Genetic and antigenic characterization of sigma C protein from avian reovirus

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.

Recombinant linear multiple epitopes of σB protein protect Muscovy ducks against novel duck reovirus infection

Infection by the novel duck reovirus (NDRV) in ducklings causes high mortality, which leads to substantial economic losses in the duck industry in China. To date, no commercial vaccine is available for this disease. In this study, linear B cell epitopes of the σB protein of the NDRV were predicted and recombinant multiple linear B cell epitopes (MLBEs) were constructed through linkers. The recombinant MLBEs were then expressed and purified. One-day-old Muscovy ducklings were immunized with different doses of MLBEs and challenged with 5 × 104 ELD50 of the virulent CHY strain of NDRV 14 days after immunization. The ducklings vaccinated with 20 and 40 μg of MLBE performed no clinical signs or gross or histopathological lesions, indicating 100% protection against infection. The viral load in the liver and spleens of these birds was significantly lower than that in the control group. Additionally, these ducklings exhibited positive seroconversion at 7 days after vaccination on enzyme-linked immunosorbent assay. These results indicate that MLBE of σB could be used as a candidate for developing vaccines against NDRV infection.

Genetic characterization of newly emerging avian reovirus variants in chickens with viral arthritis/tenosynovitis in Israel

In recent years, new avian reovirus (ARV) variants caused a variety of symptoms in chickens worldwide, the most important of which was Viral arthritis/tenosynovitis which caused substantial economic losses and has become a concern to the worldwide chicken industry. In this study, we characterized emerging ARV variants in Israel and analyzed their genetic relationship with reference strains. One hundred thirty-four ARV variants were isolated from tendons and synovial fluids of commercial broiler chickens with signs of arthritis/tenosynovitis. Phylogenetic analysis of the partial segment of the sigma C (σC) gene confirmed that these field isolates from Israel could be clustered into all six known clusters. The majority of ARV isolates in Israel belonged to the genotypic cluster 5 (GC5). The strains in this study had a low sequence identity when compared to the commercial vaccine (strain S1133). The findings of this study demonstrated the genetic diversity of ARV strains in Israel from 2015 to 2022. It is reasonable to conclude from the preliminary results of this investigation that Israel has not been subject to selection pressure or the emergence of new ARV variants since the introduction of the live vaccine (ISR-7585). Due to the ongoing emergence of ARV variants, a robust epidemiological monitoring program supported by molecular biology techniques is required to track ARV strains in Israeli poultry flocks.

Molecular Detection and Genetic Characterization of Vertically Transmitted Viruses in Ducks

To investigate the distribution and genetic variation in four vertically transmitted duck pathogens, including duck hepatitis B virus (DHBV), duck circovirus (DuCV), duck hepatitis A virus 3 (DHAV-3), and avian reoviruses (ARV), we conducted an epidemiology study using PCR and RT-PCR assays on a duck population. We found that DHBV was the most prevalent virus (69.74%), followed by DuCV (39.48%), and then ARV (19.92%) and DHAV-3 (8.49%). Among the 271 duck samples, two, three or four viruses were detected in the same samples, indicating that the coinfection of vertical transmission agents is common in ducks. The genetic analysis results showed that all four identified DuCV strains belonged to genotype 1, the DHAV-3 strain was closely clustered with previously identified strains from China, and the ARV stain was clustered under genotype 1. These indicate that different viral strains are circulating among the ducks. Our findings will improve the knowledge of the evolution of DuCV, DHAV-3, and ARV, and help choose suitable strains for vaccination.

Development of a multivalent adjuvanted inactivated vaccine against variant arthrotropic avian reoviruses

Variant avian reoviruses (ARVs) are economically important emerging pathogens of poultry, which mainly affect young broiler chickens and cause significant production losses. Currently, there are no effective commercial vaccines available for control and prevention of emerging variant ARVs. In this study, monovalent inactivated adjuvated (20% Emulsigen D) broiler breeder vaccines containing antigens from ARV genotype cluster (C) group -2, -4, -5, or -6, and a multivalent vaccine containing antigens from all the four indicated genotypic cluster groups were developed and evaluated for their efficacy in protecting broiler progenies against homologous or heterologous ARV challenge. The use of monovalent or multivalent inactivated vaccines in a prime-boost immunization strategy induced the production of ARV specific antibodies in broiler breeders. The maternal antibodies were effectively transferred to broiler progenies. Broiler progenies obtained from immunized breeders demonstrated milder clinical symptoms and reduced gross and histopathological lesions after homologous ARV challenge. More severe gross and histological lesions were observed in challenged progenies from unvaccinated broiler breeders. However, cross protection was not observed when either of the monovalent-vaccine groups were challenged with a heterologous virus. In addition, the progenies from the unvaccinated ARV challenged control or heterologous ARV challenged vaccinated groups had significantly reduced body weight gain (p < 0.01) than the unchallenged-control, challenged-multivalent, or homologous ARV-challenged monovalent vaccine groups. However, homologous ARV challenged progenies in the multivalent or monovalent vaccine groups had similar body weight gain as the control unchallenged group with significantly reduced viral load (p < 0.01) in the gastrocnemius tendon tissue. This study indicates that broad-spectrum protection of broiler progenies from variant ARV infections is feasible through the development of multivalent vaccines after proper characterization, selection and incorporation of multiple antigens based on circulating ARV genotypes in targeted regions.

