Analysis of the complete genome of Tembusu virus, a flavivirus isolated from ducks in China

Unveiling Amaryllidaceae alkaloids: from biosynthesis to antiviral potential - a review

Covering: 2017 to 2023 (now)Amaryllidaceae alkaloids (AAs) are a unique class of specialized metabolites containing heterocyclic nitrogen bridging that play a distinct role in higher plants. Irrespective of their diverse structures, most AAs are biosynthesized via intramolecular oxidative coupling. The complex organization of biosynthetic pathways is constantly enlightened by new insights owing to the advancement of natural product chemistry, synthetic organic chemistry, biochemistry, systems and synthetic biology tools and applications. These promote novel compound identification, trace-level metabolite quantification, synthesis, and characterization of enzymes engaged in AA catalysis, enabling the recognition of biosynthetic pathways. A complete understanding of the pathway benefits biotechnological applications in the long run. This review emphasizes the structural diversity of the AA specialized metabolites involved in biogenesis although the process is not entirely defined yet. Moreover, this work underscores the pivotal role of synthetic and enantioselective studies in justifying biosynthetic conclusions. Their prospective candidacy as lead constituents for antiviral drug discovery has also been established. However, a complete understanding of the pathway requires further interdisciplinary efforts in which antiviral studies address the structure-activity relationship. This review presents current knowledge on the topic.

Advancements in Research on Duck Tembusu Virus Infections

Duck Tembusu Virus (DTMUV) is a pathogen of the Flaviviridae family that causes infections in poultry, leading to significant economic losses in the duck farming industry in recent years. Ducks infected with this virus exhibit clinical symptoms such as decreased egg production and neurological disorders, along with serious consequences such as ovarian hemorrhage, organ enlargement, and necrosis. Variations in morbidity and mortality rates exist across different age groups of ducks. It is worth noting that DTMUV is not limited to ducks alone; it can also spread to other poultry such as chickens and geese, and antibodies related to DTMUV have even been found in duck farm workers, suggesting a potential risk of zoonotic transmission. This article provides a detailed overview of DTMUV research, delving into its genomic characteristics, vaccines, and the interplay with host immune responses. These in-depth research findings contribute to a more comprehensive understanding of the virus's transmission mechanism and pathogenic process, offering crucial scientific support for epidemic prevention and control.

CDK5-mediated rearrangement of vimentin during Duck Tembusu virus infection inhibits viral replication

Duck Tembusu virus (DTMUV) is a newly emerging pathogen that causes massive economic losses to the poultry industry in China and neighbouring countries. Vimentin, an intermediate filament protein, has been demonstrated to be involved in viral replication during infection. However, the specific role of vimentin in DTMUV replication has not been determined. In this study, we found that overexpression of vimentin in BHK-21 cells can inhibit DTMUV replication. Moreover, DTMUV replication was enhanced after vimentin expression was reduced in BHK-21 cells via small interfering RNA (siRNA). Further research indicated that DTMUV infection had no effect on the transcription or expression of vimentin. However, we found that DTMUV infection induced vimentin rearrangement, and the rearrangement of vimentin was subsequently confirmed to negatively modulate viral replication through the use of a vimentin network disrupting agent. Vimentin rearrangement is closely associated with its phosphorylation. Our experiments revealed that the phosphorylation of vimentin at Ser56 was promoted in the early stage of DTMUV infection. In addition, by inhibiting the phosphorylation of vimentin at Ser56 with a CDK5 inhibitor, vimentin rearrangement was suppressed, and DTMUV replication was significantly enhanced. These results indicated that DTMUV infection induced vimentin phosphorylation and rearrangement through CDK5, resulting in the inhibition of DTMUV replication. In summary, our study reveals a role for vimentin as a negative factor in the process of DTMUV replication, which helps to elucidate the function of cellular proteins in regulating DTMUV replication.

Bacillus subtilis expressing duck Tembusu virus E protein induces immune protection in ducklings

Duck Tembusu virus (DTMUV) is an infectious disease that emerged in China in 2010. It has caused serious economic losses to the poultry industry and may pose a threat to public health. We aimed to develop a new Bacillus subtilis (B. subtilis)-based oral vaccine to control DTMUV transmission among poultry; to this end, we constructed a B. subtilis strain that can secrete DTMUV E protein. Ducklings were orally immunized, and serum antibodies, mucosal antibodies, and splenic cytokines were detected. The results showed that, in addition to high levels of specific IgG, there were also high levels of specific secretory immunoglobulin A (sIgA) in ducklings orally treated with recombinant B. subtilis. In addition, the levels of IFN-γ, IL-2, IL-4, and IL-10 in spleens were significantly boosted by recombinant B. subtilis. Recombinant B. subtilis could effectively enhance ducklings resistance to DTMUV and significantly reduce viral load (p<0.01), along with pathological damage in the brain, heart, and spleen. This is the first study to apply a B. subtilis live-vector vaccine platform for DTMUV disease prevention and control, and our results suggest that B. subtilis expressing DTMUV E protein may be a candidate vaccine against DTMUV.

Development of a reverse transcription loop-mediated isothermal amplification based clustered regularly interspaced short palindromic repeats Cas12a assay for duck Tembusu virus

Duck Tembusu virus (DTMUV) is an emerging pathogen that poses a serious threat to the duck industry in China. Currently, polymerase chain reaction (PCR), quantitative PCR (qPCR) and reverse transcription loop-mediated isothermal amplification (RT-LAMP) are commonly used for DTMUV detection. However, these methods require complex steps and special equipment and easily cause false-positive results. Therefore, we urgently need to establish a simple, sensitive and specific method for the clinical field detection of DTMUV. In this study, we developed an RT-LAMP-based CRISPR-Cas12a assay targeting the C gene to detect DTMUV with a limited detection of 3 copies/μL. This assay was specific for DTMUV without cross-reaction with other common avian viruses and only required some simple pieces of equipment, such as a thermostat water bath and blue/UV light transilluminator. Furthermore, this assay showed 100% positive predictive agreement (PPA) and negative predictive agreement (NPA) relative to SYBR Green qPCR for DTMUV detection in 32 cloacal swabs and 22 tissue samples, supporting its application for clinical field detection.

Duck Tembusu virus induces incomplete autophagy via the ERK/mTOR and AMPK/mTOR signalling pathways to promote viral replication in neuronal cells

Duck Tembusu virus (DTMUV) is a neurotropic virus in the genus Flavivirus that causes massive economic losses to the poultry industry in China and neighbouring countries. Autophagy is pivotal in cellular responses to pathogens and in viral pathogenesis. However, little is known about the roles of autophagy in DTMUV replication and viral pathogenesis, especially in neuropathogenesis. In this study, mouse neuroblastoma cells (Neuro-2a) were used to establish a cell model of DTMUV infection. Our experiments indicated that DTMUV infection induced incomplete autophagy in Neuro-2a cells. Then, we used different autophagy regulators to alter the autophagy induced by DTMUV and found that incomplete autophagy promoted DTMUV replication. Furthermore, we showed that DTMUV infection activated the ERK and AMPK pathways, resulting in decreased phosphorylation of the autophagy repressor mTOR, subsequently leading to autophagic induction. In addition, we utilized ICR mice in an animal model of DTMUV infection to evaluate the autophagic responses in brain tissues and investigate the effects of autophagy on viral replication and tissue lesions. Our results confirmed that DTMUV induced incomplete autophagy in mouse brain tissues and that autophagy inducer treatment promoted DTMUV replication and aggravated DTMUV-induced lesions, whereas autophagy inhibitor treatment had the opposite effects. In summary, DTMUV infection induced incomplete autophagy through the ERK/mTOR and AMPK/mTOR signalling pathways to promote viral replication in mouse neuronal cells, and DTMUV-induced incomplete autophagy contributed to the neuropathogenesis of DTMUV.

