Duck hepatitis A virus structural proteins expressed in insect cells self-assemble into virus-like particles with strong immunogenicity in ducklings

Surface Display of Duck Hepatitis A Virus Type 1 VP1 Protein on Bacillus subtilis Spores Elicits Specific Systemic and Mucosal Immune Responses on Mice

Duck viral hepatitis, primarily caused by duck hepatitis A virus type 1 (DHAV-1), poses a significant threat to the global duck industry. Bacillus subtilis is commonly utilized as a safe probiotic in the development of mucosal vaccines. In this study, a recombinant strain of B. subtilis, designated as B. subtilis RV, was constructed to display the DHAV-1 capsid protein VP1 on its spore surface using the outer coat protein B as an anchoring agent. The immunogenicity of this recombinant strain was evaluated in a mouse model through mixed feeding immunization. The results indicated that B. subtilis RV could elicit specific systemic and mucosal immune responses in mice, as evidenced by the high levels of serum IgG, intestinal secretory IgA, and potent virus-neutralizing antibodies produced. Furthermore, the recombinant strain significantly upregulated the expression levels of IL-2, IL-6, IL-10, TNF-α, and IFN-γ in the intestinal mucosa. Thus, the recombinant strain maintained the balance of the Th1/Th2 immune response and demonstrated an excellent mucosal immune adjuvant function. In summary, this study suggests that B. subtilis RV can be a novel alternative for effectively controlling DHAV-1 infection as a vaccine-based feed additive.

Construction and immune evaluation of the recombinant duck adenovirus type 3 delivering capsid protein VP1 of the type 1 duck hepatitis virus

Adenovirus serves as an excellent viral vector and is employed in vector vaccine research. Duck hepatitis A virus type 1 (DHAV1) and duck adenovirus type 3 (DAdV3) cause significant economic losses in the Chinese duck industry. In this study, we found an excellent exogenous gene insertion site in DAdV3 genome of CH-GD-12-2014 strain, within 3 intergenic regions (IGR). Subsequently, we generated a recombinant duck adenovirus named rDAdV3-VP1-188, which exhibits excellent replication characteristics and immunogenicity of DAdV3 and DHAV1. Animal experiments showed that rDAdV3-VP1-188 can provide 100% protection against the DAdV3 and 80% protection against DHAV1. These results showed that rDAdV3-VP1-188 could induce protection against DAdV3 and DHAV1 in ducks, thus indicating the feasibility of DAdV3 as a vector for the development of avian vector vaccines. These insights contribute to the further development of DAdV3 vectors and other adenovirus vectors.

A meta-analysis for vaccine protection rate of duck hepatitis a virus in mainland China in 2009-2021

BACKGROUND

Duck hepatitis A virus (DHAV) is a single-stranded, positive-strand small RNA virus that causes a very high mortality rate in ducklings. The DHAV-3 subtype incidence rate has recently increased in China, causing great economic losses to the waterfowl breeding industry. We analyzed the protection rate of DHAV vaccines used in mainland China from 2009 to 2021 and evaluated the effectiveness of vaccine prevention and control to reduce the economic losses caused by DHAV to the waterfowl breeding industry. We screened five electronic research databases and obtained 14 studies and patents on the protection efficiency of DHAV-1 and DHAV-3 vaccines.

RESULTS

Meta-analysis demonstrated that immunized ducklings produced higher antibody levels and had a significantly higher survival rate than non-immunized ducklings [relative risk (RR) = 12, 95% confidence interval (CI) 6-26, P < 0.01]. The age of the ducks and vaccine valence did not affect protection efficiency. Data source analysis of the vaccine protection rate demonstrated that the vaccines conferred immune protection for ducklings in both small-scale experiments and large-scale clinical conditions. The analysis results revealed that although the vaccines conferred protection, the immune protective effect differed between small-scale experimental conditions and large-scale clinical conditions. This might have been due to non-standard vaccination and environmental factors.

CONCLUSIONS

Domestic DHAV vaccines can protect ducklings effectively. The subjects immunized (breeding ducks or ducklings) and vaccine valence had no effect on the protective effect. Both small-scale experiments and large-scale clinical conditions conferred immune protection on ducklings, but vaccine immunization under small-scale experimental conditions had slightly better protective effects than large-scale clinical immunization.

Current status and future direction of duck hepatitis A virus vaccines

Duck viral hepatitis (DVH), mainly caused by duck hepatitis A virus (DHAV), is a highly fatal and rapidly spreading infectious disease of young ducklings that seriously jeopardizes the duck industry worldwide. DHAV type 1 (DHAV-1) is the main genotype responsible for disease outbreaks since 1945, and the disease situation is complicated by the emergence and dissemination of a novel genotype (DHAV-3) in some countries in Asia and Africa. Live attenuated DHAV vaccines are widely used to induce a considerable degree of protection in ducklings. Breeder ducks are immunized with inactivated or/and live DHAV vaccines to achieve satisfactory levels of passive immunity in progeny. In addition, novel characteristics of virus transmission, pathogenicity and pathogenesis of DHAV were recently characterized, necessitating the development of new vaccines and effective vaccination programmes against DVH. Therefore, a systematic dissection of the profiles, strengths and shortcomings of the available DHAV vaccines is essential. Moreover, to further increase the efficiency of vaccine production and administration, the development of next-generation DHAV vaccines using cutting-edge technologies is also required. In this review, based on a comprehensive summary of the research advances in the epidemiology, pathogenicity, and genomic features of DHAV, we focus on reviewing and analysing the features of the commercial and experimental DHAV vaccines. We also propose perspectives for disease control based on the specific disease situations in different countries. This review provides essential information for vaccine development and disease control of DVH.

