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

A rapid, ultrasensitive, and highly specific method for detecting fowl adenovirus serotype 4 based on the LAMP-CRISPR/Cas12a system

Fowl adenovirus serotype 4 (FAdV-4) is the causative agent of hydropericardium hepatitis syndrome in chickens, which causes severe economic impact to the poultry industry. A simple, swift and reliable detection is crucial for timely identification of FAdV-4 infection, promoting effective viral prevention and control measures. Herein, the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 12a (Cas12a) system detection platform based on loop-mediated isothermal amplification (LAMP) was studied. The CRISPR RNA (crRNA) and LAMP primers were designed and screened based on the highly conserved region of the FAdV-4 hexon gene. The parameters were then optimized individually to achieve the ideal reaction performance. The platform could lead visual detection of FAdV-4 to achieve as low as 1 copy in less than 40 min without the need for specialized instrumentation or complex equipment. Moreover, it was greatly specific, and did not cross-react with other common avian viruses. Following the validation of 30 clinical samples of suspected FAdV-4 infection, the results LAMP-CRISPR/Cas12a method generated showed fully concordance with which of the gold standard quantitative real-time PCR. To summarize, this study presented a novel, swift, expedient and inexpensive detection platform for FAdV-4, which is beneficial to viral inchoate diagnosis and point-of-care testing.

Pyrococcus furiosus argonaute combined with loop-mediated isothermal amplification for rapid, ultrasensitive, and visual detection of fowl adenovirus serotype 4

Since 2015, an outbreak of an infectious disease in broilers caused by fowl adenovirus serotype 4 (FAdV-4) has occurred in China, resulting in substantial economic losses. Rapid, accurate, and specific detection are significant in the prevention and control of FAdV-4. In this study, an FAdV-4 detection method combining loop-mediated isothermal amplification (LAMP) and Pyrococcus furiosus Argonaute (PfAgo) was established. Specific primers, guide DNAs (gDNAs), and molecular beacons were designed to target a conserved region of the FAdV-4 hexon gene. After optimizing the reaction conditions, the minimum detection of this assay could reach 5 copies. It only amplified FAdV-4, and there was no cross-reactivity with other pathogens. The assay took about only 50 min, and the results could be visualized with the naked eye under ultraviolet or blue light, getting rid of specialized instruments. This novel LAMP-PfAgo assay was validated by using 20 clinical samples and the results were identical to gold-standard real-time polymerase chain reaction method. In summary, the LAMP-PfAgo assay established in the paper provides a rapid, reliable, convenient, ultra-sensitive and highly specific tool for the on-site detection and clinical diagnosis of FAdV-4.

Hypervirulent fowl adenovirus serotype 4 elicits early innate immune response and promotes virus-induced cellular autophagy in the spleen

The recent emergence of hepatitis-hydropericardium syndrome caused by highly pathogenic fowl adenovirus serotype 4 (FAdV-4) has resulted in significant economic losses to the poultry industry. However, the early innate immune response of immune organs within 24 hpi and the induction of autophagy in vivo after FAdV-4 infection have not been fully elucidated. In this study, 35-day-old specific pathogen-free (SPF) chickens were artificially infected with hypervirulent FAdV-4, which resulted in a mortality rate of up to 90%. The results showed that FAdV-4 infection rapidly triggered the innate immune response in vivo of chickens, with the spleen eliciting a stronger innate immune response than the thymus and bursa. During the early stage of viral infection within 24 hpi, the main receptors TLR3/7/21, MDA5, and cGAS were activated via the NF-κB and TBK1/IRF7-dependent signaling pathways, which up-regulated production of inflammatory cytokines and type I interferons. Additionally, the expression levels of the autophagy-related molecules LC3B, Beclin1, and ATG5 were significantly up-regulated at 24 hpi, while degradation of SQSTM1/p62 was observed, suggesting that FAdV-4 infection elicits a complete autophagy response in the spleen. Besides, the colocalization of Fiber2 and LC3B suggested that FAdV-4 infection induced autophagy which benefits FAdV-4 replication in vivo. This study provides new insights into the immunoregulation signal pathways of the early innate immunity in response to hypervirulent FAdV-4 infection in vivo within 24 hpi and the close relationship between viral replication and autophagy.

