Avian nephritis virus (ANV) as a new member of the family Astroviridae and construction of infectious ANV cDNA

Detection and genetic characterization of chicken astrovirus and avian nephritis virus from hatchery to farm

RESEARCH HIGHLIGHTS

Identified the role of the hatchery in astrovirus transmission.Sequenced the avian nephritis virus complete genome.Investigated tissue distribution of astrovirus from egg to chicks.Demonstrated co-infection of ANV/CAstV.

Development of a fast and sensitive RT-qPCR assay based on SYBR® green for diagnostic and quantification of Avian Nephritis Virus (ANV) in chickens affected with enteric disease

BACKGROUND

Enteric viruses are among the most prominent etiological agents of Runting-Stunting Syndrome (RSS). The Avian Nephritis Virus (ANV) is an astrovirus associated with enteric diseases in poultry, whose early diagnosis is essential for maintaining a good poultry breeding environment. ANV is an RNA virus that rapidly mutates, except for some conserved regions such as ORF1b. Therefore, the approach of a diagnostic method based on fast-RT-qPCR using SYBR® Green that focuses on the amplification of a fragment of ORF1b is presented as a feasible alternative for the diagnosis of this viral agent. In this study, the proposed assay showed a standard curve with an efficiency of 103.8% and a LoD and LoQ of 1 gene viral copies. The assay was specific to amplify the ORF 1b gene, and no amplification was shown from other viral genomes or in the negative controls. 200 enteric (feces) samples from chickens (broilers) and laying hens with signs of RSS from Ecuadorian poultry flocks were examined to validate the proposed method.

RESULTS

Using our method, 164 positive results were obtained out of the total number of samples run, while the presence of viral RNA was detected in samples collected from one day to 44 weeks old in both avian lines.

CONCLUSIONS

Our study presents a novel, rapid, robust, and sensitive molecular assay capable of detecting and quantifying even low copy numbers of the ANV in commercial birds, therefore introducing a handy tool in the early diagnosis of ANV in enteric disease outbreaks in poultry.

Identification of Astrovirus in the virome of the upper and lower respiratory tracts of calves with acute signs of bronchopneumonia

IMPORTANCE

Astroviruses (AstV) are known suspects of enteric disease in humans and livestock. Recently, AstV have been linked to encephalitis in immunocompromised patients and other animals, such as cattle, minks, and swine. In our study, we also identified AstV in the respiratory samples of calves with signs of bronchopneumonia, suggesting that their tropism could be even broader. We obtained one bovine AstV (BAstV) complete genome sequence by next-generation sequencing and showed that respiratory and enteric AstV from different species formed a divergent genetic cluster with AstV isolated from encephalitis cases, indicating that tropism might be strain-specific. These data provide further insight into understanding the biology of these understudied pathogens and suggest BAstV as a potential new candidate for bovine respiratory disease.

Molecular characteristics and pathogenicity of a novel chicken astrovirus variant

It is well-established that the genetic diversity, regional prevalence, and broad host range of astroviruses significantly impact the poultry industry. In July 2022, a small-scale commercial broiler farm in China reported cases of growth retardation and a 3% mortality rate. From chickens displaying proventriculitis and pancreatitis, three chicken astroviruses (CAstV) isolates were obtained and named SDAU2022-1-3. Complete genomic sequencing and analysis revealed the unique characteristics of these isolates from known CAstV strains in ORF1a, ORF1b, and ORF2 genes, characterized by an unusually high variability. Analysis of amino acid mutations in ORF1a, ORF1b, and ORF2 indicated that the accumulation of these mutations played a pivotal role in the emergence of the variant strain. Inoculation experiments demonstrated that affected chickens exhibited liver and kidney enlargement, localized proventricular hemorrhage, and a dark reddish-brown appearance in about two-thirds of the pancreas. Histopathological examination unveiled hepatic lymphocytic infiltration, renal tubular epithelial cell swelling, along with lymphocytic proventriculitis and pancreatitis. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis indicated viremia and viral shedding at 3 days post-infection (dpi). The proventriculus displayed the highest viral loads, followed by the liver, kidney, duodenum, and pancreas. Liver parameters (AST and ALT) and kidney parameters (UA and UN) demonstrated mild damage consistent with earlier findings. While the possibility of new mutations in the ORF2 gene of CAstV causing proventriculitis and pancreatitis warrants further investigation, these findings deepen our comprehension of CAstV's pathogenicity in chickens. Additionally, they serve as valuable references for subsequent research endeavors.

Genetic characterization of canine astrovirus in non-diarrhea dogs and diarrhea dogs in Vietnam and Thailand reveals the presence of a unique lineage

The role of canine astrovirus (CaAstV) in canine gastrointestinal disease (GID) is unknown. In this study, a total of 327 fecal swab (FS) samples were collected, including 113 FSs in Vietnam (46 samples from healthy dogs and 67 samples from GID dogs) and 214 FSs in Thailand (107 samples from healthy dogs and 107 samples from GID dogs). Overall, the prevalence of CaAstV in Vietnam and Thailand was 25.7% (29/113) and 8.9% (19/214), respectively. CaAstV was detected in both non-diarrhea dogs (21.7 and 7.5%) and diarrhea dogs (28.4% and 10.3%), respectively, in Vietnam and Thailand. In both countries, CaAstV was frequently detected in puppies under 6 months of age (23.3%) (p = 0.02). CaAstV-positive samples in Vietnam and Thailand were identified as co-infected with canine parvovirus, canine enteric coronavirus, canine distemper virus, and canine kobuvirus. The complete coding sequence of seven Vietnamese CaAstV and two Thai CaAstV strains were successfully characterized. Phylogenetic analyses showed that Vietnamese and Thai CaAstV strains were genetically close to each other and related to the Chinese strains. Furthermore, analysis of complete coding sequences indicated that the OR220030_G21/Thailand/2021 strain formed a unique lineage, whereas no recombination event was found in this study, suggesting that this strain might be an original lineage. In summary, this is the first study to report the presence of CaAstV in dogs with and without diarrhea in Vietnam and Thailand, and it was most often found in puppies with diarrhea. Our results highlight the importance of the CaAstV in dog populations and the need for continued surveillance of these emerging pathogens.

Chicken Astro virus (CAstV): Isolation and characterization of new strains in broiler flocks with poor performance

Chicken astroviruses (CAstV) were associated with retarded growth, enteritis, kidney diseases, and white chick syndrome. In the current study, we aimed to evaluate the effect of CAstV infection on growth, performance, and gross and histopathological picture of commercial chicken flocks suffering increased culling rate and decreased performance. Samples were collected for virus isolation, identification, and sequencing on day one, 15 days, and 30 days of age. Body weight, feed conversion rate, and mortality rates were determined. A gross examination was performed, and tissue samples from the liver, intestine, kidneys, heart, and lungs were kept in formalin for histopathological evaluation. Embryos inoculated with CAstV revealed dwarfism, and edema. The cytopathic effect on CAstV inoculated cells included aggregation,, and sloughing. The isolated Egyptian isolates shared the highest nucleotide homology (93%) with the Korean isolate Kr/ADL102655-1/2010 and showed the most distant relation to the Indian isolate Indovax/APF/1319 with 82-83% homology. Body weight exhibited significant reduction with a decrease in feed conversion rate in CAstV infected flocks. Gross examination of CAstV-infected chickens revealed white feathered chicks on day one, and poor body condition in older chickens as well as swollen kidneys. Histopathological examination of CAstV-infected birds showed mild proventriculitis, shortening of intestinal villi, enteritis, focal hepatocellular necrosis, pericarditis, myocarditis, and proliferative response in lung tissue. Kidneys showed interstitial nephritis, urate deposition, and glomerular hypercellularity. CAstV is a chicken pathogen that could be related to decreased performance, and screening of flocks for CAstV might be an essential step for breeders.

