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

Novel pathogenic adenovirus in Timneh grey parrot (Psittacus timneh) unveils distinct lineage within Aviadenovirus

Wild birds harbour a vast diversity of adenoviruses that remain uncharacterised with respect to their genome organisation and evolutionary relatedness within complex host ecosystems. Here, we characterise a novel adenovirus type within Aviadenovirus genus associated with severe necrotising hepatitis in a captive Timneh grey parrot, tentatively named as Timneh grey parrot adenovirus 1 (TpAdV-1). The TpAdV-1 genome is 39,867 bp and encodes 46 putative genes with seven hitherto not described ones. Comparative genomics and phylogenetic analyses revealed highest nucleotide identity with psittacine adenovirus 1 and psittacine adenovirus 4 that formed a discrete monophyletic clade within Aviadenovirus lineage suggesting a deep host co-divergent lineage within Psittaciformes hosts. Several recombination breakpoints were identified within the TpAdV-1 genome, which highlighted an ancient evolutionary relationship across the genera Aviadenovirus, Mastadenovirus and Atadenovirus. This study hints towards a host-adapted sub-lineage of avian adenovirus capable of having significant host virulence in Psittaciformes birds augmented with ecological opportunity.

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.

Isolation, characterization, evaluation of pathogenicity, and immunomodulation through interferon production of duck adenovirus type-3 (DAdV-3)

Duck adenovirus type-3 (DAdV-3) is a poorly characterized duck virus. A comprehensive analysis of the DAdV-3 pathogenicity and host immune response could be a valuable addition. Herein, DAdV-3 was isolated from Muscovy duck and virus-specific genes were confirmed by polymerase chain reaction (PCR). The obtained gene fragments were sequenced and compared with the reference sequence. Results confirmed that the clinically isolated virus was DAdV-3, named as HF-AN-2020. To evaluate DAdV-3 host immune response, the expression levels of MDA5, STING, IRF7, MAVS, and NF-κB, and inflammatory cytokines (IFN-β, IFN-γ, and IL-1β) were determined by quantitative reverse transcriptase PCR (qRT-PCR). The expression levels of IFN-β and IFN-γ were 32.6- and 28.6-fold, respectively, higher (P < 0.01) than the control group. It was found that the upregulation of STING and NF-κB pathways was directly involved in the regulation of inflammatory cytokines (IFN-β, IFN-γ, and IL-1β). Furthermore, the gene regulation pathways consecutively upregulated the expression levels of MDA5, STING, IRF7, MAVS, and NF-κB up to 31.6, 10.5, 31.4, 2.2, and 2.6-fold, respectively, higher (P < 0.01) than the control group. The TCID50 of DAdV-3 for Muscovy duck and chicken was 10-3.24/0.1 mL with 0% mortality, indicating low pathogenicity in both Muscovy ducks and chickens, but DAdV-3 can induce higher expression of interferons. Genome analysis showed mutations in 4 amino acids located in ORF19B (Ser to Thr), ORF66 (Leu to Phe, Ile to Leu), and ORF67 (Gly to stop codon). This study provides essential and basic information for further research on the mechanism of the cellular immune responses against adenoviruses.

Construction and immune evaluation of the recombinant duck adenovirus type 3 delivering capsid protein VP1 of the type 1 duck hepatitis virus

Adenovirus serves as an excellent viral vector and is employed in vector vaccine research. Duck hepatitis A virus type 1 (DHAV1) and duck adenovirus type 3 (DAdV3) cause significant economic losses in the Chinese duck industry. In this study, we found an excellent exogenous gene insertion site in DAdV3 genome of CH-GD-12-2014 strain, within 3 intergenic regions (IGR). Subsequently, we generated a recombinant duck adenovirus named rDAdV3-VP1-188, which exhibits excellent replication characteristics and immunogenicity of DAdV3 and DHAV1. Animal experiments showed that rDAdV3-VP1-188 can provide 100% protection against the DAdV3 and 80% protection against DHAV1. These results showed that rDAdV3-VP1-188 could induce protection against DAdV3 and DHAV1 in ducks, thus indicating the feasibility of DAdV3 as a vector for the development of avian vector vaccines. These insights contribute to the further development of DAdV3 vectors and other adenovirus vectors.

