Comparison of the fibers of Fowl adenovirus A serotype 1 isolates from chickens with gizzard erosions in Europe and apathogenic reference strains

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.

Genomic Epidemiology and Evolution of Fowl Adenovirus 1

Fowl adenovirus 1 (FAdV-1) is the main cause of gizzard erosion in chickens. Whole genome sequencing and sequence analyses of 32 FAdV-1 strains from a global collection provided evidence that multiple recombination events have occurred along the entire genome. In gene-wise phylogenies, only the adenoviral pol gene formed a tree topology that corresponded to whole genome-based phylogeny. Virus genetic features that were clearly connected to gizzard erosion were not identified in our analyses. However, some genome variants tended to be more frequently identified from birds with gizzard erosion and strains isolated from healthy birds or birds with non-specific pathologies tended to form common clusters in multiple gene phylogenies. Our data show that the genetic diversity is greater, and the evolutionary mechanisms are more complex within FAdV-1 than previously thought. The implications of these findings for viral pathogenesis and epidemiology await further investigation.

Pathogenicity and innate immune responses induced by fowl adenovirus serotype 8b in specific pathogen-free chicken

Fowl adenovirus serotype 8b (FAdV-8b), as causative agent of inclusion body hepatitis (IBH), poses a great threat to the poultry industry. Considering the importance of innate immune response in host against viral infections, we investigated pathogenicity of a FAdV-8b strain HLJ/151129 in 1-mo-old specific pathogen-free (SPF) chickens and immune responses of host to FAdV-8b infection in this study. The results demonstrated that no obvious clinical signs were observed in infected birds. Neither mobility nor mortality was observed in both FAdV-8b infected and control chickens, as well. However, hepatic necrosis and a small amount of inflammatory cell infiltration were observed by pathological analysis. Viral load was detected in bursa of Fabricius, cecal tonsils, liver, heart, spleen, Harderian glands, and thymus. Virus shedding and viremia generated as early as 3 days postinfection (dpi) (9/10) and reached the peak at 7 dpi (10/10). In addition, the infected birds had developed FAdV-specific antibodies at 7 dpi, and the antibody titers reached the peak at 14 dpi. Furthermore, the results demonstrated that the mRNA expression levels of most of toll-like receptors (TLRs), most of avian β-defensins (AvBDs), and cytokines [interleukin (IL)-2, IL-6, and interferon (IFN)-γ], were significantly upregulated in most tissues at early phases of FAdV-8b infection, especially in liver and spleen. In contrast, FAdV-8b infection results in downregulation of TLR4, TLR5, and TLR21 expressions in some tissues of infected chickens. In addition, FAdV-8b infection upregulated myeloid differentiation factor 88 (MyD88), nuclear factor-kappa B (NF-κB) p65, and TIR-domain-containing adapter inducing interferon-β (TRIF) expression in some tissues, while decreased NF-κBp65 and TRIF in spleen at both 72 hpi and 21 dpi. Taken together, these results confirmed that FAdV-8b could replicate in all investigated tissues of infected birds, and then, result in production of FAdV-specific antibody titers. Meanwhile, the FAdV-8b infection induces strong innate immune responses at early stage in chickens, which may associate with the viral pathogenesis.

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

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

Pathogenicity and epidemiological survey of fowl adenovirus in Shandong Province from 2021 to 2022

In recent years, the poultry industry had been markedly affected by adenoviral diseases such as hydropericardium syndrome and inclusion body hepatitis caused by fowl adenovirus (FAdV), which have become increasingly prevalent in China. Shandong Province, China, is an important area for poultry breeding where various complex and diverse FAdV serotypes were isolated. However, the dominant strains and their pathogenic characteristics are not yet reported. Therefore, a pathogenicity and epidemiological survey of FAdV was conducted, showing that the local dominant serotypes of FAdV epidemics were FAdV-2, FAdV-4, FAdV-8b, and FAdV-11. Their mortality rates in the 17-day-old specific-pathogen-free (SPF) chicks ranged from 10 to 80%; clinical signs included mental depression, diarrhea, and wasting. The maximum duration of viral shedding was 14 days. The highest incidence in all infected groups was on days 5-9, and then gradual regression occurred thereafter. The most pronounced symptoms occurred in chicks infected with FAdV-4, including pericardial effusion and inclusion body hepatitis lesions. Our results add to the current epidemiological data on FAdV in poultry flocks in Shandong and elucidate the pathogenicity of dominant serotypes. This information may be important for FAdV vaccine development and comprehensive epidemic prevention and control.

Epidemiology, pathology, prevention, and control strategies of inclusion body hepatitis and hepatitis-hydropericardium syndrome in poultry: A comprehensive review

Infection with fowl adenoviruses (FAdVs) can result in a number of syndromes in the production of chicken, including inclusion body hepatitis (IBH), hepatitis-hydropericardium syndrome (HHS), and others, causing enormous economic losses around the globe. FAdVs are divided into 12 serotypes and five species (A-E; 1-8a and 8b-11). Most avian species are prone to infection due to the widespread distribution of FAdV strains. The genus aviadenovirus, which is a member of the adenoviridae family, is responsible for both IBH and HHS. The most popular types of transmission are mechanical, vertical, and horizontal. Hepatitis with basophilic intranuclear inclusion bodies distinguishes IBH, but the buildup of translucent or straw-colored fluid in the pericardial sac distinguishes HHS. IBH and HHS require a confirmatory diagnosis because their clinical symptoms and postmortem abnormalities are not unique to those conditions. Under a microscope, the presence of particular lesions and inclusion bodies may provide clues. Traditional virus isolation in avian tissue culture is more delicate than in avian embryonated eggs. Additionally, aviadenovirus may now be quickly and precisely detected using molecular diagnostic tools. Preventive techniques should rely on efficient biosecurity controls and immunize breeders prior to production in order to protect progeny. This current review gives a general overview of the current local and global scenario of IBH, and HHS brought on by FAdVs and covers both their issues and preventative vaccination methods.

