The avian reovirus genome segment S1 is a functionally tricistronic gene that expresses one structural and two nonstructural proteins in infected cells

Diagnostic investigation of avian reovirus field variants circulating in broiler chickens in Pennsylvania of United States between 2017 and 2022

Avian reovirus (ARV) has been continuously affecting the poultry industry in Pennsylvania (PA) in recent years. This report provides our diagnostic investigation on monitoring ARV field variants from broiler chickens in Pennsylvania. Genomic characterization findings of 72 ARV field isolates obtained from broiler cases during the last 6 years indicated that six distinct cluster variant strains (genotype I-VI), which were genetically diverse and distant from the vaccine and vaccine-related field strains, continuously circulated in PA poultry. Most of the variants clustered within genotype V (24/72, 33.3%), followed by genotype II (16/72, 22.2%), genotype IV (13/72, 18.1%), genotype III (13/72, 18.1%), genotype VI (05/72, 6.94%), and genotype I (1/72, 1.38%). The amino acid identity between 72 field variants and the vaccine strains (1133, 1733, 2408, 2177) varied from 45.3% to 99.7%, while the difference in amino acid counts ranged from 1-164. Among the field variants, the amino acid identity and count difference ranged from 43.3% to 100% and 0 to 170, respectively. Variants within genotype V had maximum amino acid identity (94.7-100%), whereas none of the variants within genotypes II and VI were alike. These findings indicate the continuing occurrence of multiple ARV genotypes in the environment.

Detection of avian reovirus (ARV) by ELISA based on recombinant σB, σC and σNS full-length proteins and protein fragments

Introduction. Avian reovirus (ARV) is associated with arthritis/tenosynovitis and malabsorption syndrome in chickens. The σC and σB proteins, both exposed to the virus capsid, are highly immunogenic and could form the basis for diagnostic devices designed to assess the immunological status of the flock.Gap Statement. Commercial ARV ELISAs cannot distinguish between vaccinated and infected animals and might not detect circulating ARV strains.Aim. We aimed to develop a customized test to detect the circulating field ARV strains as well as distinguish between vaccinated and unvaccinated animals.Methodology. We developed ELISA assays based on recombinant (r) σB, σC and the nonstructural protein σNS and tested them using antisera of vaccinated and unvaccinated chickens as well as negative controls. Fragments of σB and σC proteins were also used to study regions that could be further exploited in diagnostic tests.Results. Vaccinated and unvaccinated birds were positive by commercial ELISA, with no difference in optical density values. In contrast, samples of unvaccinated animals showed lower absorbance in the rσB and rσC ELISA tests and higher absorbance in the rσNS ELISA test than the vaccinated animals. Negative control samples were negative in all tests. Fragmentation of σB and σC proteins showed that some regions can differentiate between vaccinated and unvaccinated animals. For example, σB amino acids 128-179 (σB-F4) and σC amino acids 121-165 (σC-F4) exhibited 85 and 95% positivity among samples of vaccinated animals but only 5% and zero positivity among samples of unvaccinated animals, respectively.Conclusion. These data suggest that unvaccinated birds might have been exposed to field strains of ARV. The reduction in absorbance in the recombinant tests possibly reflects an increased specificity of our test since unvaccinated samples showed less cross-reactivity with the vaccine proteins immobilized on ELISAs. The discrepant results obtained with the protein fragment tests between vaccinated and unvaccinated animals are discussed in light of the diversity between ARV strains.

Identification, pathological, and genomic characterization of novel goose reovirus associated with liver necrosis in geese, China

Since 2021, a novel strain of goose reovirus (GRV) has emerged within the goose farming industry in Guangdong province, China. This particular viral variant is distinguished by the presence of white necrotic foci primarily localized in the liver and spleen, leading to substantial economic losses for the poultry industry. However, the etiology, prevalence and genomic characteristics of the causative agent have not been thoroughly investigated. In this study, we conducted an epidemiological inquiry employing suspected GRV samples collected from May 2021 to September 2022. The macroscopic pathological and histopathological lesions associated with GRV-infected clinical specimens were examined. Moreover, we successfully isolated the GRV strain and elucidated the complete genome sequence of the isolate GD21/88. Through phylogenetic and recombination analysis, we unveiled that the GRV strains represent a novel variant resulting from multiple reassortment events. Specifically, the μNS, λC, and σNS genes of GRV were found to have originated from chicken reovirus, while the σA gene of GRV exhibited a higher degree of similarity with a novel duck reovirus. The remaining genes of GRV were traced back to Muscovy duck reovirus. Collectively, our findings underscore the significance of GRV as a pathogenic agent impacting the goose farming industry. The insights gleaned from this study contribute to a more comprehensive understanding of the epidemiology of GRV in Southern China and shed light on the genetic reassortment events exhibited by the virus.

Research Note: Genetic characterization of novel duck reoviruses from Shandong Province, China in 2022

Since 2005, novel duck reoviruses have been outbreaks in duck breeding areas such as central China and South China. In recent years, the incidence rate of this disease is still increasing, bringing serious economic losses to waterfowl breeding industry. This study isolated 3 novel duck reoviruses (NDRV-SDLS, NDRV-SDWF, and NDRV-SDYC) from sick ducks in 3 local duck farms in Shandong Province. The study aimed to investigate the characteristics of these viruses. The virus is inoculated into duck embryo fibroblasts, where the virus replicates to produce syncytium and dies within 3 to 5 d. The viruses were also isolated from infected ducks, and RT-PCR amplified the whole genomes after passage purification in duck embryos. The resulting whole genome was analyzed for genetic evolution. The total length of the gene sequencing was 23,418 bp, divided into 10 fragments. Gene sequence comparison showed that the 3 strains had high similarity with novel duck reoviruses (NDRV) but low similarity with chicken-origin reovirus (chicken ARV) and Muscovy duck reovirus (MDRV), especially in the σC segment. Phylogenetic analysis of the 10 fragments showed that the 3 isolates constituted the same evolutionary clade as other DRV reference strains and were far related to ARV and MDRV in different evolutionary clades. The results of all 10 segments indicate that the isolates are in the evolutionary branch of NDRV, suggesting that the novel waterfowl reovirus is the dominant circulating strain in Shandong. This study complements the gene bank information of NDRV and provides references for vaccine research and disease prediction of NDRV in Shandong.

Avian Reovirus σA Protein Inhibits Type I Interferon Production by Abrogating Interferon Regulatory Factor 7 Activation

Type I interferon (IFN) response is the first line of host-based innate immune defense against viral infections. However, viruses have developed multiple strategies to counter host IFN responses, so they may continue infecting hosts via effective replication. Avian reovirus (ARV), an RNA virus, causes viral arthritis or tenosynovitis in chickens. Previous studies have shown that ARV is highly resistant to the antiviral effects of IFN. However, the underlying mechanisms that enable ARV to block the IFN pathway remain unclear. In this study, we found that ectopic expression of ARV protein, σA, significantly inhibited the production of IFN-β induced by melanoma-differentiation-associated gene 5 (MDA5) and poly(I·C). Knockdown of σA during ARV infection enhances the IFN-β response and suppresses viral replication. ARV σA inhibited the MDA5-mediated IFN-β activation by targeting interferon regulatory factor 7 (IRF7). Further studies demonstrated that σA interacts with IRF7, thereby blocking IRF7 dimerization and nuclear translocation, finally leading to the inhibition of IFN-β production. These findings reveal a novel mechanism that allows ARV to evade host antiviral immunity. IMPORTANCE ARV, the causative agent of viral arthritis or tenosynovitis in chickens, has a significant economic impact as it results in poor weight gain and increased feed conversion ratios. The MDA5-mediated IFN-β signal pathway plays an important role in host antiviral defense. Therefore, RNA viruses have developed mechanisms to counter this signaling pathway and successfully establish infection. However, the strategies adopted by ARV to block MDA5-IRF7 signaling remain unclear. In the current study, we demonstrated that ARV σA inhibits this pathway by binding to IRF7, which blocked IRF7 dimerization and nuclear translocation. Our findings may provide insights into how avian reovirus counteracts the innate antiviral immunity of the host to ensure viral replication.

