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

Isolation, identification and genetic variation analysis of avian orthoreovirus in commercial broilers in China from 2016 to 2021

In the last decade, the emergence of variant strains of avian orthoreovirus (ARV) has caused an enormous economic impact on the poultry industry across China and other countries. This study aimed to evaluate the molecular evolution of the ARV lineages detected in Chinese commercial broiler farms. Firstly, ARV isolation and identification of commercial broiler arthritis cases from different provinces in China from 2016 to 2021 were conducted. A total of 51 pure ARV isolates were obtained. Sequencing results showed that there were five genotypes of the strains isolated in this study, of which genotype 1 ARV predominated, accounting for 56.9% (29/51). The whole gene sequences of 19 ARV representative isolates were successfully obtained. The genetic evolution analysis of 10 genome segments of 19 ARV isolates showed that the σC-encoding gene had evolved into six different lineages, while the other genome segments only differentiated into two to four different lineages. The results of recombination analysis showed that recombination events were present in the L3, M1 and S1 genome segments. Analysis of the variation of the key factor σC protein showed that the nucleotide and amino acid homologies of the σC were low among the different genotypes. Three-dimensional structural visualization analysis showed that all the structural changes of σC protein were concentrated in the spherical domain at the C-terminal, which is associated with host receptor binding.

Characterization and pathogenicity of a novel avian orthoreovirus in China

Introduction

Avian orthoreovirus (ARV) is a significant pathogen causing viral arthritis, leading to substantial economic losses in the poultry industry worldwide.

Methods

A novel ARV strain, designated FJ202311, was isolated from a broiler farm in Fujian Province, China. Whole-genome sequencing was conducted using next-generation sequencing with MGI technology, and phylogenetic analysis of the sigma C amino acid sequence was performed. Comparative sequence analysis identified unique genetic features of FJ202311. Pathogenicity studies were carried out by inoculating broilers with the isolated strain and monitoring clinical signs, weight gain, and histopathological changes.

Results

The complete genome of FJ202311 was determined to be 23,495 base pairs in length, encoding 12 major proteins. Phylogenetic analysis revealed that FJ202311 forms a distinct genotypic cluster, exhibiting only 47.1% to 59.3% sequence identity to 16 reference ARV strains. Notably, 50 unique amino acid substitutions were identified in the sigma C protein. Pathogenicity tests demonstrated that FJ202311 caused severe arthritis and tenosynovitis in broilers. Infected birds exhibited significant weight loss compared to controls, with reductions of 11.78% and 8.93% at 14 and 21 days post-infection, respectively.

Discussion

This study highlights the unique molecular and pathogenic characteristics of the novel ARV strain FJ202311, contributing to our understanding of ARV diversity and epidemiology in China. These findings underscore the importance of continuous monitoring and provide insights for developing improved prevention and control strategies against ARV.

Avian Reovirus: From Molecular Biology to Pathogenesis and Control

Avian reoviruses (ARVs) represent a significant economic burden on the poultry industry due to their widespread prevalence and potential pathogenicity. These viruses, capable of infecting a diverse range of avian species, can lead to a variety of clinical manifestations, most notably tenosynovitis/arthritis. While many ARV strains are asymptomatic, pathogenic variants can cause severe inflammation and tissue damage in organs such as the tendons, heart, and liver. In broilers and turkeys, ARVs can induce severe arthritis/tenosynovitis, characterized by swollen hock joints and lesions in the gastrocnemius tendons. Additionally, ARVs have been implicated in other diseases, although their precise role in these conditions remains to be fully elucidated. In recent years, ARV cases have surged in the United States, emphasizing the need for effective control measures. Routine vaccination with commercial or autogenous vaccines is currently the primary strategy for mitigating ARV's impact. Future research efforts should focus on enhancing our understanding of ARV-induced pathogenesis, identifying host factors that influence disease severity, and developing novel vaccines based on ongoing surveillance of circulating ARV strains. This review aims to explore the molecular aspects of ARV, including virus structure, replication, molecular epidemiology, the roles of its encoded proteins in host pathogenesis, and the immune response to ARV infection. Furthermore, we discuss the diagnostic approaches of avian reovirus and the potential biosecurity measures and vaccination trials in combating ARV and developing effective antiviral strategies.