Self-assembled nanoparticle with E protein domain III of DTMUV based on ferritin as carrier can induce a more comprehensive immune response and against DTMUV challenge in duck

Duck Tembusu virus (DTMUV) causes severe reduction in egg production and neurological symptoms in ducklings. Vaccination is the primary measure used to prevent DTMUV infections. In this study, self-assembled nanoparticles with the E protein domain III of DTMUV, using ferritin as a carrier (EDⅢ-RFNp), were prepared using a prokaryotic expression system. Ducks were intramuscularly vaccinated with EDⅢ-RFNp, EDⅢ protein, an inactivated vaccine HB strain (InV-HB), and PBS. At 0, 4, and 6 weeks post-primary vaccination, the EDIII protein-specific antibody titre, IL-4, and IFN-γ concentrations in serum were determined by ELISA, and neutralising antibodies titres in sera were determined by virus neutralising assay. Peripheral blood lymphocytes proliferation was determined by CCK-8 kit. Following challenge with the virulent DTMUV strain, the clinical signals and survival rate of the vaccinated ducks were recorded, and DTMUV RNA levels in the blood and tissues of the surviving ducks were determined by real-time quantitative RT-PCR. The near-spherical EDⅢ-RFNp nanoparticles with 13.29 ± 1.43 nm diameter were observed by transmission electron microscope. At 4 and 6 weeks post-primary vaccination, special and Virus neutralisation (VN) antibodies, lymphocyte proliferation (stimulator index, SI), and concentrations of IL-4 and IFN-γ in the EDⅢ-RFNp group were significantly higher than in the EDⅢ and PBS groups. In the DTMUV virulent strain challenge test, the EDⅢ-RFNp-vaccinated ducks showed milder clinical signs and higher survival rates than EDⅢ- and PBS-vaccinated ducks. The DTMUV RNA levels in the blood and tissues of EDⅢ-RFNp-vaccinated ducks were significantly lower than those in EDⅢ- and PBS-vaccinated ducks. Additionally, the EDⅢ protein-special and VN antibodies, SI value, and concentration of IL-4 and IFN-γ in the InV-HB group was significantly higher than that of the PBS group at 4 and 6 weeks post-primary vaccination. InV-HB provided more efficient protection than PBS based on a higher survival rate, milder signals, and lower levels of the DTMUV virus in the blood and tissues. These results indicated that EDⅢ-RFNp effectively protected ducks against DTMUV challenge and could be a vaccine candidate to prevent DTMUV infection.

Self-Assembled Nanoparticles with E Protein Domains I and II of Duck Tembusu Virus Can Induce a More Comprehensive Immune Response Against the Duck Tembusu Virus Challenge

Duck Tembusu virus (DTMUV) is a pathogenic flavivirus that causes a substantial drop in egg production and severe neurological disorders in domestic waterfowl. Self-assembled ferritin nanoparticles with E protein domains I and II (EDI-II) of DTMUV (EDI-II-RFNp) were prepared, and its morphology was observed. Two independent experiments were conducted. First, Cherry Valley ducks aged 14 days were vaccinated with EDI-II-RFNp, EDI-II, and phosphate buffered solution (PBS, pH 7.4), and special and virus neutralization (VN) antibodies, interleukin 4 (IL-4) and interferon gamma (IFN-γ) in serum, and lymphocyte proliferation were detected. Second, the vaccinated ducks with EDI-II-RFNp, EDI-II, and PBS were injected with virulent DTMUV, clinical signs at 7 days postinfection (dpi) were observed, and mRNA levels of DTMUV in the lungs, liver, and brain at 7 and 14 dpi were detected. The results showed near-spherical nanoparticles EDI-II-RFNp with a 16.46 ± 4.70 nm diameters. The levels of specific and VN antibodies, IL-4 and IFN-γ, and lymphocyte proliferation in the EDI-II-RFNp group were significantly higher than those in the EDI-II and PBS groups. In the DTMUV challenge test, clinical signs and mRNA levels in tissue were used to evaluate protection of EDI-II-RFNp. EDI-II-RFNp-vaccinated ducks showed milder clinical signs and lower levels of DTMUV RNA in the lungs, liver, and brain. These results indicate that EDI-II-RFNp effectively protects ducks against the DTMUV challenge and could be a vaccine candidate to provide an effective and safe method for preventing and controlling DTMUV infection.

Duck TRIM35 Promotes Tembusu Virus Replication by Interfering with RIG-I-Mediated Antiviral Signaling in Duck Embryo Fibroblasts

In China, the duck industry has been severely impacted by the newly emerging duck Tembusu virus (DTMUV). For DTMUV to successfully infect host cells, it employs several strategies that subvert the host's innate immune response. It has been found that several viral proteins encoded by DTMUV have strategically targeted the crucial molecules of the RIG-I-like Receptor (RLR) signaling pathway to antagonize host antiviral responses. However, it is not well known how the host proteins manipulated by DTMUV contribute to innate immune evasion. The present study reports that duck TRIM35 (duTRIM35) antagonizes DTMUV-induced innate immune responses by targeting duck RIG-I (duRIG-I) in duck embryo fibroblasts. A significant increase in duTRIM35 expression occurred during DTMUV infection. DuTRIM35 overexpression suppressed DTMUV-triggered expression of interferon beta (IFN-β) and interferon-stimulated genes (ISGs), promoting viral replication, whereas knockdown of duTRIM35 augments the innate immune response, reducing viral replication. Furthermore, duTRIM35 significantly impaired the IFN-β expression mediated by duRIG-I but not by other RLR signaling molecules. Mechanistically, duTRIM35 interfered with duRIG-I-duTRIM25 interaction and impeded duTRIM25-mediated duRIG-I ubiquitination by interacting with both duRIG-I and duTRIM25. Our findings indicate that duTRIM35 expression induced by DTMUV infection interfered with the duRIG-I-mediated antiviral response, illustrating a novel strategy in which DTMUV can evade the host's innate immunity. IMPORTANCE Duck Tembusu virus (DTMUV), an emerging flavivirus pathogen causing a substantial drop in egg production and severe neurological disorders in duck populations, has led to massive economic losses in the global duck industry. DTMUV has employed various strategies to subvert the host's innate immune response to establish a productive infection in host cells. In this study, we report that duck TRIM35 (duTRIM35) expression was upregulated upon DTMUV infection in vitro and in vivo, and its expression antagonized DTMUV-induced innate immune responses by targeting duck RIG-I (duRIG-I) in duck embryo fibroblasts. Further studies suggest that duTRIM35 interfered with duRIG-I-duTRIM25 interaction and impeded duTRIM25-mediated duRIG-I ubiquitination by interacting with both duRIG-I and duTRIM25. Together, these results revealed that duTRIM35 expression induced by DTMUV infection downregulated duRIG-I-mediated host antiviral response, which elucidated a novel strategy of DTMUV for innate immune evasion.

Tembusu Virus Nonstructural Protein 2B Antagonizes Type I Interferon Production by Targeting MAVS for Degradation

Tembusu virus (TMUV) is a newly emerged avian flavivirus that has caused severe egg-drop syndrome and fatal encephalitis in domestic ducks. It has spread widely throughout the main duck-producing areas in Asia, resulting in substantial economic losses to the duck industry. Previous studies have reported that TMUV has evolved several strategies to counteract the duck's innate immune responses to successfully establish infection in its host cells. However, the mechanisms underlying this phenomenon have not been elucidated. Here, we discovered that TMUV-encoded NS2B is a negative regulator of poly(I:C)-induced duck interferon-β (IFN-β) expression. Mechanistically, TMUV NS2B was found to interact specifically with the mitochondrial antiviral-signaling protein (duMAVS). Consequently, duMAVS was degraded through the K48-linked ubiquitination and proteasomal pathway, leading to the interruption of the RIG-I-like receptor (RLR) signaling. Further analyses also identified K321, K354, K398, and K411 as crucial residues for NS2B-mediated ubiquitination and degradation of duMAVS. Additionally, we demonstrated that NS2B functions by recruiting the E3 ubiquitin ligase duck membrane-associated RING-CH-type finger 5 (duMARCH5) to modify duMAVS via polyubiquitination, blocking the duMAVS-mediated innate immune response and promoting TMUV replication. Taken together, our findings revealed a novel mechanism by which TMUV evades the duck's antiviral innate immune responses. IMPORTANCE Tembusu virus (TMUV), an emerging pathogenic flavivirus, has spread to most duck farming areas in Asia since 2010, causing significant economic losses to the duck industry. Recently, TMUV has expanded its host range and may pose a potential threat to mammals, including humans. Understanding the interaction between TMUV and its host is essential for the development of effective vaccines and therapeutics. Here, we show that NS2B encoded by TMUV inhibits IFN production by interacting with duck MAVS (duMAVS) to mediate ubiquitination and proteasomal degradation. Further studies suggest that the E3 ubiquitin ligase duck membrane-associated RING-CH-type finger 5 (duMARCH5) is recruited by NS2B to mediate proteasomal degradation of duMAVS. As a result, the innate immune response triggered by the RIG-I-like receptor (RLR) is disrupted, facilitating viral replication. Overall, our results reveal a novel mechanism by which TMUV evades host innate immunity and provide new therapeutic strategies to prevent TMUV infection.