A Novel Variant of Avian Reovirus Is Pathogenic to Vaccinated Chickens

Avian reovirus (ARV) infections, characterized by severe arthritis, tenosynovitis, pericarditis, and poor weight gain, have become increasingly serious in recent years. The economic impact is significant as it causes growth inhibition and immunosuppression. Some commercial poultry in China have been widely vaccinated with available ARV vaccines; however, infections continue to occur even after vaccination. This study aimed to isolate a novel variant, ARV-SD19/11103, from the joint tissues of infected broiler chickens vaccinated with ARV vaccines in Shandong Province. Genetic evolution analysis of the major protective antigen σC gene in ARVs showed that ARV-SD19/11103 was located in the genotype cluster I but not in the same sub-cluster as the S1133 vaccine strain. The amino acid sequence similarity between SD19/11103 and vaccine strains S1133, 1733, and 2408 was <80%. After analyzing the amino acid sequences of the σC protein, 33 amino acid differences were found between the new variant isolate and the vaccine strains. This novel variant showed obvious pathogenicity in specific pathogen-free chicken embryos and chicks and could cause serious disease in chickens vaccinated with commercially available ARV vaccines. Cross-neutralization experiments further demonstrated a significant antigenic difference between the novel variant and genotype cluster I ARV strains. The novel variant strain isolated in this study provides an important theoretical basis for understanding the prevalence and genetic evolutionary characteristics of ARV variant strains in our country. This study identified the causes of ARVs circulating and emphasizes the needs for developing new vaccines against novel ARV variants.

Marked Genotype Diversity among Reoviruses Isolated from Chicken in Selected East-Central European Countries

The concern that the vaccines currently used against Avian orthoreovirus (ARV) infections are less efficient in the field justifies the need for the close monitoring of circulating ARV strains. In this study, we collected necropsy samples from various chicken breeds and tested for ARV by virus isolation, RT-PCR assay and sequence analysis. ARVs were isolated from birds showing runting-stunting syndrome, uneven growth, lameness or increased mortality, with relative detection rates of 38%, 35%, 6% and 25%, respectively. Partial σC gene sequences were determined for nearly 90% of ARV isolates. The isolates could be classified into one of the major genetic clusters. Interestingly, cluster 2 and cluster 5 were isolated from vaccinated broiler breeders, while clusters 1 to 4 were isolated from unvaccinated broilers. The isolates shared less than 75% amino acid identities with the vaccine strains (range, 44.3-74.6%). This study reaffirms the global distribution of the major genetic clusters of ARVs in chicken. The diversity of ARV strains isolated from unvaccinated broilers was greater than those detected from vaccinated animals, however, the relative importance of passive and active immunity on the selection of novel strains in different chicken breeds needs to be better understood.

Molecular and pathological investigation of avian reovirus (ARV) in Egypt with the assessment of the genetic variability of field strains compared to vaccine strains

Avian orthoreovirus (ARV) is among the important viruses that cause drastic economic losses in the Egyptian poultry industry. Despite regular vaccination of breeder birds, a high prevalence of ARV infection in broilers has been noted in recent years. However, no reports have revealed the genetic and antigenic characteristics of Egyptian field ARV and vaccines used against it. Thus, this study was conducted to detect the molecular nature of emerging ARV strains in broiler chickens suffering from arthritis and tenosynovitis in comparison to vaccine strains. Synovial fluid samples (n = 400) were collected from 40 commercial broiler flocks in the Gharbia governorate, Egypt, and then pooled to obtain 40 samples, which were then used to screen ARV using reverse transcriptase polymerase chain reaction (RT-PCR) with the partial amplification of ARV sigma C gene. The obtained RT-PCR products were then sequenced, and their nucleotide and deduced amino acid sequences were analyzed together with other ARV field and vaccine strains from GenBank. RT-PCR successfully amplified the predicted 940 bp PCR products from all tested samples. The phylogenetic tree revealed that the analyzed ARV strains were clustered into six genotypic clusters and six protein clusters, with high antigenic diversity between the genotypic clusters. Surprisingly, our isolates were genetically different from vaccine strains, which aligned in genotypic cluster I/protein cluster I, while our strains were aligned in genotypic cluster V/protein cluster V. More importantly, our strains were highly divergent from vaccine strains used in Egypt, with 55.09-56.23% diversity. Sequence analysis using BioEdit software revealed high genetic and protein diversity between our isolates and vaccine strains (397/797 nucleotide substitutions and 148-149/265 amino acid substitutions). This high genetic diversity explains the vaccination failure and recurrent circulation of ARV in Egypt. The present data highlight the need to formulate a new effective vaccine from locally isolated ARV strains after a thorough screening of the molecular nature of circulating ARV in Egypt.

