An ELISA optimized for porcine epidemic diarrhoea virus detection in faeces

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.

Porcine Epidemic Diarrhea: Causative Agent, Epidemiology, Clinical Characteristics, and Treatment Strategy Targeting Main Protease

Aims:

This aimed to study the causative agent, epidemiology, clinical characteristics, and treatment strategy targeting the main protease in porcine epidemic diarrhea.

Background:

Porcine epidemic diarrhea (PED) is a contagious intestinal viral infection causing severe diarrhea, vomiting, and dehydration in pigs. High rates of mortalities and severe morbidities, approaching 100%, are reported in piglets infected with PEDV. In recent years, PED has been observed to influence the swine-farming nations in Europe, Asia, the USA, South Korea, and Canada. The PED virus (PEDV) transmission takes place through a faecal-oral route.

Objective:

The objective is to review the characteristics of PEDV and its role in the disease. In addition, we aim to outline some possible methods to combat PED infection, including targeting the main protease of coronavirus and their future perspectives.

Method:

This study is a review of literature on the PED virus.

Results:

Apart from symptomatic treatment and supportive care, there is no available specific treatment for PEDV. Appropriate disinfectants and cleaning are pivotal for the control of PEDV. To date, apart from anti-PEDV inhibitors, there are no specific drugs available commercially to treat the disease. Therefore, 3C-like protease (3CLpro) in PEDV that has highly conserved structure and catalytic mechanism serves as an alluring drug as it plays a vital role during viral polyprotein processing at the time of infection.

Conclusion:

A well synchronized and collective effort of scientists, swine veterinarians, pork industry experts, and associated authorities is essential for the accomplishment of proper execution of these required measures.

Development of a Novel Double Antibody Sandwich Quantitative Enzyme-Linked Immunosorbent Assay for Detection of Porcine Epidemic Diarrhea Virus Antigen

Porcine epidemic diarrhea virus (PEDV) causes acute diarrhea and dehydration in sucking piglets with a high mortality rate. Here, we developed a double antibody sandwich quantitative enzyme-linked immunosorbent assay (DAS-qELISA) for detection of PEDV using a specific monoclonal antibody against PEDV N protein and anti-PEDV rabbit serum. Using DAS-qELISA, the detection limit of recombinant PEDV N protein and virus titer were approximately 1 μg/L and 10^2.0 TCID₅₀/ml, respectively. A total of 90 intestinal and 237 fecal samples were then screened for the presence of PEDV using DAS-qELISA and reverse transcriptase PCR (RT-PCR). DAS-qELISA had a high specificity of 98.1% and sensitivity of 93.5%. The accuracy rate between DAS-qELISA and RT-PCR was 95.7%. More importantly, the viral antigen concentrations remained unchanged before and after one inactivated vaccine preparation by using the DAS-qELISA. These results suggest DAS-qELISA could be used for antigen detection of inactivated vaccine samples and clinical samples. It is a novel method for diagnosing diseases and evaluation of the PEDV vaccine.

Use of Target-Specific Liposome and Magnetic Nanoparticle Conjugation for the Amplified Detection of Norovirus

Viral diseases are one of the most life-threatening diseases as they can erupt unpredictably and spread rapidly in any medium with a very small number of particles. Therefore, the key for lethal virus detection should be highly sensitive in the early-stage detection, which can help increase the chance of survival. Amplification of the detecting signal is one of the most promising mechanisms for the detection of low-concentration analytes. A proper amplification can develop such a kind of system where a small number of particles can produce intense signals for a prominent detection. Keeping this in mind, in this report, we have presented a fluorometric method to detect norovirus (NoV) by a newly developed fluorophore-labeled liposome and a magnetically modified Fe₃O₄ combined system. Homogeneously distributed amine-functionalized liposomes have been constructed filled with a strong fluorophore of calcein. Simultaneously, (3-aminopropyl)-triethoxysilane (APTES)-functionalized Fe₃O₄ nanoparticles are also synthesized by the standard silanization process, and these two separately synthesized nanoparticles were functionalized with an antibody to achieve specificity. The Fe₃O₄ and calcein-liposome system has been applied for NoV detection, which was magnetically separated from the analyte medium and then externally burst to release the fluorophores from the core of the liposome. The easiness, rapidity, and sensitivity in a wide linear range can offer a huge potential of this method in point-of-care diagnostics.

