Real-time PCR assay for universal detection and quantitation of all five species of fowl adenoviruses (FAdV-A to FAdV-E)

Gizzard Erosion and Ulceration Syndrome in Moroccan Poultry Flocks and Molecular Characterization of Fowl Adenoviruses (FAdV)

Gizzard erosion and ulceration syndrome (GEUS) is caused by a fowl adenovirus serotype 1 (FAdV-1) and was first reported in laying hens in Japan in 1993. This syndrome has emerged as an epizootic in Morocco since 2014, causing significant economic losses for the poultry industry, but no involvement of a FAdV has been confirmed. Thus, the objective of this work was to assess GEUS cases that occurred in the country and to determine the role of FAdVs in their occurrence. Investigations were based on a retrospective reassessment of tissue sections and paraffin blocks of gizzards and livers from GEUS cases between 2014 and 2021 coupled with a prospective search of cases in 2022. Gizzards and livers were fixed in 10% neutral buffered formalin for histopathologic examinations according to standard methods and stored at -20 C for molecular analysis. After deparaffinizing, 10-µm-thick tissue sections along with fresh organs were subjected to DNA extraction using a commercial kit. A primer pair specific for the Hexon gene of FAdVs was used in conventional PCR; in contrast, for real-time PCR, a primer pair targeting the 52K gene was employed. In total, 24 flock cases with characteristic GEUS were assessed between 2014 and 2022. They were nine broiler cases aged between 11 and 39 days, 11 layer cases with an age between 17 and 29 wk, two cases in meat-type breeders aged 10 and 27 wk, and two flock cases of turkey poults aged 22 and 23 days. In most cases, microscopic lesions were consistent with an ulcerative and lymphoplasmocytic ventriculitis, and pathognomonic viral intranuclear inclusion bodies within degenerate epithelial cells were identified in four broiler flock cases, four layer cases, and one case in breeders and hence were highly suggestive of a FAdV infection. Among these nine cases that were positive at the histopathologic examination, six cases were found to be FAdV-PCR positive; another four cases were negative to histology but FAdV-PCR positive. Furthermore, a sequencing analysis was conducted, providing the initial evidence of the implication of FAdV-1 from species A as the cause of GEUS in Moroccan poultry. Additionally, a phylogenetic analysis was executed to facilitate a comparison between the strains investigated in this study and those identified in diverse geographic regions and across various time periods.

Genetic Sequence and Pathogenicity of Infectious Bursal Disease Virus in Chickens in Egypt During 2017-2021

The continued circulation of infectious bursal disease virus (IBDV) in Egypt, despite the use of various vaccines, is a serious problem that requires continuous detection of IBDV. In the current study, real-time reverse transcriptase polymerase chain reaction testing of 100 diseased chicken flocks during 2017-2021 revealed the presence of very virulent IBDV (vvIBDV) in 67% of the flocks, non-vvIBDV in 11%, and a mixture of both vvIBDV and non-vvIBDV in 4%. Twenty-nine IBDV isolates were submitted for partial sequencing of the viral protein 2 hypervariable region (VP2-HVR), and 27 isolates were confirmed to be genogroup A3 (vvIBDV) with 96.3%-98.5% similarity to the global A3 (vvIBDV) and 88.9%-97% similarity to genogroup A1 vaccine strains. The remaining two isolates were non-vvIBDV and showed 91.1% and 100% identity with classical genogroup A1 strains, respectively. Furthermore, the sequence and phylogenetic analysis of VP1 (amino acids 33-254) of two selected isolates of A3, 5/2017 and 98/2021, clustered them as B2, vvIBDV-like, strains with high similarity (99.5%) to four Egyptian, 99% to Chinese and European, and 97.7% to Chinese and Polish vvIBDV isolates. Experimental infection of commercial broiler chickens with two vvIBDV-A3B2 isolates (5/2017 and 98/2021) showed no mortality despite typical tissue lesions, clear histopathological changes, and strong ELISA antibody response. Isolate 98/2021 was more pathogenic, as confirmed by histopathology, whereas isolate 5/2017 induced a stronger serological response. In conclusion, vvIBDV (A3B2) strains with two amino acid (aa) substitutions in VP1 as V141I and V234I as well as VP2 as Y220F and G254S are still circulating in Egypt.

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.

Isolation, Molecular, and Histopathological Patterns of a Novel Variant of Infectious Bursal Disease Virus in Chicken Flocks in Egypt

After an extended period of detecting classical virulent, attenuated, and very virulent IBDV, a novel variant (nVarIBDV) was confirmed in Egypt in this study in 18, IBD vaccinated, chicken flocks aged 19-49 days. Partial sequence of viral protein 2 (VP2) [219 aa, 147-366, resembling 657 bp] of two obtained isolates (nos. 3 and 4) revealed nVarIBDV (genotype A2d) and OR682618 and OR682619 GenBank accession numbers were obtained. Phylogenetic analysis revealed that both nVarIBDV isolates were closely related to nVarIBDV strains (A2d) circulating in China, exhibiting 100% identity to SD-2020 and 99.5-98.1% similarity to ZD-2018-1, QZ, GX and SG19 strains, respectively. Similarity to USA variant strains, belonging to genotypes A2b (9109), A2c (GLS) and A2a (variant E), respectively, was 95.5-92.6%. Also, the VP2 hypervariable region in those two, A2d, isolates revealed greater similarities to Faragher 52/70 (Vaxxitek®) at 90.4% and to an Indian strain (Ventri-Plus®) and V217 (Xtreme®) at 89.7% and 86-88.9% in other vaccines. Histopathological examination of both the bursa of Fabricius and spleen collected from diseased chickens in flock no. 18 revealed severe atrophy. In conclusion, further studies are required to investigate the epidemiological situation of this novel genotype across the country, and to assess various vaccine protections against nVarIBDV. Additionally, vaccination of breeders with inactivated IBD vaccines including this nVarIBDV is essential to obtain specific maternal antibodies in their broilers.

Development of an ELISA for the detection of fowl adenovirus serotype -4 utilizing fiber protein

Hydropericardium syndrome (HPS), caused by the Fowl adenovirus 4 (FAdV-4) has led to significant financial losses for the poultry industry globally, including Pakistan over the past few years. Conventional serological methods are time consuming, laborious and less sensitive therefore, a rapid and sensitive ELISA kit is required for the reliable detection of FAdV-4 infection. In the current research, fiber proteins (1 &2) of FAdV-4 were successfully expressed in Escherichia coli and purified using metal affinity chromatography. Using these proteins as antigens, an indirect ELISA for detecting FAdV-4 infection was developed. The developed ELISA showed superior performances upon comparison with Serum neutralization test (SNT). This ELISA also showed reliable detection of FAdV specific antibodies in experimentally infected and vaccinated chickens. This assay produced good correlation on the samples collected from the field with SNT and found essential for large scale serology of the FAdV. No cross reactivity was observed in the ELISA following the testing of the serum samples of different other avian pathogens which showed that this ELISA is specific in detecting the FAdV infection. In conclusion, the developed Fiber protein ELISA is highly sensitive and specific in the detecting the FAdV infection and can be utilized for large scale sero-epidemiology of the disease.

Recombinant fiber-1 protein of fowl adenovirus serotype 4 induces high levels of neutralizing antibodies in immunized chickens

Virulent fowl adenovirus serotype 4 (FAdV-4) causes hydropericardium syndrome (HPS) with high mortality in chickens, leading to significant economic losses to the poultry industry. The development of an effective vaccine is essential for successful disease control. Here, we produced recombinant fiber-1 protein of FAdV-4, isolated from a Japanese HPS outbreak strain, JP/LVP-1/96, using a baculovirus expression system and evaluated its immunogenicity and protective efficacy. Recombinant fiber-1 protein induced high levels of neutralizing antibodies in immunized chickens, which were maintained for a minimum of 10 weeks. After being challenged with the virulent FAdV-4 strain JP/LVP-1/96, the immunized chickens did not exhibit clinical signs of infection or histopathological changes, there was a significant reduction in the viral load in various organs and total serum proteins, and albumin levels did not decline. These results suggest that the recombinant fiber-1 protein produced in this study can serve as a subunit vaccine to control HPS in chickens.

