The hydropericardium syndrome in poultry--a current scenario

Biological features of fowl adenovirus serotype-4

Fowl adenovirus serotype 4 (FAdV-4) is highly pathogenic to broilers aged 3 to 5 weeks and has caused considerable economic loss in the poultry industry worldwide. FAdV-4 is the causative agent of hydropericardium-hepatitis syndrome (HHS) or hydropericardium syndrome (HPS). The virus targets mainly the liver, and HPS symptoms are observed in infected chickens. This disease was first reported in Pakistan but has now spread worldwide, and over time, various deletions in the FAdV genome and mutations in its major structural proteins have been detected. This review provides detailed information about FAdV-4 genome organization, physiological features, epidemiology, coinfection with other viruses, and host immune suppression. Moreover, we investigated the role and functions of important structural proteins in FAdV-4 pathogenesis. Finally, the potential regulatory effects of FAdV-4 infection on ncRNAs are also discussed.

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.

Evidence of vertical transmission of fowl adenovirus 8b in ducks

Fowl adenovirus mainly causes hydropericardium hepatitis syndrome (HHS), inclusion body hepatitis (IBH) and gizzard erosion (GE), etc. In 2015, the first outbreak of HHS was reported in broiler chickens in central China, followed by an outbreak in waterfowl. The first outbreak of HHS in broiler flocks in central China in 2015, followed by outbreaks in waterfowl, has severely restricted the healthy development of the poultry industry. During the investigation, fowl adenovirus was detected in ducklings from a total of seven hatcheries in Shandong, Inner Mongolia and Jiangsu provinces. In addition, the DNA of fowl adenovirus was detected in breeding ducks and their progeny. To test the hypothesis that FAdV can be transmitted vertically, sixty 250-day-old Cherry Valley breeder ducks were divided equally into three groups for experimental infection. FAdV-8b SDLY isolate (duck/Shandong/SDLY/2021, SDLY) preserved in our laboratory was injected intramuscularly into group A and inoculated orally into group B. FAdV-8b DNA was detected in the yolk membranes, embryos and allantoic fluid of duck embryos in the FAdV-infected group after inoculation. In addition, the FAdV-8b hexon gene isolated from yolk membranes, embryos, allantoic fluid and duck eggs was close to 100% nucleotide homology to the FAdV-8b hexon gene isolated from laying duck ovaries, indicating that fowl adenovirus can be transmitted vertically in ducks. These findings provide evidence for the possible vertical transmission of fowl adenovirus from breeder ducks to ducklings.

Genetic modification regulates pathogenicity of a fowl adenovirus 4 strain after cell line adaptation (genetic mutation in FAdV-4 lowered pathogenicity)

Fowl adenovirus 4 (FAdV-4) is a major avian virus that induces fatal diseases in chicken such as, hydropericardium and hepatitis. The viral structure consists of hexon, penton, fiber-1, and fiber-2 which are associated with immunopathogenesis. In this study, we investigated the genetic modification of a FAdV-4 strain after continuous passages in a cell line and evaluated the pathogenicity associated with mutations. We used the FadV-4 KNU14061 strain, which was isolated from layers in 2014. The virus went through 80 passages in the Leghorn male hepatoma (LMH) cell line. The full genetic sequence was identified, and we found a frameshift in the fiber-2 amino acid sequence after the initial thirty passages. To examine whether the frameshift in the fiber-2 gene affects the pathogenicity in chicken, we inoculated LMH80 (80 times passaged) and LMH10 (10 times passaged) into 3-day-old chickens and examined the pathogenesis. LMH10 infection via intramuscular route induced fatal pathology, but LMH80 did not. Furthermore, LHM80 pre-treatment protected hosts from the LMH10 challenge. Thus, the genetic modification isolated by serial passage lowered pathogenicity and the resulting virus acted as an attenuated vaccine that can be a FAdV-4 vaccine strain candidate.

Complete genome sequence and pathogenicity analysis of a highly pathogenic FAdV-4 strain

Fowl adenovirus serotype 4 (FAdV-4) is a double-stranded DNA virus that mainly infects broiler chickens and has caused huge economic losses to the poultry industry. Recently, an FAdV-4 strain, SDLC202009, the causative pathogen of hydropericardium-hepatitis syndrome (HHS) in Liaocheng, Shandong, was isolated from commercial laying hens and propagated in specific pathogen free SPF chicken embryos. Pathogenicity studies showed that SDLC202009 could infect SPF chicken embryos and chickens, with a mortality rate of 100%. The complete genome was sequenced, and phylogenetic analysis showed that SDLC202009 belonged to the FAdV-4 cluster, with a genome length of 43, 077 bp. The SDLC202009 had 99.9% identity with the JSJ13 and SD1601, which were recently isolated in China. Compared to the recently isolated strain in China, SDLC202009 had deleted open reading frame 19 (ORF19), ORF27, ORF48, and ORF0. SDLC202009 harbored amino acid site mutations in the main structural proteins hexon, fiber1, and fiber2 similar with those in highly pathogenic strains. Furthermore, SDLC202009 showed unique mutations in hexon A571P, fiber1 E216K, and fiber2 N98K. In summary, our findings provide theoretical support for prevention and control of the HHS.

Genetic evolution of fowl adenovirus serotype 4 and its pathogenicity to Cherry Valley ducks in China

Hydropericardium hepatitis syndrome (HHS), a novel poultry disease, is caused by fowl adenovirus 4 (FAdV-4). It mainly infects 3-5-week-old broilers. In July 2015, the first outbreak of HHS occurred in the broilers in east China, which caused great economic losses to the poultry industry. In June 2019, infectious disease was detected with suspected HHS symptoms on a duck farm in Linyi City, Shandong Province. The main necropsy lesions included pericardial effusion and hepatitis. In this study, we isolated a strain of FAdV-4 from naturally infected ducks and named it SDLY190604, and the hexon gene sequence was amplified and analyzed using polymerase chain reaction (PCR). In order to study the effect of FAdV-4 on Cherry Valley ducks, we inoculated three-week-old ducks with 0.2 ml of FAdV-4 virus fluid (TCID₅₀ of 10^-6.3/0.1 ml) by orally, subcutaneously and intramuscularly. Clinical signs, gross lesions and histopathological changes, cytokines and viral load were detected and recorded within 15 days after infection. The results showed that ducks in the experimental groups exhibited typical symptoms of hydropericardium and hepatitis. The histopathological sections showed multiple-organ damage, including serious liver and kidney damage with elevated levels of inflammatory cytokines, probably due to the infection and innate immune response. Later, immunosuppression occurred, resulting in decreased levels of cytokines. The viral load indicated that the virus could be present in several organs of the ducks, with the highest viral DNA found in the liver, followed by the kidney. Compared to the subcutaneous and oral groups, the intramuscular group exhibited the highest viral load. In summary, this study can increase our understanding of the pathogenicity of FAdV-4 in ducks and provide a basis for further understanding of the virus, imparting new insights into disease research.

