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

Development of a colloidal gold immunochromatographic strip for the simultaneous detection of porcine epidemic diarrhea virus and transmissible gastroenteritis virus

In recent years, porcine diarrhea-associated viruses have caused significant economic losses globally. These viruses present similar clinical symptoms, such as watery diarrhea, dehydration, and vomiting. Co-infections with porcine epidemic diarrhea virus (PEDV) and transmissible gastroenteritis virus (TGEV) are common. For the rapid and on-site preliminary diagnosis on the pig farms, this study aimed to develop a colloidal gold immunochromatography assay (GICA) strip for the detection of PEDV and TGEV simultaneously. The GICA kit showed that there was no cross-reactivity with the other five common porcine viruses. With visual observation, the lower limits were approximately 104 TCID50/mL and 104 TCID50/mL for PEDV and TGEV, respectively. The GICA strip could be stored at 4°C or 25°C for 12 months without affecting its efficacy. To validate the GICA strip, 121 clinical samples were tested. The positive rates of PEDV and TGEV were 42.9 and 9.9%, respectively, and the co-infection rate of the two viruses was 5.8% based on the duplex GICA strip. Thus, the established GICA strip is a rapid, specific, and stable tool for on-site preliminary diagnosis of PEDV- and TGEV-associated diarrhea.

Prevalence and Genetic Characterization of Porcine Respiratory Coronavirus in Korean Pig Farms

Porcine respiratory coronavirus (PRCV) is a member of the species Alphacoronavirus 1 within the genus Alphacoronavirus of the family Coronaviridae. A few studies have been conducted on the prevalence of PRCV since its first identification in 1997, but there have been no recent studies on the prevalence and genetic characterization of the virus in Korea. In this study, the seroprevalence of PRCV was determined in Korean pig farms using a commercially available TGEV/PRCV differential enzyme-linked immunosorbent assay kit. The farm-level seroprevalence of PRCV was determined to be 68.6% (48/70), similar to previous reports in Korea, suggesting that PRCV is still circulating in Korean pig herds nationwide. Among the 20 PRCV-seropositive farms tested in this study, PRCV RNAs were detected in 17 oral fluid samples (28.3%) from nine farms (45.0%), while TGEV RNAs were not detected in any sample. To investigate the genetic characteristics of Korean PRCV strains, genetic and phylogenetic analyses were conducted on PRCV spike gene sequences obtained in this study. The three Korean PRCV strains (KPRCV2401, KPRCV2402, and KPRCV2403) shared 98.5-100% homology with each other and 96.2-96.6% and 91.6-94.5% homology with European and American strains, respectively. A 224-amino acid deletion was found in the S gene of both Korean and European PRCVs but not in that of American PRCVs, suggesting a European origin for Korean PRCVs. Phylogenetic analysis showed that Korean PRCVs are more closely related to European PRCVs than American PRCVs but clustered apart from both, suggesting that Korean PRCV has evolved independently since its emergence in Korean PRCVs. The results of this study will help expand knowledge on the epidemiology and molecular biology of PRCV currently circulating in Korea.

Development of a triplex quantitative reverse transcription-polymerase chain reaction for the detection of porcine epidemic diarrhea virus, porcine transmissible gastroenteritis virus, and porcine rotavirus A

Porcine viral diarrhea is caused by many pathogens and can result in watery diarrhea, dehydration and death. Various detection methods, such as polymerase chain reaction (PCR) and real-time quantitative PCR (qPCR), have been widely used for molecular diagnosis. We developed a triplex real-time quantitative reverse transcription PCR (qRT-PCR) for the simultaneous detection of three RNA viruses potentially associated with porcine viral diarrhea: porcine epidemic diarrhea virus (PEDV), porcine transmissible gastroenteritis virus (TGEV), and porcine rotavirus A (PoRVA). The triplex qRT-PCR had R2 values of 0.999 for the standard curves of PEDV, TGEV and PoRVA. Importantly, the limits of detection for PEDV, TGEV and PoRVA were 10 copies/μL. The specificity test showed that the triplex qRT-PCR detected these three pathogens specifically, without cross-reaction with other pathogens. In addition, the approach had good repeatability and reproducibility, with intra-and inter-assay coefficients of variation <1%. Finally, this approach was evaluated for its practicality in the field using 256 anal swab samples. The positive rates of PEDV, TGEV and PoRVA were 2.73% (7/256), 3.91% (10/256) and 19.14% (49/256), respectively. The co-infection rate of two or more pathogens was 2.73% (7/256). The new triplex qRT-PCR was compared with the triplex RT-PCR recommended by the Chinese national standard (GB/T 36871-2018) and showed 100% agreement for PEDV and TGEV and 95.70% for PoRVA. Therefore, the triplex qRT-PCR provided an accurate and sensitive method for identifying three potential RNA viruses for porcine viral diarrhea that could be applied to diagnosis, surveillance and epidemiological investigation.

Phylogenetically evolutionary analysis provides insights into the genetic diversity and adaptive evolution of porcine deltacoronavirus

BACKGROUND

Porcine deltacoronavirus (PDCoV) is one of the emerging swine enteric coronaviruses (SECoVs), which has been widely prevalent in the North America and Asia. In addition to causing severe diarrhea in piglets, PDCoV also shows the potential to infect diverse host species, including calves, chickens, turkey poults, and humans. However, the clinical pathogenicity and genetic evolution of PDCoV is still not fully understood.

RESULTS

Here, we recorded an outbreak of a novel recombinant PDCoV strain (CHN-HeN06-2022) in a large nursery fattening pig farm. Genomic analysis showed that the CHN-HeN06-2022 strain shared 98.3-98.7% sequence identities with the Chinese and American reference strains. To clarify the evolutionary relationships, phylogenetic analysis was performed using the PDCoV genome sequences available in the GenBank database. Based on genetic distance and geographical distribution, the phylogenetic tree clearly showed that all the PDCoV sequences could be divided into lineage 1 and lineage 2, which were further classified into sublineage 1.1 (Chinese strains), 1.2 (the North American strains), 2.1 (the Southeast Asian strains), and 2.2 (Chinese strains). Corresponding to the evolutionary tree, we found that, compared to lineage 1, lineage 2 strains usually contain a continuous 6-nt deletion in Nsp2 and a 9-nt deletion in Nsp3, respectively. Furthermore, recombination analysis suggested that the CHN-HeN06-2022 occurred segments exchange crossed Nsp2 and Nsp3 region between sublineage 1.1 and sublineage 2.1. Combined with previously reported recombinant strains, the highest recombination frequency occurred in Nsp2, Nsp3, and S gene. Additionally, we identified a total of 14 amino acid sites under positive selection in spike protein, most of which are located in the regions related with the viral attachment, receptor binding, and membrane fusion.

CONCLUSIONS

Taken together, our studies provide novel insights into the genetic diversity and adaptive evolution of PDCoV. It would be helpful to the development of vaccine and potential antiviral agent.

A Rapid and Novel Multiplex PCR Assay for Simultaneous Detection of Multiple Viruses Associated with Bovine Gastroenteritis

Bovine viral diarrheal virus (BVDV) and bovine coronavirus (BCoV) are prevalent viral infections in buffalo calves that result in significant economic losses globally. However, Bovine picobirnavirus (BPBV) Group I and II has been an emerging causes of gastrointestinal infection as has been detected with mixed of BVDV as well as BCV. To combat economic losses and viral infection, a rapid and innovative multiplex-PCR assay (M-PCR) was developed to simultaneously identify BVDV, BCV, and BPBV. The assay employed three primer pairs, each specific to a particular virus. Notably, the primers for BCV and BVDV, targeting the transmembrane (M) Mebus gene and 5'UTR genes, respectively, were self-designed. To validate the assay, 300 samples of buffalo calf feces were subjected to the standardized multiplex PCR. The results demonstrated that 54 (18%) samples tested positive for multiple viruses, with 16.67% samples infected by BVDV, 0.9% by BCoV, and 0.13% by BPBV, as detected by the M-PCR assay. In summary, this developed assay is characterized by high specificity, sensitivity, throughput, and speed, enabling the simultaneous detection of the three viruses in a single reaction tube. Consequently, it holds potential for epidemiological investigations. It is worth noting that, to the best of our knowledge, this is the first reported multiplex assay for the worldwide detection of BVDV, BCoV, and BPBV. This novel assay promises to aid in the detection of mixed infections in the gastrointestinal tract.

