Characterization of a hypervirulent fowl adenovirus 4 with the novel genotype newly prevalent in China and establishment of reproduction infection model of hydropericardium syndrome in chickens

Differential innate immune responses to fowl adenovirus serotype 4 infection in Leghorn male hepatocellular and chicken embryo fibroblast cells

Fowl adenovirus serotype 4 (FAdV-4) infections result in substantial economic losses in the poultry industry. Recent findings have revealed that FAdV-4 significantly suppresses the host immune response upon infection; however, the specific viral and host factors contributing to this immunomodulatory activity remain poorly characterized. Moreover, diverse cell types exhibit differential immune responses to FAdV-4 infection. To elucidate cell-specific host responses, we performed transcriptomic analysis of FAdV-4 infected leghorn male hepatocellular (LMH) and chicken embryo fibroblast (CEF) cells. Although FAdV-4 replicated more efficiently in LMH cells, it provoked limited interferon-stimulated gene induction. In contrast, FAdV-4 infection triggered robust antiviral responses in CEF cells, including upregulation of cytosolic DNA sensing and interferon-stimulated genes. Knockdown of key cytosolic DNA sensing molecules enhanced FAdV-4 replication in LMH cells while reducing interferon-stimulated gene expression. Our findings reveal cell-specific virus-host interactions that provide insight into FAdV-4 pathogenesis while identifying factors that mediate antiviral immunity against FAdV-4.

Immunoprotection of FliBc chimeric fiber2 fusion proteins targeting dendritic cells against Fowl adenovirus serotype 4 infection

Hepatitis-hydropericardium syndrome (HHS) is a highly fatal disease in chickens caused by the highly pathogenic fowl adenovirus serotype 4 (FAdV-4), which has severe economic consequences. The fiber2 protein exhibits excellent potential as a candidate for a subunit vaccination against FAdV-4. Despite having a high safety profile, subunit vaccines have low immunogenicity due to their lack of infectivity, which leads to low levels of immune response. As a vaccine adjuvant, Salmonella flagellin possesses the potential to augment the immunological response to vaccinations. Additionally, a crucial strategy for enhancing vaccine efficacy is efficient presentation of immune antigens to dendritic cells (DC) for targeted vaccination. In this study, we designed FAdV-4-fiber2 protein, and a recombinant protein called FliBc-fiber2-SP which based on FAdV-4-fiber2 protein, was generated using the gene sequence FliBc, which retains only the conserved sequence at the amino and carboxyl termini of the flagellin B subunit, and a short peptide SPHLHTSSPWER (SP), which targets chicken bone marrow-derived DC. They were separately administered via intramuscular injection to 14-day-old specific pathogen-free (SPF) chickens, and their immunogenicity was compared. At 21 d postvaccination (dpv), it was found that the FliBc-fiber2-SP recombinant protein elicited significantly higher levels of IgG antibodies and conferred a vaccine protection rate of up to 100% compared to its counterpart fiber2 protein. These results suggest that the DC-targeted peptide fusion strategy for flagellin chimeric antigen construction can effectively enhance the immune protective efficacy of antigen proteins.

Development of an ELISA for the detection of fowl adenovirus serotype -4 utilizing fiber protein

Hydropericardium syndrome (HPS), caused by the Fowl adenovirus 4 (FAdV-4) has led to significant financial losses for the poultry industry globally, including Pakistan over the past few years. Conventional serological methods are time consuming, laborious and less sensitive therefore, a rapid and sensitive ELISA kit is required for the reliable detection of FAdV-4 infection. In the current research, fiber proteins (1 &2) of FAdV-4 were successfully expressed in Escherichia coli and purified using metal affinity chromatography. Using these proteins as antigens, an indirect ELISA for detecting FAdV-4 infection was developed. The developed ELISA showed superior performances upon comparison with Serum neutralization test (SNT). This ELISA also showed reliable detection of FAdV specific antibodies in experimentally infected and vaccinated chickens. This assay produced good correlation on the samples collected from the field with SNT and found essential for large scale serology of the FAdV. No cross reactivity was observed in the ELISA following the testing of the serum samples of different other avian pathogens which showed that this ELISA is specific in detecting the FAdV infection. In conclusion, the developed Fiber protein ELISA is highly sensitive and specific in the detecting the FAdV infection and can be utilized for large scale sero-epidemiology of the disease.

Adenovirus type D and type E infection in broiler chickens: the effect on CD4 and CD8 T cell response, cytokines expression and their immunopathology

1. A total of 150-day-old chicks were divided into three groups of 50 birds (G1-G3); G1 and G2 were orally inoculated at 1-day old with 0.5 ml of 107 TCID50/ml FAdV-D serotype 2 (MT386509.1) and FAdV-E serotype 8a (MW847902), respectively, and G3 was blank control group.2. Cell-mediated immune response was evaluated by detection of CD4, CD8 T lymphocytes and the mRNA expression of IL6 and IL8 in the chicken spleen using q-PCR. Additionally, immunopathology was performed at 3, 5 and 7 day post infection (dpi) and weekly until the end of the experiment.3. Results revealed that transcription of inflammatory cytokines (IL6, IL8) was up regulated in the spleen of FAdV type D and type E infected chickens at various time points relative to the control group. A marked decrease in the number of CD4 and CD8 T lymphocytes at 5 and 7 dpi in G1 of chickens infected with FAdV type D. Whereas, in chickens infected with FAdV type E, the CD4 and CD8 T lymphocytes were markedly decreased at 7 dpi.4. In contrast, there were no significant differences in humoral immune responses against NDV vaccine in (G1 and G2) at different intervals post-vaccination compared to the control group. The histopathology of the bursa, thymus, and spleen in the infected groups showed lymphocytolysis with severe reticular cells hyperplasia and lymphoid depletion.5. In conclusion, fowl adenovirus types D and E have an immunosuppressive effect in broilers which may be considered one of the main causes of the continuous co-infections with other viruses reported in the field during the last 10 years.

Genomic and Pathologic Characterization of the First FAdV-C Serotype 4 Isolate from Black-Necked Crane

Fowl adenoviruses (FAdVs) are distributed worldwide in poultry and incriminated as the etiological agents for several health problems in fowls, and are capable of crossing species barriers between domestic and wild fowls. An FAdV strain was, for the first time, isolated from black-necked crane in this study, and was designated as serotype 4 Fowl aviadenovirus C (abbreviated as BNC2021) according to the phylogenetic analysis of its DNA polymerase and hexon gene. The viral genomic sequence analysis demonstrated that the isolate possessed the ORF deletions that are present in FAdV4 strains circulating in poultry fowls in China and the amino acid mutations associated with viral pathogenicity in the hexon and fiber 2 proteins. A viral challenge experiment with mallard ducks demonstrated systemic viral infection and horizontal transmission. BNC2021 induced the typical clinical signs of hepatitis-hydropericardium syndrome (HHS) with swelling and inflammation in multiple organs and showed significant viral replication in all eight organs tested in the virus-inoculated ducks and their contactees at 6 dpi. The findings highlight the importance of surveillance of FAdVs in wild birds.

