TaqMan real-time reverse transcription-PCR assay for universal detection and quantification of avian hepatitis E virus from clinical samples in the presence of a heterologous internal control RNA

Duplex Droplet Digital PCR Assay for Quantification of Hepatitis E Virus in Food

Hepatitis E virus (HEV) represents an emerging risk in industrialized countries where the consumption of contaminated food plays a pivotal role. Quantitative real-time RT-PCR (RT-qPCR) is one of the most suitable methods for the detection and quantification of viruses in food. Nevertheless, quantification using RT-qPCR has limitations. Droplet digital PCR (ddPCR) provides the precise quantification of nucleic acids without the need for a standard curve and a reduction in the effect on virus quantification due to the presence of inhibitors. The objectives of the present work were (i) to develop a method for the absolute quantification of HEV in swine tissues based on ddPCR technology and provide internal process control for recovery assessment and (ii) to evaluate the performance of the method by analyzing a selection of naturally contaminated wild boar muscle samples previously tested using RT-qPCR. The method was optimized using a set of in vitro synthesized HEV RNA and quantified dsDNA. The limit of detection of the developed ddPCR assay was 0.34 genome copies/µL. The analysis of the wild boar samples confirmed the validity of the ddPCR assay. The duplex ddPCR method showed no reduction in efficiency compared to individual assays. The method developed in the present study could represent a sensitive assay for the detection and absolute quantification of HEV RNA in food samples with the advantage of presenting the co-amplification of internal process control.

FAdV-4 Promotes Expression of Multiple Cytokines and Inhibits the Proliferation of aHEV in LMH Cells

Single or mixed infections of multiple pathogens such as avian hepatitis E virus (aHEV) and avian leukosis virus subgroup J (ALV-J) have been detected in numerous laying hens with severe liver injury in China. Thus, aHEV and immunosuppressive viruses are speculated to cause co-infections. In this study, co-infection with aHEV and fowl adenovirus (FAdV) was confirmed by nested RT-PCR and recombinase-aided amplification combined with gene sequencing in two flocks with severe liver injury. Subsequently, the two reference strains, aHEV and FAdV-4, were inoculated into LMH cells to identify their co-infection potential. Confocal microscopy revealed aHEV and FAdV-4 co-infected LMH cells. In addition, the replication dynamics of aHEV and FAdV-4 along with the expression levels of immuno-cytokines were measured. The results indicated colocalization of aHEV and FAdV-4 and inhibition of viral replication in LMH cells. The transcription levels of MDA5, Mx, OASL, and IFN-α were significantly upregulated in LMH cells, whereas those of immune-related factors induced by FAdV-4 were downregulated upon FAdV-4 and aHEV co-infection. These results confirmed the co-infection of aHEV and FAdV-4 in vitro and prompted the antagonistic pathogenic effects of FAdV-4 and aHEV, thereby providing novel insights into the counterbalancing effects of these viruses.

Establishment of a Novel Detection Platform for Clostridioides difficile Toxin Genes Based on Orthogonal CRISPR