Identification and characterization of a novel avian nephritis virus variant in chickens with enteritis in Hunan province, China

Avian nephritis virus (ANV) infection is associated with diarrhea, uricosis, stunting, tubulonephrosis, interstitial nephritis, and mortality of chicken flocks, leading to economic losses in the poultry industry. In this study, an ANV strain designated as HNU-ANV-ML-2020 was identified in tissue samples collected from chickens with severe enteritis on a poultry farm in Hunan province, China, and analyzed. The genome of HNU-ANV-ML-2020 is 6943 nucleotides in length. It showed the highest sequence identity (88.1%) to ANV strain CHN/GXJL815/2017 (MN732559) from Guangxi province, China, while it showed less than 86% identity to other astrovirus (AstV) genome sequences available in the GenBank database. The capsid protein of this virus showed the highest sequence identity to ANV strains HQ330482 and HQ330498 from the UK (81.2% and 81.06%, respectively), while it showed only 73.9% identity to MN732559 and less than 80% identity to the capsid proteins of other AstVs available in GenBank. Further phylogenetic analysis demonstrated that HNU-ANV-ML-2020 belongs to group 4, together with ANV strains identified in Australia, Brazil, the UK, and the Netherlands. Furthermore, ANV strains identified in chickens in China were found to be separated into four distinct groups/genotypes, indicating substantial genetic divergence and a complex circulation pattern in China. The virus characterized in the present study is a novel ANV variant identified for the first time in Hunan province, China.

The Genomic and Genetic Evolution Analysis of Rabbit Astrovirus

Rabbit astrovirus (RAstV) is a pathogen that causes diarrhea in rabbits, with high infection rate at various stages, which can often cause secondary or mixed infections with other pathogens, bringing great economic losses to the rabbit industry. In this study, 10 samples were collected from cases of rabbits with diarrhea on a rabbit meat farm in the Shandong area of China. The positive sample for astrovirus detected by RT-PCR was inoculated into an RK 13 cell line. A rabbit astrovirus strain named Z317 was successfully isolated, which produced an obvious cytopathic effect 48 h post-inoculation in the RK 13 cell line. The genome structure of this isolate was studied by high-throughput sequencing, showing that the Z317 strain had the highest similarity with the American strain TN/2208/2010, with 92.43% nucleotide homology, belonging to group MRAstV-23. The basic properties of the Z317 capsid (Cap) protein were analyzed, and 10 liner B cell epitopes were screened with the online biosoft Bepipred 2.0 and SVMTriP, including 445–464, 186–205, 655–674, 88–107, 792–811, 45–64, and 257–276 amino acids. This is the first contribution concerning RAstV genomes in China; more studies are needed to understand the diversity and impact of RAstV on rabbit health.

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.

Pathogenesis of Chicken Astrovirus Related Illnesses

Of the several known viruses, chicken astrovirus (CAstV) has been associated with diarrhea, runting-stunting syndrome, severe kidney disease, and gout, and white chick syndrome (WCS) in young broiler chicks. Discovered in 2004, CAstV consists of two genogroups with an expanding subgroup because of the diversity exhibited in its viral capsid sequence. Despite these findings, there exists a dearth of knowledge on its pathogenesis. This review highlights the pathogenesis and development of in vivo and in vitro models.

Bovine Astrovirus—A Comprehensive Review

Bovine astrovirus (BoAstV) is a small non-enveloped virus with a single-stranded positive-sense RNA. In 1978, BoAstV was first found in calf diarrhea fecal samples in the United Kingdom and since then it has been reported in many other countries. It has wide tissue tropism and can infect multiple organs, including the intestine, nerves and respiratory tract. Since BoAstV is prevalent in healthy as well as clinically infected bovines, and is mostly associated with co-infection with other viruses, the pathogenic nature of BoAstV is still unclear. At present, there are no stable passage cell lines available for the study of BoAstV and animal model experiments have not been described. In addition, it has been reported that BoAstV may have the possibility of cross-species transmission. This review summarizes the current state of knowledge about BoAstV, including the epidemiology, evolution analysis, detection methods, pathogenesis and potential cross species transmission, to provide reference for further research of BoAstV.

An Insight into the Molecular Characteristics and Associated Pathology of Chicken Astroviruses

The chicken astrovirus (CAstV) is a ubiquitous enteric RNA virus that has been associated mainly with conditions, such as the runting-stunting syndrome, severe kidney disease, visceral gout, and white chick syndrome, in broiler-type chickens worldwide. Sequence analysis of the capsid genes’ amino acids of the strains involved in these conditions reveals a genetic relationship and diversity between and within the CAstV genogroups and subgroups based on phylogenetic analysis, genetic distance (p-dist), and pathogenicity. While the two genogroups (A and B) are demarcated phylogenetically, their pairwise amino acid sequence identity is 39% to 42% at a p-dist of 0.59 to 0.62. Group-A consists of three subgroups (Ai, Aii, and Aiii) with an inter- and intra-subgroup amino acid identity of 78% to 82% and 92% to 100%, respectively, and a p-dist of 0.18 to 0.22. On the other hand, the six subgroups (Bi, Bii, Biii, Biv, Bv, and Bvi) in Group-B, with a p-dist of 0.07 to 0.18, have an inter- and intra-subgroup amino acid identity of 82% to 93% and 93% to 100%, respectively. However, these groupings have little to no effect on determining the type of CAstV-associated pathology in chickens.

First Isolation and Molecular Characterization of Chicken Astrovirus and Avian Nephritis Virus in Chickens in Bangladesh

Chicken astrovirus (CAstV) and avian nephritis virus (ANV) are enteric viruses of poultry and have infected a wide range of poultry species worldwide, causing runting-stunting syndrome (RSS), which requires virus screening and results in serious economic damage. No confirmed cases have been reported from Bangladesh. In the present study, CAstV and ANV were monitored in Bangladesh. We monitored samples for CAstV and ANV and compared their genomic sequences to other reference strains. We found 8/31 flocks (25.8%) were positive for CAstV, 6/31 flocks (19.3%) had mixed infection of CAstV and ANV, and 1 flock (3.2%) was positive for ANV. Only ANV and a combination of CAstV and ANV were found in broilers and broiler breeders, but CAstV was found in all types of chickens. We isolated two of each from CAstV and ANV through specific pathogen-free chicken embryonated eggs via the yolk sac route. Phylogenetic analysis based on the ORF1b conserved region of CAstV and ANV suggested that the locally circulating strain was closely related to the strains isolated from India and Brazil. This report is the first molecular characterization of CAstV and ANV in Bangladesh. This study highlights that CAstV and ANV are circulating in Bangladeshi poultry.

