Pathogenicity of a variant duck orthoreovirus strain in Cherry Valley Ducklings

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.

Molecular characterization, complete genome sequencing, and pathogenicity of Novel Duck Reovirus from South Coastal Area in China

Novel Duck Reovirus (NDRV) that has been found throughout the world in waterfowl, and it has been extensively described. Here, we report the complete genome sequence of a NDRV strain isolated in China called NDRV YF10. This strain was collected from 87 samples with infected ducks in South Coastal Area. The NDRV genome consists of 23,419 bp. With the assistance of computer analysis, the promoter and terminator of each gene segment and 10 viral genes segments were identified, which encode polypeptides ranging from 98 to 1,294 amino acids. All gene fragments of this virus strain were determined and compared to previously reported strains, revealing genetic variation with similarity rates ranging from 96 to 99% for each gene segment. Each gene segment formed 2 host-associated groups, the waterfowl-derived reovirus and the avian-derived reovirus, except for the S1 gene segment, which was closely related to ARV evolution and formed a host-independent subcluster. This difference may be due to Avian Reovirus (ARV) evolving in a host-dependent manner. In order to evaluate the pathogenicity of YF10, a novel isolated strain of NDRV was tested in 2 types of ducks. It was observed that the YF10 isolated strain exhibits varying degrees of virulence, highlighting the potential risk posed to different types of ducks. In conclusion, our findings emphasize the importance of epidemiology studies, molecular characterization, and prevention of NDRV in waterfowl.

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 investigation of infectious diseases in geese on mainland China during 2018-2021

Geese play an important role in agricultural economics, with China producing the vast majority of goose meat consumed worldwide annually. The variations in the avian viruses and co-infections result in substantial economic losses to the goose industry in China. To understand the evolutionary characteristics and co-infections of viruses, a broad epidemiological investigation of epizootic viruses of goose was carried out in nine provinces of China during 2018-2021. Here, the results indicated that, among the 1970 clinical samples, 50.81% (1001/1970) were positive for goose astrovirus (GAstV), 18.22% (359/1970) for avian orthoreovirus, 12.74% (251/1970) for goose parvovirus, 11.02% (217/1970) for H9N2 subtype avian influenza virus, 4.01% (79/1970) for Newcastle disease virus, and 2.08% (41/1970) for fowl adenovirus. Among the six viruses, co-infections comprised a large proportion (66.37%) in the field, of which the dual infection was more common. Additionally, phylogenetic analysis of GAstVs indicated that Chinese GAstVs had formed two distinct groups, that is, GAstV-1 and GAstV-2. GAstV-2 sub-genotype II-c had arisen as the dominant genotype in the whole country. Notably, all the H9N2-AIV isolated strains harboured the mammalian adaptation markers I155T, H183N, and Q226L (H3 numbering) in the HA gene, which promotes preferential binding to human-like α2-6-linked sialic acid receptors. And beyond that, we determined that the goose-origin Muscovy Duck Reovirus isolates, showing 51.7%-96% similarities to that of other waterfowl-origin orthoreovirus isolates in sequence homology analysis of the representative part of σC, are a new variant of waterfowl-origin orthoreovirus. These data provide valuable information about the prevalence of infectious diseases in geese on mainland China.

Intergrated Transcriptomic and Proteomic Analysis Revealed the Differential Responses to Novel Duck Reovirus Infection in the Bursa of Fabricius of Cairna moschata

The bursa of Fabricius is an immunologically organ against the invasion of duck reovirus (DRV), which is a fatal bird virus belonging to the Reoviridae family. However, responses of the bursa of Fabricius of Cairna moschata to novel DRV (NDRV) infection are largely unknown. Transcriptomes and proteomes of the samples from control and two NDRV strain (HN10 and JDm10) with different virulence were analyzed. Differentially expressed genes and differential accumulated proteins were enriched in the serine protease system and innate immune response clusters. Most of the immune-related genes were up-regulated under both JDm10/HN10 infections. However, the immune-related proteins were only accumulated under HN10 infection. For the serine protease system, coagulation factor IX, three chains of fibrinogen, and complements C8, C5, and C2s were significantly up-regulated by the HN10 infection, suggesting that the serine protease-mediated immune system might be involved in the resistance to NDRV infection. For the innate and adaptive immune system, RIG-I, MDA5, MAPK20, and IRF3 were significantly up-regulated, indicating their important roles against invaded virus. TLR-3 and IKBKB were only up-regulated in the liver cells, MAPK20 was only up-regulated in the bursa of Fabricius cells, and IRAK2 was only up-regulated in the spleen samples. Coagulation factor IX was increased in the bursa of Fabricius, not in the liver and spleen samples. The data provides a detailed resource for studying the proteins participating in the resistances of the bursa of Fabricius of duck to NDRV infections.

