Emergence of spontaneously occurring neoplastic disease caused by reticuloendotheliosis virus in breeding Muscovy ducks in China, 2019

First Complete Genome of Reticuloendotheliosis Virus in a Mallard Duck from Brazil: Phylogenetic Insights and Evolutionary Analysis

Reticuloendotheliosis virus (REV) is an oncogenic retrovirus that affects both commercial and free-ranging birds. To date, only two complete REV genome sequences have been identified in chickens from South America, with no records in other avian species. This study reports the first complete genome of REV detected in a mallard duck (Anas platyrhynchos domesticus) in South America. In 2021, a mallard duck in Brazil died from severe lymphoproliferative disease affecting multiple organs. Molecular detection and histopathological analysis confirmed REV as the causative agent. Using dideoxy sequencing and phylogenetic analysis, the virus was classified as subtype 3 (REV-3). The phylogenetic analysis identified three clades, each with a bootstrap value of 100, corresponding to the three REV subtypes. Furthermore, a comprehensive comparative genomic analysis revealed two distinct REV-3 subclusters-'East' (38 strains) and 'West' (24 strains)-with notable geographical associations. Additionally, 27 genomes in chimeric states with fowlpox virus (FWPV) were distributed across the phylogenetic tree, emphasizing the critical role of FWPV in the dissemination of REV. Selective pressure analysis revealed evidence of positive selection acting on several codons within the gag, pol, and env genes, particularly in domains such as matrix, p18, reverse transcriptase/ribonuclease H, and surface. These findings provide valuable insights into REV evolution and underscore the importance of genomic surveillance for detecting REV circulation in diverse hosts.

Lymphoproliferative Disease Virus and Reticuloendotheliosis Virus Detection and Disease in Wild Turkeys (Meleagris gallopavo)

Lymphoproliferative disease virus (LPDV) and reticuloendotheliosis virus (REV) are oncogenic retroviruses that can cause disease in wild and domestic fowl. Lymphoproliferative disease virus infections are common and widespread in Wild Turkeys (Meleagris gallopavo) in the US and east-central Canada, while REV has been detected worldwide in numerous avian host species. We tested tissues (spleen, liver, and/or bone marrow, plus neoplastic tissue, if present) from 172 Wild Turkeys that underwent necropsy from December 2018 through October 2021 for both viruses using PCR. We evaluated demographic, geographic, temporal, and seasonal data by chi-square test of independence and logistic regression for turkeys infected with LPDV and/or REV. At least one of these retroviruses was detected in 80.8% (139/172) of Wild Turkeys from 15 US states, with significantly more turkeys being positive for LPDV (72.1%, 124/172) versus REV (43.6%, 75/172; P<0.001). Both viruses (coinfections) were detected in 34.9% (60/172) of turkeys. Among LPDV-infected turkeys (including coinfections), bone marrow had the highest detection rate (38/58, 65.5%), significantly higher than spleen (30/58, 51.7%) and liver (20/58, 34.5%; P<0.001). In REV-infected turkeys, bone marrow had the highest detection rate (24/58, 41.4%). All three tissues (spleen, liver, bone marrow) concurrently tested positive in most (15/25, 60%) REV-infected turkeys. These results suggest LPDV tissue tropism for bone marrow, whereas REV may have broader tissue tropism. Histopathology consistent with lymphoid proliferation and/or neoplasia characteristic of lymphoproliferative disease was evident in 29/172 (16.9%) turkeys assessed, including two REV-only-infected turkeys. Season was significantly associated with LPDV prevalence (highest in winter); year and season were both significantly associated with REV prevalence (highest in 2020 and winter). These data contribute to optimizing diagnostic strategies that may aid in pathogen monitoring and improve detections to increase our understanding of the potential impacts of these viruses on Wild Turkey populations.