Identification of novel B cell epitopes in Fiber-2 protein of duck adenovirus 3 and their application

Duck adenovirus 3 (DAdV-3), a newly emerged duck adenovirus, has resulted in significant economic losses to the duck industry across China since 2014. However, little is known about the B cell epitopes in major antigen of DAdV-3 and the serological approach for detection of DAdV-3 is not available. In this study, four monoclonal antibodies (mAbs) specific to Fiber-2 protein of DAdV-3 were first generated and designated as 2G10, 3D9, 5E6, and 6B12. Indirect immunofluorescence assay (IFA) showed that all of the mAbs reacted with the Fiber-2. Moreover, mAbs 2G10, 5E6, and 6B12 demonstrated good activity with Fiber-2 in Western blot. Notably, the Fiber-2 could be immunoprecipitated efficiently by mAb 3D9. Epitope mapping revealed that mAbs 2G10, 3D9, 5E6, and 6B12 recognized 397-429aa, 463-481aa, 67-99aa, and 1-66aa of Fiber-2, respectively. Besides, a novel sandwich ELISA for efficient detection of DAdV-3 was developed based on mAb 3D9 and horseradish peroxidase (HRP) conjugated mAb 3D9. The sandwich ELISA only reacted with DAdV-3 but not with other duck-associated viruses. The limit of detection of the ELISA was 6.25 × 10³ TCID₅₀/mL. Overall, the mAbs generated laid the foundation for elucidating the critical role of Fiber-2 in mediating infection and pathogenesis, and the sandwich ELISA approach established here provided efficient and rapid serological diagnostic tool for DAdV-3.

A novel monoclonal antibody efficiently blocks the infection of duck adenovirus 3 by targeting Fiber-2

Duck adenovirus 3 (DAdV-3), identified as the causative agent of a disease characterized by swelling and hemorrhage of liver and kidney, has caused substantial economic losses to duck industry in China. However, the neutralizing epitopes and the infection mechanism of DAdV-3 have not been extensively elucidated. In this study, a novel monoclonal antibody (mAb) targeting Fiber-2 protein of DAdV-3 was generated and designated as mAb 3E7. Indirect immunofluorescence assay showed that mAb 3E7 specifically reacted with the Fiber-2 in LMH cells transfected with pcDNA3.1-Fiber-2 or infected with DAdV-3. Moreover, mAb 3E7 could immunoprecipitate the Fiber-2 and efficiently inhibit the infection of DAdV-3 in vitro. Further epitope mapping revealed mAb 3E7 recognized the epitope ¹⁰⁸LALGDGLE¹¹⁵ in Fiber-2, which was highly conserved among DAdV-3 strains. These findings not only identified a novel neutralizing epitope in Fiber-2, but also paved the way for further elucidating the vital roles of Fiber-2 in the infection and pathogenesis of DAdV-3.

Novel monoclonal antibodies against Fiber-1 of duck adenovirus 3 and their B cell epitopes

Recently, the outbreak of the infection of Duck adenovirus 3 (DAdV-3) characterized by swelling and hemorrhagic liver and kidney has caused huge economic losses to duck industry since 2014 in China. To date, the B cell epitopes in the Fiber-1 protein and the underlying infection mechanism of DAdV-3 have not been investigated. In this study, the recombinant Fiber-1 protein was first expressed in E. coli and six novel monoclonal antibodies (mAbs) against Fiber-1 were generated, designated as 1D8, 1E6, 3G6, 4G1, 4G2, and 6F10, respectively. Moreover, mAbs 3G6 and 6F10 could efficiently immunoprecipitate the Fiber-1 in LMH cells infected with DAdV-3 or transfected with pcDNA3.1-Fiber-1. Notably, mAbs 3G6 and 4G2 also showed certain neutralizing activity against DAdV-3 infection in vitro. Epitopes mapping revealed that the B cell epitope recognized by 6F10, 3G6, 4G1, 1D8, 4G2, and 1E6 was located in 34-66aa, 67-99aa, 64-296aa, 297-329aa, 330-362aa, and 363-395aa, respectively. Sequence alignments further found that the six epitopes recognized by these mAbs were highly conserved among different DAdV-3 isolates. The generated mAbs specific to Fiber-1 and their defined epitopes provide powerful tools for establishing rapid and efficient diagnostics for the detection of DAdV-3 and pave the way for further studying on the critical role of Fiber-1 in mediating the infection of DAdV-3.