Gizzard erosions in broiler chickens in Sweden caused by fowl adenovirus serotype 1 (FAdV-1): investigation of outbreaks, including whole-genome sequencing of an isolate

AbstractThe present paper describes the investigation of the first outbreaks of adenoviral gizzard erosions (AGE) in Sweden, in five broiler flocks. The investigation includes whole viral genome sequencing and investigation of genomic organisation and sequence relationships with other adenoviruses. All five flocks had a history of decreased growth and uneven size of birds since nine to ten days of age. Macroscopically, lesions consistent with AGE (detached koilin layers, discoloration, bleeding, erosions) were identified in gizzards in all five flocks. In four flocks histology was performed, and degeneration and inflammation of the koilin layer and gizzard mucosa were identified in all four. In one flock, intranuclear inclusion bodies typical for fowl adenovirus (FAdV) were detected in trapped epithelial cells in the koilin layer. In four flocks in situ hybridization was performed, and cells positive for FAdV serotype 1 (FAdV-1) were demonstrated in the koilin layer and gizzard mucosa. FAdV species A (FAdV-A) was detected in gizzard, liver, caecal tonsils and bursa of Fabricii by polymerase chain reaction (PCR) and sequencing. Ten out of ten examined parent flocks of the affected chickens were seropositive for FAdV, indicating former or on-going infection. However, FAdV was not detected in embryos from seropositive parent flocks and thus vertical transmission was not demonstrated. The entire nucleotide sequence of one sample was determined and found to be 43,856 base pairs (bp) in length. The genome sequence and organisation were found to be similar to that of the reference apathogenic avian adenovirus "chicken embryo lethal orphan" (CELO).

High Phenotypic Variation between an In Vitro-Passaged Fowl Adenovirus Serotype 1 (FAdV-1) and Its Virulent Progenitor Strain despite Almost Complete Sequence Identity of the Whole Genomes

Adenoviral gizzard erosion is an emerging disease with negative impact on health and production of chickens. In this study, we compared in vitro and in vivo characteristics of a fowl adenovirus serotype 1 (FAdV-1), attenuated by 53 consecutive passages in primary chicken embryo liver (CEL) cell cultures (11/7127-AT), with the virulent strain (11/7127-VT). Whole genome analysis revealed near-complete sequence identity between the strains. However, a length polymorphism in a non-coding adenine repeat sequence (11/7127-AT: 11 instead of 9) immediately downstream of the hexon open reading frame was revealed. One-step growth kinetics showed delayed multiplication of 11/7127-AT together with significantly lower titers in cell culture (up to 4 log₁₀ difference), indicating reduced replication efficiency in vitro. In vivo pathogenicity and immunogenicity were determined in day-old specific pathogen-free layer chicks inoculated orally with the respective viruses. In contrast to birds infected with 11/7127-VT, birds infected with 11/7127-AT did not exhibit body weight loss or severe pathological lesions in the gizzard. Virus detection rates, viral load in organs and virus excretion were significantly lower in birds inoculated with 11/7127-AT. Throughout the experimental period, these birds did not develop measurable neutralizing antibodies, prevalent in birds in response to 11/7127-VT infection. Differences in pathogenicity between the virulent FAdV-1 and the attenuated strain could not be correlated to prominently discriminate genomic features. We conclude that differential in vitro growth profiles indicate that attenuation is linked to modulation of viral replication during interaction of the virus with the host cells. Thus, hosts would be unable to prevent the rapid replication of virulent FAdV leading to severe tissue damage, a phenomenon broadly applicable to further FAdV serotypes, considering the substantial intra-serotype virulence differences of FAdVs and the variation of diseases.

Detection and Typing of a Fowl Adenovirus Type 1 Agent of Pancreatitis in Guinea Fowl

Adenoviral pancreatitis has been amply described for decades in guinea fowl. Although its pathologic picture has been characterized fairly well, its etiology still remains only partially clarified. Based on several outbreaks diagnosed on commercial guinea flocks raised in France since 2017, we performed direct whole-genome sequencing from pancreatic lesional tissue by using the Oxford Nanopore Technologies (ONT) sequencing method. We generated 4781 viral reads and assembled a whole genome of 43,509 bp, clustering within fowl adenovirus type 1 (FAdV-1). A phylogenetic analysis based on a partial sequence of the hexon and short fiber genes on viruses collected in France showed 98.7% and 99.8% nucleotide identity, respectively. Altogether, these results confirm that an FAdV-1 closely related to chicken and other avian strains is the agent of pancreatitis in guinea fowl. This study illustrates the potential of ONT sequencing method to achieve rapid whole-genome sequencing directly from pathologic material.

Reduced Performance Due to Adenoviral Gizzard Erosion in 16-Day-Old Commercial Broiler Chickens in Iran, Confirmed Experimentally

Adenoviral gizzard erosion (AGE) in broilers is an emerging infectious disease with negative impact on flock productivity. Despite of known primary etiological role of fowl adenovirus serotype 1 (FAdV-1) in AGE, there are a limited number of field reports worldwide, possibly because the disease is less noticeable and clinically difficult to assess. The present study documents an outbreak of AGE in 16-day-old broiler chickens on a farm in the north of Iran and the reproduction of the disease in an experimental setting. In the field, a sudden onset of mortality was noticed in affected broilers resulting in 6% total mortality and decreased weight gain leading to approximately 1-week delay to reach the target slaughter weight. Necropsy findings in dead broilers revealed black colored content in crop, proventriculus and gizzard together with severe gizzard erosions characterized by multiple black-brown areas of variable size in the koilin layer and mucosal inflammation. Microscopic examination revealed necrotizing ventriculitis marked with severe dissociation of koilin layer and degeneration of glandular epithelium with infiltration of mononuclear inflammatory cells. FAdV-1 was isolated from affected gizzards. Phylogenetic analysis of the hexon loop-1 (L1) sequence of the isolated virus showed 100% identity with pathogenic FAdV-1 strains previously reported from broiler chickens with AGE. Subsequently, an in vivo study infecting day-old commercial layer chickens with the field isolate demonstrated characteristic lesions and histopathological changes of AGE together with decreased weight gain in the infected birds. For the first time, the progress of a natural outbreak of AGE in Iran is described and experimental reproduction of the disease is demonstrated. The findings highlight the economic impact of the disease for regional poultry production due to mortality and impaired weight gain of the affected broilers.

