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.

Pathogenicity of field strain of fowl aviadenovirus serotype 11 isolated from chickens with inclusion body hepatitis in Morocco.

Outbreaks of inclusion body hepatitis have emerged in Morocco since 2013 and has resulted in significant economic losses to poultry farms. Three isolates of the causative virus, Fowl adenonovirus (FAdV)were characterized from chickens with IBH, but their pathogenicity has never been investigated. In this work, the pathogenicity of an isolate FAdV 11 (MOR300315 strain) was evaluated by inoculating a group of 40 SPF chickens at 3 days of age by oral route. A group of 40 chicks injected with phosphate-buffered saline solution was used as a control group. The infected chickens showed decreased weight gain from 3dpi. Necropsy displayed pallor and enlargement in liver, swelling and slight hemorrhage in kidney and spleen at 6 dpi. Histopathological changes were mainly characterized by severe and extensive hepatic necrosis associated with the presence of basophilic intra-nuclear inclusion bodies within hepatocytes. The FAdV was reisolated in chicken embryo fibroblast cell culture from liver tissue homogenate of infected chicken from 3 to 6 dpi. Viral DNA was detected by PCR in liver, kidney, spleen and cloacal swabs from 3 to 13 dpi. Antibody response against inoculated FAdV was appeared from 9 dpi. These results confirmed that the FAdV 11 strain is pathogenic in chicken. This study is the first experimental infection of FAdV 11 in chicken in Morocco, which increase our understanding of its pathogenicity in chickens and indicate that preventive measures against FAdV infection in poultry farms should be implemented in Morocco.

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.

Nota de investigación­Caracterización genética y análisis de patogenicidad de un adenovirus del pollo 8b aislado recientemente en Corea. Se aisló una cepa de campo coreana de adenovirus del pollo (FAdV) 8b de aves que mostraban una alta mortalidad. Se analizaron genéticamente cepas de FAdV-8b aisladas mediante los genes de hexón y de la fibra. La cepa coreana FAdV-8b (K194/19) aislada en 2019 mostró una mayor identidad de secuencia con la cepa FAdV-8b aislada en China, pero una menor identidad de secuencia con la cepa coreana FAdV-8b (K187/08) aislada en 2008. La cepa K194/19 formó un subgrupo distinto dentro del grupo de adenovirus del pollo 8b en un árbol filogenético basado en los genes de las fibras y hexones. El FAdV puede infectar a pollitos de un día a través de la transmisión vertical, por lo que se obtuvieron muestras de sangre de pollos reproductores de 54, 60 y 63 semanas de edad. Los niveles de anticuerpos específicos de FAdV se investigaron con ELISA y pruebas de neutralización de virus (VN) con las cepas K194/19 y K187/08 como antígenos. En las pruebas de neutralización, todos los sueros neutralizaron a la cepa K187/08. Sin embargo, la cepa K194/19 fue neutralizada por sueros recolectados de pollos de 60 y 63 semanas de edad, pero no por los sueros obtenidos de pollos de 54 semanas de edad, lo que indica una infección natural. Finalmente, para determinar la patogenicidad de la cepa K194/19, se infectaron aves libres de patógenos específicos de un día y cuatro semanas de edad con las cepas K194/19 y K187/08. No se observaron diferencias significativas en la patogenicidad entre las dos cepas. Aunque la cepa K194/19 mostró una patogenicidad similar con la cepa K187/08, las diferencias en las secuencias de nucleótidos y aminoácidos de los genes del hexón y de la fibra pueden determinar la capacidad para evadir los anticuerpos neutralizantes K187/08, lo que indica la necesidad de desarrollar una nueva vacuna contra adenovirus del pollo.

Domain in Fiber-2 interacted with KPNA3/4 significantly affects the replication and pathogenicity of the highly pathogenic FAdV-4.