An insertion and deletion mutant of adenovirus in Muscovy ducks

Duck adenovirus 3 (DuAdV-3; strain HB) was isolated and sequenced. The genome of the Muscovy-duck-origin virus contains a 54-bp insertion in pVIII, a 3-bp deletion in the overlap region of 100K, 22K, and 33K, a 42-bp deletion at the junction of ORF64 and ORF67, and a 715-bp deletion in right noncoding region of the genome. Notably, HB has a strikingly shorter right inverted terminal repeat (ITR) of 50 bp, whereas all other DuAdV-3 isolates have a 721-bp ITR. These findings demonstrate that HB is an insertion and deletion mutant of DuAdV-3.

Epidemiological investigation of duck adenovirus 3 in southern China, during 2018-2020

Duck adenovirus 3 (DAdV-3) has been identified as the causative agent of a disease characterized by swelling and hemorrhages in liver and kidney of Muscovy ducks, causing huge economic losses to the waterfowl industry in China. In this study, a total of 54 DAdV-3 outbreaks from 2018 to 2020 in China were monitored with samples being collected and analyzed. The hexon amino acid sequences of the 54 DAdV-3 outbreaks and the DAdV-3 reference strains from GenBank were 98.7% to 100% identical. Epidemiological analysis showed that DAdV-3 circulated in meat-type and egg-laying Muscovy ducks, and co-infections with other viral and bacterial pathogens, such as Muscovy duck parvovirus (MDPV), Muscovy duck-origin goose parvovirus (MDGPV), Adeno-associated virus (AAV), Duck hepatitis B virus (DHBV), R. anatipestifer, and E. coli were identified. In addition, 12 out of the 23 (52.2%) DAdV-3 strains were isolated by LMH cells and identified by DAdV-3 real-time PCR. The whole-genome sequence analysis demonstrated that 12 new DAdV-3 isolates share 99.8-100% identity with the DAdV-3 reference strains, and 9 new DAdV-3 isolates exhibit a truncated ORF67 gene. Our results enhance the understanding of the epidemiology and molecular characterization associated with DAdV-3 infection in China.Highlights First report of the epidemiology of duck adenovirus 3 infection in China.Mutant DAdV-3 strains (truncated ORF67) became the predominant virus.

Isolation and characterization of a novel strain of duck aviadenovirus B from Muscovy ducklings with acute hepatitis in China

A new disease designated as Pale liver disease (PLD) has been circulating in Chinese Muscovy duck flocks since 2014, which is characterized by fatigue, diarrhoea, sudden death and acute hepatitis with pale and haemorrhagic liver. In this study, the etiological agents of PLD were isolated, causing a significant cytopathic effect (CPE) by cell rounding. Virus particles were observed by transmission electron microscopic (TEM) observation. The same disease was reproduced by experimental infection with the isolate BG61. The whole genomes of isolates were 43,842 nt in length with a GC content of 47.11%, similar to French Muscovy duck adenovirus strain GR with a GC content of 46.08%. The isolates shared 99.71-99.95% and 93.31-93.33% identity with Chinese Muscovy duck adenovirus isolates and GR strain, respectively. The DNA polymerase gene of all Muscovy duck adenovirus strains formed a separate genetic lineage with 99.55-100% amino acid sequence identity. All Chinese Muscovy duck adenovirus isolates contained two fibre genes. In contrast, only one fibre gene was found in GR, the only representative strain in species Duck aviadenovirus B. Anti-DAdV-2 serum antibodies had a weak neutralizing activity against Chinese Muscovy duck adenovirus isolates. The phylogenetic trees of the complete genome, hexon and fibre proteins revealed that all Muscovy duck adenovirus strains formed a major genetic lineage consisting of two clades. Thus, both GR and Chinese Muscovy duck adenovirus strains were proposed to be included in the same species of Duck aviadenovirus B belonging to the genus Aviadenovirus. The species Duck aviadenovirus B included two serotypes or genotypes, such as GR, which represents the strain of serotype 1 or genotype 1 (DAdV B1) and Chinese Muscovy duck adenovirus strains, which belong to serotype 2 or genotype 2 (DAdV B2).

