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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. • This is the first time to report the complete viral genome of DAdV-1 in breeding ducks. • This study provides scientific evidence that DAdV-1 could be one of the pathogens of duck egg drop. • This study provides evidence of possible vertical transmission of DAdV-1. [ABSTRACT FROM AUTHOR]

Highlights • The DTMUV virus strain was attenuated via passaging serially in chicken embryos and duck embryos alternately for 100 passages. • The 70th adapted strain, designated SDS-70, was used as the live attenuated vaccine candidate. • After immunization with SDS-70 strain, the ducklings obtained the protection of 100% against the attack of the SDS-10 virulent strain. • Substitutions of 33 base were present in the SDS-20/40/60/80/100 sequence, which included 15 neutral mutations and 18 amino acid mutations. Abstract Infection with duck Tembusu virus (DTMUV) can cause large economic losses to the duck-rearing industry in China. In this study, we isolated a virulent strain of DTMUV (SDS) from sparrows near a duck farm and attenuated it via serially passaging (alternately for 100 passages) in specific pathogen-free chicken and duck embryos. We attenuated the virus after the 60th passage (SDS-60), based on the production of embryos that were free of visible lesions and still alive. The 70th adapted strain (SDS-70), obtained with a virus titer of 10−2.46 EID 50 was chosen to be the live attenuated vaccine. After immunizing ducklings with the SDS-70 strain, they obtained 100% protection against infection by the SDS-10 virulent strain. Our data demonstrate that the vaccine can protect ducks from becoming infected with TMUV. Our study also shows that this newly developed attenuated vaccine candidate provides excellent immunogenicity, is safe, and has the potential to control DTMUV infections in ducks. [ABSTRACT FROM AUTHOR]

Hydropericardium hepatitis syndrome (HHS), a novel poultry disease, is caused by fowl adenovirus 4 (FAdV-4). It mainly infects 3–5-week-old broilers. In July 2015, the first outbreak of HHS occurred in the broilers in east China, which caused great economic losses to the poultry industry. In June 2019, infectious disease was detected with suspected HHS symptoms on a duck farm in Linyi City, Shandong Province. The main necropsy lesions included pericardial effusion and hepatitis. In this study, we isolated a strain of FAdV-4 from naturally infected ducks and named it SDLY190604, and the hexon gene sequence was amplified and analyzed using polymerase chain reaction (PCR). In order to study the effect of FAdV-4 on Cherry Valley ducks, we inoculated three-week-old ducks with 0.2 ml of FAdV-4 virus fluid (TCID 50 of 10-6.3/0.1 ml) by orally, subcutaneously and intramuscularly. Clinical signs, gross lesions and histopathological changes, cytokines and viral load were detected and recorded within 15 days after infection. The results showed that ducks in the experimental groups exhibited typical symptoms of hydropericardium and hepatitis. The histopathological sections showed multiple-organ damage, including serious liver and kidney damage with elevated levels of inflammatory cytokines, probably due to the infection and innate immune response. Later, immunosuppression occurred, resulting in decreased levels of cytokines. The viral load indicated that the virus could be present in several organs of the ducks, with the highest viral DNA found in the liver, followed by the kidney. Compared to the subcutaneous and oral groups, the intramuscular group exhibited the highest viral load. In summary, this study can increase our understanding of the pathogenicity of FAdV-4 in ducks and provide a basis for further understanding of the virus, imparting new insights into disease research. • A pathogenic model of FAdV-4 isolates to three-week-old commercial ducks was established. • Different routes of infection can lead to duck mortality, more pronounced in the intramuscular injection group. • FAdV-4 has caused varying degrees of damage to various tissues and organs. [ABSTRACT FROM AUTHOR]

Since 2017, duck spleen necrosis caused by new variant duck orthoreovirus (N-DRV) infection had been observed in several provinces in China. This disease retards the growth and development of ducks, thereby reducing feed return rate. N-DRV infection causes damage to duck spleen and other immune organs, leading to immunosuppression and susceptibility to other pathogens. In this study, we successfully constructed a breeding duck artificial infection model and found that N-DRV infection can cause pathologic changes, such as ovarian hemorrhage, follicle atrophy, and fallopian tube bleeding in breeding ducks, resulting in significantly reduced fertilization rate and egg hatching rate. Viral RNA was present in egg vitelline membrane, duck embryo, and duckling's spleen samples, as determined through quantitative polymerase chain reaction (qPCR). Autopsy revealed obvious pathologic changes in the spleen and other organs, although there were no obvious early clinical symptoms observed in ducklings. Sequence distance and phylogenetic analysis confirmed that N-DRV-SD19 re-isolated from the spleen samples of ducklings was consistent with the strain N-DRV-XT18 used for infecting breeding ducks. The findings in this study confirmed that N-DRV can be vertically transmitted through eggs, which provide an important reference for the disease prevention and control. [ABSTRACT FROM AUTHOR]

• The strain in this study which we named N-DRV-XT18 is a new epidemic variant strain, which has obvious genetic evolution difference compared with the previously reported strains. • There is no report on the pathogenicity of the variant duck orthoreovirus. • This is the first report on the pathogenicity of this strain on cherry valley duckling. • N-DRV-XT18 strain can significantly inhibit the weight growth of infected ducks, reduce the feed return rate, and cause severe spleen necrosis and other immune organ damage. • N-DRV RNA can be detected continuously in cloacal swabs of both oral and injection group post infection. N-DRV has extensive tissue tropism and can quickly invade and replicate in various tissues and organs, including the brain. Since 2017, a disease that is characterized by spleen necrosis and swelling has emerged in China's main meat duck breeding provinces, this disease generally causes a large number of ducks to develop a poor mental state and either an increase or loss of appetite, as well as potentially resulting in death. Necrosis of spleen in this disease weakens the duck's immunity, therefore often leading to secondary infection. The net result of this is significant economic loss to China's duck breeding industry. In our previous research, we determined that the pathogen causing this disease is a new variant duck orthoreovirus (N-DRV). Because the morbidity and mortality rates of the isolate were higher than those of the previously reported strains, 180 healthy 1-day-old Cherry Valley ducklings were selected to be artificially infected in order to determine the pathogenicity of the strain. The weight gains of numbers of the infected group were significantly inhibited after they had been inoculated with the virus, which continued to detoxify in the blood and the cloaca. The main target organ of the virus is the spleen, although the virus can also attack the brain, this does not lead to any obvious pathology in this organ. These findings have enriched our understanding of the N-DRV-XT18 virus and have lain the foundation for further study of the pathogenic mechanism of this virus. [ABSTRACT FROM AUTHOR]