Molecular Epidemiology Of Subgroup J Avian Leukosis Virus Isolates From Sichuan Area And Its Impact On Immune Responses Against IB-ND Live Vaccines

Subgroup J avian leukosis virus is a kind of exogenous avian leukosis virus and avian endogenous retrovirus envelope (E51) reorganization of the new avian leukosis subgroup,It caused great damage to the chicken,and also caused serious losses in production. To investigate the epidemiology of subgroup J avian leukosis (ALV-J) in Sichuan area and effect of infection of ALV-J on immune responses to vaccines in chickens, The specific effect on the immune effect of variation monitoring wild virus and understanding of the existing vaccine virus is very important.From 2011 to 2013,839 blood samples of 8 chicken farms were detected by PCR and 62 blood samples were positive, including 39 blood samples and 23 tissue samples,the average infection rate of ALV-J in chickens is 7.4%. The nucleotide homologies of those 20 positive samples were 87.3% to 99.8%, of which the nucleotide homologies were 87.3% to 98.2% for HPRS-103 strain and 87.9% to 94.4% for SCGS-1 strain. Taking HPRS-103 as the reference strains, some unique mutations showed characteristic patterns in Sichuan most sequencing samples, respectively in the 209th and 246. Among the 20 sequenced samples, E209K/N amino acid mutations was 85%(17/20), the mutation of K was 14, and the N was 3; E246K/N/A amino acid mutations was 90%(18/20), the mutation of K was 14, and the N was 3?the A was 1. Phylogenetic analysis showed that the 20 samples belong to different genetic branch, and the sample SM from Shimian country had the longest genetic distance to other samples. In conclusion, ALV-J infection was common in Sichuan area, and a genetic diversity was detected in the gp85 gene of ALV-J positive samples, and this could be related to the introduction of chickens fromother areas. In addition, immune responses to vaccines in chickens showed that ALV-J infection was significantly inhibited the immune responses to vaccines, the antibody titer in chicken infected with ALV-J was all significantly lower than the normal chicken with the increasing of infection rate,which indicated that ALV-J infection was significantly inhibited the immune responses to vaccines and the vaccines can't protect the chicken after the infection.In a word, the study showed that the main characteristics of gp85 gene of ALV-J circulating in recent years in Sichuan, China.The gene and amino acid mutations could be considered as the molecular marks of the ALV-J circulating presently in some regions of China, also discusses the impact of ALV-J on immune response. The conclusion supplies some valuable information not only for the moleculer features of ALV-J but also for control and prevention of ALV-J in Sichuan.