The outbreaks of hepatitis-hydropericardium syndrome (HPS) caused by the highly pathogenic serotype 4 fowl adenovirus (FAdV-4) have caused a huge economic loss to the poultry industry globally since 2013. Although the Fiber-2 has been identified as a key virulent related factor for FAdV-4, little is known about its molecular basis. In this study, we identified the efficient interaction of the Fiber-2 with the karyopherin alpha 3/4 (KPNA3/4) protein via its N-terminus of 1-40aa. The analysis of the overexpression and knockout of KPNA3/4 showed that KPNA3/4 could efficiently assist the replication of FAdV-4. Moreover, a fiber-2-edited virus FAV-4_Del with a deletion of 7-40aa in Fiber-2 was rescued through the CRISPR-Cas9 technique. In comparison with the wild type FAdV-4, FAV-4_Del was highly attenuated in vitro and in vivo. Notably, the inoculation of FAV-4_Del in chickens could provide full protection against the lethal challenge with the wild type FAdV-4. All these findings not only give novel insights into the molecular basis for the pathogenesis of Fiber-2 but also provide efficient targets for developing antiviral strategies and live-attenuated vaccine candidates against the highly pathogenic FAdV-4.

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

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

Pathogenesis of Hypervirulent Fowl Adenovirus Serotype 4: The Contributions of Viral and Host Factors.

Since 2015, severe outbreaks of hepatitis-hydropericardium syndrome (HHS), caused by hypervirulent fowl adenovirus serotype 4 (FAdV-4), have emerged in several provinces in China, posing a great threat to poultry industry. So far, factors contributing to the pathogenesis of hypervirulent FAdV-4 have not been fully uncovered. Elucidation of the pathogenesis of FAdV-4 will facilitate the development of effective FAdV-4 vaccine candidates for the control of HHS and vaccine vector. The interaction between pathogen and host defense system determines the pathogenicity of the pathogen. Therefore, the present review highlights the knowledge of both viral and host factors contributing to the pathogenesis of hypervirulent FAdV-4 strains to facilitate the related further studies.

Molecular characterization of fowl adenovirus isolate of Malaysia attenuated in chicken embryo liver cells and its pathogenicity and immunogenicity in chickens.

Fowl adenovirus (FAdV) is the causative agent of inclusion body hepatitis (IBH) in chickens with significant economic losses due to high mortality and poor production. It was objectives of the study to attenuate and determine the molecular characteristic of FAdV isolate (UPM1137) of Malaysia passages in primary chicken embryo liver (CEL) cells. The cytopathic effect (CPE) was recorded and the present of the virus was detected by polymerase chain reaction (PCR). Nucleotide and amino acid changes were determined and a phylogenetic tree was constructed. The pathogenicity and immunogenicity of the virus at passage 35 (CEL35) with virus titre of 106.7TCID50/mL was determined in day old specific pathogen free (SPF) chicks via oral or subcutaneous route of inoculation. The study demonstrated that the FAdV isolate was successfully propagated and attenuated in CEL cells up to 35th consecutive passages (CEL35) with delayed of CPE formation within 48 to 72 post inoculation (pi) from CEL20 onwards. The virus caused typical CPE with basophilic intranuclear inclusion bodies, refractile and clumping of cells. The virus is belong to serotype 8b with substitution of amino acid at position 44, 133 and 185 in L1 loop of hexon gene and in knob of fiber gene at position 348 and 360 at CEL35. It is non-pathogenic, but immunogenic in SPF chickens. It was concluded that the FAdV isolate was successfully attenuated in CEL cells with molecular changes in major capsid proteins which affect its infectivity in cell culture and SPF chickens.

Hexon and fiber gene changes in an attenuated fowl adenovirus isolate from Malaysia in embryonated chicken eggs and its infectivity in chickens.