Detection, Quantification and Molecular Characterization of Fowl Adenoviruses Circulating in Ecuadorian Chicken Flocks during 2019-2021

Fowl adenoviruses are a group of pathogens that cause large economic losses worldwide in the poultry industry, in addition to producing a wide range of diseases, such as IBH, HHS, and enteric and respiratory diseases. The objective of this study was to quantify, identify, and molecularly characterize the types of FAdV circulating in commercial poultry farms (broilers, breeders, and layers) in Ecuador from 2019 to 2021. Molecular characterization was performed by PCR, quantification by qPCR, and subsequent sequencing for each positive sample. The results indicated that the FAdV genotypes circulating in our country are FAdV-2/D2, FAdV-6/E1, FAdV-8a/E2, and FAdV-11/D3; the samples were grouped into different groups that contain sequences that were obtained from countries in Africa, Asia, and America, and that are found in birds at different ages, since early age where can cause different clinical signs, such as diarrhea, ruffled feathers and dwarfism. Therefore, these results indicate that several genotypes of the virus are circulating in commercial poultry flocks, suggesting that biosecurity measures on farms should be improved, in addition to carrying out new or improved vaccination plans.

First Evidence of Fowl Adenovirus Induced Inclusion Body Hepatitis in Chicken in Bangladesh

Background

The livestock sector contributes 1.90% to the GDP in Bangladesh during 2021-22. Poultry is one of the important subsectors struggling with diseases. Fowl adenoviruses (FAdVs) cause numerous diseases resulting in economic losses to the poultry industry worldwide. Several FAdV serotypes cause inclusion body hepatitis in chicken. Although FAdV infection was suspected, there was no confirmatory report from Bangladesh. The study was conducted to investigate the FAdV infection and antibodies in chicken.

Methods

A total of 50 samples, each composed of liver and spleen, were collected from different chickens of Gazipur, Dinajpur, and Panchagarh district. Each location belongs to A, B, and C poultry zones of Bangladesh, respectively. Viruses were detected by real-time PCR and conventional PCR. Blood samples (n = 303) were collected at the beginning and after the recovery from infection and tested by indirect ELISA. Sequencing of PCR products was done for serotyping and phylogenetic analysis.

Results

Clinical signs were observed including anorexia, drowsiness, ruffled feathers, reduced body weight, lack of uniformity, and high mortality (15-25%). Enlarged friable liver with yellow to tan color mottled with the focal soft area, fluid in pericardial sac, swollen and hemorrhagic kidneys, enlarged congested spleen and pancreas, etc. were found on postmortem examination. FAdVs were detected in 90% of the flocks except commercial layer flock from Dinajpur. Three serotypes, namely, 8b (70%), 11 (10%), and 5 (10%) were detected. Anti-FAdV antibody was detected in 80% flocks at the beginning of infection and in 90% of the flocks after recovery from infection. The antibody titer increases significantly (p < 0.05) after recovery from infection. Phylogenetic analysis revealed that the Bangladeshi FAdVs have close identity with viruses from Asia, Europe, and South and North America.

Conclusions

These findings suggested that several introductions of FAdVs were taken place in Bangladesh. To combat the disease, vaccination along with maintenance of biosecurity is essential.

Efficacy, humoral, and cell-mediated immune response of inactivated fowl adenovirus 8b propagated in chicken embryo liver cells using bioreactor in broiler chickens

Background and Aim

Fowl adenovirus (FAdV) 8b causes inclusion body hepatitis, resulting in major economic losses globally among chickens. The objectives were to inactivate FAdV 8b isolate propagated in chicken embryo liver (CEL) cells using a stirred tank bioreactor (UPM08136P5B1) and determine the humoral and cell-mediated immune response, efficacy, and virus shedding in broiler chickens.

Materials and Methods

The FAdV 8b isolate UPM08136P5B1 was inactivated using binary ethyleneimine, adjuvanted with Montanide 71VG, inoculated into day-old broiler chickens in a booster group (BG) and non-booster group (NBG), and challenged with a pathogenic FAdV 8b strain. Clinical signs, gross lesions, body weight (BW), liver: body weight ratio, FAdV antibody titer using enzyme-linked immunosorbent assay, and histopathological changes were recorded. The CD3+, CD4+, and CD8+ T-lymphocyte profiles of the liver, spleen, and thymus using flow cytometry, and viral load in liver and cloacal shedding using quantitative polymerase chain reaction were evaluated.

Results

Chickens in the challenged control group (CCG) exhibited mild clinical signs, gross lesions, and histopathological changes, which were absent in the inoculated groups, and had lower BW and higher liver BW ratio than chickens in the unchallenged control group (UCG); BG and NBG on 35- and 42-days post-inoculation (DPI). Chickens in NBG and BG had higher antibodies than UCG on 7, 21, 35, and 42 DPI. The challenged BG and NBG produced higher antibodies than the CCG on 35 DPI. T-lymphocytes were higher among the inoculated groups than UCG in the liver, spleen, and thymus. Inoculated challenged groups recorded higher CD3+, CD4+, and CD8+ T-lymphocytes on 35 and 42 DPI than CCG. The challenged control group had a significantly higher viral load in the liver than challenged that in BG on 35 DPI and BG and NBG on 42 DPI. The challenged control group had significantly higher challenge FAdV shedding than challenged inoculated groups on 35 and NBG on 42 DPI.

Conclusion

UPM08136P5B1 was successfully inactivated and mixed with Montanide 71VG. The inactivated vaccine candidate that induced humoral and cellular immunity was effective, reduced FAdV load in the liver, and shedding in the cloaca, and could be useful against FAdV 8b infections in chickens.

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.

The first complete genome sequence and pathogenicity characterization of fowl adenovirus serotype 2 with inclusion body hepatitis and hydropericardium in China

Since 2015, fowl adenovirus (FAdV) has been frequently reported worldwide, causing serious economic losses to the poultry industry. In this study, a FAdV-2, namely GX01, was isolated from liver samples of chickens with hepatitis and hydropericardium in Guangxi Province, China. The complete genome sequence of GX01 was determined about 43,663 base pairs (bp) with 53% G+C content. To our knowledge, this is the first FAdV-2 complete genome in China. There was a deleting fragment in ORF25 gene. Phylogenetic analysis based on the hexon loop-1 gene showed that GX01 is most closely related to FAdV-2 strain 685. Pathogenicity experiment of GX01 in 3-day-old and 10-day-old specific-pathogen-free chickens showed that although no mortality was observed within 21 days post infection (dpi), strain GX01 significantly inhibited weight gain of infected chickens. Moreover, FAdV-2 was still detectable in the anal swabs of infected chickens at 21 dpi. Necropsy analysis showed that the main lesions were observed in liver, heart, and spleen. Of note, hepatitis and hydropericardium were observed in the infected chickens. In addition, massive necrosis of lymphocyte was observed in spleen of infected 3-days-old chickens. We concluded that FAdV-2 strain GX01 is capable of causing hepatitis and hydropericardium, which will make serious impact on the growth of chickens. Our research lays a foundation to investigate the molecular epidemiology and etiology of FAdV.

Molecular characterization of chicken astrovirus from high embryonic mortality based on the capsid protein (ORF2) gene, in Brazil

ABSTRACTIn recent years, reports of chicken astrovirus (CAstV) infections in commercial birds have increased, affecting the poultry industries in Brazil and worldwide. The objective of this study was to use molecular methods to characterize the CAstV found in one breeding and three different incubation companies that reported increased embryonic mortality and the appearance of birds with white chick syndrome (WCS). RT-qPCR with SyBR green chemistry were used to determine the presence of the virus in the feces of breeders, organs of newborn chickens, and unhatched embryos. By sequencing the ORF2 that codes for the viral capsid, the strains responsible for these clinical signs were characterized using strains previously reported in Brazil, North America, Europe, and Asia. The percentage of identity of the amino acid sequences compared with those from group A was less than 41% (37.01% to 40.52%) and the identity with those from subgroups Bi, Bii, and Biii was less than 90% (81.81% to 89.85%). Therefore, the sequences were characterized within subgroup Biv with identity greater than 95% (95.26% to 99.59%), together with CAstV strains previously found in Brazil, Canada, and the United States. Using antigenicity prediction tools, 14 highly conserved peptides located on the surface of the capsid protein were considered potentially responsible for inducing the immune response in the host. Our data provide important information related to the increase in embryo mortality in vertically infected birds, reinforcing the potential association of WCS with CAstV Biv subgroup.

Probiotics Surface-Delivering Fiber2 Protein of Fowl Adenovirus 4 Stimulate Protective Immunity Against Hepatitis-Hydropericardium Syndrome in Chickens

Background and Objectives

Hepatitis-hydropericardium syndrome (HHS) caused by Fowl adenoviruses serotype 4 (FAdV-4) leads to severe economic losses to the poultry industry. Although various vaccines are available, vaccines that effectively stimulate intestinal mucosal immunity are still deficient. In the present study, novel probiotics that surface-deliver Fiber2 protein, the major virulence determiner and efficient immunogen for FAdV-4, were explored to prevent this fecal–oral-transmitted virus, and the induced protective immunity was evaluated after oral immunization.