Computationally-driven epitope identification of PEDV N-protein and its application in development of immunoassay for PEDV detection

The nucleocapsid (N) protein is a suitable candidate for early diagnosis of porcine epidemic diarrhea virus (PEDV). Here, we identified the linear B-cell epitopes of the PEDV N-protein by integrating a computational-experimental framework and constructed three-dimensional (3D) structure model of the N protein using the ColabFold program in Google Colaboratory. Furthermore, we prepared the monoclonal antibodies against the predicted epitopes and recombinant N protein, respectively, and selected pairing mAbs (named 9C4 and 3C5) to develop a double-antibody sandwich immunochromatographic test strip using CdSe/ZnS quantum dots (QDs)-labelled 9C4 and 3C5 as capture and detection antibodies, respectively. This strip can specifically detect PEDV within 10 min with a detection limit of less than 6.25 × 103 TCID50/mL. In comparison with RT-PCR for testing 90 clinical samples, the relative sensitivity and specificity of the strip were found to be 98.0% and 100%, respectively, with a concordance rate of 98.9% and a kappa value of 0.978, indicating that QDs-ICTS is a reliable method for the application of PEDV detection in clinical samples.

Coinfection of porcine astrovirus and other porcine viruses in diarrheic pigs in Haryana, India

In this study, 306 rectal swabs from diarrheal pigs of various ages (0-3 weeks, 3-6 weeks, and >6 weeks) were collected from 54 piggery units in different climatic zones in Haryana state, India. These samples were tested for the presence of porcine astrovirus (PAstV), porcine rotavirus group A (PRV-A), and classical swine fever virus (CSFV) by reverse transcription polymerase chain reaction (RT-PCR), and porcine circovirus 2 (PCV-2) by polymerase chain reaction (PCR). Out of the 306 samples tested, 153 (50%), 108 (35.3%), 32 (10.6%), and three (0.9%) tested positive for PAstV, PCV-2, PRV-A, and CSFV, respectively. A single infection was detected in 135 samples, while mixed infections were found in 77 samples: 70 with two viruses and seven samples with more than two. PAstV was detected most frequently (55.31%) in pigs aged 3-6 weeks. PCV-2 was more predominant in pigs aged 0-3 weeks (36.53%), whereas PRV-A was more common in pigs aged 3-6 weeks (11.3%). CSFV was observed in the age group of 0-3 weeks (1.92%). Phylogenetic analysis revealed the circulation of lineages 2 and 4 of PAstV in this region. Thus, it can be concluded that one or more than one virus is circulating in piggery units in Haryana, India.

Porcine Sapovirus in Northern Vietnam: Genetic Detection and Characterization Reveals Co-Circulation of Multiple Genotypes

Porcine sapovirus (PoSaV) has been reported in many countries over the world, which may cause gastroenteritis symptoms in pigs with all ages. There has been no report on PoSaV infection in Vietnam up to now. In this study, a total of 102 samples were collected from piglets, fattening pigs, and sows with diarrhea in several cities and provinces in northern Vietnam. The PoSaV genome was examined using polymerase chain reaction (PCR). Sequencing of the partial RNA-dependent RNA polymerase (RdRp) gene sequences (324 bp) was performed. Of the 102 tested samples, 10 (9.8%) and 7/20 (35%) were detected as positive for the PoSaV RdRp gene using the PCR method at the individual and farm levels, respectively. Genetic analysis of the partial RdRp gene region of about 324 bp indicated that the nucleotide identity of the current 10 Vietnamese viral strains ranged from 61.39% to 100%. Among the 10 strains obtained, 8 belonged to genotype III and the remaining 2 strains were clustered in genotype VIII. The Vietnamese genotype III viruses formed two sub-clusters. The Vietnamese PoSaV strains were closely related to PoSaVs reported in South Korea, Venezuela, and the Netherlands. This research was the first to describe PoSaV infection in northern Vietnam during 2022-2023.

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

This study developed a novel, ultrasensitive sandwich-type electrochemical immunosensor for detecting the porcine epidemic diarrhea virus (PEDV). By electrochemical co-deposition of graphene and Prussian blue, a Prussian blue-reduced graphene oxide-modified glassy carbon electrode was made, further modified with PEDV-monoclonal antibodies (mAbs) to create a new PEDV immunosensor using the double antibody sandwich technique. The electrochemical characteristics of several modified electrodes were investigated using cyclic voltammetry (CV). We optimized the pH levels and scan rate. Additionally, we examined specificity, reproducibility, repeatability, accuracy, and stability. The study indicates that the immunosensor has good performance in the concentration range of 1 × 10^1.88 to 1 × 10^5.38 TCID₅₀/mL of PEDV, with a detection limit of 1 × 10^1.93 TCID₅₀/mL at a signal-to-noise ratio of 3σ. The composite membranes produced via co-deposition of graphene and Prussian blue effectively increased electron transport to the glassy carbon electrode, boosted response signals, and increased the sensitivity, specificity, and stability of the immunosensor. The immunosensor could accurately detect PEDV, with results comparable to real-time quantitative PCR. This technique was applied to PEDV detection and served as a model for developing additional immunosensors for detecting hazardous chemicals and pathogenic microbes.

Visual and Rapid Detection of Porcine Epidemic Diarrhea Virus (PEDV) Using Reverse Transcription Loop-Mediated Isothermal Amplification Method

Porcine epidemic diarrhea virus (PEDV) can cause severe infectious porcine epidemic diarrhea (PED) and infect different ages of pigs, resulting in sickness and death among suckling pigs. For PEDV detection, finding an effective and rapid method is a priority. In this study, we established an effective reverse transcription loop-mediated isothermal amplification (RT-LAMP) method for PEDV detection. Three sets of primers, specific for eight different sequences of the PEDV N gene, were designed in this study. The optimized RT-LAMP amplification program was as follows: 59 min at 61.9 °C and 3 min at 80 °C. The RT-LAMP results were confirmed with the addition of SYBR Green I fluorescence dye and with the detection of a ladder-like band by conventional gel electrophoresis analysis, which demonstrated a significant agreement between the two methods. The LOD of PEDV by RT-LAMP was 0.0001 ng/μL. Compared with RT-LAMP, the traditional RT-PCR method is 100-fold less sensitive. The RT-LAMP results had no cross-reaction with porcine parvovirus (PPV), porcine circovirus type 1 (PCV1), porcine pseudorabies virus (PRV), porcine circovirus type 2 (PCV2), rotavirus (RV), transmissible gastroenteritis virus (TGEV) and porcine reproductive and respiratory syndrome virus (PRRSV). Consequently, the newly developed RT-LAMP method could provide an accurate and reliable tool for PEDV diagnosis.

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

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

Assessing the Epidemiology of Rotavirus A, B, C and H in Diarrheic Pigs of Different Ages in Northern Italy

Rotaviruses are classified in 10 groups (A to J), where rotavirus A (RVA) is the major cause of diarrhea in humans and animals. With some exceptions, there is scarce information on the epidemiology of non-A rotaviruses in human and animal hosts. Currently, five species (A, B, C, E and H) have been identified in pigs. In the present study we investigated the prevalence of RVA, RVB, RVC and RVH among diarrheic pigs of different ages, in different seasons and in the presence of co-infections. Two molecular assays were developed for the detection of porcine RVA, RVB, RVC and RVH and were used to screen 962 stool specimens from suckling, weaning and fattening pigs with acute enteritis. Overall, rotaviruses were detected in a high percentage of samples (78%), with RVA being predominant (53%), followed by RVC (45%), RVB (43%) and RVH (14%). RVA was more common in the suckling (58%) and weaning cohorts (64%), while RVB, RVC and RVH were also frequently detected in fattening pigs. Only RVA and RVB infections followed a seasonal trend and exhibited age-related differences. Rotavirus infections were frequently present in combination with other pathogens. The present study depicts a portrait of rich rotavirus diversity in porcine herds, identifying seasonal and age-related patterns of circulation of the different rotavirus species in the surveyed areas.