A 24-Year-Old Sample Contributes the Complete Genome Sequence of Fowl Aviadenovirus D from the United States

Here, we report the complete genome sequence of fowl aviadenovirus D (FAdV-D) isolated from a preserved 24-year-old pancreas sample of a broiler chicken embryo. The results of the sequence showed that the viral genome is 44,079 bp long.

Genetic Characterization and Pathogenicity Analysis of Recently Isolated Fowl Adenovirus 8b in Korea

A Korean field strain of fowl adenovirus (FAdV) 8b was isolated from chickens showing high mortality. Isolated FAdV-8b strains with the hexon and fiber genes were genetically analyzed. The Korean FAdV-8b (K194/19) strain isolated in 2019 showed higher sequence identity with the FAdV-8b strain isolated in China but lower sequence identity with the Korean FAdV-8b (K187/08) strain isolated in 2008. The K194/19 strain formed a distinct subcluster within the FAdV-8b cluster in a phylogenetic tree based on hexon and fiber genes. FAdV can infect day-old chicks through vertical transmission, and so blood samples were obtained from 54-, 60-, and 63-wk-old parent chickens. FAdV-specific antibody levels were investigated with ELISA and virus neutralization (VN) tests with the K194/19 and K187/08 strains as antigens. In VN tests, all sera neutralized the K187/08 strain. However, the K194/19 strain was neutralized by sera collected from 60- and 63-wk-old chickens but not sera obtained from 54-wk-old chickens, indicating natural infection. Finally, to determine the pathogenicity of the K194/19 strain, 1-day-old and 4-wk-old specific-pathogen-free birds were infected with the K194/19 and K187/08 strains. No significant difference in pathogenicity was observed between the two strains. Although the K194/19 strain showed similar pathogenicity with the K187/08 strain, differences in nucleotide and amino acid sequences of the hexon and fiber genes may determine the evasion ability of the K187/08 neutralizing antibody, indicating the need for development of a novel FAdV vaccine.

Propagation and Molecular Characterization of Fowl Adenovirus Serotype 8b Isolates in Chicken Embryo Liver Cells Adapted on Cytodex™ 1 Microcarrier Using Stirred Tank Bioreactor

Large volume production of vaccine virus is essential for prevention and control of viral diseases. The objectives of this study were to propagate Fowl adenovirus (FAdV) isolate (UPM08136) in chicken embryo liver (CEL) cells adapted to Cytodex™ 1 microcarriers using stirred tank bioreactor (STB) and molecularly characterize the virus. CEL cells were prepared and seeded onto prepared Cytodex™ 1 microcarriers and incubated first in stationary phase for 3 h and in STB at 37 °C, 5% CO2, and 20 rpm for 24 h. The CEL cells were infected with FAdV isolate (UPM08136) passage 5 (UPM08136CELP5) or passage 20 (UPM08136CELP20) and monitored until cell detachment. Immunofluorescence, TCID50, sequencing, alignment of hexon and fiber genes, and phylogenetic analysis were carried out. CEL cells were adapted well to Cytodex™ 1 microcarriers and successfully propagated the FAdV isolates in STB with virus titer of 107.5 (UPM08136CELP5B1) and 106.5 (UPM08136CELP20B1) TCID50/mL. These isolates clustered with the reference FAdV serotype 8b in the same evolutionary clade. The molecular characteristics remained unchanged, except for a point substitution at position 4 of the hexon gene of UPM08136CELP20B1, suggesting that propagation of the FAdV isolate in STB is stable and suitable for large volume production and could be a breakthrough in the scale-up process.

Gizzard Erosion Associated with Fowl Adenovirus Infection in Slaughtered Broiler Chickens in Iran

Gizzard erosions have been noticed in slaughtered broiler chickens during inspection at a processing plant in Iran. The condition was detected in piled gizzards derived from seven commercial broiler farms brought to slaughter on the same day. In total, 48 gizzards with lesions underwent thorough pathologic and virologic investigation. Perforation, roughening, and discoloration of the koilin layer as well as inflammation of the mucosa were observed macroscopically. Histologic examination showed dissociation of and cellular debris in the koilin layer accompanied by a loss and degeneration of glandular epithelium with mild to marked infiltration of inflammatory cells in the mucosa, submucosa, and muscular layer. Fowl adenovirus serotypes 1 (FAdV-1), 11 (FAdV-11), and 8a (FAdV-8a) were found in 13, 12, and 1 gizzard(s), respectively. Therein included were two gizzards that showed mixed infections with FAdV-1 and FAdV-11. Detailed analysis of the hexon gene revealed that the Iranian FAdV-1 isolates could be divided into two subclusters, more closely related to either the European (CELO) or the Asian (Ote) FAdV-1 reference strains. The present study, for the first time, describes not only the appearance of gizzard erosion but also the isolation of FAdV-1 and FAdV-8a from broilers in Iran and offers insights on the epidemiology of FAdV infection in Iranian flocks.