Clostridioides difficile is one of the leading pathogens causing nosocomial infection. The infection can range from mild to severe, and rapid identification is pivotal for early clinical diagnosis and appropriate treatment. Here, a genetic testing platform for toxins, referred to as OC-MAB (orthogonal CRISPR system combined with multiple recombinase polymerase amplification [RPA]), was developed to detect the C. difficile toxin genes tcdA and tcdB. While recognizing the amplified products of the tcdA gene and the tcdB gene, Cas13a and Cas12a could activate their cleavage activities to cut labeled RNA and DNA probes, respectively. The cleaved products were subsequently identified by dual-channel fluorescence using a quantitative PCR (qPCR) instrument. Finally, they could also be combined with labeled antibodies on immunochromatographic test strips to achieve visual detection. The OC-MAB platform exhibited ultrahigh sensitivity in detecting the tcdA and tcdB genes at levels of as low as 102 to 101 copies/mL. When testing 72 clinical stool samples, the sensitivity (95% confidence interval [CI], 0.90, 1) and specificity (95% CI, 0.84, 1) of the single-tube method based on the fluorescence readout was 100%, with a positive predictive value (PPA) value of 100% (95% CI, 0.90, 1) and a negative predictive value (NPA) value of 100% (95% CI, 0.84, 1), compared to the results of qPCR. Likewise, the sensitivity of the 2-step method based on the test strip readout was 100% (95% CI, 0.90, 1), while the specificity was 96.3% (95% CI, 0.79, 0.99), with a PPA of 98% (95% CI, 0.87, 0.99) and an NPA of 100% (95% CI, 0.90, 1). In short, orthogonal CRISPR technology is a promising tool for the detection of C. difficile toxin genes. IMPORTANCE C. difficile is currently the primary causative agent of hospital-acquired antibiotic-induced diarrhea, and timely and accurate diagnosis is crucial for hospital-acquired infection control and epidemiological investigation. Here, a new method for the identification of C. difficile was developed based on the recently popular CRISPR technology, and an orthogonal CRISPR dual system was utilized for the simultaneous detection of toxin genes A and B. It also uses a currently rare CRISPR dual-target lateral flow strip with powerful color-changing capabilities, which is appropriate for point-of-care testing (POCT).

An Explorative Study of the Causal Pathogenesis of Green Liver Discoloration in Organically Reared Female Bronze Turkeys (Meleagris gallopavo) Considering the Infectious Risk Factors

A recent study revealed that organically raised Bronze turkeys showed a high prevalence of green liver discoloration. This alteration is commonly associated with the Turkey Osteomyelitis Complex and potentially caused by opportunistic bacteria. Therefore, 360 organically fattened Bronze turkeys were examined post-mortem throughout two fattening trials with two examinations each to determine possible infectious risk factors and reduce disease prevalence. Clinical and pathoanatomical examinations were performed on every hen. Histopathological, bacteriological, parasitological, and virological examinations were performed on at least six hens without and, if applicable, six hens with green livers on each examination date. Overall, 9.0% of all hens had a green liver without a correlation with bacterial or parasitological findings but multiple health impairments. The discoloration correlated significantly with the detection of immunosuppressive turkey hemorrhagic enteritis virus at the early stage and macro- and histological joint/bone lesions at the late fattening stage, indicating the presence of two different predisposing pathogeneses. Flocks not being vaccinated against hemorrhagic enteritis but having a virus-positive sample showed the highest prevalence of green liver discoloration and developed worse in various parameters. In conclusion, an adequate vaccination schedule and the prevention of field infections may lead to a decreased risk of performance reduction and improved animal health.

A novel genotype of avian hepatitis E virus identified in chickens and common pheasants (Phasianus colchicus), extending its host range

In 2019, outbreaks of hepatitis-splenomegaly syndrome (HSS) were observed in six commercial layer chicken flocks, belonging to three different Polish farms, and characterized by increased mortality, hemorrhagic hepatitis with attached blood clots on the liver surface, and splenomegaly. Diseased flocks were initially investigated for the presence of avian hepatitis E virus (aHEV) - the etiological agent of HSS - by conventional reverse transcriptase polymerase chain reaction, which revealed aHEV sequences clustering separately from all known aHEV genotypes. Additionally, an aHEV genome was identified for the first time in common pheasants, from a flock in France, using Next Generation Sequencing. This genome clustered together with the Polish aHEVs here investigated. Complete genome aHEV sequences from the HSS outbreaks confirmed the divergent cluster, with a shared nucleotide sequence identity of 79.6-83.2% with other aHEVs, which we propose to comprise a novel aHEV genotype - genotype 7. Histology and immunohistochemistry investigations in the liver and spleen established an association between aHEV and the observed lesions in the affected birds, consolidating the knowledge on the pathogenesis of aHEV, which is still largely unknown. Thus, the present investigation extends the natural host range and genotypes of aHEV and strengthens knowledge on the pathogenesis of HSS.