Methods

The probiotic Enterococcus faecalis strain MDXEF-1 and Lactococcus lactis NZ9000 were used as host strains to deliver surface-anchoring Fiber2 protein of FAdV-4. Then the constructed live recombinant bacteria were orally vaccinated thrice with chickens at intervals of 2 weeks. Following each immunization, immunoglobulin G (IgG) in sera, secretory immunoglobulin A (sIgA) in jejunum lavage, immune-related cytokines, and T-cell proliferation were detected. Following challenge with the highly virulent FAdV-4, the protective effects of the probiotics surface-delivering Fiber2 protein were evaluated by verifying inflammatory factors, viral load, liver function, and survival rate.

Results

The results demonstrated that probiotics surface-delivering Fiber2 protein stimulated humoral and intestinal mucosal immune responses in chickens, shown by high levels of sIgA and IgG antibodies, substantial rise in mRNA levels of cytokines, increased proliferative ability of T cells in peripheral blood, improved liver function, and reduced viral load in liver. Accordingly, adequate protection against homologous challenges and a significant increase in the overall survival rate were observed. Notably, chickens orally immunized with E. faecalis/DCpep-Fiber2-CWA were completely protected from the FAdV-4 challenge, which is better than L. lactis/DCpep-Fiber2-CWA.

Conclusion

The recombinant probiotics surface-expressing Fiber2 protein could evoke remarkable humoral and cellular immune responses, relieve injury, and functionally damage target organs. The current study indicates a promising method used for preventing FAdV-4 infection in chickens.

Oral immunization of recombinant Saccharomyces cerevisiae expressing fiber-2 of fowl adenovirus serotype 4 induces protective immunity against homologous infection

Hydropericardium-hepatitis syndrome (HHS) caused by fowl adenovirus (FAdV) serotype 4 strains is a highly contagious disease that causes significant economic loss to the global poultry industry. However, subunit vaccine against FAdV-4 infection is not yet commercially available to date. This study aims to explore the potential for oral immunization of recombinant Saccharomyces cerevisiae expressing Fiber-2 of FAdV-4 as a subunit vaccine. Here, we constructed recombinant S. cerevisiae (ST1814G/Fiber-2) expressing recombinant Fiber-2 (rFiber-2), which was displayed on the cell surface. To evaluate the immune response and protective effect of live recombinant S. cerevisiae, chickens were orally immunized with the constructed live ST1814G/Fiber-2, three times at 5-day intervals, and then challenged with FAdV-4. The results showed that oral administration of live ST1814G/Fiber-2 could stimulate the production of humoral immunity, enhance the body's antiviral activity and immune regulation ability, improve the composition of gut microbiota, provide protection against FAdV-4 challenge, reduce viral load in the liver, and alleviate the pathological damage of heart, liver, and spleen for chicken. In addition, we found the synergistic effect in combining the ST1814G/Fiber-2 yeast and inactivated vaccine to trigger stronger humoral immunity and mucosal immunity. Our results suggest that oral live ST1814G/Fiber-2 is a potentially safer auxiliary preparation strategy in controlling FAdV-4 infection.

Necrotizing Salpingitis by Fowl Adenovirus in a Backyard Hen

A 3-yr-old Ameraucana hen was received for postmortem examination following a 1-day history of lethargy and death. Gross lesions observed during necropsy were limited to pulmonary congestion and a small clump of egg yolk material in the oviductal lumen. On histopathology, there was a necrotizing salpingitis of the infundibular and isthmus mucosa with amphophilic, intranuclear inclusion bodies in superficial epithelial cells. Transmission electron microscopy identified the intranuclear inclusions as aggregates of adenovirus virions. Fowl adenovirus (FAdV) type A was identified with PCR and sequencing. Although the cause of death was not determined in this case, this is the first report of FAdV type A-associated salpingitis in a hen.

Complete Genome Characterization of Reticuloendotheliosis Virus Detected in Chickens with Multiple Viral Coinfections

Reticuloendotheliosis virus (REV) is a retroviral pathogen capable of infecting several avian hosts and is associated with immunosuppression, anemia, proventriculitis, neoplasia, and runting–stunting syndrome. Its genome contains the three major genes, gag, pol, and env, and two flanking long terminal repeat (LTR) regions. Complete genome sequences of REV are limited in terms of geographical origin. The aim of this study was to characterize the complete genome of REV detected in Brazilian chickens with multiple viral coinfections and analyze the polymorphisms in the deduced amino acids sequences corresponding to its encoded proteins. We tested the presence and completeness of REV as well as other viral pathogens in samples from Brazilian poultry farms by qPCR. The complete genomes of two REV strains were sequenced by overlapping fragments through the dideoxy method. Phylogenetic analysis, pairwise identity matrix, polymorphism identification and protein modeling were performed along the entire genome. We detected REV in 65% (26/40) of the tested samples. Concomitant viral infections were detected in 82.5% (33/40) of the samples and in 90% (9/10) of the farms. Multiple infections included up to seven viruses. Phylogenetic analysis classified both Brazilian strains into REV subtype 3, and the pairwise comparison indicated that strains from the USA and fowlpox virus (FWPV)-related strains were the most identical. The subdomain p18 in gag, the reverse transcriptase/ribonuclease H in pol, and the surface (SU) in the env protein were the most polymorphic in genomic comparisons. The relevant motifs for each protein were highly conserved, with fewer polymorphisms in the fusion peptide, immunosuppression domain, and disulfide bonds on the surface (SU) and transmembrane (TM) of env. This is the first study to include complete genomes of REV in Brazil and South America detected in farms with multiple viral coinfections. Our findings suggest an involvement of REV as an immunosuppressor and active agent in the emergence and progression of multiple infectious diseases. We also found a possible etiological relationship between Brazilian strains and the USA and FWPV recombinant strains. This information highlights the need for epidemiological vigilance regarding REV in association with another pathogens.

First Detection and Identification of FAdV-8b as the Causative Agent of an Outbreak of Inclusion Body Hepatitis in a Commercial Broiler Farm in Greece

Inclusion body hepatitis (IBH) is an economically important disease of chickens, with a worldwide distribution, caused by Fowl Aviadenoviruses (FAdVs). Currently, the increased number of cases, the virulence of the isolate strains, as well as the lack of cross-species protection highlight that detailed in-field data are fundamental for the development of successful control strategies. This case report provides a detailed clinicopathological investigation of an unusual IBH outbreak in a commercial broiler farm in the region of Macedonia, Greece. The farm consisted of 64,000 birds, originated from the same breeder stock and placed in three different houses (Flock A–C). At 20 days of age, a sudden increase in daily mortality was recorded in Flock A. It is worth mentioning that, although all flocks were serologically (indirect ELISA) and molecularly (RT-PCR) positive for FAdV, the mortality rate, attributed to IBH, was much higher in Flock A compared to others. The clinical manifestation included non-specific symptoms such as depression, inappetence, yellowish mucoid diarrhea, and lack of uniformity. At necropsy, typically, enlarged, pale, and friable livers were dominant, while sporadically lesions were recorded in the pancreas, kidneys, skeletal muscles, and lymphoid organs. The histopathological examination of liver samples showed multifocal inflammation, necrosis, and the presence of basophilic/ eosinophilic inclusion bodies in hepatocytes. In addition, the loss of the architecture of pancreatic lobules and the presence of fibrosis and foci of mononuclear cell aggregates were suggestive of chronic pancreatic inflammation. PCR analysis confirmed the presence of FAdV, belonging to species E, serotype FAdV-8b. Performance and financial calculations revealed that IBH increased Feed Conversion Ratio (FCR), feed cost/chick as well as feed cost/kg live weight, whereas the Livability (%) and the European Production Efficiency Factor (EPEF) were decreased in the most severely affected flocks (Flock A). This study is the first report of the detection and identification of FAdV serotypes associated with IBH in commercial broiler flocks in Greece. However, there is still a lack of information about the circulating FAdV serotypes in the country, and therefore epidemiological studies are needed to establish control strategies for IBH.

Pathology and Molecular Epidemiology of Fowl Adenovirus Serotype 4 Outbreaks in Broiler Chicken in Abu Dhabi Emirate, UAE

BACKGROUND

Fowl adenovirus serotype 4 (FAdV-4), causing inclusion body hepatitis (IBH) and hydropericardium hepatitis syndrome (HPS), is responsible for the significant economic losses in poultry industry worldwide. This study describes FAdV disease and molecular characteristics of the virus as the first report in UAE.