An outbreak of neonatal enteritis in buffalo calves associated with astrovirus

Background

Enteritis of an infectious origin is a major cause of productivity and economic losses to cattle producers worldwide. Several pathogens are believed to cause or contribute to the development of calf diarrhea. Astroviruses (AstVs) are neglected enteric pathogens in ruminants, but they have recently gained attention because of their possible association with encephalitis in humans and various animal species, including cattle.

Objectives

This paper describes a large outbreak of neonatal diarrhea in buffalo calves (Bubalus bubalis), characterized by high mortality, which was associated with an AstV infection.

Methods

Following an enteritis outbreak characterized by high morbidity (100%) and mortality (46.2%) in a herd of Mediterranean buffaloes (B. bubalis) in Italy, 16 samples from buffalo calves were tested with the molecular tools for common and uncommon enteric pathogens, including AstV, kobuvirus, and torovirus.

Results

The samples tested negative for common enteric viral agents, including Rotavirus A, coronavirus, calicivirus, pestivirus, kobuvirus, and torovirus, while they tested positive for AstV. Overall, 62.5% (10/16) of the samples were positive in a single round reverse transcription polymerase chain reaction (PCR) assay for AstV, and 100% (16/16) were positive when nested PCR was performed. The strains identified in the outbreak showed a clonal origin and shared the closest genetic relationship with bovine AstVs (up to 85% amino acid identity in the capsid).

Conclusions

This report indicates that AstVs should be included in a differential diagnosis of infectious diarrhea in buffalo calves.

Characterization and pathogenicity of a novel avian nephritis virus isolated in China

AbstractAvian nephritis virus (ANV) infections of chicken flocks cause enteric and kidney disease, uneven growth, and runting stunting syndrome, leading to economic losses in the poultry industry. In this study, one ANV strain, designated as AH202017, was isolated from a diseased broiler flock in Anhui province, China, in 2020. Virus production in LMH cell culture was confirmed by real-time RT-PCR and immunofluorescence assay. The complete genome sequencing analysis indicated that AH202017 shares 77.5%-85.5% identity with 12 reference strains in GenBank. Phylogenetic analysis of the capsid protein revealed that AH202017 is more closely related to VIC-6a/Australia/2014 belonging to ANV genotype 2. However, the phylogenetic tree, based on the ORF1a protein and ORF1b protein, indicated that AH202017 manifests a close relationship with GXJL815/China/2017 belonging to genotype 8. In infection experiments, four infected chickens showed depression and one chicken died at 6 days post-infection, corresponding to 5% mortality. The virus was shed daily in the feces of infected chickens, and was found distributed in multiple organs. Macroscopic and microscopic lesions in the kidneys were observed. This is the first paper that describes the genomic characteristics and pathogenicity of a novel ANV strain in China.

Genomic features of first bovine astrovirus detected in Egypt

Bovine astrovirus (BAstV) is a small single-stranded RNA virus, which belongs taxonomically to genus Mamastrovirus under the family Astroviridae. The BAstV is strongly linked to neonatal diarrhea of calves. A few studies are available on BAstV, mainly from Asia, and to a lesser extent from Europe, South America, and Africa. There is only one report from Egypt, in which BAstV was found in diarrheic calves, either in single- or co-infections, based on reverse transcription polymerase chain reaction (RT-PCR) and BAstV-polymerase enzyme targeting primers. One of the samples was further subjected to genomic characterization using Illumina platform for next generation sequencing (NGS). After being processed, the returned BAstV complete genome was subjected to sequence and phylogenetic analysis in comparison to reference strains. The BAstV open reading frames (ORF1a, ORF1b, and ORF2) followed a nearly similar genetic topology, as they belonged to the same unclassified lineage, which was earlier proposed as BAstV-lineage 1, and is known to be disseminated worldwide. This close phylogenetic relationship between the study strain and other members of this lineage was further confirmed by high nucleotide and amino acid (aa) identities. Additionally, a total of 24 unique aa residues were found through the entire BAstV genome. As being the first report in Egypt, indeed Africa, we believe that this record shall be useful in either taxonomic classification or epidemiological tracking of BAstV. The status of BAstV in Egypt should be carefully investigated with possible to-be-implemented precautions for the protection of animal-raising industries.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13337-021-00668-5.

Spectrophotometric microplate assay for titration and neutralization of avian nephritis virus based on the virus cytopathicity

INTRODUCTION

Plaque assay (PA) is a gold standard for virus titration and neutralization of various cytopathic viruses, including avian nephritis virus (ANV), the etiological agent associated with kidney disorders in chickens. In this study, as an alternative to the labor-intensive PA, we developed a spectrophotometric microplate assay (MA) for ANV titration and neutralization based on the virus cytopathicity to primary chicken kidney (CK) cells.

METHODS

CK cells were infected with ANV in the presence or absence of chicken serum in a 96-well microplate, and the virus-induced cytolysis was quantified by measurement of neutral red uptake using a spectrophotometer. The absorbance values obtained were subjected to a sigmoidal four-parameter logistic regression analysis for the virus titer determination and serum neutralization assessment. Accuracy and reliability of the serum neutralization MA in comparison to the standard PA was statistically evaluated.

RESULTS

The ANV-MA was capable of quantifying infectious virus titers based on a virus dose-dependent cytolysis of CK cells, and serum neutralization could be assessed as an inhibition of the virus-induced cytolysis accordingly. Statistical evaluation using a 2 × 2 contingency table and receiver-operating characteristic analyses showed 82 % sensitivity, 99 % specificity and 0.97 area under the curve, supporting an overall diagnostic accuracy of the neutralization MA.

CONCLUSION

The newly developed MA using simplified experimental procedures in the microplate format and direct spectophotometric data readout is readily applicable to general laboratories for high-throughput screening of serum neutralization of ANV.

Beyond the Gastrointestinal Tract: The Emerging and Diverse Tissue Tropisms of Astroviruses

Astroviruses are single stranded, positive-sense RNA viruses that have been historically associated with diseases of the gastrointestinal tract of vertebrates, including humans. However, there is now a multitude of evidence demonstrating the capacity of these viruses to cause extraintestinal diseases. The most striking causal relationship is neurological diseases in humans, cattle, pigs, and other mammals, caused by astrovirus infection. Astroviruses have also been associated with disseminated infections, localized disease of the liver or kidneys, and there is increasing evidence suggesting a potential tropism to the respiratory tract. This review will discuss the current understanding of the tissue tropisms for astroviruses and their emerging capacity to cause disease in multiple organ systems.

