Comparative pathogenesis of enteric viral infections of swine

Development and Immunogenicity Study of Subunit Vaccines Based on Spike Proteins of Porcine Epidemic Diarrhea Virus and Porcine Transmissible Gastroenteritis Virus

Porcine epidemic diarrhea virus (PEDV) and transmissible gastroenteritis virus (TGEV) are responsible for significant economic losses in the swine industry. The S1 proteins of these viruses serve as key targets for vaccine development. In this study, prokaryotic expression vectors for pCZN1-PEDV S1, pCZN1-TGEV S1, and pCZN1-PEDV S1-TGEV S1 were constructed. The corresponding proteins were expressed, purified, and used to prepare monovalent, bivalent, and mixed (PEDV S1 + TGEV S1) vaccines. Kunming (KM) mice were immunized with subunit vaccines, with PBS as the negative control (NC) and a commercial inactivated vaccine as the positive control (PC). Immune responses, including specific antibody (IgG, IgG1, IgG2a) levels, virus neutralization, and IFN-γ production, were evaluated. All vaccines induced high levels of specific IgG, IgG1, and IgG2a antibodies. At weeks 2 and 8, the PEDV S1 + TGEV S1 vaccine induced significantly higher levels of specific IgG and IgG1 compared to the PC (p < 0.001). The PEDV S1 vaccine also induced significantly higher specific IgG2a levels than the PC at week 4 (p < 0.0001). Virus neutralization assays demonstrated that the subunit vaccines induced neutralizing antibody levels comparable to or exceeding those of the PC. Furthermore, IFN-γ levels were significantly elevated in all vaccinated groups compared to the NC (p < 0.0001), indicating a robust immune response. These results suggest that the subunit vaccines are promising candidates for the safe and effective control of both PEDV and TGEV infections.

Prevention and Control of Swine Enteric Coronaviruses in China: A Review of Vaccine Development and Application

Swine enteric coronaviruses (SECs) cause significant economic losses to the pig industry in China. Although many commercialized vaccines against transmissible gastroenteritis virus (TGEV) and porcine epidemic diarrhea virus (PEDV) are available, viruses are still widespread. The recent emergence of porcine deltacoronavirus (PDCoV) and swine acute diarrhea syndrome coronavirus (SADS-CoV), for which no vaccines are available, increases the disease burden. In this review, we first introduced the genomic organization and epidemiology of SECs in China. Then, we discussed the current vaccine development and application in China, aiming to provide suggestions for better prevention and control of SECs in China and other countries.

Transmissible Gastroenteritis Virus: An Update Review and Perspective

Transmissible gastroenteritis virus (TGEV) is a member of the alphacoronavirus genus, which has caused huge threats and losses to pig husbandry with a 100% mortality in infected piglets. TGEV is observed to be recombining and evolving unstoppably in recent years, with some of these recombinant strains spreading across species, which makes the detection and prevention of TGEV more complex. This paper reviews and discusses the basic biological properties of TGEV, factors affecting virulence, viral receptors, and the latest research advances in TGEV infection-induced apoptosis and autophagy to improve understanding of the current status of TGEV and related research processes. We also highlight a possible risk of TGEV being zoonotic, which could be evidenced by the detection of CCoV-HuPn-2018 in humans.

Molecular epidemiological investigation of group A porcine rotavirus in East China

Group A porcine rotavirus (RVA) is a serious threat to the breeding industry worldwide, which was associated with severe diarrhea in piglets. However, the prevalence and molecular characterizations of RVA circulating in farms of East China remains largely unknown. Five hundred and ninety-four samples were collected from 35 farms in East China from September 2017 to December 2019. The results showed that 16.8% was positive for RVA of all samples. Among different types of samples, the highest positive rate of RVA was intestinal samples (19.5%), and among pigs at different growth stages, the highest detection rate of RVA in piglets was 18.5%. Furthermore, the VP7 and VP4 genes of nine positive samples were sequenced for alignment and phylogenetic analysis. Phylogenetic analysis revealed that the nine isolates belong to four kinds of genotype combinations correspondingly: G9P[7](5/9), G5P[13](2/9), G9P[13](1/9), and G5P[7](1/9).The data suggested that multiple genotypes combinations of RVA were circulating in pigs in East China. Thus, it's necessary to continuously survey the prevalence of RVA in pigs, aiding the rational application of vaccines or other measures for the prevention and control of RVA spread.

