Complete genome sequence of a novel avastrovirus in goose

Rapid detection of avipoxvirus using a fluorescent probe-based multienzyme isothermal amplification assay

Avipoxvirus (APV) is a prevalent DNA virus in avian species, causing clinical symptoms of fowlpox and leading to reduced egg production, slower broiler growth, and increased mortality. The spread of APV poses a significant threat to the global poultry industry, potentially causing substantial economic losses. Effective control of APV, particularly its major species such as fowlpoxvirus and pigeonpoxvirus, requires the development of rapid and specific diagnostic tools. In this study, a novel multi-enzyme isothermal rapid amplification (MIRA) assay was developed to detect APV. Various primer-probe combinations were screened to identify an optimal pair targeting a conserved region of the viral P4b gene. The MIRA assay operates at a constant temperature and results can be visualized through fluorescence signal detection. The sensitivity, specificity, and applicability of the MIRA assay were evaluated. Additionally, 86 clinical samples were tested to assess the accuracy of the MIRA assay. The MIRA assay provides results within 15 minutes demonstrated high specificity, with no cross-reactivity with other avian pathogens. It achieved a detection limit of 50 copies/μl, which is consistent with the qPCR assay. Further evaluation with 86 clinical samples showed that the accuracy of the MIRA assay was comparable to that of qPCR in detecting fowlpoxvirus and pigeonpoxvirus. The results highlight the convenience, sensitivity, and rapidity of the MIRA assay as a promising tool for diagnosing APV.

Screening and identification of protein interacting with goose astrovirus

Introduction

Goose Astrovirus (GoAstV), a recently identified member of the Astroviridae family in China, predominantly affects goslings, resulting in substantial economic losses to the goose farming industry due to its high infection and mortality rates. Currently, the infection mechanism and pathogenesis of GoAstV remain unknown.

Methods

Given this, the Viral Overlay Protein Blot Assay was utilized to identify and characterize proteins on the LMH (Leghorn Male Hepatoma) cell membrane that interact with Goose Astrovirus. The identities of the candidate proteins were determined via LC-MS mass spectrometry analysis, bioinformatics analysis, and UniProt database search. The interaction between HSPA5 and the astrovirus protein was further validated in vitro through Western blot and Coimmunoprecipitation experiments. Finally, bioinformatics tools such as SWISSMODEL, AlphaFold, and ZDOCK were employed to construct and analyze the docking complex model between the candidate protein and GoAstV protein, including their key binding residue sites.

Results

We successfully identified a 70 kDa protein in the plasma membrane protein extracts of LMH cells and confirmed the identity of this candidate protein as HSPA5. Meanwhile, in vitro experiments further validated the interaction between HSPA5 and astrovirus proteins. Subsequently, we successfully predicted the docking complex model of HSPA5 protein with GoAstV protein. Further prediction of the binding residue sites revealed that seven residues of the GoAstV-P2 protein (THR124, ILE22, VAL24, TRP51, PRO66, GLN100, and VAL125) and twelve residues of the HSPA5 protein (ARG2, HIS3, LEU4, LEU6, ALA7, LEU8, LEU9, LEU10, LEU11, ASP411, VAL413, and LEU415) may be involved in the interaction between these two proteins.

Discussion

Our research results have preliminarily elucidated the interaction mechanisms between viral proteins and receptors, facilitating exploration from multiple angles of the roles of candidate protein in the process of GoAstV infecting host cells. This provides a theoretical basis for further identification of GoAstV receptors and clarification of its infection mechanisms.

Identification of a novel linear B-cell epitope recognized by a monoclonal antibody against the capsid protein of goose astrovirus genotypes 2

BACKGROUND

Goose astrovirus genotype 2 (GoAstV-2) is a novel and highly infectious pathogen characterized by symptoms of gout, swelling, and hemorrhage of the kidneys in 5-15-day-old goslings. The virus has caused severe economic losses for the goose husbandry industry. The capsid protein of GoAstV-2 is involved in viral packaging and immunogenicity, and it has served as a target antigen for diagnostic methods.

RESULTS

In this study, the N-terminus of the GoAstV-2 Cap protein (rCap) was successfully expressed and used to immunize BALB/c mice. A new monoclonal antibody (mAb) named 7B2 against the GoAstV-2 rCap protein was prepared. Immunofluorescence assay and Western blot analysis showed that mAb 7B2 had a strong binding affinity to the GoAstV-2 rCap protein. The results of epitope mapping demonstrated that the minimum linear epitope recognized by mAb 7B2 was located in the amino acids 153NTAGPESIDT162. Sequence homology analysis revealed that this epitope was highly conserved among the GoAstV-2 strains analyzed and that it showed 90% sequence similarity with turkey astrovirus 2 strains and low similarity (less than 50%) with other astroviruses.

CONCLUSIONS

These findings will be useful for the development of diagnostic kits for GoAstV-2 and will aid further research on the structure and function of the capsid protein.

Molecular evidence for goose astrovirus 2 and goose astrovirus 3 coinfection in goslings with gout

Gosling gout is usually considered to be caused by goose astrovirus 2 (GoAstV-2); however, goose astrovirus 3 (GoAstV-3) has also been shown to play a pathogenic role in this disease. Here, we developed new assays for specific detection of goose astroviruses, including GoAstV-2- and GoAstV-3-specific reverse transcription (RT)-PCR and real-time fluorescence quantitative PCR (RT-qPCR) assays. These assays revealed coinfection with GoAstV-2 and GoAstV-3 in 19 (57.6%) out of 33 cases examined, with GoAstV-2 producing 1,000- to 100,000-fold higher viral loads than GoAstV-3. These findings will stimulate further studies on the roles of GoAstV-2 and GoAstV-3 in the occurrence of gosling gout.

Current Situation of Goose Astrovirus in China: A Review

Gosling gout disease is an infectious disease caused by goose astrovirus (GAstV), which can result in urate deposition in the internal organs and joints of goslings. Since 2015, outbreaks of gosling gout disease have occurred in several goose-producing areas in China. Subsequently, the disease spread to the vast majority of eastern China, becoming a major threat to goose farms and causing huge economic losses to the goose industry. Meanwhile, GAstV can infect species of birds other than geese. It is worth noting that, as an emerging virus, the research on GAstV is still in the early stages. Therefore, the investigation of GAstV has become an urgent issue, which can improve understanding of GAstV and develop effective measures to control its threat to poultry. The purpose of this review is to summarize the latest research progress on GAstV in recent years, mainly focusing on the genetic evolution, pathogenesis, diagnostic detection, and control strategies of GAstV, aiming to provide a reference for scientific prevention and control of GAstV infection.

Goose astrovirus induces apoptosis and endoplasmic reticulum stress in gosling hepatocytes

The ongoing Goose astrovirus (GoAstV) epidemic, which primarily infects goslings causing severe liver damage, has inflicted considerable damage on the poultry industry. Endoplasmic reticulum stress (ERS) is a significant modulator of several viral infections, while severe ERS may result in apoptosis. This study examined the roles and possible mechanisms of ERS and apoptosis in GoAstV-induced liver injury in goslings. Two hundred Xingguo gray geese were chosen and randomly separated into two groups (Con and Dis). The Dis group received a subcutaneous injection of GoAstV genotype 2 (GoAstV-2) JX01 (2 × 106 TCID50/0.2 mL), whereas the Con group received a subcutaneous injection of 0.2 mL physiological saline, both at 1 day of life. Subsequent analyses demonstrate that the levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) increased following GoAstV infection. Hematoxylin and eosin (HE) staining revealed swollen and ruptured hepatocytes, with significant inflammatory cell infiltration. Electron microscopy revealed expansion of the endoplasmic reticulum (ER) and aggregation of chromatin at the periphery. TUNEL testing further demonstrated an increase in the quantity of positive cells. RT-qPCR and Western blot analyses indicated that GoAstV infection enhanced the expression of ER Ca2+ release channels (IP3R and RYR) and calmodulin-dependent protein kinase II (CaMKII), while decreasing the expression of ER Ca2+ uptake channels (SERCA). Further, GoAstV infection activated ERS-related factors, including GRP78, IRE1α, PERK, ATF6, eIF2α, ATF4, CHOP, TRAF2, and JNK, induced the expression of pro-apoptotic factors (Caspase-3, Caspase-9, and Bax), and inhibited the mRNA and protein expression of the anti-apoptotic factor Bcl-2. Correlation analysis further revealed a potential relationship among ERS gene expression, apoptotic gene expression, and liver injury. In summary, GoAstV infection can lead to liver injury by interfering with ER Ca2+ homeostasis, exacerbating ERS and inducing hepatocyte apoptosis.

