Electron microscopic studies of the morphogenesis of duck enteritis virus

Effects of US3 protein kinase activity on localization of UL31/UL34 protein and nucleocapsids egress of duck plague virus

Duck plague virus (DPV) is a pathogen causing duck plague and has caused huge economic losses in poultry industry. In our previous report, US3 gene deletion from DPV genome seriously impaired virus replication. In this study, we constructed a US3 kinase-inactive mutant (US3K213A) to further explore the function of US3 protein (pUS3) in DPV. Our results showed that the loss of pUS3 kinase activity caused lower viral titers, smaller plaque sizes and a blockage of capsids nuclear egress including primary enveloped virion (PEV) accumulation compared to the parental virus infection. It indicates that the effects of DPV pUS3 on viral propagation depended on its kinase activity. In addition, we conducted electron microscopy analysis to show the outer nuclear membrane (ONM) evaginations and the nuclear envelope (NE) deep invagination in US3K213A-infected cells. Finally, an irregular distribution of pUL31/pUL34 in the NE in △US3- and US3K213A-infected cells and an interaction of pUS3 and pUL31 were found, which suggests that pUS3 potentially targets pUL31 and regulates the localization of pUL31/pUL34 to promote nucleocapsids egress through its kinase activity.

Duck plague virus infection alter the microbiota composition and intestinal functional activity in Muscovy ducks

Intestinal damage from the duck plague virus (DPV) infection affects intestinal inflammation factors expression and barrier dysfunction. Here we report findings from the pathogenicity of the intestinal tract, intestinal morphological, intestinal permeability, inflammatory cytokines, and tight junction gene expression in 72 two-wk-old Muscovy ducks exposed to DPV. The characterization of intestinal metabolites and their classification were examined using 16-sequencing technology. The primary outcomes of the study evaluated the correlation between intestinal microbiota characteristics and the degree of infected tissue. The secondary outcomes were to determine whether the biosignatures that defined the microbiota were positively or negatively correlated with viral infection. The tissue was infected accompanied a mild damage of liver and spleen, and severe intestinal bleeding. Two inoculation routes were constructed with susceptible animals to assess the pathogenicity of the DPV in order to enrich the status of infection in Muscovy ducks. High levels of virus titer from Muscovy ducks were found being in the intestine. The expression of INF-α and IL-β with viral infection increased at 4, and 6 dpi, respectively, after detecting of the inflammatory factor and barrier function genes. At 4 and 6 dpi, barrier function gene of ZO-1 and Occludin reduced. The severity of viral infection was significantly correlated with the characteristics of the intestinal microbiota. Ducks infected with the DPV had an increase in the phylum Firmicutes, a decrease in the phylum Actinobacteriota, and differential enrichment with the genus Bacteroides, Tyzzerella, Enterococcus, and Escherchia-Shigella, while the genus Rothia, Streptococcus, and Ralstonia were differentially enriched in the control group. The findings from the current study demonstrated that DPV infection leads to an imbalance of the intestinal microbiota and disruption of the microbial homeostasis in the intestinal tissue in ducks, which might be one of the mechanisms whereby DPV infection might be established in Muscovy ducks. Na⁺/K⁺-ATPase and Ca²⁺/Mg²⁺-ATPase activity monitoring also showed that viral infection reduced these activities. These findings imply that changes in intestinal microbiota, intestinal barrier gene expression, and inflammatory factor are related to viral infection. When taken as a whole, this work provides fresh perspectives on the characteristics of intestinal microbiota and the infection damage caused by the DPV.

Evaluation of safety and immunogenicity of duck-plague virus gC/gE double gene deletion

Duck plague caused by duck plague virus (DPV) is a highly contagious disease that can cause serious morbidity and death in waterfowl such as ducks and geese, and bring huge economic losses to the duck industry. In this study, on the basis of the duck plague virus gC gene deletion strain CHv-ΔgC, based on the duck plague virus bacterial artificial chromosome (BAC) platform in our laboratory, the gE gene was knocked out using the traceless deletion technology to obtain gC/gE double gene deletion candidate vaccine strain CHv-ΔgC/gE. The double gene deletion strain (CHv-ΔgC/gE) constructed in this study has greatly weakened virulence, no pathogenicity to ducks, and stable genetic characteristics in vitro and in vivo. Ducks immunized with CHv-ΔgC/gE can produce neutralizing antibodies and ELISA antibody levels comparable to those of commercial duck plague attenuated vaccine immunization, and can resist 100 LD₅₀ CHv challenge of ducks, with good immune protection effect. It has the potential to be further developed into duck plague gC/gE double gene deletion, marked attenuated vaccine.

Alphaherpesvirus glycoprotein E: A review of its interactions with other proteins of the virus and its application in vaccinology

The viral envelope glycoprotein E (gE) is required for cell-to-cell transmission, anterograde and retrograde neurotransmission, and immune evasion of alphaherpesviruses. gE can also interact with other proteins of the virus and perform various functions in the virus life cycle. In addition, the gE gene is often the target gene for the construction of gene-deleted attenuated marker vaccines. In recent years, new progress has been made in the research and vaccine application of gE with other proteins of the virus. This article reviews the structure of gE, the relationship between gE and other proteins of the virus, and the application of gE in vaccinology, which provides useful information for further research on gE.

Features and Functions of the Conserved Herpesvirus Tegument Protein UL11 and Its Binding Partners

The herpesvirus UL11 protein is encoded by the UL11 gene and is a membrane-anchored protein with multiple functions. In the last stage of viral replication, UL11 participates in the secondary envelopment process. It also plays a key role in primary envelopment, the transportation of newly assembled viral particles through cytoplasmic vesicles, and virion egress from the cell. UL11 is an important accessory protein and sometimes cooperates with other proteins that participate in virus-induced cell fusion. Cell fusion is necessary for cell-to-cell transmissions. This review summarizes the latest literature and discusses the roles of UL11 in viral assembly, primary and secondary envelopment, and cell-to-cell transmission to obtain a better understanding of the UL11 protein in the life cycle of herpesviruses and to serve as a reference for studying other viruses. Additionally, some recently discovered characteristics of UL11 are summarized.