First description of natural concomitant infection of avian nephritis virus and infectious bronchitis virus reveals exacerbated inflammatory response and renal damage in broiler chicks

We describe the first report on spontaneous Avian Nephritis Virus (ANV) and Infectious Bronchitis Virus (IBV) concurrent infection in broiler chicks. On necropsy, the kidneys were found swollen with its parenchyma and ureters stuffed with urate flakes. Histopathologically, the renal tubular damage and inflammatory response were severe in concurrently infected birds compared to the cases infected only with ANV, which had direct correlation with significantly (p < 0.001) increased expression of IL-1 β, IL-4, IL-12, IL-13, iNOS and IFN-γ transcripts in the kidneys of concurrently infected birds. Relative decrease in IFN-β transcript levels in the concurrently infected birds indicates suppression of antiviral response; the iNOS level was manifold increased which can be attributed to the enhanced macrophage response. Nucleotide sequencing of S1-spike glycoprotein gene of IBV and RNA dependent RNA polymerase gene of ANV confirmed etiologies as Igacovirus of Gammacoronavirus and ANV-2 of Avastrovirus 2, respectively. Both ANV and IBV virus affect kidneys. Our findings suggested that concurrent infections of these two viruses might have enhanced the transcripts of Th1, Th2 and proinflammatory cytokines with reduced IFN-β transcripts resulting in decreased host innate antiviral mechanisms leading to exacerbated renal lesions. Future experimental co-infection studies could throw more lights on pathology and pathogenesis during concurrent infections of ANV and IBV in poultry.

The First Whole Genome Sequence and Characterisation of Avian Nephritis Virus Genotype 3

Avian nephritis virus (ANV) is classified in the Avastroviridae family with disease associations with nephritis, uneven flock growth and runting stunting syndrome (RSS) in chicken and turkey flocks, and other avian species. The whole genome of ANV genotype 3 (ANV-3) of 6959 nucleotides including the untranslated 5′ and 3′ regions and polyadenylated tail was detected in a metagenomic virome investigation of RSS-affected chicken broiler flocks. This report characterises the ANV-3 genome, identifying partially overlapping open reading frames (ORFs), ORF1a and ORF1b, and an opposing secondary pseudoknot prior to a ribosomal frameshift stemloop structure, with a separate ORF2, whilst observing conserved astrovirus motifs. Phylogenetic analysis of the Avastroviridae whole genome and ORF2 capsid polyprotein classified the first complete whole genome of ANV-3 within Avastroviridae genogroup 2.

First Detection of Bat Astroviruses (BtAstVs) among Bats in Poland: The Genetic BtAstVs Diversity Reveals Multiple Co-Infection of Bats with Different Strains

Background: Astroviruses (AstVs) are common pathogens of a wide range of animal hosts, including mammals and avians, causing gastrointestinal diseases, mainly gastroenteritis and diarrhea. They prompt a significant health problem in newborns and young children and economic losses in the poultry sector and mink farms. Recent studies revealed a growing number of bat species carrying astroviruses with a noticeable prevalence and diversity. Here, we demonstrate the first detection of bat astroviruses (BtAstVs) circulating in the population of insectivorous bats in the territory of Poland. Results: Genetically diverse BtAstVs (n = 18) were found with a varying degree of bat species specificity in five out of 15 bat species in Poland previously recognized as BtAstV hosts. Astroviral RNA was found in 12 out of 98 (12.2%, 95% CI 7.1–20.2) bat intestines, six bat kidneys (6.1%, 95% CI 2.8–12.7) and two bat livers (2.0%, 95% CI 0.4–7.1). Deep sequencing of the astroviral RNA-dependent RNA polymerase (RdRp) region revealed co-infections in five single bat individuals with highly distinct astrovirus strains. Conclusions: The detection of highly distinct bat astroviruses in Polish bats favors virus recombination and the generation of novel divergent AstVs and creates a potential risk of virus transmission to domestic animals and humans in the country. These findings provide a new insight into molecular epidemiology, prevalence of astroviruses in European bat populations and the risk of interspecies transmission to other animals including humans.

Occurrence and Role of Selected RNA-Viruses as Potential Causative Agents of Watery Droppings in Pigeons

The diseases with watery droppings (diarrhea and/or polyuria) can be considered some of the most severe health problems in domestic pigeons of various ages. Although they do not always lead to bird death, they can contribute to poor weight gains and hindered development of young pigeons and, potentially, to poor racing results in sports birds. The gastrointestinal tract disorders of pigeons may be of various etiology, but some of the causative agents are viral infections. This review article provides information collected from scientific reports on RNA-viruses belonging to the Astroviridae, Picornaviridae, and Coronaviridae families; the Avulavirinae subfamily; and the Rotavirus genus that might be implicated in such health problems. It presents a brief characterization, and possible interspecies transmission of these viruses. We believe that this review article will help clinical signs of infection, isolation methods, occurrence in pigeons and poultry, systemize and summarize knowledge on pigeon enteropathogenic viruses and raise awareness of the importance of disease control in pigeons.

Analysis of astrovirus transmission pathways in a free-ranging fission-fusion colony of Natterer’s bats (Myotis nattereri)

Abstract

Bats are a diverse and widespread order of mammals. They fulfill critical ecosystem roles but may also act as reservoirs and spreaders for zoonotic agents. Consequently, many recent studies have focused on the potential of bats to spread diseases to other animals and to humans. However, virus transmission networks within bat colonies remain largely unexplored. We studied the detection rate and transmission pathway of astroviruses in a free-ranging Natterer’s bat colony (Myotis nattereri) that exhibits a high fission-fusion dynamic. Based on automatic roost monitoring data of radio-frequency identification tagged bats, we assessed the impact of the strength of an individual’s roosting associations with all other colony members (weighted degree), and the number of roost sites (bat boxes) an individual used—both being proxies for individual exposure risk—on the detected presence of astrovirus-related nucleic acid in individual swab samples. Moreover, we tested to which degree astrovirus sequence types were shared between individuals that frequently roosted together, as proxy for direct transmission risk, and between bats sharing the same roost sites in close temporal succession, as proxy for indirect transmission risk. Neither roosting associations nor the number of different roost sites had an effect on detected virus presence in individual bats. Transmission network data suggest that astroviruses are transmitted both via direct and indirect contact, implying that roost sites pose a risk of astrovirus infection for several days after the bats leave them. Our study offers novel insights in the presence and transmission of viruses within social networks of bat colonies.

Significance statement

Bats provide many ecosystem services but have moved into the focus of virological research as potential carriers of zoonotic disease agents. However, the sparse information available about virus transmission within bat colonies is solely based on simulated transmission data. In this field study, we examined the daily roosting behavior in a wild bat colony in relation to the presence of viruses in individual colony members. Our findings suggest that astroviruses are transmitted by direct contact and via contaminated roost sites. Bats typically defecate in their roost sites, and astroviruses can remain infectious in feces for several days. The here observed virus diversity and roosting behavior suggest that bats can contract astroviruses even if they use contaminated roost sites days after infected individuals have left. This study provides first-time insights in the transmission of astroviruses within bat colonies in the wild.