METHODOLOGY

Clinical, necropsy, histopathology, qPCR and phylogenetic analysis of hexon gene were used to diagnose and characterize the virus.

RESULTS

The age of the infected broiler chicken was 2-4 weeks. The morbidity and mortality rates ranged between 50 and 100% and 44 and 100%, respectively. Clinically, sudden onset, diarrhea, anemia and general weakness were recorded. At necropsy, acute necrotic hepatitis, with swollen, yellowish discoloration, enlarged and friable liver; hydropericarditis with hydropericardium effusions; and enlarged mottled spleen were observed. Histopathology examination revealed degeneration and necrosis, lymphocytic infiltration and inclusion bodies. The qPCR analysis detected the virus in all samples tested. Hexon gene sequence analysis identified FAdV serotype 4, species C as the major cause of FAdV infections in UAE in 2020, and this strain was closely related to FAdV-4 circulating in Saudi Arabia, Pakistan, Nepal and China.

CONCLUSION

The serotype 4, species C, was the common FAdV strain causing IBH and HPS episodes in the region. This result may help design effective vaccination programs that rely on field serotypes.

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.

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.

Recombinantly Expressed Chimeric Fibers Demonstrate Discrete Type-Specific Neutralizing Epitopes in the Fowl Aviadenovirus E (FAdV-E) Fiber, Promoting the Optimization of FAdV Fiber Subunit Vaccines towards Cross-Protection in vivo

Vaccines against inclusion body hepatitis in chickens are complicated by the involvement of antigenically diverse fowl adenovirus types. Though immunization with fiber protein confers robust protection, type specificity of fiber antibodies is an obstacle for the desired broad coverage. In this study, we utilized information on multiple linear epitopes predicted in the Fowl Aviadenovirus E (FAdV-E) fiber head (knob) to develop chimeric fibers with an exchange between two serotypes’ sequences, each containing proposed epitopes. Two consecutive segments pertaining to amino acid positions 1 to 441 and 442 to 525/523 in the fibers of FAdV-8a and -8b, types of Fowl Aviadenovirus E that cause inclusion body hepatitis, were swapped reciprocally to result in novel chimeras, crecFib-8a/8b and crecFib-8b/8a. crecFib was indistinguishable from monospecific recombinant fibers in its eactivity with different FAdV antisera in Western blotting. However, contrary to the results for monospecific fibers, crecFib induced cross-neutralizing antibodies against both serotypes in chickens. This demonstrates three nonidentical epitopes in the FAdV-E fiber, the conserved epitope detected in Western blotting and at least two epitopes participating in neutralization, being type specific and located opposite residue position 441-442. Furthermore, we supply conformational evidence for a site in the fiber knob with accessibility critical for neutralization. With such an extended neutralization spectrum compared to those of individual fibers, crecFib was anticipated to fulfill and even extend the mechanistic basis of fiber-mediated protection toward bivalent coverage. Accordingly, crecFib, administered as a single-antigen component, protected chickens simultaneously against challenge with FAdV-8a or -8b, demonstrated by up-to-complete resistance to clinical disease, prevention of target organ-related changes, and significant reduction of viral load.

IMPORTANCE The control of inclusion body hepatitis, a disease of economic importance for chicken production worldwide, is complicated by an etiology involving multiple divergent fowl adenovirus types. The fiber protein is principally efficacious in inducing neutralizing and protective antibodies in vaccinated chickens; however, it faces limitations due to its intrinsic type specificity for neutralization. In this study, based on an in silico-guided prediction of multiple epitopes in the fowl adenovirus fiber head’s loops, we designed chimeric proteins, swapping N- and C-distal fiber portions, each containing putative epitopes, between divergent types FAdV-8a and -8b. In in vitro and in vivo studies, the chimeric fiber displayed extended properties compared to those of individual monotype-specific fibers, allowing the number, distribution, functionality, and conformational bearings of epitopes of the fowl adenovirus fiber to be characterized in more detail. Importantly, the chimeric fiber induced cross-neutralizing antibodies and protective responses in chickens against infections by both serotypes, promoting the advancement of broadly protective subunit vaccination strategies against FAdV.

Molecular-based monitoring of live vaccines in dust samples from experimental and commercial chicken flocks and its potential use as a screening test

Despite the high cost of vaccination programmes, conventional methods to evaluate vaccine uptake are often impractical and costly. More recently, molecular-based testing of poultry dust has been used to monitor the "take" of Marek's disease virus and infectious laryngotracheitis virus (ILTV) live vaccines. This study aimed to provide proof-of-concept for detecting other poultry pathogens by using molecular detection of vaccine microorganisms in poultry dust of vaccinated flocks. Dust and choanal cleft and cloacal swabs were collected from chickens vaccinated against avian encephalomyelitis virus (AEV), fowlpox virus (FPV), Mycoplasma gallisepticum (MG) and Mycoplasma synoviae (MS) using live vaccines in an experimental flock. Dust samples were collected weekly from 5 commercial breeder or layer flocks from day-old up to 25 weeks of age. These flocks were vaccinated against Newcastle disease virus (NDV), infectious bronchitis virus (IBV), infectious bursal disease virus (IBDV), ILTV, fowl adenovirus (FAdV), MG and MS. Samples were tested for nucleic acids of these microorganisms by PCR or reverse transcriptase PCR. Genomes of all targeted vaccines were detected in dust samples from the experimental and commercial flocks except for FPV, which was detected only in the experimental flock. FAdV was detected in unvaccinated commercial flocks. These findings suggest that PCR detection of target organisms in dust samples has potential as a relatively simple and inexpensive population-level test to monitor vaccine take and/or pathogen status in chicken flocks. Further studies comparing the detection of each of these microorganisms in poultry dust with individual birds samples are required to validate this approach.

Identification of a novel immunological epitope on Hexon of fowl adenovirus serotype 4

Fowl adenovirus serotype 4 (FAdV-4), the causative agent of hepatitis-hydropericardium syndrome (HHS), distributed widely in the poultry farms in China. Hexon is one of the major capsid proteins associated with viral species or serotypes. However, the epitopes of Hexon protein remain largely unknown. In this study, a monoclonal antibody (mAb) specific to Hexon protein of FAdV-4, designated as 3G8, was generated. Subsequently, the linear peptide recognized by 3G8 was mapped and identified as ²¹³AYGAYVK²¹⁹ using a series of overlapping peptides generated from Hexon protein. Amino acid sequence analysis revealed that the epitope recognized by 3G8 was highly conserved across all the FAdVs. The epitope was immunogenic and could be recognized by FAdV-4 positive chicken serum samples. These findings will enrich our knowledge regarding the epitope on Hexon and provide valuable information for further characterization of the antigenicity of Hexon protein.

Pathogenicity and Immune Responses in Specific-Pathogen-Free Chickens During Fowl Adenovirus Serotype 4 Infection

Hydropericardium-hepatitis syndrome, a recently emerged disease of chickens, is caused by some strains of fowl adenovirus serotype 4 (FAdV-4). However, the relationship between the immune response and cytokine expression during FAdV-4 infection is largely unknown. In this study, our data showed that all chickens exhibited typical clinical signs and lesions and that the viral load was significantly increased in both the liver and thymus following FAdV-4 infection. We also found that the appearance of tissue lesions in the liver and thymus was consistent with the viral copy numbers, indicating that virus replication in systemic organs closely correlated with disease progression. In addition, the effects of FAdV-4 infection on the transcription of some avian cytokines were studied in vivo. In general, expression of the proinflammatory cytokines interleukin (IL)-2 and interferon (IFN)-α and IFN-β in the liver and thymus was strongly upregulated. Interestingly, the expression of IL-2 was the most highly upregulated. Expression of the anti-inflammatory cytokines IL-4, IL-10, and transforming growth factor (TGF)-β1 and TGF-β2, were also upregulated. Moreover, we investigated both the humoral and cellular immune responses in chickens infected with FAdV-4. Compared to those in the noninfected chickens, the antibody levels in chickens infected with FAdV-4 were significantly increased within 30 days postinfection. In addition, the ratio of CD4+/CD8+ T cells was decreased in FAdV-4-infected chickens. Taken together, these findings increase our understanding of the pathogenesis of FAdV-4 in chickens and provide a foundation for additional pathogenesis studies.