Development and Application of a Reverse-Transcription Recombinase-Aided Amplification Assay for Porcine Epidemic Diarrhea Virus

Porcine epidemic diarrhea virus (PEDV) is a coronavirus currently widespread worldwide in the swine industry. Since PEDV was discovered in China in 1984, it has caused huge economic losses in the swine industry. PEDV can infect pigs of all ages, but piglets have the highest infection with a death rate as high as 100%, and the clinical symptoms are watery diarrhea, vomiting, and dehydration. At present, there is not any report on PEDV detection by RT-RAA. In this study, we developed an isothermal amplification technology by using reverse-transcription recombinase-aided amplification assay (RT-RAA) combined with portable instruments to achieve a molecular diagnosis of PEDV in clinical samples from China. By designing a pair of RT-RAA primers and probes based on the PEDV N gene, this method breaks the limitations of existing detection methods. The assay time was within 30 min at 41 °C and can detect as few as 10 copies of PEDV DNA molecules per reaction. Sixty-two clinical tissue samples were detected by RT-qPCR and RT-RAA. The positive and negative rates for the two methods were 24.19% and 75.81%, respectively. Specificity assay showed that the RT-RAA had specifically detected PEDV and was not reactive for porcine parvovirus (PPV), transmissible gastroenteritis virus (TGEV), porcine circovirus type 2 (PCV2), porcine pseudorabies virus (PRV), porcine reproductive and respiratory syndrome virus (PRRSV), classical swine fever virus (CSFV), swine flu virus (SIV), or porcine Japanese encephalitis virus (JEV). The results suggested that RT-RAA had a strong specificity and high detection sensitivity when combined with a portable instrument to complete the detection under a constant temperature of 30 min, which are more suitable for preventing and controlling PEDV onsite in China.

iTRAQ-based proteome analysis of porcine group A rotavirus-infected porcine IPEC-J2 intestinal epithelial cells

Porcine rotavirus (PoRV), particularly group A, is one of the most important swine pathogens, causing substantial economic losses in the animal husbandry industry. To improve understanding of host responses to PoRV infection, we applied isobaric tags for relative and absolute quantification (iTRAQ) labeling coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) to quantitatively identify the differentially expressed proteins in PoRV-infected IPEC-J2 cells and confirmed the differentially accumulated proteins (DAPs) expression differences by performing RT-qPCR and Western blot analysis. Herein, in PoRV- and mock-infected IPEC-J2 cells, relative quantitative data were identified for 4724 proteins, 223 of which were DAPs (125 up-accumulated and 98 down-accumulated). Bioinformatics analyses further revealed that a majority of the DAPs are involved in numerous crucial biological processes and signaling pathways, such as metabolic process, immune system process, amino acid metabolism, energy metabolism, immune system, MHC class I peptide loading complex, Hippo signaling pathway, Th1 and Th2 cell differentiation, antigen processing and presentation, and tubule bicarbonate reclamation. The cellular localization prediction analysis indicated that these DAPs may be located in the Golgi apparatus, nucleus, peroxisomal, cytoplasm, mitochondria, extracellular, plasma membrane, and endoplasmic reticulum (ER). Expression levels of three up-accumulated (VAMP4, IKBKE, and TJP3) or two down-accumulated (SOD3 and DHX9) DAPs upon PoRV infection, were further validated by RT-qPCR and Western blot analysis. Collectively, this work is the first time to investigate the protein profile of PoRV-infected IPEC-J2 cells using quantitative proteomics; these findings provide valuable information to better understand the mechanisms underlying the host responses to PoRV infection in piglets. SIGNIFICANCE: The proteomics analysis of this study uncovered the target associated with PoRV-induced innate immune response or cellular damage, and provided relevant insights into the molecular functions, biological processes, and signaling pathway in these targets. Out of these 223 DAPs, the expression levels of three up-accumulated (VAMP4, IKBKE, and TJP3) and two down-accumulated (SOD3 and DHX9) DAPs upon PoRV infection, have been further validated using RT-qPCR and Western blot analysis. These outcomes could uncover how PoRV manipulated the cellular machinery, which could further our understanding of PoRV pathogenesis in piglets.

Novel universal primer-pentaplex PCR assay based on chimeric primers for simultaneous detection of five common pig viruses associated with diarrhea

Viral pathogens associated with diarrhea in pigs include porcine circovirus 2 (PCV2), porcine epidemic diarrhea virus (PEDV), transmissible gastroenteritis virus (TGEV), porcine rotavirus A (RVA) and C (RVC) among others. In this study, a novel universal primer-based pentaplex PCR (UP-M-PCR) assay was developed for simultaneous detection and differentiation of these five viruses. The assay uses a short-cycle multiplex amplification by chimeric primers (CP), which are virus specific, with a tail added at the 5' end of the universal primer (UP), followed by universal amplification using UPs and a regular cycle amplification. Five universal primers with CPs (UP1-5) were designed and evaluated in an UP-based single PCR (UP-S-PCR). All five UPs were found to work efficiently and UP2 exhibited the best performance. After system optimizations, the analytical sensitivity of the UP-M-PCR, using plasmids containing the specific viral target fragments, was 5 copies/reaction for each of the five viruses irrespective of presence of a single or multiple viruses in the reaction. No cross-reaction was observed with other non-target viruses. When 273 fecal samples from clinically healthy pigs were tested, the assay sensitivity was 90.9-100%, the specificity was 98.0-100%, and the agreement rate with the UP-S-PCR was 98.5-99.6% with a Kappa value being 0.95-0.98. In summary, the UP-M-PCR developed here is a rapid and highly sensitive and specific detection method that can be used to demonstrate mixed infections in pigs with diarrhea.

Molecular Characterization of Porcine Epidemic Diarrhea Virus and Its New Genetic Classification Based on the Nucleocapsid Gene

Porcine epidemic diarrhea virus (PEDV) causes continuous, significant damage to the swine industry worldwide. By RT-PCR-based methods, this study demonstrated the ongoing presence of PEDV in pigs of all ages in Korea at the average detection rate of 9.92%. By the application of Bayesian phylogenetic analysis, it was found that the nucleocapsid (N) gene of PEDV could evolve at similar rates to the spike (S) gene at the order of 10^-4 substitutions/site/year. Based on branching patterns of PEDV strains, three main N gene-base genogroups (N1, N2, and N3) and two sub-genogroups (N3a, N3b) were proposed in this study. By analyzing the antigenic index, possible antigenic differences also emerged in both the spike and nucleocapsid proteins between the three genogroups. The antigenic indexes of genogroup N3 strains were significantly lower compared with those of genogroups N1 and N2 strains in the B-cell epitope of the nucleocapsid protein. Similarly, significantly lower antigenic indexes in some parts of the B-cell epitope sequences of the spike protein (COE, S1D, and 2C10) were also identified. PEDV mutants derived from genetic mutations of the S and N genes may cause severe damage to swine farms by evading established host immunities.

Development of real-time RT-PCR assay for diagnosis of viral enteritis in neonatal goat kids

Rotavirus gastroenteritis is a worldwide disease affecting primarily infants, young children and young ones of wide variety of mammalian and avian species. Diarrhoea in goat kids is most frequently found associated with Group A rotavirus (GARV) and another enteric pathogen bovine coronavirus (BCoV), a major viral pathogen associated with neonatal diarrhoea. Enteric BCoV replicates in epithelial cells of gut, destroying villi, resulting in severe, often bloody diarrhoea in calves. It requires highly sensitive and specific assays to diagnose the disease at field level. In the present study, a real-time reverse-transcriptase (RT) polymerase chain reaction (PCR) were developed and validated for specific detection and quantification of GARV and BCoV with high sensitivity and specificity. For real-time RT-PCR, primers were designed to target nucleocapsid gene for BCoV; NSP4 gene and VP6 gene were designed for GARV using discontiguous conserved sequences. Real-time RT-PCR assay was standardized by serial dilution of positive GARV and BCoV RNA. The rotavirus real-time RT-PCR assay was found to be specific to rotavirus, but broadly reactive to GARV. The sensitivity of the assay for detecting rotavirus and BCoV in faecal samples and tissue sample was found to be high in such reactions. The real-time RT-PCR assay was effective in detecting GARV and BCoV in all positive samples obtained from sheds, farms and outbreaks. The results of this study demonstrate that the real-time RT-PCR assay for viral enteritis is broadly reactive, specific, and sensitive for detection of GARV and BCoV in faecal sample and tissue samples.

