Etiology surveys and phylogenetic analyses of avian leukosis virus subgroup A isolated from breeder chickens farms

【Objective】To investigate the prevalence of breeders infected by avian leukosis virus subgroup A (ALV-A) in Guangdong Province of China.【Method】A total of 1 561 plasma samples of breeders collected from four different farms(A,B,C,D) were inoculated into DF-1 cell cultures for 7 days; the positive samples were detected by antigen p27 ELISA test and identified via PCR and IFA.【Result and conclusion】Results showed that 71 positive samples were detected from four farms and the positive rate of exogenous ALV isolation was 4.6%. Two ALV-A viruses were isolated from antigen p27 ELISA positive samples of the breeder chickens farm C, which were designed as GD13-1 and GD13-2, and the GD13-2 was determined for mixed infection with ALV-J. The full length proviral genomes of two isolates were 7 721, 7 715 bp after PCR amplification and sequencing. In comparison to the LTR and gp85 sequence of the other ALV-A strains at home and abroad, the isolates had the highest similarity with that of subgroup A strain SDAU09E2. The nucleotide similarity of LTR and gp85 were 96.9%, 97.2% and 98.4%, 98.7% respectively. In comparison to the LTR and gp85 sequence of ALV-A GD08 isolated from Guangdong five years ago, the similarity of LTR and gp85 were 88.9%,89.5% and 98.5%,98.8% respectively. The survey results show that ALV-A still exist in some breeder farms, but it is not prevalent any more.