Integrative transcriptomics and proteomics analysis provide a deep insight into goose astrovirus-host interactions during GAstV infection

Goose astrovirus (GAstV) is a newly discovered astrovirus. GAstV causes gout and death in 4- to -16-day-old goslings. For the past few years, fatal gout, the cardinal clinical symptom of gosling infected with GAstV, has been spreading rapidly in some goose Chinese farms, which caused continuous economic losses to the goose breeding industry in China. Currently, several underlying mechanisms involved in viral replication, inflammatory reaction, virions release, and viral pathogenesis of GAstV remain to be elucidated. In this study, we explored the mechanisms of GAstV-host interactions, the transcriptome and proteome profiles of GAstV-infected LMH cells were sequenced by RNA-seq and data-independent acquisition (DIA) techniques, respectively, and followed using an integrative analysis. Compared with uninfected LMH cells, a total of 322 differentially expressed genes (DEG) (195 up-regulated, 127 down-regulated) and 36 differentially expressed proteins (DEP) (31 up-regulated, 5 down-regulated) were detected. Nine DEGs were randomly selected for further validation by quantitative real-time polymerase chain reaction (qPCR). Through GO and KEGG enrichment analysis, DEG and DEP were significantly enriched in several important cellular signaling pathways, including MAPK, PI3K-Akt, cAMP, chemokine, calcium, phospholipase D, Ras, TNF, IL-17, Rap1, NF-kappa B signaling pathways, indicating that GAstV affects cell growth and immune signaling. This study provided an overview of changes in transcriptome and proteome profiles of GAstV-infected LMH cells, therefore, providing a crucial basis to further explore the mechanisms of GAstV-host interactions.

Comparative transcriptomic analysis of goose astrovirus genotype 1 and 2 in goose embryonic fibroblasts

Gout in goslings has become widespread and caused huge economic losses for the goose industry. Emerging evidence suggests that goose astrovirus (GAstV) is a prominent etiological factor of gout in goslings. At present, 2 genotypes of GAstV have been identified named GAstV-1 and GAstV-2. Here, we isolated the GAstV-1 HBLY strain and GAstV-2 XT1 strain from HeBei province of China. The genome and proliferation characteristics of GAstV-1 and GAstV-2 were analyzed and the results showed that the whole genome identity was 53.8% to 55.8%, especially the nucleotide and amino acids identity of ORF2 and Cap protein was only 49.5% to 50.5% and 19.6% to 22.6 %. Interestingly, GAstV-1 and GAstV-2 with such low homology both can cause gout in goslings. To further explore this phenomenon, the whole genomic expression profile of goose embryonic fibroblasts (GEFs) infected with GAstV-1 was investigated in comparison with GAstV-2. The results revealed that 126 differentially expressed genes (DEGs) were identified between GAstV-1-infected and uninfected cells at 48 h postinfection (hpi), and 262 DEGs between GAstV-2 and uninfected. Among these, there are 15 commonly up-regulated genes and 19 commonly down-regulated genes. Gene ontology (GO) enrichment analysis, Kyoto encyclopedia of genes and genomes (KEGG) pathway analysis, and short time-series expression miner (STEM) analysis suggested that GAstV-1 can induce a higher innate immune response to GEFs, while GAstV-2 has a more pronounced effect on GEFs metabolic pathways. The transcriptomic analysis results significantly enhance our comprehension of the pathogenic mechanisms of GAstV.

Development of a multienzyme isothermal and lateral flow dipstick combination assay for the rapid detection of goose astrovirus II

Introduction

Goose astrovirus (GAstV) is a newly emerging pathogen that is currently widespread among geese, causing visceral gout and leading to substantial gosling mortalities, posing a severe threat to the waterfowl industry. GAstV II is the predominant epidemic strain, characterized by its high morbidity and mortality rate. Consequently, there is an urgent necessity to develop an effective diagnostic approach to control the dissemination of GAstV II, particularly in clinical farms with limited laboratory resources.

Methods

In this study, a novel multi-enzyme isothermal rapid amplification (MIRA) and lateral flow dipstick (LFD) combined assay was developed. Different primers designed specific targeting a highly conserved region within the viral RdRp gene for the detection of GAstV II. Primers optimized and MIRA-LFD assay analyzed its performance regarding limits of detection, specificity, and efficiency of detection.

Results

The developed MIRA amplification is conducted at a constant temperature and accomplished within 10 minutes. Subsequent naked-eye observation of the LFD strips merely takes 5 minutes. The established MIRA-LFD method exhibits high specificity, with no cross-reaction with other pathogens and attains a detection sensitivity of 1 copy/μl, which is consistent with the reverse transcription quantitative PCR (RT-qPCR) assay. Further evaluation with clinical samples indicates that the accuracy of this MIRA-LFD method correlates well with RT-qPCR for the detection of GAstV II.

Conclusion

In summary, the convenience, sensitivity, and rapidity of this newly developed detection method offer a significant advantage for on-site diagnosis of GAstV II.

Alteration of gut microbiome in goslings infected with goose astrovirus

Goose astrovirus (GoAstV) is an emerging avian pathogen that induces gout in goslings with a mortality of up to 50%. Organ damage caused by GoAstV infection was considered the cause of gout, but it is still unclear whether other factors are involved. Human and murine studies have linked the gut microbiome-derived urate and gout, thus we hypothesized that gut microbiome may also play an important role in gout induced by GoAstV infection. This study tested the pathogenicity of our isolated GoAstV genotype 2 strain on goslings, while the appearance of clinical signs, histopathological changes, viral distribution and the blood level of cytokines were monitored for 18 d postinfection (dpi). The dynamics in the gut microbiome were profiled by 16S sequencing and then correlated with GoAstV infection. Results showed that this study successfully developed an experimental infection model for studying the pathogenicity of the GoAstV infection which induces typical symptoms of gout. GoAstV infection significantly altered the gut microbiome of goslings with the enrichment of potential proinflammatory bacteria and depletion of beneficial bacteria that can produce short-chain fatty acids. More importantly, the microbial pathway involved in urate production was significantly increased in goslings infected with GoAstV, suggesting that gut microbiome-derived urate may also contribute to the gout symptoms. Overall, this study demonstrated the role of gut microbiome in the pathogenesis of GoAstV infection, highlighting the potential of gut microbiome-based therapeutics against gout symptoms.

Development of a label-free photoelectrochemical immunosensor for novel astrovirus detection

Since 2017, an infectious goose gout disease characterized by urate precipitation in viscera, mainly caused by novel goose astrovirus (GoAstV) infection, has emerged in the main goose-producing region of China. The current challenge in managing goose gout disease is largely due to the absence of a rapid and efficient detection method for the GoAstV pathogen. Notably, the potential application of immunosensors in detecting GoAstV has not yet been explored. Herein, a label-free PEC immunosensor was fabricated by using purchased TiO2 as the photoactive material and antibody against GoAstV P2 proteins as the specific recognition element. First, we successfully expressed the capsid spike domain P2 protein of ORF2 from GoAstV CHSH01 by using the pET prokaryotic expression system. Meanwhile, the polyclonal antibody against GoAstV capsid P2 protein was produced by purified protein. To our knowledge, this is the first establishment and preliminary application of the label-free photoelectrochemical immunosensor method in the detection of AstV. The PEC immunosensor had a linear range of 1.83 fg mL-1 to 3.02 ng mL-1, and the limit of detection (LOD) was as low as 0.61 fg mL-1. This immunosensor exhibited high sensitivity, great specificity, and good stability in detecting GoAstV P2 proteins. To evaluate the practical application of the immunosensor in real-world sample detection, allantoic fluid from goose embryos was collected as test samples. The results indicated that of the eight positive samples, one false negative result was detected, while both negative samples were accurately detected, suggesting that the constructed PEC immunosensor had good applicability and practical application value, providing a platform for the qualitative detection of GoAstV.