Identification of Novel Astroviruses in the Gastrointestinal Tract of Domestic Cats

Astroviruses, isolated from numerous avian and mammalian species including humans, are commonly associated with enteritis and encephalitis. Two astroviruses have previously been identified in cats, and while definitive evidence is lacking, an association with enteritis is suggested. Using metagenomic next-generation sequencing of viral nucleic acids from faecal samples, we identified two novel feline astroviruses termed Feline astrovirus 3 and 4. These viruses were isolated from healthy shelter-housed kittens (Feline astrovirus 3; 6448 bp) and from a kitten with diarrhoea that was co-infected with Feline parvovirus (Feline astrovirus 4, 6549 bp). Both novel astroviruses shared a genome arrangement of three open reading frames (ORFs) comparable to that of other astroviruses. Phylogenetic analysis of the concatenated ORFs, ORF1a, ORF1b and capsid protein revealed that both viruses were phylogenetically distinct from other feline astroviruses, although their precise evolutionary history could not be accurately determined due to a lack of resolution at key nodes. Large-scale molecular surveillance studies of healthy and diseased cats are needed to determine the pathogenicity of feline astroviruses as single virus infections or in co-infections with other enteric viruses.

Diversity of Astroviruses Circulating in Humans, Bats, and Wild Birds in Egypt

Astroviruses belong to Astroviridae family which includes two main genera: Mamastroviruses that infect mammals, and Avastroviruses that infect avian hosts. Bats and wild birds are considered among the natural reservoirs for astroviruses. Infections in humans are associated with severe gastroenteritis, especially among children. We conducted surveillance for astroviruses in bats, wild birds, and humans in Egypt. Our results indicated relatively high prevalence of astroviruses in those hosts. Phylogenetic analysis revealed diversity of these viruses within hosts. Detected human viruses showed similarity with classic and variant human astroviruses, as well as similarity with animal-origin viruses. Viruses in bats were dispersed, with similarities to other bat viruses as well as other mammalian, including human, viruses. Wild bird viruses varied and were related to other avastroviruses, as well as human astroviruses. Our results indicate that astroviruses are common in bats, wild birds, and humans in Egypt, with a wide gene pool. Potential cross-species transmission may be occurring but should be verified by further surveillance and molecular studies.

Complete genome sequence and phylogenetic analysis of novel avastroviruses circulating in China from 2016 to 2018

Avastrovirus-specific antibodies are widely detected in chickens in China. However, there are currently no commercially available vaccines for this group of viruses. To address this issue, we collected 76 tissue samples from Avastrovirus (AAstVs) antibody-positive chickens from farms across eight provinces in China from 2016 to 2018. The samples were then screened for the presence of AAstVs sequences by polymerase chain reaction analysis and a phylogenetic tree was constructed. Specific primers were designed to amplify the whole genome sequences of the viruses from four positive samples, with the genetic characteristics and structures of the resulting genomes then analyzed further. Overall, 42 (55.3 %) of the 76 samples were positive for AAstVs RNA. Phylogenetic analysis along with the ORF1b gene showed that 15 isolates were grouped in AAstV-1 and 27 of them were grouped in AAstV-2. None of the isolates was belonged to AAstV-3. Sequencing and structural analyses revealed that the genomes of the four isolates showed the typical characteristics of AAstVs genomes but were genetically distinct from other AAstVs. The results of this study will contribute to our understanding of the genetic characteristics of AAstVs in China.

Identification of a Type-Specific Epitope in the ORF2 Protein of Duck Astrovirus Type 1

Simple Summary

Duck astrovirus type 1 (DAstV-1) infection constitutes a cause of viral hepatitis in ducklings and little is known about the B-cell epitope of DAstV-1. In this study, using a monoclonal antibody (mAb) 3D2 against ORF2 protein of DAstV-1, a highly conserved linear B-cell epitope of ⁴⁵⁴ STTESA⁴⁵⁹ in DAstV-1 ORF2 was identified. The mAb 3D2 showed no neutralizing activity to DAstV-1 and had no cross-reactivity with other DAstV serotypes.

Abstract

Duck astrovirus type 1 (DAstV-1) infection constitutes a cause of viral hepatitis in ducklings and little is known about the B-cell epitope of DAstV-1. In this study, a monoclonal antibody (mAb) 3D2 against open reading frame 2 (ORF2) protein of DAstV-1 was used to identify the possible epitope in the four serotypes of DAstV. The mAb 3D2 showed no neutralization activity to DAstV-1, and reacted with the conserved linear B-cell epitopes of ⁴⁵⁴STTESA⁴⁵⁹ in DAstV-1 ORF2 protein. Sequence analysis, dot blot assay, and cross-reactivity test indicated that the epitope peptide was highly conserved in DAstV-1 sequence and mAb 3D2 had no cross-reactivity with other DAstV serotypes. To the best of our knowledge, this is the first report about identification of the specific conserved linear B-cell epitope of DAstV-1, which will facilitate the serologic diagnosis of DAstV-1 infection.

Molecular characterization of chicken astroviruses in gout-affected commercial broiler chickens in Haryana, India

Chicken astroviruses (CAstVs) infect young chicks and are associated with gastroenteritis, stunted growth or visceral gout (gout). True incidence and distribution of CAstVs as well as virus variants circulating in India is not well understood. In this study, 80 gout-affected broiler chicken flocks from Haryana, a north-western state of India, were tested for the presence of astroviruses by targeting the polymerase gene of both CAstV and avian nephritis virus (ANV) and capsid gene of CAstV. Of these, 22 (27.5%) flocks were found positive for CAstV, 7(8.75%) for ANV and 2 (2.5%) for both CAstV and ANV genome by reverse-transcription-polymerase chain reaction. CAstV was isolated by inoculating tissue (kidney) homogenate from gout-affected birds into specific-pathogen free embryonated chicken eggs where the infected embryos showed stunted growth with necrosis of liver and enlarged kidney with urate deposits. Capsid gene-based phylogenetic analysis revealed the clustering of CAstV strains from this study with Indian strains of serogroup Biii suggesting their antigenic relatedness. Thus the present study reveals the presence of chicken astroviruses in broiler chickens affected with gout.

A novel method to rescue and culture duck Astrovirus type 1 in vitro

Background

Reverse genetics systems enable the manipulation of viral genomes and therefore serve as robust reverse genetic tools to study RNA viruses. A DNA-launched rescue system initiates the transcription of viral genomic cDNA from eukaryotic promoter in transfected cells, generating homogenous RNA transcripts in vitro and thus enhancing virus rescue efficiency. As one of the hazardous pathogens to ducklings, the current knowledge of the pathogenesis of duck astrovirus type 1 (DAstV-1) is limited. The construction of a DNA-launched rescue system can help to accelerate the study of the virus pathogenesis. However, there is no report of such a system for DAstV-1.

Methods

In this study, a DNA-launched infectious clone of DAstV-1 was constructed from a cDNA plasmid, which contains a viral cDNA sequence flanked by hammerhead ribozyme (HamRz) and a hepatitis delta virus ribozyme (HdvRz) sequence at both terminals of the viral genome. A silent nucleotide mutation creating a Bgl II site in the ORF2 gene was made to distinguish the rescued virus (rDAstV-1) from the parental virus (pDAstV-1). Immunofluorescence assay (IFA) and western blot were conducted for rescued virus identification in duck embryo fibroblast (DEF) cells pre-treated with trypsin. The growth characteristics of rDAstV-1 and pDAstV-1 in DEF cells and the tissue tropism in 2-day-old ducklings of rDAstV-1 and pDAstV-1 were determined.

