Efficient strategy for constructing duck enteritis virus-based live attenuated vaccine against homologous and heterologous H5N1 avian influenza virus and duck enteritis virus infection

Pathogenicity and transmissibility studies on live attenuated duck enteritis virus vaccine in non-target species

In the second half of 2021, a highly pathogenic case occurred in a mixed chicken and duck family farm in Guangdong, China. After the duck flocks were immunized with live attenuated duck enteritis virus vaccine (live attenuated DEV vaccine), the chickens of the same farm showed clinical symptoms similar to duck enteritis, such as pericardial effusion, hepatic hemorrhagic spots, kidney enlargement, and intestinal bleeding, with mass mortality. The infection model of target animal tested, as well as the non-target species, was established according to the risk of live attenuated DEV vaccine and transmission in chickens. Live attenuated DEV vaccine was initially replicated in host animals, released the virus, and effectively colonized in the common environment, according to birds challenged experiments. There was evidence to suggest the mode of transmission of duck enteritis virus, and horizontal transmission is the main route of DEV transmission. In addition, high levels of virus titer were detected in chicken embryos and different tissues of SPF chickens. Different degrees of pathological damage occurred in the tissue of chickens. After the SPF chickens were inoculated with live attenuated DEV vaccine, different degrees of virulence were exhibited, pointing to a potential risk to other domestic bird species.

Simultaneous Protective Immune Responses of Ducks against Duck Plague and Fowl Cholera by Recombinant Duck Enteritis Virus Vector Expressing Pasteurella multocida OmpH Gene

Duck enteritis virus and Pasteurella multocida are major duck pathogens that induce duck plague and fowl cholera, respectively, in ducks and other waterfowl populations, leading to high levels of morbidity and mortality. Immunization with live attenuated DEV vaccine containing P. multocida outer membrane protein H (OmpH) can provide the most effective protection against these two infectious diseases in ducks. We have recently reported the construction of recombinant DEV expressing P. multocida ompH gene using the CRISPR/Cas9 gene editing strategy with the goal of using it as a bivalent vaccine that can simultaneously protect against both infections. Here we describe the findings of our investigation into the systemic immune responses, potency and clinical protection induced by the two recombinant DEV-ompH vaccine constructs, where one copy each of the ompH gene was inserted into the DEV genome at the UL55-LORF11 and UL44-44.5 intergenic regions, respectively. Our study demonstrated that the insertion of the ompH gene exerted no adverse effect on the DEV parental virus. Moreover, ducklings immunized with the rDEV-ompH-UL55 and rDEV-ompH-UL44 vaccines induced promising levels of P. multocida OmpH-specific as well as DEV-specific antibodies and were completely protected from both diseases. Analysis of the humoral and cellular immunity confirmed the immunogenicity of both recombinant vaccines, which provided strong immune responses against DEV and P. multocida. This study not only provides insights into understanding the immune responses of ducks to recombinant DEV-ompH vaccines but also demonstrates the potential for simultaneous prevention of viral and bacterial infections using viral vectors expressing bacterial immunogens.