Dual priming oligonucleotide (DPO)-based real-time RT-PCR assay for accurate differentiation of four major viruses causing porcine viral diarrhea

Currently in China, porcine epidemic diarrhea virus (PEDV), transmissible gastroenteritis virus (TGEV), porcine rotavirus (PoRV), and porcine deltacoronavirus (PDCoV) are the major causes of porcine viral diarrhea, and mixed infections in clinics are common, resulting in significant economic losses in pig industry. Here, a dual priming oligonucleotide (DPO)-based multiplex real-time SYBR Green RT-PCR assay were developed for accurately differentiating PEDV, TGEV, PoRV, and PDCoV in clinical specimens targeting the N gene of TGEV, PEDV, and PDCoV, and the VP7 gene of PoRV. Results showed that the DPO primer allowed a wider annealing temperature range (40–65 °C) and had a higher priming specificity compared to conventional primer, in which more than 3 nucleotides in the 3′- or 5′-segment of DPO primer mismatched with DNA template, PCR amplification efficiency would decrease substantially or extension would not proceed. DPO-based multiplex real-time RT-PCR method had analytical detection limit of 8.63 × 10² copies/μL, 1.92 × 10² copies/μL, 1.74 × 10² copies/μL, and 1.76 × 10² copies/μL for PEDV, TGEV, PoRV, and PDCoV in clinical specimens, respectively. A total of 672 clinical specimens of piglets with diarrheal symptoms were collected in Northeastern China from 2017 to 2018 followed by analysis using the assay, and epidemiological investigation results showed that PEDV, TGEV, PoRV, and PDCoV prevalence was 19.05%, 5.21%, 4.32%, and 3.87%, respectively. The assay developed in this study showed higher detection accuracy than conventional RT-PCR method, suggesting a useful tool for the accurate differentiation of the four major viruses causing porcine viral diarrhea in practice.

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DPO-based real-time RT-PCR assay for differentiating PEDV, TGEV, PoRV, and PDCoV was developed.

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The assay has strong specificity and high sensitivity.

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The test of clinical specimens showed that accuracy of the assay was higher than traditional RT-PCR.

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The assay is useful tool for epidemiological investigation of the four viruses.

Visual detection of porcine epidemic diarrhea virus using a novel reverse transcription polymerase spiral reaction method

BACKGROUND

Porcine epidemic diarrhea virus (PEDV) is a major etiological agent of porcine epidemic diarrhea around the world. Point-of-care testing in the field is lacking owing to the requirement for a simple, robust field applicable test that does not require professional laboratory equipment. The aim of this study was to establish a novel reverse transcription polymerase spiral reaction (RT-PSR) assay for the rapid detection of porcine epidemic diarrhea virus (PEDV). For the assay, a specific RT-PSR primer pair was designed against a conserved region in PEDV ORF3.

RESULTS

The RT-PSR was optimized, and PEDV could be detected after a 50 min incubation at 62 °C, in addition to the 15 min required for reverse transcription. No cross-reaction with other porcine infectious viruses was observed. This new method for PEDV detection was 10 times more sensitive than the conventional reverse transcription-polymerase chain reaction (RT-PCR) assay. The positive rates for 65 clinical samples using the new RT-PSR assay and the conventional RT-PCR assay were 58.46% (38/65) and 53.84% (35/65), respectively. In the RT-PSR assay, the addition of a mixture of dyes allowed a positive reaction to be directly observed by the naked eye.

CONCLUSIONS

These results indicate that this RT-PSR assay is capable of accurately detecting PEDV, and has the advantages of high specificity and sensitivity for the detection of PEDV.