One-step triplex reverse-transcription PCR detection of porcine epidemic diarrhea virus, porcine sapelovirus, and porcine sapovirus

Swine diarrhea can be caused by multiple agents, including porcine epidemic diarrhea virus (PEDV), porcine sapelovirus (PSV), and porcine sapovirus (SaV). We designed a one-step triplex reverse-transcription PCR (RT-PCR) detection method including 3 pairs of primers that focused on the S1 gene of PEDV, a conserved gene of PSV, and the VP1 gene of SaV. The optimal concentrations of upstream and downstream primers in the triplex RT-PCR were 0.24 μM for PEDV, 0.15 μM for PSV, and 0.2 μM for SaV, and the optimal annealing temperature was 55.5°C. Triplex RT-PCR assessment of 402 piglet diarrhea samples was compared with conventional individual RT-PCR. Concordance rates in both tests for individual viruses were 100%, 97.6%, and 94.4% for PEDV, PSV, and SaV, respectively. PEDV, PSV, and SaV were detected in 57.2%, 10.4%, and 9.0% of the samples, respectively. The high sensitivity and specificity of this triplex RT-PCR-based detection method for PEDV, PSV, and SaV could allow rapid detection and analysis of mixed infections by these 3 viruses.

A novel biotinylated nanobody-based blocking ELISA for the rapid and sensitive clinical detection of porcine epidemic diarrhea virus

Background

Porcine epidemic diarrhea virus (PEDV), which is characterized by severe watery diarrhea, vomiting, dehydration and a high mortality rate in piglets, leads to enormous economic losses to the pork industry and remains a large challenge worldwide. Thus, a rapid and reliable method is required for epidemiological investigations and to evaluate the effect of immunization. However, the current diagnostic methods for PEDV are time-consuming and very expensive and rarely meet the requirements for clinical application. Nanobodies have been used in the clinic to overcome these problems because of the advantages of their easy expression and high level of stability. In the present work, a novel biotinylated nanobody-based blocking ELISA (bELISA) was developed to detect anti-PEDV antibodies in clinical pig serum.

Results

Using phage display technology and periplasmic extraction ELISA (PE-ELISA), anti-PEDV N protein nanobodies from three strains of PEDV were successfully isolated after three consecutive rounds of bio-panning from a high quality phage display VHH library. Then, purified Nb2-Avi-tag fusion protein was biotinylated in vitro. A novel bELISA was subsequently developed for the first time with biotinylated Nb2. The cutoff value for bELISA was 29.27%. One hundred and fifty clinical serum samples were tested by both newly developed bELISA and commercial kits. The sensitivity and specificity of bELISA were 100% and 93.18%, respectively, and the coincidence rate between the two methods was 94%.

Conclusions

In brief, bELISA is a rapid, low-cost, reliable and useful nanobody-based tool for the serological evaluation of current PEDV vaccines efficacy and indirect diagnosis of PEDV infection.

A TaqMan-probe-based multiplex real-time RT-qPCR for simultaneous detection of porcine enteric coronaviruses

Swine enteric coronaviruses are a group of most significant pathogens causing diarrhea in piglets with similar clinical symptoms and pathological changes. To develop a simple, rapid, accurate, and high-throughput detection method for diagnosis and differential diagnosis on swine enteric coronaviruses, specific primers and probes were designed based on the highly conserved regions of transmissible gastroenteritis virus (TGEV) N, porcine epidemic diarrhea virus (PEDV) M, porcine deltacoronavirus (PDCoV) M, and porcine enteric alphacoronavirus (PEAV) N genes respectively. A TaqMan-probe-based multiplex real-time RT-qPCR assay was developed and optimized to simultaneously detect these swine enteric coronaviruses. The results showed that the limit of detection can reach as low as 10 copies in singular real-time RT-qPCR assays and 100 copies in multiplex real-time RT-qPCR assay, with all correlation coefficients (R²) at above 0.99, and the amplification efficiency at between 90 and 120%. This multiplex real-time RT-qPCR assay demonstrated high sensitivity, extreme specificity, and excellent repeatability. The multiplex real-time RT-qPCR assay was then employed to detect the swine enteric coronavirus from 354 field diarrheal samples. The results manifested that TGEV and PDCoV were the main pathogens in these samples, accompanied by co-infections. This well-established multiplex real-time RT-qPCR assay provided a rapid, efficient, specific, and sensitive tool for detection of swine enteric coronaviruses.

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

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

Characterization and epidemiological survey of porcine sapelovirus in China

Porcine sapelovirus (PSV) is a causative agent of acute diarrhoea, respiratory distress, reproductive failure, and polioencephalomyelitis in swine. Here, we report the isolation, genomic sequence, and biological characterization of PSV isolated from pig diarrhoeal samples. In our study, two PSV strains were identified with a diameter of approximately 25 nm, and their full genomes were 7564 nucleotides in length. We named the strains PSV-JXXY-a2 and PSV-JXXY-c. Phylogenetic analysis showed that the two virus isolates were classified into the China cluster. Moreover, the PSV-JXXY-a2 strain could be inactivated quickly at 54℃ and adapted to grow on different cell lines of porcine, human, and baby hamster origin. Pathogenicity investigation showed that the isolated PSV could infect neonatal piglets efficiently and caused diarrhoea in piglets. Further epidemiological investigation revealed a high prevalence of PSV in pig herds, and the PSV-positive rates in pigs with diarrhoea were much higher than in asymptomatic samples in China. Together, our findings demonstrate that PSV-JXXY-a2 is pathogenic to neonatal piglets and advance knowledge on the prevalence of PSV infection.

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.

A new immunochromatographic assay for on-site detection of porcine epidemic diarrhea virus based on monoclonal antibodies prepared by using cell surface fluorescence immunosorbent assay

BACKGROUND

Porcine epidemic diarrhea virus (PEDV) is a highly effective pathogen that can cause death of new-born piglet, resulting in big economical loss in pig farming industry. For rapid detection of PEDV, a new immunochromatographic assay (ICA) based on monoclonal antibodies (mAbs) was developed in this study.

RESULTS

The mAbs were prepared by using PEDV positive hybridoma cells that were selected by using cell surface fluorescence immunosorbent assay (CSFIA). Fourteen mAbs against PEDV strain isolated from south of China were prepared. The optimal mAb 4A11 was coated on NC membrane as the capturing reagent and the mAb A11H7 was coupled to gold nanoparticles (AuNPs) as detection reagent for the new ICA. The new ICA was used to measure PEDV in phosphate buffer containing tween-20. Results indicated that the limit of detection (LOD) of the new ICA was 0.47 μg/mL (5.9 × 10³ TCID₅₀/mL) and the liner detection range of the ICA was 0.625-10 μg/mL (7.8 × 10³-10⁵ TCID₅₀/mL). The specificity analysis results showed that this new ICA had no cross reaction in the presence of other porcine viruses. The ICA was also validated for the detection of PEDV in swine stool samples with little interference from swine stool. To compare its accuracy to other traditional detection methods, 27 swine stool samples from south of China were investigated with the new developed ICA, commercial strip and RT-PCR. Results showed that the new ICA was more comparable to RT-PCR than commercial test strip.

CONCLUSIONS

A new ICA based on mAbs prepared by CSFIA was developed in this study. It was a sensitive, specific and rapid method that could be used for on-site detection of PEDV and therefore was useful for the diagnosis and prevention of PED.