Molecular characterization of duck plague virus from selected Haor areas of Bangladesh

Background:

Duck viral enteritis, commonly known as duck plague (DP), is an acute and contagious fatal disease in ducks, geese, and swans caused by the DP virus (DPV). It poses a serious threat to the growth of duck farming in the Haor (wetland) areas of Bangladesh.

Aim:

This study aimed to detect the circulating DPV by molecular characterization, followed by phylogenetic analysis, targeting the UL30 gene in infected ducks from five Haor districts in Bangladesh and to observe the variation in the genome sequence between the field virus and vaccine strain of DPV.

Methods:

A total of 150 samples (liver, 50; intestine, 50; and oropharyngeal tissue, 50) were collected from DP-suspected sick/dead ducks from 50 affected farms in Kishoreganj, Netrokona, B. Baria, Habiganj, and Sunamganj districts in Bangladesh. For the identification of DPV in collected samples, polymerase chain reaction (PCR) was utilized. Nucleotide sequences of the amplified UL30 gene were compared with those of other DPV strains available in GenBank.

Results:

Of the 150 samples, 90 (60%) were found to be positive for DPV, as confirmed by PCR. Organ-wise prevalence was higher in the liver (72%), followed by the intestine (64%) and oropharyngeal tissue (44%). Regarding areas, the highest and lowest prevalence in the liver and intestine was observed in Habiganj and B. Baria, respectively, whereas the highest and lowest prevalence in the oropharyngeal tissue was observed in B. Baria and Habiganj, respectively. Two isolates, BAU/KA/DPV(B1)/2014 from Kishoreganj and BAU/KA/DPV(B4)/2014 from Sunamganj were sequenced, and phylogenetic analysis revealed that these isolates are evolutionarily closely related to Chinese isolates of DPV. Additionally, the isolates of DPV BAU/KA/DPV(B1)/2014 and BAU/KA/DPV(B4)/2014 showed the highest (98%) similarity to each other. The nucleotide sequence of the isolate BAU/KA/DPV(B1)/2014 exhibited higher nucleotide variability (246 nucleotides) than that of the vaccine strain (accession no. EU082088), which may affect protein function and additional drug sensitivity.

Conclusion:

Based on the findings of the molecular study, it can be assumed that the Bangladeshi isolates and all Chinese isolates of DPV may have a common ancestry.

The Role of VP16 in the Life Cycle of Alphaherpesviruses

The protein encoded by the UL48 gene of alphaherpesviruses is named VP16 or alpha-gene-transactivating factor (α-TIF). In the early stage of viral replication, VP16 is an important transactivator that can activate the transcription of viral immediate-early genes, and in the late stage of viral replication, VP16, as a tegument, is involved in viral assembly. This review will explain the mechanism of VP16 acting as α-TIF to activate the transcription of viral immediate-early genes, its role in the transition from viral latency to reactivation, and its effects on viral assembly and maturation. In addition, this review also provides new insights for further research on the life cycle of alphaherpesviruses and the role of VP16 in the viral life cycle.

Duck Enteritis Virus VP16 Antagonizes IFN-β-Mediated Antiviral Innate Immunity

Duck enteritis virus (DEV) can successfully evade the host innate immune responses and establish a lifelong latent infection in the infected host. However, the study about how DEV escapes host innate immunity is still deficient up to now. In this study, for the first time, we identified a viral protein VP16 by which DEV can obviously downregulate the production of IFN-β in duck embryo fibroblast (DEF). Our results showed that ectopic expression of VP16 decreased duck IFN-β (duIFN-β) promoter activation and significantly inhibited the mRNA transcription of IFN-β. Further study showed that VP16 can also obviously inhibit the mRNA transcription of interferon-stimulated genes (ISGs), such as myxovirus resistance protein (Mx) and interferon-induced oligoadenylate synthetase-like (OASL). Furthermore, we found that this anti-interferon activity of VP16 depended on its N-terminus (aa1-200). Coexpression analysis revealed that VP16 selectively blocked duIFN-β promoter activity at the duIRF7 level rather than duIRF1. Based on the results of coimmunoprecipitation analysis (co-IP) and indirect immunofluorescence assay (IFA), VP16 was able to bind to duck IRF7 (duIRF7) directly, but did not interact with duck IRF1 (duIRF1) in vitro.

Duck plague virus gE serves essential functions during the virion final envelopment through influence capsids budding into the cytoplasmic vesicles

Duck plague virus (DPV), a member of the alphaherpesviruses subfamily, causes massive ducks death and results in a devastating hit to duck industries in China. It is of great significance for us to analyze the functions of DPV genes for controlling the outbreak of duck plague. Thus, glycoproteins E (gE) of DPV, which requires viral cell-to-cell spreading and the final envelopment in herpes simplex virus 1 (HSV-1) and pseudorabies virus (PRV), was chosen herein. The gE mutant virus BAC-CHv-ΔgE was constructed by using a markerless two-step Red recombination system implemented on the DPV genome cloned into a bacterial artificial chromosome (BAC). Viral plaques on duck embryo fibroblast (DEF) cells of BAC-CHv-ΔgE were on average approximately 60% smaller than those produced by BAC-CHv virus. Viral replication kinetics showed that BAC-CHv-ΔgE grew to lower titers than BAC-CHv virus did in DEF cells. Electron microscopy confirmed that deleting of DPV gE resulted in a large number of capsids accumulating around vesicles and very few of them could bud into vesicles. The drastic inhibition of virion formation in the absence of the DPV gE indicated that it played an important role in virion morphogenesis before the final envelopment of intracytoplasmic nucleocapsids.