Cell Division Control Protein 42 Interacts With Hepatitis E Virus Capsid Protein and Participates in Hepatitis E Virus Infection

Hepatitis E Virus (HEV) causes viral hepatitis in humans worldwide, while a subset of HEV species, avian HEV, causes hepatitis-splenomegaly syndrome in chickens. To date, there are few reports on the host proteins interacting with HEV and being involved in viral infection. Previous pull-down assay combining mass spectrometry indicated that cell division control protein 42 (CDC42), a member belonging to the Rho GTPase family, was pulled down by avian HEV capsid protein. We confirmed the direct interaction between CDC42 and avian and mammalian HEV capsid proteins. The interaction can increase the amount of active guanosine triphosphate binding CDC42 state (GTP-CDC42). Subsequently, we determined that the expression and activity of CDC42 were positively correlated with HEV infection in the host cells. Using the different inhibitors of CDC42 downstream signaling pathways, we found that CDC42-MRCK (a CDC42-binding kinase)-non-myosin IIA (NMIIA) pathway is involved in naked avian and mammalian HEV infection, CDC42-associated p21-activated kinase 1 (PAK1)-NMIIA/Cofilin pathway is involved in quasi-enveloped mammalian HEV infection and CDC42-neural Wiskott-Aldrich syndrome protein-actin-polymerizing protein Arp2/3 pathway (CDC42-(N-)WASP-Arp2/3) pathway participates in naked and quasi-enveloped mammalian HEV infection. Collectively, these results demonstrated for the first time that HEV capsid protein can directly bind to CDC42, and non- and quasi-enveloped HEV use different CDC42 downstream signaling pathways to participate in viral infection. The study provided some new insights to understand the life cycle of HEV in host cells and a new target of drug design for combating HEV infection.

Avian Hepatitis E Virus: With the Trend of Genotypes and Host Expansion

Avian hepatitis E virus (HEV) is a single-stranded, positive-sense RNA virus with a complete genome of approximately 6.6 kb in size. To date, four major genotypes of avian HEV have been identified and classified into the Orthohepevirus B genus of the family Hepeviridae. The avian HEV associated with hepatitis-splenomegaly syndrome, big liver and spleen disease or hepatic rupture hemorrhage syndrome in chickens is genetically and antigenically related to mammalian HEV. With the increased genotypes of avian HEV identified, a broader host tropism is also notable in the epidemiological studies. Due to the lack of an efficient cell culture system, the mechanisms of avian HEV replication and pathogenesis are still poorly understood. The recent identification and characterization of animal strains of avian HEV has demonstrated the virus' ability of cross-species infection. Although it has not yet been detected in humans, the potential threat of a zoonotic HEV capable of transmission to humans needs to be taken into consideration. This review article focuses on the current knowledge regarding avian HEV in virology, epidemiology, pathogenesis, clinical presentation, transmission, diagnosis and prevention.

HIGHLIGHTS

- The mechanisms of avian HEV replication and pathogenesis are still poorly understood due to the lack of an efficient cell culture system.- A broader host tropism is also notable in the epidemiological studies with the increased genotypes of avian HEV identified.- The recent identification and characterization of animal strains of avian HEV has demonstrated the virus' ability of cross-species infection.- The potential threat of a zoonotic HEV capable of transmission to humans needs to be taken into consideration.

Chicken Organic Anion-Transporting Polypeptide 1A2, a Novel Avian Hepatitis E Virus (HEV) ORF2-Interacting Protein, Is Involved in Avian HEV Infection

