Porcine epidemic diarrhea (PED) infection, diagnosis and vaccination: A mini review

CRISPR-Mediated Library Screening of Gene-Knockout Cell Lines for Investigating Antiviral Innate Immunity

The application of CRISPR-mediated library screening has fundamentally transformed functional genomics by revealing the complexity of virus-host interactions. This protocol describes the use of CRISPR-mediated library screening to identify key functional genes regulating the innate immune response to PEDV infection. We detail a step-by-step process, starting from the design and construction of a customized CRISPR knockout library targeting genes involved in innate immunity to the effective delivery of these constructs into cells using lentiviral vectors. Subsequently, we outline the process of identifying functional genes postviral attack, including the use of next-generation sequencing (NGS), to analyze and identify knockout cells that exhibit altered responses to infection. This integrated approach provides researchers in immunology and virology with a resource and a robust framework for uncovering the genetic basis of host-pathogen interactions and the arsenal of the innate immune system against viral invasions.

Lectin histochemistry in the small intestines of piglets naturally infected with porcine epidemic diarrhea virus

IMPORTANCE

Porcine epidemic diarrhea virus (PEDV) binds to particular cell surface receptors to penetrate cells. The virus specifically identifies certain carbohydrate structures present on the surface of the cell to facilitate the binding process. Nevertheless, the influence of viral infections on specific alterations of glycoconjugates in the small intestines remains unexplored.

OBJECTIVE

This work aimed to examine the alterations in glycoconjugates in the small intestines of piglets naturally infected with PEDV using lectin histochemistry.

METHODS

Six piglets including three PEDV-infected and three non-infected piglets were evaluated. Small intestinal samples were histopathologically examined, and lectin histochemistry was performed.

RESULTS

Piglets infected with PEDV had significant histological abnormalities in their small intestines, such as pronounced villous atrophy, varying degrees of villous fusion, and diverse mucosal alterations. Specific regions of the duodenum, jejunum, and ileum showed discernible variations in glycoconjugate distribution, as determined by lectin histochemistry. Compared with the controls, the PEDV-infected piglets showed significant changes in N-acetylglucosamine- and galactose-binding lectins (particularly wheat germ agglutinin and Arachis hypogaea (peanut) agglutinin) in multiple intestinal regions.

CONCLUSIONS AND RELEVANCE

These findings can enhance understanding of how viruses such as PEDV impact the glycoconjugate composition of the small intestines and emphasize the potential connection between the pathogenesis of PEDV and glycoconjugate.

Epitopes screening and vaccine molecular design of PEDV S protein based on immunoinformatics

Porcine epidemic diarrhea virus (PEDV) is a serious disease that poses a significant threat to the pig industry. This study focused on analyzing the Spike protein of PEDV, which harbors crucial antigenic determinants, in identifying dominant epitopes. Immunoinformatics tools were used to screen for B-cell, CD4+ and CD8+ predominance epitopes. These epitopes were then connected to the N-terminal of ferritin to form a self-assembled nanoparticle vaccine. Various physical and chemical properties of the candidate vaccine were analyzed, including secondary structure prediction, tertiary structure modeling, molecular docking, immune response simulation and computer cloning. The results demonstrated that the candidate vaccine was antigenic, soluble, stable, non-allergic, and formed a stable complex with the target receptor TLR-3. Immune simulation analysis showed that the candidate vaccine effectively stimulated both cellular and humoral reactions, leading to increased related cytokines production. Furthermore, efficient and stable expression of the candidate vaccine was achieved through reverse translation in the Escherichia coli K12 expression system following codon optimization and in silico cloning. The developed nanoparticle candidate vaccine in this study holds promise as an effective PEDV vaccine candidate, offering a new approach for the research, development and improvement of vaccines targeting porcine enteric diarrhea coronavirus.

A one-step immunoassay based on switching peptides for diagnosis of porcine epidemic diarrhea virus (PEDV) using screened Fv-antibodies

In this study, a one-step immunoassay for porcine epidemic diarrhea virus (PEDV) based on Fv-antibodies and switching peptides was developed, and the assay results of PEDV were obtained by just mixing samples without any further reaction or washing steps. The Fv-antibodies with binding affinity to the spike protein of PEDV were screened from the Fv-antibody library using the receptor-binding domain (RBD) of the spike protein as a screening probe. Screened Fv-antibodies with binding affinities to the RBD antigen were expressed, and the binding constants (KD) were calculated to be 83-142 nM. The one-step immunoassay for the detection of PEDV was configured as a displacement immunoassay using a fluorescence-labeled switching peptide. The one-step immunoassay based on switching peptides was performed using PEDV, and the limit of detection (LOD) values for PEDV detection were estimated to be Ct = 39.7-36.4. Compared with the LOD value for a conventional lateral flow immunoassay (Ct = 33.0), the one-step immunoassay showed a remarkably improved LOD for the detection of PEDV. Finally, the interaction between the screened Fv-antibodies and the PEDV RBD was investigated using docking simulations and compared with the amino acid sequences of the receptors on host cells, such as aminopeptidase N (APN) and angiotensin-converting enzyme-2 (ACE-2).