Research Note: Molecular and pathologic characterization of avian adenovirus isolated from the oviducts of laying hens in eastern Japan

Cases of poor egg production were investigated in 2 layer farms from Ibaraki Prefecture in eastern Japan. To identify any microbial agents that may have caused the problem, necropsy, bacterial isolation, histopathology, and virus detection were performed. Members of the avian adenoviruses was detected by PCR in oviduct samples from both farms; chicken anemia virus coinfection was also confirmed in one of the farms. Avian adenovirus was isolated from the oviducts of the affected chickens on each farm. Inoculation into chick embryos showed tropism for the chorio-allantoic membrane. Stunting and hemorrhaging was observed in all infected embryos, as well as death in a few. Inoculation of 1-day-old specific pathogen-free chicks, and 400-day-old commercial hens, did not result in any significant findings. The isolated viruses were analyzed by sequencing of the hexon gene and were confirmed as fowl adenovirus type-c serotype-4 (FAdV-4). The 2 virus strains were found to be 99.29% similar to each other. One of the strains, Japan/Ibaraki/Y-H6/2016, was 99.15% similar to the KR5 strain. The other, Japan/Ibaraki/M-HB2/2016, was 99.57% similar to the KR5 strain. Fiber-2 gene analysis confirmed the identity as FAdV-4 that is closely related to nonpathogenic strains. Although nonpathogenic to chicks and laying hens, this infection can possibly cause economic damage. Perhaps the bigger concern is the effect on infected breeder operations. Because the virus is fatal to 9.09% of infected embryos, this could translate to a considerable loss in chick production owing to embryonic death. This is the first report of detection and isolation of FAdV-4 from the chicken oviduct; however, further studies are needed to elucidate its impact on both layer and breeder flocks. Indeed, FAdV-4 has negative effects on the avian reproductive tract as well.

Adenoviral Gizzard Erosions in Two Belgian Broiler Farms

Fowl adenovirus infections are widely prevalent in poultry. Many of the viruses can infect chickens without resulting in overt disease. Nevertheless, some fowl adenoviruses can cause important disease complexes in chickens such as inclusion body hepatitis, hydropericardium syndrome, necrotic pancreatitis, and gizzard erosion. Adenoviral gizzard erosions have been regularly reported from Japan, but detailed reports from Europe are scarce and available only from Italy, Poland, Hungary, and Germany. This case report describes two concurrent outbreaks of gizzard erosions caused by fowl adenovirus A in two Belgian broiler farms. Clinical signs observed were signs of depression, reduced feed intake, reduced weight gain, and lack of uniformity of the flocks. At necropsy, typically multiple erosions within the koilin layer of the gizzard were observed. Histopathological examination showed a multifocal, erosive ventriculitis with basophilic intranuclear inclusions in the epithelium. PCR analysis confirmed the diagnosis of fowl adenovirus. These findings suggest that outbreaks of adenoviral gizzard erosion can also lead to significant economic losses in Belgium.

Chronologic Analysis of Gross and Histologic Lesions Induced by Field Strains of FAdV-1, FAdV-8b, and FAdV-11 in Six-Week-Old Chickens

Inclusion body hepatitis (IBH) is a disease affecting broiler chicken flocks worldwide. Several serotypes of fowl adenovirus (FAdV) have been implicated in disease outbreaks, with and without immunosuppression as a predisposing factor. IBH usually occurs in flocks up to 30 days of age; it is seldom seen in older birds. The objective of this study was to determine whether the pathogenicity for older birds of three FAdV field strains, belonging to serotypes 1, 8b, and 11, in the absence of immunosuppressive factors, was akin to that for younger birds, and to establish an effective and economical disease model for assessing cross-protection between serotypes. To achieve this objective, the gross pathology, histopathology, and dissemination of virus were examined at multiple time points after inoculation of 6-wk-old, specific-pathogen-free chickens via intraperitoneal injection. Both FAdV-8b and FAdV-11 generated lesions typical of those associated with outbreaks of IBH, and they were shown to be primary pathogens. The presence and severity of hepatic lesions were used to define two disease stages: degeneration (1-5 days postinoculation) and convalescence (6-14 days postinoculation). During the degenerative stage, FAdV-8b was detected in the liver, kidney, and gizzard of most birds, whereas FAdV-11 was predominantly detected in the liver, and both viruses persisted in the gizzard into convalescence. The pathogenesis of two IBH-associated FAdV strains in 6-wk-old chickens confirms their high level of virulence and also provides an effective experimental model for investigation of cross-protection between FAdVs. It also demonstrates persistence of the virus in the gizzard long after infection, supporting the notion that it is a site of viral shedding.

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.

A comparative pathogenicity analysis of two adenovirus strains, 1/A and 8a/E, isolated from poultry in Poland

Fowl adenoviruses (FAdVs) are the causative agents of multietiological syndromes and diseases in poultry flocks. During a routine diagnostic examination, two FAdVs strains were isolated. Molecular typing of these isolates based on the partial loop L1 HVR1-4 region of the hexon gene sequence revealed the presence of different FAdV isolates: 1/A-61/11z (GenBank accession number KX247012, APP94082), and 8a/E-6/12j (GenBank accession number: KP890032, ALB00550), and comparative genome analysis indicated small differences between these two viruses. The next step of the study was the estimation of the pathogenicity of these isolates in specific-pathogen-free (SPF) chickens. Chickens were divided into three groups, with 20 chickens per group infected intraperitoneally on the first day after hatching. Group I consisted of chickens infected with strain FAdV-1/A-61/11z, group II consisted of chickens infected with strain FAdV-8a/E-6/12j, and group III consisted of uninfected birds. Clinical signs observed in infected chickens included poor growth, apathy, prostration, ruffled feathers, crouching position, and huddling behavior. The mortality rate in chickens infected with FAdV-1/A-61/11z was 10% at 10 days postinfection (dpi), and no mortality was observed in chickens infected with the FAdV-8a-6/12j strain. The mean real-time PCR threshold cycle (Ct) value was 39.70%. The detection limit of these assays was 8 copies, with an efficiency of 91.03% and 95.17% and regression square (R2) values of 0.991 and 0.997, respectively, with a mean pathogen load of 4.8 × 10^6.0 copies/µl. The assays did not demonstrate cross-reactivity between types 1/A and 8a/E and non-targeted poultry viruses. Adenoviral DNA was detected in the liver, spleen, kidney, gizzard, intestine, bursa of Fabricius, and thymus of every examined dead and euthanized chicken from groups I and II between the third and fourth week postinfection. This is the first study conducted on the pathogenic and apathogenic strains FAdV-1/A and FAdV-8a/E, showing the presence of the virus in multiple tissues in chickens in Poland. This study revealed that it is very likely that the FAdV-1/A-61/11z strain is able to cause clinical inclusion body hepatitis (IBH) in chickens and that it is slightly more virulent than the FAdV-8a/E-6/12j strain, although both are primary pathogens of the disease.

