A simple and rapid identification method for newly emerged porcine Deltacoronavirus with loop-mediated isothermal amplification

Epidemiological monitoring and genetic variation analysis of pathogens associated with porcine viral diarrhea in southern China from 2021 to 2023

Large-scale outbreaks of virus-associated severe diarrhea have occurred in pig populations since 2010. To investigate the prevalence and genetic evolution of the diarrhea-associated viruses responsible for the outbreaks, we tested 1,791 diarrhea samples collected from 213 pig farms in five provinces in southern China between 2021 and 2023. The test results showed that porcine epidemic diarrhea virus (PEDV) was the most frequently detected virus. The prevalence rates ranged from 47.40 to 52.22% in samples and 76.06% (162/213) in pig farms. Porcine rotavirus (PoRV) was the second common virus, with prevalence rates ranging from 25.81 to 50.81% in samples and 72.77%(155/213) in pig farms. Porcine delta coronavirus (PDCoV) was the third common virus, with prevalence rates ranging from 16.33 to 17.48% in samples and 38.50% (82/213) in pig farms. The detection rates of both transmissible gastroenteritis virus (TGEV) and porcine acute diarrheal syndrome coronavirus (SADS-CoV) were very low, less than 1.01% in samples and less than 3.76% in pig farms. In this study, we found SADS-CoV only in piglet diarrhea samples from Jiangxi, Guangdong, and Guangxi provinces in China, with a prevalence rate of 5.16% (11/213) in pig farms. Co-infection with these diarrhea-associated viruses is a common occurrence. The most common co-infections were PEDV and PoRV, with a prevalence rate of 6.64% (119/1,791), followed by PDCoV and PoRV, with a prevalence rate of 4.19% (75/1,791). Phylogenetic analyses showed that PEDV and PEDV variants prevalent in southern China during the past three years clustered into genotype GIIb and recombinant PEDV subtypes. Among the currently endemic PEDV, the most common mutations occurred in the collagenase equivalent (COE) and epitope regions of the spike gene. PoRV strains were mainly dominated by the G9 subtype, followed by the G5, G3 and G4 subtypes. Our results suggest that variant PEDV, PDCoV and PoRV are the main pathogens of swine diarrhea, and singular- or co-infection with pathogenic enteric CoV is common in pig herds in southern China. Therefore, prevention and control of porcine viral diarrhea should be given high attention.

Isothermal nucleic acid amplification combined with gold nanoparticles assisted electrochemical impedance for the sensitive and efficient porcine delta coronavirus detection

The emergence of porcine delta coronavirus (PDCoV) has caused huge economic losses in the global pig industry. How to realize the sensitive and efficient detection for it is a difficult problem that need to be resolved. In this work, loop-mediated isothermal amplification (LAMP)-electrochemical impedance spectroscopy (EIS) detection platform for PDCoV based on nucleic acid level was constructed by combining the advantages of efficient amplification for LAMP and sensitive detection for EIS. Referring to a 159 bp fragment of PDCoV N gene (Genbank：KY078891, 641 bp-799 bp), primers (HS-FIP、BIP、F3、B3) were designed to screened and sulfhydryl groups were activated, and then loop-mediated isothermal amplification was carried out. Subsequently, gold nanoparticles were loaded on indium tin oxide glass by electrodeposition technology, and the amplified products were connected to the electrode surface through the formation of Au-S bonds. According to the difference of charge transfer resistance after double-stranded DNA was connected on the electrode surface, the detection platform can achieve valid detection of PDCoV in the concentration range of 102-107 copies/μL, the limit of detection is 28 copies/μL, and can be used for practical analysis of pig small intestine samples.