Wastewater-based epidemiology: a new frontier for tracking environmental persistence and community transmission of COVID-19

Recent research in many parts of the world has pointed towards evidence of SARS-CoV-2 RNA in both treated and raw municipal wastewater discharged by communities. Therefore, concerns regarding it being a possible enteric virus are abundant. Past history of SARS-CoV-1 outbreaks and viral survival information helps in establishing information regarding possible viral infectivity and survival of SARS-CoV-2. The paper examines the existing strategies and techniques including the efficacy of laboratory-based RT-qPCR technique for tracking environmental persistence and community transmission of COVID-19. Analysis of studies targeting untreated and treated wastewater as source of samples is carried out. The analysis shows that untreated samples were mostly positive for SARS-CoV-2 RNA in the target studies. Infectivity estimation from viral load data was found to be about two orders of magnitude higher than actual case data in one of the studies. Additionally, relevant research on environmental survivability of SARS-CoV-2 and possible gaps are examined. Biosensors and excretion metabolite tracking in viral detection are also examined, which hold tremendous importance for future research. Wastewater-based epidemiology (WBE) shows incredible promise in the near future for tracking environmental persistence and community transmission of highly infectious diseases such as SARS-CoV-2. With limited research available on SARS-CoV-2 with regard to WBE, it is imperative that focus be established on the evidence-based targeted studies.

Genetic Diversity of Porcine Group A Rotavirus Strains from Pigs in South Korea

Porcine group A rotavirus (PoRVA; family, Reovirideae) strains cause acute viral gastroenteritis in piglets (especially suckling and weaned pigs), resulting in significant economic losses. In this study, we analyzed the VP7 and VP4 genes of PoRVA isolated between 2014 and 2018 from domestic pigs in South Korea to investigate the prevalence of predominant circulating genotypes (G and P types). The prevalence of the PoRVA antigen in the diarrheic fecal samples was 14.1% (53/377). Further genetic characterization of the VP7 and VP4 genes of 53 PoRVA isolates identified six different G-genotypes and five different P genotypes. The G4 and G9 genotypes were the most common (each 39.6%) in PoRVA-positive pigs, followed by P[7] and P[6] (33.9% and 30.1%, respectively). Because the G5 and G9 genotype vaccines are currently mainly used in South Korea, this result provides valuable epidemiological information about the genetic characteristics of PoRVA circulating on domestic pig farms. Development of a novel PoRVA vaccine that targets the current strains circulating in South Korea may be required for more effective virus control on pig farms.

Establishment of a reverse transcription recombinase-aided amplification detection method for porcine group a rotavirus

Porcine rotavirus type A (PoRVA) is the main cause of dehydration and diarrhea in piglets, which has a great impact on the development of the pig industry worldwide. A rapid, accurate and sensitive detection method is conducive to the monitoring, control, and removal of PoRVA. In this study, a PoRVA real-time fluorescent reverse transcription recombinase-aided amplification (RT-RAA) assay was developed. Based on the PoRVA VP6 gene, specific primers and probes were designed and synthesized. The sensitivity of RT-RAA and TaqMan probe-based RT-qPCR was 7 copies per reaction and 5 copies per reaction, respectively. The sensitivity of the RT-RAA method was close to TaqMan probe-based RT-qPCR. The detection results of RT-RAA and TaqMan probe-based quantitative real-time RT-PCR methods were completely consistent in 241 clinical samples. Therefore, we successfully established a rapid and specific RT-RAA diagnostic method for PoRVA.

A total infectome approach to understand the etiology of infectious disease in pigs

BACKGROUND

The global pork industry is continuously affected by infectious diseases that can result in large-scale mortality, trade restrictions, and major reductions in production. Nevertheless, the cause of many infectious diseases in pigs remains unclear, largely because commonly used diagnostic tools fail to capture the full diversity of potential pathogens and because pathogen co-infection is common.

RESULTS

We used a meta-transcriptomic approach to systematically characterize the pathogens in 136 clinical cases representing different disease syndromes in pigs, as well as in 12 non-diseased controls. This enabled us to simultaneously determine the diversity, abundance, genomic information, and detailed epidemiological history of a wide range of potential pathogens. We identified 34 species of RNA viruses, nine species of DNA viruses, seven species of bacteria, and three species of fungi, including two novel divergent members of the genus Pneumocystis. While most of these pathogens were only apparent in diseased animals or were at higher abundance in diseased animals than in healthy animals, others were present in healthy controls, suggesting opportunistic infections. Importantly, most of the cases examined here were characterized by co-infection with more than two species of viral, bacterial, or fungal pathogens, some with highly correlated occurrence and abundance levels. Examination of clinical signs and necropsy results in the context of relevant pathogens revealed that a multiple-pathogen model was better associated with the data than a single-pathogen model was.

