Development of a polymerase chain reaction to detect Vietnamese isolates of duck virus enteritis

Genomic characteristics, pathogenicity and viral shedding of a novel DVEV variant derived from goose

Duck virus enteritis (DVE), caused by the DVE virus (DVEV), is an acute, septicemic, and contagious disease affecting ducks of different breeds, ages, and sexes. In late spring and summer 2019, several outbreaks of DVE were reported in areas with large waterfowl industries in central and southern China. A goose farm located in Jining County, Shandong Province, was impacted by an acute DVE outbreak in July 2019. The causative DVEV field strain (Goose/DVEV/SDJN/China/2019) was subsequently isolated from the liver specimens collected from acute cases of dead geese, which showed severe hemorrhagic lesions on the esophageal mucosal membranes of specimens collected from all the postmortem cases. Comparison of the genome sequence of this newly isolated field strain (Goose/DVEV/SDJN/China/2019) with the common DVEV strains revealed insertions or mutations in the gB and gC genes, which possibly caused the observed high morbidity and mortality in this acute outbreak. We conducted a trial among geese to evaluate the pathogenicity of this strain. Healthy experimental goslings aged 15 d old were inoculated with 10^-5.53 ELD₅₀/0.2 mL doses orally or through intramuscular injection. Clinical signs and esophageal erosion appeared in infected geese. Necropsy revealed hemorrhage and necrosis of the cloacal mucosa and liver. Detection of the virus using real-time PCR in the liver, brain, and spleen indicated that they were the hotspots of DVEV infections. One day after the DVEV infection, virus release and seroconvert were observed in infected geese. Thus, our studies demonstrate that DVEV is highly pathogenic and contagious in geese. To the best of our knowledge, this is the first study on the pathogenicity of mutant duck viral enteritis virus in goslings. This study serves as a foundation for further investigations into the pathophysiology of the recently identified variant DVEV strains.

Adaptation and characterization of Anatid herpesvirus 1 in different permissible cell lines

Duck viral enteritis is an acute, contagious infection of Anatidae family members. The disease is caused by Anatid herpesvirus 1 (AnHV-1). The infection of AnHV-1 is controlled by vaccination to the flock with chick embryo adapted attenuated vaccine in developed countries. However, its economic impact in developing countries is substantial and there is a need to understand the cell culture spectrum of the virus to produce its vaccine on a mass scale. In the present study, the permissivity of AnHV-1 for different cells was analyzed. The AnHV-1 showed enhanced replication following its serial passage in CEF, DF-1, Vero, MDCK, and QT-35 cells. The characteristic cytopathic effect (CPE) of rounding and clumping of cells were observed in CEF, DF-1, Vero, and QT-35 cell lines. The infectivity and viral replication were highest in CEF, DF-1, Vero, and QT-35 cells. In contrast, the results suggested that MDCK cells are less permissive for AnHV-1 infection with negligible CPE and reduced viral replication. Heterologous cell culture systems other than chicken embryo fibroblasts to adapted live vaccine viruses will provide a system devoid of other avian infectious agents. Moreover, it can be used for the propagation and cultivation of AnHV-1 vaccine strain for developing cell culture-based vaccines with high titer and could be an economical alternative for the existing options.

Molecular and pathological characterization of duck enteritis virus in Egypt

In winter 2016, a fatal disease outbreak suspected to be duck virus enteritis (DVE) stroke over a million ducklings in 10 white Pekin and Muscovy ducks flocks in Dakahlia and Gharbia Governorates, Egypt, causing heavy economic losses. The disease quickly killed 20%-60% of affected farms. The clinical signs were inappetence, ataxia, crowding in corners, partially closed eye lids and blue beaks. Post mortem examination revealed white necrotic foci in liver, mottled spleen and sometimes cecal core. A total of 10 intestines, livers and spleens samples were collected from diseased flocks. Each sample was pooled randomly from eight to ten ducklings. Polymerase chain reaction (PCR) and histopathological examination were utilized for DEV identification in collected samples. Nucleotides sequences of the amplified DNA polymerase gene were compared with the other DEVs available on GeneBank. Also, existence of co-infection with Salmonella spp. was verified via PCR. DEV nucleic acid was detected by PCR in 8 of 10 collected samples (80%) with positive amplification of polymerase gene. Histopathological examination revealed eosinophilic and basophilic intranuclear inclusion bodies in enterocytes. In some infected enterocytes, intranuclear and intracytoplasmic inclusions were observed in the same cell. Respectively, eosinophilic intranuclear inclusion bodies found in hepatocytes and reticular cells of liver and spleen of diseased ducklings. Four of the 10 collected samples showed positive results for Salmonella spp. infection that may be involved in enhancing infection with DEV. The identified DEVs revealed close genetic relationship with DEVs detected previously in India and China indicating potential transmission of the virus from there that crucially needs further work for better understanding of virus origin. In conclusion, our study revealed infection of duckling farms with DEV and Salmonella that necessitate the implementation of restricted early preventive and control measures for both diseases to decrease the expected economic losses.

