Complete Genome Characterization of Reticuloendotheliosis Virus Detected in Chickens with Multiple Viral Coinfections

Abstract

Reticuloendotheliosis virus (REV) is a retroviral pathogen capable of infecting several avian hosts and is associated with immunosuppression, anemia, proventriculitis, neoplasia, and runting–stunting syndrome. Its genome contains the three major genes, gag, pol, and env, and two flanking long terminal repeat (LTR) regions. Complete genome sequences of REV are limited in terms of geographical origin. The aim of this study was to characterize the complete genome of REV detected in Brazilian chickens with multiple viral coinfections and analyze the polymorphisms in the deduced amino acids sequences corresponding to its encoded proteins. We tested the presence and completeness of REV as well as other viral pathogens in samples from Brazilian poultry farms by qPCR. The complete genomes of two REV strains were sequenced by overlapping fragments through the dideoxy method. Phylogenetic analysis, pairwise identity matrix, polymorphism identification and protein modeling were performed along the entire genome. We detected REV in 65% (26/40) of the tested samples. Concomitant viral infections were detected in 82.5% (33/40) of the samples and in 90% (9/10) of the farms. Multiple infections included up to seven viruses. Phylogenetic analysis classified both Brazilian strains into REV subtype 3, and the pairwise comparison indicated that strains from the USA and fowlpox virus (FWPV)-related strains were the most identical. The subdomain p18 in gag, the reverse transcriptase/ribonuclease H in pol, and the surface (SU) in the env protein were the most polymorphic in genomic comparisons. The relevant motifs for each protein were highly conserved, with fewer polymorphisms in the fusion peptide, immunosuppression domain, and disulfide bonds on the surface (SU) and transmembrane (TM) of env. This is the first study to include complete genomes of REV in Brazil and South America detected in farms with multiple viral coinfections. Our findings suggest an involvement of REV as an immunosuppressor and active agent in the emergence and progression of multiple infectious diseases. We also found a possible etiological relationship between Brazilian strains and the USA and FWPV recombinant strains. This information highlights the need for epidemiological vigilance regarding REV in association with another pathogens.

Molecular characterization of the meq oncogene of Marek’s disease virus in vaccinated Brazilian poultry farms reveals selective pressure on prevalent strains

“…The proximity of oncogenic viruses between the USA and Brazil was also previously documented, suggesting a possible etiological relationship (Chacón et al. 2022 ). The obtained potential routes associating the Brazilian MDV strains with those from Japan and the USA are probably related to commercial exchange, including the trade in poultry meat and derivatives, given Japan’s high interaction with Brazil (ABPA 2023), or the importation of chicken lineages or vaccines for avian use in Brazil from the USA (Ferreira 2011 ).…”

“…Previous studies have shown the presence of REV in commercial birds in Brazil (Chacón et al. 2019 , 2020 , 2022 ). Furthermore, the co-infection of MDV and REV is a well-documented event and may cause a synergistic effect (Cui et al.…”

“… 2013 ; Chacón et al. 2020 , 2022 ). The complete meq gene of MDV was amplified as previously described (López-Osorio et al.…”

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

“…Reticuloendotheliosis virus (REV) is an immunosuppressive virus which affects both cellular and humoral immunity of infected chickens ( Woźniakowski et al, 2018 ). REV genome comprises 3 major genes, gag, pol , and env , along with 2 flanking long terminal repeat ( LTR ) regions ( Chacón et al, 2022 ). The LTR regions of REV include signals for initiation and termination of the genome transcription ( Ridgway, 1992 ).…”

Investigação e caracterização molecular do retrovírus da reticuloendoteliose aviária (REV) no Brasil

“…Após estes, outros trabalhos realizaram reconstruções filogenéticas do REV, agrupando as cepas entre os principais ramos definidores dos tipos (subtipo I, II e III), porém com o aumento de sequências de REV, foi possível notar que alguns genomas não pareciam consistentes nessa classificação, em particular nas árvores de genomas completos. Por exemplo, nas árvores de LTR e de gag do trabalho de Chacón et al (2022), esse problema fica claro 32 . Essa inconsistência filogenética pode ser observada também no trabalho de Liu et al (2020), onde a cepa recombinante GQ375848 não é agrupada dentro do subtipo I e tampouco do subtipo II, permanecendo isolada em um ramo separado 33 .…”