Isolation,Identification And Pathogenicity Of Fowl Adenovirus Serotype 4(FAdV-4) In Jinzhong Area

Fowl adenoviruses(FAdV)are a very diverse group of pathogens,which can cause many diseases.Usually,growth and replication of the FAdV within chickens does not cause obvious clinical symptoms.However,they can quickly take on the role of opportunistic pathogens when additional factors,particularly concurrent infections,adversely affect the health of the avian host.Avian adenovirus of all serotypes can induce inclusion body hepatitis in chickens,but only group Ⅰ 4 avian adenovirus is the specific pathogen of pericardial hydronephrosis and inclusion body hepatitis syndrome(HPS-IBH).The aim of the study is to determine the serotype and pathogenicity of FAdV in Jinzhong area.To achieve this,diseased chickens were diagnosed by clinical diagnosis and pathological examination,and tissue samples were detected via amplifying the hexon gene by PCR using DNA extracted from liver.Then,inoculating samples into SPF chick embryo eggs combined with PCR amplification were conducted to isolate fowl adenovirus serotype 4(FAdV-4);Finally,the isolated strain was inoculated into chickens to analyze its pathogenicity.1.Clinical signs were depression and messy feathers.Pathological changes of 8 chickens were characterized by pericardial effusion,hepatitis and other characteristic pathological changes of FAdV-4.After electrophoresis,the amplified product size was 330 bp,which was consistent with the expected size of the FAdV-4 hexon gene fragment.The sequencing results were analyzed by Basic Local Alignment Search Tool(BLAST)in NCBI,which revealed that it had 100%sequence identity to the sequence of FAdV-4 hexon gene.2.The death of chick embryo came in 3rd-4th days after inoculation.the dead chick embryo appeared bleeding point on its body;The chick embryo infected was small compared with the chicken embryo of the same age in control group,which revealed that its growth and development were restrained;Dissection observed was that the liver enlarged with yellow brown coloring.The results of PCR amplification of DNA extracted from allantoic fluid by using specific primers of FAdV-4 hexon gene were in line with the expectation,as the amplified product size was 330 bp.PCR amplification of the genes of AIV-H5,AIV-H9,NDV and IBV-SI-2 using specific primers,respectively,showed on band after electrophoresis.3.Twenty 20-day-old SPF chickens were randomly divided into two groups of 10 chickens each.It was found that the chickens began to die in the 5th day after infection.a clear,straw-colored fluid in the pericardial sac;the liver was enlarged and coloured to brown-yellow,and its texture was brittle and fragile,as well as hemorrhagic necrotic foci were seen on the surface of the liver.The kidneys are swollen,pale and characterized by uric acid deposition.4.Histopathological observation showed that myocardial fibers of chickens in experimental group became thicker together with intercalated disc disappeared,large area edema,hemorrhage and degenerative lesion.The appearance of hepatocyte necrosis,monocyte infiltration and basophilic intranuclear inclusion bodies in hepatocytes were observed.Central diffuse swelling,degeneration and necrosis occured in the hepatic lobules.Meanwhile,cytoplasm vacuolation and cell membrane rupture were observed.Also,hepatic sinusoids became smaller,and hepatocyte atrophy and nuclear pyknosis occured.Histopathological changes of kidney were characterized by extensive congestion,renal tubular epithelial cell granulosa degeneration and urinary cast.However,there were no clinical symptom and histopathological change in the control group.To sum up,isolation and identification of adenovirus were firstly carried out from chickens suspected to be infected with avian adenovirus in Jinzhong area,and the results showed that the diseased chickens from different chicken farms in Jinzhong area were infected with FAdV-4.Then the pathogenicity of the isolated FAdV-4 showed that its infection was characterized by acute symptoms.and high mortality rate.The results of our study will provide important clues for the prevention and control of avian adenovirus in this area.