Probiotics Surface-Delivering Fiber2 Protein of Fowl Adenovirus 4 Stimulate Protective Immunity Against Hepatitis-Hydropericardium Syndrome in Chickens

Background and Objectives

Hepatitis-hydropericardium syndrome (HHS) caused by Fowl adenoviruses serotype 4 (FAdV-4) leads to severe economic losses to the poultry industry. Although various vaccines are available, vaccines that effectively stimulate intestinal mucosal immunity are still deficient. In the present study, novel probiotics that surface-deliver Fiber2 protein, the major virulence determiner and efficient immunogen for FAdV-4, were explored to prevent this fecal–oral-transmitted virus, and the induced protective immunity was evaluated after oral immunization.

Methods

The probiotic Enterococcus faecalis strain MDXEF-1 and Lactococcus lactis NZ9000 were used as host strains to deliver surface-anchoring Fiber2 protein of FAdV-4. Then the constructed live recombinant bacteria were orally vaccinated thrice with chickens at intervals of 2 weeks. Following each immunization, immunoglobulin G (IgG) in sera, secretory immunoglobulin A (sIgA) in jejunum lavage, immune-related cytokines, and T-cell proliferation were detected. Following challenge with the highly virulent FAdV-4, the protective effects of the probiotics surface-delivering Fiber2 protein were evaluated by verifying inflammatory factors, viral load, liver function, and survival rate.

Results

The results demonstrated that probiotics surface-delivering Fiber2 protein stimulated humoral and intestinal mucosal immune responses in chickens, shown by high levels of sIgA and IgG antibodies, substantial rise in mRNA levels of cytokines, increased proliferative ability of T cells in peripheral blood, improved liver function, and reduced viral load in liver. Accordingly, adequate protection against homologous challenges and a significant increase in the overall survival rate were observed. Notably, chickens orally immunized with E. faecalis/DCpep-Fiber2-CWA were completely protected from the FAdV-4 challenge, which is better than L. lactis/DCpep-Fiber2-CWA.

Conclusion

The recombinant probiotics surface-expressing Fiber2 protein could evoke remarkable humoral and cellular immune responses, relieve injury, and functionally damage target organs. The current study indicates a promising method used for preventing FAdV-4 infection in chickens.

The First Occurrence of Hepatitis-Hydropericardium Syndrome in Iran and Effective Applied Control Measures in the Affected Commercial Broiler Flock

Fowl adenoviruses cause three economically important diseases in broiler chicken flocks: hepatitis-hydropericardium syndrome (HHS), inclusion body hepatitis (IBH), and adenoviral gizzard erosion. IBH has not been considered a serious threat in northeast Iran since the last decade, because no major effect on flock performance has been noticed along with a low mortality rate. During this period, all the sporadic IBH outbreaks have also been investigated for HHS without finding any confirmed case. In March 2021, a 15-day-old commercial broiler flock in northeast Iran showed a 50% mortality rate, and birds underwent postmortem examination, histopathology, molecular testing, and phylogenetic analysis for possible disease agents. Typical gross lesions of HHS were observed postmortem that included hydropericardium with an unusual accumulation of jelly-like and straw-colored fluid in the pericardial sac (without right ventricular failure); petechial or ecchymotic hemorrhages on the myocardium, myocardial valves, and endocardium; and discolored and mottled liver along with small white foci and petechial or ecchymotic hemorrhages. Histopathologic analysis showed necrosis of hepatocytes and basophilic inclusion bodies in the livers. The molecular tests performed for detection of fowl adenovirus (FAdV), H5 avian influenza virus, Newcastle disease virus, avian infectious bronchitis virus (IBV), H9N2, chicken infectious anemia virus (CIAV), infectious bursal disease (IBD) virus, Marek's disease virus, Ornithobacterium rhinotracheale, Mycoplasma gallisepticum, and Mycoplasma synoviae turned out positive for FAdV, CIAV, IBD vaccine virus, and IBV serotypes 793B and variant I. The phylogenetic tree based on the hexon gene loop 1 demonstrated a FAdV serotype 4 (FAdV-4) that was identical to Pakistani isolate PARC-1/98. Because it was the first detection of a FAdV-4 in Iran, the stamping out program was applied immediately on the basis of HHS gross lesions and positive PCR reaction on pericardial jelly-like fluid. It seems that this eradication strategy was successful because no outbreaks were noticed for 2 mo after the initial outbreak. It was concluded that the use of gross pathologic baselines, quick diagnosis of disease, and close collaboration between governmental and private sectors were the critical factors that helped locally control the first occurrence of HHS in Iran.

Oral immunization of recombinant Saccharomyces cerevisiae expressing fiber-2 of fowl adenovirus serotype 4 induces protective immunity against homologous infection

Hydropericardium-hepatitis syndrome (HHS) caused by fowl adenovirus (FAdV) serotype 4 strains is a highly contagious disease that causes significant economic loss to the global poultry industry. However, subunit vaccine against FAdV-4 infection is not yet commercially available to date. This study aims to explore the potential for oral immunization of recombinant Saccharomyces cerevisiae expressing Fiber-2 of FAdV-4 as a subunit vaccine. Here, we constructed recombinant S. cerevisiae (ST1814G/Fiber-2) expressing recombinant Fiber-2 (rFiber-2), which was displayed on the cell surface. To evaluate the immune response and protective effect of live recombinant S. cerevisiae, chickens were orally immunized with the constructed live ST1814G/Fiber-2, three times at 5-day intervals, and then challenged with FAdV-4. The results showed that oral administration of live ST1814G/Fiber-2 could stimulate the production of humoral immunity, enhance the body's antiviral activity and immune regulation ability, improve the composition of gut microbiota, provide protection against FAdV-4 challenge, reduce viral load in the liver, and alleviate the pathological damage of heart, liver, and spleen for chicken. In addition, we found the synergistic effect in combining the ST1814G/Fiber-2 yeast and inactivated vaccine to trigger stronger humoral immunity and mucosal immunity. Our results suggest that oral live ST1814G/Fiber-2 is a potentially safer auxiliary preparation strategy in controlling FAdV-4 infection.