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.

Avian Orthoreoviruses: A Systematic Review of Their Distribution, Dissemination Patterns, and Genotypic Clustering

Avian orthoreviruses have become a global challenge to the poultry industry, causing significant economic impacts on commercial poultry. Avian reoviruses (ARVs) are resistant to heat, proteolytic enzymes, a wide range of pH values, and disinfectants, so keeping chicken farms free of ARV infections is difficult. This review focuses on the global prevalence of ARVs and associated clinical signs and symptoms. The most common signs and symptoms include tenosynovitis/arthritis, malabsorption syndrome, runting-stunting syndrome, and respiratory diseases. Moreover, this review also focused on the characterization of ARVs in genotypic clusters (I-VI) and their relation to tissue tropism or viral distribution. The prevailing strains of ARV in Africa belong to all genotypic clusters (GCs) except for GC VI, whereas all GCs are present in Asia and the Americas. In addition, all ARV strains are associated with or belong to GC I-VI in Europe. Moreover, in Oceania, only GC V and VI are prevalent. This review also showed that, regardless of the genotypic cluster, tenosynovitis/arthritis was the predominant clinical manifestation, indicating its universal occurrence across all clusters. Globally, most avian reovirus infections can be prevented by vaccination against four major strains: S1133, 1733, 2408, and 2177. Nevertheless, these vaccines may not a provide sufficient defense against field isolates. Due to the increase in the number of ARV variants, classical vaccine approaches are being developed depending on the degree of antigenic similarity between the vaccine and field strains, which determines how successful the vaccination will be. Moreover, there is a need to look more closely at the antigenic and pathogenic properties of reported ARV strains. The information acquired will aid in the selection of more effective vaccine strains in combination with biosecurity and farm management methods to prevent ARV infections.

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.

A Snapshot on the Genomic Epidemiology of Turkey Reovirus Infections, Hungary

Reovirus infections in turkeys are associated with arthritis and lameness. Viral genome sequence data are scarce, which makes an accurate description of the viral evolution and epidemiology difficult. In this study, we isolated and characterized turkey reoviruses from Hungary. The isolates were identified in 2016; these isolates were compared with earlier Hungarian turkey reovirus strains and turkey reoviruses isolated in the 2010s in the United States. Gene-wise sequence and phylogenetic analyses identified the cell-receptor binding protein and the main neutralization antigen, σC, to be the most conserved. The most genetically diverse gene was another surface antigen coding gene, μB. This gene was shown to undergo frequent reassortment among chicken and turkey origin reoviruses. Additional reassortment events were found primarily within members of the homologous turkey reovirus clade. Our data showed evidence for low variability among strains isolated from independent outbreaks, a finding that suggests a common source of turkey reoviruses in Hungarian turkey flocks. Given that commercial vaccines are not available, identification of the source of these founder virus strains would permit a more efficient prevention of disease outbreaks before young birds are settled to fattening facilities.

Whole Genomic Constellation of Avian Reovirus Strains Isolated from Broilers with Arthritis in North Carolina, USA