Epidemiological Investigation of Goose Astrovirus in Hebei Province, China, 2019-2021

The goose astrovirus (GAstV), a key pathogen causing visceral gout and high mortality in geese, has spread widely in China, with frequent outbreaks in recent years. Outbreaks and transmissions of this virus have been reported across China, causing considerable economic losses to the goose industry worldwide, with losses exceeding tens of billions in China alone. However, there is still no effective prevention strategy against this virus. Therefore, continuous monitoring of the genetic diversity of dominant GAstV strains is crucial for developing targeted vaccines and appropriate therapeutics. As a crucial region for goose breeding in China, Hebei Province has previously lacked reports on the epidemiology of GAstV. Hence, investigating the epidemiology of GAstV in Hebei Province is highly important. From January 2019 to December 2021, 474 samples suspected of having a GAstV infection were collected in Hebei Province in this study. Through detailed histological observations, pathological examinations, virus isolation and identification, and genetic diversity analysis, we found that GAstV-2 has become the predominant circulating genotype. However, the presence of GAstV-1 and mixed infections cannot be ignored and should receive increased attention. The findings of this study not only deepened our understanding of GAstV in waterfowl in China but also provided scientific evidence for developing effective prevention and control measures, thereby promoting the healthy development of the goose industry in China.

The Development of a Sensitive Droplet Digital Polymerase Chain Reaction Test for Quantitative Detection of Goose Astrovirus

(1) Goose astrovirus (GAstV) is a novel emerging pathogen that causes significant economic losses in waterfowl farming. A convenient, sensitive, and specific detection method for GAstV in field samples is important in order to effectively control GAstV. Droplet digital polymerase chain reaction (ddPCR) is a novel, sensitive, good-precision, and absolute quantitation PCR technology which does not require calibration curves. (2) In this study, we developed a ddPCR system for the sensitive and accurate quantification of GAstV using the conserved region of the ORF2 gene. (3) The detection limit of ddPCR was 10 copies/µL, ~28 times greater sensitivity than quantitative real-time PCR (qPCR). The specificity of the test was determined by the failure of amplification of other avian viruses. Both ddPCR and qPCR tests showed good repeatability and linearity, and the established ddPCR method had high sensitivity and good specificity to GAstV. Clinical sample test results showed that the positive rate of ddPCR (88.89%) was higher than that of qPCR (58.33%). (4) As a result, our results suggest that the newly developed ddPCR method might offer improved analytical sensitivity and specificity in its GAstV measurements. The ddPCR could be widely applied in clinical tests for GAstV infections.

Molecular characterization of a virulent goose astrovirus genotype-2 with high mortality in vitro and in vivo

Goose astrovirus (GAstV) is a newly identified viral pathogen threatening waterfowl, exhibiting a high prevalence across various regions in China. Notably, the Guanghan District of Deyang City, situated in Sichuan Province, has faced a outbreak of GAstV, resulting in significant mortality among goslings due to the induction of gout-like symptoms. In our research, we successfully isolated a GAstV strain known as GAstV SCG3. This strain exhibits efficient replication capabilities, proving virulent in goslings and goose embryos. Our study delved into the characteristics of GAstV SCG3 both in vitro and in vivo. Additionally, we examined tissue phagocytosis and the distribution of GAstV SCG3 in deceased goslings using H&E staining and IHC techniques. According to the classification established by the ICTV, GAstV SCG3 falls under the category of GAstV genotype-2. Notably, it demonstrates the highest homology with the published AHAU5 sequences, reaching an impressive 98%. Furthermore, our findings revealed that GAstV SCG3 exhibits efficient proliferation exclusively in goose embryos and in LMH cells, while not manifesting in seven other types of avian and mammalian cells. Significantly, the mortality of GAstV on goslings and goose embryos are 93.1 and 80%, respectively. Moreover, the viral load in the livers of infected goslings surpasses that in the kidneys when compared with the attenuated strain GAstV SCG2. The mortality of GAstV is usually between 20% and 50%, our study marks the first report of a virulent GAstV strain with such a high mortality.

Characterization of natural co-infection with goose astrovirus genotypes I and II in gout affected goslings

RESEARCH HIGHLIGHTS

Urate tophi were found in the kidneys, liver, spleen and lungs.IFA confirmed the co-expression of GoAstV-I and II antigens in the same kidney.

Isolation, Identification, and Pathogenicity of a Goose Astrovirus Genotype 1 Strain in Goslings in China

Goose astrovirus genotype 1 (GAstV-1) has emerged in goose farms in some provinces of China in recent years and is considered to be one of the pathogens of gout in goslings in China. However, few studies have been conducted on the dynamic distribution, tissue tropism, and pathogenesis of GAstV-1 in goslings. In 2022, an epidemiological investigation of goose astrovirus (GAstV) in goslings was conducted in seven provinces of China. During the investigation, a GAstV-1 designated as GAstV-JSXZ was identified in the kidney of an 8-day-old gosling and was successfully isolated from a goose embryo. The full genome sequence of GAstV-JSXZ was determined using the next-generation sequencing technique. The complete genome of GAstV-JSXZ was 7299-nt-long. Interestingly, the phylogenetic analysis revealed that Chinese GAstV-1 has formed two distinct subgroups based on the ORF 2 genomes, designated GAstV-1 1a and GAstV-1 1b. The GAstV-JSXZ shared the highest identity with GAstV-1 1a strain FLX and TZ03 in nucleotides (ORF1a: 98.3-98.4%; ORF1b: 92.3-99.1%; ORF2: 95.8-98.8%) and amino acid sequences (ORF1a: 99.4-99.5%; ORF1b: 98.2-98.8%; ORF2: 97.0-99.4%). To evaluate the pathogenicity of GAstV-1, 1-day-old goslings were inoculated with the virus by oral and subcutaneous injection routes, respectively. The results revealed that the virus causes extensive pathological organ damage, especially in the kidney, liver, and thymus. Virus-specific genomic RNA could be detected in the cloacal swabs and tissues of infected goslings throughout the experiment. The viral copy numbers examined in the kidney and intestine were the highest, followed by the liver and spleen. These results are likely to provide a new understanding of the pathogenicity of GAstV-1 in geese.

Pathogenicity of a goose astrovirus 2 strain causing fatal gout in goslings

Gosling gout has posed a serious threat to the development of the China's goose industry since the outbreak in mainland China in 2016; goose astrovirus (GAstV) was identified as the culprit pathogen. Two genotypes of this virus have been identified: GAstV-1 and GAstV-2, of which GAstV-2 is the main epidemic strain. Our current understanding of the pathogenic mechanisms of GAstV-2 remains limited. To assess pathogenicity, 1-day-old goslings were inoculated with the GAstV-2 YC20 strain via the subcutaneous, intranasal, and oral infection routes. All the goslings showed typical gout symptoms, with those in the oral infection group exhibiting earlier and more severe clinical symptoms, the highest mortality rate, and greatest weight loss. The blood biochemical indicators, viral loads in cloacal swabs and all representative tissues, and serum antibody titers of all infection groups increased significantly, and no significant differences in these parameters were observed among the three infection groups. Histopathological studies showed that the livers, kidneys, and spleens were the main damaged organs, and the pathological changes in the oral group were more severe than those in the other groups. Further analysis revealed that hepatic sinuses narrowed or became occluded as early as 1 day post-inoculation; urate deposition occurred in the renal tubules at 2 days post-inoculation (dpi), followed by necrosis of renal tubular epithelial cells; and lymphocytic infiltration appeared in the splenic tissue at 5 dpi. These results further our understanding of the pathogenic mechanisms of GAstV-2 and provide a reference for future studies.

Isolation and genomic characterization of one novel goose astrovirus causing acute gosling gout in China

Novel goose astrovirus (NGAstV) is a member of the genus Avain Avastrovirus (AAstV) and the family Astroviridae. NGAstV-associated gout disease has caused huge economic losses to the goose industry worldwide. Since early 2020, NGAstV infections characterized by articular and visceral gout emerged continuously in China. Herein, we isolated a GAstV strain from goslings with fatal gout disease and sequenced its complete genome nucleotide sequence. Then we conducted systematic genetic diversity and evolutionary analysis. The results demonstrated that two genotypic species of GAstV (GAstV-I and GAstV-II) were circulating in China, and GAstV-II sub-genotype IId had become the dominant one. Multiple alignments of amino acid sequences of GAstV capsid protein revealed that several characteristic mutations (E456D, A464N, and L540Q) in GAstV-II d strains, as well as additional residues in the newly identified isolate which varied over time. These findings enrich the understanding of the genetic diversity and evolution of GAstV and may facilitate the development of effective preventive strategies.

