The role of egg drop syndrome virus in acute respiratory disease of goslings

The isolation and characterizations of a duck adenovirus 1 causing Egg Drop Syndrome in ducks, China

A fowl adenovirus variant designated as DAdV-JSXZ strain was isolated from the tissue specimen of fallopian tubes of a duck case, which was submitted from a 276-day-old Cherry valley breeding duck flock experienced egg-dropping syndromes in March 2022. Full-genome sequence of the DAdV-I JSXZ strain by next-generation sequencing revealed that the complete genome length of DAdV-JSXZ strain was 33,213 nucleotides and shared a high degree of nucleotide identity (97.0-99.4 %) with other DAdV-I reference strains. In pathogenicity studies, this isolated duck JSXZ strain reproduced similar egg-dropping symptoms in healthy breeding ducks, pathologic lesions of follicular hemorrhage, and the laid eggs in low fertilization and hatchability rates. Our research findings demonstrated that DAdV-I JSXZ strain was one of the causative agents of duck egg dropping syndrome in egg-laying ducks and could cause acute respiratory symptoms in ducklings.

Fiber Protein Produced in Escherichia coli as a Subunit Vaccine Candidate Against Egg-Drop Syndrome 76

The egg-drop syndrome ‘76 (EDS ‘76) caused by duck atadenovirus A (DAdV-1) infection in laying hens leads to the decrease in egg production, causing heavy economic losses in the poultry industry; thus, vaccines with high safety and immunogenicity are needed. In this study, the DAdV-1 fiber protein expressed in Escherichia coli with codon optimization showed the hemagglutination (HA) titer of 13 log2 after purification (0.6 mg/mL). Compared with inactivated EDS ‘76 vaccine, the specific pathogen-free chickens immunized with 0.4 mL fiber protein (HA titer of 11 log2) induced an equal level of HA inhibition (HI) titer and neutralizing antibodies. Meanwhile, after immunization with fiber protein, the lowest HI titer that could provide the effect to reduce egg production rate in laying hens after the challenge was 7 log2. Moreover, fiber protein with an HA titer of 7 log2 could induce an HI titer no <7 log2 in laying hens, which was equal to or higher than the lowest HI titer (7 log2) that could reduce egg production against DAdV-1 infection significantly, indicating that it is economically feasible for vaccine development. Importantly, the HI antibodies maintained at a high level up to 180 days postimmunization contribute to the clinical application of the vaccine candidate. Overall, the fiber protein produced in E. coli is an effective subunit vaccine candidate in EDS ‘76 control for its high immunogenicity and protection in chickens.

Pathogenicity of fowl adenovirus (FAdV) serotype 4 strain SDJN in Taizhou geese

Hydropericardium hepatitis syndrome (HHS) is a fatal disease in chickens, mainly caused by fowl adenovirus serotype 4 (FAdV-4). Since June 2015, HHS has appeared in many provinces in China. The disease has spread from broilers to laying hens, breeders and Cherry Valley ducks, seriously endangering the health of the poultry industry in China. In July 2016, an infectious disease was noticed in a goose farm in Jinan, Shandong Province, China, and hydropericardium was the main finding in post mortem investigations. In the actual study, we isolated a FAdV-4 strain from the livers of naturally-infected goslings and designated it as SDJN. We first evaluated its pathogenicity by inoculating Taizhou geese at 10, 20, and 30 days of age with 10^-7.15EID₅₀/0.2 ml doses of the SDJN strain in 1 ml allantoic fluid via subcutaneous injection or oral infection. Clinical signs and pericardial effusion appeared in geese infected subcutaneously at 10 days of age, whereas 20- and 30-day-old geese were not susceptible to FAdV-4. The results of real-time PCR showed that the replication ability of FAdV-4 in geese correlated with the age. Furthermore, results from clinical chemistry showed that FAdV-4 damaged the liver and kidney in geese and the results paralleled viral load and gross lesions. Consequently, FAdV-4 was pathogenic in geese, and the pathogenicity was related to age and mode of infection. This study is the first experimental infection of FAdV-4 in geese, which will provide a basis for further understanding of the disease. RESEARCH HIGHLIGHTS Pathogenicity tests with a FAdV-4 were conducted in geese, which included data on clinical signs, gross pathology, histopathology, clinical chemistry and viral load. FAdV-4 could replicate in geese and HHS was successfully induced. Pathogenicity of FAdV-4 in geese was related to the age and routes of infection.

