Isolation and pathogenicity of a fowl adenovirus 8b (FAdV-8b) strain in Cherry Valley ducks.

AbstractInclusion body hepatitis (IBH) is an economically important viral disease primarily affecting the poultry industry. In this study, we isolated a strain of FAdV-8b (strain SDYT) from naturally infected ducks and the hexon and fiber gene sequences were analysed by polymerase chain reaction (PCR) amplification. In order to study the pathogenicity of FAdV-8b on Cherry Valley ducks, we inoculated 10- and 20-day-old ducks with 0.3 ml of FAdV-4 virus (TCID50 of 105.5/0.1 ml) either orally or intramuscularly. Clinical signs, gross lesions and histopathological changes, cytokines, viral load and antibody levels were noticed and recorded within 15 days after infection.Pathomorphological investigations revealed that ducks in the experimental group exhibited hepatitis symptoms. Histopathology showed multiple-organ damage, including serious liver and kidney lesions. Furthermore, elevated levels of inflammatory cytokines and antibodies was noticed, due to the infection and innate immune response. At later stage of infection immunosuppression occurred, resulting in decreased levels of cytokines. Determination of viral load indicated that the virus was present in several organs, with the highest viral DNA load found in the liver, followed by the kidney. Compared to birds infected orally, the intramuscular group exhibited the highest viral load. In summary, this study increases our understanding of the pathogenicity of FAdV-8b in ducks and establishes a model that will inform antiviral drug testing and vaccine evaluation for IBH, thereby preventing and reducing the spread of IBH in the poultry industry.

Epidemiological investigation of fowl adenovirus (FAdV) infections in ducks and geese in Shandong Province, China.

RESEARCH HIGHLIGHTS: Samples of suspected FAdV-infected waterfowl from farms in Shandong Province were collected from 2019 to 2022.Single infections with FAdV were less frequent than mixed infections.477 out of 792 samples (60.23%) tested positive for FAdV nucleic acids.Detection rate of FAdV was 65.47% in fattening duck farms, 55.73% in breeder duck farms and 54.55% in fattening geese farms.

Molecular characterisation of fowl adenovirus associated with hydropericardium hepatitis syndrome in broiler and layer breeders in Azerbaijan.

BACKGROUND: Fowl adenovirus-4 is a causative agent of hydropericardium hepatitis syndrome (HHS) in chickens and has been frequently reported from many countries. Fowl adenoviruses cause severe disease and mortality in broiler and layer breeders in Azerbaijan. Therefore, in this study, pathological lesions and the dissemination of fowl adenovirus-4 into the visceral organs of infected birds were investigated as well as molecular characterisation of detected strains. For this, liver, heart and spleen from 20 necropsied chickens originated from a broiler breeder flock and a layer breeder flock were embeded on the FTA cards and the samples were analysed for adenovirus-DNA by PCR and sequencing. RESULTS: The findings of necropsy in both broiler and layer breeder chickens were similar, and the liver was severely effected showing hepatitis, and the heart with hydropericardium lesions. The kidneys were swollen with haemorrhages and small white foci on the surface of the spleens were noted. Intestinal congestion and ecchymotic hemorrhages were also observed in some birds. Fowl adenovirus-4-DNA was detected by PCR in all collected organs of 20 birds. The sequence analysis revealed that fowl adenovirus-4 present in Azerbaijan and close similarity of the hexon genes of the adenoviruses existing in the Middle East, North America, far east and Indian subcontinent were determined by phylogenetic analysis. However, sequence diversity was detected from the adenovirus strains circulating in Europe, North and South America. CONCLUSIONS: This study indicates the impact of fowl adenovirus-4 on the poultry health and production, and improved disease control and prevention strategies are necessary to reduce the HHS disease in chickens in Azerbaijan.

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.

Hsp70 Inhibits the Replication of Fowl Adenovirus Serotype 4 by Suppressing Viral Hexon with the Assistance of DnaJC7.

