Isolation,Identification And Epidemiological Investigation Of Group?Fowl Adenovirus Serotype 4

Hydropericardium hepatitis syndrome is a new domestic poultry disease caused by Fowl Adenovirus serotype 4.The disease has been identified can infect multiple varieties of chickens and ducks.Sick poultry mainly showed no obvious signs of suddenly felling to the ground,feet down,died within a few minutes.The disease mainly occurred in the 3 to 5 week old broiler chickens and breeders and ducks could also be infected.It causes high morbidity and the mortality rate was 20%~75%,up to 80%.Studies have indicated that chicken immune suppression diseases will increase the risk of infection.In this study,we isolated a strain of FAV4 from the liver tissue of the commercial chicken,and some biological characteristics of the virus were studied,as well as the epidemiological investigation of chicken and duck infected with FAV4.The aim of this study is to provide a theoretical basis for its prevention.1.Isolation and identification of fowl adenovirus serotype 4.In this study,we isolated a strain of virus from the liver tissues of chickens suspected of FAV4 infection in Shandong Province.A series of laboratory tests were conducted on the isolated strains.The results shown,the isolated strains of chickens and ducks cannot agglutination of erythrocyte,but can agglutination of in rats;the chick embryo lethal median dose was 10-3.33/0.2mL.Histological changes show fibrosis and fatty degeneration of the liver cells;swelling and degeneration of renal tubular epithelial cells;edema of myocardial fibers and granular degeneration of renal tubular epithelial cells.Serum collected on clinical test results indicates there was a presence of latent infection in chicken flocks.The hexon genome of the isolated strain was compared with the fowl adenovirus serotype 4 gene which has been published,it was found that the homology of the isolates strain was more than 99.6% in the same branch of India,and it was far from South Korea,Europe and America.The 10 day old chicks infected with the isolated strains can cause pericardial effusion,liver hemorrhage,kidney enlargement.These results indicate that the isolated strains of fowl adenovirus serotype 4.2.Establishment and application of Taqman real-time PCR for detection of fowl adenovirus serotype 4The distinctive Taqman probes and a pairs of primers were designed according to the nucleotide sequence of fowl adenovirus serotype 4 taken from GenBank,and a real time PCR for detection of fowl adenovirus serotype 4 was established successfully through optimizing the reaction condition.With the 10-fold serial dilutions of standard products for constructing real time quantitative PCR standard curve,the sensitivity,specificity and reproducibility of the assay were assessed.And 223 clinical samples were collected from Shandong province,compared with conventional PCR assay.The results shown that the linear relationship between the standard curve and the template concentration was well,This method can detect the minimum template concentration of 20copies/?L,100 times higher than the conventional PCR detection method.Clinical samples tested show that the positive rates of Taqman and conventional PCR were 86.76% and 75% respectively.The specifity of method was high and there were no cross-reactivity with other fowl adenovirus serotype of group I.The results show that the method with sensitivity,specificity and repeatability,it can be used in clinical diagnosis and epidemiological investigation of FAV4.3.Epidemiological investigation of FAV4 in Shandong provinceA total of 679 samples were collected from the farms in Shandong province,and the positive rate of FAV4 was 65.2%.The detection rate of commercial chickens was 71.9%,the breeder chickens was 34.2%,the rate of commercial chickens was significantly higher than that of breeder chickens,indicating that the virus was mainly infected with commercial chickens.While the breeder duck and commercial duck detection rate respectively were 68.6% and 79.2%,but the positive rate of ducks was higher than that in chicken.Detection of immunosuppressive pathogens such as H9N2,CIAV and IBDV in 172 samples of chickens,which the H9N2 and CIAV detection rate is higher,and the mixed infection rate is relatively high,indicating that immunization of poultry can promote the occurrence of FAV4.At the same time the immunosuppressive pathogens of H9N2,CIAV and IBDV were tested for 149 commercial broilers samples.With the 358 duck samples were detected,FAV4 positive rate was 77.1%,the detection of H9N2 and IBDV was carried out on 276 samples of FAV4,ducks positive rate of H9N2 infection was 41.67%,the commercial ducks positive rates of H9N2 and IBDV were 38.6% and 26.7% respectively.The results showed that the ducks detection rate(77.10%)was significantly higher than that of chicken 51.20%.and the infection of FAV4 was correlated with the infection of H9N2 and IBDV.Therefore,it is necessary to further study on FAV4 infection in poultry immunosuppressive agents.