Novel variant infectious bursal disease virus diminishes FAdV-4 vaccination and enhances pathogenicity of FAdV-4

Infectious bursal disease virus (IBDV) caused an acute and highly contagious infectious disease characterized by severe immunosuppression, causing considerable economic losses to the poultry industry globally. Although this disease was well-controlled under the widely use of commercial vaccines in the past decades, the novel variant IBDV strains emerged recently because of the highly immunized-selection pressure in the field, posting new threats to poultry industry. Here, we reported novel variant IBDV is responsible for a disease outbreak, and assessed the epidemic and pathogenicity of IBDV in this study. Moreover, we constructed a challenge model using Fowl adenovirus serotype 4 (FAdV-4) to study on the immunosuppressive effect. Our findings underscore the importance of IBDV surveillance, and provide evidence for understanding the pathogenicity of IBDV.

Chicken Interferon-Alpha and -Lambda Exhibit Antiviral Effects against Fowl Adenovirus Serotype 4 in Leghorn Male Hepatocellular Cells

Hydropericardium hepatitis syndrome (HHS) is primarily caused by fowl adenovirus serotype 4 (FAdV-4), causing high mortality in chickens. Although vaccination strategies against FAdV-4 have been adopted, HHS still occurs sporadically. Furthermore, no effective drugs are available for controlling FAdV-4 infection. However, type I and III interferon (IFN) are crucial therapeutic agents against viral infection. The following experiments were conducted to investigate the inhibitory effect of chicken IFN against FadV-4. We expressed recombinant chicken type I IFN-α (ChIFN-α) and type III IFN-λ (ChIFN-λ) in Escherichia coli and systemically investigated their antiviral activity against FAdV-4 infection in Leghorn male hepatocellular (LMH) cells. ChIFN-α and ChIFN-λ dose dependently inhibited FAdV-4 replication in LMH cells. Compared with ChIFN-λ, ChIFN-α more significantly inhibited viral genome transcription but less significantly suppressed FAdV-4 release. ChIFN-α- and ChIFN-λ-induced IFN-stimulated gene (ISG) expression, such as PKR, ZAP, IRF7, MX1, Viperin, IFIT5, OASL, and IFI6, in LMH cells; however, ChIFN-α induced a stronger expression level than ChIFN-λ. Thus, our data revealed that ChIFN-α and ChIFN-λ might trigger different ISG expression levels, inhibiting FAdV-4 replication via different steps of the FAdV-4 lifecycle, which furthers the potential applications of IFN antiviral drugs in chickens.

An efficient and convenient Fiber -2- based latex agglutination test for the detection of antibodies against fowl adenovirus serotype 4 in clinical samples

To detect the antibody against fowl adenovirus serotype 4 (FAdV-4) in clinical practice, the latex agglutination test (LAT) was developed by using the Fiber-2 protein of FAdV-4 as an antigen bound to sensitized latex microspheres. The concentration, time, and temperature of sensitization latex microspheres by the Fiber-2 protein were studied and optimized; the specificity, sensitivity, and repeatability of LAT were tested; and the method developed in the study was applied. The results showed that the optimum sensitization concentration of Fiber-2 protein was 0.8mg/mL, the time was 120min, and the temperature was 37℃. Except for antiserum against FAdV-4 and FAdV-10, LAT developed in the study could not agglutinate antisera against FAdV-1, FAdV-2, FAdV-3, FAdV-4, FAdV-5, FAdV-6, FAdV-8a, FAdV-8b, FAdV-11, Newcastle disease virus, infectious bronchitis virus, egg drop syndrome virus and Clostridium perfringens. Compared with the commercial FAdV-4 ELISA Kit, the titers in 21 clinical samples were low when tested by the developed LAT method, but there was no significant difference. The coefficients of variation among different batches and the same batch of latex-sensitized particles were between 0-13.3% and 0-8.7%, respectively. The critical value of immune protective antibody against FAdV-4 was 2⁵, and the titers in 40.9% of clinical samples were higher than the immune critical point. The results showed that the Fiber-2-based LAT developed in the study has the characteristics of high specificity, sensitivity and repeatability, has the advantages of free equipment, long shelf life, and fast and easy operation, and is an effective and convenient method for serological diagnosis of FAdV-4 infection and evaluating the efficacy of vaccines.