Structure of Senecavirus A 3C Protease Revealed the Cleavage Pattern of 3C Protease in Picornaviruses

Senecavirus A (SVA) is an emerging picornavirus infecting porcine of all age groups and causing foot and mouth disease (FMD)-like symptoms. One of its key enzymes is the 3C protease (3C^pro), which is similar to other picornaviruses and essential for virus maturation by controlling polyprotein cleavage and RNA replication. In this study, we reported the crystal structure of SVA 3C^pro at a resolution of 1.9 Šand a thorough structural comparison against all published picornavirus 3C^pro structures. Using statistical and graphical visualization techniques, we also investigated the sequence specificity of the 3C^pro. The structure revealed that SVA 3C^pro adopted a typical chymotrypsin-like fold with the S1 subsite as the most conservative site among picornavirus 3C^pro. The surface loop, A1-B1 hairpin, adopted a novel conformation in SVA 3C^pro and formed a positively charged protrusion around S' subsites. Correspondingly, SVA scissile bonds preferred Asp rather than neutral amino acids at P3' and P4'. Moreover, SVA 3C^pro showed a wide range tolerance to P4 residue volume (acceptable range: 67 ų to 141 ų), such as aromatic side chain, in contrast to other picornaviruses. In summary, our results provided valuable information for understanding the cleavage pattern of 3C^pro. IMPORTANCE Picornaviridae is a group of RNA viruses that harm both humans and livestock. 3C^pro is an essential enzyme for picornavirus maturation, which makes it a promising target for antiviral drug development and a critical component for virus-like particle (VLP) production. However, the current challenge in the development of antiviral drugs and VLP vaccines includes the limited knowledge of how subsite structure determines the 3C^pro cleavage pattern. Thus, an extensive comparative study of various picornaviral 3C^pro was required. Here, we showed the 1.9 Šcrystal structure of SVA 3C^pro. The structure revealed similarities and differences in the substrate-binding groove among picornaviruses, providing new insights into the development of inhibitors and VLP.

Development of a Subunit Vaccine against Duck Hepatitis A Virus Serotype 3

In this study, we sought to develop a subunit vaccine against the increasingly prevalent Duck hepatitis A virus serotype 3 (DHAV-3). The VP1 protein of DHAV-3 and a truncated version containing the C-terminal region of VP1, termed VP1-C, were expressed recombinantly in Escherichia coli as vaccine antigens. For enhanced immune response, a truncated version of flagellin, nFliC, was included as vaccine adjuvant. Ducklings were vaccinated once for immune response analysis and challenge test. Results showed that VP1-C elicited a higher level of virus-specific antibody response and neutralization titer than VP1. The addition of nFliC further enhanced the antibody response. In terms of cellular immune response, the VP1-C + nFliC vaccine elicited the highest level of T cell proliferation among the vaccine formulations tested. Examination of the cytokine expression profile showed that peripheral blood mononuclear cells from the VP1-C + nFliC vaccine group expressed the highest levels of pro-inflammatory (IL-6) and TH-1 type (IL-12 and IFN-γ) cytokines. Finally, in a DHAV-3 challenge test, the VP1-C + nFliC vaccine provided a 75% protection rate (n = 8), in contrast to 25% for the VP1 vaccine. In conclusion, E. coli-expressed VP1-C has been shown to be a promising antigen when combined with nFliC and may be further developed as a single-dose subunit vaccine against DHAV-3.

Recombinant Duck Enteritis Virus-Vectored Bivalent Vaccine Effectively Protects Against Duck Hepatitis A Virus Infection in Ducks

Duck enteritis virus (DEV) and duck hepatitis A virus (DHAV) are prevalent duck pathogens, causing significant economic losses in the duck industry annually. Using a fosmid-based rescue system, we generated two DEV recombinants, rDEV-UL26/27-P13C and rDEV-US7/8-P13C, in which the P1 and 3C genes from DHAV type 3 (DHAV-3) were inserted into the DEV genome between genes UL26 and UL27 or genes US7 and US8. We inserted a self-cleaving 2A-element between P1 and 3C, allowing the production of both proteins from a single open reading frame. P1 and 3C were simultaneously expressed in infected chicken embryo fibroblasts, with no difference in growth kinetics between cells infected with the recombinant viruses and those infected with the parent DEV. Both recombinant viruses induced neutralizing antibodies against DHAV-3 and DEV in ducks. A single dose of the recombinant viruses induced solid protection against lethal DEV challenge and completely prevented DHAV-3 infection as early as 7 days post-vaccination. These recombinant P1- and 3C-expressing DEVs provide potential bivalent vaccines against DEV and DHAV-3 infection in ducks.

