Molecular epidemiology analysis of fowl adenovirus detected from apparently healthy birds in eastern China

Identification and characterization of pigeon adenovirus 1 as an emerging pathogen in pigeons from Northern and Northwest China

BACKGROUND

In 2022, a new infectious disease characterized by severe acute hepatitis, sudden death, and high mortality among breeding pigeons, was reported in China.

RESULTS

In naturally infected pigeons, key necropsy findings comprised hepatic swelling with patchy hemorrhage and pericardial effusion. Histopathological examination further revealed degeneration, necrosis, and basophilic intranuclear inclusion bodies affecting hepatocytes, cardiomyocytes, and vascular endothelial cells. Transmission electron microscopy revealed a typical icosahedral virus structure and crystal-like arrangement of viral particles in the nucleus. Metagenomic next-generation sequencing (mNGS) of pericardial effusion samples revealed the presence of pigeon adenovirus. Sequencing analysis of the hexon and fiber-2 genes suggested that it constituted pigeon adenovirus 1 (PiAdV-1). The complete genome of CH/BJ/1/2022 was determined to be 48,071 nucleotides in length, with a 10-amino acid deletion in the fiber-2 gene at residues 627-636 and a 95-animo acid insertion in the 100 K gene at residue 75. The same disease was reproduced in pigeons by experimental infection.

CONCLUSION

Collectively, our analyses confirmed that the etiological agent was PiAdV-1, an emerging pathogen that causes severe acute hepatitis and high mortality in pigeons. This virus merits close attention because it could be catastrophic for the pigeon industry.

Isolation and identification of pigeon adenovirus 1 and analysis of its pathogenicity in pigeons and chickens

Pigeon adenovirus type 1 predominantly infects pigeons under 12 months of age (mainly 3-5 months old), causing major clinical symptoms such as vomiting, dehydration, and discharge of thin yellow feces. In February 2023, an outbreak of a pathogen with symptoms similar to pigeon adenovirus infections occurred on a pigeon farm in Shandong Province, which was eventually identified as pigeon adenovirus type 1. In this study, a strain of PiAdV-1 was isolated from naturally infected pigeons and named pigeon-adenovirus-1-isolate-CH-SD-2023, and the hexon gene sequence as amplified and analyzed using polymerase chain reaction (PCR). To assess its pathogenicity, PiAdV-1 viral fluids were injected intramuscularly into 4-month-old pigeons and 10-day-old chickens with specific pathogen free (SPF), respectively. The results showed that the pigeons in the experimental group exhibited watery feces, whereas the chickens showed typical symptoms of thin yellow feces. Histopathologic sections showed multiple organ damage, including severe liver and intestinal damage. Liver viral load peaked on the seventh day post-infection and then declined. Viral shedding was detectable in the cloaca from the third day of infection, peaked on the seventh day, and remained detectable until 15 days post-infection. Inflammatory cytokine levels were elevated, which may have been due to infection and innate immune response. In addition, the changes in inflammatory cytokines and the damage to the bone marrow suggested that the strain may have caused severe damage to their immune system. In conclusion, these findings add to our understanding of the pathogenicity of PiAdV-1 in pigeons and chickens. The developed model will be valuable for antiviral drug testing and vaccine evaluation to prevent and reduce the spread of PiAdV-1 in the poultry industry.

Detection and molecular characterisation of fowl adenovirus associated with inclusion body hepatitis and hydropericardium syndrome in Uganda

Fowl Adenovirus (FAdV) infections and associated clinical conditions are of major economic significance in broiler chickens but have never been reported in Uganda and East Africa. Between July 2020 and June 2021, 120 farms submitted chicken diagnostic samples to Central Diagnostic Laboratory (CDL), Makerere University, Uganda, of which FAdV infections were suspected in 19 flocks during necropsy. Following bacteriology, histopathology and Polymerase Chain Reaction (PCR), FAdV infections were confirmed in ten flocks. The 10 flocks were aged between 9 and 24 days. They had a history of sudden onset of depression, anorexia and huddling together and high mortality rates (range = 12%-89%). Necropsy revealed hepatomegaly with pale yellow discolourations, multiple petechial haemorrhages, icterus and necrosis. Hydropericardium was evident in nine of the 10 flocks but was more frequent in a flock which had 89% mortality rate. Histopathology revealed multifocal hepatocytic necrosis and diffuse hepatocytic spherical vacuolations with large basophilic inclusion bodies. Confirmation of the FAdV infections was undertaken using two diagnostic PCRs on liver samples which targeted 590 bp and 900 bp conserved segments of the hexon gene, respectively. PCR-restriction enzyme analysis of the 900 bp amplicons categorized the viruses into serotypes 5 and 8. Sanger sequencing of the 900 bp amplicons and phylogenetic analysis clustered the FAdVs among the D and E species. This study presents the first report of FAdV in Uganda and in East Africa. FAdV infections should be included among differential diagnoses in broiler flocks. Further surveillance to determine the spread of the disease in poultry is recommended.