Virome Profiling of Chickens with Hepatomegaly Rupture Syndrome Reveals Coinfection of Multiple Viruses

Liver diseases seriously challenge the health of chickens raised on scaled farms and cause tremendous economic losses to farm owners. The causative agents for liver diseases are still elusive, even though various pathogens, such as the hepatitis E virus, have been reported. In the winter of 2021, a liver disease was observed on a chicken farm in Dalian, China, which increased chicken mortality by up to 18%. We conducted panvirome profiling of the livers, spleens, kidneys, and recta of 20 diseased chickens. The viromic results revealed coinfection of multiple viruses, including pathogenic ones, in these organs. The viruses were highly identical to those detected in other provinces, and the vaccine and field strains of avian encephalomyelitis virus (AEV) and chicken infectious anemia virus (CIAV) cocirculated on the farm. In particular, the liver showed higher abundance of AEV and multiple fowl adenoviruses than other organs. Furthermore, the liver also contracted avian leukemia virus and CIAV. Experimental animals with infected liver samples developed minor to medium lesions of the liver and showed a virus abundance profile for AEV across internal organs similar to that in the original samples. These results suggest that coinfection with multiple pathogenic viruses influences the occurrence and development of infectious liver disease. The results also highlight that strong farm management standards with strict biosafety measures are needed to minimize the risk of pathogenic virus introduction to the farm.

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.

Local cellular immune response plays a key role in protecting chickens against hepatitis-hydropericardium syndrome (HHS) by vaccination with a recombinant fowl adenovirus (FAdV) chimeric fiber protein

Fowl adenovirus (FAdV)-induced diseases hepatitis-hydropericardium syndrome (HHS) and inclusion body hepatitis (IBH) have been affecting the poultry industry with increasing severity in the last two decades. Recently, a subunit vaccine based on a chimeric fiber protein with epitopes from different fowl adenovirus serotypes (named crecFib-4/11) has been shown to confer simultaneous protection against both HHS and IBH. However, the underlying immune mechanisms in chickens are still enigmatic, especially because of frequently absent neutralizing response despite high levels of protection. In this study, we investigated the kinetics of the humoral and cellular immune responses in specific pathogen-free chickens after vaccination with crecFib-4/11 and/or challenge with a HHS-causing strain, on a systemic level, as well as locally in target and lymphoid organs. The humoral response was assessed via enzyme-linked immunosorbent assay (ELISA) and virus neutralization test in serum, while the cellular immune response was determined by phenotyping using flow cytometry. Although vaccination induced serum antibodies, as confirmed by ELISA, such antibodies exhibited no pre-challenge neutralizing activity against FAdV-4. Nevertheless, immunized birds experienced a significant B cell increase in the liver upon challenge, remaining high throughout the experiment. Furthermore, vaccination stimulated the proliferation of cytotoxic T lymphocytes, with earlier circulation in the blood compared to the challenge control and subsequent increase in liver and spleen. Overall, these findings imply that protection of chickens from HHS after crecFib-4/11 vaccination relies on a prominent local immune response in the target organs, instead of circulating neutralizing antibodies.

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.

Genotyping and pathogenicity of fowl adenovirus isolated from broiler chickens in Egypt

Background

Over the past 10 years, inclusion body hepatitis outbreaks, essentially from commercial broiler flocks, have been detected in different geographic regions highlighting the wide distribution of FAdVs around the world resulting in serious economic losses due to increased mortalities as well as poor performance within poultry farms in Assiut province, Egypt. Thus, this study was achieved to detect fowl adenovirus in broiler chicken flocks in Assiut province, Egypt and to recognize the pathogenicity of the isolated virus.