Analysis of the Immune Response and Identification of Antibody Epitopes Against the Sigma C Protein of Avian Orthoreovirus Following Immunization with Live or Inactivated Vaccines

Avian orthoreoviruses are causative agents of tenosynovitis and viral arthritis in both chickens and turkeys. Current commercial reovirus vaccines do not protect against disease caused by emerging variants. Custom-made inactivated reovirus vaccines are commonly utilized to help protect commercial poultry against disease. Antibody epitopes located on the viral attachment protein, σC, involved in virus neutralization, have not been clearly identified. In this study, the S1133 vaccine strain (Genetic Cluster 1 [GC1], a GC1 field isolate (117816), and a GC5 field isolate (94826) were determined to be genetically and serologically unrelated. In addition, chickens were vaccinated with either a commercial S1133 vaccine, 117816 GC1, or 94826 GC5, and sera were used in peptide microarrays to identify linear B-cell epitopes within the σC protein. Specific-pathogen-free (SPF) chickens were vaccinated twice with either: 1) live and live, 2) inactivated and inactivated, or 3) a combination of live and inactivated vaccines. Epitope mapping was performed on individual serum samples from birds in each group using S1133, 117816, and 94826 σC sequences translated into an overlapping peptides and spotted onto microarray chips. Vaccination with a combination of live and inactivated viruses resulted in a greater number of B-cell binding sites on the outer-capsid domains of σC for 117816 and 94826, but not for S1133. In contrast, the S1133-vaccinated birds demonstrated fewer epitopes, and those epitopes were located in the stalk region of the protein. However, within each of the vaccinated groups, the highest virus-neutralization titers were observed in the live/inactivated groups. This study demonstrates differences in antibody binding sites within σC between genetically and antigenically distinct reoviruses and provides initial antigenic characterization of avian orthoreoviruses and insight into the inability of vaccine-induced antibodies to provide adequate protection against variant reovirus-induced disease.

Seroprevalence of infectious bronchitis virus and avian reovirus in free backyard chickens

Infectious bronchitis virus (IBV) and avian reovirus (ARV) cause significant losses in the poultry industry throughout the world. A cross-sectional study was conducted in four villages in Manjacaze district, Southern Mozambique, to determine the seroprevalence of IBV and ARV. A total of 467 serum samples from adult unvaccinated backyard chickens were screened using commercial and competitive enzyme-linked immunoabsorbent assay kits. Our results showed anti-IBV and anti-ARV antibodies in all surveyed households and villages. The overall seroprevalence was 89.5% (95% confidence interval [CI]: 77.2-97.4) and 95.7% (95% CI: 88.0-99.2) for IBV and ARV, respectively. The risk of becoming exposed to IBV was lower in Chidenguele village compared with the other three villages (p  0.05). However, no statistically significant differences were observed for becoming exposed to ARV between villages (p  0.05). The backyard chickens tested in this study had no previous history of vaccination, outbreaks or typical clinical signs of IB and AR diseases. Therefore, the presence of antibodies to IBV and ARV was considered clear evidence that the birds have been naturally exposed to those two infectious agents, and the infection was of subclinical type. It is concluded that IBV and ARV are widespread in backyard chickens in the studied area. These obtained data are essential for design and implementation of chicken health development programmes.Contribution: The epidemiology of IBV and ARV of backyard chicken in Mozambique is unknown. This study determined the seroprevalence of IBV and ARV in backyard chicken health. The obtained data are essential for design and implementation of chicken health development programmes.

The nonstructural p17 protein of a fusogenic bat-borne reovirus regulates viral replication in virus species- and host-specific manners

Nelson Bay orthoreovirus (NBV), a member of the family Reoviridae, genus Orthoreovirus, is a bat-borne virus that causes respiratory diseases in humans. NBV encodes two unique nonstructural proteins, fusion-associated small transmembrane (FAST) protein and p17 protein, in the S1 gene segment. FAST induces cell–cell fusion between infected cells and neighboring cells and the fusogenic activity is required for efficient viral replication. However, the function of p17 in the virus cycle is not fully understood. Here, various p17 mutant viruses including p17-deficient viruses were generated by a reverse genetics system for NBV. The results demonstrated that p17 is not essential for viral replication and does not play an important role in viral pathogenesis. On the other hand, NBV p17 regulated viral replication in a bat cell line but not in other human and animal cell lines. Nuclear localization of p17 is associated with the regulation of NBV replication in bat cells. We also found that p17 dramatically enhances the cell–cell fusion activity of NBV FAST protein for efficient replication in bat cells. Furthermore, we found that a protein homologue of NBV p17 from another bat-borne orthoreovirus, but not those of avian orthoreovirus or baboon orthoreovirus, also supported efficient viral replication in bat cells using a p17-deficient virus-based complementation approach. These results provide critical insights into the functioning of the unique replication machinery of bat-borne viruses in their natural hosts.

Bat-borne viruses including the severe acute respiratory syndrome coronavirus and Nipah virus generally cause highly pathogenic diseases in humans but not in their bat reservoirs. Nelson Bay orthoreovirus (NBV), a bat-borne virus associated with acute respiratory tract infections in humans, possesses two unique nonstructural proteins, FAST and p17. FAST enhances viral replication through its cell–cell fusion activity, while the function of p17 in the viral life cycle is poorly understood. In this study, we show that p17 is non-essential for viral replication in several human and animal cell lines and does not play a critical role in pathogenesis in vivo. However, p17 localizes to the nucleus and regulates viral replication specifically in cells derived from bats by enhancing the cell–cell fusion activity of FAST in a host-specific manner. Furthermore, the expression of NBV p17 or an NBV p17 homologue from another bat-borne orthoreovirus enhanced the replication of an NBV mutant deficient in p17 in bat cells, suggesting that the function of p17 is virus species-specific. These findings will contribute to our understanding of how the replication of viruses is regulated in their natural reservoirs.

Advances on Innate Immune Evasion by Avian Immunosuppressive Viruses

Innate immunity is not only the first line of host defense against pathogenic infection, but also the cornerstone of adaptive immune response. Upon pathogenic infection, pattern recognition receptors (PRRs) of host engage pathogen-associated molecular patterns (PAMPs) of pathogens, which initiates IFN production by activating interferon regulatory transcription factors (IRFs), nuclear factor-kappa B (NF-κB), and/or activating protein-1 (AP-1) signal transduction pathways in host cells. In order to replicate and survive, pathogens have evolved multiple strategies to evade host innate immune responses, including IFN-I signal transduction, autophagy, apoptosis, necrosis, inflammasome and/or metabolic pathways. Some avian viruses may not be highly pathogenic but they have evolved varied strategies to evade or suppress host immune response for survival, causing huge impacts on the poultry industry worldwide. In this review, we focus on the advances on innate immune evasion by several important avian immunosuppressive viruses (infectious bursal disease virus (IBDV), Marek’s disease virus (MDV), avian leukosis virus (ALV), etc.), especially their evasion of PRRs-mediated signal transduction pathways (IFN-I signal transduction pathway) and IFNAR-JAK-STAT signal pathways. A comprehensive understanding of the mechanism by which avian viruses evade or suppress host immune responses will be of help to the development of novel vaccines and therapeutic reagents for the prevention and control of infectious diseases in chickens.

Identification and Functional Analyses of Host Proteins Interacting with the p17 Protein of Avian Reovirus

Avian reovirus (ARV) causes viral arthritis, chronic respiratory diseases, retarded growth and malabsorption syndrome. However, the precise molecular mechanism remains unclear. Here, we report the host cellular proteins that interact with ARV p17 by yeast two-hybrid screening. In this study, the p17 gene was cloned into pGBKT7 to obtain the bait plasmid pGBKT7-p17. After several rounds of screening of a chicken cDNA library, 43 positive clones were identified as possible host factors that interacted with p17. A BLAST search of the sequences was performed on the NCBI website, which ultimately revealed 19 interacting proteins. Gene ontology enrichment and Kyoto Encyclopedia of Genes and Genome analyses indicated that the acquired proteins were involved in multicellular organismal processes, metabolic processes, and biological regulation. When the subcellular localization of the host protein and ARV p17 protein was investigated, we observed colocalization of p17-GFP with IGF2BP1-RED and PQBP1-RED in the transfected cells but not with FGF1-RED. The direct interaction of ARV p17 protein with IGF2BP1 and PQBP1 was confirmed by coimmunoprecipitation and GST pulldown assays. We used RT-qPCR to assess the expression variation during ARV infection. The results showed that IGF2BP1, PAPSS2, RPL5, NEDD4L, PRPS2 and IFI16 were significantly upregulated, whereas the expression of FGF1, CDH2 and PQBP1 was markedly decreased in DF-1 cells infected with ARV. Finally, we demonstrated that IGF2BP1 had a positive effect on ARV replication, while PQBP1 had the opposite effect. Our findings provide valuable information for better insights into ARV's pathogenesis and the role of the p17 protein in this process.

