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Fowl adenovirus mainly causes hydropericardium hepatitis syndrome (HHS), inclusion body hepatitis (IBH) and gizzard erosion (GE), etc. In 2015, the first outbreak of HHS was reported in broiler chickens in central China, followed by an outbreak in waterfowl. The first outbreak of HHS in broiler flocks in central China in 2015, followed by outbreaks in waterfowl, has severely restricted the healthy development of the poultry industry. During the investigation, fowl adenovirus was detected in ducklings from a total of seven hatcheries in Shandong, Inner Mongolia and Jiangsu provinces. In addition, the DNA of fowl adenovirus was detected in breeding ducks and their progeny. To test the hypothesis that FAdV can be transmitted vertically, sixty 250-day-old Cherry Valley breeder ducks were divided equally into three groups for experimental infection. FAdV-8b SDLY isolate (duck/Shandong/SDLY/2021, SDLY) preserved in our laboratory was injected intramuscularly into group A and inoculated orally into group B. FAdV-8b DNA was detected in the yolk membranes, embryos and allantoic fluid of duck embryos in the FAdV-infected group after inoculation. In addition, the FAdV-8b hexon gene isolated from yolk membranes, embryos, allantoic fluid and duck eggs was close to 100% nucleotide homology to the FAdV-8b hexon gene isolated from laying duck ovaries, indicating that fowl adenovirus can be transmitted vertically in ducks. These findings provide evidence for the possible vertical transmission of fowl adenovirus from breeder ducks to ducklings. • A high prevalence of FAdVs was observed in breeding duck flocks. • Sixty 250-day-old Cherry Valley breeder ducks were randomly divided into three groups for experimental infection. • After the inoculation, FAdV-8b could be detected in anal swabs of the infected groups. • FAdV-8b DNA can be detected in the offspring hatched after infection, and some clinical symptoms can be observed. • FAdV-8b may be transmitted vertically in breeding ducks. [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]

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]

• After attacked by TMUV, the immune system especially innate immunity is activated immediately, which acts as the first line to resist viral invasion. • The adaptive immunity strengthens subsequently as TMUV further infection and maintains for a long time. • Dynamic variations of lymphoid organs after challenging were monitored, demonstrating that the damage of immune organs (spleen, thymus and bursa) may be a direct factor causing ducklings to be susceptible to TMUV attacks. Tembusu Virus (TMUV), a pathogenic member of Flavivirus family, acts as the causative agent of egg-laying and has severely threatened the duck industry over the past few years. Thus far, the pathogenicity of such virus has been extensively studied, whereas TMUV on immune system has been less comprehensively assessed, especially on ducklings that exhibit more susceptible to TMUV attack. Accordingly, in the present study, 5-day-old ducklings were infected with TMUV-TC2B (104 TCID 50) via intravenous injection, and mock ones were inoculated with phosphate-buffered saline (PBS) in identical manner as control. At 1 day-post inoculation (dpi), the innate immunity was strongly activated, and reacted rapidly to TMUV invasion, which was reflected as the significantly up-regulated IFN-stimulated genes (ISGs), especially in immune organs (e.g., thymus, bursa of Fabricius (BF) and spleen). Subsequently, under the continuous monitoring, the levels of IgA, IgM and IgG acting as the representative immunoglobulins (Igs) were constantly higher than those of mock ducklings, demonstrating that humoral immunity also played a major role in anti-virus infection. Despite the immune system activated positively, TMUV still caused systemic infection, and in particular, the immune organs were subject to severe damage in the early infection. With our constant observation, the injury of spleen and BF turned out to be getting more serious, and at 6 dpi, TMUV antigen was widely detected in both of two immune organs by immunohistochemistry (IHC) and main histopathological lesion presented as lymphocytopenia. Moreover, the elevated apoptosis rate of splenic lymphocytes and the alteration of immune organ index also revealed the damage of lymphoid organs and similarly, it is worth noting that severe damages were detected in thymus of TMUV-infected ducklings as well. In brief, the present study systematically described the dynamic damage of immune system after being attacked by TMUV and presented insights into the research of pathogenicity. [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]