Results

The phylogeny of the L1 loop of the hexon gene exposed that the isolated virus clustered and belonged to the reference strains serotype D FAdV. The isolated virus is closely related to inclusion body hepatitis (IBH) strains causing extensive economic losses. The pathogenicity study of the virus showed typical macroscopic lesions with 6% mortality; furthermore, histopathological inspection exhibited severe hepatitis and degenerative changes after 5d from infection in the immune system. 

Conclusion

Results in this research support the primary pathogenicity and mortality caused by FADV serotype 2 (IBH) alone without immunosuppressive agents thus robust control measures should be implanted against FAdV to evade the serious economic losses in poultry farms.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-022-03422-1.

Arginine regulates inflammation response-induced by Fowl Adenovirus serotype 4 via JAK2/STAT3 pathway

Background

Fowl Adenovirus serotype 4 (FAdV-4) infection causes severe inflammatory response leading to hepatitis-hydropericardium syndrome (HHS) in poultry. As an essential functional amino acid of poultry, arginine plays a critical role in anti-inflammatory and anti-oxidative stress.

Results

In this study, the differential expression genes (DEGs) were screened by transcriptomic techniques, and the DEGs in gene networks of inflammatory response-induced by FAdV-4 in broiler’s liver were analyzed by Kyoto encyclopedia of genes and genomes (KEGG) enrichment. The results showed that the cytokines pathway and JAK/STAT pathway were significantly enriched, in which the DEGs levels of IL-6, IL-1β, IFN-α, JAK and STAT were significantly up-regulated after FAdV-4 infection. It was further verified with real-time fluorescence quantitative polymerase chain reaction (Real-time qPCR) and Western blotting (WB) in vitro and in vivo. The findings demonstrated that FAdV-4 induced inflammatory response and activated JAK2/STAT3 pathway. Furthermore, we investigated whether arginine could alleviate the liver inflammation induced by FAdV-4. After treatment with 1.92% arginine level diet to broilers or 300 μg/mL arginine culture medium to LMH cell line with FAdV-4 infection at the same time, we found that the mRNA levels of IL-6, IL-1β, IFN-α and the protein levels of p-JAK2, p-STAT3 were down-regulated, compared with FAdV-4 infection group. Furthermore, we confirmed that the inflammation induced by FAdV-4 was ameliorated by pre-treatment with JAK inhibitor AG490 in LMH cells, and it was further alleviated in LMH cells treatment with AG490 and ARG.

Conclusions

These above results provide new insight that arginine protects hepatocytes against inflammation induced by FAdV-4 through JAK2/STAT3 signaling pathway.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-022-03282-9.

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.

Immunity analysis against Fowl Adenovirus serotype 4 (FAdV-4) based on Fiber-2 trimer Protein with the different virulence

Since June 2015, Fowl adenovirus outbreaks have occurred in China, causing significant economic losses to poultry industry. The FAdV-4 Fiber-2 proteins could induce effective protection, but the precise mechanism of immune protection remains unknown. Here, we have compared the biological characteristics of Fiber-2 protein of the very virulent WZ strain of FAdV-4 (vvFAdV-4) with that of non-virulent ON1 strain. The sequence analysis revealed natural deletions and sequence differences between the classical non-pathogenic strain ON1 and the vvFAdV-4 isolate. These two Fiber-2 proteins successfully expressed in E. coli resemble in structure and function to the native-like trimeric protein. The trimeric structure and bioreactivity of the recombinant Fiber-2 proteins to FAdV-4 specific antibodies were characterized. The immune protection induced by Fiber-2 proteins of FAdV-4 WZ and ON1 strains were compared in SPF chickens. All birds in the WZ-Fiber-2 immunized group generated systemic specific antibodies compared with both ON1-Fiber-2 protein and PBS immunized groups. According to the results of attack mortalities, viral shedding and tissue gross lesion, the WZ Fiber-2 protein induced complete protection at a dose of 2 μg per chicken, whereas the ON1-Fiber-2 protein induced 0 protection at 3 dpc. In view of the characteristics of Fiber-2 proteins of different strains, this study can help us to further understand the mechanism of protective immunity and provide a basis for the prevention and control of FAdV-4 in chickens.