Development of a wide-range real-time RT-PCR assay for detection of Avian reovirus (ARV)

Avian reovirus (ARV) is a common pathogen in chickens and other birds causing a variety of clinical symptoms such as arthritis and tenosynovitis but also enteric and respiratory symptoms. A rapid method that detects as many ARV genotypes as possible, will contribute to the early identification and control of the virus infection that causes high economic damage to the poultry industry worldwide. In this study, a real-time reverse transcription polymerase chain reaction (RT-qPCR) assay for the detection of ARV was developed. The RT-qPCR detection threshold for ARV genomic RNA standard cases was 10 copies/µL. Reproducibility of the RT-qPCR was confirmed by intra- and inter-assays. When the nucleic acids of different ARV genotypes and other common avian pathogens (IBDV, AIV, NDV, and IBV) were subjected to that RT-qPCR test, only ARV samples tested positive while all other pathogens tested negative. Due to the simplicity, convenience, high sensitivity, and specificity of the assay, the probe-based RT-qPCR is proposed to be used as an alternative diagnostic assay for the detection of ARVs in veterinary diagnostic laboratories.

Avian Reovirus in Israel, Variants and Vaccines-A Review

Avian reovirus (ARV) has been determined to be the etiologic agent of viral arthritis/tenosynovitis. In Israel, meat-type chickens, including broilers and breeders, are the most affected. Severe disease symptoms can appear in broiler flocks at a very young age because of early exposure and vertical transmission, causing significant welfare problems. Jewish laws define birds with inflamed, damaged, or torn gastrocnemius and digital flexor tendons as religious condemnations (non-kosher), resulting in severe economic losses for the poultry industry. Vaccination of breeders is a strategy to control the disease by reducing vertical transmission and providing maternal-derived antibodies to the progeny. This review describes Israel's ARV variants and the various vaccines developed over the years. Identification of co-circulating variants triggered the development of multivalent autogenous inactivated vaccines. However, the genotype-matched vaccines failed to provide protection, resulting in an increased prevalence of Cluster II ARV (classified as genotyping cluster 5 in the ARV common world classification). Since 2014, ARV Cluster II has been dominant in Israel. In 2015, the dominant variant s7585 tropism changed the virus pathogenesis and affected broilers with severe clinical signs between 12 and 15 days of age. A new vaccine approach developed in Israel used controlled exposure of the breeding flock to virulent ARV at the age when they are resistant to infection. This approach significantly reduced clinical field cases and reovirus isolations of breeding and broiler flocks between 2020 and 2022.

A Universal, Single-Primer Amplification Protocol to Perform Whole-Genome Sequencing of Segmented dsRNA Avian Orthoreoviruses

The Reoviridae family represents the largest family of double-stranded RNA viruses, and members have been isolated from a wide range of mammals, birds, reptiles, fishes, insects, and plants. Orthoreoviruses, one of the 15 recognized genera in the Reoviridae family, can infect humans and nearly all mammals and birds. Genomic characterization of reoviruses has not been adopted on a large scale because of the complexity of obtaining sequences for all 10 segments. In this study, we develop a time-efficient and practical method to enrich reovirus sequencing reads from isolates that allows for full-genome recovery using a single-primer amplification method coupled with next-generation sequencing. We refer to this protocol as reovirus-single-primer amplification (R-SPA). Our results demonstrate that most of the genes are covered with at least 500 reads per base space. Furthermore, R-SPA covers both the 5' and 3' ends of each reovirus genes. In summary, this study presents a universal and fast amplification protocol that yields sufficient double-stranded cDNA and facilitates and expedites the whole-genome sequencing of reoviruses.

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.

Virulence of Emerging Arthrotropic Avian Reoviruses Correlates With Their Ability to Activate and Traffic Interferon-γ Producing Cytotoxic CD8+ T Cells Into Gastrocnemius Tendon