CONCLUSIONS

Our data demonstrate that most of the pig diseases examined were better explained by the presence of multiple rather than single pathogens and that infection with one pathogen can facilitate infection or increase the prevalence/abundance of another. Consequently, it is generally preferable to consider the cause of a disease based on a panel of co-infecting pathogens rather than on individual infectious agents. Video abstract.

Development of a Multiplex RT-PCR Assay for Simultaneous Detection of Four Potential Zoonotic Swine RNA Viruses

Swine viruses like porcine sapovirus (SaV), porcine encephalomyocarditis virus (EMCV), porcine rotavirus A (RVA) and porcine astroviruses (AstV) are potentially zoonotic viruses or suspected of potential zoonosis. These viruses have been detected in pigs with or without clinical signs and often occur as coinfections. Despite the potential public health risks, no assay for detecting them all at once has been developed. Hence, in this study, a multiplex RT-PCR (mRT-PCR) assay was developed for the simultaneous detection of SaV, EMCV, RVA and AstV from swine fecal samples. The PCR parameters were optimized using specific primers for each target virus. The assay’s sensitivity, specificity, reproducibility, and application to field samples have been evaluated. Using a pool of plasmids containing the respective viral target fragments as a template, the developed mRT-PCR successfully detected 2.5 × 10³ copies of each target virus. The assay’s specificity was tested using six other swine viruses as a template and did not show any cross-reactivity. A total of 280 field samples were tested with the developed mRT-PCR assay. Positive rates for SaV, EMCV, RVA, and AstV were found to be 24.6% (69/280), 5% (14/280), 4.3% (12/280), and 17.5% (49/280), respectively. Compared to performing separate assays for each virus, this mRT-PCR assay is a simple, rapid, and cost-effective method for detecting mixed or single infections of SaV, EMCV, RVA, and AstV.

Modulation of Innate Antiviral Immune Response by Porcine Enteric Coronavirus

Host’s innate immunity is the front-line defense against viral infections, but some viruses have evolved multiple strategies for evasion of antiviral innate immunity. The porcine enteric coronaviruses (PECs) consist of porcine epidemic diarrhea virus (PEDV), porcine deltacoronavirus (PDCoV), transmissible gastroenteritis coronavirus (TGEV), and swine acute diarrhea syndrome-coronavirus (SADS-CoV), which cause lethal diarrhea in neonatal pigs and threaten the swine industry worldwide. PECs interact with host cells to inhibit and evade innate antiviral immune responses like other coronaviruses. Moreover, the immune escape of porcine enteric coronaviruses is the key pathogenic mechanism causing infection. Here, we review the most recent advances in the interactions between viral and host’s factors, focusing on the mechanisms by which viral components antagonize interferon (IFN)-mediated innate antiviral immune responses, trying to shed light on new targets and strategies effective for controlling and eliminating porcine enteric coronaviruses.

Protective effects of sodium butyrate on rotavirus inducing endoplasmic reticulum stress-mediated apoptosis via PERK-eIF2α signaling pathway in IPEC-J2 cells

BACKGROUND

Rotavirus (RV) is a major pathogen that causes severe gastroenteritis in infants and young animals. Endoplasmic reticulum (ER) stress and subsequent apoptosis play pivotal role in virus infection. However, the protective mechanisms of intestinal damage caused by RV are poorly defined, especially the molecular pathways related to enterocytes apoptosis. Thus, the aim of this study was to investigate the protective effect and mechanism of sodium butyrate (SB) on RV-induced apoptosis of IPEC-J2 cells.

RESULTS

The RV infection led to significant cell apoptosis, increased the expression levels of ER stress (ERS) markers, phosphorylated protein kinase-like ER kinase (PERK), eukaryotic initiation factor 2 alpha (eIF2α), caspase9, and caspase3. Blocking PERK pathway using specific inhibitor GSK subsequently reversed RV-induced cell apoptosis. The SB treatment significantly inhibited RV-induced ERS by decreasing the expression of glucose regulated protein 78 (GRP78), PERK, and eIF2α. In addition, SB treatment restrained the ERS-mediated apoptotic pathway, as indicated by downregulation of C/EBP homologous protein (CHOP) mRNA level, as well as decreased cleaved caspase9 and caspase3 protein levels. Furthermore, siRNA-induced GPR109a knockdown significantly suppressed the protective effect of SB on RV-induced cell apoptosis.