Two critical N-terminal epitopes of the nucleocapsid protein contribute to the cross-reactivity between porcine epidemic diarrhea virus and porcine transmissible gastroenteritis virus

Both porcine epidemic diarrhoea virus (PEDV) and porcine transmissible gastroenteritis virus (TGEV), which cause high mortality in piglets and produce similar clinical symptoms and histopathological morphology, belong to the genus Alphacoronavirus. Serological diagnosis plays an important role in distinguishing pathogen species. Together with the spike (S) protein, the nucleocapsid (N) protein is one of the immunodominant regions among coronaviruses. In this study, two-way antigenic cross-reactivity between the N proteins of PEDV and TGEV was observed by indirect immunofluorescence assay (IFA) and Western blot analysis. Furthermore, the PEDV N protein harbouring truncations of amino acids (aa) 1 to 170 or aa 125 to 301 was demonstrated to cross-react with the anti-TGEV N polyclonal antibody (PAb), whereas the truncation-expressing aa 302 to 401 resulted in a specific reaction with the anti-PEDV N PAb but not with the anti-TGEV N PAb. Mutants of the PEDV N protein were generated based on sequence alignment and structural analysis; we then confirmed that the N-terminal residues 58-RWRMRRGERIE-68 and 78-LGTGPHAD-85 contributed to the cross-reactivity. All the results provide vital clues for the development of precise diagnostic assays for porcine coronaviruses.

Development of rapid immunochromatographic strip test for the detection of porcine epidemic diarrhoea virus

Porcine epidemic diarrhoea virus (PEDV) causes acute and severe watery diarrhoea and dehydration, as well as 50–100 per cent mortality in piglets. For the PEDV diagnosis, a rapid test kit that is specific and sensitive to PEDV is critical to monitor this disease at pig farms. The present study aimed to develop an immunochromatographic assay (ICA) strip test for detecting PEDV in faecal swabs. The newly developed diagnostic test showed a detection limit of 10^4.0 TCID₅₀/ml of PEDV. Using faecal swab samples, the relative sensitivity and specificity of the ICA kit were 95.0 per cent and 98.6 per cent, respectively, compared with those of real-time RT-PCR. In samples from piglets experimentally infected with PEDV, the results showed 100 per cent agreement with those found by real-time RT-PCR. Our developed test strip will be useful for rapid diagnosis and can be used for epidemiological surveillance of PEDV infection.

First Detection and Clinical Presentation of Porcine Epidemic Diarrhea Virus (Pedv) in Serbia

During 2015/2016, fecal and intestinal samples from live diseased and/or dead pigs with suspected PEDV and/or TGEV and signs of rotavirus infection were collected from in total seven different farrow-to-finish swine farms located in Northern Serbia region (Vojvodina Province). A total of 14 samples (2 pools per farm) of small intestine with fecal content were submitted to laboratory molecular investigation (multiplex RTPCR). On these farms the clinical signs included the occurrence of diarrhea in suckling and weaned piglets, with weak or no response to the applied antimicrobial therapy. The epidemic of severe diarrhea affecting pigs of all ages on one farrow-to finish swine farm was detected in January 2016. Watery diarrhea in all swine categories was associated with vomiting and a reduction in feed consumption. Diarrheic, gaunt and dehydrated piglets, covered with feces were found in 90% litters. The disease affected most severely the suckling piglets, and the mortality in newborn piglets was up to 35%. In the weaned piglets and fatteners the mortality was up to 2.5% and 1.2%, respectively. The PEDV RNA was detected in pooled feces and samples of small intestines derived from diseased and dead suckling piglets from only one investigated farm. The PEDV positive samples showed to be negative for rotavirus group A and TGEV. The transport vehicles were identified as the main possible route of PEDV introduction. This is the first report demonstrating the presence of PEDV in Serbia.

Development and Validation of Monoclonal Antibody-Based Antigen Capture ELISA for Detection of Group A Porcine Rotavirus

Porcine rotavirus-A (PoRVA) is one of the common causes of mild to severe dehydrating diarrhea, leading to losses in weaning and postweaning piglets. A rapid, highly specific, and sensitive antigen-capture enzyme-linked immunosorbent assay (AC-ELISA) was developed for detection of PoRVA, by using VP6 (a highly conserved and antigenic protein of group-A rotavirus)-directed rabbit polyclonal antibodies (capture antibody) and murine monoclonal antibodies (detector antibody). The detection limit of AC-ELISA was found to be equal to that of conventional reverse transcription-polymerase chain reaction (RT-PCR; about 10^2.5 TCID₅₀/mL). For validation of the in-house AC-ELISA, 295 porcine fecal/diarrhea samples, collected from different provinces of China, were evaluated and compared with conventional RT-PCR and TaqMan RT-quantitative PCR (qPCR). The sensitivity and specificity of this in-house AC-ELISA relative to RT-qPCR were found to be 91.67% and 100%, respectively, with the strong agreement (kappa = 0.972) between these two techniques. Total detection rate with AC-ELISA, conventional RT-PCR, and RT-qPCR were found to be 11.2%, 11.5%, and 12.2%, respectively, without any statistical significant difference. Moreover, AC-ELISA failed to detect any cross-reactivity with porcine epidemic diarrhea virus, transmissible gastroenteritis virus, pseudorabies virus, and porcine circovirus-2. These results suggested that our developed method was rapid, highly specific, and sensitive, which may help in large-scale surveillance, timely detection, and preventive control of rotavirus infection in porcine farms.

Reactivity of Porcine Epidemic Diarrhea Virus Structural Proteins to Antibodies against Porcine Enteric Coronaviruses: Diagnostic Implications

The development of porcine epidemic diarrhea virus (PEDV) antibody-based assays is important for detecting infected animals, confirming previous virus exposure, and monitoring sow herd immunity. However, the potential cross-reactivity among porcine coronaviruses is a major concern for the development of pathogen-specific assays. In this study, we used serum samples (n = 792) from pigs of precisely known infection status and a multiplex fluorescent microbead-based immunoassay and/or enzyme-linked immunoassay platform to characterize the antibody response to PEDV whole-virus (WV) particles and recombinant polypeptides derived from the four PEDV structural proteins, i.e., spike (S), nucleocapsid (N), membrane (M), and envelope (E). Antibody assay cutoff values were selected to provide 100% diagnostic specificity for each target. The earliest IgG antibody response, mainly directed against S1 polypeptides, was observed at days 7 to 10 postinfection. With the exception of nonreactive protein E, we observed similar antibody ontogenies and patterns of seroconversion for S1, N, M, and WV antigens. Recombinant S1 provided the best diagnostic sensitivity, regardless of the PEDV strain, with no cross-reactivity detected against transmissible gastroenteritis virus (TGEV), porcine respiratory coronavirus (PRCV), or porcine deltacoronavirus (PDCoV) pig antisera. The WV particles showed some cross-reactivity to TGEV Miller and TGEV Purdue antisera, while N protein presented some cross-reactivity to TGEV Miller. The M protein was highly cross-reactive to TGEV and PRCV antisera. Differences in the antibody responses to specific PEDV structural proteins have important implications in the development and performance of antibody assays for the diagnosis of PEDV enteric disease.

Comparison and evaluation of conventional RT-PCR, SYBR green I and TaqMan real-time RT-PCR assays for the detection of porcine epidemic diarrhea virus

Porcine epidemic diarrhea (PED) caused by porcine epidemic diarrhea virus (PEDV) is a highly contagious intestinal disease, resulting in substantial economic losses to the swine industry worldwide. In this study, three assays, namely a conventional reverse transcription-polymerase chain reaction (RT-PCR), a SYBR Green I real-time RT-PCR and a TaqMan real-time RT-PCR targeting the highly conserved M gene of PEDV, were developed and evaluated. Then, the analytical specificity, sensitivity and reproducibility of these assays were determined and compared. The TaqMan real-time RT-PCR was 100-fold and 10,000-fold more sensitive than that of the SYBR Green I real-time RT-PCR and the conventional RT-PCR, respectively. The analytical sensitivity of TaqMan real-time RT-PCR was 10 copies/μl of target gene and no cross amplification with other viruses tested was observed. With the features of high specificity, sensitivity, and reproducibility, the TaqMan real-time RT-PCR established in this study could be a useful tool for clinical diagnosis, epidemiological surveys and outbreak investigations of PED.