Newly emerging arthrotropic avian reoviruses (ARVs) are genetically divergent, antigenically heterogeneous, and economically costly. Nevertheless, the mechanism of emerging ARV-induced disease pathogenesis and potential differences in virulence between virus genotypes have not been adequately addressed. In this study, the life cycle of ARV, including the formation of cytoplasmic ARV neo-organelles, paracrystalline structures, and virus release mechanisms, were characterized in the infected host cell by transmission electron microscopy (TEM). In addition, progressive changes in the structure of infected cells were investigated by time-lapse and field emission scanning electron (FE-SE) microscopy. ARVs from the four genotypic cluster groups included in the study caused gross and microscopic lesions in the infected birds. Marked infiltration of γδT cells, CD4⁺ and CD8⁺ T lymphocytes were observed in ARV infected tendon tissues starting day 3 post-infection. The ARV variant from genotype cluster-2 triggered significantly high trafficking of IFN-γ producing CD8⁺ T lymphocytes in tendon tissues and concomitantly showed high morbidity and severe disease manifestations. In contrast, the ARV variant from genotype cluster-4 was less virulent, caused milder disease, and accompanied less infiltration of IFN-γ producing CD8⁺ T cells. Interestingly, when we blunted antiviral immune responses using clodronate liposomes (which depletes antigen-presenting cells) or cyclosporin (which inhibits cytokine production that regulates T-cell proliferation), significantly lower IFN-γ producing CD8⁺ T cells infiltrated into tendon tissues, resulting in reduced tendon tissues apoptosis and milder disease manifestations. In summary, these data suggest that the degree of ARV virulence and tenosynovitis/arthritis are potentially directly associated with the ability of the virus to traffic massive infiltration of cytotoxic CD8⁺ T cells into the infected tissues. Moreover, the ability to traffic cytotoxic CD8⁺ T cells into infected tendon tissues and the severity of tenosynovitis differ between variants from different ARV genotype cluster groups. However, more than one virus isolate per genotype group needs to be tested to further confirm the association of pathogenicity with genotype. These findings can be used to further examine the interaction of viral and cellular pathways which are essential for the pathogenesis of the disease at the molecular level and to develop effective disease control strategies.

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.

Genetic Analysis of Avian Reovirus Isolated from Chickens in Japan

Sigma C protein-coding sequences have been used to phylogenetically classify avian reovirus (ARV) strains. However, the relationship between serotype and phylogenetic cluster classification of the five prototype serotype strains of ARV in Japan has not been established. Thus, we used sigma C protein-coding sequences to characterize avian reoviruses (ARVs) isolated from chickens with tendonitis in Japan together with the five prototype serotype strains of ARV in Japan. Phylogenetic analysis of ARVs based on the sigma C protein-coding sequences revealed that the five prototype serotype strains of ARV were each classified into different, independent clusters. Two field isolates (JP/Tottori/2016 and JP/Nagasaki/2017) that were isolated from chickens with arthritis/tenosynovitis were classified into different clusters. JP/Tottori/2016 was classified into cluster VI with the CS-108 strain, and JP/Nagasaki/2017 was classified into cluster I with strain TS-142. Serologically, JP/Tottori/2016 was well-neutralized by antisera against the CS-108 strain, whereas JP/Nagasaki/2017 cross-reacted with antisera against both the CS-108 and TS-142 strains. Embryo lethality test revealed that the two field isolates induced 80% and 67% embryo mortality, respectively, whereas the five prototype strains induced 0%-33% embryo mortality. Our findings will contribute to understanding the characteristics of ARV strains in Japan.

Emerging new avian reovirus variants from cases of enteric disorders and arthritis/tenosynovitis in Brazilian poultry flocks

1. The objective of this study was to characterise circulating Brazilian avian reovirus (ARV) strains by genetic analysis of the σC protein encoded by segment 1 of the viral genome and compare these with those of viral strains used for immunising commercial poultry.2. The analysis detected the presence of ARV genomes by quantitative reverse transcriptase PCR (RT-qPCR) in the enteric samples and the joint tissues (JT) of birds with signs of viral arthritis/tenosynovitis. Nucleotide sequencing used 16 strains (three commercial vaccines, 10 from enteric tissues and three from JT). The results indicated high variability in the amino acid sequences of 13 wild strains, showing between 40% and 75% similarity compared with the vaccine strains (S1133 and 2177).3. The sequences were grouped into three well-defined clusters in a phylogenetic tree, two of these clusters together with previous Brazilian σC ARV sequences, and one cluster (VII) that was novel for Brazilian strains. Antigenic analysis showed that there were amino acids within putative epitopes located on the surface of the receptor-binding region of the σC protein with a high degree of variability.4. The study confirmed the presence of ARV genetic variants circulating in commercial birds in Brazil, and according to the antigenic prediction, the possibility of antigenic variants appears to be high.

Metagenomic characterisation of additional and novel avian viruses from Australian wild ducks

Birds, notably wild ducks, are reservoirs of pathogenic and zoonotic viruses such as influenza viruses and coronaviruses. In the current study, we used metagenomics to detect and characterise avian DNA and RNA viruses from wild Pacific black ducks, Chestnut teals and Grey teals collected at different time points from a single location. We characterised a likely new species of duck aviadenovirus and a novel duck gyrovirus. We also report what, to the best of our knowledge, is the first finding of an avian orthoreovirus from Pacific black ducks and a rotavirus F from Chestnut teals. Other viruses characterised from the samples from these wild ducks belong to the virus families Astroviridae, Caliciviridae and Coronaviridae. Some of the viruses may have potential cross-species transmissibility, while others indicated a wide genetic diversity of duck viruses within a genus. The study also showed evidence of potential transmission of viruses along the East Asian-Australasian Flyway; potentially facilitated by migrating shorebirds. The detection and characterisation of several avian viruses not previously described, and causing asymptomatic but potentially also symptomatic infections suggest the need for more virus surveillance studies for pathogenic and potential zoonotic viruses in wildlife reservoirs.