Development of a SYBR green I-based duplex real-time fluorescence quantitative PCR assay for the simultaneous detection of porcine epidemic diarrhea virus and porcine circovirus 3

The development of a rapid, specific, and sensitive SYBR Green I-based duplex real-time quantitative PCR assay is described for the simultaneous detection of porcine epidemic diarrhea virus (PEDV) and porcine circovirus type 3 (PCV3). The assay specifically detected PEDV and PCV3, with no fluorescence detected for other non-targeted pig pathogens. The assay showed a good linear relationship, and the limits of detection for this assay were 34.6 copies/μL and 61.2 copies/μL for PEDV and PCV3, respectively. The assay exhibited high repeatability and reproducibility, with intra-assay and inter-assay variation coefficients less than 2.0%. A clinical evaluation using intestinal tissue and fecal samples from piglets suffering from diarrhea at different pig farms in China revealed that the singular infection rates of PEDV and PCV3 were 43.94% (29/66) and 16.67% (11/66), respectively, while the co-infection rate of PCV3 with PEDV was 27.27% (18/66). The results indicate this assay is a rapid and reliable diagnostic tool for PEDV and PCV3 monitoring and surveillance in the field, and provides technical support for the quantitative detection of clinical samples infected or co-infected with PEDV and PCV3.

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PED outbreaks have been resulted in a huge economic loss in the pig farming industry.

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PCV3 is a novel virus and has been detected in piglets affected with diarrhea.

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A duplex qPCR assay was developed for the simultaneous detection of PEDV and PCV3.

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The LOD for this assay were 34.6 copies/μL and 61.2 copies/μL for PEDV and PCV3, respectively.

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.

Virus detection by transmission electron microscopy: Still useful for diagnosis and a plus for biosafety

Transmission electron microscopy (TEM) is the only imaging technique allowing the direct visualization of viruses, due to its nanometer‐scale resolution. Between the 1960s and 1990s, TEM contributed to the discovery of many types of viruses and served as a diagnostic tool for identifying viruses directly in biological samples, either in suspension or in sections of tissues or mammalian cells grown in vitro in contact with clinical samples. The diagnosis of viral infections improved considerably during the 1990s, with the advent of highly sensitive techniques, such as enzyme‐linked immunosorbent assay (ELISA) and PCR, rendering TEM obsolete for this purpose. However, the last 20 years have demonstrated the utility of this technique in particular situations, due to its “catch‐all” nature, making diagnosis possible through visualization of the virus, without the need of prior assumptions about the infectious agent sought. Thus, in several major outbreaks in which molecular techniques failed to identify the infectious agent, TEM provided the answer. TEM is also still occasionally used in routine diagnosis to characterize infections not diagnosed by molecular assays. It is also used to check the microbiological safety of biological products. Many biopharmaceuticals are produced in animal cells that might contain little‐known, difficult‐to‐detect viruses. In this context, the “catch‐all” properties of TEM make it possible to document the presence of viruses or virus‐like particles in these products.

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.

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.

Detection of immunoglobulin (Ig) A antibodies against porcine epidemic diarrhea virus (PEDV) in fecal and serum samples

Many assays for detection of antibodies against porcine epidemic diarrhea virus (PEDV) are based on detection of neutralizing antibodies or immunoglobulin (Ig) G in serum samples. However, due to the particular features of the mucosal immune system, presence of serum antibodies against enteric pathogens, such as PEDV, not always correlates with protection. In contrast, anti-PEDV IgA antibodies correlate with protection against subsequent challenges. An indirect PEDV IgA ELISA was previously developed to monitor IgA levels in colostrum and milk samples. In the present paper we describe an adaptation of the protocol for detection of IgA antibodies in serum and fecal samples.•

The adapted protocol will aid in future assessment of protective levels of humoral response against PEDV infection by measuring IgA levels in serum and fecal samples.

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Fecal samples are non-invasive and easy to collect at any time by animal caretakers and therefore offering advantages over the serum sample collection procedure.

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A strong positive correlation between the anti-PEDV levels in fecal and serum samples was identified; however, detection of IgA antibodies was often more successful in serum than in paired fecal samples due to overall lower sample-to-positive (S/P) ratios for the latter sample type.

Porcine epidemic diarrhoea: new insights into an old disease

Porcine epidemic diarrhea (PED) is an enteric disease in swine caused by an alphacoronavirus. It affects swine of all ages causing acute diarrhoea and can lead to severe dehydration and death in suckling piglets. Being recognized for the first time in Europe and Asia during the seventies and the eighties, respectively, it has remained a relevant cause of diarrhea outbreaks in Asia for years and to the present. It has become a major concern in swine production since 2013 when the virus was detected for first time in the USA and in other American countries causing a high number of pig deaths and significant economic losses. The present review aims at approaching the reader to the state of the art of PED giving answer to some of the most recent questions which have arisen related to this disease.