Avian hepatitis E virus (HEV) is the main causative agent of big liver and spleen disease in chickens. Due to the absence of a highly effective cell culture system, there are few reports about the interaction between avian HEV and host cells. In this study, organic anion-transporting polypeptide 1A2 (OATP1A2) from chicken liver cells was identified to interact with ap237, a truncated avian HEV capsid protein spanning amino acids 313 to 549, by a glutathione S-transferase (GST) pulldown assay. GST pulldown and indirect enzyme-linked immunosorbent assays (ELISAs) further confirmed that the extracellular domain of OATP1A2 directly binds with ap237. The expression levels of OATP1A2 in host cells are positively correlated with the amounts of ap237 attachment and virus infection. The distribution of OATP1A2 in different tissues is consistent with avian HEV infection in vivo Finally, when the functions of OATP1A2 in cells are inhibited by its substrates or an inhibitor or blocked by ap237 or anti-OATP1A2 sera, attachment to and infection of host cells by avian HEV are significantly reduced. Collectively, these results displayed for the first time that OATP1A2 interacts with the avian HEV capsid protein and can influence viral infection in host cells. The present study provides new insight to understand the process of avian HEV infection of host cells.IMPORTANCE The process of viral infection is centered around the interaction between the virus and host cells. Due to the lack of a highly effective cell culture system in vitro, there is little understanding about the interaction between avian HEV and its host cells. In this study, a total of seven host proteins were screened in chicken liver cells by a truncated avian HEV capsid protein (ap237) in which the host protein OATP1A2 interacted with ap237. Overexpression of OATP1A2 in the cells can promote ap237 adsorption as well as avian HEV adsorption and infection of the cells. When the function of OATP1A2 in cells was inhibited by substrates or inhibitors, attachment and infection by avian HEV significantly decreased. The distribution of OATP1A2 in different chicken tissues corresponded with that in tissues during avian HEV infection. This is the first finding that OATP1A2 is involved in viral infection of host cells.

Detection and quantification of hepatitis E virus in the absence of IgG and IgM anti-HEV in HIV-positive patients

AIMS

To improve RT-qPCR with an internal control and a synthetic standard curve to detect HEV in HIV co-infected patients.

METHODS AND RESULTS

A single-stranded RNA (ssRNA) and a double-stranded DNA (dsDNA) synthetic curve were designed, compared to the international reference panel for HEV genotypes, and tested to quantify and detect a reference panel for HEV genotypes. The detection limit of the RNA synthetic curve (50 copies per ml) was better than the DNA synthetic curve (100 copies per ml) and the WHO standard curve (250 copies per ml). Then, 280 serum samples from HIV-positive patients were tested for HEV RNA, which was detected in 3·6% of serum samples. The viral load ranged from 2 × 10² copies per ml to 4·78 × 10⁸ copies per ml. HEV IgM/IgG antibodies were not detected in the RNA-positive patients. Sequencing analysis of HEV showed that the virus belongs to genotype 3 (HEV GT3).

CONCLUSIONS

Real-time PCR was a useful tool to estimate co-infection with HEV/HIV, even in patients with low viral loads and undetectable anti-HEV IgG and IgM antibodies.

SIGNIFICANCE AND IMPACT OF THE STUDY

Hepatitis E virus genotype 3 (HEV GT3) has been associated with silent chronic hepatitis and cirrhosis in HIV-positive subjects worldwide, but there is a lack of data on this co-infection in Brazil.

3D printing and milling a real-time PCR device for infectious disease diagnostics

Diagnosing infectious diseases using quantitative polymerase chain reaction (qPCR) offers a conclusive result in determining the infection, the strain or type of pathogen, and the level of infection. However, due to the high-cost instrumentation involved and the complexity in maintenance, it is rarely used in the field to make a quick turnaround diagnosis. In order to provide a higher level of accessibility than current qPCR devices, a set of 3D manufacturing methods is explored as a possible option to fabricate a low-cost and portable qPCR device. The key advantage of this approach is the ability to upload the digital format of the design files on the internet for wide distribution so that people at any location can simply download and feed into their 3D printers for quick manufacturing. The material and design are carefully selected to minimize the number of custom parts that depend on advanced manufacturing processes which lower accessibility. The presented 3D manufactured qPCR device is tested with 20-μL samples that contain various concentrations of lentivirus, the same type as HIV. A reverse-transcription step is a part of the device's operation, which takes place prior to the qPCR step to reverse transcribe the target RNA from the lentivirus into complementary DNA (cDNA). This is immediately followed by qPCR which quantifies the target sequence molecules in the sample during the PCR amplification process. The entire process of thermal control and time-coordinated fluorescence reading is automated by closed-loop feedback and a microcontroller. The resulting device is portable and battery-operated, with a size of 12 × 7 × 6 cm3 and mass of only 214 g. By uploading and sharing the design files online, the presented low-cost qPCR device may provide easier access to a robust diagnosis protocol for various infectious diseases, such as HIV and malaria.

