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

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.

Evaluation of probiotic properties of a Brevibacillus laterosporus strain

Brevibacillus laterosporus is a strain of probiotic bacteria that has been widely used in pest control, cash crop, and other production areas. However, few studies have been conducted on its use as a feed additive in animals. Therefore, the probiotic potential of B. laterosporus PBC01 was evaluated by characterizing hydrophobicity, auto-aggregation activity, bile salt and simulated gastrointestinal fluid tolerance, bienzymatic, and antibacterial activity. Antibiotic susceptibility, hemolysis assays, and supplemental feeding of mice were also performed to evaluate safety features. Our results showed that B. laterosporus PBC01 had moderate hydrophobicity, high auto-agglutination ability. Meanwhile, B. laterosporus PBC01 had good tolerance to bile salt and simulated gastrointestinal fluid. It had the ability to secrete protease, cellulase, and to inhibit various pathogens. In addition, B. laterosporus PBC01 was sensitive to many antibiotics, and did not produce hemolysin. In the safety assessment of mice, it did not cause any deaths, nor did it affect the cell components of blood, antioxidant capacity, and reproductive health. The study indicated the great probiotic characteristics and safety of B. laterosporus PBC01. This may provide a theoretical basis for the clinical application and development of probiotic-based feed additives.

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

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

First isolation and genomic characterization of avian reovirus from black swans (Cygnus atratus) in China

Identification and analysis of the avian reovirus from black swan. Isolation of the strain through the chorioallantoic membrane route of duck embryos, identified through transmission electron microscopy and RT-PCR based on the ARV S2 gene. The complete genome of the ARV strain was obtained using next-generation sequencing technology. The isolated strain of ARV was named CD200801 and was identified through transmission electron microscopy and RT-PCR based on the ARV S2 gene. Experimental infection with CD200801 resulted in the death of ducklings with serious spleen and liver focal necrosis. BLAST analysis of CD200801 sequences showed a 35.5 to 98.6% similarity to a novel duck reovirus that was isolated in recent years. Phylogenetic analysis revealed that CD200801 was closely related to ARV isolates YL, GX-Y7, and XT-18. We report the first avian reovirus infection in the black swan. This study provides important new insights into the evolutionary relationships among different ARV strains and highlights the need for continued surveillance and monitoring of these viruses in both domestic and wild bird flocks. These findings have significant implications for the development of effective strategies for disease prevention and control in the poultry industry.

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.

Distinct Whole Transcriptomic Profiles of the Bursa of Fabricius in Muscovy Ducklings Infected by Novel Duck Reovirus with Different Virulence

Novel duck reovirus (NDRV) is a newly identified reovirus that brings about more severe damage on multiple organs and mortality in various species of waterfowl. We previously characterized the transcriptomic profiles responding to NDRV in the bursa of Fabricius of Muscovy ducklings, which is a major immunological organ against virus infection. However, the molecular mechanisms of variant cell responses in the bursa of Fabricius to NDRV with different virulence is unclear. Here, we conducted a whole transcriptomic analysis to study the effects of two strains, HN10 (virulent NDRV) and JDm10 (artificially attenuated NDRV), on the bursa of Fabricius of Muscovy ducklings. We harvested a large number of differentially expressed genes (DEGs) of the bursa of Fabricius specially induced by HN10 and JDm10, and we found that HN10 induced DEGs enriched in differentiation and development in multiple organs beyond JDm10. Moreover, the ceRNA regulatory network also indicated the different connections among mRNA, lncRNA and miRNA. Interestingly, we further noticed that a population of differential expressed miRNA could particularly target to transcripts of HN10 and JDm10. We took miR-24 as an example and observed that miR-24 could reduce the transcription of GLI family zinc finger 3 (Gli3) and membrane-associated guanylate kinase, WW and PDZ domain containing 1 (Magi1) via recognition 3' UTR of these two genes by a dual luciferase reporter gene assay in vitro. However, this effect could be compromised by HN10 infection or the ectopic over-expression of the putative miR-24 targeting regions in L1 and L3 fragments of HN10. Taken together, we examined and proposed a novel regulatory competitive mechanism between transcripts of NDRV and Muscovy ducklings for miRNA. These findings may advance the understanding of the molecular pathogenesis of NDRV in Muscovy ducklings, and help provide the potential targets for vaccine and drug development against NDRV.