Pathogenicity and virus shedding ability of fowl adenovirus serotype 4 to ducks

Fowl adenovirus serotype 4 (FAdV-4) is the pathogen causing hepatitis-hydropericardium syndrome (HHS) in broilers. Since June 2015, it has emerged as one of the leading causes of economic losses in the poultry industry in China. Although most studies on FAdV-4 have focused on its pathogenicity to broilers, limited studies have been performed on other natural hosts such as ducks and geese. In this study, we assessed the pathogenicity of FAdV-4 to ducks of different ages through intramuscular injection and found that infected ducks showed severe growth depression. The infected ducks also suffered from extensive organ damage and had histopathological changes in the liver, spleen, and kidney. Although the virus infection caused lymphocyte necrosis of immune organs and the development of the bursa of Fabricius (bursa) was inhibited, the humoral immune response of infected ducks to FAdV-4 remained strong. The infected ducks also had high viral load in tissues and shed virus after the challenge. Overall, our research demonstrates that FAdV-4 can infect ducks and adversely affect the productivity of animals. And the viruses shed by infected ducks can pose a potential risk to the same or other poultry flocks.

Historical Investigation of Fowl Adenovirus Outbreaks in South Korea from 2007 to 2021: A Comprehensive Review

Fowl adenoviruses (FAdVs) have long been recognized as critical viral pathogens within the poultry industry, associated with severe economic implications worldwide. This specific group of viruses is responsible for a broad spectrum of diseases in birds, and an increasing occurrence of outbreaks was observed in the last ten years. Since their first discovery forty years ago in South Korea, twelve antigenically distinct serotypes of fowl adenoviruses have been described. This comprehensive review covers the history of fowl adenovirus outbreaks in South Korea and updates the current epidemiological landscape of serotype diversity and replacement as well as challenges in developing effective broadly protective vaccines. In addition, transitions in the prevalence of dominant fowl adenovirus serotypes from 2007 to 2021, alongside the history of intervention strategies, are brought into focus. Finally, future aspects are also discussed.

A recent perspective on fiber and hexon genes proteins analyses of fowl adenovirus toward virus infectivity-A review

Fowl adenovirus (FAdV) is a double-stranded DNA virus with a non-enveloped structure comprising three major proteins known as hexon, penton, and fiber. Molecular analysis which emphasizes on hexon and fiber proteins is currently the major focus of curiosity for FAdV antigenicity and pathogenicity. Recently, disease outbreaks associated with FAdV infections such as inclusion body hepatitis, hepatitis hydropericardium syndrome, and gizzard erosion, were commonly reported and continue to increase worldwide. Studies on the virulence gene of the virus were intensively conducted to provide a better understanding on the role of these major capsid proteins in the development of a safe and effective vaccine against the disease in the poultry industry. This paper highlights the variations of the fiber and hexon genes, their importance in genotypes and serotypes differentiation, and infectivity between FAdV strains. It appears that the L1 loop of hexon and the knob of fiber genes are the infectivity markers for FAdV infection. The fiber-2 protein plays a major role in FAdV pathogenicity than the hexon protein, while the fiber-1 protein is important for viral replication and assembly, regardless of virulence capability instead of infectivity. The hexon protein plays a major role in virus infectivity and tissue tropism. These findings could further enhance the knowledge of FAdV strains’ classification and evolution, diagnosis, and strategies to prevent and control FAdV infection and outbreaks in chicken farms.