Fowl adenovirus (FAdV) is distributed worldwide and causes economic losses in the poultry industry. The objectives of this study were to determine the hexon and fiber gene changes in an attenuated FAdV isolate from Malaysia in specific pathogen-free chicken embryonated eggs (SPF CEE) and its infectivity in commercial broiler chickens. SPF CEE were inoculated with 0.1 mL FAdV inoculum via the chorioallantoic membrane (CAM) for 20 consecutive passages. The isolate at passage 20 (E20), with a virus titer of 108.7TCID50/mL (TCID50, 50% tissue culture infective dose), was inoculated (0.5 mL) into one-day-old commercial broiler chicks either via oral or intraperitoneal routes. The study demonstrated that 100% embryonic mortality was recorded from E2 to E20 with a delayed pattern at E17 onwards. The lesions were confined to the liver and CAM. Substitutions of amino acids in the L1 loop of hexon at positions 49 and 66, and in the knob of fiber at positions 318 and 322 were recorded in the E20 isolate. The isolate belongs to serotype 8b and is non-pathogenic to broiler chickens, but it is able to induce a FAdV antibody titer. It appears that molecular changes in the L1 loop of hexon and the knob of fiber are markers for FAdV infectivity.

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

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

Immune responses to in ovo vaccine formulations containing inactivated fowl adenovirus 8b with poly[di(sodium carboxylatoethylphenoxy)]phosphazene (PCEP) and avian beta defensin as adjuvants in chickens.

Inclusion body hepatitis (IBH) is one of the major viral infections causing substantial economic loss to the global poultry industry. The disease is characterized by a sudden onset of mortality (2-30%) and high morbidity (60-70%). IBH is caused by a number of serotypes of fowl adenovirus with substantially low levels of serotype cross protection. Thus far, there is no effective and safe vaccine commercially available in the North America for the control of IBH in chickens. Poly[di(sodium carboxylatoethylphenoxy)]phosphazene (PCEP) is a high molecular weight, biodegradable water soluble polymer that has been well characterized as a safe and effective adjuvant for a number of experimental veterinary vaccines. Similarly, host defence peptides, including ß-defensins, have also been shown to exhibit strong adjuvant potential. In this study, we evaluated the adjuvant activity of PCEP and avian beta defensin (ABD) in a vaccine formulation containing inactivated fowl adenovirus (FAdV) serotype 8b administered in ovo. Our data showed that a combination of PCEP and inactivated virus is capable of inducing a robust and long lasting antibody response. Moreover, significant enhancement of IFN-γ, IFN-α, IL-12(p40) and IL-6 gene expression under the influence of PCEP suggests that as an in ovo adjuvant PCEP has the ability to activate a substantial balanced immune response in chickens. To our knowledge, these are the first studies in which PCEP and ABD have been characterized as adjuvants for the development of an in ovo poultry vaccine. It is expected that these preliminary studies will be helpful in the development of safer and more effective in ovo vaccine against IBH and other infectious diseases affecting chickens.

Infection with an apathogenic fowl adenovirus serotype-1 strain (CELO) prevents adenoviral gizzard erosion in broilers.

Gizzard erosion in broilers due to an infection with virulent fowl adenovirus serotype 1 (FAdV-1) is an emerging disease. Although experimental studies were performed, a possible prevention strategy was not reported so far. The present study was set up to determine (i) a possible influence of birds' age at time of inoculation on the pathogenicity of a European FAdV-1 field strain (PA7127), (ii) the virulence of a apathogenic FAdV-1 strain (CELO), and (iii) its capability to protect SPF broilers from adenoviral gizzard erosion caused by the field virus. Oral infection of birds with PA7127 at 1-, 10- and 21-days of life, resulted in reduced weight gain compared to non-infected birds, with significance for birds infected at day-old. Independent of the birds' age at time of inoculation, clinical signs appearing approximately one week after challenge coincided with gizzard lesions. Birds infected exclusively with CELO at the first day of life did not show any clinical signs or pathological changes in the gizzard, confirming the apathogenicity of this European FAdV-1. A similar result was obtained for birds orally infected at the first day of life with CELO and challenged three weeks later with the pathogenic PA7127 strain. Therefore, complete protection of adenoviral gizzard erosion in broilers by vaccination of day-old birds could be demonstrated for the first time, although virus excretion was detected post challenge. Establishment of an amplification refractory mutation system quantitative PCR (ARMS-qPCR) facilitated the identification of the FAdV-1 strain and presence of challenges virus was confirmed in one sample.