Detection and phylogenetic analysis of porcine epidemic diarrhea virus in central China based on the ORF3 gene and the S1 gene

BACKGROUND

Porcine epidemic diarrhea (PED) has increased in severity in China since 2010. To investigate further the infectivity, genetic diversity and molecular epidemiology of its causative agent, the porcine epidemic diarrhea virus (PEDV), we assessed 129 clinical samples, which were the intestinal tissue of piglets with severe diarrhea, from 17 cities in central China. Both the spike (S) glycoprotein (S1, 1-789 amino acids (aa)) and the full-length ORF3 gene of 21 representative field strains from 21 farms in 11 cities were sequenced and analysed.

METHODS

PEDV was detected by reverse transcription-polymerase chain reaction (RT-PCR), and S1 and ORF3 sequences were processed by the Clustal W method via DNAMAN 8 software, and phylogenetic trees were constructed by the neighbor-joining method using MEGA 6 software.

RESULTS

The prevalence of PEDV was 92.25% and was detected in 119 of 129 samples, with 94.03% (63 of 67) of pig farms harbouring the disease. According to the phylogenetic analysis of the S1 genes, our isolates all fell into group G2 (variants) and showed a close relationship to isolates from Chinese (HN1303, CH/ZMDZY/11 and AJ1102), Korean (AD01), American (MN, IA1, IA2 and 13-019349) sources, and these isolates differed genetically from other Chinese (LZC, CH/HNZZ/2011 and SD-M) and Korean (SM98) strains as well Japanese (83-P5 and MK) strains. In addition, our isolates differed from attenuated vaccine strains, CV777 (used in China) and DR13 (used in Korea). According to our derived amino acid sequence analysis, we detected one novel variant PEDV, viz: CH/HNLY, with 4-aa insertion/deletion (RSSS/T) at position 375 and 1-aa (D) deletion at position 430 compared to the CV777 attenuated strain. These mutations were located on the receptor binding domain. Our ORF3 gene analyses showed that the prevalent PEDV isolates were variants, and the isolated strains differed genetically from the vaccine strains.

CONCLUSIONS

These findings illustrated the existence of genetic diversity among geographically distinct PEDV strains, and our study has provided an impetus to conduct further research on the PEDV receptor binding protein and on the new and efficacious vaccines design.

Evidence of Aujeszky's disease in wild boar in Serbia

BACKGROUND

Aujeszky's disease is a viral disease of suids caused by Suid Herpesvirus 1. The disease has worldwide distribution with significant economic impact. In Serbia, there is neither an Aujeszky's disease eradication nor national vaccination programme of domestic pigs. Since clinical symptoms of Aujeszky's disease are not specific, it is important to establish a link between clinical signs and presence of ADV active infection in wild boars. The aim of this study was to investigate the possibility of active infection within wild boar showing signs of ADV and also to examine relationship between isolates from domestic pigs and wild boar. Having in mind that virus has not been previously isolated from wild boars in Serbia, we report the first isolation of Suid Herpesvirus 1 from this species in Serbia.

RESULTS

Tissue and serum samples from 40 wild boars from eastern Serbia were examined for evidence of Aujeszky's disease (AD). Suid Herpesvirus 1 (SHV1), the cause of AD was isolated on PK15 cell line from three tissue samples, inducing cytopathic effect (CPE) with syncytia forming, and viral genome was detected by polymerase chain reaction (PCR) in eight samples. Genetic analysis of us4, us9 and ul49.5 partial sequences showed high homology between ADV isolates from wild boars and between isolates from wild boars and domestic animals. Neutralizing antibodies were not detected by virus neutralisation test (VNT) in sera from four out of eight PCR positive wild boars suggesting recent infection in those animals.

CONCLUSIONS

This is the first demonstration of Aujeszky's disease virus (ADV) in the wild boar population in Serbia although seroconversion has been detected previously.

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.

First detection, clinical presentation and phylogenetic characterization of Porcine epidemic diarrhea virus in Austria

Background

Porcine epidemic diarrhea (PED) is a syndrome that is characterized by rapidly spreading watery diarrhea affecting pigs of all ages, but with major effects on suckling piglets. The disease, as well as the causative Alphacoronavirus, the Porcine epidemic diarrhea virus (PEDV), was first described in Europe in the 1970s and since then has spread over many Asian and American countries, where it recently led to devastating effects on swine health and pork industry. While the disease was seldom reported in Europe within the last few decades, a few recent reports re-emergence of PED in German pig farms. The hitherto isolated German strain seems to be closely related to a low pathogenic PEDV variant from the USA. This case report describes the first detection of PEDV in Austria.

Case presentation

Reduced feed uptake and occasional diarrhea were observed in December 2014 in a group of fattening pigs, kept on an Austrian swine farm. The concerned pigs had been recently purchased from Germany. Within a few weeks, diarrhea became apparent also in pigs of Austrian origin, which were kept in a different stable on the same farm. Gastrointestinal symptoms among fattening pigs were generally mild, quickly resolving and did not lead to death. PEDV RNA was identified by RT-qPCR in pooled feces and serum and PEDV antibodies were detectable in serum in both groups of pigs. Phylogenetic analysis of the nearly complete PEDV spike gene shows that the Austrian PEDV strain is highly similar to other strains involved in recent outbreaks in Western and Central Europe.

Conclusion

This is the first report demonstrating the presence of PEDV in Austria. The virus was probably introduced by purchasing piglets from a German source, which underlines the significance of trans-boundary animal trade for the distribution of highly contagious diseases, such as PED.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-015-0624-1) contains supplementary material, which is available to authorized users.

Evaluation of two real-time polymerase chain reaction assays for Porcine epidemic diarrhea virus (PEDV) to assess PEDV transmission in growing pigs

In April 2013, a Porcine epidemic diarrhea virus (PEDV) epidemic began in the United States. As part of the response, real-time reverse transcription polymerase chain reaction (RT-PCR) assays to detect PEDV were developed by several veterinary diagnostic laboratories. Our study evaluated RT-PCR PEDV assays that detect the N gene (gN) and S gene (gS) for their ability to detect PEDV infection and the transmission potential of pigs experimentally exposed to PEDV. Detection limits and quantification cycle (Cq) values of real-time RT-PCR were assayed for PEDV samples and positive controls for both gN and gS. The limit of detection for the gN assay was 10(-6) (mean Cq: 39.82 ± 0.30) and 10(-5) (mean Cq: 39.39 ± 0.72) for the gS assay with PEDV strain USA/Colorado/2013. Following recommended guidelines, rectal swabs (n = 1,064) were tested; 354 samples were positive by gN assay and 349 samples were positive by gS assay (Cq ≤ 34.99), 710 samples were negative by gN assay and 715 were negative by gS assay (Cq > 34.99) of which 355 and 344 were "undetermined" (i.e., undetected within a threshold of 40 RT-PCR cycles, by gN and gS assays, respectively). The coefficient of variation (intra-assay variation) ranged from 0.00% to 2.65% and interassay variation had an average of 2.75%. PEDV could be detected in rectal swabs from all pigs for ~2 weeks postinfection at which time the prevalence began to decrease until all pigs were RT-PCR negative by 5 weeks postinfection. Our study demonstrated that RT-PCR assays functioned well to detect PEDV and that the gN assay was slightly better.

Probability of introducing porcine epidemic diarrhea virus into Danish pig herds by imported spray-dried porcine plasma

BACKGROUND

Porcine epidemic diarrhea virus (PEDV) has never been reported in Denmark, but it has been found in Europe, Asia and North America. Ultimately, PEDV has been associated with devastating outbreaks in pig farms. We developed a stochastic simulation model to carry out a quantitative risk assessment and to estimate the annual probability (PPlasma) of introducing PEDV into the Danish pig population, by imported spray-dried porcine plasma (SDPP). The model was based on information from literature and Danish feed companies. Moreover testing the batch of raw blood (before the spray-drying) was considered as potential risk mitigation measure in the future.

RESULTS

The median PPlasma was 0.2 % (90 % P.I.: 0.003 %; 2.6 %). Hence, the annual probability of introducing PEDV into the Danish pig population by imported SDPP appeared very low, and on average at least one introduction each 500 years - corresponding to 1/0.002 - could be expected. However, if PEDV survived the spray-drying process and storage was insufficient to completely remove the remaining viable virus (e.g. due to storage at low environmental temperatures during a short time period) the PPlasma was 4.7 % (0.06 %; 57.4 %). In that case, on average, at least one PEDV introduction each 21 years could be expected. This probability could be reduced to 0.3 % (0.004 %; 6.0 %) if the raw batch of blood could be tested before drying (corresponding to at least one introduction each 333 years on average).