The Isolation and Characterization of Goose Astrovirus Genotype 2 from Laying Hens with Nephritis in Shandong Province, China

Goose astrovirus genotype 2 (GoAstV2), as a contagious pathogen of fatal visceral gout in goslings, has been widely distributed in major goose-producing regions in China since 2017, leading to significant economic losses to the Chinese goose industry. In this study, a novel goose astrovirus (GoAstV-SDHZ) was isolated and identified from laying hens with nephritis for the first time. Phylogenetic analysis of the sequenced genome of ORF2 gene revealed that the GoAstV-SDHZ strain clustered into Group 2 GoAstVs and shared the highest identity with the other representative GoAstV2 in the nucleotide (ORF1a: 97.2-99.7%; ORF1b: 98.4-99.8%; ORF2: 97.2-99.9%) and amino acid sequence (ORF1a: 98.2-100%; ORF1b: 98.8-99.6%; ORF2: 97.4-99.6%). In summary, this study provides the first evidence of the GoAstV2 infection in Chinese laying hens, which raises potential threat to the poultry industry in China.

Rapid diagnosis of different goose astrovirus genotypes with Taqman-based duplex real-time quantitative PCR

The epidemic of goose astrovirus (GoAstV) caused huge losses to the poultry industry. Epidemiological studies in China revealed 2 circulating genotypes of GoAstV, but there is a lack of differential diagnosis tools. By analyzing all published genomes of GoAstV, this study designed specific PCR primers and Taqman probes to recognize different genotypes of GoAstV. After optimization and verification, this study developed a Taqman-based real-time quantitative PCR method that is capable of differential diagnosis. The established qPCR exhibited detection limitations of 100 copies/μL or 10 copies/μL, respectively, for GoAstV genotype 1 and genotype 2, and showed no false positive for other common avian viruses. This method was then used to analyze 72 samples collected from different regions in Jiangxi, and the results were verified by genome sequencing and phylogenetic analysis. These results revealed a complex coinfection of GoAstV different genotypes in China, highlighting the importance of long-term focus on the prevalence and genome evolution of GoAstV.

Establishment and Application of Indirect ELISAs for Detecting Antibodies against Goose Astrovirus Genotype 1 and 2

Goose astrovirus (GAstV) was classified into GAstV-1 and GAstV-2, and both caused gosling viral gout. Recently, there has been no effective commercial vaccine to control the infection. It is important to establish serological methods to distinguish between the two genotypes. In this study, we reported the development and application of two indirect enzyme-linked immunosorbent assays (ELISAs) using the GAstV-1 virus and a recombinant GAstV-2 capsid protein as specific antigens to detect antibodies against GAstV-1 and GAstV-2, respectively. The optimal coating antigen concentration of indirect GAstV-1-ELISA and GAstV-2-Cap-ELISA was 1.2 µg/well and 125 ng/well, respectively. In addition, the antigen coating temperature and time, sera dilution and reaction time, and the dilution and reaction time of HRP-conjugated secondary antibody were optimized. The cut-off values were 0.315 and 0.305, and the analytical sensitivity was 1:6400 and 1:3200 for indirect GAstV-1-ELISA and GAstV-2-Cap-ELISA, respectively. The assays were able to differentiate specific sera against GAstVs, TUMV, GPV, and H9N2-AIV. The intra- and inter-plate variabilities of indirect ELISAs were less than 10%. The coincidence rate of positive sera was higher than 90%. The indirect ELISAs were further applied to test 595 goose serum samples. The results showed that the detection rates were 33.3% and 71.4% in GAstV-1-ELISA and GAstV-2-Cap-ELISA, respectively, and the co-detection rate was 31.1%, which indicates that the seroprevalence rate of GAstv-2 was higher than that of GastV-1, and the co-infection existed between GAstV-1 and GAstV-2. In summary, the developed GAstV-1-ELISA and GAstV-2-Cap-ELISA have high specificity, sensitivity, and reproducibility and can be used in the clinical detection of the antibody against GAstV-1 and GAstV-2.

Detection and Characterization of Goose Astrovirus Infections in Hatcheries and Commercial Goose Flocks

Goose astrovirus (GoAstV) has frequently been isolated in China since it was first identified as the etiological agent of visceral gout in goslings in 2017. However, the actual prevalence of GoAstV infection and its economic impact on commercial goose production remain poorly characterized. Here, virus detection and serological testing were conducted to determine the extent of GoAstV infection in commercial goose flocks. We detected GoAstV RNA in 2% (6/300) of dead-in-shell embryos and day-old hatched goslings by RT-PCR, indicating vertical transmission under natural conditions. Using a virus neutralization test, GoAstV antibodies were detected in 41.7%-61.1% of serum samples from four commercial goose flocks, indicating that infections were common. To determine the virus types circulating in the commercial flocks, we isolated 15 GoAstVs from goose tissue samples from farms located in five provinces during 2018-2022. Genomic sequence analysis showed that all sequences were corresponded to GoAstV group 2 (GoAstV-2) but were assigned into three capsid subgroups based on sequence variations in the capsid protein. Representative isolates of capsid subgroups were also antigenically evaluated using cross-neutralization tests in LMH cell cultures. The antigenic relatedness values (R) calculated using the Horsfall formula were between 62% and 86%, indicating that no significant antigenic differences exist between the isolates. Our findings indicate that GoAstV-2 viruses are an important cause of fatal gout in goose flocks, as well as hatchery contamination in China.

Infection and innate immune mechanism of goose astrovirus

Goose astrovirus (GAstV, genus Avian Astrovirus, family Astrovirus) was first discovered in 2005, but was not considered as a pathogen of gosling gout until 2016. Since then, goose astrovirus has erupted in Chinese goslings, causing at most 50% of gosling deaths. By December 2022, the disease had become epidemic and prevailed in goose farms in Jiangsu, Shandong, Anhui, Henan, Guangdong, Liaoning, Sichuan and other places in China. The disease mainly affects goslings within 3 weeks old. The typical symptoms of goose astrovirus are large deposits of urate in the viscera, joint cavity and ureter surface of infected goslings. Goose astrovirus infection can trigger high levels of iNOS, limiting goose astrovirus replication. The ORF2 domain P2 of the goose astrovirus activates the OASL protein, limiting its replication. Goose astrovirus can also activate pattern recognition receptors (RIG-I, MDA-5, TLR-3), causing an increase in MHC-Ia, MHC-Ib and CD81 mRNA, activating humoral and cellular immunity, thereby hindering virus invasion. Goose astrovirus also regulates the activation of IFNs and other antiviral proteins (Mx1, IFITM3, and PKR) in the spleens and kidneys to inhibit viral replication. The innate immune response process in goslings also activates TGF-β, which may be closely related to the immune escape of goose astrovirus. Gaining insight into the infection and innate immune mechanism of goose astrovirus can help researchers study and prevent the severe disease in goslings better.

Discovery of novel Mamastroviruses in Bactrian camels and dromedaries reveals complex recombination history

Virus emergence may occur through interspecies transmission and recombination of viruses coinfecting a host, with potential to pair novel and adaptive gene combinations. Camels are known to harbor diverse ribonucleic acid viruses with zoonotic and epizootic potential. Among them, astroviruses are of particular interest due to their cross-species transmission potential and endemicity in diverse host species, including humans. We conducted a molecular epidemiological survey of astroviruses in dromedaries from Saudi Arabia and Bactrian camels from Inner Mongolia, China. Herein, we deployed a hybrid sequencing approach coupling deep sequencing with rapid amplification of complementary deoxyribonucleic acid ends to characterize two novel Bactrian and eight dromedary camel astroviruses, including both partial and complete genomes. Our reported sequences expand the known diversity of dromedary camel astroviruses, highlighting potential recombination events among the astroviruses of camelids and other host species. In Bactrian camels, we detected partially conserved gene regions bearing resemblance to human astrovirus types 1, 4, and 8 although we were unable to recover complete reading frames from these samples. Continued surveillance of astroviruses in camelids, particularly Bactrian species and associated livestock, is highly recommended to identify patterns of cross-species transmission and to determine any epizootic threats and zoonotic risks posed to humans. Phylogenomic approaches are needed to investigate complex patterns of recombination among the astroviruses and to infer their evolutionary history across diverse host species.