Isolation and Selection of Duck Primary Cells as Pathogenic and Innate Immunologic Cell Models for Duck Plague Virus

Duck plague virus (DPV) is a representative pathogen transmitted among aquatic animals that causes gross lesions and immune inhibition in geese and ducks. The mechanism of organ tropism and innate immune evasion of DPV has not been completely deciphered due to a lack of cell models to study the innate immune manipulation and pathogenicity of aquatic viruses. In the present study, we isolated five types of duck primary cells [duck embryo fibroblasts (DEFs), neurons, astrocytes, peripheral blood mononuclear cells (PBMCs), and monocytes/macrophages] to identify appropriate cell models for DPV, using tropism infection and innate immunologic assays. Cells responded differently to stimulation with DNA viruses or RNA virus analogs. DPV infection exhibited broad tropism, as the recombinant virulent strain (CHv-GFP) infected DEFs, neurons, astrocytes, and monocytes/macrophages, but not the PBMCs, as the expression of EGFP was negligible. The basal levels of innate immunity molecules were highest in monocytes/macrophages and lower in DEFs and astrocytes. Conversely, the titer and genomic copy number of the attenuated virus strain was higher in DEFs and astrocytes than in neurons and monocytes/macrophages. The titer and genomic copy number of the attenuated virus strain were higher compared with the virulent strain in DEFs, neurons, and astrocytes. The innate immune response was not significantly induced by either DPV strain in DEFs, neurons, or astrocytes. The virulent strain persistently infected monocytes/macrophages, but the attenuated strain did so abortively, and this was accompanied by the phenomenon of innate immune inhibition and activation by the virulent and attenuated strains, respectively. Blockage of IFNAR signaling promoted replication of the attenuated strain. Pre-activation of IFNAR signaling inhibited infection by the virulent strain. The selection assay results indicated that induction of innate immunity plays an essential role in controlling DPV infection, and monocytes/macrophages are an important cell model for further investigations. Our study provided practical methods for isolating and culturing duck primary cells, and our results will facilitate further investigations of organ tropism, innate immune responses, latent infection, and the effectiveness of antiviral drugs for treating DPV and potentially other aerial bird pathogens.

Development of a simple and rapid immunochromatographic strip test for detecting duck plague virus antibodies based on gI protein

A colloidal gold strip (CGS) for detecting antibodies to duck plague virus (DPV) was developed. Colloidal gold-labeled DPV gI protein and goat anti-rabbit IgG were dispensed on a conjugate pad as tracers. The recombinant DPV gI protein and rabbit IgG were used as capture reagents at the test line and control line, respectively. The detection limit of this assay was 1:256. Additionally, the CGS did not react with antisera from other common duck diseases, only reacting with anti-DPV serum and yielding a specific and strong red signal. 123 serum samples were tested by CGS and enzyme-linked immunosorbent assay (ELISA), and the results showed good agreement. The CGS test results can be observed in 15 min with the naked eye, should be suitable for clinical testing and large-scale detection.

Alpha-Herpesvirus Thymidine Kinase Genes Mediate Viral Virulence and Are Potential Therapeutic Targets

Alpha-herpesvirus thymidine kinase (TK) genes are virulence-related genes and are nonessential for viral replication; they are often preferred target genes for the construction of gene-deleted attenuated vaccines and genetically engineered vectors for inserting and expressing foreign genes. The enzymes encoded by TK genes are key kinases in the nucleoside salvage pathway and have significant substrate diversity, especially the herpes simplex virus 1 (HSV-1) TK enzyme, which phosphorylates four nucleosides and various nucleoside analogues. Hence, the HSV-1 TK gene is exploited for the treatment of viral infections, as a suicide gene in antitumor therapy, and even for the regulation of stem cell transplantation and treatment of parasitic infection. This review introduces the effects of α-herpesvirus TK genes on viral virulence and infection in the host and classifies and summarizes the current main application domains and potential uses of these genes. In particular, mechanisms of action, clinical limitations, and antiviral and antitumor therapy development strategies are discussed.

Duck Plague Virus Promotes DEF Cell Apoptosis by Activating Caspases, Increasing Intracellular ROS Levels and Inducing Cell Cycle S-Phase Arrest

Background: Duck plague virus (DPV) can induce apoptosis in duck embryo fibroblasts (DEFs) and in infected ducks, but the molecular mechanism of DPV-induced apoptosis remains unknown. Methods: We first used qRT-PCR and a Caspase-Glo assay to determine whether the caspase protein family plays an important role in DPV-induced apoptosis. Then, we used an intracellular ROS detection kit and the mitochondrial probe JC-1 to respectively detect ROS levels and mitochondrial membrane potential (MMP). Finally, flow cytometry was used to detect apoptosis and cell cycle progression. Results: In this study, the mRNA levels and enzymatic activities of caspase-3, caspase-7, caspase-8, and caspase-9 were significantly increased during DPV-induced apoptosis. The caspase inhibitors Z-DEVD-FMK, Z-LEHD-FMK, and Q-VD-Oph could inhibit DPV-induced apoptosis and promote viral replication. Subsequently, a significant decrease in MMP and an increase in the intracellular ROS levels were observed. Further study showed that pretreating infected cells with NAC (a ROS scavenger) decreased the intracellular ROS levels, increased the MMP, inhibited apoptosis, and promoted viral replication. Finally, we showed that DPV infection can cause cell cycle S-phase arrest. Conclusions: This study shows that DPV causes cell cycle S-phase arrest and leads to apoptosis through caspase activation and increased intracellular ROS levels. These findings may be useful for gaining an understanding of the pathogenesis of DPV and the apoptotic pathways induced by α-herpesviruses.