CONCLUSIONS

This study provides preliminary and important information on the probability of introducing PEDV into the Danish pig population by use of SDPP. Currently PED is not a notifiable disease in the EU and uncertainty was present in our estimates due to possible underreporting in EU Member States, from which SDPP is imported into Denmark. In the future, PED might become a notifiable disease, and in such a case, new knowledge could become available on its epidemiology. Moreover, SDPP could be imported more safely if: producers find a way to substantiate freedom from disease (at least) in herds delivering blood for SDPP, the batch of blood tests negative for PEDV and conditions for processing/storage required by the international laws are respected.

A novel diagnostic approach to detecting porcine epidemic diarrhea virus: The lateral immunochromatography assay

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A novel lateral immunochromatography (IC) assay was developed to detect PEDV antigen.

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The IC assay has 96.0% sensitivity and 98.5% specificity compared with real-time reverse transcriptase PCR.

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The detection limit for PEDV was 1 × 10³ copies.

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The IC assay could be stored at 4 °C or room temperature for 15 months without affecting its efficacy.

Porcine epidemic diarrhea virus (PEDV) causes acute diarrhea and dehydration in sucking piglets and has a high mortality rate. An immunochromatography (IC) assay, known as a lateral flow test, is a simple device intended to detect the presence of target pathogens. Here, we developed an IC assay that detected PEDV antigens with 96.0% (218/227) sensitivity and 98.5% (262/266) specificity when compared with real-time reverse transcriptase (RT)-PCR using FAM-labeled probes based on sequences from nucleocapsid genes. The detection limits of the real-time RT-PCR and IC assays were 1 × 10² and 1 × 10³ copies, respectively. The IC assay developed herein did not detect non-specific reactions with other viral or bacterial pathogens, and the assay could be stored at 4 °C or room temperature for 15 months without affecting its efficacy. Thus, the IC assay may result in improved PED detection and control on farms, and is a viable alternative to current diagnostic tools for PEDV.

Development of an enzyme-linked immunosorbent assay for the monitoring and surveillance of antibodies to porcine epidemic diarrhea virus based on a recombinant membrane protein

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Expressed membrane protein of porcine epidemic diarrhea virus in Escherichia coli.

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An indirect ELISA was developed using purified recombinant M protein as detection antigen.

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Assessing fit for immunologic surveillance and sero-diagnosis of PEDV.

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The developed iELISA is specific, sensitive and does not require PEDV cultivation.

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This iELISA could be used for large-scale serological testing.

The recent dramatic increase in reported cases of porcine epidemic diarrhea (PED) in pig farms is a potential threat to the global swine industry. Therefore, the accurate diagnosis, serological monitoring, and surveillance of specific antibodies in pigs resulting from porcine epidemic diarrhea virus (PEDV) infection or vaccination would be essential in helping to control the spread of PED. We developed and validated an indirect enzyme-linked immunosorbent assay (ELISA) based on the recombinant membrane (M) protein of PEDV. To detect PEDV antibodies in eight herds, 382 serum samples were collected from sows that had been immunized with a PED vaccine, and screened using the developed ELISA in parallel with a serum neutralization (SN) assay. Of the tested samples, 276 were positive for the presence of PEDV antibodies according to both assays, while 98 were negative. An excellent agreement between the ELISA and the SN assay was observed (kappa = 0.947; 95% confidence interval = 0.910–0.984; McNemar's test, P = 0.727). No cross-reaction was detected for the developed ELISA with other coronaviruses or other common pig pathogens. The developed ELISA could be used for serological evaluation and indirect diagnosis of PED infection.

Porcine epidemic diarrhea: a review of current epidemiology and available vaccines

Porcine epidemic diarrhea virus (PEDV), an Alphacoronavirus in the family Coronaviridae, causes acute diarrhea, vomiting, dehydration, and high mortality rates in neonatal piglets. PEDV can also cause diarrhea, agalactia, and abnormal reproductive cycles in pregnant sows. Although PEDV was first identified in Europe, it has resulted in significant economic losses in many Asian swine-raising countries, including Korea, China, Japan, Vietnam, and the Philippines. However, from April 2013 to the present, major outbreaks of PEDV have been reported in the United States, Canada, and Mexico. Moreover, intercontinental transmission of PEDV has increased mortality rates in seronegative neonatal piglets, resulting in 10% loss of the US pig population. The emergence and re-emergence of PEDV indicates that the virus is able to evade current vaccine strategies. Continuous emergence of multiple mutant strains from several regions has aggravated porcine epidemic diarrhea endemic conditions and highlighted the need for new vaccines based on the current circulating PEDV. Epidemic PEDV strains tend to be more pathogenic and cause increased death in pigs, thereby causing substantial financial losses for swine producers. In this review, we described the epidemiology of PEDV in several countries and present molecular characterization of current strains. We also discuss PEDV vaccines and related issues.

Evidence of recombinant strains of porcine epidemic diarrhea virus, United States, 2013

To investigate the evolutionary process by which porcine epidemic diarrhea virus (PEDV) in the United States hypothetically descended from strains in China, we analyzed PEDV-positive samples collected in China during January 2012–July 2013. Recombination in 2 strain sublineages was likely associated with identification of PEDV in the United States in 2013.

Development of a nanoparticle-assisted PCR assay for detection of porcine epidemic diarrhea virus

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A nanoPCR method was developed for the detection of PEDV.

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The nanoPCR assay was 100-fold more sensitive than a conventional RT-PCR assay.

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The lower detection limit was 2.7 × 10⁻⁶  ng/μL of PEDV RNA.

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This test could be applied for clinical diagnosis and field surveillance of PEDV.

Porcine epidemic diarrhea virus (PEDV) is an important pig pathogen that can cause vomiting, diarrhea, and dehydration, leading to serious damage to the swine industry worldwide. In this study, a nanoparticle-assisted polymerase chain reaction (nanoPCR) assay targeting the N gene of PEDV was developed and the sensitivity and specificity were investigated. Under the optimized conditions for detection of PEDV RNA, the nanoPCR assay was 100-fold more sensitive than a conventional RT-PCR assay. The lower detection limit of the nanoPCR assay was 2.7 × 10⁻⁶ ng/μL of PEDV RNA and no cross-reaction was observed with other viruses. This is the first report to demonstrate the application of a nanoPCR assay for the detection of PEDV. The sensitive and specific nanoPCR assay developed in this study can be applied widely in clinical diagnosis and field surveillance of PEDV-infection.

Porcine epidemic diarrhea virus infects and replicates in porcine alveolar macrophages

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Porcine epidemic diarrhea virus (PEDV) is a causative agent of porcine epidemic diarrhea; consequently, the small intestine was believed to be its only target organ.

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We found that PEDV infected not only the small intestines, but also the respiratory tract.

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Infection and replication of PEDV in the respiratory tract from naturally PEDV-infected piglets were examined by reverse transcription polymerase chain reaction, immunohistochemistry, and virus re-isolation.

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Our observations were confirmed by experimental inoculation, and we found that PEDV infection in the respiratory tract was specifically associated with alveolar macrophages in the lung.

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The discovery that PEDV infects and replicates in alveolar macrophages provides new insights into its pathogenesis.

Porcine epidemic diarrhea virus (PEDV) is a causative agent of porcine epidemic diarrhea; consequently, the small intestine was believed to be its only target organ. In this study, we found that PEDV infected not only the small intestines, but also the respiratory tract. Infection and replication of PEDV in the respiratory tract from naturally PEDV-infected piglets were examined by reverse transcription polymerase chain reaction, immunohistochemistry, and virus re-isolation. Our observations were confirmed by experimental inoculation, and we found that PEDV infection in the respiratory tract was specifically associated with alveolar macrophages in the lung. Vero cell-adapted PEDV was able to replicate in both primary alveolar macrophages and continuous porcine alveolar macrophage cells. Sequencing analysis of the spike (S) glycoprotein revealed that mutations in S might be a potential determinant of auxiliary targets for PEDV. The discovery that PEDV infects and replicates in alveolar macrophages provides new insights into its pathogenesis.

