Establishment of an indirect ELISA-based method involving the use of a multiepitope recombinant S protein to detect antibodies against canine coronavirus.

Here, we report the development of an indirect enzyme-linked immunosorbent assay (ELISA) method that involves using multiepitope recombinant S protein (rSP) as the coating antigen to detect antibodies against canine coronavirus (CCoV). rSP was designed by arranging its four S fragments (91-135 aa, S1 gene; 377-434 aa, S2 gene; 647-671 aa, S3 gene; 951-971 aa, S4 gene; 207-227 aa) and two T-cell epitopes in tandem: T-E1-E2-E3-E4-T. This multiepitope antigen, which has a molecular weight of approximately 25 kDa and contains a His-tag, was recognized by a CCoV-positive serum in a Western blot assay. The optimal concentration of rSP as a coating antigen in the ELISA was 2 µg/mL, and the optimal dilution of enzyme-labeled secondary antibody was 1:10,000. The cutoff OD450 value was established at 0.2395. No reactivity was observed with antisera against canine distemper virus, canine parvovirus, or feline calicivirus, indicating that this assay is highly specific. We also tested 64 clinical serum samples using our newly established method, and the positive rate was found to be 82.8%. In conclusion, our assay was found to be highly sensitive and specific for the detection of antibodies against CCoV, and it can therefore serve as a new, efficient diagnostic method.

Development of a nanoparticle-assisted PCR assay to distinguish canine coronaviruses I and II.

Nanoparticle-assisted PCR (nanoPCR) is a novel method for the simple, rapid, and specific detection of viruses. We developed a nanoPCR method to detect and differentiate canine coronavirus I (CCoV I) and II (CCoV II). Primer pairs were designed against the M gene conserved region of CCoV I and CCoV II, producing specific fragments of 239 bp (CCoV I) and 105 bp (CCoV II). We optimized the annealing temperature and primer concentrations for the CCoV nanoPCR assay and assessed its sensitivity and specificity. Under optimized nanoPCR reaction conditions, the detection limits were 6.47 × 101 copies/µL for CCoV I and 6.91 × 102 copies/µL for CCoV II. No fragments were amplified using other canine viruses as templates. The sensitivity of the nanoPCR assay was 100-fold higher than that of a conventional RT-PCR assay. Among 60 clinical samples collected from Beijing, China, the assay detected 12% positive for CCoV I and 48% positive for CCoV II. Our nanoPCR method is an effective method to rapidly detect CCoV I and CCoV II alone, or as a mixed infection, in dogs.

Isolation and Characterization of Encephalomyocarditis Virus from Dogs in China.

Encephalomyocarditis virus (EMCV) is as a potential zoonotic agent with a wide host range. Here, we describe an EMC virus isolate, identified as EMCV C15, which was successfully obtained from the serum of dogs from animal hospitals. Virus production in cell culture was confirmed by EMCV-specific real-time RT-PCR, indirect immunofluorescence assays and electron microscopy. In addition, the open reading frame sequence (ORF) of the EMCV C15 virus was determined. From sequence comparison and phylogenetic analysis among 24 reference EMCV strains, it appears that the EMCV C15 strain is closely genetically related to strain BEL2887A/91 (>99.0% nucleotide identity). In artificially challenged dogs, the heart and brain were important targets of EMCV C15. This study provides genetic and pathogenic characterization of the EMCV C15 strain isolated in Beijing and calls for sustained surveillance of EMCV infection in China to support better prevention and control of the disease.

Establishment of a nanoparticle-assisted RT-PCR assay to distinguish field strains and attenuated strains of porcine epidemic diarrhea virus.

Porcine epidemic diarrhea virus (PEDV) can cause serious disease and even death in neonatal piglets, resulting in serious damage to the swine industry worldwide. Open reading frame 3 (ORF3) is the only accessory gene in the PEDV genome. Previous studies have indicated that PEDV vaccine strains have a partial deletion in ORF3. In this study, a nanoparticle-assisted polymerase chain reaction (nanoparticle-assisted RT-PCR) assay targeting the ORF3 of PEDV was developed to distinguish PEDV field strains from attenuated strains by using a specific pair of primers. The PCR products of field strains and attenuated strains were 264 bp and 215 bp in length, respectively. The sensitivity and specificity of this assay were also assessed. The nanoparticle-assisted RT-PCR assay was 10-100 times more sensitive than the conventional RT-PCR assay, with no cross-reactions when amplifying porcine pseudorabies virus (PRV), porcine circovirus type 2 (PCV2), classical swine fever virus (CSFV), porcine parvovirus (PPV), porcine reproductive and respiratory syndrome virus (PRRSV), porcine rotavirus (RV), and porcine transmissible gastroenteritis virus (TGEV). The nanoparticle-assisted RT-PCR assay we describe here can be used to distinguish field strains from vaccine strains of PEDV, and it shows promise for reducing economic loss due to PEDV infection.