Structure and expression identification of Cherry Valley duck IRF8

Interferon regulatory factor 8 (IRF8) is also known as interferon (IFN) consensus sequence binding protein (ICSBP), which plays an important role in IFN signal transduction. In this study, we cloned the full-length coding sequence of Cherry Valley duck IRF8 (duIRF8) and analyzed its structure. In addition, we tested the distribution of IRF8 in the tissues of healthy Cherry Valley ducks, and the changes in IRF8 expression levels in the tissues after virus infection. The results show that the open reading frame (ORF) of IRF8 is 1293 bp, encodes 430 amino acids, and have 3 conserved domains: the N-terminal DBD domain, the C-terminal IAD domain, and the NLS domain. Besides, from the analysis of the phylogenetic tree, it can be known that the duIRF8 has the highest homology with the anser cygnoides, and has less homology with the fish. Analyzing the distribution level of IRF8 in the tissues, it is found that the expression level of IRF8 in the liver of Cherry Valley duck is the highest. However, after infection with duck Tambusu virus, novel duck reovirus, and duck plague virus, the expression of IRF8 in the spleen and brain all showed up-regulation. These data indicate that IRF8 is involved in the host's innate immune response against virus in Cherry Valley duck.

Antiviral and virucidal activities of lycorine on duck tembusu virus in vitro by blocking viral internalization and entry

Duck tembusu virus (DTMUV) was firstly identified in 2010 in China; since then, it has caused enormous economic loss to breeding industry. Great efforts have been made to develop drugs and vaccines against DTMUV. However, current available vaccines or anti-DTMUV drugs are consistently inefficient. Hence, various more broadly effective drugs have become important for the treatment of DTMUV infection; among these, lycorine, one of the important sources of active alkaloids, is a promising example. Nevertheless, it is not known whether lycorine has any antiviral activities against DTMUV. Therefore, the purpose of the present study is to investigate the anti-DTMUV abilities of lycorine. The cytotoxicity of lycorine was evaluated on BHK-21 cells by CCK-8 assay, and its antiviral effect against DTMUV was examined by real-time PCR assays, virus titer determination, Western blot and immunofluorescence (IFA) assays, respectively. Furthermore, the underlying mechanisms of the anti-DTMUV effects of lycorine were also investigated. The results indicated that the highest nontoxicity concentration of lycorine on BHK-21 cells was 5 µM. Lycorine possessed the antiviral ability against DTMUV on BHK-21 cells, as demonstrated by the reduction of virus titers and copy numbers in vitro. Western blot and IFA analysis showed the inhibitory effect of lycorine on DTMUV envelope (E) protein expression. Moreover, using time-of-addition assays, we found that lycorine displays its antivirus and virucidal activities through blocking viral internalization and entry in vitro. Taken together, our findings firstly demonstrate the antiviral activities of lycorine against DTMUV, suggesting that lycorine can be a potential drug for the treatment of DTMUV infection.

Amelioration of Beta Interferon Inhibition by NS4B Contributes to Attenuating Tembusu Virus Virulence in Ducks

Our previous studies reported that duck Tembusu virus nonstructural protein 2A (NS2A) is a major inhibitor of the IFNβ signaling pathway through competitively binding to STING with TBK1, leading to a reduction in TBK1 phosphorylation. Duck TMUV NS2B3 could cleave and bind STING to subvert the IFNβ signaling pathway. Here, we found that overexpression of duck TMUV NS4B could compete with TBK1 in binding to STING, reducing TBK1 phosphorylation and inhibiting the IFNβ signaling pathway by using the Dual-Glo^® Luciferase Assay System and the NanoBiT protein-protein interaction (PPI) assay. We further identified the E2, M3, G4, W5, K10 and D34 residues in NS4B that were important for its interaction with STING and its inhibition of IFNβ induction, which were subsequently introduced into a duck TMUV replicon and an infectious cDNA clone. We found that the NS4B M3A mutant enhanced RNA replication and exhibited significantly higher titer levels than WT at 48-72 hpi but significantly decreased mortality (80%) in duck embryos compared to WT (100%); the NS4B G4A and R36A mutants slightly reduced RNA replication but exhibited the same titer levels as WT. However, the NS4B R36A mutant did not attenuate the virulence in duck embryos, whereas the G4A mutant significantly decreased the mortality (70%) of duck embryos. In addition, the NS4B W5A mutant did not affect viral replication, whereas the D34A mutant slightly reduced RNA replication, and both mutants exhibited significantly lower titer levels than the WT and significantly decreased mortality (90% and 70%, respectively) in duck embryos. Hence, our findings provide new insight into the development of attenuated flaviviruses by targeting the disabling viral strategies used to evade the innate defense mechanisms.

Minocycline prevents primary duck neurons from duck Tembusu virus-induced death

Duck Tembusu virus (DTMUV), a neurotropic flavivirus, is a causative agent of severe neurological diseases in different birds. No approved vaccines or antiviral therapeutic treatments are available to date. The poultry industry experiences significant economic losses due to DTMUV infections. Minocycline is a second-generation semi-synthetic tetracycline analogue that is commonly used as an antimicrobial treatment. Experimental studies have indicated the successful protective effects of minocycline against neuronal cell death from neurodegenerative diseases and viral encephalitis. The aim of this study was to investigate the effects of minocycline on DTMUV infection in neurons. Primary duck neurons were treated with minocycline, which exhibited neuroprotective effects via anti-apoptotic function rather than through viral replication inhibition. Minocycline might serve as a potential effective drug in DTMUV infection.

Cloning, analysis, and anti-duck Tembusu virus innate immune response of Cherry Valley duck tripartite motif-containing 32

Tripartite motif-containing 32 (TRIM32) is an E3 ubiquitin ligase with multiple functions. In this study, we amplified TRIM32 gene from the Cherry Valley duck, and its cDNA sequence contained an open reading frame of 1,950 bp that encodes 649 amino acids. Duck TRIM32 (duTRIM32) mRNA was expressed in all tissues tested. A series of immune-related genes that were induced by viral infection, including interferon alfa, IL-1β, retinoic acid–inducible gene-I, Mx, and OAS, were regulated by duTRIM32 expression. DuTRIM32 overexpression inhibits duck Tembusu virus (DTMUV) replication in the early stages of viral infection. Knockdown of duTRIM32 expression by siRNA reduced the ability of duck embryo fibroblast cells to mount a type Ⅰ interferon response to DTMUV. Therefore, our results suggest that the duTRIM32-mediated signal pathway plays an essential role in DTMUV infection-induced innate immune response.

Quantitative Proteomic Analysis of Duck Embryo Fibroblasts Infected With Novel Duck Reovirus

The novel duck reovirus (NDRV) can cause hemorrhage and necrosis on the spleen of Pekin ducks; this disease has resulted in great economic losses to the duck industry. However, the molecular pathogenesis of NDRV remains poorly understood. In the current study, the quantitative proteomic analysis of NDRV-infected duck embryo fibroblasts was performed to explore the cellular protein changes in response to viral infection through iTRAQ coupled with the liquid chromatography (LC)-tandem mass spectrometry (MS/MS) method. A total of 6,137 proteins were obtained in cell samples at 24 h post-infection. Of these, 179 differentially expressed proteins (DEPs) were identified (cutoff set to 1.5-fold change), including 89 upregulated and 90 downregulated proteins. Bioinformatics analysis showed that DEPs can be divided into the cellular component, molecular function, and biological process; they were mainly involved in signal transduction, infectious diseases, cell growth and death, and the immune system. The subcellular localization of most proteins was in the cytoplasm. Importantly, the expressions of signal transducer and activator of transcription 1 (STAT1) and various interferon-stimulated genes (ISGs) were upregulated after NDRV infection. The mRNA transcripts of some ISGs were consistent with proteomic data, showing an increased trend. Results of our study suggested that NDRV infection can elicit strong expression changes of cellular proteins and activate the expression of ISGs from the point of quantitative proteomic analysis. The study provides a new insight into the understanding of NDRV pathogenesis.