Results

The infectious DAstV-1 was successfully rescued from baby hamster kidney (BHK-21) cells and could propagate in DEF cells pre-treated with 1 μg/ml trypsin. Upon infection of DEF cells pre-treated with trypsin, DAstV-1 mRNA copies were identified after serial passaging, and the result showed that rDAstV-1 and pDAstV-1 shared similar replication kinetics. Animal experiment showed that the rDAstV-1 had an extensive tissue tropism, and the virus was capable of invading both the central and the peripheral immune organs in infected ducklings.

Conclusions

An improved DNA-launched reverse genetics system for DAstV-1 was firstly constructed. Infectious virus recovered from BHK-21 cells could propagate in DEF cells pre-treated with trypsin. This is the first report of the successful in vitro cultivation of DAstV-1. We believe this valuable experimental system will contribute to the further study of DAstV-1 genome function and pathogenesis.

Investigation of Enteric Viruses Associated With Runting and Stunting in Day-Old Chicks and Older Broilers in Southwest Nigeria

Enteric viruses are known to have significant economic impact on poultry, especially broiler chicken flocks, because of production losses attributable to poor feed conversion and weight gain. To sustain the Nigerian poultry industry that contributes significantly to the livestock sector of the economy, there is a need to investigate commercial broiler flocks in the country for the presence of enteric viruses causing runting and stunting, growth retardation, and hatchery diseases. Gut contents were collected from 158 day-old and six 14-week old runted/stunted broiler chickens in commercial farms (ten) and hatcheries (six) located in Southwest Nigeria. The samples were examined for the presence of chicken astrovirus (CAstV), avian nephritis virus (ANV), avian rotavirus (AvRV), chicken parvovirus (ChPV), and turkey astroviruses (TAstV-1 and−2) by polymerase chain reaction (PCR) and reverse transcriptase-PCR (RT-PCR) whereas avian reovirus (ARV) and fowl adenovirus (FAdV) by virus isolation (VI), RT-PCR, and PCR. While CAstV was detected in all the birds (100%), sporadic detection of ANV (5%), and ChPV (5%) was observed in day-old and/or older birds. Four isolates were obtained by VI with one isolate being ARV positive and other three FAdV positive by RT-PCR and PCR, respectively. These findings strongly suggest CAstV as a major cause of runting and stunting as well as hatchery condemnations in commercial broilers in Southwest Nigeria, although co-infections with ANV, FAdV, ARV, and ChPV cannot be ruled out. In addition, the possible vertical and horizontal transmissions of these viruses are discussed.

A novel group of avian astroviruses from Neotropical passerine birds broaden the diversity and host range of Astroviridae

Metagenomics is helping to expand the known diversity of viruses, especially of those with poorly studied hosts in remote areas. The Neotropical region harbors a considerable diversity of avian species that may play a role as both host and short-distance vectors of unknown viruses. Viral metagenomics of cloacal swabs from 50 Neotropical birds collected in French Guiana revealed the presence of four complete astrovirus genomes. They constitute an early diverging novel monophyletic clade within the Avastrovirus phylogeny, representing a putative new astrovirus species (provisionally designated as Avastrovirus 5) according to the International Committee on Taxonomy of Viruses (ICTV) classification criteria. Their genomic organization shares some characteristics with Avastrovirus but also with Mamastrovirus. The pan-astrovirus RT-PCR analysis of the cloacal samples of 406 wild Neotropical birds showed a community-level prevalence of 4.9% (5.1% in passerines, the highest described so far in this order of birds). By screening birds of a remote region, we expanded the known host range of astroviruses to the avian families Cardinalidae, Conopophagidae, Furnariidae, Thamnophilidae, Turdidae and Tyrannidae. Our results provide important first insights into the unexplored viral communities, the ecology, epidemiology and features of host-pathogen interactions that shape the evolution of avastroviruses in a remote Neotropical rainforest.

Discovery of novel astrovirus and calicivirus identified in ruddy turnstones in Brazil

Birds are the natural reservoir of viruses with zoonotic potential, as well as contributing to the evolution, emergence, and dissemination of novel viruses. In this study, we applied a high-throughput screening approach to identify the diversity of viruses in 118 samples of birds captured between October 2006 to October 2010 in the North and Northeast regions of Brazil. We found nearly complete genomes of novel species of astrovirus and calicivirus in cloacal swabs of ruddy turnstones (Arenaria interpres) collected in Coroa do Avião islet, Pernambuco State. These viruses are positive-sense single-stranded RNA with a genome of ~7 to 8 kb, and were designated as Ruddy turnstone astrovirus (RtAstV) and Ruddy turnstone calicivirus (RTCV), respectively. Phylogenetic analysis showed that RtAstV and RTCV grouped in a monophyletic clade with viruses identified from poultry samples (i.e., chicken, goose, and turkey), including viruses associated with acute nephritis in chickens. Attempts of viral propagation in monkey and chicken cell lines for both viruses were unsuccessful. Also, we found genomes related with viral families that infect invertebrates and plants, suggesting that they might be ingested in the birds' diet. In sum, these findings shed new light on the diversity of viruses in migratory birds with the notable characterization of a novel astrovirus and calicivirus.

Isolation of avian nephritis virus from chickens showing enteric disorders

Runting-stunting syndrome (RSS) is one of the diseases associated with many detected viruses. In Brazil, there were reports of several enteric disease outbreaks in chickens in which avian nephritis virus (ANV) was detected; however, the role of ANV in the outbreaks and whether the virus was a causative agent of these cases of enteric diseases were not determined. The aim of this study was to isolate ANV in specific pathogen-free (SPF) chicken embryonated eggs (CEE) from the enteric contents of chickens showing signs of RSS. For this purpose, 22 samples of chicken enteric contents that were positive only for ANV were inoculated into 7 and 14-day-old SPF-CEE via the yolk sac route and incubated for 5 d, with a total of 3 passages. Virus isolation was confirmed by the presence of embryo injuries, detection of viral RNA by RT-PCR, and visualization of viral particles using electron microscopy. Therefore, the 7-day-old inoculated embryos showed dwarfism, gelatinous consistency, hemorrhage, and edema in the embryos, whereas the 14-day-old did not show any alteration. Viral RNA was detected in the embryos of both ages of inoculation, and the same viral particles were visualized. The embryos from the mock group showed no alteration and were negative for all the tests. The viral cDNA was sequenced, and the molecular and phylogenetic analyses showed that the Brazilian isolates are more related with the ANV-1 serotype group; the sequences of these isolates showed a high percentage of nucleotide (86.4 to 94.9%) and amino acid (92.3 to 98.7%) similarity with other sequences from China, Japan, Australia, and the United States that belong to this serotype previously classified group. In this study, we isolated 8 samples of ANV in SPF-CEE from enteric content samples from chickens with RSS. In doing so, we showed the pathological injuries to the embryo caused by the virus and the molecular characterization of a part of the ORF 1b gene of the virus.