CpG oligodeoxynucleotide-specific duck TLR21 mediates activation of NF-κB signaling pathway and plays an important role in the host defence of DPV infection

TLR21 can recognize unmethylated cytosine-phosphate-guanine oligodeoxynucleotides (CpG-ODN) and activates NF-κB immune signaling pathway. However, the function of TLR21 in duck remains largely unclear. Here, the complete duck TLR21 (duTLR21) cDNA was cloned from Cherry Valley duck for the first time, and its immune response was preliminarily studied. Tissue specificity analysis showed duTLR21 was higher expressed in the peripheral blood, spleen, bursa of Fabricius and cecum. The expression of duTLR21 was significantly upregulated after stimulation with CpG-ODN or duck plague virus (DPV), but not Tembusu virus (TMUV), LPS or Poly (I:C). In addition, the transfection of DEF with duTLR21 stimulated by CpG-ODN activated NF-κB, through this signal pathway, the transcription of IL-1β, IL-6 and IFN-α were promoted, whereas knockdown of duTLR21 impaired the transcription of these genes. Furthermore, the overexpression of duTLR21 inhibited the replication of the DPV and the knockdown of duTLR21 by shRNA significantly promoted DPV replication in vitro. Altogether, these results indicate that duTLR21 can be activated by CpG-ODN, which mediates activation of NF-κB signaling pathway, and plays an important role in the host defence of DPV infection.

The culture of primary duck endothelial cells for the study of avian influenza

BACKGROUND

Endothelial cells play a major role in highly pathogenic avian influenza (HPAI) virus pathogenesis in gallinaceous poultry species (e.g. chicken, turkey and quail). Upon infection of gallinaceous poultry with HPAI viruses, endothelial cells throughout the body become rapidly infected, leading to systemic dissemination of the virus, disseminated intravascular coagulation, oedema and haemorrhaging. In contrast, the pathogenesis of HPAI viruses in most wild bird species (e.g. duck, goose and gull species) is not associated with endothelial tropism. Indeed, viral antigen is not found in the endothelial cells of most wild bird species following infection with HPAI viruses. This differential endothelial cell tropism in avian species is poorly understood, mainly due to the absence of appropriate cell culture systems.

RESULTS

Here, we describe the isolation and purification of primary duck endothelial cells from the aorta or bone marrow of Pekin duck embryos. Cells were differentiated in the presence of vascular endothelial growth factor and, if needed, enriched via fluorescent-activated cell sorting based on the uptake of acetylated low-density lipoprotein. The expression of von Willebrand factor, a key marker of endothelial cells, was confirmed by polymerase chain reaction. Monocultures of duck endothelial cells, either derived from the aorta or the bone marrow, were susceptible to infection with an H5N1 HPAI virus but to a much lesser extent than chicken endothelial cells.

CONCLUSIONS

The methods described herein to isolate and purify duck endothelial cells from the aorta or bone marrow could also be applied to obtain microvascular endothelial cells from other tissues and organs, such as the lung or the intestine, and represent a valuable tool to study the pathogenesis of avian viruses.

Duck plague virus Glycoprotein J is functional but slightly impaired in viral replication and cell-to-cell spread

To analyse the function of the duck plague virus (DPV) glycoprotein J homologue (gJ), two different mutated viruses, a gJ deleted mutant ΔgJ and a gJR rescue mutant gJR with US5 restored were generated. All recombinant viruses were constructed by using two-step of RED recombination system implemented on the duck plague virus Chinese virulent strain (DPV CHv) genome cloned into a bacterial artificial chromosome. DPV-mutants were characterized on non-complementing DEF cells compared with parental virus. Viral replication kinetics of intracellular and extracellular viruses revealed that the ΔgJ virus produce a 10-fold reduction of viral titers than the gJR and parental virus, which especially the production of extracellular infectivity was affected. In addition, the ΔgJ virus produced viral plaques on DEF cells that was on average approximately 11% smaller than those produced by the gJR and parental viruses. Electron microscopy confirmed that although DPV CHv without gJ could efficiently carry out viral replication, virion assembly and envelopment within infected cells, the ΔgJ virus produced and accumulated high levels of anuclear particles in the nuclear and cytoplasm. These results show that the gJ slightly impaired in viral replication, virion assembly and cell-to-cell spread, and is not essential in virion envelopment.

Molecular characterization of duck enteritis virus UL41 protein

BACKGROUND

Duck enteritis virus (DEV) belongs to the subfamily Alphaherpesvirinae, and information on the DEV UL41 gene is limited.

METHODS

The DEV UL41 gene was cloned into the pET32a(+) vector and expressed in a prokaryotic expression system. Antiserum was raised against a bacterially expressed UL41-His fusion protein for further experiments. Transcription was quantified and UL41 protein expression levels were determined in DEV-infected cells at different time points by RT-qPCR and western blotting, respectively. DEV virions were purified by sucrose gradient centrifugation and analyzed by mass spectrometry to identify protein content. We confirmed the DEV UL41 gene kinetic class using a pharmacological test. IFA was used to analyze the intracellular localization of pUL41.

RESULTS

The recombinant expression plasmid, pET-32a(+)-UL41, which highly expresses a 76.0 kDa fusion protein, was constructed and expressed in E. coli BL21 (DE3) after induction with 0.2 mM IPTG at 30 °C for 10 h, generating a specific mouse anti-UL41 protein polyclonal antibody. RT-qPCR and western blot analyses revealed that the UL41 transcript number peaked at 36 hpi, and peak protein expression occurred at 48 hpi. The pharmacological test showed that UL41 was a γ2 gene. Mass spectrometry analysis showed that pUL41 was a virion component. IFA results revealed that pUL41 was localized throughout DEV-infected cells but only localized to the cytoplasm of transfected cells. DEV pUL47 translocated pUL41 to the nuclei of DEF cells; this translocation was dependent on predicted pUL47 NLS signals (40-50 aa and 768-777 aa).