Isolation and characterization of a duck reovirus strain from mature ducks in China

In 2018, a disease characterized by splenic hemorrhage and necrosis killed ducks in a duck farm in Guangxi province, China. A duck reovirus strain was isolated from the tissues of the dead ducks by inoculating duck embryos and BHK-21 cells. Electron microscopy of the cultured the isolate showed that the viral particles were nearly round in shape and approximately 70 nm in diameter, and they were designated DRV-GL18. Sequence analysis showed that the GL18 strain viral genome was 23,419 nt in length and had 10 dsRNA segments. Phylogenetic analysis of cDNA amplicons of segments encoding the protein σC which are outer capsid proteins showed that the isolate belongs to the branch of the epidemic strains of duck reovirus. The Recombination Detection Program (RDP) and SimPlot program analyses suggested potential genetic recombination events in the M2 segments. Pathogenicity experiments revealed that GL18 produced severe hemorrhaging in livers and necrosis in the spleen of infected SPF ducklings. A death rate of 50% in the experimental ducklings was calculated during the first 7 d, and the rest of the ducklings were observed to undergo spleen necrosis. These data suggested that GL18 is a duck reovirus isolate with severer pathogenicity, and it could be a candidate for development of vaccine. This is the first reported isolation of duck reovirus from mature ducks.

Analysis of the global origin, evolution and transmission dynamics of the emerging novel variant IBDV (A2dB1b): The accumulation of critical aa-residue mutations and commercial trade contributes to the emergence and transmission of novel variants

The Chinese IBDV novel variant (nvIBDV), belonging to the genotype A2dB1b, an emerging pathotype that can cause subclinical disease with severe, prolonged immunosuppression, poses a new threat to the poultry industry. The process of the global origin, evolution and transmission dynamics of nvIBDV, however, is poorly understood. In this study, phylogenetic trees, site substitutions of amino acid (aa) and highly accurate protein structure modelling, selection pressure, evolutionary and transmission dynamics of nvIBDV were analysed. Interestingly, nvIBDV was classified into the same genogroup with the early US antigenic variants (avIBDV) but in a new lineage with a markedly different and specific pattern of 17 aa-residual substitutions: 13 in VP2 (77D, 213N, 221K, 222T, 249K, 252I, 253Q, 254N, 284A, 286I, 299S, 318D and 323E) and four in VP1 (141I, 163V, 240E and 508K). Importantly, the aa-residues 299S and 163V may play a key role in cell binding and polymerase activity, respectively. The effective population size of the circulating avIBDV experienced two growth phases, respectively, in the years 1999-2007 (in North America) and 2015-2021 (in Asia), which is consistent with the observed trend of the epidemic outbreaks. The most recent common ancestor (tMRCA) of avIBDV most first originated in the USA and was dated around the 1970s. After its emergence, the ancestor virus of this group probably spread to China around the 1990s and the variants experienced a long-term latent circulation with the accumulation of several critical aa-residue mutations in VP2 until re-emerging in 2016. At present, central China has become the epicentre of nvIBDV spread to other parts of China and Asian countries. Importantly, a strong correlation seems to exist between the transmission patterns of virus and the flow of commercial trade of live poultry and products. These findings provide important insights into the origin, evolution and transmission of the nvIBDV and will assist in the development of programs for control strategies for these emerging viruses.

The emerging naturally reassortant strain of IBDV (genotype A2dB3) having segment A from Chinese novel variant strain and segment B from HLJ 0504-like very virulent strain showed enhanced pathogenicity to three-yellow chickens

Novel variant infectious bursal disease virus (nvIBDV) is an emerging pathotype that can cause sub-clinical disease with severe, prolonged immunosuppression in young chickens. At present, two major pathotypes, including vvIBDV and nvIBDV, are prevailing in China. In this study, we propose that the nvIBDV is a new genotype (A2dB1b) and also first isolated and characterized a nvIBDV reassortant strain YL160304 (A2dB3) with segments A and B derived, respectively, from the nvIBDV and the HLJ-0504-like vvIBDV from yellow chickens in southern China. The YL160304 causes more extensive cytotropism and can infect specific-pathogen-free chicken embryos with severe subcutaneous hemorrhage. The pathogenicity of YL160304 to 4-week-old three-yellow chickens was determined and compared with those of the nvIBDV QZ191002 and the HLJ-0504-like vvIBDV NN1172. Weight gain was significantly reduced in all the challenged birds. No clinical signs and associated mortality were observed in the birds challenged with QZ191002, while the mortalities in the birds challenged with NN1172 and YL160304 were 30% (3/10) and 10% (1/10), respectively. At 7 days postchallenge, the bursa was severely damaged and the percentage of peripheral blood B lymphocyte (PBBL) decreased significantly in all the challenged birds and the quantity of the viral RNA detected in the bursa was in accordance with the results of the histomorphometry and the depletion of PBBL. This study not only confirmed the emerging epidemic of the novel variant and its reassortant strains, but also discovered that the naturally reassortant nvIBDV strain with the segment B of HLJ 0504-like vvIBDV can significantly enhance the pathogenicity to chickens.