Duck virus enteritis (duck plague) - a comprehensive update

Duck virus enteritis (DVE), also called duck plague, is one of the major contagious and fatal diseases of ducks, geese and swan. It is caused by duck enteritis virus (DEV)/Anatid herpesvirus-1 of the genus Mardivirus, family Herpesviridae, and subfamily Alpha-herpesvirinae. Of note, DVE has worldwide distribution, wherein migratory waterfowl plays a crucial role in its transmission within and between continents. Furthermore, horizontal and/ or vertical transmission plays a significant role in disease spread through oral-fecal discharges. Either of sexes from varying age groups of ducks is vulnerable to DVE. The disease is characterized by sudden death, vascular damage and subsequent internal hemorrhage, lesions in lymphoid organs, digestive mucosal eruptions, severe diarrhea and degenerative lesions in parenchymatous organs. Huge economic losses are connected with acute nature of the disease, increased morbidity and mortality (5%-100%), condemnations of carcasses, decreased egg production and hatchability. Although clinical manifestations and histopathology can provide preliminary diagnosis, the confirmatory diagnosis involves virus isolation and detection using serological and molecular tests. For prophylaxis, both live-attenuated and killed vaccines are being used in broiler and breeder ducks above 2 weeks of age. Since DEV is capable of becoming latent as well as shed intermittently, recombinant subunit and DNA vaccines either alone or in combination (polyvalent) are being targeted for its benign prevention. This review describes DEV, epidemiology, transmission, the disease (DVE), pathogenesis, and advances in diagnosis, vaccination and antiviral agents/therapies along with appropriate prevention and control strategies.

Adaptation and growth kinetics study of an Indian isolate of virulent duck enteritis virus in Vero cells

Duck virus enteritis, also known as duck plague, is a viral infection of ducks caused by duck enteritis virus (DEV). The control of the disease is mainly done by vaccination with chicken embryo adapted live virus that is known to be poorly immunogenic and elicits only partial protection. Further, the embryo propagated vaccine virus pose a threat of harboring other infectious agents. Seeing these limitations, the present study reports for the first time regarding propagation and adaptation of a virulent Indian isolate of duck enteritis virus in Vero cell line. In this study isolation of an outbreak virus from Kerala state was done in chicken embryo fibroblast cell culture (CEF). Then adapted the DEV isolate in the Vero cell line. The characteristic cytopathic effects (CPE) of clumping and fusion of Vero cells were observed starting from the 7th passage onwards. The presence of the virus and its multiplication in Vero cells was confirmed by detection of viral specific DNA and antigen by using polymerase chain reaction (PCR) and indirect immuno fluorescent assay (IIFA), respectively. PCR detection of DEV using self designed primers for US4 (gD) and UL30 (DNA Polymerase) gene has been reported for the in the present study. The kinetics of DEV in Vero cells revealed a maximum infectivity titer of 10(5.6) TCID 50/ml after 48hr of viral infection. Compared to chicken embryo adapted DVE vaccine virus, the Vero cell culture system is free from other infectious agents. So it will be a good candidate for cultivation and propagation of duck enteritis virus vaccine strain. Further research studies are suggested to explore the feasibility of utilizing this Vero cell culture adapted DEV isolate for developing an attenuated vaccine virus against duck virus enteritis.

Detection of anatid herpesvirus 1 gC gene by TaqMan fluorescent quantitative real-time PCR with specific primers and probe

BACKGROUND

Anatid herpesvirus 1 (AHV-1) is known for the difficulty of monitoring and controlling, because it has a long period of asymptomatic carrier state in waterfowls. Furthermore, as a significant essential agent for viral attachment, release, stability and virulence, gC (UL44) gene and its protein product (glycoprotein C) may play a key role in the epidemiological screening. The objectives of this study were to rapidly, sensitively, quantitatively detect gC gene of AHV-1 and provide the underlying basis for further investigating pcDNA3.1-gC DNA vaccine in infected ducks by TaqMan fluorescent quantitative real-time PCR assay (FQ-PCR) with pcDNA3.1-gC plasmid.

RESULTS

The repeatable and reproducible quantitative assay was established by the standard curve with a wide dynamic range (eight logarithmic units of concentration) and very good correlation values (1.000). This protocol was able to detect as little as 1.0 x 101 DNA copies per reaction and it was highly specific to AHV-1. The TaqMan FQ-PCR assay successfully detected the gC gene in tissue samples from pcDNA3.1-gC and AHV-1 attenuated vaccine (AHV-1 Cha) strain inoculated ducks respectively.

CONCLUSIONS

The assay offers an attractive method for the detection of AHV-1, the investigation of distribution pattern of AHV-1 in vivo and molecular epidemiological screening. Meanwhile, this method could expedite related AHV-1 and gC DNA vaccine research.