Molecular differentiation and pathogenicity of Aviadenoviruses isolated during an outbreak of inclusion body hepatitis in South Africa.

Fowl adenovirus (FAdV) is a member of the genus Aviadenovirus and causes a number of economically important poultry diseases. One of these diseases, inclusion body hepatitis (IBH), has a worldwide distribution and is characterised by acute mortality (5% - 20%) in production chickens. The disease was first described in the United States of America in 1963 and has also been reported in Canada, the United Kingdom, Australia, France and Ireland, but until now, not in South Africa. Adenoviruses isolated from the first outbreak of IBH in South Africa were able to reproduce the disease in chicken embryo livers. The aim of the present study was to characterise the viruses and determine the pathogenicity of the FAdV strains responsible for the first reported case of IBH in South Africa. Polymerase chain reaction (PCR) amplification of the L1 loop region of the fowl adenovirus hexon gene using degenerate primer pair hexon A/B was used to identify the viruses that were isolated. Restriction fragment length polymorphism (RFLP) of the amplification products was used for the differentiation of 14 isolates of fowl adenovirus. Sequencing of the PCR products followed by amino acid comparison and phylogenetic analysis using the L1 loop region of the hexon protein was done to determine the identity of the isolates. Amino acid sequences of the hexon genes of all the South African isolates were compared with those of reference strains representing FAdV species. Amino acid comparison of 12 South Africa field isolates to FAdV reference strains revealed a high sequence identity (> 93.33%) with reference strains T8-A and 764. Two of the isolates had high sequence identity (93.40%) with reference strains P7-A, C2B and SR48. Phylogenetic analysis of the L1 loop region of the hexon protein of all 14 South African isolates was consistent with their RFLP clusters. The mortality rates of embryos challenged with 106 egg infective doses (EID50) FAdV 2 were 80% - 87% and mortality rates for embryos challenged with 105.95 (EID50) FAdV 8b were 65% - 80%.

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.

Outbreak of gizzard erosion associated with fowl adenovirus infection in Korea.

The pathogenicity of a fowl adenovirus serotype-1 (FAdV-1, K181 strain) isolated from a case of gizzard erosion in layer chickens was investigated in specific-pathogen-free (SPF) chicks. One-week-old SPF chicks were inoculated orally or intramuscularly with the isolate of FAdV-1 and euthanized for necropsy at 7, 14, and 21 d postinoculation. Although there were no clinical signs after inoculation, gizzard erosions were observed grossly and the virus was recovered from the gizzards in the inoculated chickens. Histologically, in the chickens that were infected orally, the lesions found in the gizzard consisted of severe degeneration and necrosis of glandular epitheliums and eosinophilic inclusion bodies. These results indicate that the Korean FAdV-1 isolate could induce gizzard lesions in chickens. Moreover, the present investigation reproduced an outbreak of gizzard erosion caused by FAdV-1 infection and, for the first time, described the isolation of FAdV-1 from chickens in Korea. These findings provide important information on the epidemiology and pathogenesis of FAdV-1 infection in chickens.

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

A total of 18 samples from 4 outbreaks of gizzard erosions in broiler chickens in Europe were used in the current study. Fowl adenoviruses were found in samples from all 4 outbreaks, and isolates were identified as Fowl adenovirus A (FAdV-A) serotype 1. As described earlier, polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis of the long fiber gene was conducted. However, all 18 samples showed the same pattern as apathogenic FAdV-1 strains: Ote and chicken embryo lethal orphan (CELO) viruses. Nucleotide and amino acid sequences of the long and short fiber of several isolates from broiler chickens with gizzard erosions were analyzed, and 100% identity between the field isolates on the protein level was revealed. Only 1 nonsynonymous mutation (T→A) was present in the long fiber of studied isolates compared to the CELO strain. The same mutation was also present in the Ote strain. Four nonsynonymous mutations were present in the long fiber of studied isolates compared to Ote strain. In the short fiber, 6 nonsynonymous mutations were found in the studied isolates compared to the CELO strain. However, the short fiber of pathogenic isolates was 100% identical to apathogenic Ote strain. In conclusion, the usefulness of PCR-RFLP analysis of the long fiber gene of FAdV-1 isolates in distinguishing between those that induce gizzard erosions and those that do not remains questionable for the isolates obtained from European poultry flocks. The role of certain FAdV-1 strains with their long and short fiber in pathogenicity regarding gizzard erosions is still not clear.