Isolation and characterization of a naturally attenuated novel duck reovirus strain as a live vaccine candidate

Novel duck reovirus (NDRV) causes high morbidity in ducklings, and recovered ducklings are often remarkably stunted in growth. In this study, four NDRV strains were isolated from the NDRV outbreaks that occurred in different regions of Shandong province, China. The biological characteristics and pathogenicity of the four NDRV strains were elucidated, and the N20 was identified as a naturally attenuated strain. Three-day-old ducklings were immunized with live N20 strain (100 ELD₅₀/duck), and challenged with 10^4.52 ELD₅₀ of virulent N19 strain at 7 days post immunization. The vaccinated ducklings showed no evidence of clinical signs, gross and histopathological lesions, or loss of body weight, and 100 % protection against the virulent NDRV N19 infection. The NDRV-specific antibodies were generated in the immunized ducklings and could neutralize different NDRV strains. These results indicated that the N20 strain was a promising live attenuated vaccine candidate against highly pathogenic NDRV infection.

Isolation and characterization of a new goose orthoreovirus causing liver and spleen focal necrosis in geese, China

Since July 2020, an infectious disease characterized by liver and spleen white focal necrosis has been spreading widely through geese farms in many regions of China. A novel goose orthoreovirus (GRV), designated GRV-GD2020, was isolated from the liver and spleen of dead geese. Phylogenetic analysis and sequence comparison revealed that all the genes of GRV-GD2020 clustered with other waterfowl-origin orthoreovirus. However, the gene constellation of GRV-GD2020 was not similar to that of any particular strain. Instead, the genomic segments of GRV-GD2020 showed 27.5-97.3% similarities to that of other waterfowl-origin orthoreovirus isolates. Waterfowl-origin orthoreovirus infections characterized by liver and spleen focal necrosis had not emerged in recent years. The re-emergence of the disease may be related to the recombination of the genome segments of Muscovy duck reovirus (MDRV), GRV, and new-type duck orthoreovirus. In summary, we determined that the GRV-GD2020 strain, causing goose liver and spleen focal necrosis, is a new variant of waterfowl-origin orthoreovirus.

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.

The Full Region of N-Terminal in Polymerase of IBDV Plays an Important Role in Viral Replication and Pathogenicity: Either Partial Region or Single Amino Acid V4I Substitution Does Not Completely Lead to the Virus Attenuation to Three-Yellow Chickens

Infectious Bursal Disease Virus (IBDV) has haunted the poultry industry with severe, prolonged immunosuppression of chickens when infected at an early age and can easily lead to other secondary infections. Understanding the pathogenic mechanisms could lead to effective prevention and control of Infectious Bursal Disease (IBD). Evidence suggests that the N-terminal domain of polymerase in segment B plays an important role, but it is not clear which part or residual is crucial for the pathogenicity. Using a reverse genetics technique, a molecular clone (rNN1172) of the parental vvIBDV strain NN1172 was generated, and its pathogenicity was found to be the same as the parental virus. Then, three recombinant chimeric viruses were rescued based on the rNN1172 and substituted with the counterparts in the N-terminal domain of the attenuated vaccine strain B87: the rNN1172-B87VP1a (substituting the full region of the 1–167 aa residuals), the rNN1172-B87VP1a∆4 (substituting the region of the 5–167 aa residuals), and the rNN1172-VP1∆4 (one single aa residual substitution V4I), to better explore the role of the N-terminal domain of polymerase on the viral pathogenicity. Interestingly, all these substitutions played different roles in the viral pathogenicity: the mortality of the rNN1172-B87VP1a-challenged chickens was significantly reduced from 30% to 0%. No obvious lesion was found in the histopathological examination, and the lowest viral genome copy number was also detected in the bursa when compared to the parental and two other recombinant viruses. The mortalities caused by rNN1172-B87VP1a∆4 and rNN1172-B87VP1∆4, respectively, were all reduced to 10% and had a delayed onset of death. Our results also revealed that the pathogenicity of the IBDV was consistent with the viral replication efficiency in vivo (bursae). This study demonstrated that the full region of the N-terminal of polymerase plays an important role in viral replication and pathogenicity, but the substitutions of its partial region or a single residual do not completely lead to the virus attenuation to Three-Yellow chickens, although that significantly reduces its pathogenicity.

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.