Emergent Molecular Techniques Applied to the Detection of Porcine Viruses

Molecular diagnostic tests have evolved very rapidly in the field of human health, especially with the arrival of the recent pandemic caused by the SARS-CoV-2 virus. However, the animal sector is constantly neglected, even though accurate detection by molecular tools could represent economic advantages by preventing the spread of viruses. In this regard, the swine industry is of great interest. The main viruses that affect the swine industry are described in this review, including African swine fever virus (ASFV), porcine reproductive and respiratory syndrome virus (PRRSV), porcine epidemic diarrhea virus (PEDV), and porcine circovirus (PCV), which have been effectively detected by different molecular tools in recent times. Here, we describe the rationale of molecular techniques such as multiplex PCR, isothermal methods (LAMP, NASBA, RPA, and PSR) and novel methods such as CRISPR-Cas and microfluidics platforms. Successful molecular diagnostic developments are presented by highlighting their most important findings. Finally, we describe the barriers that hinder the large-scale development of affordable, accessible, rapid, and easy-to-use molecular diagnostic tests. The evolution of diagnostic techniques is critical to prevent the spread of viruses and the development of viral reservoirs in the swine industry that impact the possible development of future pandemics and the world economy.

A nucleic acid detection assay combining reverse transcription recombinase-aided amplification with a lateral flow dipstick for the rapid visual detection of porcine deltacoronavirus

Porcine deltacoronavirus (PDCoV) is an emerging enteropathogen causing severe diarrhoea, dehydration, and death in nursing piglets and enormous economic losses for the global swine industry. Furthermore, it can infect multiple animal species including humans. Therefore, a rapid, definitive diagnostic assay is required for the effective control of this zoonotic pathogen. To identify PDCoV, we developed a nucleic acid detection assay combining reverse transcription recombinase-aided amplification (RT-RAA) with a lateral flow dipstick (LFD) targeting the highly conserved genomic region in the ORF1b gene. The RT-RAA-LFD assay exhibited good PDCoV detection reproducibility and repeatability and could be completed within 11 min. Ten minutes at 40 °C was required for nucleic acid amplification and 1 min at room temperature was needed for the visual LFD readout. The assay specifically detected PDCoV and did not cross-react with any other major swine pathogens. The 95% limit of detection (LOD) was 3.97 median tissue culture infectious dose PDCoV RNA per reaction. This performance was comparable to that of a reference TaqMan-based real-time RT-PCR (trRT-PCR) assay for PDCoV. Of 149 swine small intestine, rectal swab, and serum samples, 71 and 75 tested positive for PDCoV according to RT-RAA-LFD and trRT-PCR, respectively. The diagnostic coincidence rate for both assays was 97.32% (145/149) and the kappa value was 0.946 (p < 0.001). Overall, the RT-RAA-LFD assay is a user-friendly diagnostic tool that can rapidly and visually detect PDCoV.

A Novel, Cleaved Probe-Based Reverse Transcription Loop-Mediated Isothermal Amplification Method for Specific and Sensitive Detection of Porcine Deltacoronavirus

Porcine deltacoronavirus (PDCoV) causes watery diarrhea, vomiting, and 30–40% mortality in newborn piglets. A simple, rapid, and sensitive method for PDCoV detection is valuable in its surveillance and control. Here, we developed a novel, cleaved probe-based reverse transcription loop-mediated isothermal amplification (CP-RT-LAMP) method for PDCoV detection. A cleaved probe with a ribonucleotide insertion that targeted the N gene of PDCoV was designed. During the reaction, the enzyme ribonuclease H2 is activated only when the cleaved probe is perfectly complementary to the template, leading to the hydrolytic release of a quencher moiety and signal output. This method can be easily used on a real-time fluorescence quantitative equipment or an on-site isothermal instrument combined with a smartphone. The specificity assay showed no cross-reactivity with other porcine enteric pathogens. This method had a detection limit of 25 copies/μL, suggesting comparable sensitivity with reverse transcription quantitative PCR (RT-qPCR). In detecting 100 clinical samples (48 fecal swab specimens and 52 intestinal specimens), the detection rate of the CP-RT-LAMP method (26%) was higher than that of RT-qPCR (17%). Thus, it is a highly specific and sensitive diagnostic method for PDCoV, with a great application potential for monitoring PDCoV in the laboratory or point-of-care testing in the field.