Evaluation of the Safety and Immunogenicity of Duck-Plague Virus gE Mutants

Duck plague (DP) is an acute infectious disease in the duck industry. The duck plague virus (DPV) is the pathogen, a subfamily of alphaherpesvirinae. gE is a type I membrane protein that contains three parts: an extracellular domain, a transmembrane domain, and a cytoplasmic domain. gE is the major virulence determinant of α-herpesvirus. However, the functions of the gE extracellular and cytoplasmic domains have not been reported in DPV. In this study, a gE extracellular domain deletion mutant and a gE cytoplasmic domain deletion mutant were constructed from DPV. Virus replication kinetics showed that the growth titers of both the gE ectodomain-deleted mutant virus and the gE cytoplasmic domain-deleted virus in DEFs were lower than that of the parental virus CHv-50. DPV CHv-gEΔET and DPV CHv-gEΔCT were continuously passed to the 20th passage in DEFs and the 10th in ducklings. The mutant virus DNA after passage was extracted for identification. The results showed that the gE ectodomain and gE cytoplasmic domain deletion mutant viruses have good genetic stability. The ducklings in each group (n=10) were inoculated with the same titers of DPV CHv-gEΔET, DPV CHv-gEΔCT, DPV CHv-ΔgE, and parental CHv-50, respectively. Clinical symptoms and serum antibody levels were detected after inoculation. The results showed that the virulence of DPV CHv-gEΔCT to ducklings was reduced compared with parental CHv-50, while the virulence of DPV CHv-gEΔET to ducklings was significantly reduced. 10⁵ TCID₅₀ DPV CHv-gEΔET or DPV CHv-ΔgE can induce ducklings to produce DPV-specific antibodies, protect the ducklings from virulent CHv challenge. Therefore, DPV CHv-gEΔET may serve as a promising vaccine candidate to prevent and control duck plague.

CRISPR/Cas9 Editing of Duck Enteritis Virus Genome for the Construction of a Recombinant Vaccine Vector Expressing ompH Gene of Pasteurella multocida in Two Novel Insertion Sites

Duck enteritis virus (DEV) and Pasteurella multocida, the causative agent of duck plague and fowl cholera, are acute contagious diseases and leading causes of morbidity and mortality in duck. The NHEJ-CRISPR/Cas9-mediated gene editing strategy, accompanied with the Cre–Lox system, have been employed in the present study to show that two new sites at UL55-LORF11 and UL44-44.5 loci in the genome of the attenuated Jansen strain of DEV can be used for the stable expression of the outer membrane protein H (ompH) gene of P. multocida that could be used as a bivalent vaccine candidate with the potential of protecting ducks simultaneously against major viral and bacterial pathogens. The two recombinant viruses, DEV-OmpH-V5-UL55-LORF11 and DEV-OmpH-V5-UL44-44.5, with the insertion of ompH-V5 gene at the UL55-LORF11 and UL44-44.5 loci respectively, showed similar growth kinetics and plaque size, compared to the wildtype virus, confirming that the insertion of the foreign gene into these did not have any detrimental effects on DEV. This is the first time the CRISPR/Cas9 system has been applied to insert a highly immunogenic gene from bacteria into the DEV genome rapidly and efficiently. This approach offers an efficient way to introduce other antigens into the DEV genome for multivalent vector.

Live Recombinant NDV-Vectored H5 Vaccine Protects Chickens and Domestic Ducks From Lethal Infection of the Highly Pathogenic H5N6 Avian Influenza Virus

The H5 subtype highly pathogenic avian influenza virus (HPAIV) has been introduced to South Korea every 2 or 3 years via wild migratory waterfowls, causing devastating damages to the poultry industry. Although most damages and economic losses by HPAIV are focused on chicken layers, domestic ducks are known to play a major role in the farm-to-farm transmission. However, most HPAIV vaccine studies on poultry have been performed with oil-emulsion inactivated vaccines. In this study, we developed a live recombinant Newcastle disease virus (NDV)-vectored vaccine against H5 HPAIV (rK148/ES2-HA) using a previously established NDV vaccine strain (K148/08) isolated from a wild mallard duck. The efficacy of the vaccine when administered via the oculonasal route or as a spray was evaluated against lethal H5 HPAIV infection in domestic ducks and chickens. Oculonasal inoculation of the rK148/ES2-HA in chickens and ducks elicited antibody titers against HPAIV as early as 1 or 2 week after the single dose of vaccination, whereas spray vaccination in ducks elicited antibodies against HPAIV after the booster vaccination. The chickens and ducks vaccinated with rK148/ES2-HA showed high survival rates and low viral shedding after H5N6 HPAIV challenge. Collectively, vaccination with rK148/ES2-HA prevented lethal infection and decreased viral shedding in both chickens and ducks. The vaccine developed in this study could be useful in suppressing the viral shedding in H5 HPAIV outbreaks, with the ease of vaccine application and fast onset of immunity.

