addition, novel antiviral drugs may be developed once the host cell pathways and the molecular mechanism affecting porcine CoV replication and virulence are known. This review is focused in the host cell responses to enteric porcine CoV infection and the viral proteins involved in pathogenesis.

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

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Evolution of global PEDV strains.

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

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Pathologic features of different PEDV strains.

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

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

Characterization of anti-porcine epidemic diarrhea virus neutralizing activity in mammary secretions

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Colostrum uptake is important for early establishment of lactogenic immunity.

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Neutralizing activity in milk and colostrum is associated with anti-spike IgA.

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Sow milk is a continuous supply of IgA with neutralizing activity.

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Temporal patterns of neutralizing antibody production in milk are variable.

Porcine epidemic diarrhea virus (PEDV) causes a severe clinical enteric disease in suckling neonates with up to 100% mortality, resulting in devastating economic losses to the pork industry in recent years. Maternal immunity via colostrum and milk is a vital source to neonates of passive protection against diarrhea, dehydration and death caused by PEDV. Comprehensive information on neutralizing activity (NA) against PEDV in mammary secretions is critically important for assessing the protective capacity of sows. Therefore, the objectives of this study were to characterize anti-PEDV neutralizing activity in mammary secretions. Anti-PEDV NA was present in colostrum, milk and serum from PEDV-infected sows as determined both by immunofluorescence and ELISA-based neutralizing assays, with neutralization levels higher in colostrum and milk than in serum. The highest NA was observed in colostrum on day 1, and decreased rapidly in milk at day 3, then gradually declined from day 3 to day 19 post-farrowing. Notably, the NA in mammary secretions showed various patterns of decline over time of lactation that may contribute to variation in sow protective capacities. The kinetics of NA decline were associated with total IgA and IgG antibody levels. Neutralizing activity significantly correlated with specific IgA primarily to spike domain 1 (S1) and domain 2 (S2) proteins of PEDV rather than to specific IgG in colostrum. Subsequently, the NA in milk was mainly related to specific IgA to S1 and S2 during lactation.

Immune evasion of porcine enteric coronaviruses and viral modulation of antiviral innate signaling

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Enteric coronaviruses have evolved to modulate the host innate immunity.

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Viral IFN antagonists have been identified and they are mostly redundant.

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For protection of intestinal epithelia from enteric viruses, type III IFN plays a major role.

Porcine epidemic diarrhea virus (PEDV) and porcine deltacoronavirus (PDCoV) are emerged and reemerging viruses in pigs, and together with transmissible gastroenteritis virus (TGEV), pose significant economic concerns to the swine industry. These viruses infect epithelial cells of the small intestine and cause watery diarrhea, dehydration, and a high mortality in neonatal piglets. Type I interferons (IFN-α/β) are major antiviral cytokines forming host innate immunity, and in turn, these enteric coronaviruses have evolved to modulate the host innate immune signaling during infection. Accumulating evidence however suggests that IFN induction and signaling in the intestinal epithelial cells differ from other epithelial cells, largely due to distinct features of the gut epithelial mucosal surface and commensal microflora, and it appears that type III interferon (IFN-λ) plays a key role to maintain the antiviral state in the gut. This review describes the recent understanding on the immune evasion strategies of porcine enteric coronaviruses and the role of different types of IFNs for intestinal antiviral innate immunity.

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

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

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

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

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

Porcine deltacoronavirus infection: Etiology, cell culture for virus isolation and propagation, molecular epidemiology and pathogenesis

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Porcine deltacoronavirus (PDCoV) is a novel swine enteropathogenic coronavirus.

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The etiology and molecular epidemiology of PDCoV are described.

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The cell culture for PDCoV isolation and propagation are demonstrated.

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The disease mechanisms and pathogenesis of PDCoV are reviewed.

Porcine deltacoronavirus (PDCoV) (family Coronaviridae, genus Deltacoronavirus) is a novel swine enteropathogenic coronavirus that causes acute diarrhea/vomiting, dehydration and mortality in seronegative neonatal piglets. PDCoV diarrhea was first reported in the US in early 2014, concurrently with co-circulation of porcine epidemic diarrhea virus (PEDV) (family Coronaviridae, genus Alphacoronavirus). The origin of PDCoV in pigs and also its sudden emergence or route of introduction into the US still remains unclear. In the US, since 2013–2014, the newly emerged PDCoV and PEDV have spread nationwide, causing a high number of pig deaths and significant economic impacts. The current US PDCoV strains are enteropathogenic and infect villous epithelial cells of the entire small and large intestines although the jejunum and ileum are the primary sites of infection. Similar to PEDV infections, PDCoV infections also cause acute, severe atrophic enteritis accompanied by transient viremia (viral RNA) that leads to severe diarrhea and/or vomiting, followed by dehydration as the potential cause of death in nursing piglets. At present, differential diagnosis of PDCoV, PEDV, and transmissible gastroenteritis virus (TGEV) is essential to control viral diarrheas in US swine. Cell culture-adapted US PDCoV (TC-PDCoV) strains have been isolated and propagated by us and in several other laboratories. TC-PDCoV strains will be useful to develop serologic assays and to evaluate if serial cell-culture passage attenuates TC-PDCoV as a potential vaccine candidate strain. A comprehensive understanding of the pathogenesis and epidemiology of epidemic PDCoV strains is currently needed to prevent and control the disease in affected regions and to develop an effective vaccine. This review focuses on the etiology, cell culture isolation and propagation, molecular epidemiology, disease mechanisms and pathogenesis of PDCoV infection.

Does Circulating Antibody Play a Role in the Protection of Piglets against Porcine Epidemic Diarrhea Virus?

The contribution of circulating antibody to the protection of naïve piglets against porcine epidemic diarrhea virus (PEDV) was evaluated using a passive antibody transfer model. Piglets (n = 62) derived from 6 sows were assigned to one of 6 different treatments using a randomized block design which provided for allocation of all treatments to all sows' litters. Each treatment was designed to achieve a different level of circulating anti-PEDV antibody via intraperitoneally administration of concentrated serum antibody. Piglets were orally inoculated with PEDV (USA/IN/2013/19338E, 1 x 103 TCID50 per piglet) 24 hours later and then monitored for 14 days. Piglets remained with their dam throughout the experiment. Sow milk samples, piglet fecal samples, and data on piglet clinical signs, body weight, and body temperature were collected daily. Fecal samples were tested by PEDV real-time reverse transcriptase PCR. Serum, colostrum, and milk were tested for PEDV IgG, IgA, and virus-neutralizing antibody. The data were evaluated for the effects of systemic PEDV antibody levels on growth, body temperature, fecal shedding, survival, and antibody response. The analysis showed that circulating antibody partially ameliorated the effect of PEDV infection. Specifically, antibody-positive groups returned to normal body temperature faster and demonstrated a higher rate of survivability than piglets without PEDV antibody. When combined with previous literature on PEDV, it can be concluded that both systemic antibodies and maternal secretory IgA in milk contribute to the protection of the neonatal pig against PEDV infections. Overall, the results of this experiment suggested that passively administered circulating antibodies contributed to the protection of neonatal piglets against PEDV infection.