Fowl adenovirus (FAdV) serotype 4 causes depletion of B and T cells in lymphoid organs in specific pathogen-free chickens following experimental infection.

In the present investigation flow cytometric analysis and immunohistochemistry were applied together for the first time to gain new insights into the interaction between virulent fowl adenoviruses (FAdV) and the immune system of chickens. As a model for virulent FAdV infections a FAdV-4 strain was used, known as the aetiological agent of Hepatitis-Hydropericardium syndrome (HHS) in broilers sometimes also named Angara Disease. Specified pathogen-free chickens (SPF) were divided into three different groups. Group I was infected at first day of life with an attenuated form of the virus obtained through continuous cell culture passage with the virulent virus and then re-infected 3 weeks later with the virulent progenitor virus. Group II was solely infected with the virulent virus at 3 weeks and group III served as a negative control. Following infection with the virulent virus a decrease of CD3+, CD4+ and CD8+ cells was noticed in the spleen. This was accompanied by a decrease of CD4+ and CD8+ T-lymphocytes in the thymus. Those birds infected with the attenuated virus in first instance and challenged with the virulent virus did not show these pathological effects in the thymus. In the bursa of Fabricius a severe depletion of lymphocytes was observed by immunohistochemistry in birds, infected with the virulent virus. Taken together it can be concluded that an infection with FAdV-4 has profound effects on cells, of the humoral and cell-mediated immune responses. The effects are much more severe in the birds infected with the virulent virus only indicating that the preceding infection with the attenuated virus reduces significantly the adverse effects induced by the virulent virus.

Reproduction of adenoviral gizzard erosion by the horizontal transmission of fowl adenovirus serotype 1.

The horizontal transmission ability of fowl adenovirus (FAV) serotype 1 99ZH strain, isolated from chickens exhibiting gizzard erosion, was investigated. Twelve 13-day-old specific pathogen-free chickens were inoculated orally with 10(6) TCID(50)/0.05 ml of the strain. An in-pen contact group (chickens in the same pen with inoculated chickens), hedge contact group (chickens in a pen connected with pens housing inoculated chickens), non-contact group (chickens in a separate pen placed at a distance of 70 cm from the connected pens), human exposure group (chickens in the next room and attended last every day) and negative control group were examined. Each group consisted of 11 or 12 uninoculated chickens. Gizzard lesions were grossly or histologically observed from 10 days after exposure (DAE) in the in-pen contact group, and from 15 DAE in the hedge contact and non-contact groups. The FAV gene was detected by polymerase chain reaction performed on cloacal swabs taken on 5 and 13 DAE from chickens in both contact groups, and on 20 and 26 DAE from those in the non-contact group. Serum neutralizing antibodies against FAV serotype 1 were detected in chickens from 13 and 26 DAE in both contact groups and in the non-contact group, respectively. In the human exposure and negative control groups, no infection was observed. We conclude that FAV-99ZH strain spreads rapidly through direct contact with inoculated chickens, and slowly through non-contact transmission, and that adenoviral gizzard erosion is reproduced by this horizontal transmission.

Pathogenicity of fowl adenovirus isolated from gizzard erosions to immuno-suppressed chickens.

