Characterization and genomic analysis of emerging astroviruses causing fatal gout in goslings

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.

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.

Molecular epidemiology and virulence of goose astroviruses genotype-2 with different internal gene sequences

Goose astrovirus (GAstV) is a small, non-enveloped, single-stranded, positive-sense RNA virus. GAstV has rapidly spread across various regions in China since 2016. In Sichuan, out of 113 samples were collected from goose diseases between 2019 and 2022, 97 were positive for GAstV through PCR testing. Remarkably, over the past three years, GAstV outbreak in Sichuan has accounted for an astonishing 85.8% of all goose-origin viruses. Among these cases, 63.9% had single GAstV infections, 29.9% had dual infections, and 6.2% had quadruple infections. To comprehend the variations in virulence among distinct strains of GAstV. 12 representative strains of single GAstV infections were isolated. These strains exhibited distinct characteristics, such as prominent white urate depositions in organs and joints, as well as extensive tissues phagocytosis in major target organs' tissues. The conserved ORF1b genes and the variable ORF2 genes of these representative GAstV strains were sequenced, enabling the establishment of phylogenetic trees for GAstV. All GAstV strains were identified as belonging to genotype-2 with varying internal gene sequences. Experiments were conducted on GAstV genotype-2, both in vivo and in vitro, revealed significant variations in pathogenicity and virulence across susceptible cells, embryos, and goslings. This comprehensive study enhances researchers' understanding of the transmission characteristics and virulence of GAstV genotype-2, aiding in a better comprehension of their molecular epidemiology and pathogenic mechanism.

Pathogenicity of goose astrovirus genotype 2 in chickens

Goose astrovirus genotype 2 (GAstV-2) is the causative agent causing severe visceral gout and joint gout in goslings, with mortality rates of affected flocks up to 50%. To date, continuous GAstV-2 outbreaks still pose a great threat to goose industry in China. Although most researches on GAstV-2 have focused on its pathogenicity to geese and ducks, limited studies have been performed on chickens. Herein, we inoculated 1-day-old specific pathogen-free (SPF) White Leghorn line chickens with 0.6 mL of GAstV-2 culture supernatant (TCID50 10-5.14/0.1 mL) via orally, subcutaneously and intramuscularly, and then assessed the pathogenicity. The results revealed that the infected chickens presented depression, anorexia, diarrhea, and weight loss. The infected chickens also suffered from extensive organ damage and had histopathological changes in the heart, liver, spleen, kidney, and thymuses. The infected chickens also had high viral load in tissues and shed virus after the challenge. Overall, our research demonstrates that GAstV-2 can infect chickens and adversely affect the productivity of animals. And the viruses shed by infected chickens can pose a potential risk to the same or other domestic landfowls.

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.

Identification of new astroviruses in synanthropic squamates

Astroviruses have been identified in a wide variety of animal species and are associated with gastro-intestinal disease in humans. Pathologies due to extra-intestinal localization are known in different hosts. We report the detection of astroviruses in synanthropic squamate reptile species (Podercis siculus and Tarentola mauritanica). Fecal samples were collected from 100 squamates from urban and peri-urban areas of three regions in South Italy and tested for the presence of astroviruses using a broadly reactive (pan-astrovirus) RT-PCR protocol targeting the RNA-dependent RNA polymerase. Astrovirus RNA was detected in 11% of the samples and for six strains a 3 kb-long fragment at the 3' end of the genome was sequenced, obtaining information on the complete capsid-encoding ORF2 sequence. Viral RNA was also detected in the brain of one of the positive animals. The sequences generated from the astrovirus strains shared low nucleotide identities in the ORF2 (< 43.7%) with other known reptilian astrovirus sequences, hinting to the massive genetic diversity of members of this viral family. Based on the partial RdRp gene of the sequenced strains, however, we observed species-specific patterns, regardless of the geographic origin of the animals, and we also identified a possible inter-species transmission event between geckoes and lizards.