Design and Identification of a Novel Antiviral Affinity Peptide against Fowl Adenovirus Serotype 4 (FAdV-4) by Targeting Fiber2 Protein

Outbreaks of hydropericardium hepatitis syndrome caused by fowl adenovirus serotype 4 (FAdV-4) with a novel genotype have been reported in China since 2015, with significant economic losses to the poultry industry. Fiber2 is one of the important structural proteins on FAdV-4 virions. In this study, the C-terminal knob domain of the FAdV-4 Fiber2 protein was expressed and purified, and its trimer structure (PDB ID: 7W83) was determined for the first time. A series of affinity peptides targeting the knob domain of the Fiber2 protein were designed and synthesized on the basis of the crystal structure using computer virtual screening technology. A total of eight peptides were screened using an immunoperoxidase monolayer assay and RT-qPCR, and they exhibited strong binding affinities to the knob domain of the FAdV-4 Fiber2 protein in a surface plasmon resonance assay. Treatment with peptide number 15 (P15; WWHEKE) at different concentrations (10, 25, and 50 μM) significantly reduced the expression level of the Fiber2 protein and the viral titer during FAdV-4 infection. P15 was found to be an optimal peptide with antiviral activity against FAdV-4 in vitro with no cytotoxic effect on LMH cells up to 200 μM. This study led to the identification of a class of affinity peptides designed using computer virtual screening technology that targeted the knob domain of the FAdV-4 Fiber2 protein and may be developed as a novel potential and effective antiviral strategy in the prevention and control of FAdV-4.

Multiantigen epitope fusion recombinant proteins from capsids of serotype 4 fowl adenovirus induce chicken immunity against avian Angara disease

Avian Angara disease caused by fowl adenovirus serotype 4 (FAdV-4) has spread widely and brought economic losses to the poultry industry in some countries. Effective vaccines for Angara disease control are currently lacking. In this study, four capsid proteins (hexon, penton, fiber1 and fiber2) from FAdV-4 were selected, and their optimal efficient antigenic epitopes predicted by bioinformatics software were tandemly linked with the flexible linker GGGGS. Based on their amino acid sequences, the DNA sequences for the genes encoding the multiantigen epitope tandem proteins (MAETPs) FAdV4:F1, FAdV4:P, FAdV4:F2 and FAdV4:H were chemosynthesized and then ligated by T4 ligases at the cleavage sites of restriction endonucleases to construct DNAs encoding the multilinked fusion recombinant proteins (MLFRPs) used as protective antigens from avian Angara disease. These genes ligated into the expression vector pET-28a were successfully expressed using the Escherichia coli prokaryotic expression system to prepare five kinds of MLFRPs (FAdV4:F1-P-F2-H, FAdV4:F1-F2-P-H, FAdV4:F1-F2-H-P, FAdV4:F1-P-H-F2 and FAdV4:F1-H-F2-P) for use to immunize chicks. FAdV-4 was injected into MLFRP-immunized chickens, and the challenge protection rate was evaluated. FAdV4:F1-P-F2-H produced the best protection against FAdV-4, with a single immunization resulting in a 100 % protection rate, followed by FAdV4:F1-F2-P-H (83.33 %) and FAdV4:F1-F2-H-P (66.67 %). FAdV4:F1-P-H-F2 and FAdV4:F1-H-F2-P were not able to induce a good immune protection effect after one immunization. However, all of the MLFRPs were capable of protecting the host from FAdV-4 infection after two immunizations. In conclusion, these MLFRPs generated based on capsid proteins of FAdV-4 are promising candidate subunit vaccines against Angara disease.

Epidemiology, pathology, prevention, and control strategies of inclusion body hepatitis and hepatitis-hydropericardium syndrome in poultry: A comprehensive review

Infection with fowl adenoviruses (FAdVs) can result in a number of syndromes in the production of chicken, including inclusion body hepatitis (IBH), hepatitis-hydropericardium syndrome (HHS), and others, causing enormous economic losses around the globe. FAdVs are divided into 12 serotypes and five species (A-E; 1-8a and 8b-11). Most avian species are prone to infection due to the widespread distribution of FAdV strains. The genus aviadenovirus, which is a member of the adenoviridae family, is responsible for both IBH and HHS. The most popular types of transmission are mechanical, vertical, and horizontal. Hepatitis with basophilic intranuclear inclusion bodies distinguishes IBH, but the buildup of translucent or straw-colored fluid in the pericardial sac distinguishes HHS. IBH and HHS require a confirmatory diagnosis because their clinical symptoms and postmortem abnormalities are not unique to those conditions. Under a microscope, the presence of particular lesions and inclusion bodies may provide clues. Traditional virus isolation in avian tissue culture is more delicate than in avian embryonated eggs. Additionally, aviadenovirus may now be quickly and precisely detected using molecular diagnostic tools. Preventive techniques should rely on efficient biosecurity controls and immunize breeders prior to production in order to protect progeny. This current review gives a general overview of the current local and global scenario of IBH, and HHS brought on by FAdVs and covers both their issues and preventative vaccination methods.

Genomic characterization of a fowl adenovirus serotype 4 strain isolated from a chicken with hydropericardium syndrome in Japan

Here, we report the genomic characterization of a fowl adenovirus serotype 4 strain isolated from a chicken with hydropericardium syndrome in Japan. The viral genome of FAdV-4 strain JP/LVP-1/96 was found to be 45,688 bp long. Amino acid substitutions at position 219 (G to D) in the fiber-2 protein and at position 188 (I to R) in the hexon protein, which are commonly found in virulent FAdV-4 strains, were also found in the JP/LVP-1/96 strain. Additional specific amino acid substitutions commonly found in virulent FAdV-4 strains were found in ORFs 4 and 43, which are present only in members of the species Fowl adenovirus C. Phylogenetic analysis based on complete hexon protein gene sequences showed that strain JP/LVP-1/96 belongs to a different genetic cluster from the strains circulating in neighboring countries.