Avian reovirus (ARV) is an emerging pathogen which causes significant economic challenges to the chicken and turkey industry in the USA and globally, yet the molecular characterization of most ARV strains is restricted to a single particular gene, the sigma C gene. The genome of arthrogenic reovirus field isolates (R18-37308 and R18-38167), isolated from broiler chickens in North Carolina (NC), USA in 2018, was sequenced using long-read next-generation sequencing (NGS). The isolates were genotyped based on the amino acid sequence of sigma C (σC) followed by phylogenetic and amino acid analyses of the other 11 genomically encoded proteins for whole genomic constellation and genetic variation detection. The genomic length of the NC field strains was 23,494 bp, with 10 dsRNA segments ranging from 3959 bp (L1) to 1192 bp (S4), and the 5' and 3' untranslated regions (UTRs) of all the segments were found to be conserved. R18-37308 and R18-38167 were found to belong to genotype (G) VI based on the σC analysis and showed nucleotide and amino acid sequence identity ranging from 84.91-98.47% and 83.43-98.46%, respectively, with G VI strains. Phylogenetic analyses of individual genes of the NC strains did not define a single common ancestor among the available completely sequenced ARV strains. Nevertheless, most sequences supported the Chinese strain LY383 as a probable ancestor of these isolates. Moreover, amino acid analysis revealed multiple amino acid substitution events along the entirety of the genes, some of which were unique to each strain, which suggests significant divergence owing to the accumulation of point mutations. All genes from R18-37308 and R18-38167 were found to be clustered within genotypic clusters that included only ARVs of chicken origin, which negates the possibility of genetic pooling or host variation. Collectively, this study revealed sequence divergence between the NC field strains and reference ARV strains, including the currently used vaccine strains could help updating the vaccination regime through the inclusion of these highly divergent circulating indigenous field isolates.

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.

Avian reovirus: a furious and fast evolving pathogen

Avian reoviruses (ARVs) have a significant economic impact on the poultry industry, affecting commercial and backyard flocks. Spread feco-orally, or vertically, many do not cause morbidity, but pathogenic strains can contribute to several diseases, including tenosynovitis/arthritis, which is clinically the most significant. The last decade has seen a surge in cases in the US, and due to ongoing evolution, seven genotypic clusters have now been identified. Control efforts include strict biosecurity and vaccination with commercial and autogenous vaccines. Research priorities include improving understanding of pathogenesis and developing new vaccines guided by ongoing molecular and serologic surveillance.

Optimizing the Conditions for Whole-Genome Sequencing of Avian Reoviruses

Whole-genome sequencing (WGS) is becoming an essential tool to characterize the genomes of avian reovirus (ARV), a viral disease of economic significance to poultry producers. The current strategies and procedures used to obtain the complete genome sequences of ARV isolates are not cost-effective because most of the genetic material data resulting from next-generation sequencing belong to the host and cannot be used to assemble the viral genome. The purpose of this study was to develop a workflow to enrich the ARV genomic content in a sample before subjecting it to next-generation sequencing (NGS). Herein, we compare four different ARV purification and enrichment approaches at the virion, RNA and cDNA levels to determine which treatment or treatment combination would provide a higher proportion of ARV-specific reads after WGS. Seven ARV isolates were subjected to different combinations of virion purification via ultracentrifugation in sucrose density gradient or Capto Core 700 resin with or without a subsequent Benzonase treatment, followed by a chicken rRNA depletion step after RNA extraction and a final ARV cDNA amplification step using a single-primer amplification assay. Our results show that the combination of Capto Core 700 resin, Chicken rRNA depletion and cDNA amplification is the most cost-effective strategy to obtain ARV whole genomes after short-read sequencing.

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.

Identification and molecular characterization of novel duck reoviruses in Henan Province, China