Development of a Multiplex Conventional PCR Assay for Concurrent Detection of FAdV-4, FAdV-8b, and FAdV-11

Fowl adenovirus (FAdV) belongs to the Aviadenovirus genus within the Adenoviridae family. FAdVs are widely distributed and associated with various diseases in poultry, including adenoviral gizzard erosion (AGE), hepatitis-hydropericardium syndrome (HHS), and inclusion body hepatitis (IBH). In this study, we developed a multiplex conventional PCR for simultaneously detecting FAdV-4, -8b, and -11 by targeting the hexon gene. The multiplex PCR was optimized for primer concentrations and thermocycling conditions. The optimal primer concentration combination was set at 0.125 μM for FAdV-4, -8b, and 0.25 μM for FAdV-11. Under these conditions, the limit of detection (LOD) was 103 copies/μL of plasmid standards for FAdV-4, -8b, and -11. These results demonstrated that the developed multiplex PCR method exhibits high specificity and sensitivity, with no observed cross-reactivity among these serotypes or with other poultry viruses. Therefore, this multiplex PCR will be an effective tool for accurate serotyping of FAdV-4, -8b, and -11, enabling more precise identification and differentiation of these three serotypes.

Differences in the pathogenicity and molecular characteristics of fowl adenovirus serotype 4 epidemic strains in Guangxi Province, southern China

Starting in 2015, the widespread prevalence of hydropericardium-hepatitis syndrome (HHS) has led to considerable financial losses within China's poultry farming industry. In this study, pathogenicity assessments, whole-genome sequencing, and analyses were conducted on 10 new isolates of the novel genotype FAdV-4 during a HHS outbreak in Guangxi Province, China, from 2019 to 2020. The results indicated that strains GX2019-010 to GX2019-013 and GX2019-015 to GX2019-018 were highly virulent, while strain GX2020-019 exhibited moderate virulence. Strain GX2019-014 was characterized as a wild-type strain with low virulence, displaying no pathogenic effects when 0.5 mL containing 106 TCID50 virus was inoculated into the muscle of specific pathogen-free (SPF) chickens at 4 weeks of age, while 107 TCID50 and 108 TCID50 resulted in mortality rates of 80 and 100%, respectively. The whole genomes of strains GX2019-010 to GX2019-013, GX2019-015 to GX2019-018, and GX2020-019 showed high homology with other Chinese newly emerging highly pathogenic FAdV-4 strains, whereas GX2019-014 was closer to nonmutant strains and shared the same residues with known nonpathogenic strains (B1-7, KR5, and ON1) at positions 219AA and 380AA of the Fiber-2 protein. Our work enriches the research on prevalent strains of FAdV-4 in China, expands the knowledge on the virulence diversity of the novel genotype FAdV-4, and provides valuable reference material for further investigations into the key virulence-associated genetic loci of FAdV-4.

Preparation and evaluation of the immune efficacy of an inactivated fowl adenovirus 8a serotype oil emulsion vaccine

In recent years, fowl adenovirus (FAdV) transmission has significantly increased worldwide, leading to substantial economic losses in the poultry industry. The virus causes hepatitis-hydropericardium syndrome (HHS) and inclusion body hepatitis (IBH). The prevalent FAdV strains in China are FAdV-4, FAdV-8a, FAdV-8b, and FAdV-11. Vaccines for FAdV-4 and FAdV-8b, which prevent HHS and IBH, are available commercially, but no vaccine exists for FAdV-8a. To address this issue, we developed a vaccine using an oil emulsion to inactivate the FAdV-8a serotype. Additionally, we built a fluorescence quantitative PCR for the detection of the virus. The lowest concentration detected was 4.11 × 101 copies/μL. The study's results illustrated that the FAdV-8a oil emulsion vaccine effectively produced significant antibodies and offered ample protection for poultry. This vaccine can potentially limit the transmission of IBH resulting from FAdV-8a in China.