Evaluation of recombinant Chinese avian hepatitis E virus (CaHEV) ORF2 and ORF3 proteins for protection of chickens against CaHEV infection

Avian hepatitis E virus (HEV) is the etiologic agent of big liver and spleen disease in chickens. In 2010, the Chinese avian HEV (CaHEV) strain was isolated from chickens and demonstrated to cause the decreased egg production in layer hens. No avian HEV commercial vaccine has yet been developed to prevent virus infection in China. In this study, recombinant CaHEV truncated ORF2 and complete ORF3 proteins were evaluated separately for immunoprotection of chickens against CaHEV infection. First, truncated ORF2 and complete ORF3 proteins were expressed in Escherichia coli. Next, 48 specific-pathogen-free chickens were randomly divided into three groups. One group was immunized with truncated ORF2 protein, the second group was immunized with recombinant ORF3 protein, while the third group (control) was mock-immunized with PBS. After booster immunization, chickens in all three groups were challenged intravenously with CaHEV infectious stock and assessed for viremia, fecal virus shedding, seroconversion, and gross hepatic lesions. In the ORF2 protein-immunized group, no chickens showed evidence of avian HEV infection. In the ORF3 protein-immunized group, nine chickens exhibited viremia and seven had fecal virus shedding. In the control group, all 16 chickens showed viremia and fecal virus shedding. However, the durations in chickens from the ORF3 protein group (2-4weeks) were shorter than the ones from the control group (4-8weeks). Moreover, no gross liver lesions emerged in the ORF2 protein group, while lesions observed in the ORF3 protein group were milder than in controls. Therefore, the ORF2 protein can confer complete immunoprotection against chicken CaHEV infection, while the ORF3 protein only confers partial immunoprotection.

Characterization of Seven Outbreaks of Hemorrhagic Hepatopathy Syndrome in Commercial Pullets Following the Administration of a Salmonella Enteritidis Bacterin in California

Between April 2013 and April 2015, seven flocks belonging to three different major commercial egg producers inCalifornia experienced a mild increase in mortality 2 to 3 wk after administration of Salmonella Enteritidis bacterins. Strains of chickens involved were H&N (flock A1, A2, B2, C1, C2, and C3) and Lohmann white (flock B1). Vaccination was administered individually through injection either in the breast muscles or subcutis in the legs between 11 and 18 wk of age in all flocks. Clinical signs ranged from inapparent to lameness, reluctance to walk, greenish diarrhea, and retching-like symptoms. The mortality ranged from 0.16% to 1.38% per week, with the highest peaks occurring usually 2 to 3 wk postvaccination, and then declined rapidly. Postmortem examinations revealed enlarged livers with disseminated hemorrhages and pale foci of necrosis. Also, severe extensive hemorrhages in the intestine, heart, and proventriculus were observed in a few birds. Various degrees of productive, exudative giant cell granulomatous myositis were observed invading deeply the muscles and subcutis at the site of vaccination. The myositis was always associated with optically empty vacuoles positive for neutral lipids by Oil Red O stain. Droplets of Oil Red O material were also noticed in the affected livers and intestines. Congo red stain highlighted the presence of amyloid in moderate to severe amounts in the breast muscles and moderate amounts in livers, spleens, and intestines. Salmonella antigens were detected in the injection sites and livers by immunohistochemical staining. No viruses or toxic substances were recovered from the liver, spleen, intestine, and pectoral muscles, and the few bacteria isolated were interpreted as secondary postmortem invaders. In addition, livers and bile tested for hepatitis E virus were negative by reverse-transcriptase polymerase chain reaction.

Evidence of genotypes 1 and 3 of avian hepatitis E virus in wild birds

Although the presence of four genotypes of avian hepatitis E virus (HEV) in chickens has been demonstrated, its natural host range is still barely known. In this study, swab samples from 626 wild birds originating from 62 bird species were investigated for HEV detection by molecular methods. The aim was to explore the cross-species infection of avian HEV and to compare the genetic diversity between strains infecting chicken and wild birds. In total, 8 positive samples from 4 different bird species (song thrush, little owl, feral pigeon and common buzzard) were identified and further confirmed by partial sequencing of ORF3. Based on a 237bp fragment of the capsid gene retrieved from 5 samples, phylogenetic analysis revealed the presence of avian HEV genotypes 1 and 3 in wild birds. The wild bird isolates shared 82.7-84.8% and 85.7-100% nucleotide sequence identity, respectively, to chicken isolates from the corresponding genotype. For two of the genotype 1 samples (14-2901 and 14-2906), from feral pigeons, genotype assignment could be also confirmed by phylogenetic analysis based on partial nucleotide sequence of the helicase gene. For the first time, the appearance of genotype 1 in Europe was detected, which together with close genetic relationship between HEVs present in chickens and wild birds indicates cross-species transmission.