A Novel Recombinant FAdV-4 Virus with Fiber of FAdV-8b Provides Efficient Protection against Both FAdV-4 and FAdV-8b

Since 2015, the outbreaks of hydropericardium-hepatitis syndrome (HHS) and inclusion body hepatitis (IBH) caused by the highly pathogenic serotype 4 fowl adenovirus (FAdV-4) and serotype 8 fowl adenovirus (FAdV-8), respectively, have caused huge economic losses to the poultry industry. Although several vaccines have been developed to control HHS or IBH, a recombinant genetic engineering vaccine against both FAdV-4 and FAdV-8 has not been reported. In this study, recombinant FAdV-4 expressing the fiber of FAdV-8b, designated as FA4-F8b, expressing fiber of FAdV-8b was generated by the CRISPR-Cas9 and homologous recombinant techniques. Infection studies in vitro and in vivo revealed that the FA4-F8b replicated efficiently in LMH cells and was also highly pathogenic to 2-week-old SPF chickens. Moreover, the inoculation of inactivated the FA4-F8b in chickens could not only induce highly neutralizing antibodies, but also provide efficient protection against both FAdV-4 and FAdV-8b. All these demonstrate that the inactivated recombinant FA4-F8b generated here can act as a vaccine candidate to control HHS and IBH, and FAdV-4 can be an efficient vaccine vector to deliver foreign antigens.

Development of a Novel Avian Vaccine Vector Derived From the Emerging Fowl Adenovirus 4

Severe hepatitis-hydropericardium syndrome (HHS) associated with a novel viral genotype, fowl adenovirus 4 (FAdV-4), has emerged and widely spread in China since 2015, causing severe economic losses to the poultry industry. We previously reported that the hexon gene is responsible for pathogenicity and obtained a non-pathogenic hexon-replacement rHN20 strain; however, the lack of information about the non-essential regions for virus replication limits the development of a FAdV-4 vector. This study first established an enhanced green fluorescent protein (EGFP)-indicator virus based on the FAdV-4 reverse genetic technique, effective for batch operations in the virus genome. Based on this, 10 open reading frames (ORFs) at the left end and 13 ORFs at the right end of the novel FAdV-4 genome were deleted separately and identified as non-essential genes for viral replication, providing preliminary insertion sites for foreign genes. To further improve its feasibility as a vaccine vector, seven combinations of ORFs were successfully replaced with EGFP without affecting the immunogenicity of the vector backbone. Finally, a recombinant rHN20-vvIBDV-VP2 strain, expressing the VP2 protein of very virulent infectious bursa disease virus (vvIBDV), was rescued and showed complete protection against FAdV-4 and vvIBDV. Thus, the novel FAdV-4 vector could provide sufficient protection for HHS and efficient exogenous gene delivery. Overall, our findings systemically identified 23 non-essential ORFs for FAdV-4 replication and seven foreign gene insertion regions, providing valuable information for an in-depth understanding of the novel FAdV-4 pathogenesis and development of multivalent vaccines.

Characterization of Co-infection With Fowl Adenovirus Serotype 4 and 8a

Fowl adenoviruses (FAdVs), which are distributed worldwide, have caused considerable economic losses to poultry farms. Co-infection with FAdVs and other avian pathogens has been reported previously. However, the pathogenicity of different serotypes of FAdVs causing co-infection remains unclear. Herein, strain HN from FAdV species C serotype 4 (FAdV-4) and strain AH720 from species E serotype 8a (FAdV-8a) were used to assess the pathogenicity of their co-infection in specific-pathogen-free (SPF) chickens. Compared with chickens infected with FAdV-4 alone, those co-infected with FAdV-4 and FAdV-8a showed similar clinical symptoms, mortality rates and degree of tissue lesions, and notably decreased viral loads of HN. Conversely, the viral loads of AH720 increased markedly in the co-infection group compared with that in chickens infected with AH720 strain alone. Increased viral loads of AH720 in the liver were suspected to contribute to the pathogenicity of chickens co-infected with the HN and AH720 strains. This was further investigated by histopathology and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining analyses. Collectively, these data indicated that co-infection with FAdV-4 and FAdV-8a suppresses the replication and proliferation of FAdV-4 but enhances the replication and proliferation of FAdV-8a in chicken liver. This study will provide valuable information for the further investigation of the interactions between FAdV-4 and FAdV-8a during co-infection.

An inactivated vaccine based on artificial non-pathogenic fowl adenovirus 4 protects chickens against hepatitis-hydropericardium syndrome

Hepatitis-hydropericardium syndrome (HHS) in birds is mainly caused by virulent fowl adenovirus 4 (FAdV-4). A novel genotype, hypervirulent FAdV-4, emerged in 2015 with a high mortality rate ranging from 30 % to 100 % in chickens. Vaccination is an economically feasible method to control HHS. Although there have been various reports of inactivated vaccines from virulent wild-type FAdV-4 against HHS, biosafety threats of inactivated vaccines from potential pathogenic components have been presented to the poultry industry, and safer vaccines are urgently needed. A non-pathogenic recombinant FAdV-4 strain, designated as rHN20, was generated based on the hypervirulent strain in our previous study. Here, we developed a novel inactivated oil-adjuvanted vaccine derived from rHN20 strain and evaluated its immunogenicity in specific-pathogen-free chickens. Chickens subcutaneously or intramuscularly immunized with the inactivated vaccine produced high titers of neutralizing antibodies and were protected from a lethal dose of virulent wild-type FAdV-4 challenge. Collectively, an inactivated vaccine was developed, which was capable of providing full protection for chickens against HHS, and significantly reduced the potential biosafety threats.

Identification of a novel immunological epitope on Hexon of fowl adenovirus serotype 4

Fowl adenovirus serotype 4 (FAdV-4), the causative agent of hepatitis-hydropericardium syndrome (HHS), distributed widely in the poultry farms in China. Hexon is one of the major capsid proteins associated with viral species or serotypes. However, the epitopes of Hexon protein remain largely unknown. In this study, a monoclonal antibody (mAb) specific to Hexon protein of FAdV-4, designated as 3G8, was generated. Subsequently, the linear peptide recognized by 3G8 was mapped and identified as ²¹³AYGAYVK²¹⁹ using a series of overlapping peptides generated from Hexon protein. Amino acid sequence analysis revealed that the epitope recognized by 3G8 was highly conserved across all the FAdVs. The epitope was immunogenic and could be recognized by FAdV-4 positive chicken serum samples. These findings will enrich our knowledge regarding the epitope on Hexon and provide valuable information for further characterization of the antigenicity of Hexon protein.

Immunogenicity of Novel Live Vaccine Based on an Artificial rHN20 Strain against Emerging Fowl Adenovirus 4

In recent years, hepatitis-hydropericardium syndrome (HHS), caused by novel fowl adenovirus 4 (FAdV-4), has caused serious economic losses to the poultry industry. Vaccines are important for preventing and controlling HHS. Current FAdV-4 vaccine research and development are mainly focuses on inactivated vaccines and relatively fewer live vaccines. We previously demonstrated that the hexon gene is the key gene responsible for the high pathogenicity of FAdV-4 and constructed a non-pathogenic chimeric virus rHN20 strain based on the emerging FAdV-4. In this study, the immunogenicity of artificially rescued rHN20 was evaluated in chickens using different routes and doses as a live vaccine. The live rHN20 vaccine induced high titers of neutralizing antibodies against FAdV-4 and fully protected the immunized chickens against a lethal dose of FAdV-4. Furthermore, immunized chickens showed no clinical symptoms or histopathological changes in the FAdV-4-targeted liver, and the viral load in the tissues of immunized chickens was significantly lower than that of chickens in the challenge control group. Collectively, the live rHN20 vaccine effectively protected our sample against FAdV-4 infection and can be considered a live vaccine candidate for preventing HHS in the poultry industry.