First Report of a Novel Goose Adenovirus Outbreak in Lion Head Gooses in China

In April 2022, a novel Goose adenovirus (GoAdV) isolated from diseased Lion head gooses exhibiting swelling and hemorrhage of liver and kidney, accumulation of fluid in pericardial, in Fujian province of China. The GoAdV was propagated in goose embryo fibroblasts (GEFs), the morphological properties of the virions were studied by electron microscopy, and the full genome sequence was determined and analyzed. The results revealed that the infected cells became round and clustered like grapes, virions accumulated and were arranged in crystal lattice formations in the nucleus of GEFs with a diameter of ∼80 nm. The new isolate (named CH-FJZZ-202201) has a viral genome size of 43,480 bp and shared 96.69% sequence identity with GoAdV-4 (P29), representing the species Goose aviadenovirus A. Phylogenetic analysis showed that CH-FJZZ-202201 was in the same genetic evolutionary branch with the viruses of Aviadenovirus and was the closest relative to GoAdV-4 P29/Hungary. This is the first report of the GoAdV-4 outside of Hungary, indicating the reemergence of new AdV strains in China.

A sandwich amperometric immunosensor for the detection of fowl adenovirus group I based on bimetallic Pt/Ag nanoparticle-functionalized multiwalled carbon nanotubes

An enzyme-free sandwich amperometric immunosensor based on bimetallic Pt/Ag nanoparticle (Pt/AgNPs)-functionalized chitosan (Chi)-modified multiwalled carbon nanotubes (MWCNTs) as dual signal amplifiers and Chi-modified MWCNTs (MWCNTs-Chi) as substrate materials was developed for ultrasensitive detection of fowl adenovirus group I (FAdV-I). MWCNTs have a large specific surface area, and many accessible active sites were formed after modification with Chi. Hence, MWCNTs-Chi, as a substrate material for modifying glassy carbon electrodes (GCEs), could immobilize more antibodies (fowl adenovirus group I-monoclonal antibody, FAdV-I/MAb). Multiple Pt/AgNPs were attached to the surface of MWCNTs-Chi to generate MWCNTs-Chi-Pt/AgNPs with high catalytic ability for the reaction of H2O2 and modified active sites for fowl adenovirus group I-polyclonal antibody (FAdV-I/PAb) binding. Amperometric i-t measurements were employed to characterize the recognizability of FAdV-I. Under optimal conditions, and the developed immunosensor exhibited a wide linear range (100.93 EID50 mL-1 to 103.43 EID50 mL-1), a low detection limit (100.67 EID50 mL-1) and good selectivity, reproducibility and stability. This immunosensor can be used in clinical sample detection.

Prevalence, genomic characteristics, and pathogenicity of fowl adenovirus 2 in Southern China

In recent years, the occurrence of fowl adenovirus 2 (FAdV-2) has been on the rise in China, posing a significant threat to the poultry industry. This study aimed to investigate the epidemiology, phylogenetic relationship, genomic characteristics, and pathogenicity of FAdV-2. The epidemiological analysis revealed the detection of multiple FAdV serotypes, including FAdV-1, FAdV-2, FAdV-3, FAdV-4, FAdV-8a, FAdV-8b, and FAdV-11 serotypes. Among them, FAdV-2 exhibited the highest proportion, accounting for 21.05% (8/38). The complete genomes of these 8 FAdV-2 strains were sequenced. Genetic evolution analysis indicated that these FAdV-2 strains formed a separate branch within the FAdV-D group, sharing 94.60 to 97.90% nucleotide similarity with the reference FAdV-2 and FAdV-11 strains. Notably, the recombination analysis revealed that 5 out of the 8 FAdV-2 strains, exhibited recombination events between FAdV-2 and FAdV-11. The recombination regions involved Hexon, Fiber, ORF19 genes and 3' end. Furthermore, pathogenicity experiments demonstrated that recombinant FAdV-2 XX strain is capable of inducing mortality rate of 66.70% and causing more severe hepatitis hydropericardium syndrome (HHS) in 6-wk-old specific-pathogen-free chickens. These findings contribute to our understanding of the prevalence, genomic characteristics, and the pathogenicity of FAdV-2, providing foundations for FAdV-2 vaccine development.