Interleukin-2 shows high adjuvanticity for an inactivated vaccine against duck Tembusu virus disease

Currently, the widely used vaccine against duck Tembusu virus (DTMUV) disease is inactivated vaccine which, however, facing the limits of large inoculation dose, short immunization period, and incomplete effectiveness. Access to efficient adjuvants aiding for DTMUV inactivated vaccine seems to be of critical importance. Interleukin-2 (IL-2) was reported to induce a persistent expansion of effector T cells and could be a promising molecular adjuvant for many kinds of vaccines. In this study, the efficacy of duck interleukin (dIL)-2 as an adjuvant for a DTMUV inactivated vaccine was evaluated. Fifty-five Pekin ducks were divided into 5 groups and intramuscularly administered with 5 batches of vaccines at 42 D (A: DTUMV + dIL-2; B: 1/2DTUMV + dIL-2; C: DTUMV; D: 1/2DTUMV and E: PBS), respectively, and received the second vaccination 2 wk later. Fifty-six days after immunization, 6 ducks from each group were randomly selected to conduct a challenge protection test. Antibody titers and cytokine responses were detected to assess humoral and cellular immune responses in serum of inoculated ducks by hemagglutination inhibition and ELISA, respectively; virus isolation and RT-PCR method were used in immunity protective test. Our results showed that dIL-2 exerted an enhanced effect on the vaccine while reducing the dose of inoculated antigen highlighting high adjuvanticity of IL-2. The vaccines supplemented with IL-2 induced a higher level of antibodies and higher percentage of inhibition values than inactivated vaccines without IL-2 to a significant extent. The production level of IFN-α, IFN-γ, and IL-6 genes were elevated, enhancing both humoral and cellular responses. Furthermore, it provided higher protection after virus challenge. Therefore, IL-2 can be considered as a potential adjuvant for inactivated vaccine against DTMUV disease.

Occurrence and Molecular Characteristics of Mcr-1-Positive Escherichia coli from Healthy Meat Ducks in Shandong Province of China

Simple Summary

Colistin has been used as a growth promotant in livestock feed for many years. To date, there are few reports about the prevalence and molecular characteristics of fecal Escherichia coli bearing mcr-1 in the meat ducks. In this study, among 120 fecal Escherichia coli strains isolated from healthy meat ducks, a total of nine mcr-1-containing E. coli strains were identified and two were identified as extra-intestinal pathogenic E. coli. The 9 mcr-1-bearing E. coli isolates were clonally unrelated, carried two different genetic contexts of mcr-1, and the colistin-resistant phenotype of them was successfully transferred to the recipient strains. These results highlight that healthy meat duck is a potential reservoir for multidrug resistant mcr-1-containing E. coli strains.

Abstract

Colistin has been used as a growth promotant in livestock feed for many years. In China, mcr-1-positive Escherichia coli strains have been isolated from humans, chickens, and pigs. To date, there are few reports about the prevalence and molecular characteristics of fecal E. coli bearing mcr-1 in the meat ducks. In this study, the prevalence of mcr-1 gene was investigated among 120 fecal E. coli strains isolated from healthy meat ducks in Shandong province of China between October 2017 and February 2018. A total of nine mcr-1-containing E. coli strains were identified and two were identified as extra-intestinal pathogenic E. coli (ExPEC) among them. The clonal relationship of the nine E. coli strains was determined by multilocus sequencing typing (MLST) and pulsed field gel electrophoresis (PFGE), and the results indicated that all mcr-1-carrying isolates were clonally unrelated. Two different genetic contexts of mcr-1 were identified among these isolates. Colistin-resistant phenotype of all the isolates was successfully transferred to the recipient strains by conjugation experiments and seven transconjugants carried a single plasmid. The mcr-1 was located on three replicon plasmids: IncI2 (n = 4), IncFII (n = 2) and IncN (n = 1). Complete sequence analysis of a representative plasmid pTA9 revealed that it was strikingly similar with plasmid pMCR1-IncI2 of E. coli, plasmid pHNSHP45 of E. coli, and plasmid pWF-5-19C of Cronobacter sakazakii, implying that pTA9-like plasmids may be epidemic plasmids that mediate the spread of mcr-1 among Enterobacteriaceae. These results highlight that healthy meat duck is a potential reservoir for multidrug resistant mcr-1-containing E. coli strains.

Innate immune responses to duck Tembusu virus infection

The disease caused by duck Tembusu virus (DTMUV) is characterized by severe egg-drop in laying ducks. Currently, the disease has spread to most duck-raising areas in China, leading to great economic losses in the duck industry. In the recent years, DTMUV has raised some concerns, because of its expanding host range and increasing pathogenicity, as well as the potential threat to public health. Innate immunity is crucial for defending against invading pathogens in the early stages of infection. Recently, studies on the interaction between DTMUV and host innate immune response have made great progress. In the review, we provide an overview of DTMUV and summarize current advances in our understanding of the interaction between DTMUV and innate immunity, including the host innate immune responses to DTMUV infection through pattern recognition receptors (PRRs), signaling transducer molecules, interferon-stimulated genes (ISGs), and the immune evasion strategies employed by DTMUV. The aim of the review is to gain an in-depth understanding of DTMUV pathogenesis to facilitate future studies.

Immunogenicity and protective efficacy of an EB66® cell culture-derived duck Tembusu virus vaccine

The avian EB66^® cell line, derived from duck embryonic stem cells, has been widely used for producing human and animal therapeutic proteins and vaccines. In current study we evaluated the potential use of EB66^® cell line in a cell culture-derived duck Tembusu virus (DTMUV) vaccine development. After optimizing the growth conditions of DTMUV HB strain in EB66^® cells, we successfully generated three batches of viruses with ELD₅₀ titres of 10^5.9/0.1 ml, 10^5.3/0.1 ml and 10^5.5/0.1 ml, respectively, for using in the preparation of inactivated vaccines. The immunogenicity and protective efficacy of these EB66^® cells-derived inactivated vaccines were examined in ducks. Results indicated that all three batches of vaccines induced haemagglutination-inhibition (HI) antibody response in immunized birds at 2 weeks after a single immunization. Immunized ducks and ducklings were protected against a virulent challenge at 4 weeks after a booster immunization. The duration of immunity was for 3-4 months after a booster immunization. These results demonstrated the feasibility of using EB66^® cell line to grow up DTMUV for vaccine preparation. RESEARCH HIGHLIGHTS Duck Tembusu virus can be propagated in EB66^® cells. EB66^® cell-derived inactivated DTMUV vaccines are immunogenic and can provide protection against a virulent challenge. A long-lasting immunity is induced after a booster immunization.

Molecular cloning and functional characterization of duck TYK2

Tyrosine kinase 2 (TYK2), a member of Janus kinase family, has been identified as a crucial protein in signal transduction initiated by interferons or interleukins in mammals. However, the function of avian TYK2 in innate immune response remains largely unknown. In this study, the full-length duck TYK2 (duTYK2) cDNA was cloned for the first time, which encoded a putative protein of 1187 amino acid residues and showed the high sequence similarity with bald eagle, crested ibis, and white-tailed tropicbird TYK2s. The duTYK2 was widely expressed in all examined tissues of healthy ducks and showed diffuse cytoplasmic localization in duck embryo fibroblasts (DEFs). Overexpression of duTYK2 significantly enhanced ISRE promoter activity and induced the expression of viperin, PKR, 2',5'-OAS, Mx and ZAP in DEFs. The C-terminal kinase domain of duTYK2 is essential for duTYK2-mediated ISRE promoter activation. Furthermore, knockdown of duTYK2 dramatically decreased duck Tembusu virus (DTMUV)-, duck enteritis virus (DEV)-, poly(I:C)- or poly(dA:dT)-induced ISRE promoter activation. Additionally, duTYK2 expression exhibited antiviral activity against DTMUV. These results indicated that duTYK2 played a critical role in duck antiviral innate immunity.

Evaluation of immunogenicity and protective efficacy of a CpG-adjuvanted DNA vaccine against Tembusu virus

Tembusu virus (TMUV) is a contagious pathogen of waterfowl including ducks and geese, which causes symptoms of high fever, loss of appetite and reduced egg production. The development of an effective vaccine is important for the prevention and control of the disease. We evaluated a DNA vaccine based on a recombinant pre-membrane (prM) and envelope (E) protein, using CpG oligodeoxynucleotide (ODN) as an adjuvanted, and tested it for protection efficacy. BHK21 cells were transfected with the recombinant plasmid pVAX1-prM/E-CpG, and the antigenicity of the expressed protein was detected using an indirect immunofluorescence assay (IFA) and western blot assay. One-day-old ducklings were intramuscularly injected with 200 μg doses of pVAX1-prM/E-CpG or pVAX1-CpG, or PBS at ten day intervals. The neutralizing antibodies and cell-mediated immune responses elicited by the DNA vaccine were detected using serum neutralization tests (SNTs) and ELISAs. At 20 days old, the ducks were challenged with 10³EID50 doses of TMUV SD/02 strain and observed for 15 days post challenge. After the second DNA vaccination and during the monitoring period, the levels of TMUV neutralizing antibodies increased in the pVAX1-prM/E-CpG vaccinated ducks. Vaccination with pVAX1-prM/E-CpG resulted in 100.0% protection of the ducks, whereas approximately 40% of ducks vaccinated with pVAX-CpG or PBS manifested clinical symptoms. Expressions of IFN-γ and IL-6 in the pVAX1-prM/E-CpG group were significantly increased (p <  0.01) compared with the control groups during the entire experimental period. The results revealed that a vaccine co-expressing prM and E, and using a CpG-ODN motif as an adjuvant, could elicit effective neutralizing antibody titers and provide efficient protection to ducks against TMUV infection.