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 indirect ELISA, blocking ELISA, fluorescent microsphere immunoassay and fluorescent focus neutralization assay for serologic evaluation of exposure to North American strains of Porcine Epidemic Diarrhea Virus

Background

Recent, severe outbreaks of porcine epidemic diarrhea virus (PEDV) in Asia and North America highlight the need for well-validated diagnostic tests for the identification of PEDV infected animals and evaluation of their immune status to this virus. PEDV was first detected in the U.S. in May 2013 and spread rapidly across the country. Some serological assays for PEDV have been previously described, but few were readily available in the U.S. Several U.S. laboratories quickly developed indirect fluorescent antibody (IFA) assays for the detection of antibodies to PEDV in swine serum, indicating prior exposure. However, the IFA has several disadvantages, including low throughput and relatively subjective interpretation. Different serologic test formats have advantages and disadvantages, depending on the questions being asked, so a full repertoire of tests is useful. Therefore, the objective of this study was to develop and validate multiple improved serological assays for PEDV, including an indirect ELISA (iELISA); a highly specific monoclonal antibody-based blocking ELISA (bELISA); fluorescent microsphere immunoassays (FMIA) that can be multiplexed to monitor exposure to multiple antigens and pathogens simultaneously; and a fluorescent focus neutralization assay (FFN) to measure functional virus neutralizing antibodies.

Results

A recombinant North American nucleoprotein (NP) based iELISA was developed and validated along with a bELISA using newly developed PEDV-NP specific biotinylated monoclonal antibodies (mAbs) and an FMIA using magnetic beads coupled with expressed NA PEDV-NP. Receiver operating characteristic (ROC) analysis was performed using swine serum samples (iELISA n = 1486, bELISA n = 1186, FMIA n = 1420). The ROC analysis for the FMIA showed estimated sensitivity and specificity of 98.2 and 99.2 %, respectively. The iELISA and bELISA showed a sensitivity and specificity of 97.9 and 97.6 %; and 98.2 and 98.9 %, respectively. Inter-rater (kappa) agreement was calculated to be 0.941 between iELISA and IFA, 0.945 between bELISA and IFA and 0.932 between FMIA and IFA. Similar comparative kappa values were observed between the iELISA, bELISA and FMIA, which demonstrated a significant level of testing agreement among the three assays. No cross-reactivity with the closely related coronaviruses, transmissible gastroenteritis virus (TGEV) or porcine respiratory coronavirus (PRCV) was noted with these assays. All three assays detected seroconversion of naïve animals within 6–9 days post exposure. The FFN assay allows relative quantitation of functional neutralizing antibodies in serum, milk or colostrum samples.

Conclusion

Well-validated iELISA, bELISA and FMIA assays for the detection of PEDV antibodies were developed and showed good correlation with IFA and each other. Each assay format has advantages that dictate how they will be used in the field. Newly developed mAbs to the PEDV-NP were used in the bELISA and for expediting FFN testing in the detection and quantitation of neutralizing antibodies. In addition, these PEDV mAbs are useful for immunohistochemistry, fluorescent antibody staining and other antigen-based tests. Measurement of neutralizing antibody responses using the FFN assay may provide a valuable tool for assessment of vaccine candidates or protective immunity.

Emergence of porcine epidemic diarrhea virus in southern Germany

BACKGROUND

Over the last years, porcine epidemic diarrhea virus (PEDV) has caused devastating enteric diseases in the US and several countries in Asia, while outbreaks in Europe have only been reported sporadically since the 1980s. At present, only insufficient information is available on currently circulating PEDV strains in Europe and their impact on the European swine industry. In this case report, we present epidemic outbreaks of porcine epidemic diarrhea in three farms in South-Western Germany.

CASE PRESENTATION

Epidemic outbreaks of diarrhea affecting pigs of all age groups were reported in three farms, one fattening farm and two piglet producing farms, in South-Western Germany between May and November 2014. In the fattening farm yellowish, watery diarrhea without evidence of mucus or blood was associated with a massive reduction of feed consumption. Severity of clinical signs and mortality in young suckling pigs varied significantly between the two affected sow farms. While mortality in suckling piglets reached almost 70 % in one sow herd, no increase in suckling piglet mortality was observed in the second sow farm. In all three cases, PEDV was confirmed in feces and small intestines by RT-qPCR. Phylogenetic analyses based on full-length PEDV genomes revealed high identity among strains from all three herds. Moreover, the German strains showed very high nucleotide identity (99.4 %) with a variant of PEDV (OH851) that was isolated in the United States in January 2014. This strain with insertions and deletions in the S-gene (so called INDEL strains) was reported to show lower virulence. Slightly lower identities were found with other strains from the US and Asia.