Simultaneous tracking of capsid VP26, envelope protein gC localization in living cells infected with double fluorescent duck enteritis virus

Duck enteritis virus (DEV) can cause an acute, contagious and lethal disease of many species of waterfowl. An infectious bacterial artificial chromosome clone of DEV vaccine strain pE1 (pDEV-EF1) has been constructed in our previous study. Based on pE1, a recombinant mutated clone pDL (pVP26CFP-gCRFP), which carries a red fluorescent protein (mRFP) gene fused to the viral envelope protein gC in combination with a cyan fluorescent protein (CFP) gene fused to the viral capsid VP26, was constructed by two-step Red/ET recombination and the recombinant virus rDL (rVP26CFP-gCRFP) was rescued from chicken embryo fibroblasts (CEFs) by calcium phosphate transfection. Western blot analysis revealed that VP26-CFP and gC-mRFP were both expressed in fusion forms in rDL-infected CEFs, and subcellular localization study showed that gC-mRFP was mainly localized in whole cell at 36, 48 h post infection (p.i.); and then mostly migrated to the cytoplasm after 60 h.p.i., ; whereas VP26-CFP was localized in the nucleus in all stages of virus infection. Additionally, viral particles at different stages of morphogenesis (A capsids, B capsids, C capsids) were observed in virus-infected cells by transmission electron microscopy, indicating that exogenous gene insertion has no effect on virus assembly. This study has laid a foundation for visually studying localization, transportation of DEV capsid proteins and envelope glycoproteins as well as virus assembly, virion movement and virus-cell interaction.

Identification of a linear epitope within domain I of Duck Tembusu virus envelope protein using a novel neutralizing monoclonal antibody

Duck Tembusu virus (DTMUV) is a newly emerging pathogenic flavivirus that caused severe egg drop syndrome in laying ducks in China since 2010, leading to massive economic losses to the duck industry. Although the DTMUV E protein is considered to be critical in inducing the protective immune response, the functional epitopes within this protein remain largely unknown. In the present study, we isolated a DTMUV neutralizing monoclonal antibody (mAb) 3B8 from DTMUV E-immunized mice. Epitope mapping showed that mAb 3B8 recognized a novel linear epitope FSCLGMQNR located on the extreme N-terminal of the domain I (EDI) of E protein. Sequence alignment and Western blot analyses showed that the epitope is greatly conserved with high DTMUV-specificity. Moreover, upon cloning the heavy and light chain variable region sequences of mAb 3B8, we prepared the single-chain variable antibody fragment (scFv) 3B8 by connecting the two chains via a flexible peptide linker. The recombinant scFv 3B8 exhibited antiviral activity against DTMUV infection in vitro and in vivo. Our results provide valuable implications for the development of DTMUV vaccines and therapeutics.

Optimized Expression of Duck Tembusu Virus E Gene Delivered by a Vectored Duck Enteritis Virus In Vitro