Cellular protein HSC70 promotes fowl adenovirus serotype 4 replication in LMH cells via interacting with viral 100K protein

Fowl adenovirus serotype 4 (FAdV-4), the predominant causative agent of hepatitis-hydropericardium syndrome (HHS), has caused severe economic losses to poultry industry since 2015. Although fiber2 and hexon have been confirmed to be the virulence-related factors, the roles of nonstructural viral proteins in pathogenicity of FAdV-4 remain poorly understood. Here, a tandem mass spectrometry (MS) was used to identify host factors interacted with 100K protein of hypervirulent FAdV-4 isolate (CH/HNJZ/2015), and 2595 cellular proteins associated with many biological processes and pathways were identified according to Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses. Among the proteins, HSC70 was verified to interact with 100K through co-immunoprecipitation assay. Notably, overexpression of HSC70 promoted the replication of FAdV-4 in LMH cells, whereas blocking HSC70 with inhibitor ver-155008 markedly suppressed viral replication. Collectively, these findings suggested that many cellular proteins involved in FAdV-4 infection through interacting with 100K and HSC70 positively regulated virus replication.

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.

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.

Pathogenicity and Immune Responses in Specific-Pathogen-Free Chickens During Fowl Adenovirus Serotype 4 Infection

Hydropericardium-hepatitis syndrome, a recently emerged disease of chickens, is caused by some strains of fowl adenovirus serotype 4 (FAdV-4). However, the relationship between the immune response and cytokine expression during FAdV-4 infection is largely unknown. In this study, our data showed that all chickens exhibited typical clinical signs and lesions and that the viral load was significantly increased in both the liver and thymus following FAdV-4 infection. We also found that the appearance of tissue lesions in the liver and thymus was consistent with the viral copy numbers, indicating that virus replication in systemic organs closely correlated with disease progression. In addition, the effects of FAdV-4 infection on the transcription of some avian cytokines were studied in vivo. In general, expression of the proinflammatory cytokines interleukin (IL)-2 and interferon (IFN)-α and IFN-β in the liver and thymus was strongly upregulated. Interestingly, the expression of IL-2 was the most highly upregulated. Expression of the anti-inflammatory cytokines IL-4, IL-10, and transforming growth factor (TGF)-β1 and TGF-β2, were also upregulated. Moreover, we investigated both the humoral and cellular immune responses in chickens infected with FAdV-4. Compared to those in the noninfected chickens, the antibody levels in chickens infected with FAdV-4 were significantly increased within 30 days postinfection. In addition, the ratio of CD4+/CD8+ T cells was decreased in FAdV-4-infected chickens. Taken together, these findings increase our understanding of the pathogenesis of FAdV-4 in chickens and provide a foundation for additional pathogenesis studies.

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.

Fowl Adenovirus Serotype 4 Influences Arginine Metabolism to Benefit Replication

Hydropericardium syndrome (HPS) is caused by fowl adenovirus serotype 4 (FAdV-4). HPS has caused outbreaks in Chinese populations of broiler chickens since 2015. However, little is known about the molecular mechanisms underlying HPS. In this study, we used transcriptomic analysis to screen differentially expressed genes (DEGs) in the livers of FAdV-4-infected and noninfected chicks. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that the gene network associated with the arginine metabolism pathway was enriched in livers infected by FAdV-4; 10 genes were downregulated and 8 genes were upregulated in these livers when compared to noninfected livers. The DEGs identified in livers were reanalyzed by real-time fluorescence quantitative PCR (qPCR); results indicated that the mRNA levels of the DEGs concurred with the data derived from KEGG analysis. Next, we used qPCR to detect the DEGs of the arginine metabolism pathway in a hepatocellular carcinoma cell line (LMH) after infection with FAdV-4 for 24 hr; this also indicated that the mRNA levels of the DEGs concurred with that seen in the liver. We also used si-RNA oligonucleotides to knock down the mRNA levels of iNOS in LMH cells infected with FAdV-4 and found that the viral load of FAdV-4 was increased. Further investigation revealed that the addition of 240 µg/ml of arginine into the culture medium of LMH cells infected with FAdV-4 for 24 hr led to a significant increase in the mRNA levels of iNOS but a significant reduction in the viral load of FAdV-4. Therefore, our data indicated that when broiler chickens become infected with FAdV-4, the arginine metabolic pathway in the liver becomes dysfunctional and the iNOS mRNA level decreases. This will add benefit to the replication of FAdV-4 but can be inhibited by the addition of an appropriate amount of arginine.

Molecular characterization and pathogenicity of highly pathogenic fowl adenovirus serotype 4 isolated from laying flock with hydropericardium-hepatitis syndrome

Hydropericardium-hepatitis syndrome (HHS) is an important emerging disease responsible for huge economic losses to the poultry industry in China. HHS primarily affects 20 to 60-day-old broilers and rarely occurs in laying flock. In this study, the highly pathogenic fowl adenovirus (FAdV) strain, AH-F19, was isolated from the liver samples of 120-day-old laying flock with HHS and its phylogenetic information, genetic mutations, and pathogenicity was evaluated. The phylogenetic analysis revealed that AH-F19 belonged to the FAdV serotype 4 (FAdV-4) cluster, however, 100K differs from the other FAdV-4 strains and is divided into different branches. Amino acid variations in fiber-2 for pathogenic isolates and non-pathogenic isolates indicated that D219, T300, and T380 may not be responsible for virulence. Animal experiments revealed AH-F19 to be a highly pathogenic isolate that can cause 100% mortality in three-week-old specific pathogen-free (SPF) chickens, which exhibited typical hydropericardium and hepatitis. Microscopically, the presence of basophilic intranuclear inclusion bodies in hepatocytes, fractured heart muscle fibers, as well as kidney degeneration and necrosis was observed. Collectively, these findings enriched our understanding of FAdV-4 pathogenicity and provided a reference for further exploration into its pathogenicity.