Isolation and Genomic Characterization of Avian Reovirus From Wild Birds in South Korea

Avian reoviruses (ARVs) cause severe arthritis, tenosynovitis, pericarditis, and depressed growth in chickens, and these conditions have become increasingly frequent in recent years. Studies on the role of wild birds in the epidemiology of ARVs are insufficient. This study provides information about currently circulating ARVs in wild birds by gene detection using diagnostic RT-PCR, virus isolation, and genomic characterization. In this study, we isolated and identified 10 ARV isolates from 7,390 wild birds' fecal samples, including migratory bird species (bean goose, Eurasian teal, Indian spot-billed duck, and mallard duck) from 2015 to 2019 in South Korea. On comparing the amino acid sequences of the σC-encoding gene, most isolates, except A18-13, shared higher sequence similarity with the commercial vaccine isolate S1133 and Chinese isolates. However, the A18-13 isolate is similar to live attenuated vaccine av-S1133 and vaccine break isolates (SD09-1, LN09-1, and GX110116). For the p10- and p17-encoding genes, all isolates have identical fusion associated small transmembrane (FAST) protein and nuclear localization signal (SNL) motif to chicken-origin ARVs. Phylogenetic analysis of the amino acid sequences of the σC-encoding gene revealed that all isolates were belonged to genotypic cluster I. For the p10- and p17-encoding genes, the nucleotide sequences of all isolates indicated close relationship with commercial vaccine isolate S1133 and Chinese isolates. For the σNS-encoding gene, the nucleotide sequences of all isolates indicated close relationship with the Californian chicken-origin isolate K1600657 and belonged to chicken-origin ARV cluster. Our data indicates that wild birds ARVs were derived from the chicken farms. This finding suggests that wild birds serve as natural carriers of such viruses for domestic poultry.

Development and evaluation of an indirect ELISA based on recombinant structural protein σC to detect antibodies against avian orthoreovirus

The avian orthoreovirus (ARV) causes large economic losses to poultry industry around the whole world. ARV viral proteins can be classified into three sizes: λ (large), μ (medium) and σ (small). σC, one of the capsid protein of ARV, contains various specific neutralizing epitopes and can induce robust immune responses in infected chickens. An indirect enzyme-linked immunosorbent assay (I-ELISA) was established using the recombinant σC protein. The optimal dilutions of antigen, serum and conjugate goat anti-chicken IgY conjugate were 2.5 μg/ml, 1:80 and 1:4000, respectively. The optimal antigen coating condition was 4℃ for overnight. Hyperimmune serum of high-yielding hens of different age produced stronger reaction against σC. Chicken serum samples were randomly collected and total coincidence rate between commercial kit and σC-ARV-ELISA kit was 97.8%. Importantly, those discrepant serums were further verified using Western blot assay and three of them were determined to be positive. Thus, the method based on σC protein has higher sensitivity compared with the commercial kit and provide a rapid and simple method for serodiagnosis of ARV, contributing to convenient epidemiological monitoring of ARV.

Viral Proteins as Emerging Cancer Therapeutics

Simple Summary

This review is focused on enlisting viral proteins from different host sources, irrespective of their origin, that may act as future cancer curatives. Unlike the viral proteins that are responsible for tumor progression, these newly emerged viral proteins function as tumor suppressors. Their ability to regulate various cell signaling mechanisms specifically in cancer cells makes them interesting candidates to explore their use in cancer therapy. The discussion about such viral components may provide new insights into cancer treatment in the absence of any adverse effects to normal cells. The study also highlights avian viral proteins as a substitute to human oncolytic viruses for their ability to evade pre-existing immunity.

Abstract

Viruses are obligatory intracellular parasites that originated millions of years ago. Viral elements cover almost half of the human genome sequence and have evolved as genetic blueprints in humans. They have existed as endosymbionts as they are largely dependent on host cell metabolism. Viral proteins are known to regulate different mechanisms in the host cells by hijacking cellular metabolism to benefit viral replication. Amicable viral proteins, on the other hand, from several viruses can participate in mediating growth retardation of cancer cells based on genetic abnormalities while sparing normal cells. These proteins exert discreet yet converging pathways to regulate events like cell cycle and apoptosis in human cancer cells. This property of viral proteins could be harnessed for their use in cancer therapy. In this review, we discuss viral proteins from different sources as potential anticancer therapeutics.

Avian Reovirus P17 Suppresses Angiogenesis by Promoting DPP4 Secretion

Avian reovirus p17 (ARV p17) is a non-structural protein known to activate autophagy, interfere with gene transcription and induce a significant tumor cell growth inhibition in vitro and in vivo. In this study, we show that ARV p17 is capable of exerting potent antiangiogenic properties. The viral protein significantly inhibited the physiological angiogenesis of human endothelial cells (ECs) by affecting migration, capillary-like structure and new vessel formation. ARV p17 was not only able to suppress the EC physiological angiogenesis but also rendered ECs insensitive to two different potent proangiogenic inducers, such as VEGF-A and FGF-2 in the three-dimensional (3D) Matrigel and spheroid assay. ARV p17 was found to exert its antiangiogenic activity by upregulating transcription and release of the well-known tumor suppressor molecule dipeptidyl peptidase 4 (DPP4). The ability of ARV p17 to impact on angiogenesis is completely new and highlights the “two compartments” activity of the viral protein that is expected to hamper the tumor parenchymal/stromal crosstalk. The complex antitumor activities of ARV p17 open the way to a new promising field of research aimed to develop new therapeutic approaches for treating tumor and cancer metastasis.

Gallus NME/NM23 nucleoside diphosphate kinase 2 interacts with viral σA and affects the replication of avian reovirus

Our present study aimed to identify host cell proteins that may interact with avian reovirus (ARV) σA protein and their potential effect on ARV replication. The ARV structural protein σA has been demonstrated to suppress interferon production and confirmed to activate the PI3K/Akt pathway. However, host cell factors interacting with σA to affect ARV replication remain unknown. In current study, a cDNA library of chicken embryo fibroblasts (CEFs) was constructed, and host cell proteins interacting with σA were screened by a yeast two-hybrid system. We identified four candidate cellular proteins that interact with ARV σA protein. Among them, Gallus NME/NM23 nucleoside diphosphate kinase 2 (NME2) was further validated as a σA-binding protein through co-immunoprecipitation. The key interaction domain was identified at amino acids (aa) 121-416 in NME2 and at aa 71-139 in σA, respectively. We demonstrated that overexpression of NME2 substantially inhibited ARV replication. In addition silencing NME2 by small interfering RNAs (siRNAs) resulted in marked enhancement of ARV replication. Our work has demonstrated that NME2 is a σA-binding protein that may affect ARV replication in CEF cells.