Development and Application of RAA Nucleic Acid Test Strip Assay and Double RAA Gel Electrophoresis Detection Methods for ASFV and CSFV

African swine fever (ASF) is an acute, severe and hemorrhagic infectious disease caused by African swine fever virus (ASFV) infecting domestic pigs and wild boars. Since the outbreak of the disease in China in 2018, it has brought a great impact on China’s pig industry. Classical swine fever (CSF) is an acute contact infectious disease of pigs caused by classical swine fever virus (CSFV) infection. Clinically, acute CSF usually shows persistent high fever, anorexia, extensive congestion and bleeding of the skin and mucosa, which are similar to ASF. It is of great significance to prevent, control and accurately detect ASF and CSF in pig farms. In this study, Recombinase aided amplification (RAA) technology combined with a nucleic acid test strip (RAA-strip) was established for simple and specific detection of ASFV/CSFV. The sensitivity and preliminary clinical application results showed that the RAA test strip established in this study could detect recombinant plasmids containing ASFV/CSFV gene fragments as low as 103 copies/µL. The minimum detection limits of virus DNA/cDNA were 10 and 12 pg respectively, and there was no cross-reaction with other porcine viruses. The specificity of the method was good. We used 37–42 clinical samples to evaluate the performance of our established method, and the positive concordance rates with conventional PCR were 94.1 and 57.1%, respectively. In addition, ASFV and CSFV double RAA agarose gel electrophoresis detection methods were established. The results showed that the method had good specificity. The detection limit of this method is 106 copies for ASFV p72 gene recombinant plasmid and 105 copies for CSFV NS5B Gene recombinant plasmid. The use of this method for clinical material detection was consistent with the PCR method. In summary, the developed method of RAA-strip assay for ASFV and CSFV realized the visual detection of pathogens, and the developed method of dual RAA agarose gel electrophoresis assay for ASFV and CSFV realized the simultaneous detection of two pathogens in one reaction, with good specificity, high sensitivity and rapid reaction rate, which was expected to be clinically feasible for the differential diagnosis of ASF and CSF provided technical support.

Development of Recombinase Aided Amplification Combined With Disposable Nucleic Acid Test Strip for Rapid Detection of Porcine Circovirus Type 2

Porcine circovirus type 2 (PCV2) is the dominant causative agent of PCV2 systemic disease (PCV2-SD) in pigs. It can also associate with other diseases such as respiratory and enteric diseases, reproductive failure, porcine dermatitis and nephropathy syndrome in pigs. Currently, PCV2 infection is a considerable threat in the swine industry. Therefore, it is of great significance to prevent, control, and accurately detect PCV2 in pig farms. Recombinase aided amplification (RAA) technology is an isothermal nucleic acid amplification technology that could rapidly amplify the target gene fragment at a constant temperature. The amplification products labeled with specific molecules could be visually detected using the test strip with the corresponding antibody. In the present study, the RAA technology combined with a nucleic acid test strip (RAA-strip) was established for simple and specific detection of PCV2. Primers and probes targeting the PCV2 ORF2 gene were designed according to the RAA technology principles. The PCV2 RAA-strip established in this study could detect as low as 10³ copies/μL of recombinant plasmids containing the PCV2 ORF2 gene fragment. The lowest detection limit about viral DNA and virus titers was 6.7 × 10^-6 ng/μL and 10 TCID50/mL, respectively. Furthermore, no cross-reaction with other porcine viruses occurred at 37°C and within 15 min. We used 42 clinical samples to assess the performance of our established method. The positive rate of clinical samples detected by PCV2 RAA-strip was 50.00%. This was similar to that detected by PCV2 PCR (45.24%). In conclusion, due to the advantages of strong specificity, high sensitivity, excellent reproducibility, and simple operation method, our PCV2 RAA-strip is suitable for the rapid clinical detection of PCV2 on-site.

