Isolation, identification and evolution analysis of a novel subgroup of avian leukosis virus isolated from a local Chinese yellow broiler in South China.

Avian leukosis virus (ALV) causes high mortality associated with tumor formation and decreased fertility, and results in major economic losses in the poultry industry worldwide. Recently, a putative novel ALV subgroup virus named ALV-K was observed in Chinese local chickens. In this study, a novel ALV strain named GD14LZ was isolated from a Chinese local yellow broiler in 2014. The proviral genome was sequenced and phylogenetically analyzed. The replication ability and pathogenicity of this virus were also evaluated. The complete proviral genome sequence of GD14LZ was 7482 nt in length, with a genetic organization typical of replication-competent type C retroviruses lacking viral oncogenes. Sequence analysis showed that the gag, pol and gp37 genes of GD14LZ have high sequence similarity to those of other ALV strains (A-E subgroups), especially to those of ALV-E. The gp85 gene of the GD14LZ isolate showed a low sequence similarity to those other ALV strains (A-E subgroups) but showed high similarity to strains previously described as ALV-K. Phylogenetic analysis of gp85 also suggested that the GD14LZ isolate was related to ALV-K strains. Further study showed that this isolate replicated more slowly and was less pathogenic than other ALV strains. These results indicate that the GD14LZ isolate belongs to the novel subgroup ALV-K and probably arose by recombination of ALV-K with endogenous viruses with low replication and pathogenicity. This virus might have existed in local Chinese chickens for a long time.