Fowl adenovirus serotype 4 (FAdV-4) infection results in serious hepatitis-hydropericardium syndrome (HHS) in broilers, which has caused great economic losses to the poultry industry; however, the specific host responses to FAdV-4 remain unknown. In this study, we identified 141 high-confidence protein-protein interactions (PPIs) between the main viral proteins (Hexon, Fiber 1, Fiber 2, and Penton bases) and host proteins via a liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay. We found that heat shock protein 70 (Hsp70), the protein with the highest score, and its cofactor DnaJ heat shock protein 40 family member C7 (DnaJC7) could negatively regulate the replication of FAdV-4. Furthermore, the nucleotide binding domain (NBD) of Hsp70 and the J domain of DnaJC7 were necessary for inhibiting FAdV-4 replication. We verified that DnaJC7 as a bridge could bind to Hsp70 and Hexon, assisting the indirect interaction between Hsp70 and Hexon. In addition, we found that FAdV-4 infection strongly induced the expression of autophagy proteins and cellular Hsp70 in a dose-dependent manner. Blockage of Hexon by Hsp70 overexpression was significantly reduced when the autophagy pathway was blocked by the specific inhibitor chloroquine (CQ). Our results showed that Hsp70 was co-opted by DnaJC7 to interact with viral Hexon and inhibited Hexon through the autophagy pathway, leading to a considerable restriction of FAdV-4 replication. IMPORTANCE FAdV-4, as the main cause of HHS, has quickly spread all over the world in recent years, seriously threatening the poultry industry. The aim of this study was to identify the important host proteins that have the potential to regulate the life cycle of FAdV-4. We found that Hsp70 and DnaJC7 played crucial roles in regulating the amount of viral Hexon and extracellular viral titers. Moreover, we demonstrated that Hsp70 interacted with viral Hexon with the assistance of DnaJC7, followed by suppressing Hexon protein through the autophagy pathway. These results provide new insight into the role of the molecular chaperone complex Hsp70-DnaJC7 in FAdV-4 infection and suggest a novel strategy for anti-FAdV-4 drug development by targeting the specific interactions among Hsp70, DnaJC7 and Hexon.

Molecular phylodynamics of fowl adenovirus serotype 11 and 8b from inclusion body hepatitis outbreaks.

Fowl adenovirus (FAdV) serotypes are involved in a variety of clinical manifestations in poultry and has resulted in substantial economic loss to the poultry farmers. Despite the endemicity of Inclusion body hepatitis (IBH) in South Asian countries, including India, its etiology is not well studied. In western India, the rural poultry flocks obtained from the vaccinated parents were experiencing disease outbreaks with substantial economic losses due to heavy outbreaks and mortality. Therefore, the study was conducted to decipher the molecular epidemiology of the FAdV from field outbreaks in western India. A total of 37 commercial broiler poultry flocks and 29 village poultry flocks of western India were visited during 2019 to 2021. Out of these, 19.14% flocks showed incidence of IBH during the age of 15 to 35 days. The mortality ranged from 3.3 percent to 55.28 percent. The samples were subjected for amplification of partial hexon gene covering loop 1 and loop 2. The results revealed 48.28% positivity by PCR. The sequence analysis identified 14 isolates as species D serotype 11 with 0.97 to 0.99% divergence and two as species E serotype 8b with 0.99% divergence. The FAdV-11 isolates showed amino acid substitutions D195N, T399A, N417S, and N496H. The amino acids I188 and N195 were conserved in FAdV-11. The molecular clock in Bayesian methods was used to determine most common ancestor. The isolates MH379249 and MH379248 were determined the most recent common ancestor for FAdV-11 and FAdV-8b isolates. The analysis suggested evolution of 10 FAdV-11 strains in 2012, and four FAdV-11 strains and two FAdV-8b strains in 2018.

Recombinant Fowl aviadenovirus E (FAdV-E) penton base vaccination fails to confer protection against inclusion body hepatitis (IBH) in chickens.

Inclusion body hepatitis (IBH) is a metabolic disease affecting chickens, associated with different serotypes of fowl adenovirus (FAdV). Experimentally tested vaccines against IBH include several capsid-based subunit vaccines, but not the penton base protein. In the present study, specific pathogen-free chickens were vaccinated with recombinant penton base expressed from each of two different FAdV serotypes (FAdV-7 and FAdV-8b), followed by challenge with a virulent IBH-causing strain. No protection was observed with either vaccine, possibly due to the low immunogenicity of each protein and their inability to induce neutralizing antibodies in the host.

Visual detection of fowl adenovirus serotype 4 via a portable CRISPR/Cas13a-based lateral flow assay.