The genomic constellation of a novel duck reovirus strain associated with hemorrhagic necrotizing hepatitis and splenitis in Muscovy ducklings in Fujian, China

The complete sequence of a reovirus, strain NP03 associated with necrotic focus formation in the liver and spleen of Muscovy ducklings in Fujian Province, China in 2009, was determined and compared with sequences of other waterfowl and chicken-origin avian reoviruses (ARVs). Sequencing of the complete genomes of strain NP03 showed that they consisted of 23,418 bp and were divided into 10 segments, ranging from 1191 bp (S4) to 3959 bp (L1) in length, and all segments contained conserved sequences in the 5' non-coding region (GCUUUU) and 3' non-coding region (UCAUC). Pairwise sequence comparisons demonstrated that NP03 strain showed the highest similarity with novel waterfowl origin reoviruses (WRVs). The genome analysis revealed that the S1 segment of novel WRV is a tricistronic gene, encoding the overlapping open reading frames (ORFs) for p10, p18, and σC, similar to the ARV S1 gene, but distinct from classical WRV S4 genome segment, which contained two overlapping ORFs encoding p10 and σC. Phylogenetic analyses of the nucleotide sequences of all 10 segments revealed that NP03 strain was clustered together with other novel WRVs and were distinct from classical WRVs and chicken-origin ARVs. The analyses also showed possible intra-segmental reassortment events in the segments encoding λA, λB, μB, μNS, σA, and σNS between novel and classical WRVs. Potential recombination events detection in segment L1 suggests that NP03 strain may be recombinants of novel WRVs. Based on our genetic analyses, multiple reassortment events, intra-segmental recombination, and accumulation of point mutations have possibly contributed to the emergence of this novel genotype of WRV, identified in China.

Enhanced X-ray diffraction of in vivo-grown μNS crystals by viscous jets at XFELs

μNS is a 70 kDa major nonstructural protein of avian reoviruses, which cause significant economic losses in the poultry industry. They replicate inside viral factories in host cells, and the μNS protein has been suggested to be the minimal viral factor required for factory formation. Thus, determining the structure of μNS is of great importance for understanding its role in viral infection. In the study presented here, a fragment consisting of residues 448-605 of μNS was expressed as an EGFP fusion protein in Sf9 insect cells. EGFP-μNS(448-605) crystallization in Sf9 cells was monitored and verified by several imaging techniques. Cells infected with the EGFP-μNS(448-605) baculovirus formed rod-shaped microcrystals (5-15 µm in length) which were reconstituted in high-viscosity media (LCP and agarose) and investigated by serial femtosecond X-ray diffraction using viscous jets at an X-ray free-electron laser (XFEL). The crystals diffracted to 4.5 Å resolution. A total of 4227 diffraction snapshots were successfully indexed into a hexagonal lattice with unit-cell parameters a = 109.29, b = 110.29, c = 324.97 Å. The final data set was merged and refined to 7.0 Å resolution. Preliminary electron-density maps were obtained. While more diffraction data are required to solve the structure of μNS(448-605), the current experimental strategy, which couples high-viscosity crystal delivery at an XFEL with in cellulo crystallization, paves the way towards structure determination of the μNS protein.

The diagnosis and successful replication of a clinical case of Duck Spleen Necrosis Disease: An experimental co-infection of an emerging unique reovirus and Salmonella indiana reveals the roles of each of the pathogens

Duck spleen necrosis disease (DSND) is an emerging infectious disease that causes significant economic loss in the duck industry. In 2018, a duck reovirus (named DRV/GX-Y7) and Salmonella indiana were both isolated from the spleens and livers of diseased ducks with DSND in China. The DRV/GX-Y7 strain could propagate in the Vero, LMH, DF-1 and DEF cells with obvious cytopathic effects. The genome of DRV/GX-Y7 was 23,418 bp in length, contained 10 dsRNA segments, ranging from 3959 nt (L1) to 1191 nt (S4). The phylogenetic analysis showed that the DRV/GX-Y7 strain was in the same branch with the new waterfowl-origin reovirus cluster, but was obviously far distant from the clusters of other previous waterfowl-origin reoviruses Muscovy duck reovirus (MDRV) and goose-origin reovirus (GRV), broiler/layer-origin reovirus (ARV) and turkey-origin reovirus (TRV). The RDP and SimPlot program analysis revealed that there were two potential genetic reassortment events in the M2 and S1 segments of the genome. In order to have a clear insight into the pathogenic mechanism of DRV/GX-Y7 and S. Indiana in clinical DSND, an infection experiment was further conducted by challenging commercial ducklings with the two isolates individually and with both. The results showed that DRV/GX-Y7 produced severe hemorrhagic and/or necrotic lesions in the immune organs (thymus, spleen, and bursae) of experimentally infected ducklings. And, that the co-infection of DRV/GX-Y7 and S. Indiana could greatly enhance the pathogenesis by increasing the morbidity and mortality in ducklings whose clinical symptoms and lesions were similar to the natural clinical DSND cases. In summary, the results suggested that the pathogen causing duck spleen necrosis was an emerging unique genetic reassortment strain of duck Orthoreovirus that was significantly different from any previously reported waterfowl-derived Orthoreovirus and the co-infection with the Salmonella isolate could increase the severity of the disease.

Pathogenicity of a variant duck orthoreovirus strain in Cherry Valley Ducklings

Since 2017, a disease that is characterized by spleen necrosis and swelling has emerged in China's main meat duck breeding provinces, this disease generally causes a large number of ducks to develop a poor mental state and either an increase or loss of appetite, as well as potentially resulting in death. Necrosis of spleen in this disease weakens the duck's immunity, therefore often leading to secondary infection. The net result of this is significant economic loss to China's duck breeding industry. In our previous research, we determined that the pathogen causing this disease is a new variant duck orthoreovirus (N-DRV). Because the morbidity and mortality rates of the isolate were higher than those of the previously reported strains, 180 healthy 1-day-old Cherry Valley ducklings were selected to be artificially infected in order to determine the pathogenicity of the strain. The weight gains of numbers of the infected group were significantly inhibited after they had been inoculated with the virus, which continued to detoxify in the blood and the cloaca. The main target organ of the virus is the spleen, although the virus can also attack the brain, this does not lead to any obvious pathology in this organ. These findings have enriched our understanding of the N-DRV-XT18 virus and have lain the foundation for further study of the pathogenic mechanism of this virus.

Fusogenic Reoviruses and Their Fusion-Associated Small Transmembrane (FAST) Proteins

With no limiting membrane surrounding virions, nonenveloped viruses have no need for membrane fusion to gain access to intracellular replication compartments. Consequently, nonenveloped viruses do not encode membrane fusion proteins. The only exception to this dogma is the fusogenic reoviruses that encode fusion-associated small transmembrane (FAST) proteins that induce syncytium formation. FAST proteins are the smallest viral membrane fusion proteins and, unlike their enveloped virus counterparts, are nonstructural proteins that evolved specifically to induce cell-to-cell, not virus-cell, membrane fusion. This distinct evolutionary imperative is reflected in structural and functional features that distinguish this singular family of viral fusogens from all other protein fusogens. These rudimentary fusogens comprise specific combinations of different membrane effector motifs assembled into small, modular membrane fusogens. FAST proteins offer a minimalist model to better understand the ubiquitous process of protein-mediated membrane fusion and to reveal novel mechanisms of nonenveloped virus dissemination that contribute to virulence.

Phenotypic and genetic characterisation of an emerging reovirus from Pekin ducks in China

In June 2016, a disease characterised by intestinal haemorrhage with a mortality rate of approximately 5% was observed in a duck farm in Shandong province, China. Here, we report the isolation and characterisation of a reovirus from duck tissue samples by inoculating duck embryos and duck embryo fibroblasts (DEF). The isolate replicated in DEF and Vero cells and formed syncytia. Sequence analysis revealed that the viral genome was 23,434 nt in length with typical structure organization, consisting of 10 dsRNA segments ranging from 3998 nt (L1) to 1190 nt (S4) in size, and was genetically distinct from previous Chinese duck-origin reoviruses. Phylogenetic analyses showed that the isolate was most closely related to the recently reported duck reovirus D2533/6/1-10 isolated in Germany, forming a monophyletic branch different from known reference avian reoviruses. Experimental infection results indicated that the isolate replicated transiently in ducklings and was shed via faeces. Infection with the isolate caused epithelial cell damage and lymphocyte apoptotic death in the bursa of Fabricius, which may result in immunosuppression in infected ducklings. The role of the isolate in current duck haemorrhage enteritis remains to be determined, but its damage to the bursa warrants further investigation of the duck immune response.