CONCLUSION

Phylogenetic information on the distribution of PEDV strains in Europe is severely lacking. In this case report we demonstrate that acute outbreaks of PEDV occurred in southern Germany in 2014. Current strains were clearly different from isolates found in the 1980s and were closely related to a PEDV variant found in the US in 2014. Moreover, the present case report indicates that variant strains of PEDV, containing insertions and deletions in the S gene, which were reported to be of lower virulence, might be able to cause high mortality in suckling piglets.

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.

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.

Development of an antigen capture enzyme-linked immunosorbent assay for virus detection based on porcine epidemic diarrhea virus monoclonal antibodies

Porcine epidemic diarrhea virus (PEDV), a coronavirus, can cause acute diarrhea and dehydration in pigs. In the current study, two positive monoclonal cell lines (5D7 and 3H4) specific for PEDV were established, and the immunoreactivity of the monoclonal antibodies was confirmed by immunofluorescence and dot-immunobinding assays. A method, termed antigen capture enzyme-linked immunosorbent assay (AC-ELISA), which used the monoclonal antibody 5D7 as the detecting antibody and rabbit antiserum of PEDV protein S as the capture antibody, was developed. Compared with the reverse transcription polymerase chain reaction method of detecting PEDV in fecal samples, AC-ELISA showed similar sensitivity and specificity. These results suggested that AC-ELISA would be useful for the diagnosis and epidemiological studies of PEDV.

Rapid and sensitive detection of porcine epidemic diarrhea virus by reverse transcription loop-mediated isothermal amplification combined with a vertical flow visualization strip

Porcine epidemic diarrhea virus (PEDV) is an important pathogen that causes vomiting, diarrhea, and dehydration, leading to serious damage to the swine industry worldwide. The establishment of effective diagnostic methods is imperative. However, traditional methods are often unsuitable. In this study, reverse transcription loop-mediated isothermal amplification (RT-LAMP) was combined with a vertical flow (VF) nucleic acid detection strip to detect PEDV. Parameters that affect the RT-LAMP reaction were optimized. The RT-LAMP-VF assay that we established was performed at 62 °C for 40 min, and then directly evaluated on the VF visualization strip cassette. The method demonstrated high specificity for PEDV. The detection limit was 10 pg of ribonucleic acid, consistent with RT-PCR, RT-LAMP detected products on agarose gels and by direct calcein fluorescence. Application of this method to clinical samples yielded a positivity rate that was comparable to that obtained for RT-PCR. This technique saves time and is efficient, and is thus expected to be useful for the diagnosis of PEDV infection in the field.

Comparison of serum neutralization and enzyme-linked immunosorbent assay on sera from porcine epidemic diarrhea virus vaccinated pigs

BACKGROUND

Porcine epidemic diarrhea virus (PEDV) is an economically important pathogen of swine.

OBJECTIVE

Serum neutralization (SN) and enzyme-linked immunosorbent assay (ELISA) test results as well as the utility of spike proteins S1, S2, and S3 and entire nucleocapsid protein were compared.

ANIMALS AND METHODS

Serum samples from 400 pigs vaccinated against PEDV strain SM98P were collected from 78 farms in Korea. SN test and ELISA were performed to confirm the presence of antibodies. For prokaryotic expression of partial fragments of spike protein the size and location of S1, S2, and S3, and full nucleocapsid protein, polymerase chain reaction was performed using specific primers.

RESULTS

Comparison of these results demonstrated that there was a correlation between the SN and ELISA results. Sera with higher neutralizing activity also had higher IgG titer. The antibody profiling data presented the correlation of neutralizing activity with the level of spike protein antibody. In particular, the S3 region may have an important role in neutralizing activity.

CONCLUSIONS

We confirmed that the carboxy-terminal region that includes the endodomain of the S protein induced stronger neutralizing activity than the region that includes the ectodomain.