Development of a subunit vaccine based on fiber2 and hexon against fowl adenovirus serotype 4

Hepatitis-hydropericardium syndrome (HHS) is widespread in China and causes high chicken mortality that results in great economic losses. A safe and effective vaccine is needed, and a subunit vaccine has potential for development. In this study, a truncated region of the FAdV-4 fiber 2 fused with coding sequence of one epitope of hexon was expressed in a prokaryotic expression system, and the immune protective effects of different doses of recombinant fiber 2 subunit vaccine on SPF chickens were compared. The recombinant fiber2 (Gly275- Pro479 aa)-hexon (Met21-Val51 aa) protein (rFH) obtained in Escherichia coli showed good solubility. The chicken survival rate at the lowest dose (2.5 μg/bird) was 75% (6/8), and at higher doses (≥5 μg/bird) was 100% (8/8) in challenge experiment. Two chickens in the 2.5 μg/bird treatment showed severe lesions, while birds in the higher dose treatments showed no obvious tissue damage as determined by histopathologic analysis of liver and spleen. Absolute quantitative real-time PCR showed no viral load in the ≥5 μg/bird treatments, but two chickens in the 2.5 μg/bird treatment had high viral loads. The challenge experience demonstrated that the rFH vaccine provided 100% protection at ≥5 μg/bird. These results suggested that rFH protein as an effective vaccine to protect against FAdV-4 and provided a new idea for the development of vaccine against HHS.

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.

A tandem mass tag-based quantitative proteomic analysis of fowl adenovirus serotype 4-infected LMH cells

Fowl adenovirus serotype 4 (FAdV-4) is recognized as an economically important pathogen for the poultry industry worldwide. FAdV-4 infection causes a metabolic disturbance of hepatocytes, leading to hydropericardium-hepatitis syndrome (HHS) in poultry. However, the metabolic response of hepatocytes to FAdV-4 infection remains poorly investigated. Here, a tandem mass tag (TMT)-based approach was first used to quantitatively identify differentially expressed proteins (DEPs) in leghorn male hepatoma (LMH) cells infected with the virulent FAdV-4 strain GY. We identified 666 DEPs associated with many biological processes and pathways, according to Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses. Functional enrichment analysis revealed that three pathways, including metabolism-related signaling pathways, apoptosis, and autophagy responses, were enriched during FAdV-4 infection. Moreover, excessive induction of metabolism-related signaling pathways by FAdV-4 infection might be associated with HHS induced by the virus. Meanwhile, among the proteins in these pathways, RRM2, SAE1, AEN, and RAD50 were verified through western blotting to be markedly altered in FAdV-4-infected LMH cells. Notably, overexpression of SAE1 inhibited the replication of FAdV-4 in vitro, whereas silencing of SAE1 expression promoted the replication of the virus. Collectively, our findings show for the first time that SAE1 is a host cellular protein that plays roles in regulating the life cycle of FAdV-4.

Research Note: Molecular relationship of the fowl adenovirus serotype 4 isolated from the contaminated live vaccine and wild strains isolated in China, 2013-2018

Since June 2013, hydropericardium-hepatitis syndrome caused by putative novel fowl adenovirus 4 (FAdV-4) infection has spread all over China, leading to great economic losses. Previous study found that the use of attenuated vaccines contaminated with FAdV-4 is likely to be an important cause of such large-scale transmission. Here, we sequenced the whole genome of this strain through the next-generation sequencing and carried out a retrospective analysis of the FAdV-4 strains that have been determined in China recently. Results show the vaccine strain was almost 100% identical with wild virus strains, especially with 4 strains considering the difference of the GA repeat region, further linking the relationship between vaccine contamination and FAdV-4 prevalence in China. Meanwhile, there is no time and regional preference for the emergence of FAdV-4 strains with different molecular characteristics in China, which indicates that there may be multiple routes of transmission of this virus, suggesting that we still need to pay more attention to and formulate correct prevention and control in the future.