CONCLUSIONS

DEV UL41 is a γ2 gene that encodes a virion structural protein, pUL41 localizes throughout DEV-infected cells but only localizes to the cytoplasm of transfected cells. pUL41 cannot autonomously localize to the nucleus, as this nuclear localization is dependent on predicted DEV pUL47 NLS signals (40-50 aa and 768-777 aa).

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.

Characterization of the duck enteritis virus UL55 protein

Background

Characteration of the newly identified duck enteritis virus UL55 gene product has not been reported yet. Knowledge of the protein UL55 can provide useful insights about its function.

Results

The newly identified duck enteritis virus UL55 gene was about 561 bp, it was amplified and digested for construction of a recombinant plasmid pET32a(+)/UL55 for expression in Escherichia coli. SDS-PAGE analysis revealed the recombinant protein UL55(pUL55) was overexpressed in Escherichia coli BL21 host cells after induction by 0.2 mM IPTG at 37°C for 4 h and aggregated as inclusion bodies. The denatured protein about 40 KDa named pUL55 was purified by washing five times, and used to immune rabbits for preparation of polyclonal antibody. The prepared polyclonal antibody against pUL55 was detected and determined by Agar immundiffusion and Neutralization test. The results of Wstern blotting assay and intracellular analysis revealed that pUL55 was expressed most abundantly during the late phase of replication and mainly distributed in cytoplasm in duck enteritis virus infected cells.

Conclusions

In this study, the duck enteritis virus UL55 protein was successfully expressed in prokaryotic expression system. Besides, we have prepared the polyclonal antibody against recombinant prtein UL55, and characterized some properties of the duck enteritis virus UL55 protein for the first time. The research will be useful for further functional analysis of this gene.

Development and application of an indirect immunohistochemical method for the detection of duck plague virus vaccine antigens in paraffin sections and localization in the vaccinated duckling tissues

The objective of the present study was to develop and apply a streptavidin-alkaline phosphatase labeling system of indirect immunohistochemistry (SP-IHC) to detect antigenic distribution and localization regularity of duck plague virus (DPV) vaccine antigens in paraformaldehyde-fixed paraffin-embedded tissues of experimentally vaccinated ducklings. Male New Zealand rabbits were immunized with purified DPV antigens, which were engaged by a combination of differential centrifugation and sucrose-density gradient ultracentrifugation. The rabbit anti-DPV polyclonal antibodies were purified and used as the primary antibodies. Forty-eight 28-d-old DPV-free Pekin ducklings were subcutaneously inoculated with attenuated DPV vaccine in the immunization group and sterile PBS in the control group. The tissues were collected at sequential time points between 4 h and 18 wk postvaccination (PV) and were prepared for SP-IHC observation. The presence of DPV-specific antigens was first observed in the liver and spleen at 12 h PV; in the bursa of Fabricius, thymus, Harderian gland, esophagus, and intestinal tract at 1 d PV; and in the heart, lung, kidney, pancreas, and brain at 3 d PV. The positive staining reaction could be detected in the vaccinated duckling tissues until 18 wk PV, and no positive staining cells could be observed in the controls. The highest levels of positive staining reaction were found in the liver, spleen, bursa of Fabricius, thymus, and intestinal tract, whereas a few DPV vaccine antigens were distributed in the heart, pancreas, and esophagus. The target cells had a ubiquitous distribution, especially in the mucosal epithelial cells, lamina propria cells, macrophages, hepatocytes, and lymphocytes, which served as the principal sites for antigen localization. These findings demonstrated that SP-IHC was a reliable method for detecting antigenic distribution and localization regularity of DPV vaccine antigens in routine paraffin sections. The present study may be useful for describing proliferation and distribution regularity of DPV vaccine in the vaccinated duckling tissues and enhance further studies and clinical application of attenuated DPV vaccine.

Expressing gK gene of duck enteritis virus guided by bioinformatics and its applied prospect in diagnosis

Background

Duck viral enteritis, which is caused by duck enteritis virus (DEV), causes significant economic losses in domestic and wild waterfowls because of the high mortality and low egg production rates. With the purpose of eliminating this disease and decreasing economic loss in the commercial duck industry, researching on glycoprotein K (gK) of DEV may be a new kind of method for preventing and curing this disease. Because glycoproteins project from the virus envelope as spikes and are directly involved in the host immune system and elicitation of the host immune responses, and also play an important role in mediating infection of target cells, the entry into cell for free virus and the maturation or egress of virus. The gK is one of the major envelope glycoproteins of DEV. However, little information correlated with gK is known, such as antigenic and functional characterization.

Results

Bioinformatic predictions revealed that the expression of the full-length gK gene (fgK) in a prokaryotic system is difficult because of the presence of suboptimal exon and transmembrane domains at the C-terminal. In this study, we found that the fgK gene might not be expressed in a prokaryotic system in accordance with the bioinformatic predictions. Further, we successfully used bioinformatics tools to guide the prokaryotic expression of the gK gene by designing a novel truncated gK gene (tgK). These findings indicated that bioinformatics provides theoretical data for target gene expression and saves time for our research. The recombinant tgK protein (tgK) was expressed and purified by immobilized metal affinity chromatography (IMAC). Western blotting and indirect enzyme-linked immunosorbent assay (ELISA) showed that the tgK possessed antigenic characteristics similar to native DEV-gK.

Conclusions

In this work, the DEV-tgK was expressed successfully in prokaryotic system for the first time, which will provide usefull information for prokaryotic expression of alphaherpesvirus gK homologs, and the recombinant truncated gK possessed antigenic characteristics similar to native DEV gK. Because of the good reactionogenicity, specificity and sensitivity, the purified tgK could be useful for developing a sensitive serum diagnostic kit to monitor DEV outbreaks.