Epizootiology, Clinical Signs, and Phylogenetic Analysis of Fowl Adenovirus in Chicken Farms in Indonesia from 2018 to 2019

Fowl adenovirus (FAdV) infection is an emerging problem in the world poultry industry, especially in broilers, as the causal agent of inclusion body hepatitis or hepatitis-hydropericardium syndrome. From December 2017 to January 2019, we recorded 116 cases of suspected hepatitis-hydropericardium syndrome in chicken farms throughout Indonesia. Necropsy was done on each farm site with three to five freshly dead birds per farm. Tissue samples were collected in virus transport medium and frozen at -20 C. The virus was cultivated in 9-day-old fertilized specific-pathogenic-free chicken eggs. FAdV was detected using polymerase chain reaction with a published primer set. The polymerase chain reaction products were sequenced and subjected to a BLAST search. The phylogeny was inferred using the neighbor-joining method and tested using the bootstrap test. FadV-D and -E are present in Indonesia and confirmed in 40 of 116 suspected cases. The affected chicken ages were 27.27 ± 8.94 days. Most affected farms were raising broiler chickens. The only typical clinical sign was unusual daily mortality of >1%, while the three most frequent pathologic lesions were swelling and hemorrhage of kidney and liver, as well as hydropericardium. To reduce economic loss, a vaccine should be developed immediately.

The increased virulence of hypervirulent fowl adenovirus 4 is independent of fiber-1 and penton

Hepatitis-hydropericardium syndrome (HHS) caused by hypervirulent fowl adenovirus 4 (FAdV-4) have been causing great economic losses to Chinese poultry industry since 2015. Elucidation of the pathogenesis of FAdV-4 will lay solid foundation for developing attenuated FAdV-4 vaccine and vaccine vector. Our previous study has demonstrated that the increased virulence of hypervirulent FAdV-4 was associated with fiber-2 and hexon genes. However, the roles of fiber-1 and penton in virulence of FAdV-4 have never been elucidated. To further investigate the roles of the major structural proteins fiber-1 and penton in the virulence of hypervirulent FAdV-4, the fiber-1- and penton-replaced mutant viruses were constructed based on the FAdV-4 infectious clones of hypervirulent strain HNJZ using Redαβ recombineering techniques. The pathogenicity of the rescued viruses was evaluated in 3-week-old SPF chickens. Chickens infected with the rescued recombinant viruses carrying the fiber-1 or penton base gene from a nonpathogenic strain ON1 developed similar clinical signs to the natural hypervirulent FAdV-4 infection, including HHS-indicative gross lesions and histopathological changes in sick/dead chickens. Our results suggested that the increased virulence of hypervirulent FAdV-4 was independent of fiber-1 and penton. The detailed pathogenesis of FAdV-4 and the roles of fiber-1 and penton in the viral replication and infection process need to be further explored.

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.

Airborne Transmission of a Serotype 4 Fowl Adenovirus in Chickens

Serotype 4 fowl adenovirus (FAdV-4) is the main pathogen for hydropericardium syndrome (HPS) in chickens. It has caused major economic losses in the global poultry industry. Currently, FAdV-4's transmission routes in chickens remain unclear. Here we investigate the airborne transmission routes of FAdV-4 in chickens. A total of 45 ten-day-old chickens were equally divided into three groups (infected group/isolator A, airborne group/isolator B, and control group/isolator C). Of note, isolators A and B were connected by a leak-free pipe. The results showed that the virus could form a viral aerosol, detected in isolators two days post infection (dpi). The viral aerosol reached a peak at 4 dpi in the infected group. Healthy chickens in the airborne group were infected by the virus at 8 dpi. The chickens of the airborne group demonstrated subclinical symptoms capable of shedding the virus for some time. This finding suggests that FAdV-4 can be efficiently transmitted among chickens by aerosol transmission. These findings have significant implications for developing strategies to control this infectious disease epidemic.

Fiber2 and hexon genes are closely associated with the virulence of the emerging and highly pathogenic fowl adenovirus 4

Since May 2015, outbreaks of hydropericardium-hepatitis syndrome (HHS) caused by fowl adenovirus 4 (FAdV-4) with a novel genotype have been reported in China, causing significant economic losses to the poultry industry. A previous comparative analysis revealed that highly virulent FAdV-4 isolates contain various genomic deletions and multiple distinct mutations in the major structural genes fiber2 and hexon. To identify the genes responsible for the virulence of HHS-associated novel FAdV-4 isolates, FAdV-4 infectious clones were constructed by directly cloning the whole genome of a highly pathogenic FAdV-4 isolate (CH/HNJZ/2015) and that of a nonpathogenic strain (ON1) into a p15A-cm vector using the ExoCET method. Subsequently, the fiber2, hexon, and 1966-bp fragment-replaced mutant/recombinant viruses were constructed using Redαβ recombineering and ccdB counter-selection techniques. The pathogenicity of the rescued viruses was compared with that of the rescued parent viruses rHNJZ and rON1 in 3-week-old SPF chickens. Chickens infected with the rescued viruses carrying the fiber2 and/or hexon gene of the HNJZ strain developed similar clinical signs to the natural infection, with distinctive gross lesions and characteristic histological signs indicative of HHS observed in sick/dead chickens. Our results clearly demonstrated that the virulence of the novel highly pathogenic FAdV-4 strain was independent of the 1966-bp deletion and that the fiber2 and hexon genes have crucial roles in FAdV-4 pathogenicity. The data presented in this report will provide further insights into the crucial factors determining the pathogenicity of FAdV strains. Furthermore, the infectious clones generated based on the FAdV-4 genome can be used as a platform for studies of gene function and for the development of recombinant vaccines.

Characterization of strain of fowl adenoviruses circulating in Morocco

Infection of fowl with adenoviruses raises concerns for poultry production, thus making the detection of adenovirus infection crucial. Fowl adenovirus is the causal agent of inclusion body hepatitis (IBH) and other avian syndromes that affect the production; since the epidemiological point of view it is important to differentiate the serotype of the virus. Between September 2016 and February 2017 several cases of IBH in broiler flocks were reported in Morocco. Molecular detection of the fowl adenovirus and sequencing also allowed determining the strain of the virus. The strain detected was identified as fowl adenovirus closely related to serotype 11 and 8a based on nucleotide sequence analyses of hexon gene loop 1. This is the first time that FadV has been detected in Morocco.