Novel Duck reovirus (NDRV) is an ongoing non-enveloped virus with ten double-stranded RNA genome segments that belong to the genus Orthoreovirus, in the family Reoviridae. NDRV-associated spleen swelling, and necrosis disease have caused considerable economic losses to the waterfowl industry worldwide. Since 2017, a significant number of NDRV outbreaks have emerged in China. Herein, we described two cases of duck spleen necrosis disease among ducklings on duck farms in Henan province, central China. Other potential causative agent, including Muscovy duck reovirus (MDRV), Duck hepatitis A virus type 1 (DHAV-1), Duck hepatitis A virus type 3 (DHAV-3), Newcastle disease virus (NDV), and Duck tembusu virus (DTMUV), were excluded by reverse transcription-polymerase chain reaction (RT-PCR), and two NDRV strains, HeNXX-1/2021 and HNJZ-2/2021, were isolated. Sequencing and phylogenetic analysis of the σC genes revealed that both newly identified NDRV isolates were closely related to DRV/SDHZ17/Shandong/2017. The results further showed that Chinese NDRVs had formed two distinct clades, with late 2017 as the turning point, suggesting that Chinese NDRVs have been evolving in different directions. This study identified and genetic characteristics of two NDRV strains in Henan province, China, indicating NDRVs have evolved in different directions in China. This study provides an insight into the ongoing emerged duck spleen necrosis disease and enriches our understanding of the genetic diversity and evolution of NDRVs.

Epidemiological Analysis of Avian Reovirus in China and Research on the Immune Protection of Different Genotype Strains from 2019 to 2020

Avian reovirus (ARV) is the primary pathogen responsible for viral arthritis. In this study, 2340 samples with suspected viral arthritis were collected from 2019 to 2020 in 16 provinces of China to investigate the prevalence of ARV in China and to characterize the molecular genetic evolution of epidemic strains. From 113 samples analyzed by RT-PCR, 46 strains of avian reovirus were successfully isolated and identified. The genetic evolution of the σC gene showed that 46 strains were distributed in 1-5 branches, with the largest number of strains in branches 1 and 2. The σC gene homology among the strains was low, with approximately 62% homology in branches 4 and 5 and about 55% in the remaining branches. The strains circulating during the ARV epidemic in different provinces were distributed in different branches. The SPF chickens were immunized with inactivated vaccines containing strains from branches 1 and 4 to analyze the cross-immune protection elicited by different branches of ARV strains. A challenge protection test was performed using strains in branches 1, 2, 4, and 5. Our results showed that inactivated vaccines containing strains from branches 1 and 4 could fully protect from strains in branches 1, 4, and 5. The results of this study revealed the genetic diversity among the endemic strains of ARV in China from 2019 to 2020. Each genotype strain elicited partial cross-protection, providing a scientific basis for the prevention and control of ARV.

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.

Avian Reoviruses from Clinical Cases of Tenosynovitis: An Overview of Diagnostic Approaches and 10-Year Review of Isolations and Genetic Characterization

Reoviral-induced tenosynovitis/viral arthritis is an economically significant disease of poultry. Affected birds present with lameness, unilateral or bilateral swollen hock joints or shanks, and/or reluctance to move. In severe cases, rupture of the gastrocnemius or digital flexor tendons may occur, and significant culling may be necessary. Historically, vaccination with a combination of modified live and inactivated vaccines has successfully controlled disease. Proper vaccination reduced vertical transmission and provided maternal-derived antibodies to progeny to protect against disease, at an age when they were most susceptible. Starting in 2011-2012, an increased incidence of tenosynovitis/viral arthritis was observed in chickens and turkeys. In chickens, progeny from reovirus-vaccinated breeders were affected, suggesting commercial vaccines did not provide adequate protection against disease. In turkeys, clinical disease was primarily in males, although females can also be affected. The most significant signs were observed around 14-16 wks of age and include reluctance to move, lameness, and limping on one or both legs. The incidence of tenosynovitis/viral arthritis presently remains high. Reoviruses isolated from clinical cases are genetically and antigenically characterized as variants, meaning they are different from vaccine strains. Characterization of the field isolates reveals multiple new genotypes and serotypes that are significantly different from commercial vaccines and each other. In 2012, a single prevalent virus was isolated from a majority of the cases submitted to the Poultry Diagnostic and Research Center at the University of Georgia. Genetic characterization of the σC protein revealed the early isolates belonged to genetic cluster (GC) 5. Soon after the initial identification of the GC5 variant reovirus, many broiler companies incorporated these isolates from their farms into their autogenous vaccines and continue to do so today. The incidence of GC5 field isolates has decreased significantly, likely because of the widespread use of the isolates in autogenous vaccines. Unfortunately, variant reoviruses belonging to multiple GCs have emerged, despite inclusion of these isolates in autogenous vaccines. In this review, an overview of nomenclature, sample collection, and diagnostic testing will be covered, and a summary of variant reoviruses isolated from clinical cases of tenosynovitis/viral arthritis over the past 10 yrs will be provided.