In our previous study, a recombinant duck enteritis virus (DEV) delivering codon-optimized E gene (named as E-ch) of duck Tembusu virus (DTMUV) optimized referring to chicken's codon bias has been obtained based on the infectious bacterial artificial chromosome (BAC) clone of duck enteritis virus vaccine strain pDEV-EF1, but the expression level of E-ch in recombinant virus rDEV-E-ch-infected cells was very low. To optimize DTMUV E gene expression delivered by the vectored DEV, different forms of E gene (collectively called EG) including origin E gene (E-ori), truncated E451-ori gene, codon-optimized E-dk gene optimized referring to duck's codon bias, as well as the truncated E451-ch and E451-dk, Etpa-ori and Etpa-451-ori, which contain prefixing chick TPA signal peptide genes, were cloned into transfer vector pEP-BGH-end, and several recombinant plasmids pEP-BGH-EG were constructed. Then the expression cassettes pCMV-EG-polyA_BGH amplified from pEP-BGH-EG by PCR were inserted into US7/US8 gene intergenic region of pDEV-EF1 by two-step Red/ET recombination, 7 strain recombinant mutated BAC clones pDEV-EG carrying different E genes were constructed. Next, the recombinant viruses rDEV-EG were reconstituted from chicken embryo fibroblasts (CEFs) by calcium phosphate precipitation. Western blot analysis showed that E or E451 protein is expressed in rDEV-E-ori, rDEV-E-ch, rDEV-Etpa-ori, rDEV-E451-ori, rDEV-E451-dk, and rDEV-E451-ch-infected CEFs, and protein expression level in rDEV-E451-dk-infected CEFs is the highest. These studies have laid a foundation for developing bivalent vaccine controlling DEV and DTMUV infection.

Highly Efficient Base Editing in Viral Genome Based on Bacterial Artificial Chromosome Using a Cas9-Cytidine Deaminase Fused Protein

Viruses evolve rapidly and continuously threaten animal health and economy, posing a great demand for rapid and efficient genome editing technologies to study virulence mechanism and develop effective vaccine. We present a highly efficient viral genome manipulation method using CRISPR-guided cytidine deaminase. We cloned pseudorabies virus genome into bacterial artificial chromosome, and used CRISPR-guided cytidine deaminase to directly convert cytidine (C) to uridine (U) to induce premature stop mutagenesis in viral genes. The editing efficiencies were 100%. Comprehensive bioinformatic analysis revealed that a large number of editable sites exist in pseudorabies virus (PRV) genomes. Notably, in our study viral genome exists as a plasmid in E. coli, suggesting that this method is virus species-independent. This application of base-editing provided an alternative approach to generate mutant virus and might accelerate study on virulence and vaccine development.

Immunization of Domestic Ducks with Live Nonpathogenic H5N3 Influenza Virus Prevents Shedding and Transmission of Highly Pathogenic H5N1 Virus to Chickens

Wild ducks are known to be able to carry avian influenza viruses over long distances and infect domestic ducks, which in their turn infect domestic chickens. Therefore, prevention of virus transmission between ducks and chickens is important to control the spread of avian influenza. Here we used a low pathogenic wild aquatic bird virus A/duck/Moscow/4182/2010 (H5N3) for prevention of highly pathogenic avian influenza virus (HPAIV) transmission between ducks and chickens. We first confirmed that the ducks orally infected with H5N1 HPAIV A/chicken/Kurgan/3/2005 excreted the virus in feces. All chickens that were in contact with the infected ducks became sick, excreted the virus, and died. However, the ducks orally inoculated with 10⁴ 50% tissue culture infective doses of A/duck/Moscow/4182/2010 and challenged 14 to 90 days later with H5N1 HPAIV did not excrete the challenge virus. All contact chickens survived and did not excrete the virus. Our results suggest that low pathogenic virus of wild aquatic birds can be used for prevention of transmission of H5N1 viruses between ducks and chickens.

The Application of NHEJ-CRISPR/Cas9 and Cre-Lox System in the Generation of Bivalent Duck Enteritis Virus Vaccine against Avian Influenza Virus

Duck-targeted vaccines to protect against avian influenza are critically needed to aid in influenza disease control efforts in regions where ducks are endemic for highly pathogenic avian influenza (HPAI). Duck enteritis virus (DEV) is a promising candidate viral vector for development of vaccines targeting ducks, owing to its large genome and narrow host range. The clustered regularly interspaced palindromic repeats (CRISPR)/Cas9 system is a versatile gene-editing tool that has proven beneficial for gene modification and construction of recombinant DNA viral vectored vaccines. Currently, there are two commonly used methods for gene insertion: non-homologous end-joining (NHEJ) and homology-directed repair (HDR). Owing to its advantages in efficiency and independence from molecular requirements of the homologous arms, we utilized NHEJ-dependent CRISPR/Cas9 to insert the influenza hemagglutinin (HA) antigen expression cassette into the DEV genome. The insert was initially tagged with reporter green fluorescence protein (GFP), and a Cre-Lox system was later used to remove the GFP gene insert. Furthermore, a universal donor plasmid system was established by introducing double bait sequences that were independent of the viral genome. In summary, we provide proof of principle for generating recombinant DEV viral vectored vaccines against the influenza virus using an integrated NHEJ-CRISPR/Cas9 and Cre-Lox system.