CLINICAL RELEVANCE

The region of the S protein may have a stronger neutralizing KPEDV-9 epitope and could be useful for the evaluation of future PEDV vaccine efficacy.

Scientific Opinion on porcine epidemic diarrhoea and emerging porcine deltacoronavirus

In the last decade, many porcine epidemic diarrhoea (PED) outbreaks have been reported by several countries in Asia whereas only a few Member States of the European Union (EU) have reported PED clinical cases and/or PED virus (PEDV)-seropositive animals. This alphacoronavirus was first reported in the USA in May 2013, followed by rapid spread throughout the country and outbreaks reported by several countries in the Americas. The recent PEDV-EU isolates have high level of sequence identity to PEDV-Am isolates. Based on nucleotide sequencing, multiple variants of PEDV are circulating in Europe, the Americas and Asia but any difference in virulence and antigenicity is currently unknown. Serological cross-reactivity has been reported between PEDV isolated in Europe and in the Americas; however no data regarding cross-protection are available. The impact of different PEDV strains is difficult to compare between one country and another, since impact is dependent not only on pathogenicity but also on factors such as biosecurity, farm management, sanitary status or herd immune status. However, the clinical signs of PEDV infections in naive pigs are similar in different countries with mortalities up to 100% in naive newborn piglets. The impact of recently reported PED outbreaks in Asia and the USA seems to be more severe than what has been described in Europe. Infected animals, faeces, feed and objects contaminated with faeces are matrices that have been reported to transmit PEDV between farms. Infectious PEDV has been detected in spray-dried porcine plasma (SDPP) in one study but the origin of the infectious PEDV in SDPP is not clear. Detection of porcine deltacoronavirus (PDCoV) has been reported in a few countries but only limited testing has been done. Based on the currently available information, it seems that PDCoV would have a lower impact than PEDV.

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.

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.

Diagnosis and prevention of porcine epidemic diarrhea

Porcine epidemic diarrhea (PED) is a severe viral infectious disease caused by porcine epidemic diarrhea virus (PEDV), which often causes serious diarrhea, vomiting, dehydration, and high mortality in suckling piglets. This paper briefly summarizes the epidemiological and genetic characteristics, clinical symptoms, laboratory diagnosis and vaccine prevention of PED, with an aim to provide reference for the prevention and control of this disease.

Isolation and characterization of a variant porcine epidemic diarrhea virus in China

An outbreak of diarrhea in pigs started in Guangdong, South China in January 2011. Cases were characterized by watery diarrhea, dehydration and vomiting, with 80–100% morbidity and 50–90% mortality in suckling piglets. The causative agent of the diarrhea was ultimately identified as porcine epidemic diarrhea virus (PEDV). In this study, we isolated a PEDV strain designated CHGD-01 from piglet intestines using Vero cell cultures, and its specific cytopathic effects were confirmed in susceptible cells by direct immunofluorescence testing and electron microscopy. The complete genome of CHGD-01 was shown to be 28,035 nucleotides in length, with a similar structure to that of PEDV reference strains. Phylogenetic analyses based on the whole genome revealed that CHGD-01 shared nucleotide sequence identities of 98.2–98.4% with two other Chinese isolates reported in the same year, thus constituting a new cluster. Amino acid sequence analysis based on individual virus genes indicated a close relationship between the spike protein gene of CHGD-01 and the field strain KNU0802 in Korea. Its ORF3 and nucleoprotein genes, however, were divergent from all other sequenced PEDV isolate clusters and therefore formed a new group, suggesting a new variant PEDV isolate in China. Further studies will be required to determine the immunogenicity and pathogenicity of this new variant.