Attenuation of duck Tembusu virus ZJSBL01 strain following serial passage in BHK-21 cells supplied with 5-Fluorouracil

Duck Tembusu virus (DTMUV) is a new pathogen that produces an acute and potent disease in ducks which has caused serious economic losses in China. In this study, a virulent strain of DTMUV, designated as ZJSBL01, was attenuated by serial passages in BHK-21 cells supplied with 5-Fluorouracil (5-FU) for 50 passages to induce mutation and attenuation. Growth kinetics of different passages of ZJSBL01 strain in BHK-21 cells show that these viruses have similar replication characteristics. The virus was highly attenuated after 40 passages in BHK-21 cells supplied with 5-FU, based on mortality, morbidity, and viral load in inoculated Sheldrake ducklings. In addition, all of the ducklings immunized with ZJSBL01-P40, the virus obtained at passage 40 of ZJSBL01, showed seroconversion on day 14 post inoculation. Moreover, P40 did not cause clinical symptom for layding ducks. Immunization with ZJSBL01-P40 could provide effective protection against the virulent parental ZJSBL01 strain. Seventeen amino acid substitutions were observed in the polyprotein of ZJSBL01-P40 compared with parental ZJSBL01. These results indicate that ZJSBL01-P40 may be a live vaccine candidate for prevention of DTMUV-disease.

Pathogenicity comparison of duck Tembusu virus in different aged Cherry Valley breeding ducks

Background

Although several studies have revealed that the sensitivity of ducklings to duck Tembusu virus (DTMUV) was related to age, however, DTMUV was originally isolated from egg-laying ducks, and the ovary was the target organ of this virus. Cherry Valley breeding ducks aged 15- and 55-week-old (they are reserve breeding ducks and the normal egg-laying breeding ducks, respectively) were infected with DTMUV, using intramuscular injection, to study the effect of age-related difference on the pathogenicity of DTMUV in breeding ducks.

Results

Examinations of clinical symptoms, gross and microscopic lesions, viral loads, cytokines and serum neutralizing antibodies were performed. Results showed that obvious clinical symptoms, such as depression, ruffled feathers, ataxia and egg-laying drop were observed in the 55-week-old laying ducks, with five ducks dying at 5–7 days post infection (dpi). The 15-week-old ducks showed slight symptoms during infection. Gross lesions were severe and characterized by the congestion, hemorrhage and swelling of some organs in the 55-week-old ducks, including the hemorrhage of endocardium, hepatomegaly, splenomegaly, oviduct hemorrhage, hyperemia and deformation of the ovary. Mild endocardial hemorrhage and hepatosplenomegaly were observed in the 15-week-old ducks. Similarly, there was a significant difference in microscopic lesions between the two groups. The older ducks displayed severe microscopic lesions, specifically in the hemorrhage, interstitial inflammatory cell infiltration of the endocardium, typical viral encephalitis and hemorrhage in the ovary. But on the whole, the 15-week-old ducks showed milder lesions. Viral loads in tissues of the older group were significantly higher than those of the younger group. The levels of interferon (IFN)-γ, interleukin (IL)-2 and neutralizing antibody in the 15-week-old ducks were higher than in the 55-week-old ducks at the early stage of the DTMUV infection, suggesting the immune response in the younger ducks to DTMUV was stronger than in the older ducks.

Conclusions

These results demonstrated that age-related differences in susceptibility to DTMUV in breeding ducks was significant, with 55-week-old egg-laying ducks being more susceptible to DTMUV than 15-week-old reserve breeding ducks.

Development of an attenuated live vaccine candidate of duck Tembusu virus strain

Infection with duck Tembusu virus (DTMUV) can cause large economic losses to the duck-rearing industry in China. In this study, we isolated a virulent strain of DTMUV (SDS) from sparrows near a duck farm and attenuated it via serially passaging (alternately for 100 passages) in specific pathogen-free chicken and duck embryos. We attenuated the virus after the 60th passage (SDS-60), based on the production of embryos that were free of visible lesions and still alive. The 70th adapted strain (SDS-70), obtained with a virus titer of 10^-2.46 EID₅₀ was chosen to be the live attenuated vaccine. After immunizing ducklings with the SDS-70 strain, they obtained 100% protection against infection by the SDS-10 virulent strain. Our data demonstrate that the vaccine can protect ducks from becoming infected with TMUV. Our study also shows that this newly developed attenuated vaccine candidate provides excellent immunogenicity, is safe, and has the potential to control DTMUV infections in ducks.

Identification of Glucose-Regulated Protein 78 (GRP78) as a Receptor in BHK-21 Cells for Duck Tembusu Virus Infection

Since 2010, outbreak and spread of tembusu virus (TMUV) caused huge losses to the breeding industry of waterfowl in several provinces of China. In this study, we identify the glucose-regulated protein 78 (GRP78) as a receptor in BHK-21 cells for duck TMUV infection. Using cell membrane from BHK-21 cells, a TMUV-binding protein of approximately 70 kDa was observed by viral overlay protein binding assay (VOPBA). LC-MS/MS analysis and co-immunoprecipitation identified GRP78 as a protein interacting with TMUV. Antibody against GRP78 inhibited the binding of TMUV to the cell surface of BHK-21 cells. Indirect immunofluorescence studies showed the colocalization of GRP78 with TMUV in virus-infected BHK-21 cells. We found that GRP78 over-expression increased TMUV infection, whereas GRP78 knockdown by using a specific small interfering RNA inhibited TMUV infection in BHK-21 cells. Taken together, our results indicate that GRP78 is a novel host factor involved in TMUV entry.

Oral Vaccination with a DNA Vaccine Encoding Capsid Protein of Duck Tembusu Virus Induces Protection Immunity

The emergence of duck tembusu virus (DTMUV), a new member of the Flavivirus genus, has caused great economical loss in the poultry industry in China. Since the outbreak and spread of DTMUV is hard to control in a clinical setting, an efficient and low-cost oral delivery DNA vaccine SL7207 (pVAX1-C) based on the capsid protein of DTMUV was developed and evaluated in this study. The antigen capsid protein was expressed from the DNA vaccine SL7207 (pVAX1-C), both in vitro and in vivo. The humoral and cellular immune responses in vivo were observed after oral immunization with the SL7207 (pVAX1-C) DNA vaccine. High titers of the specific antibody against the capsid protein and the neutralizing antibody against the DTMUV virus were both detected after inoculation. The ducks were efficiently protected from lethal DTMUV exposure by the SL7207 (pVAX1-C) vaccine in this experiment. Taken together, we demonstrated that the capsid protein of DTMUV possesses a strong immunogenicity against the DTMUV infection. Moreover, an oral delivery of the DNA vaccine SL7207 (pVAX1-C) utilizing Salmonella SL7207 was an efficient way to protect the ducks against DTMUV infection and provides an economic and fast vaccine delivery strategy for a large scale clinical use.

Proteome analysis of Duck Tembusu virus (DTMUV)-infected BHK-21 cells

Duck Tembusu virus (DTMUV) is a newly emerging pathogenic flavivirus that has caused huge economic losses to the duck industry in China since 2010. Moreover, the infection has spread rapidly, posing a potential public health concern. In this study, iTRAQ approach was first used to quantitatively identify differentially expressed cellular proteins in DTMUV-infected BHK-21 cells which are usually employed to produce veterinary vaccines for DTMUV, as well as other flaviviruses by serial passage. We identified 192 differentially expressed cellular proteins, including 11 upregulated and eight downregulated proteins at 24 h postinfection (hpi), as well as 25 upregulated and 151 downregulated proteins at 48 hpi, of which TLR9, DDX3X, and DDX5 may play important roles in virus propagation. Further, DDX3X could inhibit DTMUV replication by modulating the IFN pathway via TBK1. In conclusion, our study is the first to analyze the protein profile of DTMUV-infected cells by quantitative proteomics. We believe that our findings provide valuable information in better understanding the host response to DTMUV infection. These findings are particularly important in the development of vaccine-based strategies.