Genetic characterization of fowl aviadenovirus 4 isolates from Guangxi, China, during 2017-2019

Hepatitis-hydropericardium syndrome (HHS) is a severe disease that causes 20 to 80% mortality in chickens aged 3 to 6 wk. Fowl aviadenovirus serotype 4 (FAdV-4) plays an important role in the etiology of HHS. Since 2015, outbreaks of HHS have been reported in several provinces of China; however, details regarding the FAdV-4 genome properties are lacking. In the present study, the complete genomes of 9 isolates responsible for these outbreaks in Guangxi Province, China, were sequenced. To investigate the molecular characteristics of these FAdV-4 isolates, we compared their genomes with those of other reported pathogenic and nonpathogenic FAdV-4 isolates. A variable number of GA repeats were observed in the isolates of this study. Each of the isolates GX2017-01, GX2017-02, GX2018-08, and GX2019-09 had 11 GA repeats; GX2017-03, GX2017-04, and GX2017-05 each had 10 GA repeats, while GX2017-06 and GX2018-07 each had 8 GA repeats. We observed several deletions and distinct amino acid mutations in the major structural genes of these isolates when compared with non-Chinese isolates. We found 2 novel putative genetic markers in the hexon protein, one present in GX2017-02, in which aspartic acid (D) was changed to tyrosine (Y), and another present in each of isolates GX2018-08 and GX2019-09, in which serine (S) was changed to arginine (R), when compared with selected Chinese and some non-Chinese isolates. Moreover, the phylogenetic analysis revealed that all the isolates of this study were clustered within FAdV-C. We found that these isolates were closely related to other recently isolated Chinese strains. The data presented in this study will not only increase the understanding of the molecular epidemiology and genetic diversity of FAdV-4 isolates in China but also has an important reference value of the major factors that determine the virulence of FAdV-4 strains.

Pathogenicity of fowl adenovirus serotype 4 (FAdV-4) in chickens

Hepatitis-hydropericardium syndrome (HHS) is an acute infectious disease caused by fowl adenovirus serotype 4 (FAdV-4), which mainly infects broilers aged 3-5 weeks. In March 2018, a pathogenic disease, which was characterized by symptoms similar to HHS, broke out in 10-day-old broiler flocks in Shandong province. In this study, a strain of FAdV-4 (SDSG) was isolated from naturally infected broilers. To assess its pathogenicity, 10-day-old and 20-day-old specific pathogen-free (SPF) chickens were inoculated separately with the FAdV-4 virus fluid via oral and intramuscular injection routes. The results show that typical hydropericardium and hepatitis were observed in experimental chickens. The titer levels of the virus antibody and the levels of inflammatory cytokines were upregulated, which may be caused by the infection and innate immune response. The detection of viral load showed that the presence of virus was detected in multiple organs, in which the liver contained the highest concentration of viral DNA, and the virus content in the intramuscular injection group was higher than that of the oral injection group. In summary, these findings increase our understanding of the pathogenicity of FAdV-4 (SDSG) in chickens. The established model will be valuable for anti-viral drug testing and vaccine evaluation, which can 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.

Prevalence of Fowl Adenovirus Serotype 4 and Co-Infection by Immunosuppressive Viruses in Fowl with Hydropericardium Hepatitis Syndrome in Shandong Province, China

Fowl adenovirus serotype 4 (FAdV-4) is the pathogenic agent of hydropericardium hepatitis syndrome (HHS) in chickens and ducks, which has caused huge economic losses for the Chinese poultry industry since 2015. In order to objectively determine the prevalence and co-infection status of the virus in Shandong province in China, we analyzed a total of 679 clinical cases of chickens and ducks from 36 farms in the province. The results showed that the FAdV-4 infection rate was 65.2% (443/679), and the rate in breeder ducks was almost two-fold higher than that in breeder chickens (68.57% vs. 34.30%). Notably, co-infection by H9N2 avian influenza virus, infectious bursal disease virus, and/or chicken infectious anemia virus was very common in the 443 FAdV-4-positive cases. Furthermore, phylogenetic analysis of the hexon genes of four Shandong FAdV-4 isolates revealed that these strains clustered into Indian reference strains, indicating that the Shandong FAdV-4 strains might have originated in India. These findings provide the first data on the prevalence and co-infection status of FAdV-4 in Shandong province, which may serve as a foundation for the prevention of FAdV-4 in the field.