Construction of a minigenome rescue system for Newcastle disease virus strain Italien.

Newcastle disease virus (NDV) Italien, a velogenic strain, is an oncolytic virus that is considered to be a potential agent for antitumor viral therapy. We constructed three helper plasmids expressing the NP, P and L genes of NDV Italien based on the eukaryotic expression plasmid pcDNA3.1(+). The minigenome consisting of the 3' leader and 5' trailer regions of NDV Italien flanking a reporter gene encoding firefly luciferase was constructed to examine the efficacy of the three helper plasmids in viral genome replication and transcription. After co-transfection of BSR-T7/5 cells with the three helper plasmids and the minigenome plasmid, replication of minigenome RNA was evaluated by determining luciferase activity. In the minigenome rescue system, expression of the reporter gene was detected. Our results indicate that the three proteins NP, P, and L are correctly expressed and can assemble into a functional ribonucleoprotein complex that effectively directs the transcription of minigenome RNA.

Loop-mediated isothermal amplification for rapid detection and differentiation of wild-type pseudorabies and gene-deleted virus vaccines.

A loop-mediated isothermal amplification (LAMP) assay was developed specifically for detection and differentiation of pseudorabies virus (PRV). One group of primers was designed to detect wild-type strains (i.e., strains with the gE gene) and the other group of primers was designed to detect both PRV gE-vaccine and wild-type strains (i.e., strains with the gG gene and with or without the gE gene). After amplification by Bst enzyme at a constant temperature of 65 degrees C, a laddering of bright products was visible following electrophoresis on a 2% agarose gel. LAMP was 100-1000-fold more sensitive than the standard PCR. The assay was specific in that it did not amplify other porcine viruses including porcine parvovirus, porcine circovirus type 1, porcine circovirus type 2, porcine reproductive and respiratory syndrome virus, classical swine fever virus, swine transmissible gastroenteritis coronavirus, and porcine epidemic diarrhea virus. Because of its sensitivity, specificity, and simplicity, the LAMP assay could be a useful method for early and rapid differentiation of swine vaccinated with PRV gE-deleted vaccine from swine infected with wild virus.

Reproductive failure in wild boars associated to porcine parvovirus infection and in vivo and in vitro characterization of the causal isolate.

Investigations were made to identify the causal agent of an acute outbreak of abortions in a domesticated herd of wild boar. Only porcine parvovirus (PPV) was isolated from samples of organs from the still-born sucklings and mummified aborted fetuses. The isolated virus hemagglutinated erythrocytes of guinea pig, murine, rat, and chicken. Identity of the virus, designated the BQ strain, was confirmed by the production of a specific cytopathic effect on susceptible cells and by the results from ELISA, PCR, immunofluorescence assay, and electron microscopy. PPV BQ strain was adapted to growth in a swine testicular cell line. When inoculated into healthy sows, PPV BQ caused the same reproductive disorder observed in the affected herd.

The epitope of the VP1 protein of porcine parvovirus.

Porcine parvovirus (PPV) is the major causative agent in a syndrome of reproductive failure in swine. Much has been learned about the structure and function of PPV in recent years, but nothing is known about the epitopes of the structural protein VP1, which is an important antigen of PPV. In this study, the monoclonal antibody C4 against VP1 of PPV was prepared and was used to biopan a 12-mer phage peptide library three times. The selected phage clones were identified by ELISA and then sequencing. The amino acid sequences detected by phage display were analyzed, and a mimic immuno-dominant epitope was identified. The epitope of VP1 is located in the N-terminal and contains the role amino acid sequence R-K-R. Immunization of mice indicated that the phage-displayed peptide induces antibodies against PPV. This study shows that peptide mimotopes have potential as alternatives to the complex antigens currently used for diagnosis of PPV infection or for development of vaccines.

A multiplex reverse transcription-nested polymerase chain reaction for detection and differentiation of wild-type and vaccine strains of canine distemper virus.