Baculovirus-Derived Vectors for Immunization and Therapeutic Applications

Baculoviruses are arthropod-specific, enveloped viruses with circular, supercoiled double-stranded deoxyribonucleic acid genomes. While many viruses are studied to seek solutions for their adverse impact on human, veterinary, and plant health, the study of baculoviruses was stimulated initially by their potential utility to control insect pests. Later, the utility of baculovirus as gene expression vectors was evidenced leading to numerous applications. Several strategies are employed to obtain recombinant viruses that express large quantities of heterologous proteins. A major step forward was the development of bacmid technology (the construction of bacterial artificial chromosomes containing the genome of the baculovirus) which allows the manipulation of the baculovirus genome in bacteria. With this technology, foreign genes can be introduced into the bacmid by homologous and site-directed recombination or by transposition. Baculoviruses have been used to explore fundamental questions in molecular biology such as the nature of programmed cell-death. Moreover, the ability of baculoviruses to transduce mammalian cells led to the consideration of their use as gene-therapy and vaccine vectors. Strategies for genetic engineering of baculoviruses have been developed to meet the requirements of new application areas. Display of foreign proteins on the surface of virions or in nucleocapsid structures, the assembly of expressed proteins to form virus-like particles or protein complexes have been explored and validated as vaccines. The aim of this chapter is to update the areas of application of the baculoviruses in protein expression, alternative vaccine designs and gene therapy of infectious diseases and genetic disorders. Finally, we review the baculovirus-derived products on the market and in the pipeline for biomedical and veterinary use.

Virus-Like Particles as an Instrument of Vaccine Production

The paper discusses the techniques which are currently implemented for vaccine production based on virus-like particles (VLPs). The factors which determine the characteristics of VLP monomers assembly are provided in detail. Analysis of the literature demonstrates that the development of the techniques of VLP production and immobilization of target antigens on their surface have led to the development of universal platforms which make it possible for virtually any known antigen to be exposed on the particle surface in a highly concentrated form. As a result, the focus of attention has shifted from the approaches to VLP production to the development of a precise interface between the organism's immune system and the peptides inducing a strong immune response to pathogens or the organism's own pathological cells. Immunome-specified methods for vaccine design and the prospects of immunoprophylaxis are discussed. Certain examples of vaccines against viral diseases and cancers are considered.

A novel picornavirus in feces of a rainbow lorikeet (Trichoglossus moluccanus) shows a close relationship to members of the genus Avihepatovirus

A novel picornavirus, named "lorikeet picornavirus 1" (LoPV-1), was detected in a fecal sample from rainbow lorikeets using viral metagenomic analysis, and its complete genome sequence was determined and analyzed. The genome of LoPV-1 is 7862 nt long, including a 617-nt 5' UTR, a type IV IRES 5'UTR with an '8-like' motif, a 7032-nt polyprotein ORF, and a 213-nt 3' UTR. Phylogenetic analysis and pairwise asequence comparisons based on the amino acid sequences of P1, P2, and P3 indicated that LoPV-1 showed the closest relationship to two picornaviruses that were isolated recently from red-crowned cranes and clustered together with members of the genus Avihepatovirus.

Protection against duck hepatitis a virus type 1 conferred by a recombinant avian adeno-associated virus

The avian adeno-associated virus (AAAV) has been proved to be an efficient gene transfer vector for human gene therapy and vaccine research. In this experiment, an AAAV-based vaccine was evaluated for the development of a vaccine against duck hepatitis a virus type 1 (DHAV-1). The major capsid VP1 gene was amplified and subcloned into pFBGFP containing the inverted terminal repeats of AAAV, and then the recombinant baculovirus rBac-VP1 was generated. The recombinant AAAV expressing the VP1 protein (rAAAV-VP1) was produced by co-infecting Sf9 cells with rBac-VP1 and the other 2 baculoviruses containing AAAV functional genes and structural genes respectively, and confirmed by electron microscopy, Western blotting and immunofluorescence assays. Quantitative real-time PCR revealed that the titer of rAAAV-VP1 was about 9 × 1012 VG/mL. Immunogenicity was studied in ducklings. One day ducklings were injected intramuscularly once with rAAAV-VP1. Serum from rAAAV-VP1-vaccinated ducklings showed a systemic immune response evidenced by VP1-specific enzyme-linked immunosorbent assay and virus neutralization test. Furthermore, all ducklings inoculated with rAAAV-VP1 were protected against DHAV-1 challenge. The data of quantitative real-time RT-PCR from livers of challenged ducklings also showed that the level of virus copies in rAAAV-VP1 group was significantly lower than that of the PBS group. Collectively, these results demonstrate that the AAAV-based vaccine is a potential vaccine candidate for the control of duck viral hepatitis.