Isolation, identification and genetic characterization analysis of a fowl aviadenovirus serotype 4 strain from Tianjin, China

A fowl aviadenovirus serotype 4 (FAdV-4), Y17215-1, was isolated from the liver of chickens with Hydropericardium-hepatitissyndrome(HHS) in a chicken farm of Tianjin, China. Obvious cytopathic effects were observed in the infected chicken liver hepatocellular carcinoma cell line (LMH cells) at 24 h post infection (hpi), which consisted of enlarger and rounder shape of cells. The typical and specific green fluorescence was observed by indirect immunofluorescence assay (IFA). Tissue Culture Infectious Dose50 (TCID₅₀) of it measured after five stable passage in LMH cells reached 10^6.5TCID₅₀/0.1 mL. The strain was inoculated through allantoic membrane of 10-day specific pathogen free(SPF) Chick embryos, the thicker allantoic membranes were observed at 120 hpi. 7-day-old SPF chickens were inoculated with the strain via intramuscular (i.m.) or intranasal (i.n.) injection which resulted in 100% mortality of test chickens. Additionally, the sickness and death of cohabitation chickens in the test group were observed which indicated that the virus can infect healthy chickens by horizontal transmission. The sick chickens showed depression, anorexia and diarrhea with green watery feces. Y17215-1-inoculated chickens mainly presented swollen liver with blood spot, and the enhancement of effusion or yellow gel like effusion that were observed in the pericardium through necropsy. Histopathological examination showed focal necrosis of hepatocytes and characteristic eosinophilic inclusion bodies in the cytoplasm. The results showed that the Y17215-1 isolate had high pathogenicity to SPF chickens. The phylogenetic analysis of the major structural proteins including hexon, fiber-1 and fiber-2 revealed that Y17215-1 strain belongs to C species of fowl aviadenovirus of aviadenovirus family, and has high homology with other Chinese strains isolated in recent years, but was distinct from ON1、MX-SHP95、KR5 and other foreign isolates. This study laid a foundation for further study of epidemiological investigation, pathogenic mechanism as well as the diagnosis and control technology of FAdV-4.

A Single Amino Acid at Residue 188 of the Hexon Protein Is Responsible for the Pathogenicity of the Emerging Novel Virus Fowl Adenovirus 4

Since 2015, severe hydropericardium-hepatitis syndrome (HHS) associated with a novel fowl adenovirus 4 (FAdV-4) has emerged in China, representing a new challenge for the poultry industry. Although various highly pathogenic FAdV-4 strains have been isolated, the virulence factor and the pathogenesis of novel FAdV-4 are unclear. In our previous studies, we reported that a large genomic deletion (1,966 bp) is not related to increased virulence. Here, two recombinant chimeric viruses, rHN20 strain and rFB2 strain, were generated from a highly pathogenic FAdV-4 strain by replacing the hexon or fiber-2 gene of a nonpathogenic FAdV-4, respectively. Both chimeric strains showed similar titers to the wild-type strain in vitro. Notably, rFB2 and the wild-type strain induced 100% mortality, while no mortality or clinical signs appeared in chickens inoculated with rHN20, indicating that hexon, but not fiber-2, determines the novel FAdV-4 virulence. Furthermore, an R188I mutation in the hexon protein identified residue 188 as the key amino acid for the reduced pathogenicity. The rR188I mutant strain was significantly neutralized by chicken serum in vitro and in vivo, whereas the wild-type strain was able to replicate efficiently. Finally, the immunogenicity of the rescued rR188I was investigated. Nonpathogenic rR188I provided full protection against lethal FAdV-4 challenge. Collectively, these findings provide an in-depth understanding of the molecular basis of novel FAdV-4 pathogenicity and present rR188I as a potential live attenuated vaccine candidate or a novel vaccine vector for HHS vaccines. IMPORTANCE HHS associated with a novel FAdV-4 infection in chickens has caused huge economic losses to the poultry industry in China since 2015. The molecular basis for the increased virulence remains largely unknown. Here, we demonstrate that the hexon gene is vital for FAdV-4 pathogenicity. Furthermore, we show that the amino acid residue at position 188 of the hexon protein is responsible for pathogenicity. Importantly, the rR188I mutant strain was neutralized by chicken serum in vitro and in vivo, whereas the wild-type strain was not. Further, the rR188I mutant strain provided complete protection against FAdV-4 challenge. Our results provide a molecular basis of the increased virulence of novel FAdV-4. We propose that the rR188I mutant is a potential live attenuated vaccine against HHS and a new vaccine vector for HHS-combined vaccines.

Age-dependence of hypervirulent fowl adenovirus type 4 pathogenicity in specific-pathogen-free chickens

Hypervirulent fowl adenovirus serotype 4 (hvFAdV-4) has emerged as a major pathogen of hepatitis-hydropericardium syndrome (HHS) with increased mortality in chickens, resulting in economic losses to the Chinese poultry industry since June 2015. Here, we isolated a hypervirulent FAdV-4 (hvFAdV-4) strain (designated GD616) from 25-day-old meat-type chickens with severe HHS in Guangdong Province China in June 2017. The whole genome of the strain GD616 shares high homology with those in the recently-reported hvFAdV-4 isolates in China, with natural deletions of ORF19 and ORF27. A comparative analysis of Hexon and Fiber-2 proteins revealed that 2 unique amino acid residues at positions 378 and 453 of the Fiber-2 protein might be associated with virulence due to their occurrences in all the hvFAdV-4 isolates only. To systemically evaluate the effect of age on the susceptibility of chickens to hvFAdV-4, we used this hvFAdV-4 strain to intramuscularly inoculate 7- to 180-day-old specific-pathogen-free chickens for the evaluation of pathogenicity. These results showed that the pathogenicity of the hvFAdV-4 strain GD616 to chickens exhibited age-relatedness, with younger than 59-day-old chickens showing 100% morbidity and mortality, while 180-day-old chickens still exhibited a hydropericardium syndrome-like clinicopathology with 60% morbidity and 20% mortality. These findings enrich the current available knowledge regarding the pathogenicity of the hypervirulent FAdV-4 virus in chickens with a wide range of ages, which assists with the selection of suitable-aged chickens for the evaluation of hvFAdV-4 vaccines.