A multiplex xTAG assay for the simultaneous detection of five chicken immunosuppressive viruses

Background

Chicken anemia virus (CAV), avian reovirus (ARV), infectious bursal disease virus (IBDV), Marek’s disease virus (MDV) and reticuloendotheliosis virus (REV) all cause immunosuppressive disease in birds through vertical or horizontal transmission. Mixed infections with these immunosuppressive pathogens lead to atypical clinical signs and obstruct accurate diagnoses and epidemiological investigations. Therefore, it is essential to develop a high-throughput assay for the simultaneous detection of these immunosuppressive viruses with high specificity and sensitivity. The aim of this study was to establish a novel method using a RT-PCR assay combined with fluorescence labeled polystyrene bead microarray (multiplex xTAG assay) to detect single or mixed viral infections.

Results

The results showed that the established xTAG assay had no nonspecific reactions with avian influenza virus (AIV), infectious bronchitis virus (IBV), newcastle disease virus (NDV), infectious laryngotracheitis virus (ILTV), Mycoplasma gallisepticum (MG) and Mycoplasma synoviae (MS). The limit of detection was 1.0 × 10³ copies/μL for IBDV and 1.0 × 10²copies/μL for the other four viruses. Ninety field samples were tested and the results were confirmed using conventional RT-PCR methods. The detection results of these two methods were 100% consistent. The established multiplex xTAG assay allows a high throughput and simultaneous detection of five chicken immunosuppressive viruses.

Conclusion

The multiplex xTAG assay has been showed to be an additional tool for molecular epidemiology studies of five chicken immunosuppressive viruses in the poultry industry.

Electronic supplementary material

The online version of this article (10.1186/s12917-018-1663-1) contains supplementary material, which is available to authorized users.

The E3 Ubiquitin Ligase Siah-1 Suppresses Avian Reovirus Infection by Targeting p10 for Degradation

Avian reovirus (ARV) causes viral arthritis, chronic respiratory diseases, retarded growth, and malabsorption syndrome. The ARV p10 protein, a viroporin responsible for the induction of cell syncytium formation and apoptosis, is rapidly degraded in host cells. Our previous report demonstrated that cellular lysosome-associated membrane protein 1 (LAMP-1) interacted with p10 and was involved in its degradation. However, the molecular mechanism underlying LAMP-1-mediated p10 degradation remains elusive. We report here that the E3 ubiquitin ligase seven in absentia homolog 1 (Siah-1) is critical for p10 ubiquitylation. Our data show that Siah-1 ubiquitylated p10 and targeted it for proteasome degradation. Furthermore, the ubiquitylation of p10 by Siah-1 required the participation of LAMP-1 by forming a multicomponent complex. Thus, LAMP-1 promotes the proteasomal degradation of p10 via interacting with both p10 and the E3 ligase Siah-1. These data establish a novel host defense mechanism where LAMP-1 serves as a scaffold for both Siah-1 and p10 that allows the E3 ligase targeting p10 for ubiquitylation and degradation to suppress ARV infection.IMPORTANCE Avian reovirus (ARV) is an important poultry pathogen causing viral arthritis, chronic respiratory diseases, retarded growth, and malabsorption syndrome, leading to considerable economic losses to the poultry industry across the globe. The ARV p10 protein is a virulence factor responsible for the induction of cell syncytium formation and apoptosis and is rapidly degraded in host cells. We previously found that cellular lysosome-associated membrane protein 1 (LAMP-1) interacts with p10 and is involved in its degradation. Here we report that the E3 ubiquitin ligase seven in absentia homolog 1 (Siah-1) ubiquitylated p10 and targeted it for proteasomal degradation. Furthermore, the ubiquitylation of p10 by Siah-1 required the participation of LAMP-1 by forming a multicomponent complex. Thus, LAMP-1 serves as an adaptor to allow Siah-1 to target p10 for degradation, thereby suppressing ARV growth in host cells.

Isolation and genomic characterization of a novel avian orthoreovirus strain in Korea, 2014

In this study, we isolated a novel avian reovirus (ARV) strain, K738/14, from a broiler chicken with viral arthritis in South Korea. Genome sequence comparisons showed relatively low nucleotide identity with previously identified ARV strains. Phylogenetic analyses suggested multiple reassortment events between reovirus strain S1133 and reoviruses of Hungarian, Chinese, and US origin had occurred. In addition, recombination analyses showed evidence of intra-segmental recombination in the M2 and S2 genes. Based on our genetic analyses, multiple reassortment events, intra-segmental recombination, and accumulation of point mutations have possibly contributed to the emergence of this novel genotype of ARV, identified in Korea.

Phenotypic, genotypic and antigenic characterization of emerging avian reoviruses isolated from clinical cases of arthritis in broilers in Saskatchewan, Canada

In recent years, emerging strains of pathogenic arthrogenic avian reovirus (ARV) have become a challenge to the chicken industry across USA and Canada causing significant economic impact. In this study, we characterized emerging variant ARV strains and examined their genetic and antigenic relationship with reference strains. We isolated 37 emerging variant ARV strains from tendons of broiler chickens with clinical cases of arthritis/tenosynovitis at commercial farms in Saskatchewan, Canada. Viral characterization using immunocytochemistry, gold-immunolabeling and electron microscopy revealed distinct features characteristic of ARV. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analyses of the viral Sigma C gene revealed genetic heterogeneity between the field isolates. On phylogenetic analyses, the Sigma C amino acid sequences of the isolates were clustered into four distinct genotypic groups. These ARV field strains were genetically diverse and quite distant from the vaccine and vaccine related field strains. Antibodies produced against a commercial Reo 2177 ® vaccine did not neutralize these variants. Moreover, structure based analysis of the Sigma C protein revealed significant antigenic variability between the cluster groups and the vaccine strains. To the best of our knowledge, this is the first report on the genetic, phenotypic and antigenic characterization of emerging ARVs in Canada.

Reverse Genetics for Fusogenic Bat-Borne Orthoreovirus Associated with Acute Respiratory Tract Infections in Humans: Role of Outer Capsid Protein σC in Viral Replication and Pathogenesis

Nelson Bay orthoreoviruses (NBVs) are members of the fusogenic orthoreoviruses and possess 10-segmented double-stranded RNA genomes. NBV was first isolated from a fruit bat in Australia more than 40 years ago, but it was not associated with any disease. However, several NBV strains have been recently identified as causative agents for respiratory tract infections in humans. Isolation of these pathogenic bat reoviruses from patients suggests that NBVs have evolved to propagate in humans in the form of zoonosis. To date, no strategy has been developed to rescue infectious viruses from cloned cDNA for any member of the fusogenic orthoreoviruses. In this study, we report the development of a plasmid-based reverse genetics system free of helper viruses and independent of any selection for NBV isolated from humans with acute respiratory infection. cDNAs corresponding to each of the 10 full-length RNA gene segments of NBV were cotransfected into culture cells expressing T7 RNA polymerase, and viable NBV was isolated using a plaque assay. The growth kinetics and cell-to-cell fusion activity of recombinant strains, rescued using the reverse genetics system, were indistinguishable from those of native strains. We used the reverse genetics system to generate viruses deficient in the cell attachment protein σC to define the biological function of this protein in the viral life cycle. Our results with σC-deficient viruses demonstrated that σC is dispensable for cell attachment in several cell lines, including murine fibroblast L929 cells but not in human lung epithelial A549 cells, and plays a critical role in viral pathogenesis. We also used the system to rescue a virus that expresses a yellow fluorescent protein. The reverse genetics system developed in this study can be applied to study the propagation and pathogenesis of pathogenic NBVs and in the generation of recombinant NBVs for future vaccines and therapeutics.

Nelson Bay orthoreoviruses (NBVs) are members of the fusogenic orthoreoviruses that have various host species, including reptiles, birds, and mammals. Recently, several NBV strains have been isolated from patients with acute respiratory tract infections. Isolation of these pathogenic reoviruses raises concerns about the potential emerging infections of bat-borne orthoreoviruses in humans. The development of an entirely plasmid-based reverse genetics system for double-stranded RNA viruses has trailed other systems of major animal RNA virus groups because of the technical complexities involved in the manipulation of genomes composed of 10 or more segments. In this study, we developed a plasmid-based reverse genetics system for a pathogenic NBV strain. We used this system to generate viruses incapable of expressing the cell attachment protein σC and to rescue a replication-competent virus that expresses a yellow fluorescent protein. Our studies using σC-deficient viruses suggest that NBVs may engage multiple independent viral ligands and cellular receptors for efficient cell attachment and viral pathogenesis, thus providing new insight into the biology of orthoreoviruses. The reverse genetics approach described in this study can be exploited for fusogenic orthoreovirus biology and used to develop vaccines, diagnostics, and therapeutics.