Expression and intracellular localization of duck enteritis virus pUL38 protein

Knowledge of the intracellular location of a protein can provide useful insights into its function. Bioinformatic studies have predicted that the DEV pUL38 mainly targets the cytoplasm and nucleus. In this study, we obtained anti-pUL38 polyclonal sera. These antibodies were functional in western blotting and immunofluorescence in DEV-infected duck embryo fibroblasts (DEFs). pUL38 was expressed as a 51-kDa protein from 8 h post-infection onward, initially showing a diffuse distribution throughout the cytoplasm, and later in the nucleus. Furthermore, pUL38 was found in purified virus. These results provide the first evidence of the kinetics of expression and intracellular localization of DEV pUL38.

Polyclonal antibody against the DPV UL46M protein can be a diagnostic candidate

Background

The duck plague virus (DPV) UL46 protein (VP11/12) is a 739-amino acid tegument protein encoded by the UL46 gene. We analyzed the amino acid sequence of UL46 using bioinformatics tools and defined the main antigenic domains to be between nucleotides 700-2,220 in the UL46 sequence. This region was designated UL46M. The DPV UL46 and UL46M genes were both expressed in Escherichia coli Rosetta (DE3) induced by isopropy1-β-D-thiogalactopyranoside (IPTG) following polymerase chain reaction (PCR) amplification and subcloning into the prokaryotic expression vector pET32a(+). The recombinant proteins were purified using a Ni-NTA spin column and used to generate the polyclonal antibody against UL46 and UL46M in New Zealand white rabbits. The titer was then tested using enzyme-linked immunosorbent assay (ELISA) and agar diffusion reaction, and the specificity was tested by western blot analysis. Subsequently, we established Dot-ELISA using the polyclonal antibody and applied it to DPV detection.

Results

In our study, the DPV UL46M fusion protein, with a relative molecular mass of 79 kDa, was expressed in E. coli Rosetta (DE3). Expression of the full UL46 gene failed, which was consistent with the results from the bioinformatic analysis. The expressed product was directly purified using Ni-NTA spin column to prepare the polyclonal antibody against UL46M. The titer of the anti-UL46M antisera was over 1:819,200 as determined by ELISA and 1:8 by agar diffusion reaction. Dot-ELISA was used to detect DPV using a 1:60 dilution of anti-UL46M IgG and a 1:5,000 dilution of horseradish peroxidase (HRP)-labeled goat anti-rabbit IgG.

Conclusions

The anti-UL46M polyclonal antibody reported here specifically identifies DPV, and therefore, it is a promising diagnostic tool for DPV detection in animals. UL46M and the anti-UL46M antibody can be used for further clinical examination and research of DPV.

A Thymidine Kinase recombinant protein-based ELISA for detecting antibodies to Duck Plague Virus

BACKGROUND

Duck plague virus (DPV) is the causative agent of Duck Plague (DP) that causes significant morbidity and mortality throughout duck-producing areas of the world. The diagnosis of DP currently relies on the use of live or inactivated whole DPV virion as antigens in ELISA, but it is too laborious and expensive for routine application, and it is still difficult to get purified DPV virion with current technology.

RESULTS

In this study, we describe the expression and purification of a recombinant Thymidine Kinase (TK) protein which makes antigen in an in-house developed, optimized and standardized ELISA. The specificity of the optimized TK-ELISA was evaluated by antisera against Duck Plague Virus (DPV), Duck Hepatitis B Virus (DHBV), Duck Hepatitis Virus (DHV), Riemerella Anatipestifer(R. A), Escherichia coli (E. coli) and Salmonella anatum (S. anatum). Only antisera against DPV yielded a specific and strong signal. In order to determine the sensitivity of the TK-ELISA, a panel of diluted sera was tested, and the minimum detection limit of 1:2560 (OD450 nm = 0.401) was obtained according to the endpoint cut-off (0.2438). The repeatability and reproducibility under the experimental conditions demonstrates a low variability (P > 0.05). The suspected sera samples (n = 30) were determined by TK-ELISA and the positive rate is 90% (27/30), and the TK-ELISA showed 83.33% (22+3/30) coincidence rate with the Serum Neutralization Test (SNT) and 90% (24+3/30) coincidence rate with the whole DPV virion based-ELISA (DPV-ELISA). When defining the dynamics of antibody response to attenuated live DPV vaccine, the maximum antibodies is reached after 4 weeks.

CONCLUSIONS

The results suggest that the TK-ELISA provides high specificity, sensitivity, repeatability and reproducibility for detection of anti-DPV antibodies in duck sera, and has the potential to be much simpler than DPV-ELISA and SNT for the sera epidemiological investigation.

Development and application of an indirect immunoperoxidase assay for the detection of Duck swollen head hemorrhagic disease virus antigen in Pekin ducks (Anas platyrhynchos)

An improved indirect immunoperoxidase assay (IPA) was developed to detect antigens of Duck swollen head hemorrhagic disease virus (DSHDV) in paraformaldehyde-fixed, paraffin-embedded tissues of Pekin ducks (Anas platyrhynchos). This technique used an indirect streptavidin-alkaline phosphatase labeling system with polyclonal antiserum developed against purified DSHDV antigens. Specimens from the experimentally inoculated Pekin ducks with DSHDV and archived paraffin-embedded tissues from natural cases of Duck viral swollen head hemorrhagic disease (DVSHD) were examined by clinical and histological criteria. Positive staining was most widely observed in the cytoplasm of the following organs: immune, digestive, and urinary organs, heart, lung, and trachea, which corresponded to the intracellular distribution of reovirus. The DSHDV antigens were first detected at 4 hr postinoculation in the bursa of Fabricius of infected ducks. Therefore, this method was suitable for the early diagnosis of DVSHD. Immunoperoxidase staining was not present in tissues and organs of sham-inoculated ducks (negative control). The IPA developed in the current study is a convenient, sensitive, and specific means of detecting DSHDV and is applicable to routine diagnosis, retrospective studies, and prospective studies of DSHDV infection in ducks.