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.

Review of Viral Arthritis in Canada

Viral arthritis/tenosynovitis, a disease caused by avian reovirus (ARV), leads to great economic losses for the chicken industry worldwide. Since autumn 2011, the poultry industries in the United States and Canada have sustained significant economic losses in the progeny of broiler breeders vaccinated with classic strains of ARV. Vaccination failure has been caused by field challenge with variant ARVs. The variant field ARVs are refractory to the immunity stimulated by classic vaccines and have become the prevalent challenge in the field. Because all genotypes described in the literature have been reported to be circulating in Canada, genotyping of circulating ARVs is paramount for the selection of appropriate isolates, representative of the field challenge, for use in autogenous vaccines. In this review, the history of ARVs and the current situation in Canada are discussed. On the basis of recent field data, inadequate measures commonly used in the field are discussed, and successful vaccination strategies are recommended.

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.

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.

Chicken Astrovirus (CAstV) Molecular Studies Reveal Evidence of Multiple Past Recombination Events in Sequences Originated from Clinical Samples of White Chick Syndrome (WCS) in Western Canada

In this study, we aimed to molecularly characterize 14 whole genome sequences of chicken astrovirus (CAstV) isolated from samples obtained from white chick syndrome (WCS) outbreaks in Western Canada during the period of 2014–2019. Genome sequence comparisons showed all these sequences correspond to the novel Biv group from which no confirmed representatives were published in GenBank. Molecular recombination analyses using recombination detection software (i.e., RDP5 and SimPlot) and phylogenetic analyses suggest multiple past recombination events in open reading frame (ORF)1a, ORF1b, and ORF2. Our findings suggest that recombination events and the accumulation of point mutations may have contributed to the substantial genetic variation observed in CAstV and evidenced by the current seven antigenic sub-clusters hitherto described. This is the first paper that describes recombination events in CAstV following analysis of complete CAstV sequences originated in Canada.

Establishment of a Real-Time Recombinase Polymerase Amplification Assay for the Detection of Avian Reovirus

Avian reovirus (ARV) infection results in multiple disease manifestations in chicken. A rapid detection method will contribute to early diagnosis and control of the virus infection. The recombinase polymerase amplification (RPA) technology is a nucleic acid amplification method which is experiencing rapid development. In present study, a real-time reverse transcription (RT)-RPA assay was developed for the detection of ARV. The limit of detection of the real-time RT-RPA was 10² copies/μL of ARV genomic RNA standard in 95% of cases. The RT-RPA assay also exhibited remarkable specificity. When the nucleic acids of CRV and other common avian pathogens were subjected to the RT-RPA test, only ARV tested positive, all the other pathogens tested negative. Furthermore, the practicality of the RT-RPA assay in field was confirmed by testing 86 clinical samples. The clinical samples were also detected by qRT-PCR. The detection result by RT-RPA was 96.5% agreement with that of qRT-PCR. As a result of the simplicity and convenience of the assay with high sensitivity and specificity, the probe-based RT-RPA will be an alternative diagnostic assay for the detection of ARV in resource-limited settings.