An updated review of avian-origin Tembusu virus: a newly emerging avian Flavivirus

Tembusu virus (TMUV, genus Flavivirus, family Flaviviridae) was first isolated in 1955 from Culex tritaeniorhynchus mosquitoes in Kuala Lumpur, Malaysia. In April 2010, duck TMUV was first identified as the causative agent of egg-drop syndrome, characterized by a substantial decrease in egg laying and depression, growth retardation and neurological signs or death in infected egg-laying and breeder ducks, in the People's Republic of China. Since 2010, duck TMUV has spread to most of the duck-producing regions in China, including many of the coastal provinces, neighbouring regions and certain Southeast Asia areas (i.e. Thailand and Malaysia). This review describes the current understanding of the genome characteristics, host range, transmission, epidemiology, phylogenetic and immune evasion of avian-origin TMUV and the innate immune response of the host.

Significant inhibition of Tembusu virus envelope and NS5 gene using an adenovirus-mediated short hairpin RNA delivery system

Tembusu virus (TMUV) is a mosquito-borne flavivirus, which was first isolated in the tropics during the 1970s. Recently, a disease characterized by ovarian haemorrhage and neurological symptoms was observed in ducks in China, which threatens poultry production. However, there is no suitable vaccination strategy or effective antiviral drugs to combat TMUV infections. Consequently, there is an urgent need to develop a new anti-TMUV therapy. In this study, we report an efficient short hairpin RNA (shRNA) delivery strategy for the inhibition of TMUV production using an adenovirus vector system. Using specifically designed shRNAs based on the E and NS5 protein genes of TMUV, the vector-expressed viral genes, TMUV RNA replication and infectious virus production were downregulated at different levels in Vero cells, where the shRNA (NS52) was highly effective in inhibiting TMUV. Using the human adenovirus type 5 shRNA delivery system, the recombinant adenovirus (rAd-NS52) inhibited TMUV multiplication with high efficiency. Furthermore, the significant dose-dependent inhibition of viral RNA copies induced by rAd-NS52 was found in TMUV-infected cells, which could last for at least 96h post infection. Our results indicated that the adenovirus-mediated delivery of shRNAs could play an active role in future TMUV antiviral therapeutics.

Identification of one B-cell epitope from NS1 protein of duck Tembusu virus with monoclonal antibodies

This study describes the identification of one linear B-cell epitope on TMUV NS1 protein with monoclonal antibody (mAb) 3G2 by indirect enzyme-linked immunosorbent assay (ELISA). In this study, NS1 protein was expressed in prokaryotic expression system and purified. One mAb against NS1 protein was generated from Balb/c mice immunized with recombinant protein NS1. A set of 35 partially-overlapping polypeptides covering the entire NS1 protein was expressed with PGEX-6P-1 vector and screened with mAb 3G2. One polypeptide against the mAb was acquired and identified by indirect ELISA and western-blot. To map the epitope accurately, one or two amino acid residues were removed from the carboxy and amino terminal of polypeptide sequentially. A series of truncated oligopeptides were expressed and purified. The minimal determinant of the linear B cell epitope was recognized and identified with mAb 3G2. The accurate linear B-cell epitope was ²⁶⁹DEKEIV²⁷⁴ located in NS1 protein. Furthermore, sequence alignment showed that the epitope was highly conserved and specific among TMUV strains and other flavivirus respectively. The linear B-cell epitope of TMUV NS1 protein could benefit the development of new vaccines and diagnostic assays.

Identification of IFITM1 and IFITM3 in Goose: Gene Structure, Expression Patterns, and Immune Reponses against Tembusu Virus Infection

As interferon-stimulated genes (ISGs), interferon-inducible transmembrane proteins 1 and 3 (IFITM1 and IFITM3) can effectively inhibit the replication of multiple viruses. Here, goose IFITM1 and IFITM3 were cloned and identified for the first time. The two proteins share the same topological structure and several important sites critical for the antiviral functions in other species are conserved in the goose. Goose IFITM1 and IFITM3 are most closely related to their respective orthologs in ducks; these proteins exhibited high mRNA transcript levels in immune-related tissues, including the thymus, bursa of Fabricius, and Harderian gland, compared to other tissues. Moreover, goose IFITM1 was highly constitutively expressed in gastrointestinal tract tissues, while goose IFITM3 was expressed in respiratory organs. Furthermore, goose IFITM3 was activated in goose peripheral blood mononuclear cells (PBMCs) infected with Tembusu virus (TMUV) or treated with Toll-like receptors (TLRs) agonists, while only the R848 and Poly (I:C) agonists induced significant upregulation of goose IFITM1. Furthermore, goose IFITM1 and IFITM3 were upregulated in the sampled tissues, to some extent, after TMUV infection. Notably, significant upregulation of goose IFITM1 and IFITM3 was detected in the cecum and cecal tonsil, where TMUV was primarily distributed. These data provide new insights into the immune effectors in geese and promote our understanding of the role of IFITM1 and IFITM3 in the defense against TMUV.

Comparison of four molecular assays for the detection of Tembusu virus

Tembusu virus (TMUV) belongs to the genus Flavivirus that may cause severe egg drop in ducks. In order to evaluate the most efficient TMUV detection method, the performances of a conventional RT-PCR (C-RT-PCR), a semi-nested PCR (SN-RT-PCR), a reverse-transcriptase real-time quantitative PCR (Q-RT-PCR), and a reverse-transcription loop-mediated isothermal amplification (RT-LAMP) targeting the TMUV virus-specific NS5 gene were examined. In order to compare the sensitivity of these four techniques, two templates were used: (1) plasmid DNA that contained a partial region of the NS5 gene and (2) genomic RNA from TMUV-positive cell culture supernatants. The sensitivities using plasmid DNA detection by C-RT-PCR, SN-RT-PCR, Q-RT-PCR, and RT-LAMP were 2 × 10(4) copies/μL, 20 copies/μL, 2 copies/μL, and 20 copies/μL, respectively. The sensitivities using genomic RNA for the C-RT-PCR, SN-RT-PCR, Q-RT-PCR, and RT-LAMP were 100 pg/tube, 100, 10, and 100 fg/tube, respectively. All evaluated assays were specific for TMUV detection. The TMUV-specific RNA was detected in cloacal swabs from experimentally infected ducks using these four methods with different rates (52-92%), but not in the control (non-inoculated) samples. The sensitivities of RT-PCR, SN-RT-PCR, Q-RT-PCR, and RT-LAMP performed with cloacal swabs collected from suspected TMUV infected ducks within 2 weeks of severe egg-drop were 38/69 (55.1%), 52/69 (75.4%), 57/69 (82.6%), and 55/69 (79.7%), respectively. In conclusion, both RT-LAMP and Q-RT-PCR can provide a rapid diagnosis of TMUV infection, but RT-LAMP is more useful in TMUV field situations or poorly equipped laboratories.

Identification of heat shock protein A9 as a Tembusu virus binding protein on DF-1 cells

This study attempts to identify receptor elements for Tembusu virus (TMUV) on DF-1 cells. Using co-immunoprecipitation and virus overlay protein binding assays, we identified a TMUV-binding protein of approximately 70-kDa on DF-1 cell membranes. Mass spectroscopy identified the protein to be heat shock protein (HSP) A9, which was reconfirmed by an anti-HSPA9 antibody. Indirect immunofluorescence demonstrated a significant degree of colocalization between HSPA9 and TMUV on cell surface. Additionally, an antibody against HSPA9 could inhibit TMUV infection in DF-1 cells in a dose-dependent manner. These results might suggest that HSPA9 is a putative receptor for TMUV.