Subclinical avian hepatitis E virus infection in layer flocks in the United States

The objective of this study was to determine patterns of avian HEV infection in naturally infected chicken farms. A total of 310 serum samples and 62 pooled fecal samples were collected from 62 chicken flocks on seven commercial in-line egg farms in the Midwestern United States and tested for avian HEV circulation. Serum samples were tested for the presence of anti-avian HEV IgY antibodies by a fluorescent microbead immunoassay (FMIA) which was developed for this study. The FMIA was validated using archived samples of chickens with known exposure (n = 96) and compared to the results obtained with an enzyme-linked immunosorbent assay (ELISA) based on the same capture antigen. There was an overall substantial agreement between the two assays (κ = 0.63) with earlier detection of positive chickens by the FMIA (P = 0.04). On the seven farms investigated, the overall prevalence of anti-avian HEV IgY antibodies in serum samples from commercial chickens was 44.8% (20-82% per farm). Fecal samples were tested for avian HEV RNA by a nested reverse-transcriptase PCR. The overall detection rate of avian HEV RNA in fecal samples was 62.9% (0-100% per farm). Sequencing analyses of partial helicase and capsid genes showed that different avian HEV genotype 2 strains were circulating within a farm. However, no correlation was found between avian HEV RNA detection and egg production, egg weight or mortality. In conclusion, avian HEV infection is widespread among clinically healthy laying hens in the United States.

Development and evaluation of a SYBR Green real-time RT-PCR assay for detection of avian hepatitis E virus

BACKGROUND

Avian hepatitis E virus (HEV) is the main causative agent of big liver and spleen disease, as well as hepatitis-splenomegaly syndrome in chickens. To date, conventional reverse transcriptase polymerase chain reaction (RT-PCR) and nested RT-PCR methods have been used for the diagnosis of avian HEV infection in chickens. However, these assays are time consuming, inconvenient, and cannot detect the virus quantitatively. In this study, a rapid and sensitive SYBR Green real-time RT-PCR assay was developed to detect avian HEV RNA quantitatively in serum, liver, spleen, and fecal samples from chickens.

RESULTS

Based on the sequence of the most conserved HEV gene, ORF3, the primers for the assay were designed, and the standard plasmid was constructed. The detection limit of the assay was shown to be 10 copies/μl of standard plasmid/reaction, with a corresponding cycle-threshold value of 29.3. The standard curve exhibited a dynamic linear range across at least 7 log units of DNA copy number. The specificity and reproducibility of this assay was high, showing that the assay detected avian HEV RNA specifically and with little variability. Compared to conventional RT-PCR, the current assay is more sensitive for detecting avian HEV in serum, liver, spleen, and fecal samples from chickens.

CONCLUSIONS

A rapid, specific, and reproducible SYBR Green real-time RT-PCR assay was developed for the diagnosis of avian HEV infection in chickens. This assay can accurately detect avian HEV RNA in serum, liver, spleen, and fecal samples with more sensitivity than conventional RT-PCR.

