Molecular Detection of Reticuloendotheliosis Virus 5′ Long Terminal Repeat Integration in the Genome of Avipoxvirus Field Strains from Different Avian Species in Egypt

Abstract

Avipoxviruses (APVs) are among the most complex viruses that infect a wide range of birds’ species. The infection by APVs is often associated with breathing and swallowing difficulties, reduced growth, decreased egg production, and high mortalities in domestic poultry. In the present study, 200 cutaneous nodular samples were collected from different avian species (chicken, pigeon, turkey, and canary) suspected to be infected with APVs from Dakahlia Governorate, Egypt. Pooled samples (n = 40) were prepared and inoculated in embryonated chicken eggs (ECEs). APVs were then identified by polymerase chain reaction (PCR) and sequence analysis of the APV P4b gene. Furthermore, the forty strains of APVs were screened for the presence of reticuloendotheliosis virus (REV)-5’LTR in their genomes. Interestingly, the phylogenic tree of the APV P4b gene was separated into 2 clades: clade 1, in which our fowlpox virus (FWPV), turkeypox virus (TKPV), and canarypox virus (CNPV) isolates were grouped, along with reference FWPVs and TKPVs retrieved from GenBank, whereas, in clade2, the pigeonpox virus (PGPV) isolate was grouped with PGPVs retrieved from GenBank. Likewise, REV-5’LTR was amplified from 30 strains isolated from chicken, turkey, and canary, while PGPV strains were free from REV-5’LTR integration. To the best of our knowledge, this study involved the detection and characterization of REV-5’LTR insertions in the APVs field isolates in Egypt for the first time. Given the above information, further future research seems recommended to understand the impact of the resulting REV-5’LTR insertions on the pathogenesis, virulence, and inadequate vaccine protection against APVs.

Molecular characterization of Marek's Disease virus reveals reticuloendotheliosis virus-long terminal repeat integration in the genome of the field isolates in Egypt

“…The identified REV-LTR sequences showed a high degree of genetic identity (98.8%) with REV- 5′LTR integration identified in fowl poxvirus (FWPV) isolates identified previously in Dakahlia/2017 (MT251362.1) ( Mosad et al, 2020 ) The results indicate the circulation of REV in the Egyptian poultry farms with the possibility of integration of REV in both viruses (FWPV and MDV). the identified REV-LTR sequences showed a high degree of identity (95–98.5%) with identified REV-LTR integrated in FWPV and GaHV from China, USA, South Africa, and Australia, suggesting potential transmission of the virus from these countries.…”

Genomic characteristics of an avipoxvirus 282E4 strain

“…Poxviruses replicate in the cytoplasm of the cell and bud through cellular endocytosis. ( Mosad et al., 2020 ; Deng et al., 2022 ; Walker et al., 2021 ). Avipoxviruses extensively infect nonmammalian hosts including more than 300 species of birds ( Bolte et al., 1999 ).…”

“…Compared with that of CNPV, FWPV infection is a disease with a low mortality proportion, which diminishes egg production and damages growth and fertility. But sometimes, the fatality of fowlpox reaches 50%∼100% without vaccine protection ( Mosad et al., 2020 ; Zhao et al., 2014 ). Therefore, the vaccine is a necessary method for preventing avipoxviruses.…”

Molecular characterization of avipoxviruses circulating in Windhoek district, Namibia 2021

“…The avian retrovirus, reticuloendotheliosis virus (REV) is known to partially or completely integrate into the genome of some APV viruses and it is believed that the pathogenicity of the APV is enhanced by the presence of the integrated REV [ 8 , 10 , 16 , 20 ]. Reports from commercial flocks suggested that APV vaccine contamination with REV caused tumours in vaccinated birds [ 5 ] while, more recently, an acute outbreak of FP in China which resulted in 100% mortality of commercial chickens was caused by an APV with integrated partial REV sequences [ 22 ].…”

“…Currently in Africa, APVs have only been genetically characterised in a few countries. These include Egypt [chicken (subclade A1), pigeon (subclade A4), and turkey (subclade A2)], Nigeria [chicken (subclade A1)], Mozambique [chicken (subclade A1 and clade E), peacock (subclade A1), quail (subclade A2) and turkey (subclade A2)], South Africa [dove (subclade A3), flamingo (subclade A3), penguin (subclade A2) and pigeon (subclade A2 and A3)] and Tanzania [chicken (subclade A1)] [ 1 , 4 , 14 , 15 , 16 , 17 ]. As there was no information available on APVs in Namibia this study was undertaken to characterize viral DNA obtained from FP outbreaks in the country.…”