A portable, 3D printed, microfluidic device for multiplexed, real time, molecular detection of the porcine epidemic diarrhea virus, transmissible gastroenteritis virus, and porcine deltacoronavirus at the point of need

The porcine epidemic diarrhea virus (PEDV), transmissible gastroenteritis virus (TGEV), and porcine deltacoronavirus (PDCoV) are emerging/reemerging coronaviruses (CoVs) of neonatal pigs that cause great economic losses to pig farms and pork processors. Specific, rapid, and simple multiplex detection of these viruses is critical to enable prompt implementation of appropriate control measures. Conventional methods for molecular diagnosis require skilled personnel and relatively sophisticated equipment, restricting their use in centralized laboratories. We developed a low-cost, rapid, semi-quantitative, field deployable, 3D-printed microfluidic device for auto-distribution of samples and self-sealing and real-time and reverse transcription-loop-mediated isothermal amplification (RT-LAMP), enabling the co-detection of PEDV, TGEV and PDCoV within 30 minutes. Our assay's analytical performance is comparable with a benchtop, real-time RT-LAMP assay and the gold standard quantitative reverse transcription-polymerase chain reaction (qRT-PCR) assay with limits of detection of 10 genomic copies per reaction for PEDV and PDCoV, and 100 genomic copies per reaction for TGEV. Evaluation of clinical specimens from diseased pigs with our microfluidic device revealed excellent concordance with both benchtop RT-LAMP and qRT-PCR. Our portable RT-LAMP microfluidic chip will potentially facilitate simple, specific, rapid multiplexed detection of harmful infections in minimally equipped veterinary diagnostic laboratories and on-site in pigs' farms.

Using loop-mediated isothermal amplification for visual detection of porcine parvovirus 7

We developed and optimized a loop-mediated isothermal amplification (LAMP)-based method to detect porcine parvovirus 7 (PPV7). After using three pairs of specific primers to amplify PPV7 isothermally at 62 °C for 40 min, the amplified product was mixed with SYBR Green I, after which the sample turned green. The method detected PPV7 at concentrations as low as 40 copies/μL, and the sensitivity was consistent with that of nested polymerase chain reaction (PCR) analysis, which was tenfold higher than that of conventional PCR. No cross-reactivity occurred with porcine parvovirus 1, porcine circovirus type 3, porcine circovirus type 2, porcine pseudorabies virus, porcine epidemic diarrhea virus, or porcine reproductive and respiratory syndrome virus. Simultaneous analysis of 76 clinical samples was performed using LAMP, conventional PCR, and nested PCR. The results showed that our method is simple, rapid, sensitive, and specific for the rapid diagnosis of PPV7 in pig farms.

SUPPLEMENTARY INFORMATION

The online version of this article (10.1007/s13205-020-02623-5) contains supplementary material, which is available to authorized users.

Simple and Visible Detection of Novel Astroviruses Causing Fatal Gout in Goslings Using One-Step Reverse Transcription Polymerase Spiral Reaction Method

In this study, a one-step isothermal method combining polymerase spiral reaction (PSR) with reverse transcription (RT-PSR) was established for rapid and specific detection of novel astroviruses causing fatal gout in goslings (N-GoAstV). The one-step RT-PSR was accomplished at the optimal temperature of 62°C and time of 40 min and used primers simply designed as conventional PCR primers, and the results of detection were visible to the naked eye. The detection limit of PSR was above 34.7 copies/μL at a 95% probability level according to probit regression analysis. The assay specifically detected N-GoAstV, and no other reference viruses were detected. These results suggest that the newly established RT-PSR assay could, in one step, accomplish reverse-transcription, amplification, and result determination providing a visible, convenient, rapid, and cost-effective test that can be carried out onsite, in order to ensure timely quarantine of N-GoAstV-infected birds, leading to effective disease control.