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.

Construction of a highly efficient CRISPR/Cas9-mediated duck enteritis virus-based vaccine against H5N1 avian influenza virus and duck Tembusu virus infection

Duck enteritis virus (DEV), duck tembusu virus (DTMUV), and highly pathogenic avian influenza virus (HPAIV) H5N1 are the most important viral pathogens in ducks, as they cause significant economic losses in the duck industry. Development of a novel vaccine simultaneously effective against these three viruses is the most economical method for reducing losses. In the present study, by utilizing a clustered regularly interspaced short palindromic repeats (CRISPR)/associated 9 (Cas9)-mediated gene editing strategy, we efficiently generated DEV recombinants (C-KCE-HA/PrM-E) that simultaneously encode the hemagglutinin (HA) gene of HPAIV H5N1 and pre-membrane proteins (PrM), as well as the envelope glycoprotein (E) gene of DTMUV, and its potential as a trivalent vaccine was also evaluated. Ducks immunized with C-KCE-HA/PrM-E enhanced both humoral and cell-mediated immune responses to H5N1 and DTMUV. Importantly, a single-dose of C-KCE-HA/PrM-E conferred solid protection against virulent H5N1, DTMUV, and DEV challenges. In conclusion, these results demonstrated for the first time that the CRISPR/Cas9 system can be applied for modification of the DEV genome rapidly and efficiently, and that recombinant C-KCE-HA/PrM-E can serve as a potential candidate trivalent vaccine to prevent H5N1, DTMUV, and DEV infections in ducks.

Preliminary study of the UL55 gene based on infectious Chinese virulent duck enteritis virus bacterial artificial chromosome clone

Background

Lethal Duck Enteritis Virus (DEV) infection can cause high morbidity and mortality of many species of waterfowl within the order Anseriformes. However, little is known about the function of viral genes including the conserved UL55 gene among alpha herpes virus due to the obstacles in maintenance and manipulation of DEV genome in host cells.

Methods

In this paper, we constructed an infectious bacteria artificial chromosome (BAC) clone of the lethal clinical isolate duck enteritis virus Chinese virulent strain (DEV CHv) by inserting a transfer vector containing BAC mini-F sequence and selection marker EGFP into UL23 gene using homologous recombination. UL55 deletion and its revertant mutant were generated by two-step RED recombination in E. coli on basis of rescued recombinant virus. The function of UL55 gene in DEV replication and its effect on distribution of UL26.5 protein were carried out by growth characteristics and co-localization analysis.

Results

The complete genome of DEV CHv can be stably maintained in E. coli as a BAC clone and reconstituted again in DEF cells. The generated UL55 deletion mutant based on DEV CHv-BAC-G displayed similar growth curves, plaque morphology and virus titer of its parental virus in infected Duck Embryo Fibroblast (DEF) cells. Immunofluorescence assay indicated that the loss of UL55 gene do not affect the distribution of UL26.5 protein in intracellular. These data also suggest infectious BAC clone of DEV CHv will facilitate the gene function studies of DEV genome.

Conclusions

We have successfully developed an infectious BAC clone of lethal clinical isolate DEV CHv for the first time. The generated UL55 gene mutant based on that demonstrated this platform would be a very useful tool for functional study of DEV genes. We found the least known DEV UL55 is dispensable for virus replication and UL26.5 distribution, and it could be a very promise candidate locus for developing bivalent vaccine. Experiment are now in progress for testifying the possibility of UL55 gene locus as an exogenous gene insertion site for developing DEV vectored vaccine.