High-level mucosal and systemic immune responses induced by oral administration with Lactobacillus-expressed porcine epidemic diarrhea virus (PEDV) S1 region combined with Lactobacillus-expressed N protein

To develop effective mucosal vaccine formulation against porcine epidemic diarrhea virus (PEDV) infection, the DNA fragments encoding spike protein immunodominant region S1 and nucleocapsid N of PEDV were inserted into pPG1 (surface-displayed) or pPG2 (secretory) plasmids followed by electrotransformation into Lactobacillus casei (Lc) to yield four recombinant strains: PG1-S1, PG2-S1, PG1-N, and PG2-N. After intragastric administration, it was observed that live Lc-expressing S1 protein combined with Lc-expressing N protein could elicit much more potent mucosal and systemic immune responses than the former alone (P < 0.001), however slightly inferior to the latter alone (P > 0.05). Furthermore, the surface-displayed mixture (PG1-S1+ PG1-N) revealed stronger immunogenicity than the secretory mixture (PG2-S1+ PG2-N) as well as PEDV-neutralizing potency in vitro (P < 0.001). On 49th day after the last immunization, splenocytes were prepared from mice immunized with surface-displayed mixture, secretory mixture and negative control to be stimulated by purified N and S protein, respectively. The results of ELISA analysis showed that N protein was capable of inducing a higher level of IL-4 (P < 0.001) and IFN-γ (P < 0.001) than S1 protein in the immunized mice. Taken together, Lc-expressed N protein as molecular adjuvant or immunoenhancer was able to effectively facilitate the induction of mucosal and systemic immune responses by Lc-expressing S1 region.

Comparing electron microscopy and a competitive blocking ELISA in the detection of rotaviruses in porcine faeces

Analysis of 476 faecal samples from diarrhoeic piglets was performed using electron microscopy (EM) and a competitive blocking (CB)-ELISA based on monoclonal antibodies to the VP6 protein of group A rotavirus. Rotavirus was detected by EM and/or CB-ELISA in 111 (23.3%) samples. Of these, all groups of rotavirus were identified in 83 (74.8%) samples by EM (EM+), while group A rotavirus was identified in 90 (81.1%) samples by CB-ELISA (ELISA+). However, only 62 (55.9%) of samples were positive using both detection methods. The finding of 28 (25.2%) EM-/CB-ELISA+ samples illustrated the high sensitivity of the CB-ELISA method. On PCR analysis, groups B and C rotavirus was found in 3 and 16 of 19 EM+/CB-ELISA- samples, respectively. Although the study illustrates the high sensitivity of a CB-ELISA in rotavirus detection, the findings highlight the need to use a range of diagnostic methods in detecting these viruses in clinical samples.

Comparison of enzyme-linked immunosorbent assay and RT-PCR for the detection of porcine epidemic diarrhoea virus

Porcine epidemic diarrhoea (PED) is a contagious enteric disease of pigs caused by a coronavirus. A double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) based on the use of monoclonal antibodies was developed for the detection of porcine epidemic diarrhoea virus (PEDV). The DAS-ELISA was compared with RT-PCR in the examination of 506 specimens collected during 2006-2007 from pigs originating from different farms located in the Po valley. Both faecal samples obtained directly from the rectum of live animals showing clinical signs and intestinal samples collected from the caecum of deceased pigs were included in the study. The correlation between the two methods was higher when testing faecal samples (K=0.97, 95% CI: 0.94-1.00) than testing intestinal samples (K=0.62, 95% CI: 0.35-0.89). The use of ELISA technology provided an efficient and effective mean of evaluating the presence of coronavirus PED antigen in field samples and indicates that this procedure is a very useful tool in epidemiological studies.

Viral detection by electron microscopy: past, present and future

Viruses are very small and most of them can be seen only by TEM (transmission electron microscopy). TEM has therefore made a major contribution to virology, including the discovery of many viruses, the diagnosis of various viral infections and fundamental investigations of virus-host cell interactions. However, TEM has gradually been replaced by more sensitive methods, such as the PCR. In research, new imaging techniques for fluorescence light microscopy have supplanted TEM, making it possible to study live cells and dynamic interactions between viruses and the cellular machinery. Nevertheless, TEM remains essential for certain aspects of virology. It is very useful for the initial identification of unknown viral agents in particular outbreaks, and is recommended by regulatory agencies for investigation of the viral safety of biological products and/or the cells used to produce them. In research, only TEM has a resolution sufficiently high for discrimination between aggregated viral proteins and structured viral particles. Recent examples of different viral assembly models illustrate the value of TEM for improving our understanding of virus-cell interactions.