Genome Sequences and Characterization of Chicken Astrovirus and Avian Nephritis Virus from Tanzanian Live Bird Markets

The enteric chicken astrovirus (CAstV) and avian nephritis virus (ANV) are the type species of the genus Avastrovirus (AAstV; Astroviridae family), capable of causing considerable production losses in poultry. Using next-generation sequencing of a cloacal swab from a backyard chicken in Tanzania, we assembled genome sequences of ANV and CAstV (6918 nt and 7318 nt in length, respectively, excluding poly(A) tails, which have a typical AAstV genome architecture (5'-UTR-ORF1a-ORF1b-ORF2-'3-UTR). They are most similar to strains ck/ANV/BR/RS/6R/15 (82.72%) and ck/CAstV/PL/G059/14 (82.23%), respectively. Phylogenetic and sequence analyses of the genomes and the three open reading frames (ORFs) grouped the Tanzanian ANV and CAstV strains with Eurasian ANV-5 and CAstV-Aii viruses, respectively. Compared to other AAstVs, the Tanzanian strains have numerous amino acid variations (substitutions, insertions and deletions) in the spike region of the capsid protein. Furthermore, CAstV-A has a 4018 nt recombinant fragment in the ORF1a/1b genomic region, predicted to be from Eurasian CAstV-Bi and Bvi parental strains. These data should inform future epidemiological studies and options for AAstV diagnostics and vaccines.

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.

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, identification, and pathogenicity analysis of newly emerging gosling astrovirus in South China

Goose astroviruses (GoAstV) cause fatal gout and decrease product performance in the waterfowl industry across the world. Since no effective vaccines are available, studies on the epidemiology of the virus are necessary for vaccine development. In this study, we collected 94 gout samples from goose farms in the Guangdong Province of South China. Among them, 87 samples (92.6%) tested positive for GoAstV, out of which five GoAstV strains were isolated after four generations of blind transmission through healthy 13-day-old goose embryos. The whole genome of the isolates was sequenced and further analyzed by comparing the sequences with published sequences from China and other parts of the world. The results of the alignment analysis showed that nucleotide sequence similarities among the five GoAstV isolates were around 97.4-98.8%, 98.6-100%, 98.1-99.8%, and 96.7-100% for the whole genome, ORF1a, ORF1b, and ORF2, respectively. These results showed that the GoAstV isolates were highly similar to each other, although they were prevalent in five different regions of the Guangdong Province. The results of the phylogenetic analysis showed that the whole genome, along with the ORF1a, ORF1b, and ORF2 genes of the isolates, were clustered on a single branch, along with the recently published GoAstV-2, and were very distinct from the DNA sequences of the GoAstV-1 virus. In this study, we also reproduced the clinical symptoms of natural infection using the GoAstV-GD2101 isolates, confirming that the gout-causing pathogen in goslings was the goose astrovirus. These findings provided new insights into the pathogenicity and genetic evolution of GoAstV and laid the foundation for effectively controlling the disease.

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.

A Review of the Emerging Poultry Visceral Gout Disease Linked to Avian Astrovirus Infection

Avian astroviruses, including chicken astrovirus (CAstV), avian nephritisvirus (ANV), and goose astrovirus (GoAstV), are ubiquitous enteric RNA viruses associated with enteric disorders in avian species. Recent research has found that infection of these astroviruses usually cause visceral gout in chicken, duckling and gosling. However, the underlying mechanism remains unknown. In the current article, we review recent discoveries of genetic diversity and variation of these astroviruses, as well as pathogenesis after astrovirus infection. In addition, we discuss the relation between avian astrovirus infection and visceral gout in poultry. Our aim is to review recent discoveries about the prevention and control of the consequential visceral gout diseases in poultry, along with the attempt to reveal the possible producing process of visceral gout diseases in poultry.

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.