Electronic supplementary material

The online version of this article (doi:10.1186/s12985-017-0748-y) contains supplementary material, which is available to authorized users.

Recombinant viral-vectored vaccines for the control of avian influenza in poultry

Vaccination is a commonly used tool for the control of both low pathogenic and highly pathogenic avian influenza (AI) viruses. Traditionally, inactivated adjuvanted vaccines made from a low pathogenic field strain have been used for vaccination, but advances in molecular biology have allowed a number of different viral vectored vaccines, expressing the AI virus hemagglutinin (HA) gene, to be developed and licensed for use for control of AI. This review summarizes the licensed vector vaccines available for use in poultry. As a group, these vaccines can stimulate both a cellular and humoral immune response and, when antigenically well matched to the target AI strain, are effective at preventing clinical disease and reducing virus shedding if vaccinated birds do become infected. The vaccines can often be given to one-day old chicks in the hatchery, which can provide early protection and is a cost effective route of administration of the vaccine. All the licensed vectored vaccines, because they only express the HA gene, can potentially be used to differentiate vaccinated from vaccinated and infected birds, which is often referred to as a DIVA strategy. Although a potentially valuable tool for the surveillance of the virus in countries that vaccinate, the DIVA principle has currently not been applied. Concern remains that maternal antibody or pre-existing immunity to the vector or to the AI HA insert can suppress the immune response to the vaccine. The viral vectored vaccines appear to work well with a prime boost strategy where the vectored vaccine is given first and a different type of vaccine, often a killed adjuvanted vaccine is given two or three weeks later.

Live Attenuated Vaccine Based on Duck Enteritis Virus against Duck Hepatitis A Virus Types 1 and 3

As causative agents of duck viral hepatitis, duck hepatitis A virus type 1 (DHAV-1) and type 3 (DHAV-3) causes significant economic losses in the duck industry. However, a licensed commercial vaccine that simultaneously controls both pathogens is currently unavailable. Here, we generated duck enteritis virus recombinants (rC-KCE-2VP1) containing both VP1 from DHAV-1 (VP1/DHAV-1) and VP1 from DHAV-3 (VP1/DHAV-3) between UL27 and UL26. A self-cleaving 2A-element of FMDV was inserted between the two different types of VP1, allowing production of both proteins from a single open reading frame. Immunofluorescence and Western blot analysis results demonstrated that both VP1 proteins were robustly expressed in rC-KCE-2VP1-infected chicken embryo fibroblasts. Ducks that received a single dose of rC-KCE-2VP1 showed potent humoral and cellular immune responses and were completely protected against challenges of both pathogenic DHAV-1 and DHAV-3 strains. The protection was rapid, achieved as early as 3 days after vaccination. Moreover, viral replication was fully blocked in vaccinated ducks as early as 1 week post-vaccination. These results demonstrated, for the first time, that recombinant rC-KCE-2VP1 is potential fast-acting vaccine against DHAV-1 and DHAV-3.

Construction of a recombinant duck enteritis virus vaccine expressing hemagglutinin of H9N2 avian influenza virus and evaluation of its efficacy in ducks

H9 subtype avian influenza viruses (AIVs) remain a significant burden in the poultry industry and are considered to be one of the most likely causes of any new influenza pandemic in humans. As ducks play an important role in the maintenance of H9 viruses in nature, successful control of the spread of H9 AIVs in ducks will have significant beneficial effects on public health. Duck enteritis virus (DEV) may be a promising candidate viral vector for aquatic poultry vaccination. In this study, we constructed a recombinant DEV, rDEV-∆UL2-HA, inserting the hemagglutinin (HA) gene from duck-origin H9N2 AIV into the UL2 gene by homologous recombination. One-step growth analyses showed that the HA gene insertion had no effect on viral replication and suggested that the UL2 gene was nonessential for virus growth in vitro. In vivo tests further showed that the insertion of the HA gene in place of the UL2 gene did not affect the immunogenicity of the virus. Moreover, a single dose of 10³ TCID₅₀ of rDEV-∆UL2-HA induced solid protection against lethal DEV challenge and completely prevented H9N2 AIV viral shedding. To our knowledge, this is the first report of a DEV-vectored vaccine providing robust protection against both DEV and H9N2 AIV virus infections in ducks.