Multiplex real-time RT-PCR for the simultaneous detection and quantification of transmissible gastroenteritis virus and porcine epidemic diarrhea virus

Transmissible gastroenteritis virus (TGEV) and porcine epidemic diarrhea virus (PEDV) are major etiological agents of diarrhea and death in piglets. Multiplex real-time reverse transcriptase (RT)-PCR was developed for simultaneous differential quantification of each virus in a single reaction tube, using Cy5- and FAM-labeled TaqMan-probes based on sequences from the TGEV and PEDV nucleocapsid genes. The copy numbers for transcripts of TGEV and PEDV were quantified using this assay over a range from 9 × 10⁷ to 9 × 10¹ copies and 7 × 10⁷ to 7 × 10¹ copies, respectively. The variability of the intra-assay and inter-assay were evaluated using standard solutions of each transcript, with coefficients of variation (CV) less than 3.43 and 3.33%, respectively. Piglets were experimentally infected with virulent TGEV and PEDV, and the amounts of virus from the onset of diarrhea were measured. Samples obtained from farms experiencing PED or TGE were quantified between 10² and 10⁵ RNA copies. In conclusion, this assay provides an effective etiological diagnostic tool for detecting and quantifying viral loads. The assay may also prove useful for detecting infections, ultimately leading to better disease control on farms.

High-level prokaryotic expression of envelope exterior of membrane protein of porcine epidemic diarrhea virus

The truncated fragment M′ gene, encoding the exterior of the viral envelope protein of PEDV, was subcloned into prokaryotic expression vector pGEX-6p-1. The recombinant plasmid pGEX-6p-M′ was constructed and transformed into E. coli BL21(DE3)pLysS for expression. SDS-PAGE analysis showed recombinant truncated M′ protein was highly expressed by pGEX-6p-M′ and the product fusion protein GST-M′ reached 45% in the total bacteria proteins with the analysis of software AlphaImager2200. The preliminary purified recombinant protein was evaluated for its antigenicity and reactivity through Western blotting and indirect enzyme-linked immunosorbent assay (ELISA) with monoclonal antibody against M protein of PEDV and porcine polyclonal anti-PEDV antiserum as the primary antibody. The results indicated the recombinant truncated M′ protein should be candidate as a feasible recombinant diagnostic reagent.

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

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

Use of an internal control in a quantitative RT-PCR assay for quantitation of porcine epidemic diarrhea virus shedding in pigs

Porcine epidemic diarrhea virus (PEDV), a member of the family Coronaviridae, has caused a devastating enteric disease in the Korean swine industry. Previously, the differences between virulent field PEDV strains and a Vero cell culture adapted PEDV DR13 strain were determined using restriction fragment length polymorphism analysis (RFLP), and PEDV shedding patterns in pigs were reported. In an extension to these studies, an internal control was constructed and quantitative analysis of virus shedding after oral inoculation was established. A parent field PEDV and a cell culture adapted PEDV DR13 were inoculated orally to colostrum-deprived 1-day-old piglets, commercial 2-week-old pigs, and sows (1-5 ml dose, 10(5.8)-10(6.0) TCID(50)/0.1 ml). PEDV shedding was monitored every day and virus levels were measured using a quantitative reverse transcriptase polymerase chain reaction (RT-PCR) method. In fecal samples from experimentally-inoculated pigs, the level of virus excreted peaked at 2 days after oral inoculation and gradually decreased thereafter. In addition, PEDV from field specimens was quantified using the same RT-PCR assay to determine shedding viral load. This suggests that measurement of PEDV shedding viral load in pigs, by quantitative RT-PCR, may be a useful tool for estimating the transmission potential of PEDV in the swine population.

Use of monoclonal antibodies in blocking ELISA detection of transmissible gastroenteritis virus in faeces of piglets

Monoclonal antibodies (mAb) to the transmissible gastroenteritis virus (TGEV) nucleoprotein (N) and membrane protein (M) were prepared and used for the comparative assessment of three blocking ELISA variants to detect TGEV. The competitive blocking ELISA format showed the highest sensitivity, allowing detection of 10³ TCID₅₀ TGEV/ml in culture medium. Ninety‐nine porcine field faecal samples obtained from 37 herds affected with diarrhoea were examined, and various TGEV levels were found in nine samples from six herds. However, only in three samples were significant TGEV concentrations demonstrated. The relationship between incidence of TGEV gastroenteritis and the spread of porcine respiratory coronavirus infection in pig farms is discussed.