Molecular characterization of fowl adenovirus group I in commercial broiler chickens in Brazil

Avian adenovirus has been reported in many countries and is an infectious agent related with inclusion body hepatitis, hepatitis-hydropericardium syndrome (HHS), and respiratory and enteric conditions in chickens worldwide. The objective of this study was to detect and establish the molecular sequences of the hexon gene from the avian adenovirus strains of group I (FAdV-I) isolated from birds with hepatitis-hydropericardium syndrome (HHS), malabsorption syndrome and runting-stunting syndrome, to characterize the serotype of virus affecting commercial flocks in Brazil. Molecular characterization was performed by polymerase chain reaction (PCR), using specific primers to amplify the Loop 1 (L1) variable region of the hexon gene in the FAdV-I genome and subsequent sequencing of the PCR product for each positive sample. The results have revealed the presence of the FAdV-8a, FAdV-8b, and FAdV-11 serotypes circulating in Brazilian chicken flocks. Phylogenetic analysis grouped these sequences into three (3) distinct groups, 14 samples were aligned with the FAdV-11 group, three (3) samples in the FAdV-8b group and one (1) sample in the FAdV-8a group. The serotypes FAdV-8a, FAdV-8b, and FAdV-11 are circulating in Brazilian chicken flocks. Therefore, these results are very important for improvement biosecurity measurements and vaccine production.

Isolation and molecular characterization of prevalent Fowl adenovirus strains in southwestern China during 2015-2016 for the development of a control strategy

Fowl adenovirus (FAdV) has caused significant losses in chicken flocks throughout China in recent years. However, the current understanding of the genetic and pathogenic characteristics of the FAdV epidemic in southwestern China remains poorly understood. In this study, a total of 22 strains were isolated from liver samples of diseased chickens from farms in southwestern China. Phylogenetic analysis based on the hexon loop-1 gene showed that the 22 isolates were clustered into four distinct serotypes: FAdV serotype 4 (FAdV-4) (86.4%, 19/22), FAdV-2 (4.5%, 1/22), FAdV-8a (4.5%, 1/22), and FAdV-8b (4.5%, 1/22). FAdV-4 was the predominant serotype in southwestern China. Pathogenicity testing showed that the FAdV-4 serotype strain CH/GZXF/1602 and FAdV-8a strain CH/CQBS/1504 were pathogenic to chickens, with mortality rates reaching as high as 80% and 20%, respectively. The primary clinical feature observed following infection with strain CH/GZXF/1602 (FAdV-4) was hepatitis-hydropericardium syndrome, and that of strain CH/CQBS/1504 (FAdV-8a) was inclusion body hepatitis. Conversely, the FAdV-2 serotype strain CH/GZXF/1511 and FAdV-8b serotype strain CH/CQBS/1512 was not observed to be pathogenic in chickens. Then, CH/GZXF/1602 (FAdV-4) was selected for the preparation of an inactivated oil-emulsion vaccine. Immune studies on Partridge Shank broilers showed that a single dose immunization at 17 days of age could not only protect against homologous challenge with virulent FAdV-4 but also provided protection against clinical disease following challenge with the heterologous FAdV-8b virulent strain until 70 days of age. The characterization of newly prevalent FAdV strains provides a valuable reference for the development of an efficacious control strategy.

Fowl adenovirus-induced diseases and strategies for their control - a review on the current global situation

The stand-alone pathogenicity of fowl adenoviruses (FAdVs) had long been disputed, given the ubiquity of the viruses versus sporadic outbreaks, and variation between experimental studies. However, a globally emerging trend of FAdV-associated diseases has marked the past two decades, with hepatitis-hydropericardium syndrome mainly in Asia besides Arabian and Latin American countries, and geographically more disseminated outbreaks of inclusion body hepatitis. Finally, the appearance of FAdV-induced gizzard erosion (AGE) in Asia and Europe completed the range of diseases. Epidemiological studies confirmed serotype FAdV-4 as agent of hepatitis-hydropericardium syndrome, whereas inclusion body hepatitis is related to FAdV-2, -8a, -8b and -11. Members of the biologically more distant serotype FAdV-1 induce AGE. Urged by increasing problems in the field, numerous pathogenicity studies with FAdVs from outbreaks substantiated the primary aetiologic role of particular strains for distinct clinical conditions. Developments in the poultry industry towards highly specialized genetic breeds and rigorous biosecurity additionally contribute to the growing incidence of FAdV-related diseases. Confirming field observations, recent studies connected a higher susceptibility of broilers with their distinct physiology, implying the choice of bird type as a factor to be considered in infection studies. Furthermore, elevated biosecurity standards have generated immunologically naïve breeding stocks, putting broilers at risk in face of vertical FAdV transmission. Therefore, future prevention strategies should include adequate antibodies in breeders prior to production and - if necessary - vaccination, in order to protect progenies. This review aims to deliver a detailed overview on the current global situation about FAdV-induced diseases, their reproduction in vivo and vaccination strategies.