Isolation and pathogenic characterization of duck adenovirus 3 mutant circulating in China

Duck adenoviruses (DAdVs) include serotype 1 (DAdV-1) in the genus Atadenovirus and serotypes 2-4 (DAdV-2, 3, and 4) in the genus Aviadenovirus. DAdV-3 was initially isolated from Chinese Muscovy ducks in 2014, whereby the infected ducks exhibited yellowing and hemorrhaging in the liver, along with slight pericardial effusion, swelling, and hemorrhaging in the kidneys. In recent years, duck adenovirus infections have appeared in Muscovy duck farms in Fujian, Zhejiang, Anhui, Guangdong, and other places in China. They have an incidence rate of 40 to 55% and a mortality rate of 35 to 43%, resulting in great losses to the duck breeding industry. In this study, 7 DAdV-3 strains, designated as TZ193, FJPT20161124, GX20170519, FJZZ, GDMM, AHAQ, and GDHS were isolated from Muscovy ducks in different provinces of China during 2016-2019, and their complete genomics were sequenced. Their genomes all exhibited significant deletions in ORF67, which also had G to A transitions at the 41st and 977th nt positions, resulting in a stop codon. The pathogenicity of TZ193, a novel isolate of DAdV-3, was investigated in Muscovy ducks. TZ193 caused characteristic lesions of swelling as well as hemorrhagic liver and kidney in the infected ducklings. Moreover, the mortality rate of TZ193 in 5-day-old domestic ducks was 100%. Our data provide concrete evidence for the identification of the DAdV-3 novel variant mutant in China, which effects increased mortality in ducks. This highlights the necessity for monitoring the specific molecular epidemiology of novel DAdV-3 mutants and the development of new vaccines in the future.

Isolation and partial genetic characterization of a new duck adenovirus in China

A novel duck adenovirus, isolated from Jinding Ducks(Anas platyrhynchos domestica), was proposed to be duck adenovirus 4 (DAdV-4), extending the genus Aviadenovirus. In this study, we sequenced the central genome part from Iva2 gene to fiber gene of the DAdV-4 that is conserved in all adenovirus genera. Phylogenetic analysis and protease cleavage site analysis verified the classification of DAdV-4 in the genus Aviadenovirus. Nucleotide identity analysis showed low sequence identity between central genome part genes of DAdV-4 with that of other aviadenoviruses. The phylogenetic tree based on the full amino acid sequence of hexon and DNA polymerase showed that the DAdV-4 appeared on a relatively independent branch. Our analysis suggested that DAdV-4 is a distinct type and represents a novel species. Although DAdV-4 has not caused serious disease outbreaks among ducks yet, the virus should be considered as a potential threat to the poultry industry.