Protein profile of FAdV-4 based on SDS-PAGE and Western blot isolated from chickens in India

Fowl adenovirus-4 (FAdV-4) causes hydropericardium syndrome (HPS) in poultry worldwide. An understanding of viral structural protein composition is important for developing novel immunodiagnostics and immunoprophylactics. Here we report isolation, culture, molecular and protein profile of FAdV-4 isolates recovered from HPS outbreaks in chicken in the states of Himachal Pradesh and Tamil Nadu in India. We performed a sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting-based protein profiling of FAdV-4 isolates against a reference FAdV-1 or Chicken Embryo Lethal Orphan (CELO) virus. SDS-PAGE analysis showed that seven protein bands in FAdV-4 isolates were similar to CELO expect an additional band of 110 kDa in CELO virus. On Western blotting, two protein fractions of 43 kDa and 78 kDa size were observed in FAdV-4 isolates. Overall, results show that FAdV-4 isolates recovered from different regions of the country had similar protein profile and possibly a common source of origin.

Hydropericardium syndrome caused by fowl adenovirus serotype 4 in replacement pullets

Hydropericardium syndrome (HPS) is one of the important emerging diseases causing huge losses to the poultry industry. It affects mainly 3- to 6-week-old broiler chickens and rarely occurs in breeding and laying flocks. Recently, an HPS case was recorded with a sudden heavy mortality in a 100-day-old laying flock. A fowl adenovirus serotype 4 (FAdV-4), named as GDMZ strain, was isolated and identified using polymerase chain reaction coupled with electron microscopy. The animal experiment showed that a mortality of 100% was recorded with hydropericardium as a conspicuous lesion throughout the course of infection. Microscopically, vacuolar changes and intranuclear inclusion bodies were observed in the liver and vacuolar changes were observed in the heart. The complete genome sequence of GDMZ strain was determined to investigate the molecular properties of GDMZ strain. The comparative analysis revealed that the novel Chinese FAdV-4 isolate contained open reading frame (ORF) 19, ORF27, and ORF48 genomic deletions. The phylogenetic analysis revealed that FAdV-4 could be divided into two major clades, of which Chinese FAdV-4 were located at a distinct clade.

Fowl adenovirus serotype 4: Epidemiology, pathogenesis, diagnostic detection, and vaccine strategies

Fowl adenovirus (FAdV) serotype-4 is highly pathogenic for chickens, especially for broilers aged 3 to 5 wk, and it has emerged as one of the foremost causes of economic losses to the poultry industry in the last 30 years. The liver is a major target organ of FAdV-4 infections, and virus-infected chickens usually show symptoms of hydropericardium syndrome. The virus is very contagious, and it is spread both vertically and horizontally. It can be isolated from infected liver homogenates and detected by several laboratory diagnostic methods (including an agar gel immunodiffusion test, indirect immunofluorescence assays, counterimmunoelectrophoresis, enzyme-linked immunosorbent assays, restriction endonuclease analyses, polymerase chain reaction (PCR), real-time PCR, and high-resolution melting-curve analyses). Although inactivated vaccines have been deployed widely to control the disease, attenuated live vaccines and subunit vaccines also have been developed, and they are more attractive vaccine candidates. This article provides a comprehensive review of FAdV-4, including its epidemiology, pathogenesis, diagnostic detection, and vaccine strategies.

Pathogenicity and immunosuppressive potential of fowl adenovirus in specific pathogen free chickens

To elucidate the effect of fowl adenovirus (FAdV)-C in specific-pathogen-free (SPF) chickens, we investigated the pathogenicity, body weights, enzymatic systems, and immune organs of chickens in response to Newcastle disease virus (NDV) and avian influenza virus subtype H9 (AIV-H9) vaccination. Chickens were divided randomly into four groups, which included injection groups (FAdV-C, vaccination, and FAdV-C plus vaccination) and a negative control group. The results indicated that FAdV-C was highly pathogenic in SPF chickens and led to a 40% mortality rate and growth retardation, compared with the control birds. Significant changes in clinical chemical markers of all infected birds, together with histopathological lesions, indicated impairment of the liver and heart integrity and function. Furthermore, chickens in the FAdV-C plus vaccination group had significantly lower titers of antibodies against NDV and AIV-H9 than the uninfected and vaccinated chickens. The results of this study provide new insights into the pathogenesis of hydropericardium syndrome, a disease that progresses to a metabolic disorder and causes serious growth retardation and immunosuppression.

Newcastle disease virus-attenuated vaccine co-contaminated with fowl adenovirus and chicken infectious anemia virus results in inclusion body hepatitis-hydropericardium syndrome in poultry

Inclusion body hepatitis-hydropericardium syndrome (IBH-HPS) induced by fowl adenovirus type 4 (FAdV-4) has caused huge economic losses to the poultry industry of China, but the source of infection for different flocks, especially flocks with high biological safety conditions, has remained unclear. This study tested the pathogenicity of Newcastle disease virus (NDV)-attenuated vaccine from a large-scale poultry farm in China where IBH-HPS had appeared with high mortality. Analysis revealed that the NDV-attenuated vaccine in use from the abovementioned poultry farm was simultaneously contaminated with FAdV-4 and chicken infectious anemia virus (CIAV). The FAdV and CIAV isolated from the vaccine were purified for the artificial preparation of an NDV-attenuated vaccine singly contaminated with FAdV or CIAV, or simultaneously contaminated with both of them. Seven-day-old specific pathogen-free chicks were inoculated with the artificially prepared contaminated vaccines and tested for corresponding indices. The experiments showed that no hydropericardium syndrome (HPS) and corresponding death occurred after administering the NDV-attenuated vaccine singly contaminated with FAdV or CIAV, but a mortality of 75% with IBH-HPS was commonly found in birds after administering the NDV-attenuated vaccine co-contaminated with FAdV and CIAV. In conclusion, this study found the co-contamination of FAdV-4 and CIAV in the same attenuated vaccine and confirmed that such a contaminated attenuated vaccine was a significant source of infection for outbreaks of IBH-HPS in some flocks.

Phylogenetic Analyses of Fowl Adenoviruses (FAdV) Isolated in China and Pathogenicity of a FAdV-8 Isolate

Fowl adenoviruses (FAdVs) have a worldwide distribution and are associated with a variety of diseases, causing considerable economic losses to the poultry industry. We characterized 10 FAdVs isolated from China in 2015-2016 and assessed the pathogenicity of a FAdV-8 strain in specific-pathogen-free (SPF) chickens. Phylogenetic analysis of a hexon gene revealed that only 1 of the 10 isolates belonged to FAdV-8, whereas others belonged to FAdV-4, indicating that Chinese FAdVs were mainly FAdV-4 in recent years. The pathogenicity experiment of the FAdV-8 strain CH/SD/2015/09 showed that no clinical signs were observed in infected chickens. Necropsy displayed mild necrotic foci and petechial hemorrhage of livers collected at 5 days postinfection (dpi). Histopathologic examination identified the presence of intranuclear inclusion bodies in hepatocytes. No virus was detected in oral and cloacal swabs at 5 dpi, and only viral DNA could be measured in kidneys collected at the same time. The results revealed that CH/SD/2015/09 had no obvious pathogenicity in 5-wk-old SPF chickens, which could provide a better understanding about the pathogenicity of the FAdV-8 serotype.