The widespread occurrence of fowl adenovirus serotype 4 (FAdV-4)-induced hepatitis-hydropericardium syndrome (HHS) has led to significant economic losses for the poultry industry. A sensitive, accurate, and practical FAdV-4 diagnostic approach is urgently required to limit the incidence of the disease. In the present study, a practical method for detecting FAdV-4 was developed using the CRISPR/Cas13a system and recombinase-aided amplification. The approach was based on 37°C isothermal detection with visible results being achieved. The detection limit of the target gene with this approach was only 101 copies/µl, making it very sensitive and specific. Clinical samples fared well when tested with the Cas13a detection method. For identifying FAdV-4, this novel detection approach was found to be sensitive, specific, and effective.RESEARCH HIGHLIGHTS First study using the CRISPR/Cas13a-based lateral flow detection assay for FAdV-4 detection.The results can be observed by the naked eye.The developed assay could provide an alternative tool for detection of FAdV-4 with minimal equipment.

Fowl adenovirus-induced different manifestations of the disease in two consecutive chicken breeding flocks in a poultry hall.

This study investigated an adenovirus infection in two consecutive breeding flocks in the same poultry hall. Thirty-six thousand one-day-old chickens of the ROSS 308 hybrid broiler type were kept together in one hall. The chickens in the first breeding flock during fattening did not show any clinical signs of the disease or increased mortality. Typical clinical signs of the adenovirus infection were seen in the second breeding flock. The signs included: depression, apathy, somnolence, a crouched position with a droopy head, fuzzy feathers, anaemic combs and wattles, sporadic nervous signs, and reduced weight gain. Increased mortality was recorded from 18 to 25 days of age, the higher mortality rate resulted from dehydration and exhaustion. The surviving chickens showed growth slightly below average by the end of the fattening period. The necropsies of the chickens in the first flock showed characteristic lesions for inclusion body hepatitis (IBH). Adenoviral gizzard erosions (AGE) were found mainly in the chickens of the second consecutive breeding flock. In both breeding flocks, FAdV-A was detected by polymerase chain reaction (PCR) in the liver and gizzard samples. The presence of fowl adenovirus B was not confirmed in the evaluated samples. The results showed lesions in the first flock typical for IBH, whereas the pathological changes in the second flock were characteristic of AGE.

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.

Highly soluble and stable 'insertion domain' of the capsid penton base protein provides complete protection against infections caused by fowl adenoviruses.

In the current study, we have evaluated the protective efficacy of the 'insertion domain' which is commonly found in the capsid penton base protein of many adenoviruses. Using the 'insertion domain' of the penton base protein of a representative fowl adenovirus, fowl adenovirus serotype 4 (FAdV-4), we find that the 'insertion domain' can readily be expressed in a soluble form in the bacterial system, and can be purified in sufficient quantities through simple chromatographic methods. We demonstrate that the 'insertion domain', when employed as a subunit vaccine candidate, provides complete protection against hydropericardium syndrome, caused by FAdV-4, in chickens. The data presented here indicate that the protein, adjuvanted with Montanide™ ISA71 VG, provides complete protection in chickens against a lethal FAdV-4 challenge after administration of two doses (100 µg of the protein per dose) two weeks apart (the first dose at the 7th day of life and a booster dose at the age of 21 days). Furthermore, the purified protein can be stored at low temperatures without any observable loss in the protein integrity up to one year, tested so far. Due to the conserved nature of the 'insertion domain' across the penton base protein of fowl adenoviruses, it is suggested that homologous insertion domains could be employed as highly stable and cost-effective subunit vaccine candidates against infections caused by respective fowl adenoviruses.

An inactivated novel chimeric FAdV-4 containing fiber of FAdV-8b provides full protection against hepatitis-hydropericardium syndrome and inclusion body hepatitis.

Fowl adenovirus serotype 4 (FAdV-4) and FAdV-8b are causative agents of hepatitis-hydropericardium syndrome (HHS) and inclusion body hepatitis (IBH), respectively. HHS and IBH co-infections were often reported in clinical, yet there are no commercially available bivalent vaccines for prevention and control of both FAdV-4 and -8b. In the present study, a chimeric FAdV-4 was firstly generated by substituting fiber-1 of FAdV-4 with fiber of FAdV-8b. The chimeric virus, rFAdV-4-fiber/8b, exhibited similar replication ability in vitro and pathogenicity in vivo to the parental wild type FAdV-4. A single dosage of vaccination with the inactivated rFAdV-4-fiber/8b induced high antibody titers against fiber-2 of FAdV-4 and fiber of FAdV-8b and provided full protection against FAdV-4 and -8b challenge. These results demonstrated that fiber of FAdV-8b could replace the role of fiber-1 of FAdV-4 in the process of viral infection, and rFAdV-4-fiber/8b could be used to make a potential bivalent vaccine for the control and prevention of HHS and IBH.