Fowl aviadenovirus serotype 1 confirmed as the aetiological agent of gizzard erosions in replacement pullets and layer flocks in Great Britain by laboratory and in vivo studies

An investigation into the aetiology and pathogenesis of adenoviral gizzard erosion has been conducted following three natural outbreaks affecting one flock of 6-week-old replacement pullets and two consecutive placements of free range layers at the age of 21 and 23 weeks. Affected flocks showed increased mortality (0.12-0.30% per week), and gizzard lesions were consistent with fowl aviadenovirus (FAdV) involvement. To substantiate the initial findings, a selection of archived formalin-fixed paraffin-embedded gizzard samples from another 12 pullet and layer flocks, for which macroscopic and histopathological diagnosis of the disease were recorded in Great Britain during the period 2009-2016, were also investigated. In situ hybridization (ISH), virology and/or PCR confirmed the presence of FAdV species-A, serotype-1 (FAdV-A, FAdV-1) DNA in gizzard samples of all 15 cases investigated. Co-infections with additional FAdV serotypes including FAdV-8a were detected by serology and/or virology in two of the pullet flocks. However, species-specific in situ hybridization revealed that pathological changes of affected gizzards were only associated with the detection of FAdV-A. A subsequent in vivo study infecting 21-day-old SPF pullets with FAdV-1 or FAdV-8a strains isolated from the 6-week-old replacement pullets revealed characteristic pathomorphological changes only in the gizzards from birds infected with FAdV-1. While infection with FAdV-8a was confirmed by virology and serology, infected SPF birds did not develop pathomorphological changes. Therefore, the aetiological involvement of the isolated FAdV-8a in the development of adenoviral gizzard erosion in commercial pullets has been ruled out.

Fowl Adenoviruses D and E Cause Inclusion Body Hepatitis Outbreaks in Broiler and Broiler Breeder Pullet Flocks

Twenty-four fowl adenoviruses (FAdVs) were isolated from broiler and broiler breeder pullet flocks in Iran during 2013-2016 and were identified and characterized. All FAdVs were from inclusion body hepatitis (IBH) cases, showing an enlarged and pale yellow liver with multiple petechial hemorrhages. Phylogenetic analyses of partial hexon gene sequences are an adequate and quick method for differentiation and genotyping. The isolates were subjected to PCR to amplify a 590-bp fragment from the hexon gene. Sequence analysis revealed the presence of two species D and E. Eighty FAdV isolates were genetically related to the strain EU979378 of FAdV-11 (96.5% to 97.6% identity), and six isolates were related to the strain EU979375 of FAdV-8b (97% identity). The results indicated that two FAdV serotypes (11 and 8b) are high prevalence serotypes of FAdVs in Iran and are pathogenic enough to cause IBH in young chicks. Therefore, preventive measures against FAdV infection on poultry farms should be implemented.

Chronological analysis of gross and histological lesions induced by field strains of fowl adenovirus serotypes 1, 8b and 11 in one-day-old chickens

Fowl adenoviruses (FAdVs) cause diseases in domestic chickens, including inclusion body hepatitis (IBH), with immunosuppression believed to play a role in their pathogenesis. To gain a better understanding of the pathogenesis and chronology of disease caused by FAdVs, the gross pathology, histopathology and dissemination of virus were examined at several different time points, after inoculation of one-day-old specific pathogen-free chickens with FAdV-1, FAdV-8b or FAdV-11 via the ocular route. FAdV-8b had a slightly greater virulence than FAdV-11, but both were primary pathogens. The presence and severity of hepatic lesions were used to define the three stages of the disease: incubation (1-3 days post-inoculation, PI), degeneration (4-7 days PI) and convalescence (14 days PI). Both viruses were detected in the liver, kidney, bursa, thymus and gizzard of most birds during the degenerative stage, and persisted in the gizzard into convalescence. The FAdV-1 isolate was found to be apathogenic, but virus was detected in the bursa and/or gizzard of several birds between 2 and 7 days PI. This is the first study examining the chronology of gross and microscopic lesions of pathogenic and apathogenic FAdVs in association with viral presence in multiple tissues. It was concluded that both FAdV-8b and FAdV-11 are primary pathogens, and that these strains may play a role in immunosuppression.

Design of a predicted MHC restricted short peptide immunodiagnostic and vaccine candidate for Fowl adenovirus C in chicken infection

Fowl adenoviruses (FAdVs) are the ethiologic agents of multiple pathologies in chicken. There are five different species of FAdVs grouped as FAdV-A, FAdV-B, FAdV-C, FAdV-D, and FAdV-E. It is of interest to develop immunodiagnostics and vaccine candidate for Peruvian FAdV-C in chicken infection using MHC restricted short peptide candidates. We sequenced the complete genome of one FAdV strain isolated from a chicken of a local farm. A total of 44 protein coding genes were identified in each genome. We sequenced twelve Cobb chicken MHC alleles from animals of different farms in the central coast of Peru, and subsequently determined three optimal human MHC-I and four optimal human MHC-II substitute alleles for MHC-peptide prediction. The potential MHC restricted short peptide epitope-like candidates were predicted using human specific (with determined suitable chicken substitutes) NetMHC MHC-peptide prediction model with web server features from all the FAdV genomes available. FAdV specific peptides with calculated binding values to known substituted chicken MHC-I and MHC-II were further filtered for diagnostics and potential vaccine epitopes. Promiscuity to the 3/4 optimal human MHC-I/II alleles and conservation among the available FAdV genomes was considered in this analysis. The localization on the surface of the protein was considered for class II predicted peptides. Thus, a set of class I and class II specific peptides from FAdV were reported in this study. Hence, a multiepitopic protein was built with these peptides, and subsequently tested to confirm the production of specific antibodies in chicken.