Recombinant Muscovy Duck Parvovirus Led to Ileac Damage in Muscovy Ducklings

Waterfowl parvovirus (WPFs) has multiple effects on the intestinal tract, but the effects of recombinant Muscovy duck parvovirus (rMDPV) have not been elucidated. In this study, 48 one-day-old Muscovy ducklings were divided into an infected group and a control group. Plasma and ileal samples were collected from both groups at 2, 4, 6, and 8 days post-infection (dpi), both six ducklings at a time. Next, we analyzed the genomic sequence of the rMDPV strain. Results showed that the ileal villus structure was destroyed seriously at 4, 6, 8 dpi, and the expression of ZO-1, Occludin, and Claudin-1 decreased at 4, 6 dpi; 4, 6, 8 dpi; and 2, 6 dpi, respectively. Intestinal cytokines IFN-α, IL-1β and IL-6 increased at 6 dpi; 8 dpi; and 6, 8 dpi, respectively, whereas IL-2 decreased at 6, 8 dpi. The diversity of ileal flora increased significantly at 4 dpi and decreased at 8 dpi. The bacteria Ochrobactrum and Enterococcus increased and decreased at 4, 8 dpi; 2, 4 dpi, respectively. Plasma MDA increased at 2 dpi, SOD, CAT, and T-AOC decreased at 2, 4, 8 dpi; 4, 8 dpi; and 4, 6, 8 dpi, respectively. These results suggest that rMDPV infection led to early intestinal barrier dysfunction, inflammation, ileac microbiota disruption, and oxidative stress.

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.

Core antigenic advantage domain-based ELISA to detect antibody against novel goose astrovirus in breeding geese

Goose astrovirus (GAstV), the major causative agent of visceral and joint gout in goslings, is a novel pathogen greatly threatening waterfowl industry. Importantly, the horizontal and vertical transmissibility of GAstV posed a great challenge for disease prevention and control. Given the absence of commercial vaccine, restricting vertical transmission and protecting susceptible goslings must be a priority. Although many detection methods have been established, there is no serological method to detect GAstV-specific antibody, greatly limiting inspection and elimination of infected breeding bird. In this study, the B-cell epitopes of GAstV capsid protein were predicted, and its core antigenic advantage domain (shCAP) was expressed and purified. After authenticating the antigenicity, the recombinant shCAP protein was taken as the coating antigen, and an easily accessible indirect enzyme-linked immunosorbent assay (ELISA) was established to detect GAstV-specific antibody. The working conditions, including antigen concentration, serum dilution and incubation time, blocking buffer concentration, and color developing time, were gradually optimized by checkerboard titration. The cut-off OD₄₅₀ value of the indirect ELISA for positive sample was 0.379, and the analytical sensitivity was 1:800. There was no cross-reaction with sera against goose parvovirus (GPV), Tembusu virus (TUMV), H5 and H7 subtype avian influenza virus (AIV H5 + H7), and Newcastle disease virus (NDV). The assay was further applied to examine 73 breeding goose serum samples and shared excellent agreement of 93.5% (68/73) with western blot, which also suggested that GAstV is circulating in the goose population in China. In conclusion, the developed indirect ELISA is simple, specific, and sensitive, which will be greatly useful to screen GAstV infection and block vertical transmission. KEY POINTS: • B-cell epitopes of GAstV capsid protein were predicted and expressed as immunogen • A core antigenic advantage domain-based ELISA was established to detect GAstV-specific antibody • The established ELISA will contribute to inspection and elimination of infected breeding geese and provide a useful tool for large scale serological testing of GAstV in geese.

First report of a novel goose astrovirus outbreak in Muscovy ducklings in China

A highly acute disease characterized as visceral gout broke out in Muscovy ducklings in Henan province (China) in June 2020, with a mortality rate of up to 61%. In this study, common pathogenic agents were screened using reverse-transcription polymerase chain reaction or polymerase chain reaction. The results found the novel goose astrovirus (GoAstV) to be the pathogenic agent. We isolated the GoAstV, which has been designated as HNNY0620, using the Leghorn male chicken hepatocellular carcinoma (LMH) cell line and sequenced the complete genome. The phylogenetic tree showed that the amino acid (aa) sequences of ORF1a and ORF2 and the completed nucleotide sequences of the HNNY0620 strain were clustered in the GoAstV-I clade. ORF1a aa and whole-genome sequences were genetically close to TAstV-2 and DHV-3, whereas the ORF2 aa sequences were clustered with TAstV-2 and DHV2. Both the duck-origin GoAstVs and HNNY0620 harbored some special mutations, but ORF1a in 700 (I/T), ORF1b in 288 (F/L), and ORF2 in 306 (A/T) were only found in HNNY0620. These results suggest that the host range of GoAstV is diffusing, which can potentially affect other waterfowl.