Adenoviruses across the animal kingdom: a walk in the zoo

Adenoviruses (AdVs) infect representatives of numerous species from almost every major vertebrate class, albeit their incidence shows great variability. AdVs infecting birds, reptiles, and bats are the most common and diverse, whereas only one AdV has been so far isolated both from fish and amphibians. The family Adenoviridae is divided into five genera, each corresponding to an independent evolutionary lineage that supposedly coevolved with its respective vertebrate hosts. Members of genera Mastadenovirus and Aviadenovirus seem to infect exclusively mammals and birds, respectively. The genus Ichtadenovirus includes the single known AdV from fish. The majority of AdVs in the genus Atadenovirus originated from squamate reptiles (lizards and snakes), but also certain mammalian and avian AdVs are classified within this genus. The genus Siadenovirus contains the only AdV isolated from frog, along with numerous avian AdVs. In turtles, members of a sixth AdV lineage have been discovered, pending official recognition as an independent genus. The most likely scenario for AdV evolution includes long-term cospeciation with the hosts, as well as occasional switches between closely or, rarely, more distantly related hosts.

Isolation and Characterization of A Novel Fowl Adenovirus Serotype 8a Strain from China

Since 2012, the clinical cases of inclusion body hepatitis showed an increasing trend in China, causing considerable economic losses to the poultry industry. In this study, a fowl adenovirus strain CH/GDLZ/201801 was isolated from a chicken flock experiencing inclusion body hepatitis and analyzed by complete genome sequencing. The pathogenicity of the new virus strain was examined by experimental infection of specific pathogen free chickens. The isolate was identified by immunofluorescence and the virions presented typical icosahedral particles under transmission electron microscopy. The full genome of the isolate was 44,329 nucleotides in length with 58% G+C content. Phylogenetic analysis, based on the whole genome, revealed that the new isolate was closest to serotype 8a from the species Fowl aviadenovirus E (FAdV-E). Recombination analysis and phylogenetic analysis showed that the new isolate is a recombinant strain between FAdV-8a and FAdV-8b. In infection experiments, three infected chickens showed clinical signs and one chicken died on day 7 post infection, corresponding to 5% mortality. Macroscopic and microscopic lesions in the liver were observed, and viral antigen could be detected in the livers by immunohistochemical staining and TEM. Taken together, our study describes the genomic characteristics and pathogenicity of a FAdV-8a strain in China. It would lay a solid foundation for further study of the pathogenic mechanism and vaccine development of the virus.

Development and application of a fiber2 protein-based indirect ELISA for detection of duck adenovirus 3

Duck adenovirus 3 (DAdV-3) is a newly identified duck adenovirus that has recently emerged in China. The incidence of duck infection caused by this virus is very high, with very large economic losses to the poultry industry. Thus, there is an urgent need for a serological assay for the specific detection of DAdV-3. To this end, prokaryotic expression of the fiber2 protein of DAdV-3 was used as a coating antigen to establish an indirect enzyme linked immunosorbent assay (ELISA) method for the specific detection of antibodies against DAdV-3. The method was found to be specific, repeatable and more sensitive than the agarose gel precipitation test (AGP). This indirect ELISA method based on the recombinant fiber2 protein may be used for the clinical detection of DAdV-3 infection and for monitoring antibody levels after vaccine immunization and is of great significance for the effective prevention and control of the disease.

Isolation and characterization of duck adenovirus 3 circulating in China

Recently, infectious disease outbreaks characterized by swelling and hemorrhagic liver and kidneys occurred in Muscovy ducklings in China. Four viruses were isolated and identified as adenoviruses by transmission electron microscopy (TEM) and polymerase chain reaction (PCR). Sequence analysis identified the new isolates as duck adenovirus 3 (DAdV-3), species Duck aviadenovirus B. The pathogenicity of the new isolate DAdV-3 FJGT01 was investigated using challenge experiments. The gross lesions in the animal experiment were similar to the clinical lesions observed in the diseased ducks. TEM examination of liver sample showed that virions accumulated and arranged in crystal lattice formations in the nuclei of hepatocytes. The present study provides new information about the epidemiology and characteristics of duck adenovirus associated with Muscovy ducklings.