Sequencing and phylogenetic analysis of partial S1 genes of avian orthoreovirus isolates in Shandong province during 2015-2017

Outbreaks of avian orthoreovirus (ARV) infection with primary symptoms of arthritis/tenosynovitis syndrome have been occurring more frequently in broiler flocks in China in recent years. This study aimed to investigate the genetic characteristics of ARV field strains in broiler flocks exhibiting arthritis/tenosynovitis syndrome from 9 cities in Shandong province during 2015 to 2017. A total of 64 synovial and tendon samples were obtained from broilers with significant arthritis/tenosynovitis syndrome, and 21 ARV field strains were obtained. Phylogenetic analysis of the σC nt/aa sequences revealed that only 4 isolates were clustered in genotype I, including vaccine strains S1133, 1733, and most of the ARV field strains identified previously in China. Eleven and 6 ARV field isolates were identified in genotypes II and V, sharing 70.9 to 76.0% and 53.0 to 55.2% nt identities with the vaccine strains, respectively. Previous studies in China have not reported these 2 serotypes of field strains, and prevalence of these ARV variants may be increasing in Chinese broiler flocks. Results of this study suggest that large-scale investigation of epidemic ARV should be conducted to explore the genetic diversity of ARV field isolates in China.

Genetic and pathogenic characteristics of newly emerging avian reovirus from infected chickens with clinical arthritis in China

In recent years, emerging avian reovirus (ARV) strains causing viral arthritis have become a challenge to the worldwide chicken industry, and were responsible for significant economic losses. In this study, we characterized emerging variant ARV strains and examined their genetic relationship and pathogenicity variation with reference strains. A total of 18 emerging variant ARV strains were isolated from tendon and capsular synovial fluid of broiler chickens with clinical cases of arthritis/tenosynovitis at commercial farms in China. Comparative analysis based on σC sequence showed that 4/18 isolates were in the same cluster (Cluster 1) as vaccine strains (S1133), whereas 14 of 18 isolates were in Clusters 2, 3, and 6. The field isolates shared a rather low identity (38.1 to 81.9%) with S1133 in Cluster 1, especially for those from Cluster 6 (38.1 to 67.2%). A higher ARV isolation rate was observed in chicken embryos (47/61) compared to cell culture (37/61) through PCR with a detection primer. A total of 3 isolates were selected to infect specific-pathogen-free (SPF) chickens, showing that the tested isolates, especially that from Cluster 6, displayed greater pathogenicity than S1133 strain, characterized by higher incidence. These findings suggest that the virulence of Chinese ARVs has been increasing rapidly in recent years, and the vaccine need to be updated correspondingly.

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.

Molecular characterization of avian reovirus causing tenosynovitis outbreaks in broiler flocks, Iran

Avian reoviruses (ARVs) cause arthritis, tenosynovitis, retarded growth, and malabsorption syndrome. After a long time of effective prevention and low rates of viral arthritis/ tenosynovitis in Iran, outbreaks of tenosynovitis in broiler flocks have increased in recent years. Lameness, splay legs, high rate of cull birds, poor performance, uneven birds at harvest, and condemnation at processing cause huge economic losses. In this study, ARVs from the tendons of birds from 23 broiler flocks with marked tenosynovitis were characterized, and their genetic relationship was examined. Analysis of the amino acid sequence of Sigma C protein revealed that all ARVs detected in affected broiler flocks shared genetic homogeneity and this suggests that a single genotype is involved in recent outbreaks. This genotype, so-called "Ardehal strain", is grouped in cluster I with vaccine strains. The amino acid sequence similarity between Ardehal and vaccine strains, including S1133, 1733, and 2408 was less than 80%. As the outbreaks have occurred in progenies of vaccinated flocks, it is proposed here that the difference between vaccine and field strains might contribute to the failure of currently available vaccines to induce protective immunity against Ardehal strain and this led to widespread viral tenosynovitis in Iran.

Occurrence of Reovirus (ARV) Infections in Poultry Flocks in Poland in 2010-2017

Introduction

Avian reovirus (ARV) infections in poultry populations are reported worldwide. The reovirus belongs to the genus Orthoreovirus, family Reoviridae. The aim of the study was to evaluate the incidence of ARV infections in the poultry population based on diagnostic tests performed in 2010–2017.

