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Researchers have identified Avastrovirus as a significant genus of bird viruses, linked to various avian diseases such as enteritis, growth retardation, nephritis and hepatitis. These infections can cause substantial economic losses in agrocultureand have a widespread impact on global food production. Although there have been numerous studies on these viruses, most of them—mainly focuses on poultry. Research on astroviruses in wild bird populations has revealed a wide genetic diversity of these viruses, yet our understanding of their biological and ecological characteristics remains limited. In this study, we for the first time detected avastrovirus in wild migratory birds of the families Anatidae and Columbidae from Sakhalin Island, North Pacific Ocean. Phylogenetic analysis revealed the presence of Avastrovirus 2 in wild doves and Avastrovirus 3 in wild ducks. These findings provide valuable insights into the circulation of astroviruses in wild bird populations of Sakhalin Island, which lies along the East Asian–Australasian Flyway.

We report the complete genome sequence of a new avastrovirus of goose-origin (FLX). The 7299-nt-long genome consisted of three overlapping open reading frames (ORFs) that were in different reading frames. Pairwise comparisons showed that the FLX genome was 59% identical to its closest relatives and that the levels of amino acid identity shared by FLX with other astroviruses did not exceed 54% in ORF1a, 66% in ORF1b, and 50% in ORF2, respectively. Phylogenetic analysis based on the amino acid sequence of the full-length ORF2 demonstrated that FLX was highly divergent from all other avastroviruses. At the amino acid level the complete capsid region of FLX shared genetic distances of 0.574–0.719 with three official avastrovirus species, suggesting that it can be classified as a member of a novel species in the genus  Avastrovirus .

Astroviruses are recognized as a leading cause of gastroenteritis in humans and animals. They are also associated with extra-intestinal diseases, such as hepatitis in ducklings, nephritis in chickens, and encephalitis in cattle. In February 2017, a fatal infection of goslings characterized by visceral urate deposition was reported in the Shandong province, China. Our systematic investigation led to the isolation of an astrovirus, designated AAstV/Goose/CHN/2017/SD01, and similar disease was reproduced by experimental infection of healthy goslings, fulfilling Koch's postulates. The isolated astrovirus replicated well and resulted in 100% mortality of goose embryos. Complete genome sequence analysis revealed that the isolate was genetically distinct from known astroviruses and closely related to members of the avastrovirus genogroup II. Experimental infection showed that the isolate was highly pathogenic in goslings, causing clinical signs, growth repression and in many cases mortality. Histopathological examination indicated that lesions occurred mainly in the kidneys of infected birds. However, virus-specific genomic RNA was detected in all representative tissues, and virus shedding was detected up to 12 days after inoculation, suggesting that the isolate was able to spread systemically and replicate efficiently in vivo. Collectively, our study demonstrates, for the first time, the etiological role of a genetically distinct astrovirus in the fatal infection of goslings.

Metatranscriptomics has recently revealed greater species richness and host range of the Avastrovirus genus, quadrupling the number of avian orders known to host them in less than a decade. Despite this growing awareness of astrovirus presence in wild birds, limited attention has been paid to these viruses in the context of disease in Australian avifauna. Here we used unbiased RNA sequencing of intestinal samples from a galah (Eolophus roseicapilla) and an Australian king parrot (Alisterus scapularis) with a chronic diarrhoeal and wasting disease to detect the entire genomes of two novel astrovirus species. We propose naming these viruses Avastrovirus eolorosei (PQ893528) and Avastrovirus aliscap (PQ893527). The phylogenetic positions of these viruses highlight the importance of current and future metatranscriptomic virus screening in investigations of avian host landscapes beyond Galloanserae. This is also the first documentation of avastrovirus infections in Psittaciformes and the first to report their potential role as disease agents in them.

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.

