WHOLE-GENOME ANALYSIS REVEALS POSSIBLE SOURCES OF ALV-J INFECTION IN AN ANYI TILE-LIKE GREY CHICKEN FLOCK

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.

Molecular characteristics of avian leukosis viruses isolated from indigenous chicken breeds in Yunnan Province, Southwestern China

Indigenous chicken breeds have a large market share in China due to their superior production traits, including high meat quality and disease resistance. Yunnan Province is recognized as a major source of domestic chickens globally and boasts a diverse array of indigenous chicken resources. Avian leukosis virus (ALV) induces various tumors and immunosuppression, endangering the poultry industry. However, the prevalence of ALV infection among indigenous chickens in Yunnan Province remains unclear. In this study, we aimed to investigate the presence of ALV in these breeds. To this end, we collected 1,470 plasma samples from six indigenous chicken breeds in Yunnan province, 309 of which tested positive. The results confirmed the presence of exogenous ALV in local chicken, with a positivity rate ranging from 8.20 %-41.46 %. Furthermore, eight exogenous ALV isolates were successfully identified: four ALV subtype J (ALV-J) strains, three ALV subtype A (ALV-A) strains and one ALV subtype B (ALV-B) strain. The four ALV-J strains share relatively high sequence identity (99.55 %-99.80 %) with the GX14ZS14 strain isolated from Guangxi in 2014 and was closely related to the prototype strain HPRS103 and belongs to clade 1.1. Several substitutions were observed in gp85 proteins in the three ALV-A and ALV-B strains isolated in this study. Additionally, the four ALV-J strains exhibited 203 bp deletions in the rTM and DR1 regions, a feature commonly observed in viruses in clades 1.2 and 1.3. Overall, this study confirmed the presence of multiple ALVs in these six indigenous chicken breeds from Yunnan Province. This study provides molecular characterization of ALV in indigenous chicken breeds in Yunnan Province and provides a reference for the further eradication of ALV in China. The complex background of ALV infection highlights the urgent need for intensifying eradication efforts.

Detection and genetic diversity of subgroup K avian leukosis virus in local chicken breeds in Jiangxi from 2021 to 2023

Avian leukosis virus subgroup K (ALV-K) is a new subgroup of avian leukosis virus (ALV) that was first identified in Chinese native chickens in recent years. To further understand the molecular epidemiology and evolutionary diversity of ALV-K, this study investigated the molecular epidemiology of 73,664 chicken plasma samples collected from Jiangxi native chicken flocks. The results showed that ALV-J was the most predominant ALV subtype in Jiangxi native chickens, with a high positivity rate of 4.34%. From 2021 to 2023, there was a gradual upward trend in the proportion of positive numbers of ALV-K among ALV-positive samples, and there was a trend of outbreaks. ALV-J and ALV-K were the main co-infection patterns. Genetic evolutionary analysis based on ALV-K gp85 gene showed that the isolated ALV-K in this study were distributed in various branches of the evolutionary tree with genetic diversity. The homology results showed that the amino acid homology of the isolated ALV-K gp85 gene ranged from 33.9 to 88.1% with the reference strains of subtypes A, B, C, D, E, and J, and from 91.9 to 100% with the other ALV-K reference strains. Multiple mutations were present in the ALV-K gp85, and especially significant mutations were found in the highly variable region hr2. The results of ALV-K replication efficiency showed that the replication efficiency of ALV-K was significantly lower than that of ALV-J. These results enriched the genome sequence data of ALV-K in Chinese geoducks, and laid the foundation for further research on the pathogenesis and prevention of ALV-K.