A novel recombinant ALV-K carrying ALV-J-derived LTR, pol, and 3'UTR from Chinese indigenous chicken breeds exhibits enhanced replication and increased hemangioma-associated pathogenicity.

Avian leukosis virus (ALV) is a prototypical alpharetrovirus that can induce various tumors and cause serious immunosuppression, posing severe threats to the poultry industry. ALVs isolated from chickens are classified into seven subgroups (A to E, J, and K). In 2024, a novel ALV-K strain designated GD24LHB130 was isolated from Qingyuan Partridge chickens in Guangdong Province, China. Whole-genome sequencing revealed that GD24LHB130 is a recombinant ALV-K strain harboring the LTR, pol, and 3'UTR regions of ALV-J. In vitro infection assays and LTR promoter activity analysis demonstrated that GD24LHB130 exhibits significantly enhanced replicative capacity compared to classical ALV-K strains, with the recombination of the ALV-J LTR region strongly associated with this replication advantage. In vivo pathogenicity experiments confirmed that GD24LHB130 causes significant growth retardation, immune organ damage, persistent viremia and viral shedding, and hemangioma-like lesion formation in infected chickens. This is the first report of a recombinant ALV-K strain capable of inducing hemangioma-like lesions, which exhibits enhanced replication capacity and pathogenic potential. These findings not only expand the epidemiological knowledge of ALV but also provide critical insights into the molecular mechanisms underlying ALV-K pathogenesis.