The first complete genome sequence and pathogenicity characterization of fowl adenovirus 11 from chickens with inclusion body hepatitis in Pakistan

Inclusion body hepatitis (IBH), hydropericardium syndrome, and gizzard erosion associated with fowl adenovirus (FAdV) infections are reported globally and resulted in significant poultry industry economic losses. In 2018, severe IBH appeared in Pakistan in a 17-week-old layer flock. Subsequently, a FAdV-11 strain (designated as PKFAd18) was isolated from liver samples and identified based on phylogenetic analyses of the serotype-specific L1 region of the capsid hexon gene. There is no complete genome sequence of the Pakistani FAdV-11. This study successfully sequenced the complete genome of PKFAd18. The full genome of PKFAd18 contains 43 840 base pairs (bp) with a G + C content of 53.9 %, which is comparable to other FAdV serotypes. Similar to other FAdV-11 strains, PKFAd18 has only one fiber, while FAdV-1 and FAdV-4 have two fibers. Notably, PKFAd18 showed unique characteristics compared to other FAdV-11 strains. A natural large genomic deletion (1215 bp) appeared in tandem repeat region two, relative to the ON-NP2 strain. Phylogenetic analyses of the PKFAd18 penton gene showed higher homology with FAdV-9, highlighting potential natural recombination between FAdV-11 and FAdV-9. Moreover, the pathogenicity of PKFAd18 studied in specific-pathogen-free chickens showed that PKFAd18 is capable of inducing severe IBH and could be responsible for IBH in Pakistan. Thus, the first complete genome of FAdV-11 in Pakistan was sequenced in this study, which enriches the diversity of knowledge about FAdV-11 and is useful for developing diagnostics and vaccines for IBH induced by FAdV-11 in Pakistan.

Identification of chicken CAR homology as a cellular receptor for the emerging highly pathogenic fowl adenovirus 4 via unique binding mechanism

Since 2015, the prevalence of severe hepatitis-hydropericardium syndrome, which is caused by the novel genotype fowl adenovirus serotype 4 (FAdV-4), has increased in China and led to considerable economic losses. The replication cycle of FAdV-4, especially the emerging highly pathogenic novel genotype FAdV-4, remains largely unknown. The adenovirus fibre interacts with the cellular receptor as the initial step in adenovirus (AdV) infection. In our previous studies, the complete genome sequence showed that the fibre patterns of FAdV-4 were distinct from all other AdVs. Here, protein-blockage and antibody-neutralization assays were performed to confirm that the novel FAdV-4 short fibre was critical for binding to susceptible leghorn male hepatocellular (LMH) cells. Subsequently, fibre 1 was used as bait to investigate the receptor on LMH cells via mass spectrometry. The chicken coxsackie and adenovirus receptor (CAR) protein was confirmed as the novel FAdV-4 receptor in competition assays. We further identified the D2 domain of CAR (D2-CAR) as the active domain responsible for binding to the short fibre of the novel FAdV-4. Taken together, these findings demonstrate for the first time that the chicken CAR homolog is a cellular receptor for the novel FAdV-4, which facilitates viral entry by interacting with the viral short fibre through the D2 domain. Collectively, these findings provide an in-depth understanding of the mechanisms of the emerging novel genotype FAdV-4 invasion and pathogenesis.

Development and application of a novel ELISA for detecting antibodies against group I fowl adenoviruses

Since 2015, outbreaks of hepatitis-hydropericardium syndrome (HPS) caused by a novel genotype of fowl adenovirus 4 (FAdV-4) infection have created serious economic losses in China. Given that other serotypes of hypervirulent FAdVs have also been reported in poultry around the world, a common ELISA for all serotypes within the group I fowl adenoviruses (FAdV-I) is urgently needed, especially for clinical epidemic serotypes. In this study, we used high purity and concentration virions of FAdV-4 and developed a common ELISA for detecting antibodies against 12 FAdV-I serotypes. The developed ELISA was able to distinguish between antibodies against FAdV-I, FAdV-III, and other heterologous viruses without any cross-reaction. Furthermore, the ELISA showed higher sensitivity than the FAdV-1-based ELISA to the novel FAdV-4 found in China. Moreover, since there are no commercial vaccines against FAdVs in China, the ELISA was applied to detect sera samples from specific pathogen-free chickens inoculated with inactivated FAdV-1, FAdV-4, and FAdV-8a. The assay showed high sensitivities for all three detected serotypes within FAdV-I. In conclusion, a novel, common ELISA for FAdV-I was developed in this study and could be a powerful tool for seroepidemiological investigations and FAdVs vaccine development.

Characterization and pathogenicity of fowl adenovirus serotype 4 isolated from eastern China

BACKGROUND

Fowl adenovirus outbreaks have occurred in China since June 2015. This virus is an emerging infectious disease that causes hydropericardium syndrome and inclusion body hepatitis (HPS-IBH), resulting in significant economic loss to poultry farmers. Five fowl adenovirus (FAdV) strains (HN, AQ, AH726, JS07 and AH712) were isolated from Jiangsu and Anhui provinces.

RESULTS

Phylogenetic analysis revealed that the five isolates belonged to species C fowl adenovirus serotype 4. An 11 amino-acid deletion in ORF29, relative to an older viral isolate, JSJ13, was observed for all five strains described here. In chicken experiments, 80-100% birds died after intramuscular inoculation and displayed lesions characteristic of HPS-IBH. The viral DNA copies were further detected by hexon-probe based real-time polymerase chain reaction (PCR) in the chicken samples. The viral loads and cytokine profiles were recorded in all the organs after infections. Despite minor genetic differences, the 5 strains displayed significantly different tissue tropisms and cytokine profiles.

CONCLUSIONS

Our data enhance the current understanding some of the factors involved in the pathogenicity and genetic diversity of the FAdV serotype 4 (FAdV-4) in China. Our work provides theoretical support for the prevention and control of HPS-IBH in chickens.

Pathogenicity of a fowl adenovirus serotype 4 isolated from chickens associated with hydropericardium-hepatitis syndrome in China

Hydropericardium-hepatitis syndrome (HHS) is characterized by pericardial effusion and hepatitis and causes huge economic losses in the poultry industry in China. In this study, a strain of fowl adenoviruses (FAdV-4) (GX-1) was isolated from liver samples of diseased chickens with HHS. Phylogenetic analysis based on complete genome gene revealed that GX-1 clustered with the C-type fowl adenovirus and was serotyped as FAdV-4. Pathogenicity testing showed that the GX-1 strain caused 100% mortality in 10-day-old specific pathogen-free chickens at a dose of 104 tissue culture infective doses (TCID50) within 3 d post-infection. A viral dose of 103 TCID50 resulted in a 16% survival rate before day 9 and at 102 TCID50 an 80% rate before day 6. At necropsy, livers from infected chickens were swollen and yellow brown with necrotic foci. The hearts were flabby with amber-colored and jelly-like fluid in the pericardial sacs. The kidneys were swollen and congested. Histologically eosinophilic intranuclear inclusion body could be seen in the hepatic cell. The result of histopathological examination also revealed that heart muscle fibers were fractured with extensive congestion and hemorrhaging. Other tissues like kidney, bursa of Fabricius, thymus, and spleen were observed degeneration and necrosis. Virus-specific antibodies appeared in serum beginning at day 14 and reached statistically significant levels at 21, 28, 35, and 42 dpi (P < 0.001). In conclusion, we identified a highly virulent FAdV-4 virus as causative agent of the HHS outbreak reported here. The FAdV-4 GX-1 strain will be valuable for vaccine evaluation and development to prevent and reduce the spread of HHS in the poultry industry.