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-1ß, 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-1ß, 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.

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.

Fiber1, but not fiber2, is the essential fiber gene for fowl adenovirus 4 (FAdV-4).

Fibre is the viral protein that mediates the attachment and infection of adenovirus to the host cell. Fowl adenovirus 4 (FAdV-4) possesses two different fibre trimers on each penton capsomere, and roles of the separate fibres remain elusive. Here, we attempted to investigate the function of FAdV-4 fibres by using reverse genetics approaches. Adenoviral plasmids carrying fiber1 or fiber2 mutant genes were constructed and used to transfect chicken LMH cells. Fiber1-mutated recombinant virus could not be rescued. Such defective phenotype was complemented when a fiber1-bearing helper plasmid was included for co-transfection. The infection of fiber-intact FAdV-4 (FAdV4-GFP) to LMH cells could be blocked with purified fiber1 knob protein in a dose-dependent manner, while purifed fiber2 knob had no such function. On the contrary, fiber2-mutated FAdV-4, FAdV4XF2-GFP, was successfully rescued. The results of one-step growth curves showed that proliferative capacity of FAdV4XF2-GFP was 10 times lower than that of the control FAdV4-GFP. FAdV4XF2-GFP also caused fewer deaths of infected chicken embryos than FAdV4-GFP did, which resulted from poorer virus replication in vivo. These data illustrated that fiber1 mediated virus adsorption and was essential for FAdV-4, while fiber2 was dispensable although it significantly contributed to the virulence.

Fiber modifications enable fowl adenovirus 4 vectors to transduce human cells.

BACKGROUND: Pre-existing immunities hamper the application of human adenovirus (HAdV) vectors in gene therapy or vaccine development. Fowl adenovirus (FAdV)-based vector might represent an alternative. METHODS: An intermediate plasmid containing FAdV-4 fiber genes, pMD-FAV4Fs, was separated from FAdV-4 adenoviral plasmid pKFAV4GFP. An overlap extension polymerase chain reaction (PCR) was employed for fiber modification in pMD-FAV4Fs, and the modified fibers were restored to generate new adenoviral plasmids through restriction-assembly. FAdV-4 vectors were rescued and amplified in chicken LMH cells. Fluorescence microscopy and flow cytometry were used to evaluate the gene transfer efficiency. The amount of viruses binding to cells was determined by a real-time PCR. A plaque-forming assay and one-step growth curve were used to evaluate virus growth. RESULTS: Four sites in the CD-, DE-, HI- and IJ-loop of fiber1 knob could tolerate the insertion of exogenous peptide. The insertion of RGD4C peptide in the fiber1 knob significantly promoted FAdV-4 transduction to human adherent cells such as 293, A549 and HEp-2, and the insertion to the IJ-loop demonstrated the best performance. The replacement of the fiber2 knob of FAdV-4 with that of HAdV-35 improved the gene transfer to human suspension cells such as Jurkat, K562 and U937. Fiber-modified FAdV-4 vectors could transduce approximately 80% human cells at an acceptable multiplicity of infection. Enhanced gene transfer mainly resulted from increased virus binding. Fiber modifications did not significantly influence the growth of recombinant FAdV-4 in packaging cells. CONCLUSIONS: As a proof of principle, it was feasible to enhance gene transduction of FAdV-4 vectors to human cells by modifying the fibers.

Experimental co-infection of variant infectious bursal disease virus and fowl adenovirus serotype 4 increases mortality and reduces immune response in chickens.

Infectious bursal disease virus (IBDV) and fowl adenovirus serotype 4 (FAdV-4) cause infectious bursal disease (IBD) and hydropericardium-hepatitis syndrome, respectively. Recently, studies have reported co-infections of poultry with IBDV and FAdV-4, which is an important problem in the poultry industry. Here, the variant IBDV strain ZD-2018-1 and FAdV-4 isolate HB1501 were used to assess the pathogenicity of co-infection in 1-day-old specific pathogen-free (SPF) chickens. Compared with chickens infected with only FAdV-4, those coinfected with IBDV and FAdV-4 showed enhanced clinical symptoms, higher mortality, more severe tissue lesions, and higher biochemical index levels. Furthermore, the expression of interleukin (IL)-6, IL-1ß, and interferon-γ mRNAs in the IBDV-FAdV-4 coinfected chickens was delayed, and the antibody response levels were significantly lower in those birds compared with the FAdV-4-infected chickens. These results indicate that co-infection with variant IBDV ZD-2018-1 and FAdV-4 HB1501 could significantly promote the pathogenicity of FAdV-4 and reduce the immune response in chickens. This study provides the foundation for further investigation of the interaction mechanism in IBDV and FAdV-4 co-infection.