Genotypic characterization and molecular evolution of avian reovirus in poultry flocks from Brazil

Avian reovirus (ARV) is one of the main causes of infectious arthritis/tenosynovitis and malabsorption syndrome (MAS) in poultry. ARVs have been disseminated in Brazilian poultry flocks in the last years. This study aimed to genotype ARVs and to evaluate the molecular evolution of the more frequent ARV lineages detected in Brazilian poultry-producing farms. A total of 100 poultry flocks with clinical signs of tenosynovitis/MAS, from all Brazilian poultry-producing regions were positive for ARV by PCR. Seventeen bird tissues were submitted to cell culture and ARV RNA detection/genotyping by two PCRs. The phylogenetic classification was based on σC gene alignment using a dataset with other Brazilian and worldwide ARVs sequences. ARVs were specifically detected by both PCRs from the 17 cell cultures, and σC gene partial fragments were sequenced. All these sequences were aligned with a total of 451 ARV σC gene data available in GenBank. Phylogenetic analysis demonstrated five well-defined clusters that were classified into lineages I, II, III, IV, and V. Three lineages could be further divided into sub-lineages: I (I vaccine, Ia, Ib), II (IIa, IIb, IIc) and IV (IVa and IVb). Brazilian ARVs were from four lineages/sub-lineages: Ib (48.2%), IIb (22.2%), III (3.7%) and V (25.9%). The Bayesian analysis demonstrated that the most frequent sub-lineage Ib emerged in the world around 1968 and it was introduced into Brazil in 2010, with increasing spread soon after. In conclusion, four different ARV lineages are circulating in Brazilian poultry flocks, all associated with clinical diseases. RESEARCH HIGHLIGHTS One-hundred ARV-positive flocks were detected in all main poultry-producing regions from Brazil. A large dataset of 468 S1 sequences was constructed and divided ARVs into five lineages. Four lineages/sub-lineages (Ib, IIb, III and V) were detected in commercial poultry flocks from Brazil. Brazilian lineages shared a low identity with the commercial vaccine lineage (I vaccine). Sub-lineage Ib emerged around 1968 and was introduced into Brazil in 2010.

Partial Molecular Characterization and Pathogenicity Study of an Avian Reovirus Causing Tenosynovitis in Commercial Broilers

This study describes the molecular characterization of avian reoviruses (ARVs) isolated during an outbreak in commercial chickens between 2015 and 2016. In addition, a pathogenicity study of a selected ARV strain isolated from a field case of viral tenosynovitis in commercial broiler chickens was performed. On the basis of phylogenetic analysis of a 1088-bp fragment of the ARV S1 gene, the investigated sequences were differentiated into five distinct genotypic clusters (GCs), namely GC1, GC2, GC3, GC4, and GC6. Specific-pathogen-free (SPF) and commercial broiler chickens were challenged with the GC1 genetic type MK247011, at 14 days of age via the interdigital toe web. No significant effects in body weight gain and feed conversion were detected in both chicken types. The Δ interdigital web thickness was most severe at 4 days postchallenge (DPC) in both the SPF and broiler subgroups. The inflammation in SPF birds was slightly more severe compared with broilers. Neither mortality nor clinical signs occurred in the infected groups for the duration of the experiment, despite the presence of significant microscopic lesions in challenged birds. Microscopic changes of tenosynovitis became evident at 3 DPC, with the highest incidence and severity detected at 14 and 21 DPC, respectively. Seroconversion against ARV occurred 3 wk postchallenge, and the microscopic lesions detected in tendon and heart sections were highly compatible with those described in the field. Increased severity of tenosynovitis and epicarditis lesions were noted in the ARV-challenged groups compared with the control groups. Although SPF and broiler chickens showed comparable responses to the challenge with an ARV genetic variant, detected lesions were subclinical, denoting the limitations of our challenge approach. The age selected in this experiment possibly influenced the course of the infection. Data from this study highlight the genotypic diversity of isolates in California, and the outcome of the pathogenicity study can be used as a basis to improve protocols for pathogenicity studies to characterize ARV variants causing clinical disease in the field.