Characterization of subcellular localization of duck enteritis virus UL51 protein

Background

Knowledge of the subcellular localization of a protein can provide useful insights about its function. While the subcellular localization of many alphaherpesvirus UL51 proteins has been well characterized, little is known about where duck enteritis virus (DEV) UL51 protein (pUL51) is targeted to. Thus, in this study, we investigated the subcellular localization and distribution of DEV pUL51 by computer aided analysis, as well as indirect immunofluorescence (IIF) and transmission immunoelectron microscopy (TIEM) approaches in DEV-infected cells.

Results

The DEV UL51 gene product was identified as an approximate 34 kDa protein in DEV-infected cells analyzed by western blotting. Computer aided analysis suggested that DEV pUL51 is not targeted to the mitochondrial, extra-cellular or nucleus, but be targeted to the cytoplasmic in host cells, more specifically, palmitoylation of the pUL51 through the N-terminal cysteine at position 9 makes membrane association and Golgi localization possible. Using IIF analysis, we found that DEV pUL51 was first detected in a juxtanuclear region of DEV-infected cells at 9 h postinfection (p.i.), and then was detected widely distributed in the cytoplasm and especially was stronger in the juxtanuclear region from 12 to 60 h p.i. TIEM analysis revealed that DEV pUL51 was mainly associated with cytoplasmic virions and also with some membranous structure near the pUL51-specific immuno-labeling intracellular virion in the cytoplasmic vesicles; moreover, the pUL51 efficiently accumulated in the Golgi apparatus at first, and then was sent to the plasma membrane from the Golgi by some unknown mechanism.

Conclusion

In this work, we described the basic characteristics of pUL51 subcellular localization and distribution for the first time. From these results, we concluded that palmitoylation at the N-terminal cysteine, which is conserved in all alphaherpesvirus UL51 homologs, is required for its membrane association and Golgi localization, and the pUL51 mainly localized to the juxtanuclear region of DEV-infected cells, as well seemed to be incorporated into mature virions as a component of the tegument. The research will provide useful clues for DEV pUL51 functional analysis, and will be usefull for further understanding the localization properties of alphaherpesvirus UL51 homologs.

Identification and characterization of the duck enteritis virus UL51 gene

Compared to the UL51 gene of other alphaherpesviruses, the duck enteritis virus (DEV) UL51 gene contains ten conserved motifs and has a close evolutionary relationship with members of the genus Mardivirus. The DEV UL51 gene product was identified using a rabbit polyclonal antiserum raised against a 6-His-UL51 fusion protein expressed in Escherichia coli as a 34-kDa protein. Western blotting and RT-(real time) PCR analysis of DEV-infected cells showed that the protein was produced at the late stage of infection and that its production was highly dependent on viral DNA synthesis, suggesting that the gene should be classified as gamma2 class. Analysis of extracellular virions revealed that the protein was a component of extracellular mature DEV virions. Indirect immunofluorescence studies localized most of the protein to the juxtanuclear region. These results will provide a basis for further functional analysis of the gene.

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.

Intestinal mucosal immune response in ducklings following oral immunisation with an attenuated Duck enteritis virus vaccine

To investigate the intestinal mucosal immune responses in ducklings orally inoculated with attenuated Duck enteritis virus (DEV), the kinetics of the viral load, the specific humoral immune responses, and the distribution of immunoglobulin (Ig)A-secreting cells in the intestine were evaluated. Oral inoculation with attenuated DEV stimulated an IgA-dominant response in intestinal secretions and a IgY-dominant response in the serum. The dramatic increase in virus-specific mucosal IgA 15 days after inoculation was accompanied by reductions in the DEV intestinal load, suggesting that the IgA response has a role in controlling viral replication. The kinetics of virus-specific IgA production closely correlated with the presence of IgA+ plasma cells in the intestinal lamina propria.

Intestinal mucosal immune response against virulent duck enteritis virus infection in ducklings

Duck virus enteritis (DVE) is an acute and contagious herpes virus infection of duck, geese and swans with high morbidity and mortality. The development of specific mucosal immune system against duck enteritis virus (DEV) infection for ducks has been hindered by a lack of knowledge concerning the purification of immunoglobulin A (IgA) of duck. In the present work, the method for purification of duck immunoglobulin A was developed, and the induction of intestinal mucosal immune responses against DEV was studied by orally infected ducklings with virulent DEV. The results showed that a continuous increased DEV DNA levels were observed in blood and various organs examined of orally infected ducklings throughout the infection, which was accompanied by the development of infection in ducklings from mild progressed to severe pathological lesions. Furthermore, a marked increased level of DEV-specific IgA and IgG antibodies in bile, serum and the intestinal tract, as well as the density of IgA(+) cells in intestine were detected between 1 and 12days p.i., followed by a drastic reduction of the antibody levels and the density of IgA(+) cells at 15days p.i. The results indicate that the DVE infection can stimulate both IgA-dominated antibody immune responses in the intestinal tract, and IgG-dominated antibody systemic immunity in the serum of ducklings orally inoculated with virulent DEV. The severe lesions of the villus epithelial cells and the lymphoid organs can suppress the intestinal mucosal immune responses.