A multiplex reverse transcription-nested polymerase chain reaction (RT-nPCR) method was developed for the detection and differentiation of wild-type and vaccine strains of canine distemper virus (CDV). A pair of primers (P1 and P4) specific for CDV corresponding to the highly conserved region of the CDV genome were used as a common primer pair in the first-round PCR of the nested PCR. Primers P2 specific for CDV wild-type strains, were used as the forward primer together with the common reverse primer P4 in the second round of nested PCR. Primers P3, P5 specific for CDV wild-type strain or vaccine strain, were used as the forward primer together with the common reverse primer P4+P6 in the second round of nested PCR. A fragment of 177 bp was amplified from vaccine strain genomic RNA, and a fragment of 247 bp from wild-type strain genomic RNA in the RT-nPCR, and two fragments of 247 bp and 177 bp were amplified from the mixed samples of vaccine and wild-type strains. No amplification was achieved for uninfected cells, or cells infected with Newcastle disease virus (NDV), canine parvovirus (CPV), canine coronavirus (CCV), rabies virus (RV), or canine adenovirus (CAV). The RT-nPCR method was used to detect 30 field samples suspected of canine distemper from Heilongjiang and Jilin Provinces, and 51 samples in Shandong province. As a result of 30 samples, were found to be wild-type-like, and 5 to be vaccine-strain-like. The RT-nPCR method can be used to effectively detect and differentiate wild-type CDV-infected dogs from dogs vaccinated with CDV vaccine, and thus can be used in clinical detection and epidemiological surveillance.

Isolation and characterization of the first Chinese strain of porcine Teschovirus-8.

Investigations were carried out to identify the causal agent of acute diarrhea, respiratory distress, and death of pigs on a swine farm in Jilin Province, northern China. Only porcine Teschovirus (PTV, designated as PTV-8 Jilin/2003) was isolated from samples of organs. The presence of PTV was confirmed by the production of a specific cytopathic effect on susceptible cells and by the results of the immunoperoxidase monolayer assay (IPMA), polymerase chain reaction, and electron microscopy. Other pathogenic agents causing diarrhea, respiratory distress, and death (including porcine rotavirus, transmissible gastroenteritis virus of swine, porcine epidemic diarrhea virus, classical swine fever virus, pseudorabies virus, porcine circovirus, porcine reproductive and respiratory syndrome virus, Japanese encephalitis virus, Mycoplasma, Leptospira, Streptococcus, Listeria, and Brucella species) were excluded as possible causal agents because they were not associated consistently with the disease of the pigs. PTV-8 Jilin/2003 was adapted to grow in swine primary kidney (PK-15) cells and in a swine testicular cell line (ST cells). When inoculated into healthy pigs, PTV-8 Jilin/2003 caused the same symptoms as those observed in the affected herd. It is concluded that PTV-8 Jilin/2003 was the causal agent of this disease.

Development and validation of an immunogold chromatographic test for on-farm detection of PRRSV.

An immunochromatographic test strip was developed to detect porcine reproductive and respiratory syndrome virus (PRRSV). The test uses two gold-labeled monoclonal antibodies: D5 against recombinant nucleocapsid protein (rN) and E9 against recombinant M protein (rM). In the test, PRRSV binds to a mixture of D5 and E9 labeled with colloidal gold; the complexes move through a membrane and are captured by rabbit anti-rM and anti-rN antibodies at a test line, producing a reddish-purple band because of the increased concentration of gold. Unbound monoclonal antibodies move past the test line to be captured by goat anti-mouse antibodies, producing a band at a control line. In samples without PRRSV or with low virus concentration, a band appears only at the control line. A crossover-trial demonstrated that the test strip was highly specific for PRRSV. The test strip detection limit was between 7.8x10(3) and 1.6x10(4) TCID(50)/ml. Analysis of 100 clinical samples indicated that the sensitivity, specificity, and accuracy of the immunochromatographic test strip relative to reverse transcription polymerase chain reaction (RT-PCR) were 97.0, 93.9, and 96.0%, respectively. Because the test is simple and rapid, it can be used by an unskilled person to detect PRRSV in the field.

Real-time PCR to detect and analyze virulent PPV loads in artificially challenged sows and their fetuses.

To establish a real-time polymerase chain reaction with SYBR Green for detection and quantification of porcine parvovirus (PPV) in porcine tissues, two primers specific for the non-structural protein 1 gene were designed. The detection limit of this assay was 3-23 gene copies/reaction, equivalent to 0.001 TCID(50)/ml. The assay was linear over a 10(6) dilution range of template concentrations. Other porcine pathogens involved in reproductive disorders (porcine circovirus 2, porcine reproductive and respiratory virus, pseudorabies virus, classical swine fever virus) were negative by this assay. This assay could detect PPV titres at least 10(5) smaller than the hemagglutination assay. To better understand the pathogenesis of PPV, the levels of viral DNA in various tissues of artificially challenged sows and their fetuses were quantified with this method. The virus was found mainly in the heart, lung, spleen, kidney, and endometrium of sows, and mainly in the heart, spleen, lung, and testis of fetuses. This study provides a new tool for the study of PPV infection and distribution in sows and their fetuses.

Expression, purification, and characterization of recombinant NS-1, the porcine parvovirus non-structural protein.