Emergence of fowl aviadenovirus C-4 in a backyard chicken flock in California

Fowl aviadenovirus (FAdV) species D and E are associated with inclusion body hepatitis (IBH); species C, serotype 4 (hereafter, FAdV4) is associated with hepatitis-hydropericardium syndrome (HHS) in young chickens. Outbreaks of HHS have led to significant losses in the poultry industry in several countries, predominantly in China. In April 2020, FAdV4 was detected in a remote backyard flock in California. In a mixed flock of chickens of various breeds and ages (6 mo to 2 y old), 7 of 30 were found dead within a week without premonitory signs. One additional bird died after the flock was relocated to fresh pasture, bringing the total mortality to 8 of 30 (27%). Postmortem examination of 3 birds revealed good body condition scores and active laying. One chicken had subtle hemorrhages throughout the liver, and the other 2 had diffusely dark mahogany livers. On histopathology, 2 chickens had hepatic necrosis with hepatocytes containing large, mostly basophilic, intranuclear inclusion bodies, identified by electron microscopy as 82.2-nm diameter adenoviral particles. Virus isolation and genomic sequencing performed on a liver sample revealed strains with 99.9% homology to FAdV4 isolates reported from China. To our knowledge, FAdV4 has not been reported in the United States to date. Furthermore, the chickens affected here were all adults and exhibited a variation of serotype 4 disease in which IBH was present but not hydropericardium.

Oral Immunization of Recombinant Lactococcus lactis and Enterococcus faecalis Expressing Dendritic Cell Targeting Peptide and Hexon Protein of Fowl Adenovirus 4 Induces Protective Immunity Against Homologous Infection

Hepatitis-hydropericardium syndrome (HPS) causes severe economic losses in the global poultry industry. The present study aims to explore oral immunization of recombinant Lactococcus lactis and Enterococcus faecalis expressing Hexon protein of fowl adenovirus 4 (FAdV-4). The bacteria L. lactis NZ9000 and E. faecalis MDXEF-1 were, respectively, modified as host strain to deliver truncated Hexon protein (ΔHexon) or ΔHexon protein fusing with dendritic cell (DC) targeting peptide (DC-ΔHexon) on the surface of bacteria. The expression of target protein in L. lactis NZ9000 and E. faecalis MDXEF-1 were detected by western blot. To evaluate the immune responses and protective efficacies provided by the live recombinant bacteria, chickens were immunized with the constructed ΔHexon-expressing bacteria three times at 2-week intervals, then experimentally challenged with hypervirulent FAdV-4/GX01. The results showed that oral immunizations with the four ΔHexon-expressing bacteria (NZ9000/ΔHexon-CWA, NZ9000/DC-ΔHexon-CWA, MDXEF-1/ΔHexon-CWA, and MDXEF-1/DC-ΔHexon-CWA), especially the two bacteria carrying DC-targeting peptide, stimulated higher levels of ΔHexon-specific sera IgG and secretory IgA (sIgA) in jejunal lavage fluid, higher proliferation of peripheral blood lymphocytes (PBLs) and higher levels of Th1/Th2-type cytokines, along with significantly decreased virus loads in liver and more offered protective efficacies against FAdV infection compared with PBS and empty vector control groups (p < 0.01). For chickens in the group MDXEF-1/DC-ΔHexon-CWA, the levels of aspartate transaminase (AST), alanine transaminase (ALT) and lactate dehydrogenase (LDH) in sera, and the virus loads in livers were significantly decreased vs. the other three ΔHexon-expressing bacteria (p < 0.01). The pathological changes in the hearts, livers, spleens and kidneys of chickens in MDXEF-1/DC-ΔHexon-CWA group were relatively slight compared to infection control group and other three ΔHexon-expressing bacteria groups. The rate of protection in MDXEF-1/DC-ΔHexon-CWA group was 90%. The present work demonstrated that cell surface-displayed target protein and immune enhancers in L. lactis and E. faecalis might be a promising approach to enhance immunity and immune efficacy against pathogen FAdV-4 infection.

Longitudinal Serological Monitoring of Commercial Broiler Breeders for Fowl Adenoviruses (FAdVs)-Presence of Antibodies Is Linked with Virus Excretion

Currently, the poultry industry worldwide is facing an emerging trend of fowl adenovirus (FAdV)-associated diseases with a significant economic impact, especially in meat-type chickens. Vertical transmission is an important feature of all FAdVs; hence, preventive measures mostly revolve around breeding stocks. However, knowledge about temporal development of FAdV infections in modern commercial settings is rare or even nonexistent. In the present study, longitudinal monitoring for FAdV was conducted in broiler breeder flocks located in a confined geographical region with intensive poultry production in Iran. For this, the antibody status of birds from 4 to 32 wk of age was monitored with a commercial FAdV-ELISA and virus neutralization test (VNT). In parallel, fecal shedding of FAdV was determined at the peak of egg production with real-time PCR and virus isolation. Overall, the commercial ELISA showed seroconversion of flocks before onset of production. VNT resolved in detail infection patterns of individual serotypes with a primordial FAdV-D (FAdV-2/-11) infection, frequently followed by FAdV-E (FAdV-8a, -8b) superinfection. FAdV-A (FAdV-1) was traced in half of the investigated flocks, while no evidence of infection with FAdV-C (FAdV-4, -10) was noted. Common serological profiles between different houses of the same farm indicate an overarching biosecurity. Serological profiles coupled with virological findings at the peak of egg production indicated that higher antibody levels, determined by ELISA, correlated with lower amounts of viral DNA in fecal excretion. Simultaneously, the number of isolated FAdVs belonging to distinct serotypes declined in accordance with a rise of neutralizing antibodies in birds, underlining the significance of serotype-specific antibodies in the epidemiology of FAdV in breeders. Investigations in breeders were complemented with screening of FAdV-associated diseases in local broilers over a 3-yr period; 26 cases of inclusion body hepatitis with dominant involvement of FAdV-11/FAdV-8b, one outbreak of adenoviral gizzard erosion related to FAdV-1, and no evidence of hepatitis-hydropericardium syndrome suggest that identical serotypes are maintained in the local poultry industry.

Fowl adenovirus (FAdV) fiber-based vaccine against inclusion body hepatitis (IBH) provides type-specific protection guided by humoral immunity and regulation of B and T cell response

A recombinant fowl adenovirus (FAdV) fiber protein, derived from a FAdV-8a strain, was tested for its efficacy to protect chickens against inclusion body hepatitis (IBH). FAdV-E field isolates belonging to both a homotypic (FAdV-8a) and heterotypic (-8b) serotype were used as challenge. Mechanisms underlying fiber-induced protective immunity were investigated by fiber-based ELISA, virus neutralization assays and flow cytometry of peripheral blood mononuclear cells, monitoring the temporal developments of humoral and cellular responses after vaccination and challenge exposure. Birds were clinically protected from the homologous challenge and showed a significant reduction of viral load in investigated target organs, whereas fiber-based immunity failed to counteract the heterologous serotype infection. These findings were supported in vitro by the strictly type-specific neutralizing activity of fiber immune sera. In protected birds, fiber vaccination prevented a post-challenge drop of peripheral B cells in blood. Furthermore, fiber immunization stimulated CD4⁺ T lymphocyte proliferation while moderating the CD8α⁺ T cell response and prevented challenge-induced changes in systemic monocytes/macrophages and γδ⁺ T cell subpopulations. Both vaccinated and adjuvant-only injected birds experienced a priming of systemic B cells and TCRγδ⁺ T lymphocytes, which masked possible pre-challenge effects due to the antigen. In conclusion, within FAdV-E, recombinant fiber represents a vaccine candidate to control the adverse effects of homotypic infection by eliciting an effective humoral immunity and regulating B and T cell response, whereas the failure of heterotypic protection suggests a primordial role of humoral immunity for this vaccine.

An Outbreak of Fowl Aviadenovirus A-Associated Gizzard Erosion and Ulceration in Captive Bobwhite Quail (Colinus virginianus)

A flock of captive bobwhite quail (Colinus virginianus) experienced loose droppings, depression, and increased mortality starting at 3 wk of age. Necropsy of the affected birds revealed intestines dilated with frothy and tan fluid. Irregular dark brown fissures within the koilin layer of the gizzard were found in 20%-30% of the birds. Histologically, gizzards showed multifocal koilin degeneration or fragmentation, degeneration and necrosis of the subjacent epithelial cells, and infiltration of macrophages, lymphocytes, and heterophils. Necrotic epithelial cells occasionally contained large, smudgy, basophilic intranuclear inclusion bodies with marginated nuclear chromatin. Adenoviral paracrystalline arrays composed of icosahedral virions (60-70 nm diameter) were seen on transmission electron microscopy in the nuclei of epithelial cells in the gizzard mucosa. Adenovirus was isolated from gizzard, liver, intestine, and trachea by inoculation of specific-pathogen-free embryonated chicken eggs. Homogenates of the gizzard, liver, and intestine were positive for the adenovirus hexon gene by PCR. Sequencing of PCR amplicons confirmed the virus as fowl aviadenovirus A. The study isolates showed more than 99% and 97% nucleotide identity with quail bronchitis virus and with aviadenoviruses from gizzard erosion and ulceration (GEU) in broilers, respectively. The viral isolates showed six substitutions (G1T, C174A, A229G, C513A, T579A, and G621C) of which two were nonsynonymous (G1T and A229G), resulting in a change in the translated amino acid as A1S and S77G, respectively. These results indicate that adenoviruses of the same type or species can cause different clinical presentations in quails, e.g., bronchitis or GEU.