The dynamics of molecular evolution of emerging avian reoviruses through accumulation of point mutations and genetic re-assortment

In the last decade, the emergence of variant strains of avian reovirus (ARV) has caused enormous economic impact in the poultry industry across Canada and USA. ARVs are non-enveloped viruses with ten segments of double-stranded RNA genome. So far, only six genotyping cluster groups are identified worldwide based on sequence analysis of the σC protein encoded by the S1 segment. In this study, we performed deep next generation whole-genome sequencing and analysis of twelve purified ARVs isolated from Saskatchewan, Canada. The viruses represent different genotyping cluster. A genome-wide sequence divergence of up to 25 per cent was observed between the virus isolates with a comparable and contrasting evolutionary history. The proportion of synonymous single-nucleotide variations (sSNVs) was higher than the non-synonymous (ns) SNVs across all the genomic segments. Genomic segment S1 was the most variable as compared with the other genes followed by segment M2. Evidence of positive episodic/diversifying selection was observed at different codon positions in the σC protein sequence, which is the genetic marker for the classification of ARV genotypes. In addition, the N-terminus of σC protein had a persuasive diversifying selection, which was not detected in other genomic segments. We identified only four ARV genotypes based on the most variable σC gene sequence. However, a different pattern of phylogenetic clustering was observed with concatenated whole-genome sequences. Together with the accumulation of point mutations, multiple re-assortment events appeared as mechanisms of ARV evolution. For the first time, we determined the mean rate of molecular evolution of ARVs, which was computed as 2.3 × 10^-3 substitution/site/year. In addition, widespread geographic intermixing of ARVs was observed between Canada and USA, and between different countries of the world. In conclusion, the study provides a comprehensive analysis of the complete genome of different genotyping clusters of ARVs including their molecular rate of evolution and spatial distribution. The new findings in this study can be utilized for the development of effective vaccines and other control strategies against ARV-induced arthritis/tenosynovitis in the poultry industry worldwide.

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.

Characterization of Monoclonal Antibodies against σA Protein and Cross-Reactive Epitope Identification and Application for Detection of Duck and Chicken Reovirus Infections

Although σA is an important major core protein of duck reovirus (DRV), the B-cell epitopes of this protein remain unknown to reseacrhers. Six monoclonal antibodies (MAbs) (1A7, 3F4, 5D2, 4E2, 3C7, and 2B7) were developed by using prokaryotic-expressed recombinant His-σA protein. Five of six MAbs (1A7, 3F4, 4E2, 3C7, and 2B7) reacted with His-σA protein in a conformation-independent manner, while 5D2 reacted with σA in a conformation-dependent manner. Immunofluorescence assays showed that the MAbs could specifically bind to DRV infected BHK-21 cells. The MAbs were delineated as three groups by a competitive binding assay. By using 12-mer peptide phage display and mutagenesis, MAb 4E2 was identified to recognize minimal epitope ⁵⁶EAPYPG⁶¹ and MAb 1A7 recognize ³⁴¹WVV/MAGLI/V³⁴⁷, residues ³⁴¹V/M and ³⁴⁷I/V are replaceable. Dot blotting and sequence analysis confirmed that EAPYPG and WVV/MAGLI/V are cross-reactive epitopes in both DRV and avian reovirus (ARV). An enzyme-linked immunosorbent assay (ELISA) based on two expressed EAPYPG and WVVAGLI as antigen demonstrated its diagnostic potential by specific reacting with serum samples from DRV- or ARV-infected birds. Based on these observations, an epitope-based ELISA could be potentially used for DRV or ARV surveillance. These findings provide insights into the organization of epitopes on σA protein that might be valuable for the development of epitope-based serological diagnostic tests for DRV and ARV infection.

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.