Development of an indirect competitive ELISA method based on ORF2 detecting the antibodies of novel goose astrovirus

Goose astrovirus (GAstV) characterized by articular and visceral gout, is an emerging pathogen with a wide distribution on mainland China, leading to serious economic losses in the goose-raising industry. Because vaccines to prevent GAstV infections are not available currently, early diagnosis is critical when treating symptomatic geese and in preventing GAstV transmission. In this context, a highly sensitive indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) based on a monoclonal antibody (mAb) to detect GAstV-specific antibodies from geese was developed, and the detections were optimized. A series of experiments proved that the ic-ELISA shows excellent diagnostic performance and discriminatory power with high sensitivity and specificity. The ic-ELISA for GAstV detection was applied on 67 field serum samples, and comparing the detection results with the virus neutralization test verified the accuracy of the ic-ELISA. The correlation coefficient between the ic-ELISA and the virus neutralization test was 80%, demonstrating the proposed ic-ELISA method could be a useful and effective tool for the diagnostic, serological epidemiological investigation and immune monitoring of the GAstV in goose-producing regions.

Isolation and Pathogenicity of a Novel Goose Astrovirus from Overfed Adult Landaise Geese in China

Goose astrovirus (GAstV) is an important pathogen causing visceral gout and high mortality in goslings, which has broken out and spread across China. In 2021, a disease characterized by urate deposition on the visceral surface and 30% mortality occurred in commercial adult Landaise geese in Zhejiang Province, China. A systematic study identified an infecting astrovirus, designated ZJCX, that was efficiently isolated from a diseased goose with a chicken hepatocellular carcinoma cell line (LMH). In contrast to other GAstVs originating from goslings, ZJCX caused cytopathogenic effects in LMH cells, and the crystalline arrangement of viral particles was observed through transmission electron microscopy. Indeed, phylogenetic analysis and nucleotide homology comparison revealed that ZJCX isolate belongs to the genotype II cluster of GAstVs and displays 97.8-98.4% identity with other GAstV II strains. However, several specific mutations occurred in the polyprotein and capsid protein regions. Moreover, a pathogenicity assessment of ZJCX with a gosling model was conducted, and typical visceral gout was reproduced and led to 18% mortality. The viral loads of ZJCX in the blood, kidney, and liver were detected with specific primers after inoculation, which demonstrated that the kidney and liver presented viral loads peaking at seven days post-inoculation (dpi). Biochemical parameter examination showed that AST, ALT, γ-GT, UA, and BUN levels were significantly increased by GAstV, whereas body weight was reduced. Overall, this study indicated that the GAstV isolate could infect adult geese, and the results regarding the viral loads and biochemical parameters induced by ZJCX provide insight into GAstV pathogenicity.

Development of a duplex real-time reverse transcription-polymerase chain reaction assay for the simultaneous detection of goose astrovirus genotypes 1 and 2

Goose astrovirus (GAstV) is a highly infectious pathogen that causes gout in goslings (<15 old) with typical symptoms of white urate disposition on the surface of the visceral organs and articular cavity, and a high mortality rate up to 50 %. To establish a real-time reverse transcription-polymerase chain reaction (rRT-PCR) assay for the rapid detection of the two GastV genotypes(GAstV-1 and GAstV-2), two pairs of primers and a pair of matching TaqMan probes were designed based on conserved regions of the ORF1b gene. The established duplex rRT-PCR assay showed no cross-reactivity with 10 other common waterfowl pathogens. The minimum detection limit was 10 copies/reaction for both GAstV-1 and GAstV-2. To validate the assay, 36 cloacal swabs from experimentally infected goslings and 33 field clinical samples were tested. The assay results of the experimentally infected goslings matched the infection scheme. The positive rates of GAstV-1 and GAstV-2 in the field clinical samples were 36.36 % and 54.55 %, respectively, and the co-infection rate of the two viruses was 21.21 % based on the duplex rRT-PCR assay. In conclusion, the established assay represents a specific, sensitive, and convenient tool for detecting GAstV-1, GAstV-2, and their co-infections, and for conducting epidemiological surveys.

Isolation, identification, and pathogenicity of a goose astrovirus causing fatal gout in goslings

Since November 2016, severe infectious diseases characterized by gout and kidney swelling and caused by goose astrovirus (GoAstV) have affected goslings in major goose-producing areas in China. In 2021, a similar serious infectious disease broke out in commercial goose farms in Heilongjiang Province, China. In this study, strain HLJ2021 was successfully isolated from goose embryos. Electron microscopy showed that the viral particles are spherical, with a diameter of about 28 nm. The complete genomic length of strain HLJ2021 is 7210 nt, and it encodes three viral proteins. A phylogenetic analysis showed that strain HLJ2021 belongs to GoAstV-2 (G2). Compared with the two original GoAstV strains, amino acid site 540^Q of the strain HLJ2021 spike domain has a mutation that affects the protein structure. One potential recombination event occurred between strains HLJ2021 and AstV/HB01/Goose/0123/19, which led to the generation of recombinant strain AstV/HN03/Goose/0402/19. Strain HLJ2021 also showed strong pathogenicity in goslings. Goslings infected with GoAstV began to die at 48 h post-infection (hpi), with a mortality rate of 83.3% at 240 hpi. At autopsy, visceral urate deposits, severe renal hemorrhage and swelling, and urate in the ureter were observed in the dead goslings. These findings extend our understanding of the evolution of GoAstV, which causes gout. The isolated GoAstV strain HLJ2021 provides a potential resource for the development of biological products for the prevention of goose gout.

A Review of Emerging Goose Astrovirus Causing Gout

In recent years, an infection in geese caused by goose astrovirus (GAstV) has repeatedly occurred in coastal areas of China and rapidly spread to inland provinces. The infection is characterized by joint and visceral gout and is fatal. The disease has caused huge economic losses to China's goose industry. GAstV is a nonenveloped, single-stranded, positive-sense RNA virus. As it is a novel virus, there is no specific classification. Here, we review the current understanding of GAstV. The virus structure, isolation, diagnosis and detection, innate immune regulation, and transmission route are discussed. In addition, since GAstV can cause gout in goslings, the possible role of GAstV in gout formation and uric acid metabolism is discussed. We hope that this review will inform researchers to rapidly develop effective methods to prevent and treat this disease.

Goose Astrovirus in China: A Comprehensive Review

Goose astroviruses (GoAstVs) are small non-enveloped viruses with a genome consisting of a single-stranded positive-sense RNA molecule. A novel GoAstV was identified in Shandong in 2016 and quickly spread to other provinces in China, causing gout in goslings, with a mortality rate of approximately 50%. GoAstV can also cause gout in chickens and ducks, indicating its ability to cross the species barrier. GoAstV has only been reported in China, where it has caused serious losses to the goose-breeding industry. However, in view of its cross-species transmission ability and pathogenicity in chickens and ducks, GoAstV should be a concern to poultry breeding globally. As an emerging virus, there are few research reports concerning GoAstV. This review summarizes the current state of knowledge about GoAstV, including the epidemiology, evolution analysis, detection methods, pathogenicity, pathogenesis, and potential for cross-species transmission. We also discuss future outlooks and provide recommendations. This review can serve as a valuable reference for further research on GoAstV.

Genome Analysis of Goose-Origin Astroviruses Causing Fatal Gout in Shanghai, China Reveals One of Them Belonging to a Novel Type Is a Recombinant Strain

Since 2014, a goose-origin astroviruses disease, which is characterized by urate precipitation in viscera, has rapidly spread to major commercial goose provinces leading to huge economic losses in the poultry industry of China. In March 2020, a goose farm locates in Shanghai, China, where there was no goose astroviruses (GAstVs) infection reported before, experienced an outbreak of gout disease in geese. The etiological investigation was carried out by virus metagenomics and bacterial culture and two GAstVs strains, designated as CHSH01 and CHSH02, were determined. Their complete genomes were measured to 7,154 and 7,330 nt in length, excludingthe poly(A) tail, respectively, and had different genomic features and classifications. CHSH01 shared a very low sequence identity with other strains in terms of not only the complete genome but also different ORFs. Phylogenetic analysis showed CHSH02 belonged to GAstV-2, which was the predominant species in the geese with gout in China according to the previous study. Meanwhile, CHSH01 strain displayed low identity with other AstVs, and phylogenetic and recombination analysis suggested that CHSH01 belonging to a novel type was a recombinant strain, one parent strain of which was an AstV determined from a bar-headed goose (a kind of migrant bird). Moreover, the primary epidemiological investigation showed that the two strains were prevalent in the same goose farm and co-infection occurred. These findings arise the potential cross-species transmission of CHSH01 between domestic and wild fowl.

