Isolation and characterization of a recombinant avian leukosis virus subgroup E from a commercial layer farm in Eastern China

Avian leukosis virus (ALV) is a dangerous pathogen in poultry, causing high mortality and decreased fertility due to tumor formation. Generally, the ALV subgroup E (ALV-E) strains are typically low in pathogenicity and tumorigenicity. In this study, we isolated and identified a ALV strain JS1208 from an AL-like tumor case in a commercial Hy-Line Brown layer flock in China. Immunofluorescence assays and transmission electron microscopy revealed that the JS1208 strain replicated in chick embryo fibroblasts (CEF). Complete genome sequencing and analysis identified JS1208 as a recombinant strain, with a major parental backbone from ALV subgroup K (ALV-K) and a minor contribution from ALV-E. Infection of specific-pathogen-free chickens with JS1208 induced typical clinical signs and tumor-like lesions similar to those observed in the original infected flock. To our best knowledge, this is the first report of a recombinant ALV-E strain containing an ALV-K backbone and an ALV-E gp85 gene, resulting in a novel circulating ALV-E variant. These findings will contribute to a deeper understanding of ALV epidemiology.