Material and Methods

Samples of the liver and spleen were collected from sick birds suspected of ARV infection and sent for diagnostics. Isolation was performed in 5–7-day-old SPF chicken embryos infected into the yolk sac with homogenates of internal organs of sick birds. Four primer pairs were used to detect the σNS, σC, σA, and μA ARV RNA gene fragments. A nested PCR was used for the detection of the σNS and σC genes.

Results

In 2010–2017, ARV infection was found in birds from 81 flocks of broiler chickens and/or layers, 8 flocks of slaughter turkeys, and in 4 hatchery embryos at 17–20 days of incubation. The primers used in RT-PCR and nested PCR did not allow effective detection of ARV RNA in all virus-positive samples.

Conclusion

The problem of ARV infections in the poultry population in Poland still persist. The primers used for various ARV segments in RT-PCR and nested PCR did not allow effective detection of RNA in the visceral organs of sick birds. The presented results confirm the necessity of using classical diagnostic methods (isolation in chicken embryos, AGID).

Isolation and genomic characterization of a novel chicken-orign orthoreovirus causing goslings hepatitis

A severe infectious disease characterized by nephritis, hepatitis and splenitis has attacked goslings around Shandong province in China since 2016. A novel chicken-origin avian orthoreovirus (ARV) was isolated with LMH cells from affected goslings named Reo/Goose/SDPY/1116/17 (SDPY-ARV) strain, and the infection was successfully reproduced experimentally. The ARV-SDPY full genome sequencing was conducted using Next-Generation Sequencing (NGS) technique on Illumina HiSeq platform. The complete genome of SDPY-ARV was 23,427 bp in length and consist of 10 dsRNA segments ranged from 1192 bp (S4) to 3958 bp (L1) which encoding 12 viral proteins. Genomic sequence analysis showed that the SDPY-ARV strain is in the same branch with broiler, pheasant-origin ARV isolates, and shares 51.8-96.2% of nucleotide identity of σC gene with them; while only 49.3-50.3% with waterfowl isolates. In addition, the occurrence of 10 segments genetic reassortment of SDPY strain is confirmed among the PA15511, the 1733 and the PA13649 strains from America. In conclusion, the causative agent of gosling hemorrhagic necrotic hepatitis and nephritis occurring in China is a novel chicken-origin goose orthoreovirus.

Complete genome sequence of a novel avian orthoreovirus isolated from gosling, China

Avian orthoreovirus (ARV) has been considered as a significant pathogen causing great infectious diseases to the avian, like broiler and waterfowl. The genome of this novel ARV(Reo/SDPY/Goose) was completely sequenced by next-generation sequencing. The complete genome was found to be 23517 bp in length with 10 segments. Although the Reo/SDPY/Goose was isolated from the gosling, it shares great similarity, no matter which segment within the genome, with those published as avian-origin reovirus. Genomic analysis revealed that this virus was distinct from published ARV strains and met criteria to become a novel ARV strain.

Molecular characterization of emerging avian reovirus variants isolated from viral arthritis cases in Western Canada 2012-2017 based on partial sigma (σ)C gene

Viral Arthritis (VA), a disease caused by Avian Reovirus (ARV), has emerged as a significant cause of economic losses in broiler chicken flocks in Western Canada. These outbreaks were characterized by 4-13% morbidity, followed by a spike in mortality/culling that in extreme cases required total flock depopulation. From 2012-2017, 38 ARV isolates were recovered. Molecular characterization of a partial segment of the sigma (σ)C gene shows all six previously known ARV clusters in Western Canadian broiler chickens. The most numerous clusters were Cluster#4 and Cluster #5 while the most variable clusters were Cluster#1 (76.7-100% identity), Cluster#2 (66-99.3%), and Cluster#4 (62-100%). This variation suggests that an autogenous vaccine may not protect against a same-cluster challenge virus. This is the first publication showing the wide genetic diversity of ARV Cluster#4, the circulation of all six worldwide reported ARV clusters in Canada, and important differences in ARV Cluster classification among researchers.

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.

Current limitations in control of viral arthritis and tenosynovitis caused by avian reoviruses in commercial poultry

Avian reoviruses are the causative agent of viral arthritis/tenosynovitis in chickens and turkeys. Clinical signs of disease include swelling of the hock joints accompanied by lesions in the gastrocnemius and digital flexor tendons causing lameness in addition to hydropericardium. The economic impact is significant as it results in poor weight gain, increased feed conversion ratios and condemnations at the processing plant. Vaccination with both live attenuated and inactivated oil emulsion vaccines have been used successfully for decades to control the disease. Current commercial vaccine strains belong to the same serotype and are antigenically and serologically distinct from circulating variant field viruses isolated from clinical cases of tenosynovitis. Since 2012, there has been a dramatic increase in the number of clinical cases of tenosynovitis in commercial poultry and commercial vaccines are unable to provide adequate levels of protection against disease. Producers have elected to use custom inactivated vaccines in the absence of any commercially available homologous vaccines. Identification and selection of field isolates for use in autogenous vaccines can be difficult especially when multiple reoviruses are co-circulating among flocks. In addition, field data suggests that in some cases the custom vaccines are providing adequate protection against disease but as new genetic variants emerge, new vaccines are needed.