Investigation of Enteric Viruses Associated With Runting and Stunting in Day-Old Chicks and Older Broilers in Southwest Nigeria

Enteric viruses are known to have significant economic impact on poultry, especially broiler chicken flocks, because of production losses attributable to poor feed conversion and weight gain. To sustain the Nigerian poultry industry that contributes significantly to the livestock sector of the economy, there is a need to investigate commercial broiler flocks in the country for the presence of enteric viruses causing runting and stunting, growth retardation, and hatchery diseases. Gut contents were collected from 158 day-old and six 14-week old runted/stunted broiler chickens in commercial farms (ten) and hatcheries (six) located in Southwest Nigeria. The samples were examined for the presence of chicken astrovirus (CAstV), avian nephritis virus (ANV), avian rotavirus (AvRV), chicken parvovirus (ChPV), and turkey astroviruses (TAstV-1 and−2) by polymerase chain reaction (PCR) and reverse transcriptase-PCR (RT-PCR) whereas avian reovirus (ARV) and fowl adenovirus (FAdV) by virus isolation (VI), RT-PCR, and PCR. While CAstV was detected in all the birds (100%), sporadic detection of ANV (5%), and ChPV (5%) was observed in day-old and/or older birds. Four isolates were obtained by VI with one isolate being ARV positive and other three FAdV positive by RT-PCR and PCR, respectively. These findings strongly suggest CAstV as a major cause of runting and stunting as well as hatchery condemnations in commercial broilers in Southwest Nigeria, although co-infections with ANV, FAdV, ARV, and ChPV cannot be ruled out. In addition, the possible vertical and horizontal transmissions of these viruses are discussed.

Genotypic Characterization of Emerging Avian Reovirus Genetic Variants in California

This study focuses on virus isolation of avian reoviruses from a tenosynovitis outbreak between September 2015 and June 2018, the molecular characterization of selected isolates based on partial S1 gene sequences, and the full genome characterization of seven isolates. A total of 265 reoviruses were detected and isolated, 83.3% from tendons and joints, 12.3% from the heart and 3.7% from intestines. Eighty five out of the 150 (56.6%) selected viruses for sequencing and characterization were successfully detected, amplified and sequenced. The characterized reoviruses grouped in six distinct genotypic clusters (GC1 to GC6). The most represented clusters were GC1 (51.8%) and GC6 (24.7%), followed by GC2 (12.9%) and GC4 (7.2%), and less frequent GC5 (2.4%) and GC3 (1.2%). A shift on cluster representation throughout time occurred. A reduction of GC1 and an increase of GC6 classified strains was noticed. The highest homologies to S1133 reovirus strain were detected in GC1 (~77%) while GC2 to GC6 homologies ranged between 58.5 and 54.1%. Over time these homologies have been maintained. Seven selected isolates were full genome sequenced. Results indicated that the L3, S1 and M2 genes, coding for proteins located in the virus capsid accounted for most of the variability of these viruses. The information generated in the present study helps the understanding of the epidemiology of reoviruses in California. In addition, provides insights on how other genes that are not commonly studied add variability to the reovirus genome.

Cell-cell fusion induced by reovirus FAST proteins enhances replication and pathogenicity of non-enveloped dsRNA viruses

Fusogenic reoviruses encode fusion-associated small transmembrane (FAST) protein, which induces cell-cell fusion. FAST protein is the only known fusogenic protein in non-enveloped viruses, and its role in virus replication is not yet known. We generated replication-competent, FAST protein-deficient pteropine orthoreovirus and demonstrated that FAST protein was not essential for viral replication, but enhanced viral replication in the early phase of infection. Addition of recombinant FAST protein enhanced replication of FAST-deficient virus and other non-fusogenic viruses in a fusion-dependent and FAST-species-independent manner. In a mouse model, replication and pathogenicity of FAST-deficient virus were severely impaired relative to wild-type virus, indicating that FAST protein is a major determinant of the high pathogenicity of fusogenic reovirus. FAST-deficient virus also conferred effective protection against challenge with lethal homologous virus strains in mice. Our results demonstrate a novel role of a viral fusogenic protein and the existence of a cell-cell fusion-dependent replication system in non-enveloped viruses.