Genetic variability of the Avian leukosis virus subgroup J gp85 gene in layer flocks in Lower Egypt

Aim: This study aimed to determine the prevalence of layer flock tumor disease in Lower Egypt during the period of 2018- 2019 and to undertake molecular characterization and determine the genetic diversity of all identified viruses. Materials and Methods: Forty samples were collected from layer chicken located in six governorates of Lower Egypt during the period of 2018-2019. Samples were taken from tumors in different organs. Tumor tissues were identified by histopathological sectioning and then further confirmed by a reverse-transcription polymerase chain reaction. Finally, genetic evolution of Avian leukosis virus (ALV-J) gp85 gene was studied. Results: All the study samples were negative for Marek's disease virus, reticuloendotheliosis virus A,B,C and D and 20 samples were positive for ALV-J in backyard in six governrates. Sequencing of ALV-J gp85 gene was performed for six representative samples (one from each governorate), and they were found to be genetically related to prototype virus HPRS-1003 (identity percentage: 91.2-91.8%), but they were from a different group that was similar to the AF88-USA strain (first detected in 2000) with specific mutations, and they differed from a strain that was previously isolated in Egypt in 2005, forming two different subgroups (I and II) that had mutations in the hr1domain (V128F, R136A) and hr2 domain (S197G, E202K). Conclusion: The ALV-J virus was the main cause of neoplastic disease in layer chickens from Lower Egypt in the period of 2018-2019. We found that the genetic evolution of ALV-J gp85 gene was related to prototype virus HPRS-1003 but in a different group with a specific mutation. Further studies are needed to evaluate the antigenicity and pathogenicity of recently detected ALV-J strains.

Identification of two novel multiple recombinant avian leukosis viruses in two different lines of layer chicken

Avian leukosis virus (ALV) is the most common oncogenetic retrovirus that emerges spontaneously as a result of recombination between exogenous viruses, exogenous viruses and endogenous viruses, and exogenous viruses and non-homologous cellular genes. In the present study, two natural recombinant avian leukosis viruses (rALVs) (LC110515-5 and LC110803-5) carrying a subgroup C gp85 gene, a subgroup E gp37 gene, and a subgroup J 3′UTR and 3′LTR were isolated from two different lines of layer flocks, Black-bone silky fowl (BSF) and commercial layer chicken, that suffered from myeloid leukosis. Although tumours were not observed in rALV-infected individual chickens, other non-neoplastic inflammatory lesions were evident. The two rALVs were cultured on DF-1 cells and identified by PCR, immunofluorescence assay and gene sequencing. The gp85 nucleotide sequence in the two isolates displayed a high identity (>95 %) with that of the gp85 gene in ALV-C, but the identity was less than 90 % with ALV-A/B/D/E and only 51 % with ALV-J. Phylogenetic analysis of the nucleotide and amino acid sequences confirmed that the two isolates were recombinant between ALV-C, ALV-E and ALV-J. Subgroup C ALV is rarely found in field cases. This report is the first to provide evidence that ALV-C has recombined with ALV-E and ALV-J in two different chicken lines. The source and characteristics of the two rALVs and ALV-C need to be further investigated.

The Expression and Characterization of Gp85 Gene of Subgroup J Avian Leukosis Virus Associated with Hemangioma

The subtype of avian leukosis virus (ALV) was mainly determined by the gp85 glycoprotein. A subtype J ALV strain SCDY1 associated with hemangioma was isolated from grandparent breeding chicken and the highly antigenic region of its gp85 gene was amplified and expressed in Rosetta Escherichia coli using the pET-32a(+)vector. The fusion protein, which was expressed at a high level, was similar antigenically to the native gp85 protein as determined by Western blot assay using polyclonal antibodies against ALV-J strain. The fusion protein was also purified. This research lays a foundation for using this recombinant protein for development of indirect enzyme-linked immunosorbent assay (ELISA) for serum antibody detection or for production of monoclonal antibodies against prevalent ALV-J.