Optimized polypeptide for a subunit vaccine against avian reovirus

Avian reovirus (ARV) is a disease-causing agent. The disease is prevented by vaccination with a genotype-specific vaccine while many variants of ARV exist in the field worldwide. Production of new attenuated vaccines is a long-term process and in the case of fast-mutating viruses, an impractical one. In the era of molecular biology, vaccines may be produced by using only the relevant protein for induction of neutralizing antibodies, enabling fast adjustment to the emergence of new genetic strains. Sigma C (SC) protein of ARV is a homotrimer that facilitates host-cell attachment and induce the production and secretion of neutralizing antibodies. The aim of this study was to identify the region of SC that will elicit a protective immune response. Full-length (residues 1-326) and two partial fragments of SC (residues 122-326 and 192-326) were produced in Escherichia coli. The SC fragment of residues 122-326 include the globular head, shaft and hinge domains, while eliminating intra-capsular region. This fragment induces significantly higher levels of anti-ARV antibodies than the shorter fragment or full length SC, which neutralized embryos infection by the virulent strain to a higher extent compared with the antibodies produced in response to the whole virus vaccine. Residues 122-326 fragment is assumed to be folded correctly, exposing linear as well as conformational epitopes that are identical to those of the native protein, while possibly excluding suppressor sequences. The results of this study may serve for the development of a recombinant subunit vaccine for ARV.

Isolation and molecular characterization of newly emerging avian reovirus variants and novel strains in Pennsylvania, USA, 2011-2014

Avian reovirus (ARV) infections of broiler and turkey flocks have caused significant clinical disease and economic losses in Pennsylvania (PA) since 2011. Most of the ARV-infected birds suffered from severe arthritis, tenosynovitis, pericarditis and depressed growth or runting-stunting syndrome (RSS). A high morbidity (up to 20% to 40%) was observed in ARV-affected flocks, and the flock mortality was occasionally as high as 10%. ARV infections in turkeys were diagnosed for the first time in PA in 2011. From 2011 to 2014, a total of 301 ARV isolations were made from affected PA poultry. The molecular characterization of the Sigma C gene of 114 field isolates, representing most ARV outbreaks, revealed that only 21.93% of the 114 sequenced ARV isolates were in the same genotyping cluster (cluster 1) as the ARV vaccine strains (S1133, 1733, and 2048), whereas 78.07% of the sequenced isolates were in genotyping clusters 2, 3, 4, 5, and 6 (which were distinct from the vaccine strains) and represented newly emerging ARV variants. In particular, genotyping cluster 6 was a new ARV genotype that was identified for the first time in 10 novel PA ARV variants of field isolates.

Mortality associated with avian reovirus infection in a free-living magpie (Pica pica) in Great Britain

BACKGROUND

Avian reoviruses (ARVs) cause a range of disease presentations in domestic, captive and free-living bird species. ARVs have been reported as a cause of significant disease and mortality in free-living corvid species in North America and continental Europe. Until this report, there have been no confirmed cases of ARV-associated disease in British wild birds.

CASE PRESENTATION

Sporadic individual magpie (Pica pica) mortality was detected at a single site in Buckinghamshire, England, April-September 2013. An adult female magpie was found moribund and subsequently died. Post-mortem examination identified hepatomegaly and splenomegaly as the most severe macroscopic abnormalities. Histopathological examination revealed extensive hepatic and splenic necrosis. Transmission electron microscopy (TEM) identified virions of a size (circa 78 nm diameter) and morphology consistent with ARV in both the liver and the small intestinal (SI) contents. Nucleic acid extracted from pooled liver and spleen was positive on both a pan-reovirus nested PCR targeting the RNA-dependent RNA polymerase gene and a PCR using primers specific to the ARV sigma C protein gene. Virus isolated from the liver and the SI contents was characterised by a syncytial-type cytopathic effect, a reovirus-like appearance on TEM and sequence identical to that from PCR of tissues. In situ hybridisation confirmed co-localisation of ARV with lesions in the liver and spleen, implicating ARV as the causative agent. Splenic lymphoid atrophy and necrotic stomatitis associated with Aspergillus fumigatus infection were consistent with generalised immunosuppression and resultant opportunistic infection.

CONCLUSIONS

The pathology and comprehensive virus investigations in this case indicate ARV as the primary pathogen in this magpie, with concurrent secondary infection subsequent to immunosuppression, as has been observed with reoviral infections in other bird species. ARV should be considered as a differential diagnosis for magpie, and potentially other corvid, disease and mortality incidents. This is the first demonstration of ARV-associated mortality in a wild bird in Britain. The prevalence and significance of ARV infection in British wild birds, and its implications for poultry and captive bird health, are currently unknown.