Characterization of Two Novel Linear B-Cell Epitopes in the Capsid Protein of Avian Hepatitis E Virus (HEV) That Are Common to Avian, Swine, and Human HEVs

Antisera raised against the avian hepatitis E virus (HEV) capsid protein are cross-reactive with human and swine HEV capsid proteins. In this study, two monoclonal antibodies (MAbs) against the avian HEV capsid protein, namely, 3E8 and 1B5, were shown to cross-react with the swine HEV capsid protein. The motifs involved in binding both MAbs were identified and characterized using phage display biopanning, peptide synthesis, and truncated or mutated protein expression, along with indirect enzyme-linked immunosorbent assay (ELISA) and Western blotting. The results showed that the I/VPHD motif is a necessary core sequence and that P and H are two key amino acids for recognition by MAb 3E8. The VKLYM/TS motif is the minimal amino acid sequence necessary for recognition by MAb 1B5. Cross-reactivity between the two epitopes and antibodies against avian, swine, and human HEVs in sera showed that both epitopes are common to avian, swine, and human HEVs. In addition, amino acid sequence alignment of the capsid proteins revealed that the key motifs of both novel epitopes are the same in HEVs from different animal species, predicting that they may be common to HEV isolates from boars, rabbits, rats, ferrets, mongooses, deer, and camels as well. Protein modeling analysis showed that both epitopes are at least partially exposed on the surface of the HEV capsid protein. Protective capacity analysis demonstrated that the two epitopes are nonprotective against avian HEV infection in chickens. Collectively, these studies characterize two novel linear B-cell epitopes common to avian, swine, and human HEVs, which furthers the understanding of HEV capsid protein antigenic structure.

IMPORTANCE

More and more evidence indicates that the host range diversity of hepatitis E virus (HEV) is a global public health concern. A better understanding of the antigenic structure of the HEV capsid protein may improve disease diagnosis and prevention. In this study, binding site mapping and localization as well as the antigenic biology of two novel linear B-cell epitopes common to several different species of HEV were characterized. These findings partially reveal the antigenic structure of the HEV capsid protein and provide potential applications for the development of diagnostics and interventions for HEV infection.

A duplex real-time PCR assay for the detection and quantification of avian reovirus and Mycoplasma synoviae

BACKGROUND

Infectious arthritis in broilers represents an economic and health problem, resulting in severe losses due to retarded growth and downgrading at the slaughterhouse. The most common agents associated with cases of infectious arthritis in poultry are avian reovirus (ARV) and Mycoplasma synoviae (MS). The accurate differentiation and rapid diagnosis of ARV and MS are essential prerequisites for the effective control and prevention of these avian pathogens in poultry flocks. This study thus aimed to develop and validate a duplex real-time PCR assay for the simultaneous detection and quantification of ARV and MS.

METHODS

Specific primers and probes for each pathogen were designed to target the special sequence of the ARV σC gene or the MS phase-variable surface lipoprotein hemagglutinin (vlhA) gene. A duplex real-time PCR assay was developed, and the reaction conditions were optimized for the rapid detection and quantification of ARV and MS.

RESULTS

The duplex real-time PCR assay was capable of ARV- and MS-specific detection without cross-reaction with other non-targeted avian pathogens. The sensitivity of this assay was 2 × 10(1) copies for a recombinant plasmid containing ARV σC or MS vlhA gene, and 100 times higher than that of conventional PCR. This newly developed PCR assay was also reproducible and stable. All tested field samples of ARV and/or MS were detectable with this duplex real-time PCR assay compared with pathogen isolation and identification as well as serological tests.

CONCLUSION

This duplex real-time PCR assay is highly specific, sensitive and reproducible and thus could provide a rapid, specific and sensitive diagnostic tool for the simultaneous detection of ARV and MS in poultry flocks. The assay will be useful not only for clinical diagnostics and disease surveillance but also for the efficient control and prevention of ARV and MS infections.

A one-step duplex rRT-PCR assay for the simultaneous detection of grass carp reovirus genotypes I and II