Pathogenesis of Hypervirulent Fowl Adenovirus Serotype 4: The Contributions of Viral and Host Factors

Since 2015, severe outbreaks of hepatitis-hydropericardium syndrome (HHS), caused by hypervirulent fowl adenovirus serotype 4 (FAdV-4), have emerged in several provinces in China, posing a great threat to poultry industry. So far, factors contributing to the pathogenesis of hypervirulent FAdV-4 have not been fully uncovered. Elucidation of the pathogenesis of FAdV-4 will facilitate the development of effective FAdV-4 vaccine candidates for the control of HHS and vaccine vector. The interaction between pathogen and host defense system determines the pathogenicity of the pathogen. Therefore, the present review highlights the knowledge of both viral and host factors contributing to the pathogenesis of hypervirulent FAdV-4 strains to facilitate the related further studies.

Transcriptome analysis of fowl adenovirus serotype 4 infection in chickens

Fowl adenovirus serotype 4 (FAdV-4) is a causative agent of inclusion body hepatitis and hydropericardium–hepatitis syndrome. These diseases cause considerable economic losses in the global poultry industry and are significant stressors for infected chickens. However, the molecular mechanisms of FAdV-4 pathogenesis are poorly understood. In the present study, we identified differentially expressed genes from the livers of FAdV-4-infected chickens using RNA-seq at 7, 14 and 21 days after FAdV-4 infection. We identified 2395 differentially expressed genes at the three time points. These genes were enriched in variety of biological processes and pathways including PPAR and Notch signaling, cytokine–cytokine receptor interactions and Toll-like receptor signaling pathways. The transcriptional data were validated by quantitative real-time PCR. Our results will assist in the understanding of the molecular pathogenesis of FAdV-4 infection and for developing novel antiviral therapies.

Genetic characterization of fowl adenovirus serotype 4 isolates in Southern China reveals potential cross-species transmission

Increasing numbers of hepatitis-hydropericardium syndrome (HHS) outbreaks associated with Fowl adenovirus 4 (FAdV-4) have been confirmed in several provinces of China since 2015, mainly affecting 3-5-week-old broiler chicks, resulting in significant losses to the poultry industry. However, little is currently known regarding the molecular epidemiology and host specificity of FAdV-4 associated with HHS in Southern China. In the present study, we isolated 37 FAdV-4 strains from 52 suspected cases of HHS (33 from broilers, one from a layer, two from ducks, and one from a mandarin duck) from Guangdong province during 2016 to 2017. All 37 FAdV-4 strains obtained showed 100% identity of hexon genes at the nucleotide level, and also showed 100% nucleotide sequence identities with strains obtained from other provinces such as Shandong, Zhejiang, and Anhui, which grouped into a FAdV-C cluster. To our knowledge, this represents the first report of an FAdV-4 strain (GZ1) from a mandarin duck with HHS. Experimental infection of the GZ1 strain via intramuscular injection led to a 100% mortality rate in 21-day-old specific pathogen-free chickens. These data indicate the possibility of the cross-species transmission of FAdV-4, highlighting the need for implementing strict biosecurity measures to avoid the mixing of different bird species.

An emerging new fowl adenovirus genotype

In this work, we examined the diversity of fowl adenovirus (FAdV) types occurring in Hungary. From diseased chicken flocks in Eastern Hungary, 29 FAdV strains were isolated between 2011 and 2015. We performed molecular typing of the isolates based on their partial hexon sequences. The results showed that representatives from every FAdV species from A to E are present in Hungary, but compared to the findings from our previous survey, a lower number of different FAdV types were detected. Inclusion body hepatitis was always associated with FAdV-2 or -8b, gizzard erosion was caused in almost every case by FAdV-1. Numerous strains belonging to species FAdV-B were found. The complete genome sequence of a candidate new genotype strain, showing the highest divergence from the reference FAdV-5, was determined using next generation sequencing. In order to provide results compatible with the serology-based type classification, multiple genomic regions, including the major antigenic determinants, of the new isolate (strain 40440-M/2015) were compared to their counterparts in the prototype FAdV-5 (strain 340) from species FAdV-B, at both nucleotide and amino acid sequence levels. In different comparative analyses, the two strains were always found to have larger divergence between each other than any two of the most closely related FAdV serotypes. This new emerging FAdV genotype is already present in Hungary and Austria, though its exact pathological role requires further investigations. The introduction of a novel FAdV (geno)type for the classification of these strains is further supported.

A loop-mediated isothermal amplification coupling with a lateral flow dipstick for rapid and specific detection of fowl adenovirus serotype-4

Fowl adenovirus serotype-4 (FAdV-4) has been recognized as a predominant threat to the broilers aged from three to five weeks. Hydropericardium syndrome (HPS) is one of its major clinical diseases by FAdV-4 resulting in heavy economic losses. In this study, a loop-mediated isothermal amplification coupling with a lateral flow dipstick (LAMP-LFD) was developed for rapid and specific detection of fowl adenovirus serotype-4. The optimized LAMP-LFD can be completed in 60 min at 65 °C. The minimum detection limits of PCR, real-time PCR, nested PCR and LAMP-LFD are 1 × 10⁴ copies/μl, 1 × 10² copies/μl, 10 copies/μl and 10 copies/μl respectively. Moreover, the specificity of the LAMP-LFD assay is satisfactory and does not produce cross reactions with other species. In field samples, 150 samples were assayed by PCR and LAMP-LFD. They agreed on the diagnosis "positive" in 13% of clinical samples, and they agreed on the diagnosis "negative" in 85% of clinical samples. Their probability of agreement is p₀ = 147/150 = 13% + 85% = 98%. LAMP-LFD can potentially be modified and applied as a diagnostic tool for FAdV-4 infection especially in resource-limited areas, such as small breeding farms and basic veterinary labs to offer an affordable diagnostic.