CONCLUSIONS

These results indicate that SB exerts protective effects against RV-induced cell apoptosis through inhibiting ERS mediated apoptosis by regulating PERK-eIF2α signaling pathway via GPR109a, which provide new ideas for the prevention and control of RV.

Infection of porcine small intestinal enteroids with human and pig rotavirus A strains reveals contrasting roles for histo-blood group antigens and terminal sialic acids

Rotaviruses (RVs) are a leading cause of acute viral gastroenteritis in young children and livestock worldwide. Growing evidence suggests that host cellular glycans, such as histo-blood group antigens (HBGAs) and sialic acids (SA), are recognized by the RV surface protein VP4. However, a mechanistic understanding of these interactions and their effects on RV infection and pathogenesis is lacking. Here, we established a porcine crypt-derived 3Dintestinalenteroids (PIEs) culture system which contains all intestinal epithelial cells identified in vivo and represents a unique physiologically functional model to study RV-glycan interactions in vitro. PIEs expressing different HBGAs (A+, H+, and A+/H+) were established and isolation, propagation, differentiation and RV infection conditions were optimized. Differentiated PIEs were infected with human RV (HRV) G1P[8] Wa, porcine RV (PRV) G9P[13], PRV Gottfried G4P[6] or PRV OSU G5P[7] virulent and attenuated strains and virus replication was measured by qRT-PCR. Our results indicated that virulent HRV G1P[8] Wa replicated to the highest titers in A⁺ PIEs, while a distinct trend was observed for PRV G9P[13] or G5P[7] with highest titers in H⁺ PIEs. Attenuated Wa and Gottfried strains replicated poorly in PIEs while the replication of attenuated G9P[13] and OSU strains in PIEs was relatively efficient. However, the replication of all 4 attenuate strains was less affected by the PIE HBGA phenotypes. HBGA synthesis inhibitor 2-F-Peracetyl-Fucose (2F) treatment demonstrated that HBGAs are essential for G1P[8] Wa replication; however, they may only serve as a cofactor for PRVs G9P[13] and OSU G5P[7]. Interestingly, contrasting outcomes were observed following sialidase treatment which significantly enhanced G9P[13] replication, but inhibited the growth of G5P[7]. These observations suggest that some additional receptors recognized by G9P[13] become unmasked after removal of terminal SA. Overall, our results confirm that differential HBGAs-RV and SA-RV interactions determine replication efficacy of virulent group A RVs in PIEs. Consequently, targeting individual glycans for development of therapeutics may not yield uniform results for various RV strains.

Cell surface glycans, including histo-blood group antigens (HBGA) and sialic acids (SAs), have been shown to serve as receptors/attachment factors for many pathogens including RVs. However, how those glycans affect RV replication remains largely unknown due the lack of reliable in vitro models. To solve this problem, we established a 3D porcine intestinal enteroid (PIE) model that recapitulates the complex intestinal morphology better than conventional cell lines. By utilizing PIEs expressing different types of HBGAs, we found that several RV strains including Wa G1P[8], OSU G5P[7] and G9P[13] show preference for certain HBGA types. Interestingly, only Wa replication was reduced when HBGAs synthesis was inhibited, while that of OSU and G9P[13] was only marginally affected, which indicates that they may utilize alternative attachment factors for infection. Sialidase treatment strongly inhibited the growth of OSU, while G9P[13] replication was significantly enhanced. These findings suggest that SAs play contrasting roles in the infection of PRV OSU and G9P[13] strains. Overall, our studies demonstrate that PIEs can serve as a model to study pathogen-glycan interactions and suggest that genetically distinct RVs have evolved diverse mechanisms of cell attachment and/or entry.

Porcine enteric coronaviruses: an updated overview of the pathogenesis, prevalence, and diagnosis

The recent prevalence of coronavirus (CoV) poses a serious threat to animal and human health. Currently, porcine enteric coronaviruses (PECs), including the transmissible gastroenteritis virus (TGEV), the novel emerging swine acute diarrhoea syndrome coronavirus (SADS-CoV), porcine delta coronavirus (PDCoV), and re-emerging porcine epidemic diarrhoea virus (PEDV), which infect pigs of different ages, have caused more frequent occurrences of diarrhoea, vomiting, and dehydration with high morbidity and mortality in piglets. PECs have the potential for cross-species transmission and are causing huge economic losses in the pig industry in China and the world, which therefore needs to be urgently addressed. Accordingly, this article summarises the pathogenicity, prevalence, and diagnostic methods of PECs and provides an important reference for their improved diagnosis, prevention, and control.