Hemorrhagic disease of grass carp, caused by grass carp reovirus (GCRV), leads to severe economic losses in the grass carp farming industry in China. GCRV has been divided into three genotypes based on genome sequence. Genotypes I and II (GCRV-1 and GCRV-II, respectively) are the dominant genotypes and co-infections of GCRV-I and GCRV-II are common in grass carp aquaculture. A one-step duplex real-time reverse transcriptase polymerase chain reaction (rRT-PCR) assay was developed for simultaneous detection of GCRV-I and GCRV-II. The PCR assay is suitable for early diagnosis of grass carp hemorrhagic disease and for epidemiological surveillance. The detection limit of the assay is 10 copies for both GCRV-I and GCRV-II, which is as high as single-target rRT-PCR and higher than conventional RT-PCR. No cross reactivity with other GCRV subtypes or other viruses was observed. One hundred and twelve samples from grass carp suspected of hemorrhagic disease were collected from South and Central China. Eleven samples were positive for GCRV-I by RT-PCR alone, and fourteen samples were positive by single-target and duplex rRT-PCR. Forty two samples were positive for GCRV-II by RT-PCR alone and forty seven samples were positive by single-target and duplex rRT-PCR. Mixed infections were found in eight samples when analyzed by RT-PCR alone and in ten samples analyzed by single-target and duplex rRT-PCR. The duplex rRT-PCR system provides a sensitive and specific method to detect and differentiate between GCRV-I and GCRV-II in a single sample. This rRT-PCR assay could be a useful tool for the routine diagnosis of these two viruses and for epidemiology studies in grass carp aquaculture.

Free circulating nucleic acids in plasma and serum as a novel approach to the use of internal controls in real time PCR based detection

Internal controls (ICs), are the main components of any real-time PCR based amplification methods, which are co-purified and co-amplified with the actual target. The existence of free circulating nucleic acids in plasma and serum (CNAPS) has been known for many years. The aim of this study was to verify whether CNAPS can be used as ICs in real-time PCR based detection and quantification of DNA or RNA targets in plasma and serum samples. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) as a housekeeping gene, was chosen at random as CNAPS to serve as an intrinsic internal control in two different real-time PCR based quantification models in plasma and serum. Viral loads of hepatitis B virus (HBV) DNA and hepatitis delta virus (HDV) RNA were quantified as actual targets in parallel to GAPDH as IC in a total of 519 serum or plasma samples including 21 healthy controls, 202 positive chronic hepatitis delta patients, 37 chronic hepatitis C patients, 168 chronic hepatitis B patients, 52 patients with hepatocellular carcinoma, and 39 patients with non-alcoholic steatohepatitis/non-alcoholic fatty liver disease. GAPDH levels did not show significant variance in different patient groups and yielded positive signals in all 519 patients with persistent cycle threshold (CT) values 27.85±1.57 (mean±standard deviation (SD)). Reproducibility of the GAPDH amplification in HDV RNA and HBV DNA quantifications was shown with a SD value of CT ranging from 0.42 to 2.14 (mean SD; 1.18) and 0.24 to 1.75 (mean SD; 1.03), respectively. In conclusion, the freely circulating nucleic acids can clearly be used as internal controls for real-time PCR based detection and quantification of any RNA and mainly DNA targets (pathogens) in serum or plasma and this simply excludes the compulsory external addition of any IC molecules into the reaction.

Duplex RT-qPCR for the detection of hepatitis E virus in water, using a process control

Human hepatitis E virus (HEV) causes acute hepatitis in humans, predominantly by contamination of food and water. HEV, in particular genotype III, is currently considered to be an emerging pathogen in industrialized countries. Because of the low infectious dose, an efficient and rapid virus concentration method is required to detect low amounts of HEV in food and water samples for routine control. Because of the absence of a reliable cell culture method for the main enteric viruses most involved in the outbreaks, reverse transcription quantitative real time PCR (RT-qPCR) is now widely used for the detection of RNA viruses in food and water samples. One of the general requirements for viral diagnosis concerns the use of a process control to monitor the efficiency of the concentration of viral particles, the extraction of nucleic acid and the presence of the potential inhibitors of the RT-qPCR reaction. The aim of this study was to provide a rapid and sensitive method for detecting HEV in water. The method is based on viral concentration by filtration on membrane filters and direct lysis of adsorbed viruses from filters before RNA extraction and RT-qPCR amplification. We developed a one-step duplex RT-qPCR for detecting HEV and the murine norovirus (MNV-1) was used as a process control. The data show that MNV-1 offers a very reliable and simple way of monitoring false-negative results and is a valuable tool in the routine diagnostic laboratory. The limit of detection (LOD) was in the range of 700 to 3500 HEV genome copies/0.5L bottled water and 3500 HEV genome copies/0.5L tap water.