Mechanism of fowl adenovirus serotype 4-induced heart damage and formation of pericardial effusion

Fowl adenovirus serotype 4 (FAdV-4) is the causative agent of hydropericardium syndrome (HPS), which is characterized by the accumulation of a clear, straw-colored fluid in the pericardial sac, and high mortality rates. In order to explore the mechanism of FAdV-4-induced cardiac damage, dynamic pathology, apoptosis, and inflammatory reactions were analyzed in vivo. Moreover, we detected viral proliferation, and ultrastructure, inflammation and apoptosis of cardiomyocytes (CM) after FAdV-4 infection in vitro. The results showed that FAdV-4 impaired cardiac integrity and function by causing apoptosis and inflammation in vivo. Flow cytometry showed that CM infected with FAdV-4 did not show apoptosis in vitro. In addition, the mRNA expression of four inflammatory cytokines (interleukin (il)1B, il6, il8, and tumor necrosis factor), and activity of three myocardial enzymes were significantly different between FAdV-4 and control groups. However, in vitro, these indexes showed no significant difference between the groups. These observations collectively indicated that the heart was not the target organ of FAdV-4, and the virus may not directly lead to the occurrence of CM apoptosis and inflammation. To explore the source of pericardial effusion, we measured total protein, albumin, aspartate aminotransferase, creatine kinase isoenzyme, lactate dehydrogenase, potassium, sodium, and chloride ions in serum and pericardial effusion. Pericardial effusion was derived from vascular exudation rather than CM degeneration. Further studies are needed to investigate the exudation mechanism of vascular endothelial cells in FAdV-4 infection then weakened or eliminated pericardial effusion to minimize heart injury and/or restore damaged CM.

The Natural Large Genomic Deletion Is Unrelated to the Increased Virulence of the Novel Genotype Fowl Adenovirus 4 Recently Emerged in China

Since 2015, severe hydropericardium-hepatitis syndrome (HHS), caused by a highly pathogenic fowl adenovirus 4 (FAdV-4), emerged in China. In our previous study, the FAdV-4 has been identified as a novel genotype with a unique 1966-bp nucleotide deletion (1966Del) between open reading frame 42 and 43. In this study, the natural 1966Del was frequently identified among 17 clinical isolates and other reported Chinese clinical strains. To investigate the relationship between 1966Del and the increased virulence of the novel FAdV-4, a CRISPR/Cas9 operating platform for FAdV-4 was developed for the first time in this study. Based on this platform, a Re1966 strain was rescued, inserted the relative 1966Del sequence of a nonpathogenic strain KR5. In the pathogenicity study, the Re1966 strain retained high virulence for specific-pathogen-free chickens, similar to the parental wild-type HLJFAd15, although the survival time of chickens infected with Re1966 was much longer. Therefore, the natural 1966Del was identified as a non-essential site for the increased virulence of the emerged novel FAdV-4. Although further research on the virulence-determining region or point within the genome of the novel FAdV-4 is needed, the CRISPR/Cas9 operating platform for the novel FAdV-4 was developed and successfully applied to edit the genomic DNA for the first time, and it provides a novel powerful tool for both basic virology studies and vaccine vector development of FAdVs.

Identification of two novel fowl adenovirus C-specific B cell epitopes using monoclonal antibodies against the capsid hexon protein

The diseases associated with fowl adenovirus (FAdV) infection, such as inclusion body hepatitis (IBH), hepatitis-hydropericardium syndrome (HPS), and gizzard erosion (GE), were first reported in Pakistan in 1987, and subsequent outbreaks have been reported worldwide, especially in China, where severe outbreaks of HPS with high mortality from 30 to 100% were recently reported and resulted in significant economic losses to the poultry industry. The diagnosis methods of FAdVs were mostly limited to the nucleotide sequence of hexon by PCR and DNA sequencing. The aim of this study was to generate B cell epitope maps of the species- and serotype-specific hexon L1 using monoclonal antibodies (mAbs) and bioinformatics tools for the development of novel diagnostic methods. In this study, the hexon L1 (230 amino acids) was expressed and used to generate 10 mAb-expressing hybridoma cell lines against the relative protein peptide. Subsequently, we defined the linear peptide epitopes recognized by these mAbs using a series of partially overlapping peptides derived from the FAdV-C hexon protein amino acid sequence to map mAbs reactivity. Finally, a common B cell epitope (₃₁PLAPKESMFN₄₀) for all species FAdVs and two FAdV-C-specific epitopes (₇₉KISGVFPNP₈₇ and ₁₈₁DYDDYNIGTT₁₉₀) were identified. These mAbs and their defined epitopes may support the development of the universal or species-specific differential diagnostic methods of FAdVs.

A subunit vaccine based on fiber-2 protein provides full protection against fowl adenovirus serotype 4 and induces quicker and stronger immune responses than an inactivated oil-emulsion vaccine

As the number of hepatitis hydropericardium syndrome (HHS) cases has increased in recent years in China, development of a safe and effective vaccine is now urgent. To address this problem a subunit vaccine is a good option, we here systematically investigated the minimum immune dose of a subunit vaccine against HHS based on recombinant fowl adenovirus serotype 4 (FAdV-4) fiber-2 protein and compared the effects between this subunit vaccine and an inactivated oil-emulsion FAdV-4 vaccine in a vaccination trial. The results revealed that the lowest dose of recombinant fiber-2 protein that could provide 100% protection against challenge with virulent FAdV-4 strain HB1501 as well as elicit protective immunity was 2.5 μg/bird. Neither clinical signs nor gross lesions were observed in chickens. In addition, immunization of specific-pathogen-free (SPF) chickens with recombinant fiber-2 protein (≥2.5 μg/bird) could induce quicker and stronger immune responses than the inactivated oil-emulsion FAdV-4 vaccine. These findings provide important information about the development of subunit vaccines for the control of HHS.

Complete genome sequence and pathogenicity of fowl adenovirus serotype 4 involved in hydropericardium syndrome in Southwest China

Since 2015, an emerging infectious disease of inclusion body hepatitis and hydropericardium syndrome (IBH-HPS) has been occurred in China, which caused economic loss in poultry farming. In this study, we isolated four fowl adenovirus strains from flocks with an outbreak of HPS. The complete nucleotide sequence of SC-Neijiang was determined and its pathogenicity was evaluated. Phylogenetic analysis based on hexon gene revealed that all the isolates belonged to fowl adenovirus serotype 4. The full genome sequence of SC-Neijiang has a size of 43,719 bp, with 54.85% G + C content. Compared with JSJ13, 11-amino-acid deletion at the ORF29 was appeared on SC-Neijiang. In infectious experiments, 80% (16/20) birds died in intramuscular route and lesions characteristic for Hydropericardium Syndrome (HPS), while 5% (1/20) birds died in nasal route. The viral DNA was further detected by real-time PCR in several chicken organs. The highest titers were recorded in all the organs at day 5 post-infection. To our knowledge, this is first report on the prevalence of fowl adenovirus in Southwest China. This research elucidated the characteristics of genome sequence and pathogenicity of Chinese FAdV-4 strain and provided theoretical support for the prevention and control of the disease.