Development of a multiplex TaqMan probe-based real-time PCR for discrimination of variant and classical porcine epidemic diarrhea virus

Since October 2010, porcine diarrhea outbreaks have occurred widely, resulting in major losses in suckling piglets in China. A variant porcine epidemic diarrhea virus (PEDV), characterized by base deletion and insertion in the S gene, compared to classical PEDV CV777, was shown to be responsible for this outbreak. In this study, a multiplex TaqMan probe-based real-time PCR was developed for detecting PEDV and differentiating the variant from classical PEDV, by using two sets of primers and probes based on the S gene of PEDV. The limits of detection of both variant and classical PEDV were 5×10(2) DNA copies. Specificity was determined using eight other viral pathogens of swine. Reproducibility was evaluated using standard dilutions, with coefficients of variation <1.4%. Standard dilutions included in each test allowed quantification of the amount of PEDV. Among 42 intestinal samples from pigs with severe watery diarrhea, 36 variant PEDV and three classical PEDV samples were detected, with viral loads of 10(2)-10(8) copies/μl and 10(3)-10(5) copies/μl, respectively, which suggested that the variant PEDV was prevalent in China. The multiplex TaqMan probe-based real-time PCR should be a useful tool for quantifying viral load, detecting PEDV, and differentiating variant from classical PEDV.

Alterations in oxidant/antioxidant balance, high-mobility group box 1 protein and acute phase response in cross-bred suckling piglets suffering from rotaviral enteritis

Rotaviral enteritis has emerged as a major cause of morbidity and mortality in piglets during their post-natal life. The present study was carried out to examine high-mobility group box 1 (HMGB1) protein, acute phase response and oxidative stress indices in the serum of suckling piglets suffering from enteritis with or without association of porcine group A rotavirus infection. The present investigation utilized 23 clinical cases with signs of acute enteritis and 12 more healthy piglets of a similar age group as control animals. Out of 23 enteritis cases, 12 cases were found to be positive for porcine group A rotavirus infection as confirmed by reverse transcription-polymerase chain reaction (RT-PCR) using specific primers for group A rotavirus, and the rest were found negative. The acute enteritis cases in piglets were associated with an elevated level of HMGB1 protein and serum haptoglobin and ceruloplasmin suggestive of an acute phase response. Among the oxidative stress indices, the concentrations of malondialdehyde (MDA) and nitric oxide (NO) in serum were significantly increased. A pronounced drop of total antioxidant capacity and the activity of antioxidant enzymes such as catalase and superoxide dismutase in the serum of piglets suffering from acute enteritis compared to healthy ones were also noticed. The alterations in HMGB1 protein, acute phase response and oxidative stress indices were more pronounced in cases with the involvement of porcine rotavirus as compared to rotavirus-negative cases. It is concluded that HMGB1 protein, markers of oxidative stress and acute phase proteins might play an important role in the aetiopathogenesis of porcine diarrhoea caused by rotavirus and might be true markers in diagnosing the conditions leading to the extension of the prompt and effective therapeutic care.

A multiplex RT-PCR assay for rapid and differential diagnosis of four porcine diarrhea associated viruses in field samples from pig farms in East China from 2010 to 2012

Since October 2010, clinical outbreaks of diarrhea in suckling piglets have reemerged in pig-producing areas of China, causing an acute increase in the morbidity and mortality in young piglets. Four viruses, porcine epidemic diarrhea virus (PEDV), transmissible gastroenteritis virus (TGEV), porcine group A rotaviruses (GAR), and porcine circovirus 2 (PCV2), are the major causative agents of enteric disease in piglets. A novel multiplex reverse transcription-polymerase chain reaction (mRT-PCR) was developed for simultaneous detection of the four viruses in field samples from piglets. A mixture of four previously published pairs of primers were used for amplification of viral gene, yielding four different amplicons with sizes of 481 bp for PCV2, 651 bp for PEDV, 859 bp for TGEV, and 309 bp for GAR, respectively. The sensitivity of the mRT-PCR using plasmids containing the specific viral target fragments was 2.17 × 10(3), 2.1 × 10(3), 1.74 × 10(4) and 1.26 × 10(4)copies for the four viruses, respectively. A total of 378 field samples were collected from suckling piglets with diarrhea in East China from October 2010 to December 2012, and detected by mRT-PCR. The PEDV-positive rates of the three years were 69.2%, 62.8% and 54.9%, respectively, suggesting that PEDV was a major pathogen in these diarrheal outbreaks. Taken together, all data indicated that this mRT-PCR assay was a simple, rapid, sensitive, and cost-effective detection method for clinical diagnosis of mixed infections of porcine diarrhea associated viruses.

Sequence and phylogenetic analysis of nucleocapsid genes of porcine epidemic diarrhea virus (PEDV) strains in China

Porcine epidemic diarrhea virus (PEDV) causes acute diarrhea and dehydration with high mortality rates in swine. It has become increasingly problematic in China. Since the nucleocapsid (N) protein is highly conserved, it is a candidate protein for early diagnosis and vaccine development. In this study, the N genes of 15 PEDV strains were amplified by RT-PCR and cloned into the pMT-19T vector, sequenced, and compared to each other as well as to PEDV reference strains. The nucleotide sequences of the N gene of the Chinese PEDV strains consist of 1326 nucleotides and encode a 441-aa-long peptide. The nucleotide sequences of the fifteen PEDV strains in our study were 96.1-100 % identical to each other, and the deduced amino acid sequences were 94.8-100 % identical. Sequence comparison with other PEDV strains selected from GenBank revealed that their nucleotide sequences were 94.2-99.7 % identical to those of the Chinese PEDV strains, and their deduced amino acid sequences were 94.1-99.5 % identical. In addition, the fifteen strains showed a high degree of nucleotide sequence identity to the early domestic strains (98.4-99.7 %) except the LZC strain, but less sequence identity to the vaccine strain (CV777) used in China (94.7-97.7 %). Phylogenetic analysis showed that the Chinese PEDV strains are composed of a separate cluster including three early domestic strains (JS-2004-02, LJB/03 and DX) but differ genetically from the vaccine strain (CV777) and the early Korean strains (Chinju99 and SM98).

Progress in research of genetic characteristics of porcine epidemic diarrhea virus and diagnostic methods for porcine epidemic diarrhea

Porcine epidemic diarrhea (PED), caused by PED virus (PEDV), is a devastating contagious viral swine disease that is characterized by acute enteritis and lethal watery diarrhea. In Asia (such as Korea, Japan, and China), PEDV causes a very high mortality in suckling piglets. Some affected farms lost 100% of newborn piglets. PED can hardly be distinguished from transmissible gastroenteritis clinically and histopathologically. Identification of the causal agent is a basic prerequisite both for introduction of immunoprophylactic measures and for evaluation of prevention measures. Therefore, rapid differential diagnosis of PED and TGE is important. The purpose of the current review is to describe the molecular and genetic characteristics of PEDV, and discuss the diagnosis methods for PED.

Phylogenetic analysis of porcine astrovirus in domestic pigs and wild boars in South Korea

Porcine astrovirus (PAstV) belongs to genetically divergent lineages within the genus Mamastrovirus. In this study, 25/129 (19.4 %) domestic pig and 1/146 (0.7 %) wild boar fecal samples tested in South Korea were positive for PAstV. Positive samples were mainly from pigs under 6 weeks old. Bayesian inference (BI) tree analysis for RNA-dependent RNA polymerase (RdRp) and capsid (ORF2) gene sequences, including Mamastrovirus and Avastrovirus, revealed a relatively geographically divergent lineage. The PAstVs of Hungary and America belong to lineage PAstV 4; those of Japan belong to PAstV 1; and those of Canada belong to PAstV 1, 2, 3, and 5, but not to 4. This study revealed that the PAstVs of Korea belong predominantly to lineage PAstV 4 and secondarily to PAstV 2. It was also observed that PAstV infections are widespread in South Korea regardless of the disease state in domestic pigs and in wild boars as well.