Antigenic analysis of monoclonal antibodies against different epitopes of σB protein of avian reovirus

BACKGROUND

Avian reovirus (ARV) causes arthritis, tenosynovitis, runting-stunting syndrome (RSS), malabsorption syndrome (MAS) and immunosuppression in chickens. σB is one of the major structural proteins of ARV, which is able to induce group-specific antibodies against the virus.

METHODS AND RESULTS

The present study described the identification of two linear B-cell epitopes in ARV σB through expressing a set of partially overlapping and consecutive truncated peptides spanning σB screened with two monoclonal antibodies (mAbs) 1F4 and 1H3-1.The data indicated that (21)KTPACW(26) (epitope A) and (32)WDTVTFH(38) (epitope B) were minimal determinants of the linear B cell epitopes. Antibodies present in the serum of ARV-positive chickens recognized the minimal linear epitopes in Western blot analyses. By sequence alignment analysis, we determined that the epitopes A and B were not conserved among ARV, duck reovirus (DRV) and turkey reovirus (TRV) strains. Western blot assays, confirmed that epitopes A and B were ARV-specific epitopes, and they could not react with the corresponding peptides of DRV and TRV.

CONCLUSIONS AND SIGNIFICANCE

We identified (21)KTPACW(26) and (32)WDTVTFH(38) as σB -specific epitopes recognized by mAbs 1F4 and 1H3-1, respectively. The results in this study may have potential applications in development of diagnostic techniques and epitope-based marker vaccines against ARV groups.

Identification of a new reovirus causing substantial losses in broiler production in France, despite routine vaccination of breeders

Numerous cases of tenosynovitis appeared in France causing high morbidity in free-range and standard broilers. The main clinical findings were lameness, stunting and non-uniform bodyweights. Although the natural mortality was low, the economic losses due to birds that had to be removed from the flock prematurely, downgrading of carcases and lower average weights at slaughter were substantial. Postmortem examinations, bacteriological, virological and serological examination confirmed the aetiology of avian orthoreovirus (ARV)-induced tenosynovitis. The isolated ARVs were analysed serologically and genetically. Sequencing of σC RT-PCR products and phylogenetic analysis revealed a new type of ARV. The virus was not neutralised in serum neutralisation test using monovalent sera from vaccinated chickens. Together with the flock data, epidemiology of these recent reovirus outbreaks in France was reconstructed. It is concluded that these reovirus isolates differ serologically and genetically from the well described reovirus isolates used in commercial vaccines which were not capable of preventing the disease. The outbreaks resulted in substantial losses in broilers from vaccinated breeders.

Wide-range protection against avian reovirus conferred by vaccination with representatives of four defined genotypes

Many isolates of the contagious avian reovirus have been characterized, mainly based on the sequence of their sigma C protein. These isolates have been classified into four genotypes. Currently available vaccines are of limited effectiveness, likely due to the existence of many variants. The aim of this study was to test the efficacy of a vaccine consisting of a mixture of prototypes (representatives) of the four defined genotypic groups of avian reovirus. The prototypes were selected based on their distance from the isolates within each genotype. All prototypes were found to be virulent. Antibodies produced against each of the prototypes neutralized all members of its genotype. Birds were then vaccinated with a mixture of the four prototypes. Results suggest that the 4-valent vaccine can prevent disease and confer broad protection against field isolates of avian reovirus.

Differentiating infected from vaccinated animals, and among virulent prototypes of reovirus

Birds are most susceptible to infection by avian reovirus, genus Orthoreovirus family Reoviridae, at a young age. Although chicks are protected by antibodies transferred from vaccinated maternal flocks, due to the many variants in the field, the efficiency of the vaccines is limited. The level of antibodies against viruses is generally determined by enzyme-linked immunosorbent assay (ELISA), using the whole virus as the antigen. This has some disadvantages: first, the test measures antibodies against all capsid proteins, most of which are irrelevant for neutralizing the virus, and as such does not reflect the real protection status; second, it is impossible to distinguish between vaccine- and infection-derived antibodies. In the case of a virus that changes frequently, a third disadvantage is the inability to distinguish among serotypes. The aim of this study was to develop a test that would address these concerns. Four prototypes of the avian reovirus protein sigma C were used as antigens on the ELISA plate. Sigma C is the main protein inducing neutralizing antibodies and the most variable among strains and isolates, and it is used for reovirus classification. This differentiating ELISA enabled distinguishing between vaccine and field strains of the virus, identifying the infection source, and in the case of vaccination, exclusively determining the level of protective antibodies. Whereas the whole virus detected antibodies against all strains, differentiating ELISA enabled differentiating between infected and vaccinated animals (DIVA) and in most cases, identifying the sigma C genotype. In a field study, a correlation was found between disease symptoms and antibodies identified against virulent strains in the flock. Thus virulent strains can be identified in the field, enabling adjustment of the relevant vaccines.