Application of recombinase polymerase amplification method for rapid detection of infectious laryngotracheitis virus

Infectious laryngotracheitis is a significant respiratory disease of chickens that causes huge economic losses due to high morbidity and mortality and reduced egg production. A real-time recombinase polymerase amplification (RPA) assay was developed to accurately detect ILTV. The specific probe and primer sets were carefully designed and screened. The real-time RPA assay was carried out at 39 °C for 30 min, and results were obtained within 15 min. The results of the specificity assay showed no fluorescence signals with other avian-related viruses. The sensitivity of the assay was 1 × 10² copies/μL. The low CV value showed that the assay was reproducible. A total of 115 clinical samples were tested using the real-time RPA assay and the real-time PCR assay in parallel; the coincidence rates of the two detection methods were 100%. The results indicated that the real-time RPA assay is a specific, sensitive, rapid, and useful tool for epidemiological studies and clinical diagnosis, especially in the field and in resource-poor areas.

Rapid and visual detection of novel astroviruses causing fatal gout in goslings using one-step reverse transcription loop-mediated isothermal amplification

To visually and rapidly detect a novel goose astrovirus (N-GoAstV) causing fatal gout in goslings, an isothermal detection method based on one-step reverse transcription loop-mediated isothermal amplification (one-step RT-LAMP) was established. The one-step RT-LAMP assay for N-GoAstV detection, using Bst 3.0 DNA polymerase with strong reverse transcription activity and primer sets targeting the opening reading frame 1b (ORF1b) of N-GoAstV, could be completed in 30 min using a water bath at 61°C; the detection results could be visually observed by adding a pH-sensitive dye containing phenol red and cresol red. The detection limit of the one-step RT-LAMP assay was 57.8 copies, which was similar to that of reverse transcription–quantitative polymerase chain reaction. The assay specifically detected N-GoAstV without any cross-reaction with other reference viruses, and this was further confirmed using enzyme digestion. These results indicated that the newly established RT-LAMP assay could accomplish reverse transcription, amplification, and visual result determination in one step, and the results obtained via this rapid and cost-effective method could be used to support disease control on farms in terms of N-GoAstV infection.

Rapid and visual detection of porcine deltacoronavirus by recombinase polymerase amplification combined with a lateral flow dipstick

Background

Porcine Deltacoronavirus (PDCoV) is a newly emerging Coronavirus that was first identified in 2012 in Hong Kong, China. Since then, PDCoV has subsequently been reported worldwide, causing a high number of neonatal piglet deaths and significant economic losses to the swine industry. Therefore, it is necessary to establish a highly sensitive and specific method for the rapid diagnosis of PDCoV.

Results

In the present study, a highly sensitive and specific diagnostic method using recombinase polymerase amplification combined with a lateral flow dipstick (LFD-RPA) was developed for rapid and visual detection of PDCoV. The system can be performed under a broad range of temperature conditions from 10 to 37 °C, and the detection of PDCoV can be completed in 10 min at 37 °C. The sensitivity of this assay was 10 times higher than that of conventional PCR with a lower detection limit of 1 × 10² copies/µl of PDCoV. Meanwhile, the LFD-RPA assay specifically amplified PDCoV, while there was no cross-amplification with other swine-associated viruses, including Porcine epidemic diarrhea virus (PEDV), Transmissible gastroenteritis virus (TGEV), Porcine kobuvirus (PKoV), Foot and mouth disease virus (FMDV), Porcine reproductive and respiratory syndrome virus (PRRSV), Porcine circovirus type 2 (PCV2), Classical swine fever virus (CSFV) and Seneca valley virus (SVV). The repeatability of the test results indicated that this assay had good repeatability. In addition, 68 clinical samples (48 fecal swab specimens and 20 intestinal specimens) were further tested by LFD-RPA and RT-PCR assay. The positive rate of LFD-RPA clinical samples was 26.47% higher than that of conventional PCR (23.53%).

Conclusions

The LFD-RPA assay successfully detected PDCoV in less than 20 min in this study, providing a potentially valuable tool to improve molecular detection for PDCoV and to monitor the outbreak of PDCoV, especially in low-resource areas and laboratories.