Insight into the Epidemiology and Evolutionary History of Novel Goose Astrovirus-Associated Gout in Goslings in Southern China

A novel gout disease, characterized by visceral urate deposition with high-mortality, with outbreaks in goslings in China since 2016 was caused by a novel goose astrovirus (GoAstV) and resulted in serious economic loss. However, the epidemiology and variation of the GoAstV in goslings in southern China and its evolutionary history as well as the classification of the GoAstV are unclear. In the present study, systematic molecular epidemiology, and phylogenetic analyses of the GoAstV were conducted to address these issues. Our results showed that the GoAstV is widespread in goslings in southern China, and the genomes of six GoAstV strains were obtained. Two amino acid mutations (Y36H and E456D) were identified in capsid proteins in this study, which is the dominant antigen for the GoAstV. In addition, the GoAstV could be divided into two distinct clades, GoAstV-1 and GoAstV-2, and GoAstV-2 is responsible for gout outbreaks in goslings and could be classified into Avastrovirus 3 (AAstV-3), while GoAstV-1 belongs to Avastrovirus 1 (AAstV-1). Moreover, the emergence of GoAstV-2 in geese was estimated to have occurred in January 2010, approximately 12 years ago, while GoAstV-1 emerged earlier than GoAstV-2 and was estimated to have emerged in April 1985 based on Bayesian analysis. The mean evolutionary rate for the GoAstV was also calculated to be approximately 1.42 × 10⁻³ nucleotide substitutions per site per year. In conclusion, this study provides insight into the epidemiology of the GoAstV in goslings in southern China and is helpful for understanding the origin and evolutionary history as well as the classification of the GoAstV in geese.

First Identification and Genetic Characterization of a Novel Duck Astrovirus in Ducklings in China

Four divergent groups of duck astroviruses (DAstVs) have been identified that infect domestic ducks. In March 2021, a fatal disease characterized by visceral urate deposition broke out in 5-day-old Beijing ducks on a commercial farm in Guangdong province, China. We identified a novel duck astrovirus from the ducklings suffering from gout disease. The complete genome sequence of this DAstV was obtained by virome sequencing and amplification. Phylogenetic analyses and pairwise comparisons demonstrated that this DAstV represented a novel group of avastrovirus. Thus, we designated this duck astrovirus as DAstV-5 JM strain. DAstV-5 JM shared genome sequence identities of 15–45% with other avastroviruses. Amino acid identities with proteins from other avastroviruses did not exceed 59% for ORF1a, 79% for ORF1b, and 60% for ORF2. The capsid region of JM shared genetic distances of 0.596 to 0.695 with the three official avastrovirus species. suggesting that JM could be classified as a novel genotype species in the Avastrovirus genus. Meanwhile, JM shares genetic distances of 0.402–0.662 with all the other known unassigned avastroviruses, revealing that it represents an additional unassigned avastrovirus. In summary, we determined that the DAstV-5 JM strain is a novel genotype species of avastrovirus.

Extensive genetic heterogeneity and molecular characteristics of emerging astroviruses causing fatal gout in goslings

Since 2017, outbreaks of gosling astroviruses (GoAstV) causing the major symptoms related to gout in geese have posed a threat to China's poultry industry and caused huge economic losses. In this study, tissue samples from goslings with gout and urate deposition as the main symptoms were taken from 14 goose farms in different regions of China and screened for pathogen infection. The infection rate of GoAstV was 100%, whereas the infection rates of goose parvovirus, reovirus, Tembusu virus, and goose hemorrhagic polyomavirus were 2, 4, 0, and 0%, respectively. In total, 14 GoAstV strains were isolated and their complete genomes were sequenced. Based on the phylogenetic trees, the 14 isolated strains were classified as GoAstV (G-I) and were considered distant from strains belonging to GoAstV (G-II). The multiple sequence alignments indicated a tremendous amount of amino acid mutations in some parts of the encoding proteins of these strains; the main mutations were located in open reading frames (ORFs)—ORF1a and ORF2, such as M533V and F568S in ORF1a and A614T in ORF2. On the other hand, Further, 2 of the 14 GoAstV strains were possibly derived through inter-GoAstV-I recombination. Taken together, these findings indicate that GoAstVs are evolving in a more complex manner and have diverse transmission routes.

Genomic and Epidemiological Characteristics Provide Insights into the Phylogeographic Spread of Goose Astrovirus in China

Goose astrovirus (GAstV) is an emerging pathogen with a wide distribution in China that causes visceral gout and leads to significant economic losses in the goose industry. Here, 10 GAstV strains were isolated from different farms in southeast China. We performed an integrated analysis of the full-genome sequences of these new strains alongside comprehensive epidemiological surveillance information from the database. Interestingly, the results showed two distinct genotypes of GAstV, which were evolutionarily distant from each other. Group I GAstVs were closely related to DAstV IV, and group II strains were classified with duck astrovirus (DAstV) II and turkey astrovirus (TAstV) II. Further investigation showed that among the GAstV I strains, ZJC14 and AHDY differed from FLX. Comparative analysis of 58 available genomes clustered the GAstV II strains into two subgroups. We identified two major mutation sites, 456 (E/D) and 540 (L/Q), in the capsid protein, which were related to distinct subgroups according to evolution. GAstV II subgroup 1a strains are the predominant strains in the current prevalent epidemiology. Phylogeographic analysis based on 90 reported cases from 13 provinces revealed the complexity and severity of GAstV epidemics in China, within which Henan, Anhui and Jiangsu provinces have suffered great impacts. According to these phylogeographic investigations, following the initial introduction of GAstV from Hunan Province, the dispersal of GAstV with different subgenotypes on a nationwide scale may be explained by the live gosling trade. Our findings have important implications for the evolution and dispersal of GAstV and will contribute to understanding the potential risk of GAstV. This article is protected by copyright. All rights reserved.

Isolation and phylogenetic analysis of goose astrovirus type 1 from goslings with gout in Jiangxi province, China

Goose astrovirus (GoAstV) is a new Avastrovirus of the genus astrovirus causing gout, hemorrhage, and swellings of kidneys that have affected goslings around the major goose-producing regions in China. The GoAstV is divided into goose astrovirus type 1 (GoAstV-1) and goose astrovirus type 2 (GoAstV-2). Although GoAstV-2 is known to be the causative agent of goose gout, little published information about the relationship between GoAstV-1 and goose gout is unknown. In this study, we investigated the presence of GoAstV-1 in 293 visceral tissue/dead embryos samples with gout on different farms in Jiangxi province, China. A survey result indicated that the mono-infection of GoAstV-1 (32.08%) and co-infection of GoAstV-1 (12.28%) with GoAstV-2 in gout goslings in Jiangxi, China. JXGZ, a GoAstV-1 strain, was effectively isolated from the visceral tissue of gosling gout and serially propagated for more than 25 passages in a goose embryo. The JXGZ strain's whole genome was sequenced and investigated. Phylogenetic analysis of complete genome and capsid protein sequences of JXGZ strain show that it was more closely related to GoAstV-1 strain than GoAstV-2 strain and was grouped within the GoAstV-1 cluster. These findings will aid in the development of efficient diagnostic reagents and possible vaccinations by providing insight into the prevalence and genetic evolution of GoAstV-1 in China.

Isolation and characterization of a goose astrovirus 1 strain causing fatal gout in goslings, China

In recent years, goose gout, a severe infectious disease, has affected the development of the goose industry in China. Two different genotypes of goose astrovirus (GAstV), named as GAstV-1 and GAstV-2, were identified. GAstV-2 viruses are known to be the causative agent of goose gout; however, GAstV-1 has not been isolated, and the relationship between GAstV-1 and goose gout is unknown. One full genome sequence, designated as GAstV/CHN/TZ03/2019 (TZ03), was determined from the clinical tissue samples of a diseased gosling using next-generation sequencing. The complete genome of TZ03 was 7,262 nucleotides in length with typical genomic characteristics of avastroviruses. The TZ03 strain shares the highest identity (96.6%) with the GAstV-1 strain FLX, but only 51.5 to 61.3% identity with other astroviruses in Avastrovirus. Phylogenetic analysis revealed that the TZ03 strain clustered together with the GAstV-1 strains FLX and AHDY and was highly divergent from GAstV-2 viruses. The TZ03 strain was successfully isolated from goose embryos and caused 100% mortality of goose embryos after 5 passages. Electron microscopy showed that the virus particles were spherical with a diameter of ∼22 nm. The clinical symptoms were reproduced by experimental infection of healthy goslings, which were similar to those caused by GAstV-2 strains. Our data show that GAstV-1 is one of the causative agents of the ongoing goose gout disease in China. These findings enrich our understanding of the evolution of GAstVs that cause gout and provide potential options for developing biological products to treat goose gout.