Serological evidence of widespread West Nile virus and Japanese encephalitis virus infection in native domestic ducks (Anas platyrhynchos var domesticus) in Kuttanad region, Kerala, India

Birds can act as reservoirs of West Nile virus (WNV) with a key role in its epidemiology. WNV lineage 1 associated fatal cases of human encephalitis in 2011 and acute flaccid paralysis in 2013 were reported in Alappuzha district, Kerala, India. But no information is available on WNV circulation in domestic ducks, which are abundant, cohabit with humans and occupy wetlands and water bodies in the region. To determine the extent of WNV infection, we investigated 209 sera, 250 oral and 350 cloacal swab samples from local Chara and Chemballi domestic ducks (Anas platyrhynchos var domesticus) in the districts of Alappuzha, Kottayam, Kollam and Pathanamthitta collected during January and March 2015. The serum samples were tested for WNV antibodies first by a competition ELISA and then by a micro virus neutralization test (micro-VNT), while oral and cloacal swabs were subjected to WNV real-time RT-PCR. Ninety five ducks showed evidence of flavivirus antibodies by ELISA. End point neutralizing antibody titre against WNV and Japanese encephalitis virus (JEV) revealed WNV specific antibodies in 24 (11.5%) ducks in 3 districts, JEV specific antibodies in 21 (10%) ducks in 2 districts and flavivirus specific antibodies in 19 (9%) ducks. However, no WNV genomic RNA could be detected. The results of this study demonstrate evidence of widespread WNV and JEV infection in domestic ducks in Kuttanad region, Kerala with a higher seroprevalence to WNV than JEV. Additionally, it highlights the utility of domestic ducks as a surveillance tool to detect WNV/JEV circulation in a region.

Isolation and Characterization of a Novel Tembusu Virus Circulating in Muscovy Ducks in South China

Duck Tembusu virus (DTMUV) is an infectious pathogen that can cause epidemics in egg-laying ducks. Here, we isolated and characterized a DTMUV, designated GDLH01, thought to be responsible for the noticeable egg drop in Muscovy duck flocks in South China since 2011. The genome sequence of GDLH01 shared 97-99% homology with other avian-origin Tembusu viruses, and 99.5% homology with the mosquito-borne strain SDMS recently reported in China. Phylogenetic analysis based on the nucleotide sequence of the entire open reading frame confirmed that the isolate was of avian origin and closely related to a mosquito-borne strain. Our findings characterize a novel Tembusu virus circulating in Muscovy ducks in South China and emphasize the importance of reinforcing biosecurity measures and developing vaccines to prevent the spread of this viral pathogen.

Advanced uracil DNA glycosylase-supplemented real-time reverse transcription loop-mediated isothermal amplification (UDG-rRT-LAMP) method for universal and specific detection of Tembusu virus

Tembusu virus (TMUV) is a mosquito-borne flavivirus which threatens both poultry production and public health. In this study we developed a complete open reading frame alignment-based rRT-LAMP method for the universal detection of TUMV. To prevent false-positive results, the reaction was supplemented with uracil DNA glycosylase (UDG) to eliminate carryover contamination. The detection limit of the newly developed UDG-rRT-LAMP for TMUV was as low as 100 copies/reaction of viral RNA and 1 × 10^0.89 − 1 × 10^1.55 tissue culture infectious dose/100 μL of viruses. There were no cross-reactions with other viruses, and the reproducibility of the assay was confirmed by intra- and inter-assay tests with variability ranging from 0.22–3.33%. The new UDG-rRT-LAMP method for TMUV produced the same results as viral isolation combined with RT-PCR as the “gold standard” in 96.88% of cases for 81 clinical samples from subjects with suspected TMUV infection. The addition of UDG can eliminate as much as 1 × 10⁻¹⁶ g/reaction of contaminants, which can significantly reduce the likelihood of false-positive results during the rRT-LAMP reaction. Our result indicated that our UDG-rRT-LAMP is a rapid, sensitive, specific, and reliable method that can effectively prevent carryover contamination in the detection of TMUV.

Development of a PCR-Based Reverse Genetics System for an Attenuated Duck Tembusu Virus Strain

The infectious disease caused by the duck Tembusu virus (DTMUV) has resulted in massive economic losses to the Chinese duck industry in China since 2010. Research on the molecular basis of DTMUV pathogenicity has been hampered by the lack of a reliable reverse genetics system for this virus. Here we developed a PCR-based reverse genetics system with high fidelity for the attenuated DTMUV strain FX2010-180P. The rescued virus was characterized by using both indirect immunofluorescence assays (IFA) and whole genome sequencing. The rescued virus (rFX2010-180P) grew to similar titers as compared with the wild-type virus in DF-1 cells, and had similar replication and immunogenicity properties in ducks. To determine whether exogenous proteins could be expressed from DTMUV, both an internal ribosomal entry site (IRES) and the enhanced green fluorescent protein (eGFP) gene were introduced between the NS5 gene and the 3' non-coding sequence of FX2010-180P. A recombinant DTMUV expressing eGFP was rescued, but eGFP expression was unstable after 4 passages in DF-1 cells due to a deletion of 1,294 nucleotides. The establishment of a reliable reverse genetics system for FX2010-180P provides a foundation for future studies of DTMUV.

Liposomes containing recombinant E protein vaccine against duck Tembusu virus in ducks

To obtain an effective vaccine candidate against duck Tembusu viral (DTMUV) disease which causes egg-drop and great economical loss in the Chinese duck industry, liposome vaccines containing recombinant E protein were prepared and assessed in this study. The recombinant plasmid (PET28a-E) was constructed and transformed into BL21 (DE3) cells to produce E proteins. The recombinant E proteins were purified and entrapped by liposomes through reverse-phase evaporation. Eighty-four cherry valley ducks were randomly divided into seven groups and inoculated intramuscularly at one- or seven-day-old with liposomes-E protein or Freund's adjuvant-E protein vaccine. Blood samples were collected from the first week to the tenth week for serum antibody, plasma for viremia, as well as oropharyngeal and cloacal swabs for virus shedding analyses after being challenged with a 10(2.4) 50% tissue culture infective dose (TCID50) of duck Tembusu virus. Results showed that serum antibody level of the liposomes vaccine was higher than the Freund's adjuvant vaccine, and inoculating twice was superior to once; furthermore, the viremia and virus shedding tests also proved that the liposomes vaccine can provide complete protection against DTMUV challenge. These results demonstrated that the liposomes-E protein vaccine could be used as a potential candidate vaccine to prevent DTMUV infection in ducks.

Duck Tembusu Virus Exhibits Pathogenicity to Kunming Mice by Intracerebral Inoculation

In this study, Kunming mice were used as the animal models to study the pathogenicity of TMUV. Three groups of 3-week-old female Kunming mice (n = 15 mice per group) were infected with the SDSG strain of TMUV in 50 μL allantoic fluid (10^4.8 ELD₅₀/0.2 ml) respectively by the intracerebral (i.c.), subcutaneous (s.c.) and intranasal (i.n.) routes. The control group (n = 15 mice) was inoculated with 50 μL sterile phosphate-buffered saline. Clinical signs, gross, and microscopic lesions, viral loads in different tissues, and serum antibody titers were examined and recorded. Kunming mice infected intracerebrally showed typical clinical symptoms, including severe hindlimb paralysis, weight loss and death. Only dead mice presented severe intestinal mucosal edema. No gross lesions were observed in mice sequentially euthanized. However, microscopic lesions in the brain, spleen, liver, kidney, and lung were very typical including varying degrees of viral encephalitis, lymphocytes depletion, liver cell necrosis and nephritis, etc. Viral loads in different tissues were detected by the SYBR Green I real-time PCR assay. Viral loads in the brain, liver, and spleen were first detected and maintained a longer time, which indicated that these organs may be the target organs of TMUV. The level of viral loads was consistent with the severity of clinical signs and microscopic lesions in different tissues. The neutralizing antibody began to seroconvert at 8 dpi. Clinical signs, microscopic lesions, viral loads and serum neutralizing antibodies weren’t observed in other groups. In summary, TMUV can cause systemic infections and death in Kunming mice by i.c., which provides some experimental basis for further study of the significance of TMUV in public health.

Whole-Genome Sequence of Duck Tembusu Virus Strain DTMUV/CH/2014, Isolated in China

The whole-complete genome sequence of a strain of duck tembusu virus (DTMUV), DTMUV/CH/2014, affecting layer ducks in China, was determined and characterized. Compared with DTMUV sequences available in GenBank, DTMUV/CH/2014 has 3 amino acid mutations located in the capsid, prM, and NS3 genes of DTMUV/CH/2014.