A simple and rapid diagnostic method to detect new goose astrovirus using reverse-transcription loop-mediated isothermal amplification

In this study, we develop a reverse-transcription loop-mediated isothermal amplification (RT-LAMP) assay for rapid and easy detection of goose astroviruses (GAstVs) in clinical samples. The specific LAMP primer sets were designed targeting the ORF2 gene of GAstV. The conditions of LAMP amplification were optimized in terms of reaction time and temperature. The optimal conditions are 60 min in a 60 °C water bath. No cross-reactivity was noted with fowl adenovirus serotype 4 (FAdV-4), duck tembusu virus (DTMUV), goose parvovirus (GPV), avian infectious bronchitis virus (IBV), or chicken anemia virus (CAV). The proposed RT-LAMP method was compared with conventional RT polymerase chain reaction (RT-PCR) and with nested RT-PCR. The results showed that the sensitivity of the proposed method was comparable to that of nested RT-PCR and tenfold higher than that of the conventional RT-PCR. Clinical samples (N = 129) of the liver and kidney from sick geese collected from six commercial goose farms were tested. The positive rate was 39.5% (51/129), 38.8% (50/129), and 34.9% (45/129) using RT-LAMP, nested RT-PCR and conventional RT-PCR, respectively. The developed RT-LAMP diagnostic method is not only simple, rapid, and highly specific, but also portable for use on the field. It may be used in epidemiological investigation to detect GAstVs.

Development of a reverse transcription-loop-mediated isothermal amplification (RT-LAMP) assay for the detection of porcine pegivirus

A simple and accurate reverse transcription-loop-mediated isothermal amplification (RT-LAMP) assay was developed and evaluated for the detection of porcine pegivirus (PPgV). The specific RT-LAMP primers targeting the conserved regions of NS5A genes were designed and used to detect PPgV. The optimal reaction parameter for RT-LAMP assay was 63℃ for 60 min. The detection limit of the RT-LAMP assay was 10 copies of PPgV genome, which was 100 times more sensitive than that of the conventional RT-PCR and comparable to nested RT-PCR and quantitative RT-PCR (qRT-PCR). There was no cross amplification with other related RNA viruses. In the clinical evaluation, the RT-LAMP assay exhibited a similar sensitivity with nested RT-PCR and qRT-PCR. The results indicated that RT-LAMP assay developed in this study could be a highly specific, sensitive, and cost-effective alternative for a rapid detection of PPgV in field settings.

Point-of-care diagnostic assay for rapid detection of porcine deltacoronavirus using the recombinase polymerase amplification method

Porcine deltacoronavirus (PDCoV) has emerged and spread throughout the porcine industry in many countries over the last 6 years. PDCoV caused watery diarrhoea, vomiting and dehydration in newborn piglets. A sensitive diagnostic method would be beneficial to the prevention and control of PDCoV infection. Recombinase polymerase amplification (RPA) is an isothermal amplification method which has been widely used for virus detection. A probe-based reverse transcription RPA (RT-RPA) assay was developed for real-time detection of PDCoV. The amplification can be finished in 20 min and fluorescence monitoring was performed by a portable device. The lowest detection limit of the PDCoV RT-RPA assay was 100 copies of RNA molecules per reaction; moreover, the RT-RPA assay had no cross-reaction with other common swine viruses. The clinical performance of the RT-RPA assay was evaluated using 108 clinical samples (54 intestine specimens and 54 faecal swab specimens). The coincidence rate of the detection results for clinical samples between RT-RPA and RT-qPCR was 97.2%. In summary, the real-time RT-RPA assay offers a promising alternative to RT-qPCR for point-of-care detection of PDCoV.