Epidemiology of fowl adenovirus (FAdV) infections in South Korean chickens during 2013-2019 following introduction of FAdV-4 vaccines.

Fowl adenoviruses (FAdV) are important infectious pathogens responsible for causing substantial economic losses to the poultry industry worldwide. One hundred and forty-six FAdV strains were continuously collected and analysed from 2013 to 2019 to understand the epidemiological change and nature of the virus in South Korea from two different standpoints, before and after the release of multiple commercial FAdV-4 vaccines. Phylogenetic analysis of the hexon loop-1 gene sequences showed that 92 strains belonged to FAdV-C (63%), 35 strains to FAdV-E (24%), 18 strains to FAdV-D (12.3%), and one strain to FAdV-A (0.7%), respectively. We provide evidence that the dominant FAdV serotype has recently changed from FAdV-4 to FAdV-8b, as reflected in the proportion of each serotype in field cases in 2019 (18.5% and 77.8%, respectively). The newly emerged FAdV-8b cluster was significantly noticeable compared to the old FAdV clusters, indicating that the development of a vaccine for FAdV-8b may be necessary. Overall, this new insight into FAdV prevalence provides a foundation for strategic control and the development of efficient vaccines against FAdV cases in chickens in South Korea.RESEARCH HIGHLIGHTS The dominant FAdV serotype in South Korea shifted from FAdV-4 to FAdV-8b in 2013-2019.A new cluster of FAdV-8b has emerged in South Korea, indicating the development of new vaccines.

Spotlight on avian pathology: fowl adenovirus (FAdV) in chickens and beyond - an unresolved host-pathogen interplay.

Fowl adenovirus (FAdV) infections in chickens have undergone substantial changes in recent decades, driven by host and pathogen factors. Based on the pathogenesis of inclusion body hepatitis (IBH) and hepatitis-hydropericardium syndrome (HHS), modern broilers are much more inclined to have difficulties keeping the metabolic homeostasis, whereas adenoviral gizzard erosion (AGE) is noticed equally in broilers and egg-layers. Defining the importance of certain serotypes for specific FAdV diseases is a major achievement of recent years but the isolation of viruses from clinically healthy birds remains unexplained, as virulence factors are hardly known and continue to be a "black box". Together with further studies on pathogenesis of FAdV-induced diseases, such knowledge on virulence factors would help to improve protection strategies, which presently mainly concentrate on autogenous vaccines of breeders to prevent vertical transmission.

Molecular typing and pathogenicity assessment of fowl adenovirus associated with inclusion body hepatitis in chicken from India.

Recently, inclusion body hepatitis (IBH) outbreaks have been increasingly reported in different regions of India, particularly in broiler flocks. The present study was undertaken to characterize fowl adenovirus associated with IBH in chicken and assessment of its pathogenicity. Liver samples were collected from fowl adenovirus (FAdV) suspected 100 commercial broiler and six broiler breeder flocks from eleven different States of India from 2016 to 2019. All the samples were subjected to 897-bp FAdV hexon gene-specific PCR for confirmation and primary chicken liver cells were used to isolate the field FAdVs. Sequencing and phylogenetic analysis of 897-bp FAdV hexon gene revealed that all the isolates have showed close evolutionary relationship with fowl adenovirus serotype 11 of species D. For pathogenicity assessment, 0.5 ml of 106.5 TCID50/ml of field FAdV serotype 11 isolate was orally inoculated in 1-day-old SPF chicks and observed for 21 days. This experimental study revealed that there was no mortality in infected chicks and showed clinical signs of dullness, depression and diarrhoea between third and fifth day of oral inoculation. The FAdV was reisolated and confirmed by PCR from experimentally infected chicken. Based on this study, among all serotypes, FAdV serotype 11 is involved in pathogenesis of inclusion body hepatitis in broiler-type chickens in India.