Viral vector-based influenza vaccines

Antigenic drift of seasonal influenza viruses and the occasional introduction of influenza viruses of novel subtypes into the human population complicate the timely production of effective vaccines that antigenically match the virus strains that cause epidemic or pandemic outbreaks. The development of game-changing vaccines that induce broadly protective immunity against a wide variety of influenza viruses is an unmet need, in which recombinant viral vectors may provide. Use of viral vectors allows the delivery of any influenza virus antigen, or derivative thereof, to the immune system, resulting in the optimal induction of virus-specific B- and T-cell responses against this antigen of choice. This systematic review discusses results obtained with vectored influenza virus vaccines and advantages and disadvantages of the currently available viral vectors.

Attenuated Salmonella Typhimurium delivery of a novel DNA vaccine induces immune responses and provides protection against duck enteritis virus

DNA vaccines are widely used to prevent and treat infectious diseases, cancer and autoimmune diseases; however, their relatively low immunogenicity is an obstacle to their use. In this study, we constructed a novel and universal DNA vaccine vector (pSS898) that can be used to build DNA vaccines against duck enteritis virus (DEV) and other viruses that require DNA vaccines to provide protection. This vaccine vector has many advantages, including innate immunogenicity, efficient nuclear trafficking and resistance to attack from nucleases. UL24 and tgB from DEV were chosen as the antigens, and the heat labile enterotoxin B subunit (LTB) from Escherichia coli and the IL-2 gene (DuIL-2) from duck were used as adjuvants for the construction of DNA vaccine plasmids. Ducklings that were orally immunized with S739 (Salmonella Typhimurium Δasd-66 Δcrp-24 Δcya-25) and harboring these DEV DNA vaccines produced strong mucosal and systemic immune responses, and they resisted an otherwise lethal DEV challenge. More importantly, S739 (UL24-LTB) provided 90% protection after a priming-boost immunization. This study shows that our novel and universal DNA vaccine vector can be used efficiently in practical applications and may provide a promising method of orally inoculating ducks with a DEV DNA vaccine delivered by attenuated Salmonella Typhimurium for prevention of DVE.

Protective efficacy of an inactivated vaccine against H9N2 avian influenza virus in ducks

Background

Wild ducks play an important role in the evolution of avian influenza viruses (AIVs). Domestic ducks in China are known to carry and spread H9N2 AIVs that are thought to have contributed internal genes for the recent outbreak of zoonotic H7N9 virus. In order to protect animal and public health, an effective vaccine is urgently needed to block and prevent the spread of H9N2 virus in ducks. We developed an inactivated H9N2 vaccine (with adjuvant Montanide ISA 70VG) based on an endemic H9N2 AIV and evaluated this vaccine in ducks.

Findings

The results showed that the inactivated H9N2 vaccine was able to induce a strong and fast humoral immune response in vaccinated ducks. The hemagglutination inhibition titer in the sera increased fast, and reached its peak of 12.3 log2 at 5 weeks post-vaccination in immunized birds and remained at a high level for at least 37 weeks post-vaccination. Moreover, viral shedding was completely blocked in vaccinated ducks after challenge with a homologous H9N2 AIV at both 3 and 37 weeks post-vaccination.

Conclusions

The results of this study indicate that the inactivated H9N2 vaccine induces high and prolonged immune response in vaccinated ducks and are efficacious in protecting ducks from H9N2 infection.