A novel recombinase polymerase amplification assay for rapid detection of epidemic fowl adenovirus

Fowl adenovirus (FAdV) has posed a grave threat to the health of poultry, and the sudden outbreak highlights the importance of the new rapid diagnostic method for the control and prevention of transmission. Hence, in the present study, a novel recombinase polymerase amplification (RPA) assay, which was suitable for all 12 serotypes (FAdV-1 to 8a and 8b to 11) had been successfully launched to detect FAdV. Also, the entire amplification process could be completed in the isothermal condition when temperature ranged from 26 to 42°C within no more than 14 min, which was remarkably superior to endpoint polymerase chain reaction (98 min) with the same detecting sensitivity (as low as 0.1 fg viral DNA), avoiding sophisticated thermal cyclers with simple operation. Additionally, the same primers did not produce positive reactions with other viruses tested, demonstrating that the specificity of the RPA assay was acceptable. Moreover, this developed method could be efficiently used in the diagnosis of FAdV references and epidemic strains from different avian origins, thus making it a rapid, reliable, and point-of-care FAdV diagnostics tool, as well as an alternative to endpoint PCR.

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.

Interactions Among Expressed MicroRNAs and mRNAs in the Early Stages of Fowl Adenovirus Aerotype 4-Infected Leghorn Male Hepatocellular Cells

Hydropericardium-hepatitis syndrome (HHS) is caused by some strains of fowl adenovirus serotype 4 (FAdV-4). However, the mechanism of FAdV-4 entry is not well understood. Therefore, to investigate the changes in host cellular response at the early stage of FAdV-4 infection, a conjoint analysis of miRNA-seq and mRNA-seq was utilized with leghorn male hepatocellular (LMH) cells at 30, 60, and 120 min after FAdV-4 infection. In total, we identified 785 differentially expressed (DE) miRNAs and 725 DE mRNAs in FAdV-4-infected LMH cells. Most miRNAs and mRNAs, including gga-miR-148a-3p, gga-miR-148a-5p, gga-miR-15c-3p, CRK, SOCS3, and EGR1, have not previously been reported to be associated with FAdV-4 infection. The conjoint analysis of the obtained data identified 856 miRNA–mRNA pairs at three time points. The interaction network analysis showed that gga-miR-128-2-5p, gga-miR-7475-5p, novel_miR205, and TCF7L1 were located in the core of the network. Furthermore, the relationship between gga-miR-128-2-5p and its target OBSL1 was confirmed using a dual-luciferase reporter system and a real-time quantitative polymerase chain reaction assay. In vitro experiments revealed that both gga-miR-128-2-5p overexpression and OBSL1 loss of function inhibited FAdV-4 entry. These results suggested that gga-miR-128-2-5p plays an important role in FAdV-4 entry by targeting OBSL1. To the best of our knowledge, the present study is the first to analyze host miRNA and mRNA expression at the early stage of FAdV-4 infection; furthermore, the results of this study help to elucidate the molecular mechanisms of FAdV-4 entry.

Detection of fowl adenovirus D strains in wild birds in Poland by Loop-Mediated Isothermal Amplification (LAMP)

BACKGROUND

The present study on the role of strains of adenovirus in wildlife reservoirs, and their prevalence is under exploration. In several previous studies, the presence of adenovirus strains in wild birds has been investigated. Worldwide distribution and outbreaks of adenovirus infections have been reported by many authors. The present study investigated the prevalence of FAdVs in 317 samples of different bird species from the northwestern region of Poland. An applied specific, sensitive, and efficient, without cross-reactivity loop-mediated isothermal amplification (LAMP) method to gauge the prevalence of fowl adenovirus strains in wild birds was developed and used.

RESULTS

The method was based on the sequence of the loop L1 HVR1-4 region of the hexon gene of the FAdV genome reference strains FAdV-2 KT862805 (ANJ02325), FAdV-3 KT862807 (ANJ02399) and FAdV-11 KC750784 (AGK29904). The results obtained by LAMP were confirmed by real-time PCR. Among 317 samples obtained from wild birds, eight FAdV isolates (2.52%) were identified and produced a cytopathic effect (CPE) in chicken embryo kidney cells (CEK). Three FAdV types belonging to species Fowl adenovirus D were detected, which were isolated from three adenovirus types 2/3/11, and have been confirmed in three mute swans (Cygnus olor), three wild ducks (Anas platyrhynchos), one owl (Strigiformes), and one common wood pigeon (Columba palumbus).

CONCLUSIONS

This study provides the first accurate quantitative data for the replication of fowl adenovirus strains in wild birds in Poland, indicating adenovirus interspecies transmission, and demonstrating the circulation of FAdVs in wild birds.

Development and application of a novel ELISA for detecting antibodies against group I fowl adenoviruses

Since 2015, outbreaks of hepatitis-hydropericardium syndrome (HPS) caused by a novel genotype of fowl adenovirus 4 (FAdV-4) infection have created serious economic losses in China. Given that other serotypes of hypervirulent FAdVs have also been reported in poultry around the world, a common ELISA for all serotypes within the group I fowl adenoviruses (FAdV-I) is urgently needed, especially for clinical epidemic serotypes. In this study, we used high purity and concentration virions of FAdV-4 and developed a common ELISA for detecting antibodies against 12 FAdV-I serotypes. The developed ELISA was able to distinguish between antibodies against FAdV-I, FAdV-III, and other heterologous viruses without any cross-reaction. Furthermore, the ELISA showed higher sensitivity than the FAdV-1-based ELISA to the novel FAdV-4 found in China. Moreover, since there are no commercial vaccines against FAdVs in China, the ELISA was applied to detect sera samples from specific pathogen-free chickens inoculated with inactivated FAdV-1, FAdV-4, and FAdV-8a. The assay showed high sensitivities for all three detected serotypes within FAdV-I. In conclusion, a novel, common ELISA for FAdV-I was developed in this study and could be a powerful tool for seroepidemiological investigations and FAdVs vaccine development.

Successful reproduction of adenoviral gizzard erosion in 20-week-old SPF layer-type chickens and efficacious prophylaxis due to live vaccination with an apathogenic fowl adenovirus serotype 1 strain (CELO)

Recently, outbreaks of adenoviral gizzard erosion (AGE) have been documented in pullets and layers housed free range and in enriched cage systems characterized by increased mortality and a negative impact on egg production. In the present study the pathogenicity of a fowl adenovirus serotype 1 (FAdV-1) field strain as well as the aetiological role of a FAdV-8a strain, both isolated from AGE affected pullets, were investigated in vivo in 20-week-old specific-pathogen-free (SPF) layer-type chickens. Furthermore, the efficacy of a single (week 17) and double (week 14 and 17) application of a live vaccine consisting of an apathogenic FAdV-1 (CELO strain) against challenge with virulent FAdV-1 was investigated. For the first time, AGE was successfully reproduced in adult birds after oral infection of 20-week-old SPF birds with a virulent FAdV-1 field isolate, characterized by pathological changes of the gizzard from 7 days post challenge onwards. In addition, a negative impact of the FAdV-1 infection on the development of the reproductive tract was observed. Thus, confirming the pathogenicity and aetiological role of FAdV-1 in the development of AGE and economic losses due to AGE in layers. In contrast, no pathological changes were observed in birds infected with FAdV-8a. Independent of a single or double application of the live FAdV-1 vaccine strain CELO, no gross pathological changes were observed in gizzards post challenge with the virulent FAdV-1, indicating that complete protection of layers against horizontal induction of AGE was achieved. Nonetheless, virulent FAdV-1 was detected in cloacal swabs and gizzards in both vaccinated groups post challenge determined by the application of an amplification refractory mutation system quantitative PCR used to differentiate between vaccine and challenge strains.