Whole genome alignment based one-step real-time RT-PCR for universal detection of avian orthoreoviruses of chicken, pheasant and turkey origins

Newly emerging avian orthoreovirus (ARV) variants have been continuously detected in Pennsylvania poultry since 2011. In this paper, we report our recent diagnostic assay development of one-step real-time RT-PCR (rRT-PCR) for the rapid and universal detection of all ARVs or reference strains of chicken, pheasant and turkey origins and six σC genotypes of the newly emerging field ARV variants in Pennsylvania (PA) poultry. Primers and probes for the rRT-PCR were designed from the conserved region of the M1 genome segment 5' end based on the whole-genome alignment of various ARV strains, including six field variants or novel strains obtained in PA poultry. The detection limit of the newly developed rRT-PCR for ARV was as low as 10 copies/reaction of viral RNA, and 10(0.50)-10(0.88) tissue culture infectious dose (TCID50)/100 μL of viruses. This new rRT-PCR detected all six σC genotypes from the 66 ARV field variant strains and reference strains tested in this study. There were no cross-reactions with other avian viruses. Reproducibility of the assay was confirmed by intra- and inter-assay tests with variability from 0.12% to 2.19%. Sensitivity and specificity of this new rRT-PCR for ARV were achieved at 100% and 88%, respectively, in comparison with virus isolation as the "gold standard" in testing poultry tissue specimen.

A critical role of LAMP-1 in avian reovirus P10 degradation associated with inhibition of apoptosis and virus release

Avian reovirus (ARV) causes viral arthritis, chronic respiratory diseases, retarded growth and malabsorption syndrome. The ARV p10 protein, a viroporin responsible for the induction of cell syncytium formation and apoptosis, is rapidly degraded in host cells. However, the mechanism of p10 degradation and its relevance are still unclear. We report here the identification of cellular lysosome-associated membrane protein 1 (LAMP-1) as an interaction partner of p10 by yeast two-hybrid screening, immunoprecipitation and confocal microscopy assays. We found that rapid degradation of p10 was associated with ubiquitination. Importantly, ARV p10 degradation in host cells could be completely abolished by knockdown of LAMP-1 by siRNA, indicating that LAMP-1 is required for ARV p10 degradation in host cells. In contrast, overexpression of LAMP-1 facilitated p10 degradation. Furthermore, knockdown of LAMP-1 allowed p10 accumulation, enhancing p10-induced apoptosis and viral release. Thus, LAMP-1 plays a critical role in ARV p10 degradation associated with inhibition of apoptosis and viral release.

Nuclear localization of the p17 protein of avian reovirus is correlated with autophagy induction and an increase in viral replication

p17 is a nonstructural protein of avian reovirus (ARV) that induces autophagy in infected cells. In the present study, we investigated the effect of p17 and its nuclear localization signal (NLS) on autophagy and viral replication. When Vero cells and DF1 cells were transfected with mutant p17 in which lysine (K) at position 122 and arginine (R) at position 123 were mutated to alanine (A), the expression level of LC3 II decreased dramatically after transfection. The expression of the polypeptide encompassing the first 103 amino acids of p17, a region that did not contain the NLS, did not have a significant effect on autophagy. Moreover, when cells overexpressing mutant p17 were infected with the ARV GX2010/1 strain, the viral titer was significantly decreased compared with the expression of wild-type p17. In general, the NLS of p17 facilitates the induction of autophagy and is correlated with an increase in virus production.

RhoA/ROCK1 regulates Avian Reovirus S1133-induced switch from autophagy to apoptosis

BACKGROUND

Autophagy is an essential process in the control of cellular homeostasis. It enables cells under certain stress conditions to survive by removing toxic cellular components, and may protect cells from apoptosis. In the present study, the signaling pathways involved in ARV S1133 regulated switch from autophagy to apoptosis were investigated.

RESULTS

ARV S1133 infection caused autophagy in the early to middle infectious stages in Vero and DF1 cells, and apoptosis in the middle to late stages. Conversion of the autophagy marker LC3-I to LC3-II occurred earlier than cleavage of the apoptotic marker caspase-3. ARV S1133 also activated the Beclin-1 promoter in the early to middle stages of infection. Levels of RhoA-GTP and ROCK1 activity were elevated upon ARV S1133 infection, while inhibition of RhoA and ROCK1 reduced autophagy and subsequent apoptosis. Conversely, inhibition of caspase-3 did not affect the level of autophagy. Beclin-1 knockdown and treatment with autophagy inhibitors, 3-MA and Bafilomycin A1, suppressed ARV S1133-induced autophagy and apoptosis simultaneously, suggesting the shift from autophagy to apoptosis. A co-immunoprecipitation assay demonstrated that the formation of a RhoA, ROCK1 and Beclin-1 complex coincided with the induction of autophagy.

CONCLUSION

Our results demonstrate that RhoA/ROCK1 signaling play critical roles in the transition of cell activity from autophagy to apoptosis in ARV S1133-infected cells.

Critical role of eukaryotic elongation factor 1 alpha 1 (EEF1A1) in avian reovirus sigma-C-induced apoptosis and inhibition of viral growth

Avian reovirus (ARV) causes viral arthritis, chronic respiratory diseases, retarded growth and malabsorption syndrome. It is well established that the ARV sigma-C protein induces apoptosis in host cells. However, the underlying molecular mechanism of this induction is still unclear. We report here the identification of eukaryotic elongation factor 1 alpha 1 (EEF1A1) as the interacting partner of σC. We found that σC-induced apoptosis in DF-1 cells could be completely abolished by knockdown of EEF1A1 by siRNA. Furthermore, knockdown of EEF1A1 markedly reduced ARV-induced apoptosis associated with decreased caspase-9 and -3 activation and cytochrome C release, leading to increased ARV growth in host cells. Thus, EEF1A1 plays a critical role in σC-induced apoptosis and inhibition of viral growth.

Replicating reoviruses with a transgene replacing the codons for the head domain of the viral spike

The capacity to modify the reovirus genome facilitates generation of new therapeutic reoviruses. We describe a method for generating replication-competent reoviruses carrying a heterologous transgene. The strategy is based on the expanded-tropism reovirus mutant jin-3, which can infect cells independent of the reovirus receptor junction-adhesion molecule A (JAM-A). Jin-3 harbors a mutation in the S1 segment, resulting in a G196R substitution in the tail of the spike protein σ1. The use of the jin-3 tail-encoding S1 segment allows replacing the codons for the JAM-A-binding head domain by up to 522  nucleotides of foreign sequences, without exceeding the size of the wild-type S1 segment. We inserted the codons for the porcine teschovirus-1 2A element fused with those encoding the fluorescent protein iLOV. Replicating rS1His-2A-iLOV reoviruses were generated by co-transfection of expression plasmids for all reovirus segments. These reoviruses contain the S1His-2A-iLOV segment in the absence of the wild-type S1 segment. Density-gradient centrifugation confirmed the association of the σ1-tail fragment with the capsid. Both JAM-A-positive and -negative cells exposed to the rS1His-2A-iLOV reoviruses exhibited iLOV fluorescence, confirming the jin-3-derived expanded-tropism phenotype. These data demonstrated the feasibility of generating decapitated replication-competent T3D reoviruses carrying a heterologous transgene.

Molecular characterization of a novel reovirus isolated from Pekin ducklings in China

The complete genome sequence of a novel duck orthoreovirus, designated DRV strain TH11(DRV-TH11), was determined and characterized. The DRV-TH11 genome is comprised of 23,417 bp and its genome organization is more similar to that of avian orthoreoviruses (ARVs) of chicken origin than other reoviruses. The results of comparative sequence analysis and dendrograms based on the µB- and σC-encoding genes indicated that TH11 may be derived from the reassortment of ARVs and classic Muscovy duck reovirus (MDRV). A possible recombinant event was identified using the SimPlot program, and it occurred in the M2 segment. The results indicated that reassortment and mutation play a role in the evolution of duck reovirus.