Development of immunochromatographic strip assay for rapid detection of novel goose astrovirus

The novel goose astrovirus (GoAstV) is an emerging pathogenic virus that has resulted in large economic losses to the goose-rearing industry in China since 2016. The novel goose astrovirus cause gout in goslings with a mortality rate of around 50 %. Therefore, an effective diagnostic approach to monitor the spread of GoAstV is necessary. Here, a novel diagnostic immunochromatographic strip (ICS) assay was developed to detect GoAstV. A rapid immunochromatographic assay based on antibody colloidal gold nanoparticles specific to GoAstV was developed for the detection of GoAstV in goose allantoic fluid and supernatant of tissue homogenate. Monoclonal antibodies (Mabs) were prepared using the hybridoma technology, and the polyclonal antibodies (Pabs) were generated by immunizing the rabbits with recombinant ORF2 protein. In addition, the colloidal gold was prepared by reducing gold salt with sodium citrate coupled with Mabs against GoAstV. The optimal concentrations of the coating antibody and the capture antibody were examined as 1.6 mg/mL and 6 μg/mL. The optimal pH of the colloidal gold labeling was pH 8.0. With the visual observation, the lower limit of the ICS was reported to be approximately 1.2 μg/mL. Common diseases of goose were examined to assess the specificity of the ICS, and no cross-reaction was identified. 40 clinical positive samples were simultaneously detected by using the ICS and the PCR with a 92.5% coincidence rate between them. Furthermore, the mentioned samples could be stored at 25 °C and 4 °C for 4 and 6 months, respectively. It was proved that the ICS in this study was highly specific, sensitive, repeatable and more convenient to rapidly detect GoAstV in clinical samples.

Intra- and Cross-Species Transmission of Astroviruses

Astroviruses are non-enveloped, single-stranded RNA viruses that infect mammalian and avian species. In humans, astrovirus infections are one of the most common causes of gastroenteritis in children. Infection has also been linked to serious neurological complications, especially in immunocompromised individuals. More extensive disease has also been characterized in non-human mammalian and avian species. To date, astroviruses have been detected in over 80 different avian and mammalian hosts. As the number of hosts continues to rise, the need to understand how astroviruses transmit within a given species as well as to new host species becomes increasingly important. Here, we review the current understanding of astrovirus transmission, the factors that influence viral spread, and the potential for cross-species transmission. Additionally, we highlight the current gaps in knowledge and areas of future research that will be key to understanding astrovirus transmission and zoonotic potential.

Identification and genomic characterization of emerging goose astrovirus in central China, 2020

Astroviruses are a non-enveloped virus with large host range breadth. AstV-associated gastroenteritis in human and animal, nephritis in chicken, gout in gosling and hepatitis in duckling pose great threats to public health and poultry industry. Since early 2020, continuous emergence of fatal goose astrovirus (GAstV) infections characterized by articular and visceral gout was reported in China. Here, we described two outbreaks of emerging gout disease in two different goose farms of central China. Two virulent GAstV strains, designated as HNKF-1/China/2020 and HNSQ-6/China/2020, were isolated, and the fifth passage of the isolates could cause urate crystals accumulated in the allantoic fluid and even deposited around great vessels and embryo bodies. Meanwhile, the source of these GAstV outbreaks was tracked to goose hatcheries. The prevalence of GAstV in the goose embryos with hatch failure was confirmed, and embryo-origin HNXX-6/China/2020 was further isolated. The complete genome of these three newly isolates was then sequenced and analysed. The results showed that Chinese GAstVs have formed two distinct groups, and the three GAstV isolates, as well as most of the Chinese GAstVs, belong to the G-I group. There are several amino acid mutations in the three newly identified GAstVs, such as A520T, S535R, V555I and A782T in ORF1a and Q229P in ORF2, suggesting the field stains, HNKF-1/China/2020 and HNSQ-6/China/2020, might derive from the weak goose embryo via vertical transmission. Moreover, the phylogenetic analysis of the complete viral genome and individual viral proteins revealed that Chinese GAstV strains have been constantly evolving towards more complicated and various directions. Our study reported the recently emerging GAstV outbreaks in central China, and further analysed the genetic characteristics of three virulent G-I GAstV isolates from commercial goose farms and goose hatchery, indicating the diverse transmission of the virus and providing a basis for developing effective preventive measures and control strategies.

Isolation and characterization of a duck-origin goose astrovirus in China

In 2019, a new type of infectious disease characterized with haemorrhage and swellings of kidneys, occurred on commercial duck farms in Shandong province, China. Our systematic investigation led to the isolation of an astrovirus, designated AstV-SDTA strain and was isolated from a diseased duckling using LMH cells. Similar clinical symptoms were reproduced by experimental infection using the AstV-SDTA strain. The complete genome sequencing characterization of AstV-SDTA was conducted using next-generation sequencing (NGS) technique on Illumina HiSeq platform, and used polymerase chain reaction method to verify the NGS results for the obtained whole sequences. Phylogenetic analysis revealed that AstV-SDTA strain belongs to a novel goose astrovirus (GoAstV) branch of avian astroviruses, and the nucleotide homology based on the complete genome sequences among AstV-SDTA and other GoAstV strains deposited in Genbank was 97.2–98.8%. Taken together, these results suggest that the cross-species transmission of novel GoAstV between domestic waterfowl is possible. Further surveillance of novel GoAstV in poultry are needed in order to gain a better understanding of both the molecular and evolutionary characteristics of novel GoAstV.

Pathogenicity of novel goose-origin astrovirus causing gout in goslings

Background

A novel goose-origin astrovirus (GoAstV) has broken out across China in recent years, causing gout in goslings with a mortality rate of around 50%. However, our understanding of the dynamic distribution, tissue tropism and pathogenesis of GoAstV is incomplete. In order to assess its pathogenicity, one-day-old goslings were inoculated separately with GoAstV via oral and subcutaneous injection routes.

Results

Clinical symptoms, gross and microscopic lesions, blood biochemical parameters and viral loads were detected and recorded for 20 days after infection. Typical gout was observed in experimental goslings. GoAstV can be replicated in tissues and cause pathological damage, especially in the kidney, liver, heart and spleen. Virus-specific genomic RNA was detected in blood, cloacal swabs and all representative tissues, and virus shedding was detected up to 20 days after inoculation, suggesting that GoAstV has a wide tissue tropism and spread systematically after inoculation. The viral copy numbers examined in kidney were the highest, followed by spleen and liver.

Conclusion

This experiment determined the accurate value of viral loads and biochemical indicators of GoAstV-induced goslings. These findings increase our understanding of the pathogenicity of GoAstV in goslings and provide more reference for future research.

OASL Triggered by Novel Goose Astrovirus via ORF2 Restricts Its Replication

Although astroviruses causes enteric diseases and encephalitis in humans and nephritis and hepatitis in poultry, astrovirus infection is thought to be self-limiting. However, little is known about its molecular mechanism. In this study, we found that a novel goose astrovirus (GAstV), GAstV-GD, and its open reading frame 2 (ORF2) could efficiently activate the innate immune response and induce a high level of OASL in vitro and in vivo The truncation assay for ORF2 further revealed that the P2 domain of ORF2 contributed to stimulating OASL, whereas the acidic C terminus of ORF2 attenuated such activation. Moreover, the overexpression and knockdown of OASL could efficiently restrict and promote the viral replication of GAstV-GD, respectively. Our data not only give novel insights for elucidating self-limiting infection by astrovirus but also provide virus and host targets for fighting against astroviruses.IMPORTANCE Astroviruses cause gastroenteritis and encephalitis in human, and nephritis, hepatitis, and gout disease in poultry. However, the host immune response activated by astrovirus is mostly unknown. Here, we found that a novel goose astrovirus, GAstV-GD, and its ORF2 protein could efficiently induce a high level of OASL in vitro and in vivo, which could feed back to restrict the replication of GAstV-GD, revealing novel innate molecules triggered by astroviruses and highlighting that the ORF2 of GAstV-GD and OASL can be potential antiviral targets for astroviruses.