Metagenomic sequencing generates the whole genomes of porcine rotavirus A, C, and H from the United States

The genus Rotavirus comprises eight species, designated A to H, and two recently identified tentative species I in dogs and J in bats. Species Rotavirus A, B, C and H (RVA, RVB, RVC and RVH) have been detected in humans and animals. While human and animal RVA are well characterized and defined, complete porcine genome sequences in the GenBank are limited compared to human strains. Here, we used a metagenomic approach to sequence the 11 segments of RVA, RVC and RVH strains from piglets in the United States (US) and explore the evolutionary relations of these RV species. Metagenomics identified Astroviridae, Picornaviridae, Caliciviridae, Coronoviridae in samples MN9.65 and OK5.68 while Picobirnaviridae and Arteriviridae were only identified in sample OK5.68. Whole genome sequencing and phylogenetic analyses identified multiple genotypes with the RVA of strain MN9.65 and OK5.68, with the genome constellation of G5/G9-P[7]/P[13]-I5/I5- R1/R1-C1-M1-A8-N1-T7-E1/E1-H1 and G5/G9-P[6]/P[7]-I5-R1/R1-C1-M1-A8-N1-T1/T7-E1/E1-H1, respectively. The RVA strains had a complex evolutionary relationship with other mammalian strains. The RVC strain OK5.68 had a genome constellation of G9-P[6]-I1-R1-C5-M6-A5-N1-T1-E1-H1, and shared an evolutionary relationship with porcine strains from the US. The RVH strains MN9.65 and OK5.68 had the genome constellation of G5-P1-I1-R1-C1-M1-A5-N1-T1-E4-H1 and G5-P1-I1-R1-C1-M1-A5-N1-T1-E1-H1, indicating multiple RVH genome constellations are circulating in the US. These findings allow us to understand the complexity of the enteric virome, develop improved screening methods for RVC and RVH strains, facilitate expanded rotavirus surveillance in pigs, and increase our understanding of the origin and evolution of rotavirus species.

Rapid and efficient detection methods of pathogenic swine enteric coronaviruses

Abstract

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

Key points

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

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

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

Comparative Sequence Analysis of Historic and Current Porcine Rotavirus C Strains and Their Pathogenesis in 3-Day-Old and 3-Week-Old Piglets

The increased prevalence of porcine group C rotavirus (PRVC) in suckling piglets and the emergence of new genetically distinct PRVC strains are concerning due to the associated significant economic losses they cause to the swine industry. We sequenced and analyzed two new PRVC strains, RV0104 (G3), and RV0143 (G6) and compared their pathogenesis with that of the historic strain Cowden (G1) in gnotobiotic (Gn) pigs. Near complete genome sequence analysis confirmed that these two strains were distinct from one another and the Cowden strain. VP1, VP2, VP6, NSP1-NSP3, and NSP5 genes were more similar between Cowden and RV0143, whereas VP3, VP7, and NSP4 shared higher nucleotide identity between Cowden and RV0104. Three-day-old and 3-week-old Gn piglets were inoculated with 10⁵ FFU/piglet of Cowden, RV0104 or RV0143, or mock. All 3-day-old piglets developed severe diarrhea, anorexia, and lethargy, with mean PRVC fecal shedding titers peaking and numerically higher in RV0104 and RV0143 piglets on post infection day (PID) 2. Histopathological examination of the small intestine revealed that the 3-day-old Cowden and RV0104 inoculated piglets were mildly affected, while significant destruction of small intestinal villi was observed in the RV0143 inoculated piglets. Consistent with the highest degree of pathological changes in the small intestines, the RV0143 inoculated piglets had numerically higher levels of serum IL-17 and IFN-α cytokines and numerically lower PRVC IgA geometric mean antibody titers. Milder pathological changes and overall higher titers of PRVC IgA antibodies were observed in 3-week-old vs. 3-day-old piglets. Additionally, diarrhea was only observed in RV0104 and RV0143 (but not Cowden) inoculated 3-week-old piglets, while levels of serum IL-10 and PRVC IgA antibodies were higher in Cowden inoculated pigs, consistent with the lack of diarrhea. Thus, we confirmed that these current, genetically heterogeneous PRVC strains possess distinct pathobiological characteristics that may contribute to the increased prevalence of PRVC diarrhea in neonatal suckling piglets.