Avian Reoviruses From Wild Birds Exhibit Pathogenicity to Specific Pathogen Free Chickens by Footpad Route

Avian reoviruses (ARVs) are ubiquitous in domestic poultry with 80% of them being non-pathogenic and they are frequently found in clinically healthy birds. ARVs have also been known to be the etiological agents of viral arthritis (VA), tenosynovitis, myocarditis, runting-stunting syndrome (RSS), and respiratory and enteric disease in chickens. Significant economic losses during the process of poultry husbandry are due, in part, to unmitigated ARV infections throughout the poultry industry. Recently, many isolates shared genetic similarities between those recovered from wild birds and those recovered from poultry. One explanation may be that there is a degree of spillover and spillback of ARVs between the two groups. However, studies on the role of wild birds in the epidemiology and pathogenicity of ARVs are insufficient. Here, we describe the pathogenicity in specific pathogen-free (SPF) chickens of ARV originating from wild birds. The challenge experiment was conducted in six groups including a negative control group, a positive control group (reference strain of S1133), and four groups (A15-157, A18-13, A18-205, A19-106) infected with ARVs from wild birds. The 7-day-old SPF chickens were inoculated with 10⁶TCID₅₀ ARV to evaluate the clinical signs, changes in weight gain, gross lesions, histological changes, virus replication, and serum antibody levels. The peak of clinical signs was from 3 to 5 days post infection (dpi). In addition, the death of one chicken was found in the group infected with the A18-13 isolate. Reduced body weight was also found in chickens infected with ARVs from wild birds compared to the negative control group. All the ARVs infection groups showed noticeable swelling of the footpad. In addition, ARVs were detected in the bursa, tendon, and hock joint by reverse transcription-polymerase chain reaction (RT-PCR) in all infected groups at 5 and 15 dpi. Histopathological observations revealed acute inflammatory responses on the synovium covering the joint surfaces (arthritis) and tendon sheaths (tenosynovitis), as well as bursa atrophy and lymphocyte depletion. The analysis of the humoral response was performed by ELISA assay, and chickens infected with ARVs showed seroconverted. In conclusion, this study described the typical severe disease of acute VA and tenosynovitis in SPF chickens infected with ARVs derived from wild birds. This study confirmed the pathogenicity of ARVs infection in SPF chickens for the first time, and these results enrich our understanding of the pathogenicity of ARVs derived from wild birds.

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.

Genomic sequences and pathogenic characteristics of two variant duck reoviruses associated with spleen necrosis

Emerging variant novel duck reovirus (NDRV) strains that cause spleen swelling and necrosis have seriously threatened the waterfowl industry since 2017. However, there is no report about the complete genomic sequence of emerging variant strains isolated from Cherry valley ducks. In this study, we acquired the complete genome sequences of two variant NDRV strains, SD19/6201 and SD19/6202, and analyzed their genetic and evolutionary relationship with other orthoreoviruses. The phylogenetic analysis of σC showed that all the Chinese NDRVs were clustered into two distinct branches. The SD19/6201 strain located in branch I with most of the Chinese NDRVs, while SD19/6202 was clustered in branch II with significantly different from the existing strains. Within the branch I, the NDRVs isolated in 2017 and thereafter clustered in a new subgroup. Comparison analysis of σC amino acid sequences indicated that ten amino acid differences were found between SD19/6201 and SD19/6202. Apart from the SD19/6201 and SD19/6202 strains, isolates in 2017 and thereafter had specific mutations at residues 132A, 138R, 158H, and 258A. These two NDRV strains showed different pathogenicity in SPF duck embryos and ducks. The viral loads in the spleen of infected ducks were significantly higher than those of other organs, which might be the reason why NDRV could cause obvious spleen necrosis in ducks. This study will help us to formulate effective prevention and control strategies against NDRV and enrich our understanding of the intra- and inter-species relationships of orthoreoviruses.

Rapid and visual detection of the emerging novel duck reovirus by using a specific and sensitive reverse transcription recombinase polymerase amplification method

Duck spleen necrosis disease (DSND) caused by Novel Duck Reovirus (NDRV), is an emerging infectious disease that causes severely threaten to duck industry. Currently, the popular conventional RT-PCR technique for detecting NDRV is time consuming. So, it is essential to develop a rapid and accurate molecular diagnosis techniques of the pathogen for the purpose to effective control of the disease. In our study, a simple, rapid and reliable detection method was developed by an isothermal reverse transcription-recombinase polymerase amplification (RT-RPA). The RT-RPA primers were designed targeting the S3 gene of NDRV, and its specificity was verified by testing a series of other waterfowl pathogens. A total of 20 field and experimental samples from infected ducklings were tested by the RT-RPA and compared with the results of the conventional RT-PCR and the quantitative RT-PCR simultaneously. The RT-RPA method could detect as little as 4.14 × 10² copies/μl of the target gene in the sensitivity analysis, which was 10×higher sensitive than the conventional RT-PCR. The major advantage of the RT-RPA method is that it could be performed as an isothermal reaction at 37 ℃ and completed within 20 min. In addition, no cross-reactivity was detected with other waterfowl-origin viruses. Also, the amplified products could be visualized faster, without the gel electrophoresis, by adding the SYBR Green I and observing them under an ultraviolet light. The newly developed RT-RPA method offers a simple, rapid and accurate for rapid detection of NDRV, which especially useful in on-site facilities and resource-limited areas.