Immunohistochemical detection and localization of new type gosling viral enteritis virus in paraformaldehyde-fixed paraffin-embedded tissue

To determine the distribution and localization of new type gosling viral enteritis virus (NGVEV) in paraformaldehyde-fixed paraffin-embedded tissues of experimentally infected goslings, for the first time, an immunohistochemical (IHC) staining method was reported. Anti-NGVEV polyclonal serum was obtained from the rabbits immunized with purified NGVEV antigen, which was extracted by caprylic-ammonium sulphate method and purified through High-Q columns anion exchange chromatography. Three-day-old NGVEV-free goslings were orally inoculated with NGVEV-CN strain suspension as infection group and phosphate buffered saline solution (PBS) as control group, respectively. The tissues were collected at sequential time points between 0.5 and 720h post inoculation (PI), and prepared for IHC staining and ultra-structural observation. The positive immunoreactivity could be readily detected in the lymphoid and gastrointestinal organs of infected goslings as early as 48 h PI, in the liver, kidney, pancreas and myocardium from 72 h, and in the cerebrum and cerebellum from 96 h, while it was hardly detected in the respiratory organs at any time. The positive staining reaction could be detected in NGVEV-infected goslings until 600 h PI, and no positive staining cell could be observed in the controls. The highest levels of viral antigen were found in the bursa of Fabricius (BF), thymus, proventriculus, gizzard and intestine tract, moreover, the liver, kidney, spleen, myocardium and pancreas were intensively and widely stained. The target cells had a ubiquitous distribution, especially included the epithelial cells, endothelial cells, superficial and crypt mucosal cells, glandular cells, fibrocytes, macrophages and lymphocytes, which served as the principal sites for antigen localization. The ultra-structural observation by transmission electron microscope (TEM) further indicated that NGVEV particles could be widely detected in the lymphoid and digestive organs of infected goslings from 72 h PI onwards. This work may be useful not only for offering a possibility of routine diagnosis of NGVE, but also for better understanding of the pathogenesis of the disease.

Purification of anatid herpesvirus 1 particles by tangential-flow ultrafiltration and sucrose gradient ultracentrifugation

Anatid herpesvirus 1 (AHV-1) infection causes substantial economic losses to the world-wide waterfowl production. However, little is known about the efficient method used to study the purification of AHV-1 and the negative staining morphology of the purified virus particles. This lack of knowledge is one of the important factors that have affected the progress of research studies on AHV-1 molecular virology to such an extent that they are lagging far behind those on other members of the same family Herpesviridae. Therefore, an efficient method for purifying AHV-1 from cell-culture medium has been developed. Abundant AHV-1 particles, whose morphological features match those of herpesvirus, were obtained by using the following procedures: (1) conventional differential centrifugation for removal of debris after cell disruption, (2) tangential-flow ultrafiltration coupled with sucrose density gradient ultracentrifugation for isolation of the virus, and (3) conventional differential ultracentrifugation for virus concentration. The purified AHV-1 particles were subjected to transmission electron microscopy (TEM), infectivity and recovery tests, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), immunoblotting assay, and agar gel diffusion test (AGDT). The results of examinations revealed that purified AHV-1 particles were free of visible contamination or degradation. The purified AHV-1 particles were biologically active and were successful in initiating infection upon inoculation into susceptible duck embryo fibroblast. The procedures are reliable technically and feasible for purification of large volumes of viruses.

The pathogenesis of duck virus enteritis in experimentally infected ducks: a quantitative time-course study using TaqMan polymerase chain reaction

Duck virus enteritis is an acute and contagious herpesvirus infection of duck, geese and swans with high morbidity and mortality. The kinetics of viral DNA loads and immunohistochemical localization of virulent duck enteritis virus, as well as histopathological examination in various tissues of ducks following oral infection, were investigated. The time course for the appearance of viral antigen and tissue lesions in various tissues was coincident with the levels of duck enteritis virus at the various sites, suggesting that the levels of duck enteritis virus in systemic organs have a close correlation with the progression of disease. The abundance of target epithelial and lymphoid cells may contribute to the high levels of virus infection and replication in lymphoid and intestinal tissues.

Quantitative analysis of virulent duck enteritis virus loads in experimentally infected ducklings

To better understand the pathogenesis of duck virus enteritis (DVE), the levels of viral DNA in various tissues of ducklings during acute stage of virulent duck enteritis virus (DEV) infection were investigated by using quantitative real-time polymerase chain reaction. The results show that the viral levels of DEV in systemic organs have a close correlation with the progression of disease. The rapid dissemination and active replication of virulent DEV in multiple systemic organs at the early phase of acute infection accelerate the progression of disease. The levels of viral DNA increase sharply soon after developed clinical signs of disease, and the extent of increase and the magnitude of DEV DNA load in various tissues of ducklings after the exhibition of clinical signs may be a critical determinant of the outcome of DEV infection. The relatively high levels of DEV in bursa and small intestine tissues of dead ducklings most likely reflect the abundance of target epithelial and lymphoid cells in these tissues, which therefore play a key role in the pathogenesis of acute DVE and manifest as severe tissue lesions on the bursa and small intestine.

Application of an indirect immunofluorescent staining method for detection of Salmonella enteritidis in paraffin slices and antigen location in infected duck tissues

AIM: To detect Salmonella enteritidis (S. enteritidis) in paraffin slices and antigen location in infected duck tissues.

METHODS: Rabbits were immunized with purified bacillus to obtain S. enteritidis-specific antibody, which were then extracted by the caprylic-ammonium sulphate method, purified through High-Q columns. An indirect immuno-fluorescent staining method (IFA) was established to detect the S. enteritidis antigen in paraffin slices. S. enteritidis was detected in each organ tissue of ducklings experimentally infected with S. enteritidis.

RESULTS: The gland of Garder, heart, kidney, spleen, liver, brain, ileum, jejunum, bursa of Fabricius from S. enteritidis experimentally infected ducklings were positive or strongly positive, and the S. enteritidis antigen was mainly distributed in the infected cell cytoplasm.

CONCLUSION: IFA is an intuitionist, sensitive and specific method in detecting S. enteritidis antigen in paraffin wax slices, and it is a good method in diagnosis and antigen location of S. enteritidis. We also conclude that the gland of Garder, heart, kidney, spleen, liver, ileum, jejunum are target organs in S. enteritidis infections of duck, and S. enteritidis is an intracellular parasitic bacterium.