Real-time fluorescence loop-mediated isothermal amplification assay for direct detection of egg drop syndrome virus

Background

Egg drop syndrome (EDS), caused by the adenovirus “egg drop syndrome virus” (EDSV) causes severe economic losses through reduced egg production in breeder and layer flocks. The diagnosis of EDSV has been done by molecular tools since its complete genome sequence was identified. In order to enhance the capabilities of the real-time fluorescence loop-mediated isothermal amplification (RealAmp) assay, we aimed to apply the method for direct detection of the EDSV without viral DNA extraction. In order to detect the presence of the EDSV DNA, three pairs of primers were designed, from the conserved region of fiber gene of the EDSV.

Results

For our assay, test and control samples were directly used in the reaction mixture in 10-fold serial dilution. The target DNA was amplified at 65 °C, which yield positive results in a relatively short period of 40–45 min. The method reported in this study is highly sensitive as compared to polymerase chain reaction (PCR) and showed no sign of cross-reactivity or false positive results. The RealAmp accomplished specific identification of EDSV among a variety of poultry disease viruses.

Conclusions

The direct RealAmp can be used to detect the presence of EDSV. As our result showed, the RealAmp method could be suitable for the direct detection of other DNA viruses.

Development of a new real-time polymerase chain reaction assay to detect Duck adenovirus A DNA and application to samples from Swiss poultry flocks

Between 2008 and 2012, commercial Swiss layer and layer breeder flocks experiencing problems in laying performance were sampled and tested for infection with Duck adenovirus A (DAdV-A; previously known as Egg drop syndrome 1976 virus). Organ samples from birds sent for necropsy as well as blood samples from living animals originating from the same flocks were analyzed. To detect virus-specific DNA, a newly developed quantitative real-time polymerase chain reaction method was applied, and the presence of antibodies against DAdV-A was tested using a commercially available enzyme-linked immunosorbent assay. In 5 out of 7 investigated flocks, viral DNA was detected in tissues. In addition, antibodies against DAdV-A were detected in all of the flocks.

Full Genome Sequence of Egg Drop Syndrome Virus Strain FJ12025 Isolated from Muscovy Duckling

Egg drop syndrome virus (EDSV) strain FJ12025 was isolated from a 9-day-old Muscovy duckling. The results of the sequence showed that the genome of strain FJ12025 is 33,213 bp in length, with a G+C content of 43.03%. When comparing the genome sequence of strain FJ12025 to that of laying duck original strain AV-127, we found 50 single-nucleotide polymorphisms (SNPs) between the two viral genome sequences. A genomic sequence comparison of FJ12025 and AV-127 will help to understand the phenotypic differences between the two viruses.

Epidemiology of egg drop syndrome virus in ducks from South Korea

Egg drop syndrome virus (EDSV) is an important pathogen of poultry that decreases egg production in chickens and causes respiratory disease in goslings. In 2011, we obtained serum samples from 139 domestic Pekin ducks, 416 one-day-old Pekin ducklings, and 75 wild ducks (67 mallards and 8 pintails) to survey their exposure to EDSV. A total of 123 of 139 sera (88.5%) from Pekin ducks, 396 of the ducklings (95.2%), and 16 of 67 mallards (23.9%) were positive. Field cases of EDSV in wild and domestic ducks were investigated. Six cases from domestic Pekin ducks were identified by PCR detection and were used for virus isolation and molecular analysis. Phylogenetic analyses of the partial hexon and full fiber genes showed that the D11-JW-012 and D11-JW-017 strains among 6 isolates belonged to different clusters compared with other known strains including the 127 strain. We assessed cell growth efficiency by hemagglutination (HA) titers and cytopathic effects in duck embryo liver cells and chicken embryo liver (CEL) cells to investigate host adaptation. The D11-JW-017 strain propagated more in chicken embryo liver than the D11-JW-012 strain and the field isolate from chickens. Our results demonstrate the high prevalence of EDSV in wild and domestic ducks in South Korea and provide information on EDSV from ducks that showed variable adaptability in chickens.

Genome sequence of a waterfowl aviadenovirus, goose adenovirus 4

We present, to our knowledge, the first complete genome sequence of a waterfowl aviadenovirus, goose adenovirus (GoAdV) strain P29, and an analysis of its genetic content in comparison with five published aviadenovirus genome sequences. Of the 35 genes predicted to encode functional proteins, the central region of the genome contains 19 (IVa2 to fiber-2) that were inherited from the ancestor of all known adenoviruses. Of the remaining genes, nine have orthologues only in aviadenoviruses and seven lack orthologues in any adenovirus. We also obtained limited sequence data for a pathogenic GoAdV strain D1036/08. Phylogenetic analyses placed the two GoAdV strains monophyletically in the genus Aviadenovirus. We propose designating strains P29 and D1036/08 as GoAdV-4 and GoAdV-5, respectively.