Single Chain Fragment Variable (scFv) Antibodies Targeting the Spike Protein of Porcine Epidemic Diarrhea Virus Provide Protection against Viral Infection in Piglets

Porcine epidemic diarrhea virus (PEDV) is a highly contagious coronavirus that causes severe diarrhea and death in neonatal piglets. Passive immunization with neutralizing antibodies against PEDV is an effective prevention measure. In this study, single chain fragment variable (scFv) antibodies against PEDV were screened from the porcine scFv phage display library. After four rounds of biopanning, scFvs that showed higher affinity to the PEDV antigen were selected for further study. The scFv genes were cloned into the expression plasmid for recombinant protein expression. These scFvs were shown to inhibit PEDV infectivity by the plaque reduction neutralization assay. Immunofluorescence assay (IFA) revealed that the epitopes recognized by these scFvs were in the S1 region of the spike protein. The potential of scFvs to provide prevention against PEDV infections in piglets was further investigated. Piglets orally administered scFvs showed no to mild clinical symptoms, significantly less viral shedding, no mortality and no intestinal lesions. The field application also revealed that the survival rate of piglets was significantly increased by oral administration of scFvs. Our data support the potential role of scFvs in the prevention and treatment of PEDV infection.

Development of a Conventional RT-PCR Assay for Rapid Detection of Porcine Deltacoronavirus with the Same Detection Limit as a SYBR Green-Based Real-Time RT-PCR Assay

Porcine deltacoronavirus (PDCoV) is a newly discovered coronavirus, which belongs to the family Coronaviridae. It causes watery diarrhea, vomiting, and dehydration in newborn piglets. A sensitive RT-PCR method is urgently required to detect PDCoV infection. In this study, we developed and evaluated a conventional RT-PCR assay and a SYBR green-based real-time RT-PCR assay that targeted the PDCoV n gene. Both assays are specific and have the same limit of detection at 2 × 10¹ copies of RNA molecules per reaction. Eighty-four clinical samples were subjected to both conventional RT-PCR and real-time RT-PCR, and the same positive rate (41.7%) was achieved, which was much higher than the positive rate (26.2%) using a previously described one-step RT-PCR technique. In summary, a conventional RT-PCR technique was successfully established for the detection of PDCoV with the same detection limit as a SYBR green-based real-time RT-PCR assay.

Detection of Novel duck reovirus (NDRV) using visual reverse transcription loop-mediated isothermal amplification (RT-LAMP)

Here we present a visual reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay for detecting the gene encoding the σB major outer-capsid protein of novel duck reovirus (NDRV). A set of primers, composed of two outer primers, two inner primers and two loop primers, was designed based on the gene of interest. The LAMP reaction was conducted in a traditional laboratory water bath at 65 °C for 50 min. We compared the performance of calcein/Mn²⁺ and SYBR Green I dyes, as well as electrophoresis on agarose gel stained with GoldView nucleic acid dye to detect the RT-LAMP-amplified products and all assays could be employed to discriminate between positive and negative specimens in visible or UV light. Our data showed that there is no cross-reaction with other viruses and the RT-LAMP technique displayed high sensitivity for detecting NDRV with a minimal detection limit of 200 fg RNA input. This assay was more sensitive than conventional PCR in detecting NDRV both in natural and experimental infection. In conclusion, the RT-LAMP technique was remarkably sensitive, specific, rapid, simple and profitable for the identification of NDRV.

Development of a real time loop-mediated isothermal amplification method for detection of Senecavirus A

Senecavirus A (SVA), formerly known as Seneca Valley Virus (SVV), is one of causative agents of vesicular diseases in swine. Recently, the outbreaks associated with vesicular disease caused by SVA infection in pig herds have been reported in Brazil, USA, China, Thailand and Canada. Several molecular detection methods have been established to determine the infection of SVA, including real time reverse transcription PCR assay, nested PCR, a TaqMan-based qRT-PCR assay and RNA-based in situ hybridization method. In our study, an assay for the identification of SVA in pig herds using real time reverse transcription loop-mediated isothermal amplification (real time RT-LAMP) was developed. The limit of detection for the assay was 1 TCID₅₀/ml. One hundred and eighteen field samples from pigs were used to validate the assay for clinical application. Our result demonstrated that real time RT-LAMP assay is a cost-effective and highly specific and sensitive alternative for the rapid detection of SVA in clinical samples.