| Avian adenovirus(FAdV),which belongs to the genus adenoviridae,is a double-stranded DNA virus without envelope.According to the difference of immunogenicity,FAdV can be divided into 3 groups.Adenovirus group ?(FAdV-?),which is studied most popularly and widely,can be divided into 5 genuses and 12 serotypes,including species A(serotype 1),B(serotype 5),C(serotype 4,10),D(serotype 2,3,9,11)and E(serotype 6,7,8a,8b).At present,80% of FAdV isolates in China are associated with serum type 4(FAdV-4).FAdV-4 is the pathogen of chicken pericardial effusion syndrome(HPS),causing acute infectious diseases characterized by pericardial effusion and inclusion body hepatitis.Since the first outbreak of FAdV-4 in Chinese chicken flocks in 2015,infection has been widely reported in ducks.Mixed infection often occurs with duck circovirus,duck hepatitis virus,duck Tambusu virus and so on,which seriously threatens the healthy development of duck industry.In order to investigate the epidemic status of FAdV in ducks in Shandong Province and to explore the pathogenicity of adenoviruses from different sources to ducklings,we collected237 clinical samples from 21 duck farms in 8 regions of central and western Shandong Province from 2019 to 2020 to investigate,including pathogen detection,isolation and identification,amplification of Hexon gene of isolated strains for genetic evolution and amino acid site mutation analysis.Duck FAdV(named CHSD-2)was purified by plaque test and high-throughput sequencing,its whole genome sequence was analyzed,and the source of infection of duck adenovirus was investigated.18 batches of 93 1-day-old ducklings and 16 chicken yolk antibodies used for epidemic prevention in duck farms in Shandong Province were randomly collected for pathogen detection.Then the pathogenicity of duck FAdV-4 was compared with that of chicken FAdV-4.Through infection test in vivo and in vitro,the virus proliferation,the expression level of inflammatory factor m RNA,the level of serum antibody and the injury response of tissues and organs were studied systematically.The results showed that 68 of the 237 samples detected FAdV,positive rate of 28.69%,and the positive rate of FAdV was higher in winter and summer.In this study,16 strains of duck FAdV were all belongs to FAdV-4;.All the isolates were highly homologous to chicken FAdV-4.The amino acid homology of Hexon protein with the reference strain was99.1%-99.9%,only a few amino acid mutations occurred,and the Hexon amino acid homology among the isolates was 98.6%-100%.The genome length of the purified isolate CHSD-2 was 43724 bp,and the nucleotide homology of the whole genome between the purified isolate and the reference strain of chicken FAdV-4 was 100%.The results of traceability investigation of FAdV showed that the positive rate of FAdV,was as high as 56%in 9 out of 93 1-day-old ducklings from randomly selected duck breeding farms in Shandong Province without detection of FAdV,16 crude chicken yolk antibodies.35%.In the experiment of infection in vitro,it was found that duck-derived and chicken-derived FAdV-4 could replicate in hepatocellular carcinoma cells,but the proliferation efficiency in chicken primary fibroblasts,duck primary hepatocytes and duck primary fibroblasts was lower.Generally speaking,the proliferation ability of the two strains in liver-derived cells was stronger than that in fibroblasts.The in vivo infection experiment showed that duck and chicken FAdV-4 infected antibody negative ducklings through intramuscular injection,chicken FAdV-4 infection group could cause mental depression in ducklings,and there was no death in both infection groups.Autopsy examination showed how many yellowish pericardial effusion,liver was yellowish,slightly swollen,no necrotic foci or bleeding spots were found,and the spleen of chicken FAdV-4 infection group was dark red and slightly enlarged.Histopathological observation showed that both infection groups could cause hepatocyte granular degeneration and steatosis,brain tissue hyperemia and a small amount of glial cell proliferation.There were partial loss of lymphocytes and infiltration of heterophilic granulocytes in the spleen of the duck FAdV-4 infected group,and the immune organ indexes of spleen,bursa of Fabricius and thymus in the two infected groups were higher than those in the control group in the early stage and lower than those in the control group in the later stage.Quantitative detection of viral load in tissues showed that the number of viral copies in the liver was significantly higher than that in other tissues.The viral load reached the peak on the 3rd day in the chicken FAdV-4 infection group and on the 7th day after infection in the duck FAdV-4 infection group,and then decreased sharply.Through the detection of the levels of immune factors m RNA in the liver and heart of the two infected groups,it was found that the expression levels of IRF-1,IRF-7 and IFN-? m RNA in the liver and heart of the two infected groups were down-regulated compared with the control group,while the two viruses upregulated IFN-? from 3 to 5 days after infection.In the process of infection,the inflammatory cytokines(IL-1 ?,IL-2,IL-6,IL-8)in the liver were not upregulated in the two infection groups,but up-regulated in the heart.Isolation and identification of duck-derived adenovirus in some areas of Shandong province and comparison of the pathogenicity of duck-derived adenovirus with Chicken derived adenovirus in vitro and in vivo showed that there was a high proportion of FAdV-4infection in some areas of Shandong,and most of them were mixed with other pathogens.The epidemic strains of FAdV-4 in ducks are highly homologous to those in chickens,and the source of infection of adenoviruses in ducks may be closely related to the abuse of virus-carrying chicken egg yolk antibodies.Duck-derived and chicken-derived FAdV-4mainly damaged the liver of ducklings,but did not form inclusion bodies.It has strong infection pathogenicity to chicken liver cancer cells in vitro and low pathogenicity to chicken and duck primary cells. |
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