Pathogenicity and Complete Genome Characterization of Fowl Adenoviruses Isolated from Chickens Associated with Inclusion Body Hepatitis and Hydropericardium Syndrome in China

In this study, we determined and genetically characterized three fowl adenoviruses isolated from chickens with inclusion body hepatitis (IBH) and hydropericardium syndrome (HPS) in China and assessed their pathogenicity. The full genome of HBQ12, BJH13 and JSJ13 was found to be 44,081, 43,966 and 43,756 nucleotides long, respectively. Sequence alignment and phylogenetic analysis revealed that strain HBQ12 and BJH13 were clustered together belonging to fowl adenoviruses D species and serotyped as FAdV-11, whereas strain JSJ13 was classified into fowl adenoviruses C species and serotyped as FAdV-4. To our knowledge, this is the first report of FAdV-4 strain circulating in China. The pathogenicity test showed that mortality for chickens infected with HBQ12 and JSJ13 within 21 days post infection (dpi) was 8.6% and 28.6%, respectively. Necropsy displayed mild or severe hepatitis and hydropericardium at 3 and 5 dpi as well as dead chickens. Viral DNA was detected in almost all tissues sampled from dead chickens. These results revealed that fowl adenovirus strains HBQ12 and JSJ13 are capable of causing IBH and HPS in chickens, indicating that preventive measures against FAdV infection on poultry farms should be implemented in China.

Clinical signs and progression of lesions in the gizzard are not influenced by inclusion of ground oats or whole wheat in the diet following experimental infection with pathogenic fowl adenovirus serotype 1

In the present study the effects of dietary gizzard stimulation on the development and severity of adenoviral gizzard erosion were investigated. For this purpose, specific pathogen-free broilers were divided into six groups, investigating the influence of an oat-containing diet with higher fibre content, a whole wheat-containing diet and a control diet of nearly identical composition, but containing ground wheat. For each feed administered, one group of birds was experimentally infected on the 10th day of age by the oral route with virulent fowl adenovirus serotype 1 (FAdV-1), recently proven to induce gizzard erosions, while the respective negative control groups remained uninfected. Experimental feed was administered from 2 days post-infection onwards. No significant differences on gizzard health or in weight gain could be detected between uninfected control groups or between FAdV-1 infected groups that received different experimental feed. However, independent of the supplied diet, a significantly reduced weight gain was noted from 7 days post-infection onwards in FAdV-1 infected broilers compared to uninfected birds that received the same diet. Macroscopically, discolouration and erosion of the koilin layer and inflammation of the gizzard mucosa were observed in all FAdV-1 infected groups. Histologically, necrosis, degeneration of gizzard epithelial cells and multiple basophilic intranuclear inclusion bodies were observed. In summary, after experimental infection with FAdV-1 development of gizzard erosion in chickens was not influenced by the feeding regimes investigated. Therefore, it is unlikely that dietary gizzard stimulation influences the outcome of adenoviral gizzard erosion in vertically infected broilers.

Vertical transmission and clinical signs in broiler breeders and broilers experiencing adenoviral gizzard erosion

The present report documents an outbreak of adenoviral gizzard erosion in 22 broiler flocks in Germany. The clinical picture was characterized by uneven growth of affected broilers that resulted in considerably lower than average weight at slaughtering. Fowl adenovirus serotype 1 (FAdV-1) was isolated from gizzard lesions and histological examinations demonstrated FAdV-1-positive intranuclear inclusion bodies in gizzard epithelial cells of affected broilers by in-situ hybridization. Birds from all affected flocks originated from one broiler breeder farm. During production of affected birds, broiler breeders were between 27 and 32 weeks old. Enzyme-linked immunosorbent assay and specific virus neutralization assay of sera from parent birds demonstrated an acute FAdV-1 infection within the first 5 weeks of the production cycle. Clinically, broiler breeders exhibited a moderate fall in the hatchability of their chicks, while egg production remained normal. No further clinical signs could be observed. Genetically identical FAdV-1 strains were isolated from gizzards of embryos at the lowest point of hatchability and from affected broiler flocks raised on independent farms. For the first time, direct detection of viable FAdV-1 from gizzards of embryos and progenies of one FAdV-1-seropositive broiler breeder farm in the course of an outbreak of adenoviral gizzard erosion could be demonstrated, highlighting the importance of vertical transmission of this disease. Additionally, growth retardation and subsequent reduced average weight at the time of slaughter of broiler chickens underline the economic impact of adenoviral gizzard erosion for poultry production.

Phylogenetic analysis of fowl adenoviruses isolated from chickens with gizzard erosion in Japan

Thirty-four fowl adenoviruses (FAdVs) isolated from chickens with gizzard erosion (GE) from 1999 to 2010 were characterized phylogenetically together with foreign isolates. The phylogenetic analysis based on part of the hexon gene classified these 34 FAdV isolates into 3 groups: FAdV-1, -8a and 8b, thereby suggesting that FAdVs associated with GEs in chickens are diverse. All 30 FAdV-1 isolates were genetically identical, and they were also identical with FAdV-1 isolates from GEs in chickens in European countries (Germany, Poland, Austria, Hungary and Italy). Thus, the same type of FAdV-1 has been associated with outbreaks of GE in Japanese chickens for the past 10 years, which may have spread from a common ancestor, although the epidemiological relationship is unknown.