Characterization and pathogenicity of fowl adenovirus serotype 4 isolated from eastern China

BACKGROUND

Fowl adenovirus outbreaks have occurred in China since June 2015. This virus is an emerging infectious disease that causes hydropericardium syndrome and inclusion body hepatitis (HPS-IBH), resulting in significant economic loss to poultry farmers. Five fowl adenovirus (FAdV) strains (HN, AQ, AH726, JS07 and AH712) were isolated from Jiangsu and Anhui provinces.

RESULTS

Phylogenetic analysis revealed that the five isolates belonged to species C fowl adenovirus serotype 4. An 11 amino-acid deletion in ORF29, relative to an older viral isolate, JSJ13, was observed for all five strains described here. In chicken experiments, 80-100% birds died after intramuscular inoculation and displayed lesions characteristic of HPS-IBH. The viral DNA copies were further detected by hexon-probe based real-time polymerase chain reaction (PCR) in the chicken samples. The viral loads and cytokine profiles were recorded in all the organs after infections. Despite minor genetic differences, the 5 strains displayed significantly different tissue tropisms and cytokine profiles.

CONCLUSIONS

Our data enhance the current understanding some of the factors involved in the pathogenicity and genetic diversity of the FAdV serotype 4 (FAdV-4) in China. Our work provides theoretical support for the prevention and control of HPS-IBH in chickens.

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.

Vaccination with FAdV-8a induces protection against inclusion body hepatitis caused by homologous and heterologous strains

Fowl aviadenoviruses (FAdV) are important avian pathogens, responsible for several poultry diseases prevalent worldwide, including inclusion body hepatitis (IBH). FAdV intraspecies cross-protection has been clearly demonstrated, but there is little evidence that any interspecies cross-protection exists. The present study aimed to assess the inter- and intraspecies protection between three FAdV field isolates (FAdV-8a, FAdV-8b, FAdV-11) identified in association with severe IBH outbreaks. Inocula prepared using inactivated plaque-purified virus with adjuvant Montanide™ ISA 71VG, were injected intramuscularly into 3-week-old SPF chickens. At 6-weeks of age, the birds were challenged with 10⁶ TCID₅₀ of homologous or heterologous virus intraperitoneally, and full post mortem examination performed at 4 days post-challenge. Various tissues were examined for gross and histological lesions and assessed for the presence of virus by PCR-HRM. All homologous-type vaccine/challenge groups exhibited protection against IBH lesions with no virus detected in the tissues. Unvaccinated groups challenged with virus showed evidence of FAdV-induced lesions; however, FAdV-8a demonstrated lower pathogenicity compared with FAdV-8b and FAdV-11. In the heterologous-type vaccine/challenge groups, FAdV-8a vaccine was shown to protect against challenge with both FAdV-8b and FAdV-11. FAdV-8a and 8b belong to species E and were therefore anticipated to cross-protect. However, FAdV-11 belongs to species D and therefore cross-protection by FAdV-8a was an uncharacteristic and unique finding of this study. Further research is required to disseminate the molecular basis for the interspecies cross-protection between FAdV-8a and FAdV-11. Nonetheless, the FAdV-8a isolate was shown to have substantial potential as a vaccine candidate in countries where FAdV-8a, 8b or 11 are prevalent.

A loop-mediated isothermal amplification coupling with a lateral flow dipstick for rapid and specific detection of fowl adenovirus serotype-4

Fowl adenovirus serotype-4 (FAdV-4) has been recognized as a predominant threat to the broilers aged from three to five weeks. Hydropericardium syndrome (HPS) is one of its major clinical diseases by FAdV-4 resulting in heavy economic losses. In this study, a loop-mediated isothermal amplification coupling with a lateral flow dipstick (LAMP-LFD) was developed for rapid and specific detection of fowl adenovirus serotype-4. The optimized LAMP-LFD can be completed in 60 min at 65 °C. The minimum detection limits of PCR, real-time PCR, nested PCR and LAMP-LFD are 1 × 10⁴ copies/μl, 1 × 10² copies/μl, 10 copies/μl and 10 copies/μl respectively. Moreover, the specificity of the LAMP-LFD assay is satisfactory and does not produce cross reactions with other species. In field samples, 150 samples were assayed by PCR and LAMP-LFD. They agreed on the diagnosis "positive" in 13% of clinical samples, and they agreed on the diagnosis "negative" in 85% of clinical samples. Their probability of agreement is p₀ = 147/150 = 13% + 85% = 98%. LAMP-LFD can potentially be modified and applied as a diagnostic tool for FAdV-4 infection especially in resource-limited areas, such as small breeding farms and basic veterinary labs to offer an affordable diagnostic.

Synergetic pathogenicity of Newcastle disease vaccines LaSota strain and contaminated chicken infectious anemia virus

Newcastle disease virus (NDV)-attenuated vaccine has been widely used to prevent ND in poultry flocks, while many reports also mentioned the exogenous virus contamination in attenuated vaccines, which might be the reason for the widespread of some contagious diseases. Recently, the chicken infectious anemia virus (CIAV) contamination in the NDV-attenuated vaccine was also found in China, though no systemic study has studied the pathogenicity or infection mechanism of this special transmission route. Accordingly, simulation experiments were launched using CIAV isolated from a contaminated NDV-attenuated vaccine. Results showed that using NDV-attenuated vaccine contaminated with CIAV could cause CIA in chickens with obvious symptoms, including anemia, hemorrhage, lymphoatrophy, and growth retardation, while the synergistic reaction of CIAV and LaSota prompted their multiplication in vivo and disturbed the production of antibodies against each other. And CIAV could significantly reduce the NDV antibody titers and decrease the protective effectiveness. This study showed the synergetic pathogenicity of CIAV and LaSota strain after using contaminated NDV-attenuated vaccine, helping us to understand how the CIAV causes infection and induces severe diseases with a relatively low dose through the mouth, as well as reminding us that the damage of an attenuated vaccine contaminated with CIAV even in extremely low dose is not insignificant.

Chicken infectious anemia virus helps fowl adenovirus break the protection of maternal antibody and cause inclusion body hepatitis-hydropericardium syndrome in layers after using co-contaminated Newcastle disease virus-attenuated vaccine

Inclusion body hepatitis-hydropericardium syndrome (IBH-HPS) caused by fowl adenovirus type 4 (FAdV-4) has caused huge economic losses for China in the past five years. At present, this disease is controlled in many flocks with the inactivated FAdV vaccine, but the offspring chicks of a layer breeding flock that were vaccinated with this vaccine still became infected and developed IBH-HPS with a 20% mortality rate. Analysis revealed that the NDV-attenuated vaccine in use from the above-mentioned poultry farm was simultaneously contaminated with FAdV-4 and chicken infectious anemia virus (CIAV). The FAdV and CIAV isolated from the vaccine were purified for the artificial preparation of an NDV-attenuated vaccine singly contaminated with FAdV or CIAV, or simultaneously contaminated with both of them. Seven-day-old layers with maternal FAdV antibody were inoculated with the artificially prepared, contaminated vaccines and assessed for corresponding indices. The experiments showed that no obvious symptoms occurred after using the NDV-attenuated vaccine singly contaminated with FAdV or CIAV; however, common IBH and occasional HPS-related death was found in birds after administering the NDV-attenuated vaccine co-contaminated with FAdV and CIAV. In conclusion, this study illustrated that CIAV could assist FAdV in breaking maternal FAdV antibody protection, which then caused the IBH-HPS after vaccination with the co-contaminated NDV vaccine.

Whole genome characterisation of quail deltacoronavirus detected in Poland

Quail deltacoronavirus (QdCoV) described for the first time in the United Arab Emirates in 2018 belongs to the same deltacoronavirus species as viruses discovered in swine and tree sparrows. The full-length genome of QdCoV detected in quails with enteritis in Poland has similar organization as Middle Eastern viruses although there is no NSP7c gene. The overall degree of nucleotide sequence identity was 92.4-92.6% between Polish PL/G032/2015 and Middle Eastern UAE-HKU30 QdCoV isolates. The sequences of the individual genes show similar nucleotide identities in the range of 91.4-94.7% with the exception of the S gene with lower identity of 85.6-85.7%. The most variable part of the S gene is its fragment encoding the N-terminal domain of the S protein which is responsible for receptor binding. The amino acid homology in this region between PL/G032/2015 and UAE-HKU30 QdCoVs was 74.5-74.7%. In contrast, the C-terminal domain of the S protein which is responsible for membrane fusion had an amino acid homology of 96.9%. In the phylogenetic tree, PL/G032/2015 branched separately but clustered with the UAE-HKU30 QdCoV isolates. These data suggest that PL/G032/2015 could be a new genetic/serologic variant of QdCoV.

