Genome Analysis Of FAdV Attenuated Vaccine Contaminated Strain And Its Synergistic Pathogenicity With Newcastle Disease Attenuated Vaccine LaSota Strain

Fowl adenovirus(FAdV),it belongs to the genus Adenoviridae and adenovirus,which is a common infectious virus in chickens,ducks and other poultry.FAdV is divided into three groups according to different specific antigens.Currently,the I subgroup FAdV is mainly prevalent in chickens.Since 2013,the pericardial effusion-hepatitis syndrome characterized by pericardial effusion and inclusion body hepatitis has occurred in chickens in parts of Shandong and Henan provinces.A large number of epidemiological investigations have confirmed that the pathogen is FAdV-4.What is the cause of the prevalence and outbreak of FAdV-4 in China,there is no definitive conclusion yet.In the preliminary study of this experiment,the contamination of FAdV-4 was identified in the attenuated Newcastle disease chicken.It is speculated that vaccine contamination may be one of the important reasons for the spread of the disease.So is the contaminated FAdV-4 in the attenuated vaccine consistent with the prevalent strain? What is its genomic characteristics? FAdV is widely found in the digestive tract and respiratory tract of a variety of poultry,and it can maintain latent infections.Under normal circumstances,it does not show symptoms,but it is prone to symptoms when exposed to stress or other pathogens.In production,we found that some chickens suspected of being infected with FAdV developed symptoms after immunization with vaccines such as Newcastle disease attenuated vaccine.What effect does attenuated vaccine immunization have on the pathogenesis of FAdV in the body? In view of the above problems,based on the analysis of the genome of FAdV-4 vaccine-contaminated strains,this study observed the synergistic pathogenic effect of Newcastle disease attenuated vaccine LaSota strain and FAdV in chickens through systematic animal experiments.In order to study the genome characteristics of the FAdV-N22,after the genome sequence was obtained by amplification and sequencing,we applied the bioinformatics software such as MEGA and Editseq to analyze the genetic evolution relationship and thepartial sequence of the coding region of FAdV-N22.The results showed that the strain had a total of 43 protein coding regions(CDS).The genome phylogenetic tree showed that FAdV-N22 and serotype 4 belonged to the same branch.Through the phylogenetic tree we also analyzed the differences between the gene of Hexon,Fiber 1,Fiber 2 and Penton to other strains of FAdV.In our research,we found that the gene homology of Hexon is 98.5%-99.9%,the gene homology of Fiber 1 is 95.9%-99.8%,Fiber 2's gene homology reached96.8%-99.7%,Penton's gene homology reaches From 99.2% to 99.6%,and phylogenetic tree analysis showed that the strain has high homology with the domestic strains such as SD1601,NIVD2 and GX-1,and they were in the same evolutionary branch.In order to observe the vertical transmission of infectious FAdV-4 and Newcastle disease attenuated vaccine have synergistic pathogenic effects in vivo.In this study,50 SPF chicken embryos were randomly inoculated with yolk sac to simulate congenital FAdV-4 infection,and the same amount of SPF chicken embryos were inoculated with saline as control.After hatching,20 SPF chickens were inoculated with Newcastle Disease IV attenuated vaccine(LaSota strain)at 7 days old in the inoculated group and control group respectively,while the rest chickens in each group were inoculated with the same amount of PBS as the control group.The results showed that chickens infected with FAdV-4 were more susceptible to severe growth inhibition and immune organ damage after immunization with LaSota strain,it is suggested that immunization with LaSota strain can significantly enhance the pathogenicity of FAdV-4vertically transmitted infections.This study demonstrates that the synergistic effect of the vaccine against LaSota attenuated vaccine and the vertically-transmitted FAdV-4 in chickens not only enhances the virulence of FAdV-4 on SPF chickens,but also causes some adverse effects on the immune protection of LaSota vaccine.The impact suggests that our control of the disease cannot rely solely on vaccine immunization,but also on the eradication of disease from provenance.