Simultaneous detection of five pig viruses associated with enteric disease in pigs using EvaGreen real-time PCR combined with melting curve analysis

In recent years, a series of porcine diarrhea viruses such as porcine epidemic diarrhea virus (PEDV), transmissible gastroenteritis virus (TGEV), rotaviruses of group A (RVA), rotaviruses of group C (RVC), and porcine circovirus 2 (PCV2) caused enormous economic losses all over the world. While any of these viruses is capable to cause disease alone, there is often concurrent infection with more than one virus on pig farms. In this study, a multiplex real-time PCR method based on EvaGreen fluorescent dye and melting curve analysis was established to simultaneously detect these five viruses in a single closed tube. Five distinct melt peaks were obtained with different melting temperature (Tm) value corresponding to each of the five viruses. This method was highly sensitive to detect and distinguish TGEV, RVA, RVC, PEDV and PCV2 with the limits of detection ranging from 5 to 50 copies/μL. The intra-assay and inter-assay reproducibility were good with coefficient of variation of Tm and cycle threshold values less than 0.32% and 2.86%, respectively. Testing of 90 field samples by the single and multiplex real-time PCR assays demonstrated a concordance of 91.1%. Thus, the EvaGreen multiplex real-time PCR is a rapid, sensitive and low-cost diagnostic tool for differential detection and routine surveillance of TGEV, RVA, RVC, PEDV and PCV2 in pigs.

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.

Frequency of Enteropathogen Detection in Suckling and Weaned Pigs with Diarrhea in Japan

Fecal samples from suckling ( n = 153) and weaned ( n = 116) piglets with diarrhea in Japan were examined for shedding of viral, bacterial, and parasitic pathogens using culture, microscopic, and polymerase chain reaction methods. In suckling piglets, diarrhea was attributed to infection with a single etiologic agent in 60.8% of cases and with combinations of agents in 22.2%. In weaned piglets, diarrhea was attributed to a single etiologic agent in 43.1% and to combinations of agents in 47.4% of cases. Rotavirus was the most prevalent agent in suckling (67.3%) and weaned (65.5%) piglets. The detection of other pathogens was associated with age of the animals examined. Coccidia were predominantly isolated from suckling piglets, whereas Escherichia coli was found predominantly in weaned piglets. Although a relationship was not observed between detection rate of rotavirus and age of piglets, a single group of rotavirus was detected in 87.5% of suckling piglets whereas multiple groups were detected in 51.6% of weaned piglets. The results of this study confirm that diarrhea in piglets can, to a variable degree, be causally associated with multiple agents. Additionally, these results suggest reasons why this syndrome can be difficult to control.

Biology and Diseases of Swine

Swine are used in biomedical research as models for biomedical research and for teaching. This chapter covers normative biology and behavior along with common and emerging swine diseases. Xenotransplantation is discussed along with similarities and differences of swine immunology.

Strategies for design and application of enteric viral vaccines

Enteric viral infections in domestic animals cause significant economic losses. The recent emergence of virulent enteric coronaviruses [porcine epidemic diarrhea virus (PEDV)] in North America and Asia, for which no vaccines are available, remains a challenge for the global swine industry. Vaccination strategies against rotavirus and coronavirus (transmissible gastroenteritis virus) infections are reviewed. These vaccination principles are applicable against emerging enteric infections such as PEDV. Maternal vaccines to induce lactogenic immunity, and their transmission to suckling neonates via colostrum and milk, are critical for early passive protection. Subsequently, in weaned animals, oral vaccines incorporating novel mucosal adjuvants (e.g., vitamin A, probiotics) may provide active protection when maternal immunity wanes. Understanding intestinal and systemic immune responses to experimental rotavirus and transmissible gastroenteritis virus vaccines and infection in pigs provides a basis and model for the development of safe and effective vaccines for young animals and children against established and emerging enteric infections.

Isolation and partial characterization of a novel porcine astrovirus

Astroviral infection has been described as one of the causes of porcine diarrhoeal disease. Here we describe the detection of astrovirus-like particles by electron microscopy in a diarrhoeal specimen. Furthermore, a cytopathic virus was isolated and propagated in an established porcine kidney cell line, PK-15. Reverse transcription and PCR performed with astrovirus-specific primers amplified a product with the expected size. Sequencing of the PCR product revealed that the virus observed by electron microscopy and propagated in the porcine cell line is an astrovirus, showing 86% identity at the nucleotide level with the only known porcine astrovirus, PAstV. Phylogenetic analysis clustered the novel isolate, Sb4685, together with PAstV in a broad clade comprising mammalian astroviruses.