Characterization and epitope mapping of monoclonal antibodies against PEDV N protein

Porcine epidemic diarrhea virus (PEDV) causes acute diarrhea, vomiting, dehydration and high mortality in neonatal piglets. The nucleocapsid (N) protein of PEDV is a highly conserved protein with strong immunogenicity and palys an important role in PEDV diagnosis. However, epitopes on the PEDV N protein have not yet been well characterized. Here, 32 monoclonal antibodies (mAbs) against the PEDV N protein were produced and identified. Six new epitopes were first identified by using a high-throughput epitope mapping method named AbMap. Sequence analysis revealed that among the six epitopes five epitopes were highly conserved among different PEDV strains. We also confirmed that the mAbs derived from the six epitopes of PEDV N protein, have no cross-reactivity with transmissible gastro enteritis virus or porcine delta coronavirus. These mAbs and their defined epitopes will help to understand the N protein structure and immunological characteristics, and to develop a rapid, accurate PEDV diagnosis method.

Butyrate limits the replication of porcine epidemic diarrhea virus in intestine epithelial cells by enhancing GPR43-mediated IFN-III production

Porcine epidemic diarrhea virus (PEDV) is a threat to the health of newborn piglets and has a significant impact on the swine industry. Short-chain fatty acids (SCFAs) are gut microbial metabolites that regulate intestinal function through different mechanisms to enhance the intestinal barrier and immune function. In this study, we aimed to determine whether butyrate displayed a better effect than other SCFAs on limiting PEDV replication in porcine intestinal epithelial cells. Mechanistically, butyrate treatment activated the interferon (IFN) response and interferon-stimulated gene (ISG) expression. Further experiments showed that inhibition of GPR43 (free fatty acid receptor 2) in intestinal epithelial cells increased virus infection and reduced antiviral effects through IFN λ response. Our findings revealed that butyrate exerts its antiviral effects by inducing GPR43-mediated IFN production in intestinal epithelial cells.

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.

Point-of-Care Tests for Rapid Detection of Porcine Epidemic Diarrhea Virus: A Systematic Review and Meta-Analysis

The timely and accurate diagnosis of porcine epidemic diarrhea virus (PEDV) infection is crucial to reduce the risk of viral transmission. Therefore, the objective of this review was to evaluate the overall diagnostic accuracy of rapid point-of-care tests (POCTs) for PEDV. Studies published before 7 January 2022 were identified by searching PubMed, EMBASE, Springer Link, and Web of Science databases, using subject headings or keywords related to point of care and rapid test diagnostic for PEDV and PED. Two investigators independently extracted data, rated risk of bias, and assessed the quality using the Quality Assessment of Diagnostic Accuracy Studies-2 tool. The bivariate model and the hierarchical summary receiver operating characteristic (HSROC) model were used for performing the meta-analysis. Threshold effect, subgroup analysis, and meta-regression were applied to explore heterogeneity. Of the 2908 records identified, 24 eligible studies involving 3264 specimens were enrolled in the meta-analysis, including 11 studies on evaluation of lateral flow immunochromatography assay (ICA)-based, and 13 on nucleic acid isothermal amplification (NAIA)-based POCTs. The overall pooled sensitivity, specificity and diagnostic odds ratio (DOR) were 0.95 (95% CI: 0.92–0.97), 0.96 (95% CI 0.88–0.99) and 480 (95% CI 111–2074), respectively; for ICA-based POCTs and the corresponding values for NAIA-based, POCTs were 0.97 (95% CI 0.94–0.99), 0.98 (95% CI 0.91–0.99) and 1517 (95% CI 290–7943), respectively. The two tests showed highly comparable and satisfactory diagnostic performance in clinical utility. These results support current recommendations for the use of rapid POC tests when PEDV is suspected.

In vitro Assessment of Antiviral Effect of Natural Compounds on Porcine Epidemic Diarrhea Coronavirus

Organic acid and essential oils (EOs), well-known antimicrobials, could also possess antiviral activity, a characteristic which has not been completely addressed up to now. In this study, the effect of two organic acids (formic acid and sodium salt of coconut fatty acid distillates) and two single EO compounds (thymol and cinnamaldehye) was evaluated against porcine epidemic diarrhea virus (PEDV). The concentration used for each compound was established by cytotoxicity assays in Vero cells. The antiviral activity was then evaluated at three multiplicities of infection (MOIs) through visual cytopathic effect (CPE) evaluation and an alamarBlue assay as well as real-time reverse-transcription PCR (RT-qPCR) and viral titration of cell supernatants. Formic acid at at a dose of 1,200 ppm was the only compound which showed antiviral activity, with a weak reduction of CPE caused by PEDV. Through the alamarBlue fluorescence assay, we showed a significant anti-CPE effect of formic acid which could not be observed by using an inverted optical microscope. RT-qPCR and infectivity analysis also showed that formic acid significantly reduced viral RNA and viral titers in a PEDV MOI-dependent manner. Our results suggest that the antiviral activity of formic acid could be associated to its inhibitory effect on viral replication. Further studies are required to explore the anti-PEDV activity of formic acid under field conditions alone or together with other antiviral agents.