Wild waterfowl serve as a reservoir of some astroviruses. Fecal samples from wild waterfowl collected at Hong Kong's Marshes were tested using pan-astrovirus reverse transcription-PCR. Positive samples underwent subsequent host identification using DNA barcoding. Based on deduced partial sequences, noteworthy samples from three astrovirus groups (mammalian, avian and unclassified astroviruses) were further analyzed by next-generation sequencing. One sample of Avastrovirus 4 clade, MP22-196, had a nearly complete genome identified. The results of ORF2 phylogenetic analysis and genetic distance analysis indicate that Avastrovirus 4 is classified as a distinct subclade within Avastrovirus . MP22-196 has typical astrovirus genome characteristics. The unique characteristics and potential differences of this genome, compared to other avian astrovirus sequences, involve the identification of a modified sgRNA sequence situated near the ORF2 start codon, which precedes the ORF1b stop codon. Additionally, the 3' UTR of MP22-196 is shorter than other avian astroviruses. This study expands our understanding of the Avastrovirus 4 clade.

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.

BACKGROUND: Infectious diarrhea leads to significant mortality in children, with 40 % of these deaths occurring in Africa. Classic human astroviruses are a well-established etiology of diarrhea. In recent years, seven novel astroviruses have been discovered (MLB1, MLB2, MLB3, VA1/HMO-C, VA2/HMO-B, VA3/HMO-A, VA4); however, there have been few studies on their prevalence or potential association with diarrhea. METHODS: To investigate the prevalence and diversity of these classic and recently described astroviruses in a pediatric population, a case–control study was performed. Nine hundred and forty nine stools were previously collected from cases of moderate-to-severe diarrhea and matched controls of patients less than 5 years of age in Kenya and The Gambia. RT-PCR screening was performed using pan-astrovirus primers. RESULTS: Astroviruses were present in 9.9 % of all stool samples. MLB3 was the most common astrovirus with a prevalence of 2.6 %. Two subtypes of MLB3 were detected that varied based on location in Africa. In this case–control study, Astrovirus MLB1 was associated with diarrhea in Kenya, whereas Astrovirus MLB3 was associated with the control state in The Gambia. Classic human astrovirus was not associated with diarrhea in this study. Unexpectedly, astroviruses with high similarity to Canine Astrovirus and Avian Nephritis Virus 1 and 2 were also found in one case of diarrhea and two control stools respectively. CONCLUSIONS: Astroviruses including novel MLB- and VA-clade members are commonly found in pediatric stools in Kenya and The Gambia. The most recently discovered astrovirus, MLB3, was the most prevalent and was found more commonly in control stools in The Gambia, while astrovirus MLB1 was associated with diarrhea in Kenya. Furthermore, a distinct subtype of MLB3 was noted, as well as 3 unanticipated avian or canine astroviruses in the human stool samples. As a result of a broadly reactive PCR screen for astroviruses, new insight was gained regarding the epidemiology of astroviruses in Africa, where a large proportion of diarrheal morbidity and mortality occur.

Enteric diseases are a significant challenge for the poultry industry, causing substantial economic losses and affecting productivity. Turkey astrovirus (TAstV) types 1 and 2 and avian nephritis virus (ANV) are recognized as viral pathogens contributing with enteric diseases in turkeys, particularly in young poults. These viruses, part of the Astroviridae family, are small, round, non-enveloped, positive-sense RNA viruses with high prevalence in turkey flocks. Despite their importance, they had not been identified in Ecuador until now. This study presents the first detection and molecular characterization of TAstV-1, TAstV-2, and ANV in Ecuadorian turkeys using RT-qPCR assays based on SYBR Green, developed and optimized for high sensitivity and specificity. Two hundred intestinal samples were collected from turkeys with enteric disorders, along with fifty cloacal swabs from apparently healthy turkeys in Pichincha Province. The RT-qPCR assays developed demonstrated a limit of detection of one copy of viral genetic material and high repeatability, with inter and intra-assay coefficients of variation below 1%. Based on these tests, TAstV was detected in 93% of turkey samples with gastroenteritis, and none of the samples of the healthy group tested positive, with ANV being the most prevalent, followed by TAstV-2 and TAstV-1. Phylogenetic analysis of the partial ORF1b gene confirmed the genetic relationships between Ecuadorian strains and those from other countries, highlighting possible routes of introduction and evolution of the virus. Co-infections with TAstV-2 and ANV were common, while single infections were predominantly caused by ANV. These findings underscore the critical need for surveillance and biosecurity measures to control the spread of these viruses within Ecuador’s poultry industry. This study provides valuable insights on astrovirus presence in Ecuadorian turkey flocks and establishes robust diagnostic tools for monitoring and managing turkey astrovirus infections.

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.