Development of TaqMan MGB fluorescent real-time PCR assay for the detection of anatid herpesvirus 1

Background

Anatid herpesvirus 1 (AHV-1) is an alphaherpesvirus associated with latent infection and mortality in ducks and geese and is currently affecting the world-wide waterfowl production severely. Here we describe a fluorescent quantitative real-time PCR (FQ-PCR) method developed for fast measurement of AHV-1 DNA based on TaqMan MGB technology.

Results

The detection limit of the assay was 1 × 10¹ standard DNA copies, with a sensitivity of 2 logs higher than that of the conventional gel-based PCR assay targeting the same gene. The real-time PCR was reproducible, as shown by satisfactory low intra-assay and inter-assay coefficients of variation.

Conclusion

The high sensitivity, specificity, simplicity and reproducibility of the AHV-1 fluorogenic PCR assay, combined with its wide dynamic range and high throughput, make this method suitable for a broad spectrum of AHV-1 etiologically related application.

Development and evaluation of an antigen-capture ELISA for detection of the UL24 antigen of the duck enteritis virus, based on a polyclonal antibody against the UL24 expression protein

An antigen-capture enzyme-linked immunosorbent assay (AC-ELISA) method was developed for the efficient detection of the UL24 antigen of the duck enteritis virus (DEV) using polyclonal antibodies. Ducks and rabbits were immunized, respectively, with expressed UL24 recombinant protein. The IgG antibodies against UL24 from ducks and rabbits were purified and used as the capture antibodies. The specificity of the optimized AC-ELISA was evaluated by use of DEV, duck hepatitis virus (DHV), duck hepatitis B virus (DHBV), gosling plague virus (GPV), Riemerella anatipestifer (R.A.), Escherichia coli (E. coli), Pasteurella multocida (P.M.) and Salmonella Enteritidis (S.E.). Only DEV specimens yielded a specific and strong signal. The limit of the sensitivity of this method for the detection of DEV was 46 ng/100 microl. Compared with PCR and virus isolation, the rate of agreement for the detection of experimentally infected sera was 100%. A comparative test used on clinical specimens between the neutralization test and the AC-ELISA showed that the proportions of true positives and true negatives by the AC-ELISA were 0.90 and 0.67 respectively. These results indicated that the AC-ELISA approach is rapid, sensitive, and reliable for specific detection of DEV antigen.

Characterization of the gene encoding glycoprotein C of duck enteritis virus

A total of 2,718 bp of DNA fragment was amplified from the C-KCE strain of duck enteritis virus (DEV) genome using thermal asymmetric interlaced PCR. This newly identified viral DNA fragment contained two non-overlapping open reading frames (ORFs) oriented from the 5' to 3' direction. The first ORF was comprised of 43.5% G + C and contained the full-length genomic sequence of the UL44 gene (1,296 bp) encoding 431 amino acid residues of DEV glycoprotein C (gC). The second ORF encoded a partial peptide of the UL43 gene. The sequences of DNA and deduced amino acids of the DEV gC gene shared high homology with other members of known herpesviruses, supporting the classification of DEV. Phylogenetic analysis of the DEV gC gene revealed that the gC gene had a close evolutionary relationship with the subfamily of Alphaherpesvirinae.

Inhibition of Anatid Herpes Virus-1 replication by small interfering RNAs in cell culture system

RNA interference (RNAi) mediated by double stranded small interfering RNA (siRNA) is a novel mechanism of post-transcriptional gene silencing. It is projected as a potential tool to inhibit viral replication. In the present paper, we demonstrate the suppression of replication of an avian herpes virus (Anatid Herpes Virus-1, AHV-1) by siRNA mediated gene silencing in avian cells. The UL-6 gene of AHV-1 that codes for a protein involved in viral packaging was targeted. Both cocktail and unique siRNAs were attempted to evaluate the inhibitory potential of AHV-1 replication in duck embryo fibroblast (DEF) cell line. DEF cells were chemically transfected with different siRNAs in separate experiments followed by viral infection. The observed reduction in virus replication was evaluated by cytopathic effect, viral titration and quantitative real time PCR (QRT-PCR). Among the three siRNA targets used the unique siRNA UL-B sequence was found to be more potent in antiviral activity than the cocktail and UL6-A-siRNA sequences.

Development of Quantitative Real-Time Polymerase Chain Reaction for Duck Enteritis Virus DNA

Duck enteritis virus (DEV) is a herpesvirus that causes an acute, contagious, and fatal disease. In the present article, we introduce a quantitative real-time polymerase chain reaction (PCR) assay for DEV DNA using TaqMan technology and a two-step protocol. It was confirmed to be rapid, sensitive, and specific for DEV detection. The primers and probe were designed and directed to the DNA polymerase gene of DEV. The method will provide a valuable tool for rapid laboratory diagnosis of DEV infection. By virtue of its high-throughput format and its ability to accurately quantify the viral DNA, the method may be useful for large epidemiological surveys and clarification of pathogenesis, such as latency and reactivation of the virus.