Avian reovirus-triggered apoptosis enhances both virus spread and the processing of the viral nonstructural muNS protein

Avian reovirus non-structural protein muNS is partially cleaved in infected chicken embryo fibroblast cells to produce a 55-kDa carboxyterminal protein, termed muNSC, and a 17-kDa aminoterminal polypeptide, designated muNSN. In this study we demonstrate that muNS processing is catalyzed by a caspase 3-like protease activated during the course of avian reovirus infection. The cleavage site was mapped by site directed mutagenesis between residues Asp-154 and Ala-155 of the muNS sequence. Although muNS and muNSC, but not muNSN, are able to form inclusions when expressed individually in transfected cells, only muNS is able to recruit specific ARV proteins to these structures. Furthermore, muNSC associates with ARV factories more weakly than muNS, sigmaNS and lambdaA. Finally, the inhibition of caspase activity in ARV-infected cells does not diminish ARV gene expression and replication, but drastically reduces muNS processing and the release and dissemination of progeny viral particles.

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Avian reovirus-triggered apoptosis promotes cleavage of the viral nonstructural muNS protein.

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muNS processing is catalyzed by a caspase 3-like protease activated during avian reovirus infection.

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Cleavage occurs between residues Asp-154 and Ala-155 of the muNS sequence.

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Avian reovirus-induced apoptosis enhances the release and dissemination of progeny viral particles.

Molecular characterization of turkey enteric reovirus S3 gene

The molecular diversity in S3 gene sequences of turkey reovirus (TRV) was determined in poult enteritis syndrome (PES)-affected and apparently healthy turkey poults. Twenty-nine TRV-positive samples (15 from PES-affected flocks and 14 from apparently healthy flocks) were tested using self-designed primers for the S3 gene. Phylogenetic analysis revealed that the TRV S3 sequences of this study clustered in clade III and formed two different groups in this clade. The avian reoviruses from duck and goose formed clade I and those from chickens formed clade II. The clade III TRV sequences had a nucleotide percent identity of 88.9 to 100% among themselves but only of 59.5 to 63.5% and 69.2 to 72.6% with clades I and II, respectively. More amino acid substitutions were present in TRVs from PES-affected flocks than in those from apparently healthy flocks using ATCC VR-818 (AY444912) as a benchmark. All TRVs of this study showed substitutions at positions 244 and 285. The impact of these changes on the virulence of the virus, if any, needs to be studied.

Proteomics analysis of the DF-1 chicken fibroblasts infected with avian reovirus strain S1133

BACKGROUND

Avian reovirus (ARV) is a member of the Orthoreovirus genus in the Reoviridae family. It is the etiological agent of several diseases, among which viral arthritis and malabsorption syndrome are the most commercially important, causing considerable economic losses in the poultry industry. Although a small but increasing number of reports have characterized some aspects of ARV infection, global changes in protein expression in ARV-infected host cells have not been examined. The current study used a proteomics approach to obtain a comprehensive view of changes in protein levels in host cells upon infection by ARV.

METHODOLOGY AND PRINCIPAL FINDINGS

The proteomics profiles of DF-1 chicken fibroblast cells infected with ARV strain S1133 were analyzed by two-dimensional differential-image gel electrophoresis. The majority of protein expression changes (≥ 1.5 fold, p<0.05) occurred at 72 h post-infection. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry identified 51 proteins with differential expression levels, including 25 that were upregulated during ARV infection and 26 that were downregulated. These proteins were divided into eight groups according to biological function: signal transduction, stress response, RNA processing, the ubiquitin-proteasome pathway, lipid metabolism, carbohydrate metabolism, energy metabolism, and cytoskeleton organization. They were further examined by immunoblotting to validate the observed alterations in protein expression.

CONCLUSION/SIGNIFICANCE

This is the first report of a time-course proteomic analysis of ARV-infected host cells. Notably, all identified proteins involved in signal transduction, RNA processing, and the ubiquitin-proteasome pathway were downregulated in infected cells, whereas proteins involved in DNA synthesis, apoptosis, and energy production pathways were upregulated. In addition, other differentially expressed proteins were linked with the cytoskeleton, metabolism, redox regulation, and stress response. These proteomics data provide valuable information about host cell responses to ARV infection and will facilitate further studies of the molecular mechanisms underlying ARV pathogenesis.

Commentary on the regulation of viral proteins in autophagy process

The ability to subvert intracellular antiviral defenses is necessary for virus to survive as its replication occurs only in the host cells. Viruses have to modulate cellular processes and antiviral mechanisms to their own advantage during the entire virus life cycle. Autophagy plays important roles in cell regulation. Its function is not only to catabolize aggregate proteins and damaged organelles for recycling but also to serve as innate immunity to remove intracellular pathogenic elements such as viruses. Nevertheless, some viruses have evolved to negatively regulate autophagy by inhibiting its formation. Even more, some viruses have employed autophagy to benefit their replication. To date, there are more and more growing evidences uncovering the functions of many viral proteins to regulate autophagy through different cellular pathways. In this review, we will discuss the relationship between viruses and autophagy and summarize the current knowledge on the functions of viral proteins contributing to affect autophagy process.

Enteric viruses in turkey enteritis

Gut health is very important to get maximum returns in terms of weight gain and egg production. Enteric diseases such as poult enteritis complex (PEC) in turkeys do not allow their production potential to be achieved to its maximum. A number of viruses, bacteria, and protozoa have been implicated but the primary etiology has not been definitively established. Previously, electron microscopy was used to detect the presence of enteric viruses, which were identified solely on the basis of their morphology. With the advent of rapid molecular diagnostic methods and next generation nucleic acid sequencing, researchers have made long strides in identification and characterization of viruses associated with PEC. The molecular techniques have also helped us in identification of pathogens which were previously not known. Regional and national surveys have revealed the presence of several different enteric viruses in PEC including rotavirus, astrovirus, reovirus and coronavirus either alone or in combination. There may still be unknown pathogens that may directly or indirectly play a role in enteritis in turkeys. This review will focus on the role of turkey coronavirus, rotavirus, reovirus, and astrovirus in turkey enteritis.

Sequencing and phylogenetic analysis of an avian reovirus genome

Avian reovirus infection causes considerable economic loss to the commercial poultry industry. Live-attenuated vaccine strain S1133 (v-S1133, derived from parent strain S1133) is considered the safest and most effective vaccine and is currently used worldwide. To identify the genes responsible for its attenuation, DNA sequences of open reading frames (ORF) of S1133 and its parent strains S1133, 1733, 526, and C78 along with three field isolates (GuangxiR1, GuangxiR2, and GX110058) and one isolate (GX110116) from a vaccinated chicken were performed. The sequence data were compared with available sequences in nucleotide sequence databases of American (AVS-B, 138, 176) and Chinese (C-98 and T-98) origin. Sequence analysis identified that several v-S1133 specific nucleotide substitutions existed in the ORFs of λA, λB, λC, μA, μB, μNS, σA, σB, and σNS genes. The v-S1133 strain could be differentiated from the field-isolated strains based on single nucleotide polymorphisms. Phylogenetic analysis revealed that v-S1133 shared the highest sequence homologies with S1133 and reovirus isolates from China, grouped together in one cluster. Chinese isolates were clearly more distinct from the American reovirus AVS-B strain, which is associated with runting-stunting syndrome in broilers.