First Whole-Genome Characterization of Avian Nephritis Virus 2 of Broiler Chicken from Pará, Brazil

Our results show the first full-genome characterization of avian nephritis virus 2 recovered from stools of broiler chickens at a commercial farm located in Benevides, Pará, Brazil. Nucleotide analyses of whole-genome sequences showed the isolate to be a strain of Avastrovirus 2 in the family Astroviridae.

Detection and phylogenetic characterization of astroviruses in insectivorous bats from Central-Southern Italy

In recent years, bats have been found to harbour many viruses, raising several questions about their role as reservoirs and potential disseminators of zoonotic viruses. We investigated the presence of six virus families in bats in three regions of Central‐Southern Italy. Astroviruses were identified in seven of 13 bat species. Sequence analysis revealed marked genetic heterogeneity among the astroviruses identified, with nucleotide identity ranging between 60.26% and 87.62%. Astrovirus diversity was not associated with the bat species, the geographic areas or the bat colony, suggesting the circulation of several astrovirus strains in Italian ecosystems. Genetic diversification and interspecies transmission appear common in bat astroviruses and could provide, potentially, the bases for transmission to humans and other mammals. Yet overemphasizing this risk might have detrimental consequences for bat conservation and preservation of the important ecosystem services bats provide.

Genetic characterization of a novel group of avastroviruses in geese

As part of aetiological studies, we tested 28 samples collected from domestic geese showing enteritis and sporadic death. A novel group of avastroviruses was found in six samples. One isolate was completely sequenced, which comprised 7,148 nucleotides. Pairwise comparisons and phylogenetic analysis demonstrated that the goose astrovirus is highly divergent from all previously described avastroviruses. Our data support the view that domestic geese can be infected by astroviruses with different genetic backgrounds, and have raised a concern about the role of domestic geese as reservoirs for diverse astroviruses.

A novel group of avian Avastrovirus in domestic geese, China

Using an ORF1b-based astrovirus-specfic reverse transcription (RT)-PCR assay, a novel astrovirus-like was detected from domestic geese in China. Pairwise comparisons and phylogenetic analyzes suggested that a novel group of goose astrovirus, different with previously known astroviruses in the genus Avastrovirus, was found circulating in geese. This study has expanded our understanding about the role of domestic waterfowls as reservoirs for diverse astroviruses.

Chicken astrovirus as an aetiological agent of runting-stunting syndrome in broiler chickens

Despite descriptions of runting-stunting syndrome (RSS) in broiler chickens dating back over 40 years, the aetiology has not yet been described. A novel chicken astrovirus (CkAstV) was isolated in an LMH liver cell line from the intestines of chickens affected with RSS. Clinical RSS is characterized by retarded growth and cystic crypt lesions in the small intestine. In 1-day-old broiler chickens infected with the CkAstV isolate, virus was only detected in the intestinal epithelial cells during the first few days after infection. Notably, the preferred host cells are the crypt epithelial cells following initial replication in the villous epithelial cells, thus implying viral preference for immature intestinal cells. Nevertheless, the CkAstV isolate did not induce remarkable pathological changes, despite the presence of the virus in situ. Serial chicken-to-chicken passages of the virus induced increased virulence, as displayed by decreased weight gain and the presence of cystic lesions in the small intestine reproducing clinical RSS in chickens. The analysis of the full-length genome sequences from the isolated CkAstV and the CkAstV from the bird-to-bird passages showed >99 % similarity. The data obtained in this study suggest that the CkAstV isolate is capable of inducing RSS following serial bird-to-bird passages in broilers and is as an aetiological agent of the disease.

Detection and genetic characterization of Mamastrovirus 5 from Brazilian dogs

Mamastrovirus 5 (MAstV5), belonging to the Astroviridae (AstV) family, previously known as canine astrovirus or astrovirus-like particles, has been reported in several countries to be associated with viral enteric disease in dogs since the 1980s. Astroviruses have been detected in fecal samples from a wide variety of mammals and birds that are associated with gastroenteritis and extra enteric manifestations. In the present study, RT-PCR was used to investigate the presence of MAstV5 in 269 dog fecal samples. MAstV5 was detected in 26% (71/269) of the samples. Interestingly, all MAstV5-positive samples derived from dogs displaying clinical signs suggestive of gastroenteritis, other enteric viruses were simultaneously detected (canine parvovirus, canine distemper virus, canine coronavirus, canine adenovirus and canine rotavirus). Based on genomic sequence analysis of MAstV5 a novel classification of the species into four genotypes, MAstV5a-MAstV5d, is proposed. Phylogenetic analyses based on the ORF2 amino acid sequences, samples described herein grouped into the putative genotype ‘a’ closed related with Chinese samples. Other studies are required to attempt the clinical and antigenic implications of these astrovirus genotypes in dogs.

Detection and genetic characterization of canine astroviruses in pet dogs in Guangxi, China

Background

Astroviruses (AstVs) have been reported to infect and cause gastroenteritis in most animal species. Human AstVs were regarded the causative agent of viral diarrhea in children. In dogs, little is known about the epidemiology and clinical significance of AstV infection.

Findings

In this study, we collected and tested 253 rectal swabs from pet dogs; of which 64 samples (25.3%) tested positive for AstVs with diarrhea and 15 more samples (5.9%) also was identified as AstVs, however without any clinical signs. Phylogenetic analysis of 39 partial ORF1b sequences from these samples revealed that they are similar to AstVs, which can be subdivided into three lineages. Interestingly, out of the 39 isolates sequenced, 16 isolates are shown to be in the Mamastrovirus 5/canine astrovirus (CAstV) lineage and the remaining 23 isolates displayed higher similarities with known porcine astrovirus (PoAstV) 5 and 2. Further, analysis of 13 capsid sequences from these isolates showed that they are closely clustered with Chinese or Italy CAstV isolates.

Conclusions

The findings indicate that CAstVs commonly circulate in pet dogs, and our sequencing results have shown the genomic diversity of CAstVs leading to increasing number of clusters.

Astrovirus Biology and Pathogenesis

Astroviruses are nonenveloped, positive-sense single-stranded RNA viruses that cause gastrointestinal illness. Although a leading cause of pediatric diarrhea, human astroviruses are among the least characterized enteric RNA viruses. However, by using in vitro methods and animal models to characterize virus-host interactions, researchers have discovered several important properties of astroviruses, including the ability of the astrovirus capsid to act as an enterotoxin, disrupting the gut epithelial barrier. Improved animal models are needed to study this phenomenon, along with the pathogenesis of astroviruses, particularly in those strains that can cause extraintestinal disease. Much like for other enteric viruses, the current dogma states that astroviruses infect in a species-specific manner; however, this assumption is being challenged by growing evidence that these viruses have potential to cross species barriers. This review summarizes these remarkable facets of astrovirus biology, highlighting critical steps toward increasing our understanding of this unique enteric pathogen.

Seroprevalence of antibodies to astrovirus in chickens in Grenada, West Indies

Aim:

Chicken astroviruses (CAstV) are known to cause mild gastroenteritis, growth depression, and even mortality in poultry, especially in chickens, turkeys, and ducks. To the best our knowledge, there is no published information on CAstV in Grenada. This study was conducted to determine the prevalence of astrovirus in chickens in Grenada.