Development of a TaqMan-based real-time PCR for detecting duck adenovirus 3

Recently, a novel duck adenovirus (designated as duck adenovirus 3, DAdV-3) was discovered in Muscovy ducks, China. Here, we developed a TaqMan-based real-time PCR assay (qPCR) for the detection of DAdV-3 infection. After the optimization of the qPCR conditions, the lower limit of detection for DAdV-3 infection was 40.9 copies/μl. No cross-reactivity was observed with other duck-derived pathogens. Intra- and inter-assay variability was less than 2.30%. DAdV-3 was detected in embryos and newly hatched ducklings by qPCR assay, the findings provided evidence of possible vertical transmission of DAdV-3. The developed qPCR analysis showed high specificity, sensitivity, and reproducibility, thereby indicating that it can be used in future investigations on the pathogenesis and epidemiology of DAdV-3.

Metagenomics detection and characterisation of viruses in faecal samples from Australian wild birds

We present an optimised metagenomics method for detection and characterisation of all virus types including single and double stranded DNA/RNA and enveloped and non-enveloped viruses. Initial evaluation included both spiked and non-spiked bird faecal samples as well as non-spiked human faecal samples. From the non-spiked bird samples (Australian Muscovy duck and Pacific black ducks) we detected 21 viruses, and we also present a summary of a few viruses detected in human faecal samples. We then present a detailed analysis of selected virus sequences in the avian samples that were somewhat similar to known viruses, and had good quality (Q20 or higher) and quantity of next-generation sequencing reads, and was of interest from a virological point of view, for example, avian coronavirus and avian paramyxovirus 6. Some of these viruses were closely related to known viruses while others were more distantly related with 70% or less identity to currently known/sequenced viruses. Besides detecting viruses, the technique also allowed the characterisation of host mitochondrial DNA present and thus identifying host species, while ribosomal RNA sequences provided insight into the "ribosomal activity microbiome"; of gut parasites; and of food eaten such as plants or insects, which we correlated to non-avian host associated viruses.

Fowl Adenovirus Serotype 4 SD0828 Infections Causes High Mortality Rate and Cytokine Levels in Specific Pathogen-Free Chickens Compared to Ducks

Hydropericardium syndrome and inclusion body hepatitis, together called hydropericardium-hepatitis syndrome, are acute infectious diseases found in chickens. These diseases are caused primarily by fowl adenovirus serotype 4 (FAdV-4) strains. In this study, we isolated a FAdV-4 strain (SD0828) from clinically diseased chickens and phylogenetically analyzed the L1 loops of the hexon protein sequences in 3-week-old specific pathogen-free chickens and ducks infected intramuscularly and orally, determining differences in the pathogenicity by observing clinical signs and gross and histological lesions. We also detected the viral load in tissue samples. Postinfection necropsy showed that all chickens but no ducks exhibited typical necropsy lesions. Additionally, all chickens infected intramuscularly died within 2 days postinfection (dpi), and all those infected orally died within 5 dpi, whereas no infected ducks died before 28 dpi. Quantitative real-time polymerase chain reaction analysis was used to determine the viral load in the tissues of hearts, livers, spleens, lungs, and kidneys and in cloacal cotton swabs from infected chickens and ducks at 1, 2, 3, 5, 7, 14, 21, and 28 dpi. The greatest number of viral DNA copies was found in the livers of infected chickens, yet no virus was found in any samples from infected ducks. In addition, the viral load increased over time in both chicken and duck embryo fibroblasts (CEFs and DEFs, respectively); in the former, replication speed was significantly greater than in the latter. Innate immune responses were also studied, both in vivo and in vitro. In CEFs, DEFs, and chickens infected intramuscularly, but not in infected ducks, mRNA expression levels of proinflammatory cytokines (interleukin-6 and -8) and interferon-stimulated genes (Mx and OAS) were significantly upregulated. Although some cytokines showed significant upregulation in the oral chickens, most did not change significantly. Finally, the duck retinoic acid-inducible gene I and its caspase activation and recruitment domain both had significant antiviral functions in CEFs, particularly after 24 h postinfection. Taken together, this research provides new insights into the interactions between FAdV-4 and the innate immune systems of studied hosts (chickens and ducks).