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.

Epidemiological investigation of outbreaks of fowl adenovirus infections in commercial chickens in China

One hundred and five fowl adenovirus (FAdV) strains were isolated in China from 2015 to 2016 from poultry with inclusion body hepatitis (IBH) and hydropericardium syndrome (HPS). Polymerase chain reactions determined that 68 were FAdV species C, five were FAdV species D, two were FAdV species E, and 30 contained two or more different FAdV strains. A phylogenetic analysis showed that the isolated FAdV strains clustered into three major groups: FAdV-C, FAdV-D and FAdV-E. Based on a hexon gene sequencing analysis, these viruses were genetically related to FAdV-4, FAdV-7, FAdV-8b and FAdV-11, of which FAdV-4 was dominant (93% of the strains). An epidemiological analysis showed that FAdVs had been circulating in broilers, domestic chickens, and layers, and co-infections with other immunosuppressive pathogens, such as chicken infectious anaemia virus, Marek's disease virus and reticuloendotheliosis virus, were identified. To control FAdVs, strict biosecurity protection measures are necessary, and a continued surveillance of FAdVs is needed to increase our understanding of the epidemiology of the viruses that are associated with IBH and HPS.

Overexpression and characterization of the 100K protein of Fowl adenovirus-4 as an antiviral target

100K is an important scaffolding protein of adenoviruses including fowl adenovirus serotype 4 (FAdV-4) that causes inclusion body hepatitis-hydropericardium syndrome (IBH-HPS) in poultry. 100K carries out the trimerization of the major capsid hexon protein of the virus for the generation of new virions inside the target host cells. Despite its critical role for FAdV-4, no structural study, in particular, has been conducted so far. Here, the overexpression of soluble 100K protein was successfully carried out in E. coli using various expression constructs and purification yield of 3mg per litre culture volume was obtained. Gel filtration chromatography suggested that 100K protein exists in trimeric form. Circular dichroism and Fourier transform infrared spectroscopy clearly reveal that 100K protein folds with a high content of α-helices. The 3-dimentional homology model of the 100K protein, refined with molecular dynamics tools also depicts higher α-helical content within the protein model. Moreover, overexpressed recombinant 100K protein could be used to differentiate vaccinated and FAdV-4 infected chickens on the basis of higher serum anti 100K antibody titres. Our work provides preliminary structural and functional results to study biological role of the 100K protein and for further investigations to develop 100K inhibitors to control IBH-HPS in poultry.

Fowl adenovirus: history, emergence, biology and development of a vaccine against hydropericardium syndrome

The poultry industry has emerged as one of the largest and fastest growing public sectors in the developed and developing countries. Unfortunately, this industry is under a major threat from diseases that are viral (Newcastle disease, infectious bursal disease, influenza, hydropericardium syndrome), bacterial (colibacillosis, pasteurellosis, salmonellosis, mycoplasmosis), parasitic (coccidiosis, histoplasmosis) or nutritional (dyschondroplasia, osteoporosis). Among these diseases, hydropericardium syndrome (HPS) is one of the important emerging diseases occurring in the specific areas of the world where broilers (chickens) are reared under intensive conditions. HPS was first observed in 1987 at Angara Goth, an area near Karachi, Pakistan, where broilers are raised. Since then, HPS has been reported in many countries of the world. From these reported cases, an adenovirus that was either isolated from or visualized electron microscopically in the liver of affected broilers has been implicated in the syndrome. The syndrome has been reproduced by inoculation of isolated fowl adenovirus (FAdV) strains, and hence, the syndrome is also called infectious hydropericardium syndrome. To our knowledge, HPS has not been observed in humans, so it is not considered a zoonotic disease, but it is of economic importance and causes huge losses to the poultry industry. Efforts have been made to develop conventional vaccines against this disease, which were formulated from infected liver homogenate. Formalin-inactivated liver organ vaccines have failed to protect the poultry industry. Hence, there is a dire need to develop a suitable vaccine to combat this disease. Currently, recombinant vaccine candidates are being developed by using molecular biology and biotechnological approaches for the prevention and control of infectious diseases, including HPS. Therefore, it is suggested that the immunogenicity of these recombinant proteins should be evaluated for their use as subunit vaccines.

Commensal or pathogen - a challenge to fulfil Koch's Postulates

1. Infectious diseases have a large impact on poultry health and economics. Elucidating the pathogenesis of a certain disease is crucial to implement control strategies.

2. Multiplication of a pathogen and its characterisation in vitro are basic requirements to perform experimental studies. However, passaging of the pathogen in vitro can influence the pathogenicity, a process targeted for live vaccine development, but limits the reproduction of clinical signs.

3. Numerous factors can influence the outcome of experimental infections with some importance on the pathogen, application route and host as exemplarily outlined for Histomonas meleagridis, Gallibacterium anatis and fowl aviadenoviruses (FAdVs).

4. In future, more comprehensive and detailed settings are needed to obtain as much information as possible from animal experiments. Processing of samples with modern diagnostic tools provides the option to closely monitor the host–pathogen interaction.