Pathogenicity of a fowl adenovirus (FAV), JM1/1 strain of serotype 1 derived from gizzard erosions of a broiler chicken, was examined to specific pathogen-free (SPF) chickens pre-treated with infectious bursal disease viruses (IBDVs) or cyclophosphamide (CY). Virulent IBDVs, classical type, were inoculated orally at 3 days of age of SPF chickens. CY was treated subcutaneously for 3 days after hatch. FAV was given orally at 30 days of age. At 40 days of age, all chickens were bled and autopsied for serology and gross observation. Gizzard lesions were ranked by the scores depending on their severities. IBDV- or CY-treated chickens showed significantly higher gizzard lesion scores than non treated birds. There were no gross lesions in any other organs except for bursal atrophy. Serologically, antibody production against FAV was highly suppressed by IBDV infection or CY treatment.

Comparison of the polymerase chain reaction-restriction fragment length polymorphism pattern of the fiber gene and pathogenicity of serotype-1 fowl adenovirus isolates from gizzard erosions and from feces of clinically healthy chickens in Japan.

The fiber gene sequence and pathogenicity of the serotype-1 fowl adenovirus (FAdV-1) isolated from gizzard erosions and from clinically normal chickens were compared among isolates. The FAdV-99ZH strain, which induced gizzard erosions, had a nucleotide sequence of the long fiber gene that was different from that of the Ote strain, which did not induce gizzard erosions. The differences could be distinguished by use of polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis. The long fiber gene of 16 FAdV-1 isolates from gizzard erosions and 10 FAdV-1 isolates from the feces of clinically normal chickens was examined by use of PCR-RFLP analysis. All 16 FAdV-1 isolates from gizzard erosions had the same restriction patterns as those of strain 99ZH; however, 10 FAdV-1 isolates from normal chickens were classified into 3 groups. Specific-pathogen-free (SPF) chickens were inoculated orally with 2 FAdV-1 isolates from gizzard erosions or 3 FAdV-1 isolates from clinically normal chickens to determine the pathogenicity of each strain. Two of 2 FAdV-1 isolates from gizzard erosions induced gizzard erosions. Two of 3 FAdV-1 isolates from normal chickens had the same PCR-RFLP patterns as those of the Ote strain, but did not induce any gizzard erosions. However, 1 FAdV-1 isolate from clinically normal chickens had the same PCR-RFLP pattern as that of strain 99ZH and induced gizzard erosions. These results indicate that there are FAdV-1 strains that have different pathogenicity; one strain induces gizzard erosions, and the other does not. Use of PCR-RFLP analysis of long fiber genes may be able to distinguish between these two strains.

Deletion of open reading frames 9, 10 and 11 from the avian adenovirus CELO genome: effect on biodistribution and humoral responses.

In this study, the in vivo effect of the 3.6 kbp deletion of the three open reading frames (ORF) 9, 10 and 11 found at the right end of the CELO genome was examined. Groups of chickens were inoculated oronasally with 10(5)-10(7) p.f.u. per animal of wild-type virus and two recombinant CELO strains (rCELO) expressing luciferase and secreted alkaline phosphatase (SEAP). The tissue biodistribution, assessed by PCR, was similar for both wild-type and recombinant viruses. The infectious viral particle titre was determined by a p.f.u. counting method and the antibody responses to the CELO vector and the SEAP antigen were evaluated by ELISA. Infectious particle titres in tissues from chickens inoculated with the wild-type CELO virus increased up to 6 days post-inoculation, and declined until 11 days while titres in organs from chickens inoculated with the rCELO strain were low and only detectable at 4 days post-inoculation. Moreover, although anti-CELO antibody levels were three times lower in sera from chickens inoculated with rCELO, antibodies directed to the heterologous SEAP antigen were detected. Based on these results, no differences in tropism were observed, but the level of production of viral particles and the humoral responses appeared to decrease. Viruses replicate less efficiently with a deletion performed at the right end of the CELO genome. Nevertheless, the presence of antibodies directed to heterologous antigens makes the CELO virus an advantageous candidate for avian vaccination.