Hepatitis and hydropericardium syndrome associated with adenovirus infection in goslings

Two outbreaks of severe acute disease characterised by hepatitis and hydropericardium were observed in young goslings on large-scale farms in Hungary. Histological examination revealed multifocal necrotic areas and two types of intranuclear inclusion bodies adjacent to necrotic areas in the liver. The most prominent type of inclusion bodies showed strong basophilic staining and completely filled the enlarged nucleus. The other type was eosinophilic and occupied the centre of the nucleus, which had margination of chromatin. In the heart, haemorrhage was associated with multifocal necrosis in the myocardium. The presence of fowl adenovirus DNA in different organs of the naturally infected goslings was detected by polymerase chain reaction (PCR). The virus was isolated, and identified as a goose adenovirus by genomic analysis. This is the first report on the involvement of a goose adenovirus in severe acute disease associated with hepatitis and hydropericardium.

Detection of a novel bat gammaherpesvirus in Hungary

This paper describes the detection of a novel herpesvirus in a Serotine bat (Eptesicus serotinus) in Hungary. The rescued animal showed signs of icterus and anorexia and died within a day, in spite of immediate supportive therapy. Autopsy confirmed the clinical picture by the major lesions observed in the liver. Histopathology revealed vacuolar degeneration in the hepatocytes and leukocytosis in the sinusoidal lumina. By electron microscopy, hydropic degeneration and apoptotic cells with a pycnotic nucleus were found in the liver. Bacteriological examinations gave negative results. As part of a routine screening project, detection of adeno- and herpesviruses from homogenised samples of the liver, lungs and small intestines was attempted by nested polymerase chain reaction (PCR) assays. The adenovirus PCR ended with negative results. The herpesvirus PCR resulted in an amplification product of specific size. The nucleotide sequence of the amplicon was determined and analysed by homology search and phylogenetic analysis. A novel herpesvirus was identified, which seemed to be most closely related to members of the genus Rhadinovirus within the subfamily Gammaherpesvirinae. The causative role of the detected rhadinovirus in the fatal condition of the Serotine bat could not be proven, but it is most likely that reactivation from a latent infection allowed the detection of the virus by PCR.

Detection of antibodies to egg drop syndrome virus in chicken serum using a field-based immunofiltration (flow-through) test

A simple, user-friendly, and rapid method to detect the presence of antibodies to egg drop syndrome 76 (EDS) virus in chicken sera based on an immunofiltration (flow-through) test was developed. Purified EDS virus antigen was coated onto nitrocellulose membranes housed in a plastic module with layers of absorbent filter pads underneath. Following addition of serum to be tested and washing, monoclonal antibodies or polyclonal serum to chicken immunoglobulin G (IgG) was used as a bridge antibody to mediate binding between EDS virus-specific IgG and protein A gold conjugate. The appearance of a pink dot indicated the presence of antibodies to EDS virus in the sample tested. The results could be obtained within 5-10 min. The developed immunofiltration test could detect antibodies in the sera of experimentally vaccinated chickens from 2 wk postvaccination. With field sera samples, this test was positive in samples having hemagglutination inhibition titers of 8 and above. This test has the potential to be used as a field-based kit to assess seroconversion in EDS-vaccinated flocks.

Isolation of bovine adenovirus serotype 6 from a calf in the United Kingdom

Two viruses, designated 99-8130(C) and 99-8130(I), were isolated in calf testis cells from the colon and ileum, respectively, of a suckled beef calf which had developed dysentery and died. Electron microscopy indicated that the mean (sd) size of the viral particles, 83 (2.5) nm, and their morphology were consistent with their being members of the family Adenoviridae. They were confirmed as adenoviruses by PCR when products of the expected size (608 bp) were amplified from both isolates by using a primer pair specific for members of the genus Atadenovirus. A comparison of the sequence of a 567 bp segment of the 99-8130(C) amplicon with that of other prototype bovine adenovirus (BAdV) strains of atadenoviruses identified the isolate as BAdV serotype 6 (BAdV-6), which had 99.3 per cent and 100 per cent identities at the nucleotide and amino acid levels, respectively, with the prototype BAdV-6 strain 671130. A virus neutralisation test was developed and indicated a high prevalence of antibody to BAdV-6 in Northern Irish cattle. There was no evidence of adenoviral inclusions in tissues from the affected calf and no antigen was detected when the tissues were stained by an immunoperoxidase technique, using a homologous antiserum raised in rabbits. The two viruses were the third reported isolation of BAdV-6, and the first from a clinically ill bovine animal.

First molecular evidence for the existence of distinct fish and snake adenoviruses

From adenovirus-like viruses originating from a fish and a snake species, a conserved part of the adenoviral DNA polymerase gene was PCR amplified, cloned and sequenced. Phylogenetic analysis showed that the snake adenovirus is closely related to the members of the proposed genus Atadenovirus, whereas the fish isolate seems to represent a separate cluster, likely a new genus.