The non-structural protein NS-1 of porcine parvovirus (PPV) could be a useful antigen for differentiating pigs infected with PPV from those vaccinated with inactivated whole virus. NS-1 was expressed in Escherichia coli using the pET-32a (+) vector. The fusion protein, which was expressed at a high level, was similar antigenically to the native NS-1 protein as determined by Western blot assay using polyclonal antibodies from pigs vaccinated with alive PPV vaccine. A simple procedure was used to purify the fusion protein. This research lays the foundation for using the NS-1 protein for clinical diagnosis of pigs infected with PPV vs. those vaccinated with inactivated whole virus vaccine.

Detection of porcine parvovirus by loop-mediated isothermal amplification.

Loop-mediated isothermal amplification is a novel method for rapid amplification of DNA. It has been adopted widely for the detection of virus because of its simplicity, rapidity, and specificity. A loop-mediated isothermal amplification assay was developed for the detection of porcine parvovirus. Four primers specific for six regions of PPV non-structural protein 1 gene were designed with an online software. After amplifying at a constant temperature of 59-65 degrees C by Bst enzyme, a clear result was visible after 2.5% agarose gel electrophoresis. The sensitivity and specificity of this assay were evaluated by comparison with the polymerase chain reaction. The detection limit of the assay was shown to be equivalent to 5 PPV copies/reaction. Due to its specificity and simplicity, the assay should be a useful diagnostic tool for epidemiologic studies of PPV.

Detection of Newcastle disease virus using nucleic acid sequence-based amplification.

Newcastle disease (ND) is a contagious and widespread avian disease affecting most species of birds. ND virus (NDV) is the only member of the avian paramyxovirus serotype 1 (APMV1) causing ND outbreak in bird flocks. The technique of nucleic acid sequence-based amplification (NASBA) is a potential method to rapidly and reliably detect NDV isolates. Here, we describe an effective and unprecedented method for detecting NDV strains of all pathotypes. A conserved region of the fusion protein gene was used for designing oligonucleotides specific to all NDV pathotypes. The dynamic range of this NDV NASBA detection method is comparable to virus culture and therefore the NDV NASBA method is a potential alternative for NDV screening and surveillance.

Preparation and evaluation of anti-SARS coronavirus IgY from yolks of immunized SPF chickens.

Severe acute respiratory syndrome (SARS) is a recently discovered viral disease, characterized by fever, cough, acute fibrinous pneumonia and high infectivity. Specific pathogen-free (SPF) chickens were immunized with inactivated SARS coronavirus and their eggs were harvested at regular intervals. Yolk immunoglobulin (IgY) was extracted using the water dilution method, followed by further purification on a Sephadex G-75 column. SDS-polyacrylamide gel electrophoresis (SDS-PAGE), Western blot and neutralization test results showed that the IgY obtained was of a high purity and had a strong reactive activity with a neutralization titer of 1:640. Lyophilization and stability tests showed that lyophilized anti-SARS coronavirus IgY had promising physical properties, with no significant reduction in reactive activity and good thermal stability. All these data suggest that the anti-SARS coronavirus IgY could be a new useful biological product for specific antiviral therapy against SARS.

[Effect of Cilazapril on endothelial cell function and fibrinolysis system in the canine atrial fibrillation models].

OBJECTIVE: To investigate the effect of cilazapril on endothelial cell function and fibrinolysis system in the canine atrial fibrillation (AF) models. METHODS: All canines were divided into three groups: (1) Control group, without atrial pacing; (2) Atrial pacing group, in which atrial fibrillation was established by rapid atrial pacing at 400 bpm for 6 weeks; (3) Atrial pacing together with cilazapril group, in which cilazapril was given before and after atrial pacing. Nitric oxide (NO) of atrial endocardium was measured with NO-specific microelectrode. The expression of plasminogen activator inhibitor-1 (PAI-1) and tissue-type plasminogen activator (tPA) protein in atrium was determined by Western Blot analysis and immunohistochemical staining. Plasma levels of von Willebrand Factor (vWF), PAI-1 and tPA were analyzed by enzyme-linked immunoadsorbent assay. RESULTS: NO production from atrial endocardium was significantly increased in atrial pacing together with cilazapril group than atrial pacing group [(42.6 +/- 9.9) nmol/L vs (23.4 +/- 5.8) nmol/L, P < 0.05], whereas the plasma levels of vWF were decreased [(75.4 +/- 12.8)% vs (125.9 +/- 20.6)%, P < 0.05]. Compared to controls, the expression of atrium tPA protein in atrial pacing together with cilazapril group was significantly upregulated (4052 +/- 857 vs 1936 +/- 421, P < 0.05) and PAI-1 protein was downregulated (2487 +/- 542 vs 3164 +/- 827, P < 0.05). Cilazapril also significantly increased tPA antigen and decreased PAI-1 antigen in plasma. CONCLUSION: Cilazapril can favorably improve endothelial function and resume the balance of fibrinolysis system in AF, which might be of beneficial to hypercoagulated state in AF.