First report of fowl adenovirus 8a from commercial broiler chickens in Egypt: molecular characterization and pathogenicity

This study was performed to isolate fowl adenovirus (FAdV) circulating in commercial meat-type chicken in Egypt during 2015 and to identify the pathogenicity of the isolated virus. Cloacal swabs were collected from 9 commercial broiler farms from chickens of 3-5 wk of age in Behira province in Egypt during 2015. FAdV was isolated on chicken embryo liver cells. The virus was identified by conventional polymerase chain reaction targeting a conserved region in the hexon gene. Moreover, phylogenetic analysis of the L1 loop of the hexon gene revealed that the isolated viruses clustered with reference strains belonging to FAdV serotype 8a. This is the first record of FAdV from Egypt on the GenBank. The isolated virus is closely related to strains directly associated with inclusion body hepatitis (IBH) causing considerable economic losses. Pathogenicity study of the virus did not show any mortality, although necropsy and histopathological examination displayed severe hepatitis and degenerative changes in the immune system after 5 d from infection, proving that the virus can cause IBH with intermittent shedding.

New Method for Differentiation of Granuloviruses (Betabaculoviruses) Based on Real-Time Polymerase Chain Reaction (Real-Time PCR)

Baculoviridae is a highly diverse family of rod-shaped viruses with double-stranded DNA. To date, almost 100 species have had their complete genomic sequences deposited in the GenBank database, a quarter of which comprises granuloviruses (GVs). Many of the genomes are sequenced using next-generation sequencing, which is currently considered the best method for characterizing new species, but it is time-consuming and expensive. Baculoviruses form a safe alternative to overused chemical pesticides and therefore there is a constant need for identifying new species that can be active components of novel biological insecticides. In this study, we have described a fast and reliable method for the detection of new and differentiation of previously analyzed granulovirus species based on a real-time polymerase chain reaction (PCR) technique with melting point curve analysis. The sequences of highly conserved baculovirus genes, such as granulin and late expression factors 8 and 9 (lef-8 and lef-9), derived from GVs available to date have been analyzed and used for degenerate primer design. The developed method was tested on a representative group of eight betabaculoviruses with comparisons of melting temperatures to allow for quick and preliminary granulovirus detection. The proposed real-time PCR procedure may be a very useful tool as an easily accessible screening method in a majority of laboratories.

Epidemiological investigation of the novel genotype avian hepatitis E virus and co-infected immunosuppressive viruses in farms with hepatic rupture haemorrhage syndrome, recently emerged in China

Since 2016, hepatic rupture haemorrhage syndrome (HRHS) appeared in chickens of China and caused huge economic loss. To assess the infection status of the avian hepatitis E virus (HEV) and co-infected viruses, including avian leukosis virus (ALV), reticuloendotheliosis virus (REV), fowl adenovirus (FAdV), and chicken infectious anaemia virus (CIAV), in farms with HRHS, 180 liver samples were collected from 24 farms in different provinces and detected by strict molecular virology methods. Results showed that the positive rates of HEV, ALV, REV, FAdV, and CIAV were 74.44%, 20.00%, 27.78%, 31.11%, and 12.22%, respectively, whereas there are also 112 samples with co-infection, for a rate of 58%. Meanwhile, the positive rate of HEV decreased gradually with age; the lowest positive rate of ALV (5.76%) and REV (19.23%) appeared in 25-35 weeks age, during which the positive rate of CIAV was the highest (19.23%); the positive rate of HEV in layers (64.00%) was lower than that of broilers (83.33%), but the positive rates of ALV (38.46%) and CIAV (15.38%) in layers were higher than that of broilers (5.88%, 9.80%); the positive rates of HEV (75.88%) and CIAV (15.60%) in parental generation (PG) were higher than that of commodity generation (CG, 64.10%, 0.00%), whereas the positive rate of ALV showed inverse relationship (PG: 14.89%; CG: 38.46%). Additionally, phylogenetic analysis showed that all the avian HEV identified this study belong to a novel genotype, and found the close relationship between the wild strains (REV and CIAV) and corresponding isolates from contaminated vaccine. The data presented in this report will enhance the current understanding of the epidemiology characteristics in farms with HRHS in China.

Pathogenic, Phylogenetic, and Serological Analysis of Group I Fowl Adenovirus Serotype 4 SDSX Isolated From Shandong, China

Hydropericardium hepatitis syndrome (HHS) caused by group I fowl adenovirus serotype 4 (FAdV-4) is an acute and infectious disease in fowl, particularly in broilers aged 3–5 weeks. In June 2015, a highly pathogenic disease outbroke in 25–40 day-old ducklings in Shandong province, characterized similar symptom to HHS. In order to determine the pathogenic mechanism of FAdV-4 (SDSX strain) in meat ducks. We divided 90 25-day-old Cherry Valley meat ducks into three groups (oral, subcutaneous, and control; 30 ducks in each group) and infected them with the virus. HHS, inclusion body hepatitis, and enlargement and hemorrhage of the spleen, kidney, lung, thymus, and brain were observed in FAdV-4-infected meat ducks. Histopathological changes were mainly characterized by severe fatty degeneration in the liver, basophilic inclusion bodies in hepatocytes, and vacuolation in the bursa. More importantly, viral DNA could be detected by quantitative real-time polymerase chain reaction in several viscera tissues (e.g., heart, liver, spleen) on the third day after infection. Notably, the livers of the two infected groups contained the highest concentration of viral DNA. In addition, immune responses were studied based on titer levels of the virus antibody and the levels of inflammatory cytokines interleukin (IL)-2 and interferon (IFN)-γ, and most levels were significantly upregulated, indicating that the host immune responses were activated early in infection. These findings increase our understanding of the pathogenicity of FAdV-4 (SDSX) in meat ducks and provide the foundation for further in-depth study of the pathogenic mechanism of this virus.

Shell-Less Egg Syndrome (SES) Widespread in Western Canadian Layer Operations Is Linked to a Massachusetts (Mass) Type Infectious Bronchitis Virus (IBV) Isolate

A disease with a sudden drop in egg production and shell-less eggs called, shell-less egg syndrome (SES) has been observed in Western Canada egg layer flocks since 2010. The etiology of this disease is not known. We hypothesize that SES is caused by an infectious bronchitis virus (IBV) strain since it is known that IBV replicates in the shell gland causing various eggshell abnormalities. In this study, we screened egg layer flocks, in the provinces of Alberta (AB) and Saskatchewan (SK), with and without a history of SES for the presence of IBV infection. During 2015⁻2016, a total of 27 egg layer flocks were screened in AB (n = 7) and SK (n = 20). Eighty-one percent of the screened flocks (n = 22) were positive for IBV infection. Thirty of these isolates were successfully characterized using molecular tools targeting the most variable spike (S) 1 gene. IBV isolates from this study clustered into three genotypes based on partial S1 gene variability. The majority of the IBV isolates (70%) were Massachusetts (Mass) type, and the rest were either Connecticut (Conn) type or an uncharacterized genotype with genetic characteristics of Mass and Conn types. Since the majority of the IBV isolates included within the Mass type, we used a Mass type IBV isolate to reproduce SES in specific pathogen free (SPF) white leghorn chickens in lay. Further studies are warranted to investigate whether other IBV isolates can cause SES, to clarify the pathogenesis of SES and to develop a vaccine in order to prevent SES as observed in Western Canadian layer flocks.

Newcastle disease virus-attenuated vaccine LaSota played a key role in the pathogenicity of contaminated exogenous virus

Newcastle disease virus (NDV)-attenuated vaccine has been widely used since the 1950s and made great progress in preventing and controlling Newcastle disease. However, many reports mention exogenous virus contamination in attenuated vaccines, while co-contamination with fowl adenovirus (FAdV) and chicken infectious anaemia virus (CIAV) in the NDV-attenuated vaccine also emerged in China recently, which proved to be an important reason for the outbreaks of inclusion body hepatitis–hydropericardium syndrome in some flocks. It is amazing that exogenous virus contamination at extremely low doses still infected chickens and induced severe disease; thus, we speculated that there must be some interaction between the NDV-attenuated vaccine and the contaminated exogenous viruses within. Accordingly, simulation experiments were launched using FAdV and CIAV isolated from the abovementioned vaccine. The results showed that the pathogenicity of FAdV and CIAV co-infection through the contaminated vaccine was significantly higher than that of direct oral infection, while the synergistic reaction of these viruses and LaSota prompted their multiplication in vivo and disturbed the production of antibodies against each other. This study showed the interactions of FAdV, CIAV and LaSota after using contaminated NDV-attenuated vaccine, helping us to understand how the contaminated exogenous viruses cause infection and induce severe disease at a relatively low dose through the oral route.