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.

Neurotropic Astroviruses in Animals

Astrovirus infections are among the main causes of diarrhea in children, but their significance for animal health has remained underestimated and largely unknown. This is changing due to the increasing amount of newly identified neurotropic astroviruses in cases of nonsuppurative encephalitis and neurological disease in humans, pigs, ruminant species and minks. Neurological cases in ruminants and humans usually occur sporadically and as isolated cases. This contrasts with the situation in pigs and minks, in which diseases associated with neurotropic astroviruses are endemic and occur on the herd level. Affected animals show neurological signs such as mild ataxia to tetraplegia, loss of orientation or trembling, and the outcome is often fatal. Non-suppurative inflammation with perivascular cuffing, gliosis and neuronal necrosis are typical histological lesions of astrovirus encephalitis. Since astroviruses primarily target the gastrointestinal tract, it is assumed that they infect the brain through the circulatory system or retrograde following the nerves. The phylogenetic analysis of neurotropic astroviruses has revealed that they are genetically closely related, suggesting the presence of viral determinants for tissue tropism and neuroinvasion. In this review, we summarize the current knowledge on neurotropic astrovirus infections in animals and propose future research activities.

Goose Nephritic Astrovirus Infection of Goslings Induces Lymphocyte Apoptosis, Reticular Fiber Destruction, and CD8 T-Cell Depletion in Spleen Tissue

The emergence of a novel goose nephritic astrovirus (GNAstV) has caused economic losses to the Chinese goose industry. High viral load is found in the spleen of goslings infected with GNAstV, but pathological injuries to the spleen due to GNAstV are largely unknown. In this study, 50 two-day-old goslings were infected orally with GNAstV, and 50 goslings were treated with PBS as control. Spleens were collected at different times following infection to assess damage. GNAstV infection caused visceral gout and urate deposition in joints, and resulted in 16% mortality. GNAstV was found in the lymphocytes and macrophages within the spleen. Lymphocyte loss, especially around the white pulp, and destruction and decline in the number of reticular fibers was observed in GNAstV-infected goslings. Moreover, in GNAstV-infected goslings, ultrahistopathological examination found that splenic lymphocytes exhibited condensed chromatin and apoptotic bodies, and reticular cells displayed damage to plasma membrane integrity and swollen mitochondria. Furthermore, TUNEL staining confirmed apoptosis of lymphocytes, and the mRNA levels of Fas and FasL were significantly increased in the GNAstV-infected goslings. In addition, GNAstV infection reduced the number and protein expression of CD8. In conclusion, GNAstV infection causes lymphocyte depletion, reticular cell necrosis, reticular fiber destruction, lymphocyte apoptosis, and reduction in CD8 levels, which contribute to spleen injury.

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.

Simple and Visible Detection of Novel Astroviruses Causing Fatal Gout in Goslings Using One-Step Reverse Transcription Polymerase Spiral Reaction Method

In this study, a one-step isothermal method combining polymerase spiral reaction (PSR) with reverse transcription (RT-PSR) was established for rapid and specific detection of novel astroviruses causing fatal gout in goslings (N-GoAstV). The one-step RT-PSR was accomplished at the optimal temperature of 62°C and time of 40 min and used primers simply designed as conventional PCR primers, and the results of detection were visible to the naked eye. The detection limit of PSR was above 34.7 copies/μL at a 95% probability level according to probit regression analysis. The assay specifically detected N-GoAstV, and no other reference viruses were detected. These results suggest that the newly established RT-PSR assay could, in one step, accomplish reverse-transcription, amplification, and result determination providing a visible, convenient, rapid, and cost-effective test that can be carried out onsite, in order to ensure timely quarantine of N-GoAstV-infected birds, leading to effective disease control.