Isolation and evolutionary analyses of gout-associated goose astrovirus causing disease in experimentally infected chickens

Astroviruses are a common cause of gastroenteritis in humans and animals. They are also associated with extraintestinal infections, including hepatitis in ducklings, nephritis in chickens, as well as fatal meningitis and encephalitis in humans and other mammals. Since 2014, outbreaks of disease characterized by visceral gout and swelling of kidneys have been reported in goslings and ducklings in China, with the causative agent revealed to be a novel avian astrovirus designated goose astrovirus (GoAstV). In the present study, this novel gout-associated GoAstV was identified in diseased goslings from 2 farms in Hunan province, China. Three genomes were successfully sequenced and analyzed and were shown to have high identities of 99.7 to 99.8% between each other, with some specific amino acid alterations revealed in open reading frame 2 when compared with other gout-associated GoAstVs. Two strains were further efficiently isolated in the DF-1 chicken fibroblast cell line with high virus titers of 10¹¹ viral genomic copies per mL of culture media. A pilot virus challenge study using GoAstV in chickens demonstrated that this virus can cause clinical visceral gout in chickens, indicating its ability to cross the species barrier. Based on the phylogenetic analyses of capsid sequences, the identified GoAstVs were proposed to be classified into 2 genotypes, GoAstV1 and GoAstV2, and the novel gout-associated GoAstVs were all clustered in GoAstV2. Further Bayesian inference analyses indicated a nucleotide substitution rate of 1.46 × 10⁻³ substitutions/site/year for avian astrovirus based on open reading frame 2 sequences, and the time to the most recent common ancestor of GoAstVs was estimated to be around 2011. This is the first report to confirm GoAstV can infect chickens while also providing an estimation of the evolutionary rates of Avastroviruses.

A quantitative loop-mediated isothermal amplification assay for detecting a novel goose astrovirus

In November 2017, a severe infectious disease that devastated the major goose-producing regions in China was found to be caused by a novel goose astrovirus (N-AstV). The objective of this study was to develop a quantitative loop-mediated isothermal amplification (qLAMP) assay for the rapid diagnosis of N-AstV characterized with gout, hemorrhage, and swellings of the kidneys. A set of 4 specific primers, 2 inner and 2 outer primers, targeting the ORF1a gene of N-AstV were designed for the assay which could be completed within 60 min at 65°C in a water bath or on a real-time PCR instrument for quantitative analysis. The qLAMP assay showed a high sensitivity with a detection limit of 1 × 10¹ copies of the target DNA/μL. There were no cross-reactions with other viruses, and the reproducibility of the assay was confirmed in intrasensitivity and intersensitivity assay tests with variability ranging from 0.61 to 2.21%. The results indicated that the qLAMP assay for N-AstV was a simple, accurate, rapid, sensitive, and specific, especially useful for field detection.

Astrovirus reverse genetics systems, a story of success

Astroviruses are one of the main causes of gastroenteritis of medical and veterinary relevance worldwide. Recently, these viruses were associated with neurological disease in mammals, including humans. Reverse genetics systems are the most powerful tool to improve our understanding of the virus replication, and eventually to develop safe vaccine candidates. In the present review, it is summarized the current knowledge on the different strategies used to develop reverse genetics systems for mamastroviruses and avastroviruses, and some of the biological answers that have provided are discussed.

Rapid and visual detection of novel astroviruses causing fatal gout in goslings using one-step reverse transcription loop-mediated isothermal amplification

To visually and rapidly detect a novel goose astrovirus (N-GoAstV) causing fatal gout in goslings, an isothermal detection method based on one-step reverse transcription loop-mediated isothermal amplification (one-step RT-LAMP) was established. The one-step RT-LAMP assay for N-GoAstV detection, using Bst 3.0 DNA polymerase with strong reverse transcription activity and primer sets targeting the opening reading frame 1b (ORF1b) of N-GoAstV, could be completed in 30 min using a water bath at 61°C; the detection results could be visually observed by adding a pH-sensitive dye containing phenol red and cresol red. The detection limit of the one-step RT-LAMP assay was 57.8 copies, which was similar to that of reverse transcription–quantitative polymerase chain reaction. The assay specifically detected N-GoAstV without any cross-reaction with other reference viruses, and this was further confirmed using enzyme digestion. These results indicated that the newly established RT-LAMP assay could accomplish reverse transcription, amplification, and visual result determination in one step, and the results obtained via this rapid and cost-effective method could be used to support disease control on farms in terms of N-GoAstV infection.

Coinfection of parvovirus and astrovirus in gout-affected goslings

Outbreaks of gosling gout have occurred in China since 2017 and caused a considerable economic impact on the poultry industry. While gosling astrovirus (GoAstV) is believed to be the main causal pathogen of gout, the full-blown disease of gout cannot be well reproduced by infecting the goslings with GoAstV, suggesting the possibility of other infectious agents being involved with the development of gosling gout. To assess other possible infectious agents, we collected tissues from gout-affected goslings in 12 goose farms in China, followed by PCR detection of GoAstV, goose reovirus (GRV), goose parvovirus (GPV), fowl adenovirus (FAdV), goose circovirus (GcoV), Tembusu virus (TMUV) and goose haemorrhagic polyomavirus (GHPV). Our data showed that all gout-affected goslings carried both of GoAstV and GPV determined by PCRs, and this was further confirmed by fluorescence multiplex immunohistochemical staining, and phylogenetic analysis of ORF2 gene of GoAstV and VP3 gene of GPV. In addition to the haemorrhage in the kidney, liver, spleen and lung of the gout-affected goslings, histological examinations showed also extensive infiltration of heterophil myelocytes in the kidney, liver, spleen, bursa of Fabricius, thymus, lungs and pancreas. Our findings strongly suggest that coinfection of GoAstV and GPV increases the severity of gout. While this is the first study to report GPV in gout-affected goslings, further studies including infection model are warranted to investigate the role of GPV and its coinfection with GoAstV in the development of gosling gout.

Clinical and Histologic Characterization of Co-infection with Astrovirus and Goose Parvovirus in Goslings

Goose astrovirus is a novel and distinct astrovirus that causes fatal visceral gout in 4- to 21-day-old goslings. Goose parvovirus is the etiologic agent of Derzsy disease, an acute, contagious, and fatal disease that affects mainly young goslings. This paper describes the clinical signs and gross and histopathologic features of co-infection with astrovirus and goose parvovirus. Clinical signs and history included increased mortality, depression, anorexia, enteritis, joint swelling, and paralysis. Postmortem examination showed a considerable amount of urate covering the internal organs, especially the heart, liver, and kidney. Some goslings had swollen duodenum and ileum. Histologic lesions in the kidney, liver, spleen, lung, proventriculus, and brain included hemorrhage, congestion, edema, cell necrosis, inflammatory cell infiltration, and an eosinophilic protein-like substance in renal tubules. The extensive infiltration of heterophil myelocytes into the kidney, spleen, liver, lung, bursa of Fabricius, and pancreas is a new finding.

Simultaneous differentiation and diagnosis of goose parvovirus and astrovirus in clinical samples with duplex SYBR Green I real-time PCR

Two pairs of primers were designed to bind conserved genomic regions of goose parvovirus (GPV) and goose astrovirus (GAstV) to establish a simple, sensitive, and highly specific duplex quantitative PCR (qPCR) method to simultaneously detect the two viruses. The duplex qPCR can distinguish GPV (melting point: 82.1 °C) and GAstV (melting point: 79.8 °C) by the peaks of their individual melting curves. Mixed testing with other waterfowl viruses produced no nonspecific peaks. The established standard curves showed good linear relationships (R² > 0.997) and the limits of detection (LOD) for GPV and GAstV were 5.74 × 10¹ and 6.58 × 10¹ copies/μL, respectively. Both intra- and inter-assay coefficients of variation were <2%, indicating that the method has good repeatability. Twenty tissue samples from diseased geese were examined with the duplex qPCR assay and conventional PCR. Duplex qPCR showed positive rates of 25% for GPV and 45% for GAstV, and the positive rate for GPV and GAstV coinfection was 15%, slightly higher than the results for conventional PCR. These results indicated that this duplex qPCR method is highly sensitive, specific, and reproducible, and is suitable for epidemiological studies to effectively control the transmission of GPV and GAstV.