Effects of Reticuloendotheliosis virus on TLR-3/IFN-Β pathway in specific pathogen-free chickens

Birds infected by Reticuloendotheliosis virus (REV) are vulnerable to other microorganisms. This immunosuppression is related to the immune organs (thymus, bursa of Fabricius, and spleen) damaged by REV. The regulation of IFN-β greatly depends on pattern recognition receptor TLR-3 and nuclear factors IRF-7, NF-κB. To address if and how the TLR-3/IFN-β pathway is disturbed by REV, 60 one-day-old specific-pathogen-free chickens were intraperitoneally injected with RE virus dilution (n = 30) or stroke-physiological saline solution (n = 30). At 1, 3, 7, 21, and 28 days post-infection, after collecting thymuses, bursas, and spleens, we monitor the kinetics of TLR-3, IFN-β, NF-κB p65, and IRF-7 at transcriptional and translational levels using qPCR, Western blotting, and ELISA separately. As a result, compared with control chickens, the mRNA levels of TLR-3, IRF-7, and NF-κB p65 showed increasingly differences in the early period of REV infection. Synchronal changes occurred at translation levels. In the latter infection period, a decrease of NF-κB p65 was contemporaneous with a fall in IFN-β at both transcriptional and translational levels in the thymuses and bursas. These data suggest that the changes of IFN-β content are closely related to NF-κB p65 when REV invades chicken central immune organs. That reveals new insights into the immunosuppression mechanism of REV in avian.

Virome in the cloaca of wild and breeding birds revealed a diversity of significant viruses

BACKGROUND

Wild birds may harbor and transmit viruses that are potentially pathogenic to humans, domestic animals, and other wildlife.

RESULTS

Using the viral metagenomic approach, we investigated the virome of cloacal swab specimens collected from 3182 birds (the majority of them wild species) consisting of > 87 different species in 10 different orders within the Aves classes. The virus diversity in wild birds was higher than that in breeding birds. We acquired 707 viral genomes from 18 defined families and 4 unclassified virus groups, with 265 virus genomes sharing < 60% protein sequence identities with their best matches in GenBank comprising new virus families, genera, or species. RNA viruses containing the conserved RdRp domain with no phylogenetic affinity to currently defined virus families existed in different bird species. Genomes of the astrovirus, picornavirus, coronavirus, calicivirus, parvovirus, circovirus, retrovirus, and adenovirus families which include known avian pathogens were fully characterized. Putative cross-species transmissions were observed with viruses in wild birds showing > 95% amino acid sequence identity to previously reported viruses in domestic poultry. Genomic recombination was observed for some genomes showing discordant phylogenies based on structural and non-structural regions. Mapping the next-generation sequencing (NGS) data respectively against the 707 genomes revealed that these viruses showed distribution pattern differences among birds with different habitats (breeding or wild), orders, and sampling sites but no significant differences between birds with different behavioral features (migratory and resident).

CONCLUSIONS

The existence of a highly diverse virome highlights the challenges in elucidating the evolution, etiology, and ecology of viruses in wild birds. Video Abstract.

Reemergence of reticuloendotheliosis virus and Marek's disease virus co-infection in Yellow-Chickens in Southern China

The reticuloendotheliosis virus (REV) and the Marek's disease virus (MDV) cause reticuloendotheliosis (RE) and Marek's disease (MD) in poultry, respectively. According to epidemiological results obtained in our laboratory from 2010 to 2017, the positive rates of REV and MDV co-infection remained at low levels. In the present study, during the period of October 2018 to July 2020, 4 clinical cases with high morbidity (5%-20%) and mortality (2%-10%), caused by the co-infection of REV and vv+ MDV-like strains, were diagnosed and analyzed by histopathological observation, cell cultures and detection with ELISA and IFA, and the PCR and by sequencing of the isolates’ genes. Sequencing and the sequence analysis on the complete genomes of the REV strains and the meq genes of the MDV strains were performed. The results, based on the complete genome, LTR, gag, pol, and env genes’ nucleotide sequences of the REV strains, showed that the REV isolates and 68.0 % (17/25) of the reference strains were in a same branch, and all had a high sequence similarity (>99.0%). The similarities between the four isolates and a vv+MDV strain GX18NNM4 were very high, up to 99.3-99.8%. Also, the amino acid residuals at locations 71, 77, 80, 115, 139, 176, and 217 were all the same as A, E, Y, A, A, R, and A, respectively, in the meq gene of the four MDV isolates. In addition, the substitutes at P176R and P217A interrupted the stretches of the proline-rich repeat PPPP, indicating that these strains belonged to the vv+ MDV-like category. Our findings indicated that the more recent and frequent reemergence of REV and the subsequent co-infection with vv+ MDV-like strain has become one of the causes of the clinical outbreaks of tumors and is undoubtedly a threat to the poultry industry in southern China.