Materials and Methods:

Blood samples from 366 indigenous chickens and 92 commercial chicken layers were collected from all parishes of the island and tested for antibodies against CAstV using commercial enzyme-linked immunosorbent assay.

Results:

The seroprevalence of antibodies against astrovirus was 57.6% (95%, Confidence interval [CI]: 47.4-67.2) in commercial layers and 61.5% (95%, CI: 56.4-66.3) in indigenous chickens. The results show the presence of infection throughout the island.

Conclusion:

The results show the infection with CAstV in approximately half of the chicken population in Grenada. This is the first report on the prevalence of CAstV in chickens in Grenada and the Caribbean region.

The Broad Host Range and Genetic Diversity of Mammalian and Avian Astroviruses

Astroviruses are a diverse family of viruses that infect a wide range of mammalian and avian hosts. Here we describe the phylogenetic diversity and current classification methodology of astroviruses based on the ORF1b and ORF2 genes, highlighting the propensity of astroviruses to undergo interspecies transmission and genetic recombination which greatly increase diversity and complicate attempts at a unified and comprehensive classification strategy.

Diverse novel astroviruses identified in wild Himalayan marmots

With advances in viral surveillance and next-generation sequencing, highly diverse novel astroviruses (AstVs) and different animal hosts had been discovered in recent years. However, the existence of AstVs in marmots had yet to be shown. Here, we identified two highly divergent strains of AstVs (tentatively named Qinghai Himalayanmarmot AstVs, HHMAstV1 and HHMAstV2), by viral metagenomic analysis in liver tissues isolated from wild Marmota himalayana in China. Overall, 12 of 99 (12.1 %) M. himalayana faecal samples were positive for the presence of genetically diverse AstVs, while only HHMAstV1 and HHMAstV2 were identified in 300 liver samples. The complete genomic sequences of HHMAstV1 and HHMAstV2 were 6681 and 6610 nt in length, respectively, with the typical genomic organization of AstVs. Analysis of the complete ORF 2 sequence showed that these novel AstVs are most closely related to the rabbit AstV, mamastrovirus 23 (with 31.0 and 48.0 % shared amino acid identity, respectively). Phylogenetic analysis of the amino acid sequences of ORF1a, ORF1b and ORF2 indicated that HHMAstV1 and HHMAstV2 form two distinct clusters among the mamastroviruses, and may share a common ancestor with the rabbit-specific mamastrovirus 23. These results suggest that HHMAstV1 and HHMAstV2 are two novel species of the genus Mamastrovirus in the Astroviridae. The remarkable diversity of these novel AstVs will contribute to a greater understanding of the evolution and ecology of AstVs, although additional studies will be needed to understand the clinical significance of these novel AstVs in marmots, as well as in humans.

Isolation and detection of duck astrovirus CPH: implications for epidemiology and pathogenicity

The transmission routes of duck astrovirus CPH (DAstV/CPH) and its pathogenicity in duck embryos were investigated. Using a reverse transcription-polymerase chain reaction (RT-PCR) developed in this study, DAstV/CPH was detected in 23/50 fresh droppings of breeder ducks, 39/65 breeding eggs, 26/31 dead embryos, and 6/10 newly hatched ducklings, which were taken from a Pekin duck farm where DAstV/CPH had previously been identified. This finding, and the detection of DAstV/CPH in 36/130 dead-in-shell duck embryo samples collected from different hatcheries located in six provinces, suggests that the virus may be horizontally and vertically transmitted and associated with hatchability problems. Inoculation and repeated passages in embryonating duck eggs resulted in isolation of DAstV/CPH. The virus caused severe chorioallantoic membrane lesions as well as growth retardation and embryo mortality, indicating that DAstV/CPH is pathogenic for duck embryos. The effect of DAstV/CPH on hatching was confirmed by an embryo infection experiment in which 8/10 9-day-old duck embryos inoculated with the third passage of DAstV/CPH were unable to hatch, with most embryos succumbing in the final stage of incubation. The use of RT-PCR on the hatched ducklings provided evidence that the embryos could develop into infected ducklings.

A Review of the Strain Diversity and Pathogenesis of Chicken Astrovirus

Although a relatively recently emerged virus, identified only in 2004 as a separate species of avian astrovirus, chicken astrovirus (CAstV) has been associated with poor growth of broiler flocks, enteritis and diarrhea and is a candidate pathogen in cases of runting stunting syndrome. More recently CAstV has been implicated in cases of two other diseases of broilers as the sole etiological agent, namely severe kidney disease of young broilers with visceral gout and the “White Chicks” hatchery disease. Examination of the strains of CAstV associated with the two latter diseases reveals they are closely related genetically. This review will discuss the pathogenesis of CAstV in relation to strain diversity and the effects of vertical versus horizontal transmission, virus load, co-infections and age of bird at infection, all factors that may impact upon disease severity.

Systemic Clinical and Metabolic Diseases

Like other animals pet and companion birds are also prone to systemic illness. This is presented in the form of certain clinical signs and symptoms which is known as “ sick-bird syndrome.”

Complete genome sequence analysis of chicken astrovirus isolate from India

Objective

Chicken astroviruses have been known to cause severe disease in chickens leading to increased mortality and “white chicks” condition. Here we aim to characterize the causative agent of visceral gout suspected for astrovirus infection in broiler breeder chickens.

Methods

Total RNA isolated from allantoic fluid of SPF embryo passaged with infected chicken sample was sequenced by whole genome shotgun sequencing using ion-torrent PGM platform. The sequence was analysed for the presence of coding and non-coding features, its similarity with reported isolates and epitope analysis of capsid structural protein.

Results

The consensus length of 7513 bp genome sequence of Indian isolate of chicken astrovirus was obtained after assembly of 14,121 high quality reads. The genome was comprised of 13 bp 5′-UTR, three open reading frames (ORFs) including ORF1a encoding serine protease, ORF1b encoding RNA dependent RNA polymerase (RdRp) and ORF2 encoding capsid protein, and 298 bp of 3′-UTR which harboured two corona virus stem loop II like “s2m” motifs and a poly A stretch of 19 nucleotides. The genetic analysis of CAstV/INDIA/ANAND/2016 suggested highest sequence similarity of 86.94% with the chicken astrovirus isolate CAstV/GA2011 followed by 84.76% with CAstV/4175 and 74.48%% with CAstV/Poland/G059/2014 isolates. The capsid structural protein of CAstV/INDIA/ANAND/2016 showed 84.67% similarity with chicken astrovirus isolate CAstV/GA2011, 81.06% with CAstV/4175 and 41.18% with CAstV/Poland/G059/2014 isolates. However, the capsid protein sequence showed high degree of sequence identity at nucleotide level (98.64-99.32%) and at amino acids level (97.74–98.69%) with reported sequences of Indian isolates suggesting their common origin and limited sequence divergence. The epitope analysis by SVMTriP identified two unique epitopes in our isolate, seven shared epitopes among Indian isolates and two shared epitopes among all isolates except Poland isolate which carried all distinct epitopes.

Electronic supplementary material

The online version of this article (doi:10.1007/s11259-016-9673-6) contains supplementary material, which is available to authorized users.