Isolation and molecular characteristic of subgroup J avian leukosis virus in Guangxi and Jiangsu provinces of China during 2022-2023

Subgroup J avian leukosis virus (ALV-J) has significantly affected the global poultry industry, with rapid mutations and frequent outbreaks in the poultry industry of China, challenging the current eradication strategies. In this study, virus isolation, identification, and complete genome sequencing of suspected ALV-J-infected samples collected from Guangxi and Jiangsu provinces during 2022-2023 were performed. Four ALV-J strains (designated as, GXZM01, GXZM02, JSZM02, and JSZM963) were successfully isolated and sequenced, with genome lengths ranging from 7487 to 7636 bp and a homology of 82.8 %-96.5 % with the reference ALV-J strains. The amino acid sequences of the gag and pol genes of the isolated strains showed relatively high conservation, with homologies of 95-100 % and 97.1-99.5 % compared with the reference strains, respectively. Analysis of the 3'UTR revealed that the 4 ALV-J isolates show different type of mutations compared to the reference strains, with all the isolates containing a 175 bp deletion at the r-TM, while the JSZM02 strain uniquely showed a 127 bp deletion in the E element. The homology of Env protein and Gp85 protein between the 4 isolates and the reference strains ranged from 86.5 to 95.6 % and 83.7 to 93.8 %, respectively. Notably, in comparison with ALV-J prototype strain HPRS-103, we found that a distinct deletion of 11 aa located at 209-219 aa of Gp85 protein of GXZM02 strain which located at the receptor-binding domain (RBD) and partially overlapped with hypervariable region2 (hr2). Structural prediction analysis revealed that the Gp85 proteins of these ALV-J strains exhibited certain differences in the number of α-helices and β-sheets. Importantly, viral growth kinetic showed that the replication ability of GXZM02 was the weakest one among the 4 isolates, which is potentially related to the deletion in the RBD. Our findings contribute to enrich the epidemiological data on ALV-J and reveal the evolution of prevalent ALV-J strains in clinic, which will provide scientific basis for ALV prevention and control.