Modified live infectious bursal disease virus (IBDV) vaccine delays infection of neonatal broiler chickens with variant IBDV compared to turkey herpesvirus (HVT)-IBDV vectored vaccine

Chickens are commonly processed around 35-45days of age in broiler chicken industry hence; diseases that occur at a young age are of paramount economic importance. Early age infection with infectious bursal disease virus (IBDV) results in long-lasting immunosuppression and profound economic losses. To our knowledge, this is the first study comparing the protection efficacy of modified live (MdLV) IBDV and herpesvirus turkey (HVT)-IBDV vaccines against early age variant IBDV (varIBDV) infection in chicks. Experiments were carried out in IBDV maternal antibody (MtAb) positive chicks (n=330), divided into 6 groups (n=50-60/group), namely Group 1 (saline), Group 2 (saline+varIBDV), Group 3 (HVT-IBDV), Group 4 (HVT-IBDV+varIBDV), Group 5 (MdLV) and Group 6 (MdLV+varIBDV). HVT-IBDV vaccination was given via the in ovo route to 18-day-old embryonated eggs. MdLV was administered via the subcutaneous route in day-old broilers. Group 2, Group 4 and Group 6 were orally challenged with varIBDV (SK-09, 3×10³ EID₅₀) at day 6 post-hatch. IBDV seroconversion, bursal weight to body weight ratio (BBW) and bursal histopathology were assessed at 19 and 35days of age. Histopathological examination at day 19 revealed that varIBDV-SK09 challenge caused severe bursal atrophy and lower BBW in HVT-IBDV but not in MdLV vaccinated chicks. However by day 35, all challenged groups showed bursal atrophy and seroconversion. Interestingly, RT-qPCR analysis after varIBDV-SK09 challenge demonstrated an early (9days of age) and significantly high viral load (∼5744 folds) in HVT-IBDV vaccinated group vs unvaccinated challenged group (∼2.25 folds). Furthermore, flow cytometry analysis revealed inhibition of cytotoxic CD8⁺ T-cell response (CD44-downregulation) and decreased splenic lymphocytes counts in chicks after HVT-IBDV vaccination. Overall, our data suggest that MdLV delays varIBDV pathogenesis, whereas, HVT-IBDV vaccine is potentially immunosuppressive, which may increase the risk of early age varIBDV infection in broilers.

Genetic characterization of novel fowl aviadenovirus 4 isolates from outbreaks of hepatitis-hydropericardium syndrome in broiler chickens in China

Since May 2015, severe outbreaks of hepatitis-hydropericardium syndrome (HHS) associated with infections of fowl aviadenovirus (FAdV) have emerged in broiler chickens in several Chinese provinces. To identify the genotype and gain a better understanding of the genetic properties of the FAdV strains responsible for the recent HHS outbreaks in China, the complete genome sequences of five isolates from outbreaks of HHS in broiler chickens in five provinces were determined. The results demonstrated that a novel fowl aviadenovirus 4 (FAdV-4) genotype was epidemic in China. To investigate the molecular characteristics of these Chinese FAdV-4 isolates, their genome contents were compared with those of reported pathogenic and non-pathogenic FAdV-4 strains. The comparative analysis revealed that the novel Chinese FAdV-4 isolates contain various genomic deletions and multiple distinct amino-acid mutations in their major structural genes. Two additional putative genetic virulence markers in the fiber 2 gene were identified. These findings confirmed some of the genetic differences between the pathogenic and non-pathogenic FAdV-4 isolates. The data presented in this report will enhance the current understanding of the molecular epidemiology and genetic diversity of FAdV-4 isolates in China and will provide additional insight into the critical factors that determine the pathogenicity of FAdV-4 strains. Finally, the emergence of this novel and highly pathogenic FAdV-4 genotype emphasizes that preventive measures against FAdV-4 infections on poultry farms should be implemented in China.

Molecular characterization, phylogeny analysis and pathogenicity of a Muscovy duck adenovirus strain isolated in China in 2014

This study aimed to characterize a novel adenovirus (AdV) isolated from diseased Muscovy ducks in China. After the AdV was successfully propagated in duck embryo fibroblasts, the morphological and physicochemical properties of the virions were studied by electron microscopy and different tests. The results of the analyses were in conformity with AdV properties. The full genome sequence was determined and analyzed. The new isolate (named CH-GD-12-2014) shared over 91% sequence identity with duck AdV-2 representing the species Duck aviadenovirus B. The most important distinguishing feature between the two DAdV strains was the presence of a second fiber gene in the Chinese isolate. Phylogeny reconstruction confirmed the affiliation of the virus with goose and duck AdVs in the genus Aviadenovirus. Experimental infection resulted in embryo death, and intramuscular inoculation provoked morbidity and mortality among ducks and chickens.

An inactivated oil-emulsion fowl Adenovirus serotype 4 vaccine provides broad cross-protection against various serotypes of fowl Adenovirus

The number of clinical cases of inclusion body hepatitis (IBH) and hydropericardium-hepatitis syndrome (HHS) has been increasing, resulting in considerable economic losses in many countries. Currently, only fowl Adenovirus (FAdV) serotype 4 (FAdV-4) has been reported as the causative agent of HHS, whereas IBH can be caused by all 12 serotypes of FAdV. For protection against HHS, various live and killed FAdV serotype 4 vaccines have been developed. However, there is a concern whether these vaccines composed of FAdV-4 alone could provide protection against IBH, which is caused by other serotypes of virulent FAdVs. To date, there have been no reports evaluating the protective efficacy of the FAdV-4 vaccine against other serotypes of FAdV. Thus, we investigated the cross-protection efficacy of an inactivated oil-emulsion FAdV-4 vaccine against various serotypes of FAdV field isolates. Our study demonstrated that the inactivated oil-emulsion FAdV-4 vaccine could provide broad cross-protection against various serotypes of FAdV in not only vaccinated birds, but also the progenies of vaccinated breeder. Therefore, we conclude that the inactivated oil-emulsion FAdV-4 vaccine could be effective in preventing the spread of various other serotypes of FAdV as well as FAdV-4 infection in the poultry industry.

Epidemiological investigation of outbreaks of fowl adenovirus infection in commercial chickens in Korea

In total, 39 clinical cases of fowl adenoviruses (FAdV) infection in chickens (28 broiler, 7 native, and 4 layer chickens) between 2007 and 2010 in Korea were investigated. The FAdV types 4, 8b, and 11 comprised 18, 9, and 12 clinical cases, respectively. All FAdV type 4 cases showed clinical hydropericardium (HPS) lesions as well as inclusion body hepatitis (IBH), whereas all FAdV types 8b and 11 cases exhibited IBH lesions without HPS. All 3 types were detected in broiler (9-30 d old) and layer chickens (23-112 d old), whereas most native chickens (14-65 d old) were affected only by FAdV type 4. Infectious bursal disease virus and chicken infectious anemia virus were complications in 51.3% of FAdV cases, with mortalities of 55% to <0.1%. Chicken infectious anemia virus was detected in all native chicken cases. These results indicate that preventive measures against FAdV infection and immunosuppressive diseases on poultry farms should be implemented.