Multiplex reverse transcription-PCR for rapid differential detection of porcine epidemic diarrhea virus, transmissible gastroenteritis virus, and porcine group A rotavirus

A novel multiplex reverse transcription polymerase chain reaction (multiplex RT-PCR) that can detect porcine epidemic diarrhea virus (PEDV), transmissible gastroenteritis virus (TGEV), and porcine group A rotavirus (GAR) was developed. The 3 viruses (PEDV, TGEV, and porcine GAR) are major agents in viral enteric diseases of piglets. As the clinical signs of these diseases are similar, including watery diarrhea, differential detection is required for etiologic diagnosis. A mixture of 3 pairs of published primers was used for amplification of viral nucleic acids, yielding 3 different amplicons with sizes of 859 bp, 651 bp, and 309 bp for TGEV, PEDV, and porcine GAR, respectively. A total of 157 specimens (78 fecal and 79 intestinal samples) from piglets with acute gastroenteritis were collected in Korea between January 2004 and May 2005. They were tested for the presence of 3 viruses by multiplex RT-PCR. Coinfections with PEDV and porcine GAR were identified in 16 farms (43.2%). PEDV, porcine GAR, and TGEV infection were 26.3%, 13.2%, and 2.7% respectively. The relative sensitivity and specificity of multiplex RT-PCR were evaluated, with results suggesting that this assay is equal in quality to conventional single-agent RT-PCR assays (sensitivity:100%, 92.9%, 100% for TGEV, PEDV, GARs; specificity: 100% for all 3 viruses). This multiplex RT-PCR is a simple assay and may be a potentially useful for rapid, sensitive, and cost-effective etiological diagnostic tool for acute viral gastroenteritis in piglets.

Induction of mucosal immune responses and protection against enteric viruses: rotavirus infection of gnotobiotic pigs as a model

Enteric viruses are a major cause of diarrhea in animals and humans. Among them, rotaviruses are one of the most important causes of diarrhea in young animals and human infants. A lack of understanding of mechanisms to induce intestinal immunity and the correlates of protective immunity in neonates has impaired development of safe and effective vaccines against enteric viruses. Studies of candidate vaccines using an adult mouse model of subclinical enteric viral infections often do not predict vaccine efficacy against disease evaluated in neonatal large animals. A series of studies have been conducted using a neonatal gnotobiotic pig model of rotavirus infection and diarrhea to identify correlates of protective immunity and to evaluate traditional and novel vaccine approaches for the induction of mucosal immune responses and protection to enteric viruses. Gnotobiotic pigs recovered from infection with virulent Wa human rotavirus (HRV) (mimic natural infection) had high numbers of intestinal IgA rotavirus-specific primary antibody-secreting cells (ASCs) and memory B-cells (to recall antigen) measured by ELISPOT assay, which correlated with complete protection against rotavirus challenge. Most short-term IgA memory B-cells were resident in the ileum, the major site of rotavirus replication. Spleen, not the bone marrow, was the major resident site for longer-term IgG memory B-cells. Candidate rotavirus vaccines evaluated in pigs for their ability to induce intestinal or systemic ASC and protection against rotavirus infection and diarrhea included attenuated live virus, inactivated virus, and baculovirus-expressed double-layered rotavirus-like particles (2/6-VLPs). In combination with those candidate vaccines, various adjuvants, delivery systems, and immunization routes were tested, including incomplete Freund's adjuvant for i.m. immunization, and a mutant Escherichia coli heat labile enterotoxin R192G (mLT) for i.n. immunization. It was shown that orally administered replicating vaccines were most effective for priming for intestinal IgA ASC and memory B-cell responses, but i.n. administered non-replicating 2/6-VLPs plus mLT were effective as booster vaccines. We conclude that protective immunity depends on the magnitude, location, viral protein-specificity, and isotype of the antibody responses induced by vaccination. Therefore highly effective enteric viral vaccines should: (i) induce sufficient levels of intestinal IgA antibodies; (ii) include viral antigens that induce neutralizing antibodies; and (iii) require the use of effective mucosal adjuvants or antigen delivery systems for non-replicating oral or i.n. vaccines.