Immunogenicity and protective efficacy of recombinant fiber-2 protein in protecting SPF chickens against fowl adenovirus 4

Since a novel hyper-virulent fowl adenovirus serotype 4 (FAdV-4) infection occurred in 2015, the novel FAdV-4 has been widely spreading across China, causing significant economic losses to the poultry industry. As the urgency of the issue calls for effective and efficient solutions, the present study investigated the possibility of the fiber-2 protein of the FAdV-4 to serve as a vaccine candidate against the novel FAdV-4. In the research, fiber-2 proteins were expressed in Escherichia coli, and then purified. To evaluate the immunogenicity of the recombinant fiber-2 protein, we investigated both the humoral and cellular immune responses in chickens immunized with fiber-2. The humoral immunity was assessed by detecting IgY antibodies and virus-neutralizing antibodies in chicken serum at 7, 14, 21 days post-immunization (dpi). We examined cellular immune responses by detecting CD3+CD4+ and CD3+CD8+ changes in chickens' peripheral blood through using flow cytometry at 7, 14, 21 dpi. The cytokine production in the serum of the immunized chickens was detected by ELISA at 7, 14, 21 dpi to further explore the impact of the recombinant protein on the regulation of cytokines. The protective efficacy was determined by the survival rate of the immunized chickens challenged with the novel FAdV-4. The results show that the level of IgY antibodies of the chickens immunized with fiber-2 protein was significantly higher than that of the chickens immunized with an inactivated vaccine against FAdV-4. Moreover, 7 days after immunization, the CD4+ T-cell proliferative response of the chickens immunized with fiber-2 was significantly higher than that of the chickens immunized with the inactivated vaccine. Challenge experiment showed that the fiber-2 protein could provide full protection and the inactivated vaccine could provide 90 percent protection against the FAdV-4. These results suggest that the recombinant fiber-2 protein can be an ideal candidate for subunit vaccines against the disease.

Isolation and molecular characterization of prevalent Fowl adenovirus strains in southwestern China during 2015-2016 for the development of a control strategy

Fowl adenovirus (FAdV) has caused significant losses in chicken flocks throughout China in recent years. However, the current understanding of the genetic and pathogenic characteristics of the FAdV epidemic in southwestern China remains poorly understood. In this study, a total of 22 strains were isolated from liver samples of diseased chickens from farms in southwestern China. Phylogenetic analysis based on the hexon loop-1 gene showed that the 22 isolates were clustered into four distinct serotypes: FAdV serotype 4 (FAdV-4) (86.4%, 19/22), FAdV-2 (4.5%, 1/22), FAdV-8a (4.5%, 1/22), and FAdV-8b (4.5%, 1/22). FAdV-4 was the predominant serotype in southwestern China. Pathogenicity testing showed that the FAdV-4 serotype strain CH/GZXF/1602 and FAdV-8a strain CH/CQBS/1504 were pathogenic to chickens, with mortality rates reaching as high as 80% and 20%, respectively. The primary clinical feature observed following infection with strain CH/GZXF/1602 (FAdV-4) was hepatitis-hydropericardium syndrome, and that of strain CH/CQBS/1504 (FAdV-8a) was inclusion body hepatitis. Conversely, the FAdV-2 serotype strain CH/GZXF/1511 and FAdV-8b serotype strain CH/CQBS/1512 was not observed to be pathogenic in chickens. Then, CH/GZXF/1602 (FAdV-4) was selected for the preparation of an inactivated oil-emulsion vaccine. Immune studies on Partridge Shank broilers showed that a single dose immunization at 17 days of age could not only protect against homologous challenge with virulent FAdV-4 but also provided protection against clinical disease following challenge with the heterologous FAdV-8b virulent strain until 70 days of age. The characterization of newly prevalent FAdV strains provides a valuable reference for the development of an efficacious control strategy.

Fowl adenovirus-induced diseases and strategies for their control - a review on the current global situation

The stand-alone pathogenicity of fowl adenoviruses (FAdVs) had long been disputed, given the ubiquity of the viruses versus sporadic outbreaks, and variation between experimental studies. However, a globally emerging trend of FAdV-associated diseases has marked the past two decades, with hepatitis-hydropericardium syndrome mainly in Asia besides Arabian and Latin American countries, and geographically more disseminated outbreaks of inclusion body hepatitis. Finally, the appearance of FAdV-induced gizzard erosion (AGE) in Asia and Europe completed the range of diseases. Epidemiological studies confirmed serotype FAdV-4 as agent of hepatitis-hydropericardium syndrome, whereas inclusion body hepatitis is related to FAdV-2, -8a, -8b and -11. Members of the biologically more distant serotype FAdV-1 induce AGE. Urged by increasing problems in the field, numerous pathogenicity studies with FAdVs from outbreaks substantiated the primary aetiologic role of particular strains for distinct clinical conditions. Developments in the poultry industry towards highly specialized genetic breeds and rigorous biosecurity additionally contribute to the growing incidence of FAdV-related diseases. Confirming field observations, recent studies connected a higher susceptibility of broilers with their distinct physiology, implying the choice of bird type as a factor to be considered in infection studies. Furthermore, elevated biosecurity standards have generated immunologically naïve breeding stocks, putting broilers at risk in face of vertical FAdV transmission. Therefore, future prevention strategies should include adequate antibodies in breeders prior to production and - if necessary - vaccination, in order to protect progenies. This review aims to deliver a detailed overview on the current global situation about FAdV-induced diseases, their reproduction in vivo and vaccination strategies.

An Inactivated Novel Genotype Fowl Adenovirus 4 Protects Chickens against the Hydropericardium Syndrome That Recently Emerged in China

Since 2015, China has experienced outbreaks of severe hydropericardium syndrome (HPS), associated with a novel genotype and hypervirulent fowl adenovirus serotype 4 (FAdV-4) infection, with a prevalence in various provinces of the country. This has resulted in huge economic losses in the poultry industry. The novel FAdV-4 showed new genome characters, such as the natural deletion of open reading frame (ORF) 19 and ORF 27 (1966 bp), and high pathogenicity toward chickens. These are coupled with severe hydropericardium, inclusion body hepatitis, and mortality rates ranging from 30% to 90%. Although several inactivated and subunit vaccines against the traditional FAdV-4 have been developed, no commercial vaccine against the emerged disease caused by the novel strain has been available until now. The potential risks of infection with this novel hypervirulent FAdV-4 urgently require an effective vaccine. Thus, an inactivated oil-emulsion FAdV-4 vaccine formulated with the novel genotype virus was developed in this study. The vaccine provided a high level of antibody, preferential T helper 2 (Th2) (interleukin-4 secretion) not Th1 (interferon-γ secretion) response, and full protection against a lethal dose of the novel hypervirulent FAdV-4. Therefore, the novel genotype FAdV-4 vaccine is proposed as an attractive candidate to prevent and reduce the spread of HPS in the poultry industry of China.