Quantitative Proteomic Analysis of Duck Embryo Fibroblasts Infected With Novel Duck Reovirus

The novel duck reovirus (NDRV) can cause hemorrhage and necrosis on the spleen of Pekin ducks; this disease has resulted in great economic losses to the duck industry. However, the molecular pathogenesis of NDRV remains poorly understood. In the current study, the quantitative proteomic analysis of NDRV-infected duck embryo fibroblasts was performed to explore the cellular protein changes in response to viral infection through iTRAQ coupled with the liquid chromatography (LC)-tandem mass spectrometry (MS/MS) method. A total of 6,137 proteins were obtained in cell samples at 24 h post-infection. Of these, 179 differentially expressed proteins (DEPs) were identified (cutoff set to 1.5-fold change), including 89 upregulated and 90 downregulated proteins. Bioinformatics analysis showed that DEPs can be divided into the cellular component, molecular function, and biological process; they were mainly involved in signal transduction, infectious diseases, cell growth and death, and the immune system. The subcellular localization of most proteins was in the cytoplasm. Importantly, the expressions of signal transducer and activator of transcription 1 (STAT1) and various interferon-stimulated genes (ISGs) were upregulated after NDRV infection. The mRNA transcripts of some ISGs were consistent with proteomic data, showing an increased trend. Results of our study suggested that NDRV infection can elicit strong expression changes of cellular proteins and activate the expression of ISGs from the point of quantitative proteomic analysis. The study provides a new insight into the understanding of NDRV pathogenesis.

Evidence of vertical transmission of novel duck orthoreovirus in ducks

Since 2017, duck spleen necrosis caused by new variant duck orthoreovirus (N-DRV) infection had been observed in several provinces in China. This disease retards the growth and development of ducks, thereby reducing feed return rate. N-DRV infection causes damage to duck spleen and other immune organs, leading to immunosuppression and susceptibility to other pathogens. In this study, we successfully constructed a breeding duck artificial infection model and found that N-DRV infection can cause pathologic changes, such as ovarian hemorrhage, follicle atrophy, and fallopian tube bleeding in breeding ducks, resulting in significantly reduced fertilization rate and egg hatching rate. Viral RNA was present in egg vitelline membrane, duck embryo, and duckling's spleen samples, as determined through quantitative polymerase chain reaction (qPCR). Autopsy revealed obvious pathologic changes in the spleen and other organs, although there were no obvious early clinical symptoms observed in ducklings. Sequence distance and phylogenetic analysis confirmed that N-DRV-SD19 re-isolated from the spleen samples of ducklings was consistent with the strain N-DRV-XT18 used for infecting breeding ducks. The findings in this study confirmed that N-DRV can be vertically transmitted through eggs, which provide an important reference for the disease prevention and control.

Prevalence and multilocus sequence typing of Clostridium perfringens isolated from 4 duck farms in Shandong province, China

Clostridium perfringens is an important zoonotic microorganism. The present study was undertaken to investigate prevalence, serotype distribution, antibiotic resistance, and genetic diversity of C. perfringens isolates from 4 duck farms in Shandong, China. In total, 424 samples of cloacal swabs and environment were collected from 3 commercial meat-type duck farms in Tai'an, Liaocheng, and Weifang and one breeder duck farm in Liaocheng between December 2018 and June 2019, of which, 207 (48.82%) samples were determined to be positive for C. perfringens; a total of 402 isolates of C. perfringens were recovered, all of which were identified as type A; 30.85% of the isolates were positive for cpb2 gene; and cpe gene was found in 0.5% of the isolates. Antimicrobial susceptibility testing revealed that some of the isolates exhibited high antibiotic resistance, and 39.14% of the isolates were resistant to at least 5 classes of commonly used antibiotics. Multilocus sequence typing analysis showed that 85 representative isolates encompassed 54 different sequences types (STs), clustered in 5 clonal complexes (CCs) and 40 singletons. ST3, the most common ST in 54 STs, constituting 15.29% of all isolates, was also the most prevalent ST of isolates from the Liaocheng breeder duck farm (farm 3). CC1, the most prolific CC, containing 15.29% of the analyzed isolates, was the popular subtype of isolates from Liaocheng meat duck farm (farm 2). Although all the isolates belong to type A, the genetic diversity varied greatly in different regions; the Simpson's Diversity Index of STs for Liaocheng, Tai'an, and Weifang were 0.5941, 0.9198, and 0.9627, respectively. Some of cloacal isolates and environmental isolates were distributed in the same ST or CC, indicating close genetic relationship between cloacal isolates and environmental isolates. A portion of the strains from humans and ducks was found to be phylogenetically close. The close relationship between strains from humans and ducks, the high antibiotic resistance of C. perfringens, and the cpe-positive isolates indicated potential public health risks.