Systemic and intestinal antibody responses to NSP4 enterotoxin of Wa human rotavirus in a gnotobiotic pig model of human rotavirus disease

Antibody responses to the Wa human rotavirus (HRV) nonstructural protein NSP4, a viral enterotoxin, were evaluated in neonatal gnotobiotic (Gn) pigs. Gn pigs were inoculated orally with one dose of 10(5) fluorescent focus units (FFU) of virulent Wa HRV (HRV-V), to mimic natural infection, or with three doses of 5 x 10(7) FFU attenuated Wa HRV (HRV-A) at 10-day intervals, to mimic oral attenuated rotavirus vaccines, or they were mock inoculated (mock). Subsets of pigs were challenged with 10(6) FFU of virulent Wa HRV at post-inoculation day 28 (PID 28). Post-challenge, the HRV-V pigs were completely protected against diarrhea and virus shedding, whereas the HRV-A pigs had a 50% protection rate against diarrhea and a 67% protection rate against virus shedding. All mock-inoculated pigs shed virus and had diarrhea post-challenge. Isotype antibody titers to NSP4 were compared in serum and intestinal contents, at post-inoculation day (PID) 28 and at post-challenge day 7 (PCD 7/PID 35) by indirect ELISA, using purified recombinant NH2-6xHis-tagged NSP4 of virulent Wa HRV. Pre-challenge, both the HRV-V and HRV-A-inoculated pigs had similar moderate titers of serum IgG antibodies to NSP4. However, only the HRV-V-inoculated pigs developed detectable serum and intestinal IgA antibody titers to NSP4 pre-challenge, compared with the HRV-A-inoculated pigs. The mock-inoculated pigs had no IgM, IgA, or IgG antibodies to NSP4 pre-challenge. All Wa HRV-inoculated pigs developed low to moderate titers of serum IgM, IgG, and IgA antibodies to NSP4 post-challenge, but the mock-inoculated pigs had only IgM antibodies post-challenge. Both Wa HRV-inoculated groups developed low titers of IgA antibody to NSP4 in the small intestinal contents post-challenge, but titers were 5.8-fold higher in the HRV-V pigs. Our results concur with findings that both rotavirus vaccinated and naturally infected children seroconvert with modest IgG antibodies to NSP4 [Johansen et al. (1999) J Med Virol 59:369-367]. These data suggest that Gn pigs could be a useful model to evaluate serum and intestinal IgA antibodies to NSP4 and their role in protection against HRV infection. Further experiments may clarify whether (1) the NSP4 antibodies detected pre-challenge in the HRV-V pigs contribute to the higher protection rates observed, or (2) the reduced or delayed NSP4 antibody responses of the HRV-A pigs are associated with the lower protection rates in these pigs.

Mucosal and systemic immune responses to chimeric fimbriae expressed by Salmonella enterica serovar typhimurium vaccine strains

Recombinant live oral vaccines expressing pathogen-derived antigens offer a unique set of attractive properties. Among these are the simplicity of administration, the capacity to induce mucosal and systemic immunity, and the advantage of permitting genetic manipulation for optimal antigen presentation. In this study, the benefit of having a heterologous antigen expressed on the surface of a live vector rather than intracellularly was evaluated. Accordingly, the immune response of mice immunized with a Salmonella enterica serovar Typhimurium vaccine strain expressing the Escherichia coli 987P fimbrial antigen on its surface (Fas(+)) was compared with the expression in the periplasmic compartment (Fas(-)). Orally immunized BALB/c mice showed that 987P fimbriated Salmonella serovar Typhimurium CS3263 (aroA asd) with pCS151 (fas(+) asd(+)) elicited a significantly higher level of 987P-specific systemic immunoglobulin G (IgG) and mucosal IgA than serovar Typhimurium CS3263 with pCS152 (fasD mutant, asd(+)) expressing 987P periplasmic antigen. Further studies were aimed at determining whether the 987P fimbriae expressed by serovar Typhimurium chi4550 (cya crp asd) could be used as carriers of foreign epitopes. For this, the vaccine strain was genetically engineered to express chimeric fimbriae carrying the transmissible gastroenteritis virus (TGEV) C (379-388) and A (521-531) epitopes of the spike protein inserted into the 987P major fimbrial subunit FasA. BALB/c mice administered orally serovar Typhimurium chi4550 expressing the chimeric fimbriae from the tet promoter in pCS154 (fas(+) asd(+)) produced systemic antibodies against both fimbria and the TGEV C epitope but not against the TGEV A epitope. To improve the immunogenicity of the chimeric fimbriae, the in vivo inducible nirB promoter was inserted into pCS154, upstream of the fas genes, to create pCS155. In comparison with the previously used vaccine, BALB/c mice immunized orally with serovar Typhimurium chi4550/pCS155 demonstrated significantly higher levels of serum IgG and mucosal IgA against 987P fimbria. Moreover, mucosal IgA against the TGEV C epitope was only detected with serovar Typhimurium chi4550/pCS155. The induced antibodies also recognized the epitopes in the context of the full-length TGEV spike protein. Hence, immune responses to heterologous chimeric fimbriae on Salmonella vaccine vectors can be optimized by using promoters known to be activated in vivo.