A subunit vaccine against hydropericardium syndrome using adenovirus penton capsid protein

Hydropericardium syndrome (HPS) is a disease of poultry that is caused by fowl adenovirus-4. Inactivated liver homogenate from diseased birds is still the choice of vaccine in some countries which disseminates numerous pathogens along with inactivated virus. Moreover incomplete attenuation or inactivation, reversion to virulence and the oncogenic potential/genetic instability of the adenoviruses have prevented their use in routine vaccines. To address this problem an effort is made to develop a subunit vaccine. For this purpose penton base protein of HPS virus was expressed in Escherichia coli and used as subunit vaccine in broilers. Immunogenicity of the recombinant penton base protein and challenge protection test against pathogenic virus demonstrated the ability of recombinant penton base protein to confer (90%) protection. Results suggest that the recombinant penton base protein is a candidate for subunit vaccine against HPS.

Identification and virulence characterization of fowl adenoviruses in Korea

Since 2007, 55 adenovirus strains have been isolated from commercial chicken flocks in Korea and have been identified and the pathogenicity of these isolates was confirmed in specific-pathogen-free chickens of different age. Based on sequencing analysis of the hexon gene, 55 FAdV isolates were genetically related to the IBH-2A strain of FAdV3 (4 isolates, 99.2% to 100%), the KR5 strain of FAdV4 (22 isolates, 97.9% to 99.2%), the 764 strain of FAdV9 (11 isolates, 99.1% to 99.3%), and the 1047 strain of FAdV11 (18 isolates, > 99%). Experimental infections with four serotypes of FAdV resulted in high mortality of 18-day-old chicken embryos and 1-day-old chicks with marked liver necrosis similar to those observed in the natural outbreaks. Notably, specific hydropericardium was observed in chicks challenged with the K531 strain (serotype 4). However, 3-wk-old chickens challenged with FAdVs, regardless of serotype, did not show any clinical signs or mortality except histologic lesions of focal hepatocytic necrosis with mild lymphocytic infiltration. The results indicate that four FAdV serotypes (3, 4, 9, and 11) are the dominant serotypes of FAdVs in the Korea and are pathogenic enough to cause clinical disease in young chicks. The present investigation provides important information on the epidemiology and pathogenesis of FAdVs and highlights the importance of control strategies against FAdV infection in Korea.

Application of high-resolution melting curve analysis for typing of fowl adenoviruses in field cases of inclusion body hepatitis

OBJECTIVE

Fowl adenoviruses (FAdVs) cause inclusion body hepatitis (IBH) in chickens. In this study, clinical cases of IBH from Australian broiler flocks were screened for the presence and genotype of FAdVs.

METHODS

Twenty-six IBH cases from commercial poultry farms were screened. Polymerase chain reaction (PCR) coupled with high-resolution melt (HRM) curve analysis (PCR/HRM genotyping) was used to determine the presence and genotype of FAdVs. For comparison, field isolates were also assessed by virus microneutralisation and nucleotide sequence analysis of the hexon loop 1 (Hex L1) gene. PCR detection of chicken anaemia virus (CAV) and infectious bursal disease virus (IBDV) was also employed.

RESULTS

FAdV-8b and FAdV-11 were identified in 13 cases each. In one case, FAdV-1 was also identified. Cross-neutralisation was observed between the FAdV-11 field strain and the reference FAdV-2 and 11 antisera, a result also seen with the type 2 and 11 reference FAdVs. Field strains 1 and 8b were neutralised only by their respective type antisera. The FAdV-8b field strain was identical to the Australian FAdV vaccine strain (type 8b) in the Hex L1 region. The Hex L1 sequence of the FAdV-11 field strain had the highest identity to FAdV-11 (93.2%) and FAdV-2 (92.7%) reference strains. In the five cases tested for CAV and IBDV, neither virus was detected. The evidence suggested the presence of sufficient antibodies against CAV and IBD in the parent flocks and there was no indication of immunosuppression caused by these viruses.

CONCLUSION

These results indicate that PCR/HRM genotyping is a reliable diagnostic method for FAdV identification and is more rapid than virus neutralisation and direct sequence analysis. Furthermore, they suggest that IBH in Australian broiler flocks is a primary disease resulting from two alternative FAdV strains from different species.

Pyrosequencing analysis for a rapid classification of fowl adenovirus species

A rapid fowl adenovirus (FAdV) classification method based on a 30-bp sequence of the hexon loop (L1) was developed using the pyrosequencing technique. FAdV identification is relevant for epidemiological studies and for the adoption of a correct strategy where vaccination is to be used for the control of the disease. FAdV typing is usually performed using polymerase chain reaction coupled with either conventional DNA sequencing or restriction enzyme analysis; however, both methods can be time consuming and/or very expensive to be used as a routine tool. In the present study, polymerase chain reaction and subsequent pyrosequence analysis of the variable hexon L1 region were assessed in order to rapidly differentiate FAdV species. Forty-nine FAdV samples (22 reference strains and 27 field isolates) were tested and the results were compared with those obtained by conventional DNA sequencing. The results clearly demonstrated that pyrosequence analysis provides a new approach for a rapid differentiation and classification of the FAdV species that is faster, more cost-effective and easier to interpret than other techniques commonly used.

Classification of fowl adenovirus serotypes by use of high-resolution melting-curve analysis of the hexon gene region

Identification of fowl adenovirus (FAdV) serotypes is of importance in epidemiological studies of disease outbreaks and the adoption of vaccination strategies. In this study, real-time PCR and subsequent high-resolution melting (HRM)-curve analysis of three regions of the hexon gene were developed and assessed for their potential in differentiating 12 FAdV reference serotypes. The results were compared to previously described PCR and restriction enzyme analyses of the hexon gene. Both HRM-curve analysis of a 191-bp region of the hexon gene and restriction enzyme analysis failed to distinguish a number of serotypes used in this study. In addition, PCR of the region spanning nucleotides (nt) 144 to 1040 failed to amplify FAdV-5 in sufficient quantities for further analysis. However, HRM-curve analysis of the region spanning nt 301 to 890 proved a sensitive and specific method of differentiating all 12 serotypes. All melt curves were highly reproducible, and replicates of each serotype were correctly genotyped with a mean confidence value of more than 99% using normalized HRM curves. Sequencing analysis revealed that each profile was related to a unique sequence, with some sequences sharing greater than 94% identity. Melting-curve profiles were found to be related mainly to GC composition and distribution throughout the amplicons, regardless of sequence identity. The results presented in this study show that the closed-tube method of PCR and HRM-curve analysis provides an accurate, rapid, and robust genotyping technique for the identification of FAdV serotypes and can be used as a model for developing genotyping techniques for other pathogens.