Identification, Sequence Analysis And Pathogenicity Research Of Avian Leukosis Virus Subgroup A Isolated From Longshengfeng Chickens

Avian leukosis viruses?ALV? were discovered over 100 years ago, which is one of the earliest virus to be in-depth study. It is the first proposed that viruses can cause tumors and was awarded the Nobel Prize in 1996. ALVs are divided into ten subgroups?A-J? based on the specificity of the cell receptors and the virus' host range associated antigenicity of envelope proteins and a new subgroup named K which was identified by our laboratory in our local strain recently. Subgroup J ALV was the most widely popular and the strongest pathogenicity among various subgroups, it caused serious influence to the development of poultry industry in China. But at the same time epidemiological investigations show that the chicken group infectied avian leukosis virus is not just caused by the ALV- J, there are some chickens infected by ALV- A and B. This study for the subgroup A ALV?ALV- A? identification isolated from the local strain in the gene pool, on the basis of complete its whole genome analysis system and research on its pathogenicity was carried out, which helps to understand molecular evolution law and its pathogenicity of the ALV-A in our China local chickens, as a reference of local strain of ALV purification in China.1?Identification, sequence analysis of avian leukosis virus subgroup A isolated from Longshengfeng chickensTo understand the genome sequence characteristics and the variation of ALV in China's local strain of chicken, this study through vaccination DF-1 cell, indirect immunofluorescence?IFA? and polymerase chain reaction?PCR? method, identification a subgroup A ALV named SDAU14A1 from breeder eggs of the unique local strain Long Shengfeng. Directly by mutual overlapping primers amplification and cloning sequencing of different genetic regions get the whole genome by joining together. Multiple sequences alignment and phylogeny evolution analysis with other reference strains showed that, the whole proviral genome of SDAU14A1 had the closest phylogenetic relationship with Tyms₉0, a recombinant avian leukosis virus associated with fowl glioma in layer chickens in Japan, with a homology as high as 100% of U3 region. However, SDAU14A1 had a distant relationship with other strains isolated from different types of chinese local breed chickens earlier, which implied that SDAU14A1 might be a representative strain existed in local breed chickens in East Asia region. The study shows there existed diversity of local strain chicken infected ALV in China, it is necessary to implement strict monitoring measures to promote the local strains of chicken ALV purification in China.2?The pathogenic study on SPF chicken of the ALV-A isolated strainThis experiment select the yolk sac and one-day intraperitoneal two different inoculation ways to study the pathogenicity of SDAU14A1 SPF chicken, and at the same time set up horizontal propagation group and the blank control group to observe its lateral spreading ability.All chickens were vaccinated 0.1ml NDV and AIV-H9 inactivated vaccines at 1 w.After an immune response was generated for 3, 4 and 5 weeks, the sera of all the tested chickens were collected for haemagglutination inhibition testing to determine the concentrations of NDV and AIV-H9 antibody. At 7 weeks of age, six samples were selected from each group randomly. According to its weight and the thymus, bursa of fabricius, and spleen weight to calculate the immune organ index?immune organ weight/body weight?.Dissect and observe natural death chicken, make section of tumor tissue which had tumor and histologic observation after HE staining. The results showed that SDAU14A1 infected group could induce more growth retardation and higher mortality rate than blank control group?p<0.05?. The SDAU14A1 infected two groups also showed more severe immunosuppression with respect to normal group, which had lower immune organ to body weight ratios and lower antibody responses to newcastle disease virus and H9-avian influenza virus?p<0.05?.SDAU14A1 can also induce lymphocyte tumor, especially has the strong ability of horizontal transmission. Different infection group have extremely significant difference compared with the control group, but this two virus infection chickens' immune organ index difference is not significant.