Identification of ORF1B as a unique nonstructural protein for fowl adenovirus serotype 4

Fowl adenovirus serotype 4 (FAdV-4), the causative agent of hepatitis-hydropericardium syndrome (HHS), is a double-stranded DNA virus. Although many structural proteins have been deeply studied, the coding potential of some other open reading frames (ORFs) and the biological functions of their products during virus infection have not been fully elucidated. Here, a unique nonstructural protein ORF1B of FAdV-4 was identified and its expression kinetics along infection was analyzed. Except that of FAdV-10, a member of the same genus as FAdV-4, FAdV-4 ORF1B shared as low homologous identity as 29.2% in amino acid sequence with the other ten counterparts. Structurally, ORF1B was mapped on the N-terminal region of the genome between 1485 nt to 1808 nt and predicted to only contain two α-helix. Confocal immunofluorescence assay with homemade rabbit polyclonal antibody demonstrated that ORF1B could be simultaneously observed with structural protein Fiber 1 in FAdV-4-infected cells. Western blot further showed that ORF1B could only be detected in the infected cells but not mature virions, suggesting ORF1B was a nonstructural protein. Subsequently, the expression level of ORF1B detected by qRT-PCR and IFA was gradually decreased along with FAdV-4 infection, suggesting ORF1B was an early gene transcript. These results will lay a solid foundation to further study the biological effect of ORF1B on the replication and pathogenicity of FAdV-4.

Construction and application of adenoviral vectors

Adenoviral vectors have been widely used as vaccine candidates or potential vaccine candidates against infectious diseases due to the convenience of genome manipulation, their ability to accommodate large exogenous gene fragments, easy access of obtaining high-titer of virus, and high efficiency of transduction. At the same time, adenoviral vectors have also been used extensively in clinical research for cancer gene therapy and treatment of diseases caused by a single gene defect. However, application of adenovirus also faces a series of challenges such as poor targeting, strong immune response against the vector itself, and they cannot be used repeatedly. It is believed that these problems will be solved gradually with further research and technological development in related fields. Here, we review the construction methods of adenoviral vectors, including "gutless" adenovirus and discuss application of adenoviral vectors as prophylactic vaccines for infectious pathogens and their application prospects as therapeutic vaccines for cancer and other kinds of chronic infectious disease such as human papillomavirus, hepatitis B virus, and hepatitis C virus.

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

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

Pathogenicity and molecular characteristics of fowl adenovirus serotype 4 with moderate virulence in Guangxi Province, China

The GX2020-019 strain of fowl adenovirus serotype 4 (FAdV-4) was isolated from the liver of chickens with hydropericardium hepatitis syndrome in Guangxi Province, China, and was purified by plaque assay three times. Pathogenicity studies showed that GX2020-019 can cause typical FAdV-4 pathology, such as hydropericardium syndrome and liver yellowing and swelling. Four-week-old specific pathogen-free (SPF) chickens inoculated with the virus at doses of 10³ median tissue culture infectious dose (TCID₅₀), 10⁴ TCID₅₀, 10⁵ TCID₅₀, 10⁶ TCID₅₀, and 10⁷ TCID₅₀ had mortality rates of 0, 20, 60, 100, and 100%, respectively, which were lower than those of chickens inoculated with other highly pathogenic Chinese isolates, indicating that GX2020-019 is a moderately virulent strain. Persistent shedding occurred through the oral and cloacal routes for up to 35 days postinfection. The viral infection caused severe pathological damage to the liver, kidney, lung, bursa of Fabricius, thymus, and spleen. The damage to the liver and immune organs could not be fully restored 21 days after infection, which continued to affect the immune function of chickens. Whole genome analysis indicated that the strain belonged to the FAdV-C group, serotype 4, and had 99.7-100% homology with recent FAdV-4 strains isolated from China. However, the amino acid sequences encoded by ORF30 and ORF49 are identical to the sequences found in nonpathogenic strains, and none of the 32 amino acid mutation sites that appeared in other Chinese isolates were found. Our research expands understanding of the pathogenicity of FAdV-4 and provides a reference for further studies.