Whole-genome sequences of two turkey adenovirus types reveal the existence of two unknown lineages that merit the establishment of novel species within the genus Aviadenovirus

There are eight species established for aviadenoviruses: Fowl adenovirus A–E, Goose adenovirus A, Falcon adenovirus A and Turkey adenovirus B. The aim of this study was to sequence and analyse the complete genomes of turkey adenovirus 4 (TAdV-4) and TAdV-5 (strain 1277BT) in addition to almost two-thirds of the genome of another TAdV-5 strain (strain D1648). By applying next-generation sequencing, the full genomes were found to be 42 940 and 43 686 bp and the G+C content was 48.5 and 51.6 mol% for TAdV-4 and TAdV-5, respectively. One fiber gene was identified in TAdV-4, whereas two fiber genes were found in TAdV-5. The genome organization of TAdV-4 resembled that of fowl adenovirus 5 (FAdV-5), but it had ORF1C near the left end of the genome. TAdV-4 also had five 123 bp tandem repeats followed by five 33 bp tandem repeats, but they occurred before and not after ORF8, as in several fowl adenoviruses. The genome organization of TAdV-5 was almost the same as that of FAdV-1 but with a possible difference in the splicing pattern of ORF11 and ORF26. Phylogenetic analyses and G+C content showed differences that seem to merit the establishment of two new species within the genus Aviadenovirus: Turkey adenovirus C (for TAdV-4) and Turkey adenovirus D (for TAdV-5). Our analyses suggest a common evolutionary origin of TAdV-5 and FAdV-1.

Comparison of fiber gene sequences of inclusion body hepatitis (IBH) and non-IBH strains of serotype 8 and 11 fowl adenoviruses

Fowl adenoviruses (FAdVs) are common in broiler operations, and the most frequently isolated FAdVs belong to serotypes 1, 8, and 11. Serotype 1 viruses are considered nonpathogenic. While some serotype 8 and 11 viruses cause inclusion body hepatitis (IBH), these virus serotypes can also be isolated from non-IBH cases. The fiber protein is one of the major constituents of the adenoviral capsid, involved in virus entry, and it has been implicated in the variation of virulence of FAdVs. The fiber gene sequences of four FAdV-8 and four FAdV-11 isolates from both IBH and non-IBH cases were determined and analyzed for a possible association of the fiber gene sequence in virulence. The fiber protein can be divided into tail, shaft, and head domains comprising some specific features. The conserved "RKRP" sequence motif (aa 17-aa 20) fit the consensus sequence predicted for the nuclear localization signal, while the "VYPF" motif (aa 53-aa 56), involved in the penton base interaction, was also found. Similar to mammalian adenoviruses, 17 pseudo-repeats with an average length of 16 aa were detected in the FAdV-8 fiber shaft region, while 20 pseudo-repeats with an average length of 18 aa were found in FAdV-11 fibers. There was a 144-147 nt difference between the fiber genes of the two FAdV serotypes. In the shaft region, the TLWT motif that marks the beginning of the fiber head domain of the mastadenovirus was not evident among examined FAdVs. The FAdV-11 isolates had 99.1 % aa sequence identity and 99.3 % similarity to each other, and there was no conserved aa substitution within the fibers. The FAdV-8 fiber proteins showed an overall lower, 89 % aa sequence identity and 93.4 % similarity, to each other and 22 nonsynonymous mutations were detected. Virulence markers were not detected in the analyzed fiber gene sequences of the different pathotypes of the two FAdV serotypes.

Adenoviral gizzard erosion in broiler chickens in Germany

Avian adenovirus infections cause important disease complexes in chickens, but many of the viruses also infect chickens without resulting in overt disease. Previously several outbreaks of gizzard erosions caused by a fowl adenovirus A serotype-1 (FAdV-1) were reported from Japan. Here we report an outbreak of gizzard erosions in 12 broiler flocks in Germany in 2011. Chickens had a reduced daily weight gain and a higher total mortality rate of up to 8%. The birds showed a severe detachment of the koilin layer and ulcerative to necrotizing lesions of the underlying mucosa. Histopathologically, necrotizing ventriculitis with basophilic, intranuclear inclusion bodies in epithelial cells was diagnosed. Immunohistochemistry, egg culture, and electron microscopic examination revealed adenovirus-like particles in the samples. No concurrent infectious agent could be identified. The virus was genotyped as FAdV-1 by PCR and subsequent sequencing. Phylogenetic analysis of the hexon loop L1 gene yielded 100% sequence identity to the chicken embryo lethal orphan strain. These findings suggest that outbreaks of adenoviral gizzard erosion can lead to significant economic losses in Germany and may be caused by an unusual virulent FAdV-1 strain.

Quantity of virulent fowl adenovirus serotype 1 correlates with clinical signs, macroscopical and pathohistological lesions in gizzards following experimental induction of gizzard erosion in broilers

In the present study day-old specific-pathogen-free (SPF) and commercial broilers with maternally derived fowl adenovirus serotype 1 (FAdV-1) antibodies were orally infected with a European “pathogenic” FAdV-1, isolated from broilers showing signs of gizzard erosion. During the experiment, broilers were observed and weighed daily up to 17 days post infection (dpi). Clinically, both infected groups showed significant decrease of weight compared to respective negative control groups. Birds were examined by necropsy at 3, 7, 10, 14 and 17 dpi. Pathological changes in the gizzards were noticed in both experimentally infected groups from 7 dpi onwards. Macroscopically, erosion of the koilin layer and inflammation or ulceration of the gizzard mucosa were observed. Histologically, presence of FAdV-1 in intranuclear inclusion bodies of degenerated glandular epithelial cells was demonstrated by in-situ hybridization and inflammatory cell infiltration of the lamina propria, submucosa and muscle layer was detected. Tissue samples were investigated by a recently developed real-time PCR and the viral DNA load was calculated from gizzard, liver, spleen and cloacal swabs with the highest amounts of FAdV-1 DNA found in the gizzard. For the first time, successful reproduction of clinical signs in broilers as well as pathological lesions in the gizzard were achieved with a European FAdV-1 isolate displaying some genetic differences to so far reported virulent FAdV-1 from Japan. Furthermore, highest viral load in gizzards could be linked with macroscopical and histological lesions. Therefore, the conducted analyses provide important insights into the pathogenesis of adenoviral gizzard erosion.