Isolation and genomic characterization of a classical Muscovy duck reovirus isolated in Zhejiang, China

A classical Muscovy reovirus was isolated from a sick Muscovy duck with white necrotic foci in its liver in Zhejiang, China, in 2000. This classical reovirus was propagated in a chicken fibroblast cell line (DF-1) with obvious cytopathic effects. Its genome was 22,967 bp in length, with approximately 51.41% G+C content and 10 dsRNA segments encoding 11 proteins, which formed a 3/3/4 electrophoretic PAGE profile pattern. The length of the genomic segments was similar to those of avian orthoreoviruses (ARV and N-MDRV), ranging from 3959 nt (L1) to 1191nt (S4). All of the segments have the conserved terminal sequences 5'-GCUUUU--UUCAUC-3', and with the exception of the S4 segment, all the genome segments apparently encode one single primary translation product. The genome analysis revealed that the S4 segment of classical MDRV is a bicistronic gene, encoding the overlapping ORFs for p10 and σC but distinct from ARV and N-MDRV/N-GRV, which codes for p10, p18 and σC via the tricistronic S1 segment. A comparative sequence analysis provided evidence indicating extensive sequence divergence between classical MDRV and other avian orthoreoviruses. A phylogenetic analysis based on the RNA-dependent RNA polymerase (RdRp) and the major outer capsid proteins σC was performed. Members of the DRVs in the Avian orthoreovirus species were clustered into two genetic groups (classical MDRV and N-MDRV genotype), and the classical MDRV isolates formed distinct lineages (China and Europe lineages), suggesting that the classical MDRVs isolated in restricted geographical region are evolving by different and independent pathways.

Sequence analysis of the genome of piscine orthoreovirus (PRV) associated with heart and skeletal muscle inflammation (HSMI) in Atlantic salmon (Salmo salar)

Piscine orthoreovirus (PRV) is associated with heart- and skeletal muscle inflammation (HSMI) of farmed Atlantic salmon (Salmo salar). We have performed detailed sequence analysis of the PRV genome with focus on putative encoded proteins, compared with prototype strains from mammalian (MRV T3D)- and avian orthoreoviruses (ARV-138), and aquareovirus (GCRV-873). Amino acid identities were low for most gene segments but detailed sequence analysis showed that many protein motifs or key amino acid residues known to be central to protein function are conserved for most PRV proteins. For M-class proteins this included a proline residue in μ2 which, for MRV, has been shown to play a key role in both the formation and structural organization of virus inclusion bodies, and affect interferon-β signaling and induction of myocarditis. Predicted structural similarities in the inner core-forming proteins λ1 and σ2 suggest a conserved core structure. In contrast, low amino acid identities in the predicted PRV surface proteins μ1, σ1 and σ3 suggested differences regarding cellular interactions between the reovirus genera. However, for σ1, amino acid residues central for MRV binding to sialic acids, and cleavage- and myristoylation sites in μ1 required for endosomal membrane penetration during infection are partially or wholly conserved in the homologous PRV proteins. In PRV σ3 the only conserved element found was a zinc finger motif. We provide evidence that the S1 segment encoding σ3 also encodes a 124 aa (p13) protein, which appears to be localized to intracellular Golgi-like structures. The S2 and L2 gene segments are also potentially polycistronic, predicted to encode a 71 aa- (p8) and a 98 aa (p11) protein, respectively. It is concluded that PRV has more properties in common with orthoreoviruses than with aquareoviruses.

Complete genome sequences of an avian orthoreovirus isolated from guangxi, china

We report the complete genomic sequences of an avian orthoreovirus, strain GuangxiR1, isolated from a chicken flock in Guangxi Province, southern China, in 2000. Phylogenetic analyses suggest that the strain is closely related to the S1133 strain, which is associated with tenosynovitis, but is far different from strain AVS-B, which is associated with runting-stunting syndrome in broilers.

Piscine reovirus encodes a cytotoxic, non-fusogenic, integral membrane protein and previously unrecognized virion outer-capsid proteins

Piscine reovirus (PRV) is a tentative new member of the family Reoviridae and has been linked to heart and skeletal muscle inflammation in farmed Atlantic salmon (Salmo salar L.). Recent sequence-based evidence suggests that PRV is about equally related to members of the genera Orthoreovirus and Aquareovirus. Sequence similarities have also suggested that PRV might encode a fusion-associated small transmembrane (FAST) protein, which in turn suggests that PRV might be the prototype of a new genus with syncytium-inducing potential. In previous support of this designation has been the absence of identifiable PRV-encoded homologues of either the virion outer-clamp protein of ortho- and aquareoviruses or the virion outer-fibre protein of most orthoreoviruses. In the current report, we have provided experimental evidence that the putative p13 FAST protein of PRV lacks the defining feature of the FAST protein family – the ability to induce syncytium formation. Instead, p13 is the first example of a cytosolic, integral membrane protein encoded by ortho- or aquareoviruses, and induces cytotoxicity in the absence of cell–cell fusion. Sequence analysis also identified signature motifs of the outer-clamp and outer-fibre proteins of other reoviruses in two of the predicted PRV gene products. Based on these findings, we conclude that PRV does not encode a FAST protein and is therefore unlikely to be a new fusogenic reovirus. The presence of a novel integral membrane protein and two previously unrecognized, essential outer-capsid proteins has important implications for the biology, evolution and taxonomic classification of this virus.

Complete genomic sequence of goose-origin reovirus from China

We report the full-genome sequence of a goose-origin reovirus (GRV) strain 03G from Zhejiang Province, China. This is the first report of the complete genomic sequence (segments 1 to 10) of GRV. Phylogenetic analyses of the sequence suggest that GRV 03G represents a new species distinct from other established species within the avian reovirus (ARV) group of orthoreoviruses.

Evolutionary relationship of the L- and M-class genome segments of bat-borne fusogenic orthoreoviruses in Malaysia and Australia

We previously described three new Malaysian orthoreoviruses designated Pulau virus, Melaka virus and Kampar virus. Melaka and Kampar viruses were shown to cause respiratory disease in humans. These viruses, together with Nelson Bay virus, isolated from Australian bats, are tentatively classified as different strains within the species Pteropine orthoreovirus (PRV), formerly known as Nelson Bay orthoreovirus, based on the small (S) genome segments. Here we report the sequences of the large (L) and medium (M) segments, thus completing the whole-genome characterization of the four PRVs. All L and M segments were highly conserved in size and sequence. Conserved functional motifs previously identified in other orthoreovirus gene products were also found in the deduced proteins encoded by the cognate segments of these viruses. Detailed sequence analysis identified two genetic lineages divided into the Australian and Malaysian PRVs, and potential genetic reassortment among the M and S segments of the three Malaysian viruses.

Complete sequence and genetic characterization of Raspberry latent virus, a novel member of the family Reoviridae

A new virus isolated from red raspberry plants and detected in the main production areas in northern Washington State, USA and British Columbia, Canada was fully sequenced and found to be a novel member of the family Reoviridae. The virus was designated as Raspberry latent virus (RpLV) based on the fact that it is symptomless when present in single infections in several Rubus virus indicators and commercial raspberry cultivars. RpLV genome is 26,128 nucleotides (nt) divided into 10 dsRNA segments. The length of the genomic segments (S) was similar to those of other reoviruses ranging from 3948 nt (S1) to 1141 nt (S10). All of the segments, except S8, have the conserved terminal sequences 5'-AGUU----GAAUAC-3'. A point mutation at each terminus of S8 resulted in the sequences 5'-AGUA----GAUUAC-3'. Inverted repeats adjacent to each conserved terminus as well as stem loops and extended pan handles were identified by analyses of secondary structures of the non-coding sequences. All segments, except S3 and S10, contained a single open reading frame (ORF) on the positive sense RNAs. Two out-of-frame overlapping ORFs were identified in segments S3 (ORF S3a and S3b) and S10 (ORF S10a and S10b). Amino acid (aa) alignments of the putative proteins encoded by the main ORF in each segment revealed a high identity to several proteins encoded by reoviruses from different genera including Oryzavirus, Cypovirus, and Dinovernavirus. Alignments of the polymerase, the most conserved protein among reoviruses, revealed a 36% aa identity between RpLV and Rice ragged stunt virus (RRSV), the type member of the genus Oryzavirus, indicating that these two viruses are closely related. Phylogenetic analyses showed that RpLV clusters with members of the genera Oryzavirus, Cypovirus, Dinovernavirus and Fijivirus. These genera belong to the subfamily Spinareovirinae which includes reoviruses with spiked core particles ('turreted' reoviruses). In addition, two nucleotide binding motifs, regarded as 'signature' sequences among turreted reoviruses, were also found in RpLV P8, suggesting that RpLV is a novel dicot-infecting reovirus in the subfamily Spinareovirinae.