Rapid detection of H146-like goose calicivirus using real-time RT-PCR with a Taqman minor groove binder probe

H146-like goose-origin calicivirus (H146-like GCV) is a novel Caliciviridae family member in the Sanovirus genus that was associated with gosling growth retardation syndrome growth retardation syndrome complicated by visceral urate deposition. However, there is no accurate and high throughput real-time quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) available for the rapid and highly sensitive identification of H146-like GCV. In this study, a pair of specific primers and a TaqMan minor groove binder (MGB) probe were designed based on a conserved region in the nonstructural (NS) gene sequence. The TaqMan-MGB probe-based one-step qRT-PCR assay was capable of detecting quite low number of targeting nucleic acid as low as 5.07 copies/μL and had excellent intra-assay and inter-assay repeatability with the coefficient of variation (CV) value from 0.558% to 1.293%. The assay was highly specific for H146-like GCV, without cross-reactions with other non-targeted goose-origin viruses, and 62 suspicious tissue samples infected with H146-like GCV from different regions of Fujian Province were used in this study to verify the feasibility and effectiveness of this assay in clinical diagnosis. The results indicated that our assay for the diagnosis and quantification of H146-like GCV was highly sensitive and specific, and should provide a reliable real-time tool for epidemiological and pathogenetic study of H146-like GCV infection, enabling researchers to better understand the epidemiology and clinical presentation of this disease.

Novel goose-origin astrovirus infection in geese: the effect of age at infection

Since 2017, a serious infectious disease characterized by visceral gout has emerged in China's main goose-producing regions. The disease has caused huge economic losses to China's goose industry. In our previous study, we determined that the pathogen causing gout in goslings is a novel goose-origin astrovirus, designated as AStV/SDPY/Goose/1116/17 (AStV-SDPY) strain. To investigate the effect of host age on the outcome of novel goose-origin astrovirus infection, 200 1-day-old healthy goslings were selected to be experimentally infected at 1, 5, 15, 25, and 35 D of age. It was shown in experimental infection that the AStV-SDPY strain was highly pathogenic in goslings aged 1 to 15 D, causing growth repression, severe visceral urate deposition, and even death, whereas goslings infected at 25 and 35 D of age showed mild symptoms. Histopathologic examination indicated that lesions occurred mainly in the kidney and liver of infected goslings, which is correlated to the severity of clinical signs and gross lesions. Viral RNA was detected in all representative tissues, and virus shedding was detected continuously within 15 D after inoculation. Higher viral copy number, especially in vital organs such as the liver and kidney, was developed in the goslings infected at 1 to 15 D of age than older geese. In addition, clinical chemistry and inflammatory cytokines showed that younger geese are more sensitive to AStV infection. Overall, our study demonstrates that the pathogenicity of AStV-SDPY in goslings is partly associated with the age of infection, laying a foundation for further study of the pathogenic mechanism of this virus.

Novel genotype definition and genome characteristics of duck circovirus in central and Eastern China

To explore genetic variations in duck circovirus (DuCV) and the molecular epidemiology of its infection, tissue samples were collected from 219 dead ducks from 20 farms in the central and eastern regions of China. All farms tested positive for DuCV, with duck-origin goose parvovirus, reovirus and Tembusu virus having co-infection rates of 100%, 0% and 0%, respectively. A total of 20 strains from the DuCV-positive flock were sequenced. The total sequence length was 1987-1996 nt, and the sequences shared 82% (JX499186, DuCV2 from Sichuan province, China) to 99.7% (KY328304, DuCV1 from Shandong Province, China) sequence identity with DuCV sequences available in GenBank. Hyper-variable regions were mainly located in open reading frame (ORF)2, ORF3 and intergenic regions. The tertiary structure of ORF2 from four provinces (Henan, Anhui, Zhejiang and Fujian) in China showed a canonical viral jelly roll and the antigenic epitope of ORF2 located in the bulge of the protein surface. Overall, 15 of the 20 DuCV strains are possibly derived through inter-genotypic and intragenotypic recombination. Based on sequence and phylogenetic analyses, six strains from Fujian Province clustered into a novel genotype-DuCV-1d. These findings may enrich our understanding of DuCV evolution and circulation and lay the foundation for vaccine strain selection.

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.