Comparative Pathology Study On Pathogenicity Of FAdV-4 And FAdV-8b Isolates

Fowl adenoviruses(FAdVs)are non-enveloped double-stranded DNA virus belonging to the family Adenoviridae,genus Aviadenovirus.It is divided into three groups according to the difference in antigenicity(FAdV-?~III),group I is divided into 5 species(A~E)and 12serotypes(FAdV-1 to 11,FAdV-8 is divided into a and b types),FAdV-I can cause chicken hydropericardium syndrome(HPS)and inclusion body hepatitis(IBH).HPS is caused by infection with serotype 4 fowl adenovirus(FAdV-4),IBH can be caused by multiple serotypes FAdV of FAdV-8b,FAdV-7 and FAdV-11.The livers of HPS and IBH-affected chickens showed hemorrhagic necrosis and formation of intranuclear inclusion bodies.The liver lesions are the same in both livers,but only HPS had a pericardial effusion and caused acute death.In 2015,HPS suddenly exploded in a large area in China,and the mortality rate of chickens in the affected group was 20% to 70%,which caused the poultry industry to suffer huge economic losses.In order to explore the similarities and differences of HPS and IBH pathogenicity,this study intends to compare the pathogenicity of FAdV-4 and FAdV-8b serotypes of FAdV isolated in our laboratory,and to test for viral proliferation and inflammatory factors through in vitro and in vivo infection tests.Differential expression pathology studies were performed on mRNA expression levels and injurious responses of organs and cells.The results showed that the two viruses infected SPF chicks subcutaneously through the neck.The clinical manifestations,virus replication ability and pathological changes of the infected chickens in the two groups were different.FAdV-4 infected chicks showed obvious mental wilting and acute death.The mortality rate was 60%;the chicks in the FAdV-8b infection group only showed mental depression;by necropsy,FAdV-4 caused the capsules in the pericardial cavity of the chicks,hepatic spotted hemorrhage,point necrosis,lung,spleen,kidney,pancreas and other organs have different degrees of edema;FAdV-8b infected chickenliver spotted hemorrhage,point necrosis,but did not show pericardial effusion lesions and extensive organ tissue edema.Histopathological observation showed that both FAdV-4 and FAdV-8b could cause different degrees of inflammatory reaction in kidney,pancreas and duodenum of chicks,and necrosis of lymphocytes in bursa of fabricius,thymus and spleen.Immunohistochemical detection revealed that the livers of SPF chicks infected with FAdV-4and FAdV-8b showed obvious positive reactions.The brown virions in the nucleus of the diseased liver cells were found,but non-positive virions were found in the heart.Two virus were infected bursa thymus and immune organ index pre chicks were lower than the control group,while the latter part of the immune organ index began to rise,higher than in the late stage of infection of immune organ index of spleen.The pathogenicity of the two viruses compared to the FAdV-4 isolate was stronger than that of FAdV-8b.In vitro,infection experiments showed that the two viruses can replicate in hepatocellular carcinoma cells,and FAdV-4 proliferates in a small amount in cardiomyocytes.the proliferation efficiency of FAdV-8b is extremely low by quantitative real-time PCR.Both viruses could not proliferate in cardiac fibroblasts(CF);By detecting the mRNA expression of Il1?,Il6,Il8 and Tnf? cytokines,both viruses can cause different degrees of inflammatory damage in liver cells,chicken liver cancer cells and cardiomyocytes.In response,FAdV-8b caused obvious expression of the above four cytokine mRNAs in hepatocytes and chicken hepatoma cells,and FAdV-4 caused a strong inflammatory reaction in cardiomyocytes;while the two viruses in serum and cardiomyocyte supernatants cytokine There is no significant difference in content testing.Comparative studies of pathogenicity have shown that there is a certain difference in the ability of the two viruses to replicate in infected cells.According to the comparative study of pathogenicity,both viruses have strong infection and pathogenicity to liver and hepatocellular carcinoma cells,and the difference between them is small;FAdV-4 has a strong infection-causing capacity in the heart and cardiomyocytes.