Isolation And Characterization Of Fowl Adenovirus Type 4 And Study On The Immunogenicity Of The Strain

"Hydropericardium-hepatitis syndrome" is a poultry disease caused by serotype 4 of aviadenovirus with the characteristic of hydropericardium and inclusion body hepatitis.Outbreaks of this disease had been reported in many provinces in China since July 2015,and multiple varieties of chicken are susceptible.In this study,research on the clinical investigation of this disease and isolation of the virus were carried out by detecting serum antibody of serotype 4 of aviadenovirus via ELISA,amplifying the hexon gene by PCR,inoculating samples into SPF chick embryo eggs via yolk sac and animal regression experiment.Furthermore,the immunogenicity of one strain was evaluated by vaccination of inactivated antigen.The results shows:(1)Chicken from five farm were infected with fowl adenovirus,and 4 target genes with a size of nearly 2819bp were amplified.The 4 strains had high homology,belonging to fowl adenovirus type 4;(2)A strain of fowl adenovirus with non-hemagglutinating activity was isolated by chicken embryo eggs inoculated clinical samples from a chicken farm,and it generated the same clinical symptoms in SPF chickens by experimental infection,and typical adenovirus particles was observed with the electron microscope.The isolated strain was inoculated by three ways:yolk sac,chorioallantoic membrane and allantoic cavity,and the most suitable way for the growth of virus was by the chrioallantoic membrane which could obtain ELD50=105.1/0.1mL.The isolated strain can cause LMH cells to produce significant pathological changes;(3)The third days after the infection with the virus,the 34-day-old SPF chicken had symptoms,and the peak of death came in 4?6th days,while 7 days after infected the chicken began to recovery.The incidence was 75%,and the mortality rate was 67.86%.Serum antibody produced in the 6th day after infection and reached the highest value in the 11th day.The most obvious pathological changes were found in the liver,especially fifth days after infection.HE staining showed that there were eosinophilic and basophilic inclusion bodies in hepatocytes.Immunohistochemical staining showed that the virus was replicated in hepatocytes and splenic reticular cells;(4)21-day-old SPF chickens were administerteted with 0.2ml,0.3ml,0.5ml or lml of inactivated antigen prepared with isolated virus,and challenged with aviadenovirus type 4 on 32 days post inoculation.The mortality were 80%in control group and survival rate were 100%in immune group.Conclusion:Five poultry farm were infected with fowl adenovirus.A virulent strain of fowl adenovirus type 4 was isolated from the diseased materials collected from one of the diseased poultry farm.The strain immunized chicken after being inactivated and had a good protective effect against fowl adenovirus.