Efficacy Evaluation of an Inactivated Duck Tembusu Virus Vaccine

To evaluate the potential use of an inactivated virus-based vaccine for the control and prevention of the newly emerged duck Tembusu virus infection in China, a duck Tembusu virus isolate, Tembusu-HB, was propagated in 12-day-old duck embryos and inactivated by treatment with formaldehyde. The inactivated viral antigen was emulsified with mineral oil, and five batches of the vaccine were manufactured. The immunogenicity and protection efficacy of the vaccine were evaluated in Beijing ducks and Beijing white geese. Results showed that more than 80% of immunized ducks were protected against virulent virus challenge after two intramuscular or subcutaneous injections of the inactivated vaccine, as evidenced by the negative virus isolation results. The protection is also correlated with a positive virus-specific antibody response as detected by ELISA. In contrast, none of the control ducks and geese had any detectable antibody response. Virus was isolated from all control ducks and geese after virulent virus challenge. Interestingly, a variable level of protection (20%-80%) was observed in Beijing white geese immunized twice with the same batches of vaccine, suggesting a species-specific effect of the vaccine. Overall, the results clearly suggest that the inactivated duck Tembusu virus vaccine is immunogenic and provides protection against virulent virus challenge.

Isolation and genome characterization of a novel duck Tembusu virus with a 74 nucleotide insertion in the 3' non-translated region

During investigations into the outbreak of duck Tembusu virus (DTMUV) infection in 2011 in China, a DTMUV strain (DTMUV-AH2011) was isolated from the affected ducks. The length of the genome of the DTMUV-AH2011 strain was found to be 11,064 nucleotides and to possess 10,278 nucleotides of one open reading frame (ORF), flanked by 94 nucleotides of the 5' non-translated region (NTR) and 692 nucleotides of the 3' NTR. In comparison with five fully sequenced TMUV genomes, the genome of DTMUV-AH2011 had a 74 nucleotide insertion in the 3' NTR. Comparison of the DTMUV-AH2011 fully deduced amino acid sequences with those of other Tembusu virus strains reported recently in China showed they had a highly conserved polyprotein precursor, sharing 98.9% amino acid identities, at least. The overall divergences of amino acid substitutions were randomly distributed among viral proteins except for the protein NS4B, the protein NS4B was unchanged. Knowledge of the biological characters of DTMUV and the potential role of the insertion in the 3' NTR in RNA replication will be useful for further studies of the mechanisms of virus replication and pathogenesis.

Effect of age and inoculation route on the infection of duck Tembusu virus in Goslings

Duck Tembusu virus (TMUV) is an emerging flavivirus that has caused variable levels of outbreaks in poultry in recent years. In order to study the effect of age and inoculation routes on the TMUV infection, one hundred healthy domestic 5-day-old and 20-day-old goslings were equally divided into five groups and four experimental groups of goslings were infected with the TMUV-SDSG strain by intravenous and intranasal routes, respectively. Severe clinical signs were observed in goslings infected at 5 days of age, including listlessness, growth retardation, severe neurological dysfunction and even death. However, goslings infected at 20 days of age showed mild symptoms and no mortality. The severity of gross lesions gradually reduced as goslings matured. The severe histopathological changes were observed in 5-day-old infected goslings, including cerebral edema, viral encephalitis, myocardial necrosis, hepatic steatosis, spleen lymphoid cell depletion, pancreatic epithelial cell shedding and interstitial hemorrhage. However, 20-day-old infected goslings showed mild histopathological changes. Viral loads in different tissues were detected by the SYBR Green I real-time PCR assay. The level of viral loads in most of tissues 5-day-old infected goslings was higher than that of 20-day-old infected goslings, correlating with the severity of clinical symptoms and lesions in these tissues. 20-day-old infected goslings developed significantly higher serum neutralizing antibody titers than 5-day-old infected goslings. Furthermore, goslings infected with TMUV intravenously demonstrated more severe clinical signs, lesions and higher viral loads in tissues than those of goslings infected with TMUV intranasally. Therefore, age and inoculation routes can affect the pathogenicity of TMUV in geese and younger geese are more susceptible to the virus. Age and inoculation route factors should be considered in study of the pathogenicity, pathogenesis, folumation of prevention and therapy strategies of TMUV infection in geese.

Design and evaluation of a polytope construct with multiple B and T epitopes against Tembusu virus infection in ducks

Tembusu virus (TMUV) is a newly emerging pathogenic flavivirus that is causing massive economic loss in Chinese poultry industry; until now, there is no effective vaccine or drug for its prevention. Epitope-based vaccination is a promising approach to achieve protective immunity and to avoid immunopathology. In present study, based on in silico epitope selection, we optimized and proposed a polytope DNA vaccine (pVAX1-rTEM) consisting B-cell and T cell epitopes from the TMUV envelope (E) protein. The immunogenicity and protective efficacy of constructed polytope DNA vaccine was assessed by in vitro and in vivo experiments. In in vitro assays, the expressed pVAX1-rTEM showed reactivity with Tembusu positive serum. Its protective efficacy against TMUV infection was evaluated in ducks. The results showed that pVAX1-rTEM was highly immunogenic and could elicit high titer neutralizing antibodies and cell-mediated immune responses. These results indicate that pVAX1-rTEM may be a promising candidate vaccine for prevention of TMUV infection.

Effect of age on the pathogenesis of duck tembusu virus in Cherry Valley ducks

The effect of host age on the outcome of duck tembusu virus (DTMUV) infection was studied in ducks. Three groups of Cherry Valley ducks at 1, 3, and 7 weeks of age were intramuscularly infected with DTMUV to systematically observe the clinical symptoms, pathological changes, tissue viral loads, and immune responses. Severe clinical symptoms and neurological dysfunction were observed in 1-week-old ducks as early as 2 days post infection (dpi) and some died at 5–7 dpi. Three weeks-old ducks showed similar but milder symptoms and no deaths. However, 7-weeks-old ducks showed only transient loss of appetite. Gross lesions gradually reduced in severity as ducks matured. One-week-old ducks showed endocardial hemorrhage, splenomegaly, swelling in the lymph follicles of the ileum, liver, and kidney swelling with degeneration, and meningeal hyperemia. Three-weeks-old ducks showed only mild pathological lesions. No visible lesions were observed in 7-weeks-old ducks. However, pathological histology analysis demonstrated all infected ducks displayed viral encephalitis. DTMUV could be detected in the brains of 1-week-old ducks as early as 1 dpi and virus titers of most organs in 1-week-old ducks were significantly higher than that of 3- and 7-weeks-old ducks at 3–5 dpi. The patterns of IFN-γ, IL-2, and serum neutralizing antibodies were similar, and there were significant difference between the youngest ducks and the older ducks at early infection stage (P < 0.05). More important is that although the antibody titers of all infected ducks were similar from 9 to 17 dpi, reduced clearance of virus was observed in the youngest groups comparing with the other two groups, indicating that immune system maturity was more important than the presence of neutralizing antibody. In summary, this study demonstrates that viral pathogenesis is strongest in 1-week-old ducks and the age-related immune response plays an important role in the pathogenesis of DTMUV in ducks.

Evidence of possible vertical transmission of Tembusu virus in ducks

In 2013, Tembusu virus (TMUV) infection was successively observed on several breeding duck farms in Shandong province, China. Affected ducks showed consistently acute anorexia, diarrhea and egg production drop. 125 hatching eggs produced by TMUV infected breeding ducks from four duck farms were collected. Among them, 35 hatching eggs were selected randomly from all before incubation for vitelline membrane samples collection. The rest of 90 hatching eggs were incubated routinely. As a result, 16 hatching eggs were found non-embryonated, 28 duck embryos died during incubation and 46 newly hatched ducklings were obtained. Vitelline membranes of non-embryonated hatching eggs, vitelline membrane, brain or liver samples of dead embryos and brain samples of newly hatched ducklings were collected for virus detection. Samples collected from one egg, embryo or duckling were treated as one. Consequently, 18 of 35 (51.43%) hatching eggs, 2 of 16 (12.50%) non-embryonated duck eggs, 17 of 28 (60.71%) dead duck embryos and 5 of 46 (10.87%) newly hatched ducklings were detected positive for TMUV using NS3-based RT-PCR. Overall, 42 of 125 (33.6%) eggs were positive for TMUV. A virus strain, designated as TMUV-SDDE, was isolated from one of these dead duck embryos which were detected TMUV positive. The results of phylogenetic analysis showed that E gene of TMUV-SDDE virus was closely related to other TMUV strains isolated in China during 2010-2013. Pathogenicity studies showed that TMUV-SDDE strain was virulent to ducklings. This is the first report that TMUV is isolated from duck embryos. The findings provide evidence of possible vertical transmission of TMUV from breeding ducks to ducklings.