Detection and molecular characterization of chicken astrovirus associated with chicks that have an unusual condition known as "white chicks" in Brazil

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

RESEARCH HIGHLIGHTS

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

Molecular characterization of chicken astrovirus from high embryonic mortality based on the capsid protein (ORF2) gene, in Brazil

ABSTRACTIn recent years, reports of chicken astrovirus (CAstV) infections in commercial birds have increased, affecting the poultry industries in Brazil and worldwide. The objective of this study was to use molecular methods to characterize the CAstV found in one breeding and three different incubation companies that reported increased embryonic mortality and the appearance of birds with white chick syndrome (WCS). RT-qPCR with SyBR green chemistry were used to determine the presence of the virus in the feces of breeders, organs of newborn chickens, and unhatched embryos. By sequencing the ORF2 that codes for the viral capsid, the strains responsible for these clinical signs were characterized using strains previously reported in Brazil, North America, Europe, and Asia. The percentage of identity of the amino acid sequences compared with those from group A was less than 41% (37.01% to 40.52%) and the identity with those from subgroups Bi, Bii, and Biii was less than 90% (81.81% to 89.85%). Therefore, the sequences were characterized within subgroup Biv with identity greater than 95% (95.26% to 99.59%), together with CAstV strains previously found in Brazil, Canada, and the United States. Using antigenicity prediction tools, 14 highly conserved peptides located on the surface of the capsid protein were considered potentially responsible for inducing the immune response in the host. Our data provide important information related to the increase in embryo mortality in vertically infected birds, reinforcing the potential association of WCS with CAstV Biv subgroup.

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.

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.

A Review of the Emerging White Chick Hatchery Disease

White chick hatchery disease is an emerging disease of broiler chicks with which the virus, chicken astrovirus, has been associated. Adult birds typically show no obvious clinical signs of infection, although some broiler breeder flocks have experienced slight egg drops. Substantial decreases in hatching are experienced over a two-week period, with an increase in mid-to-late embryo deaths, chicks too weak to hatch and pale, runted chicks with high mortality. Chicken astrovirus is an enteric virus, and strains are typically transmitted horizontally within flocks via the faecal-oral route; however, dead-in-shell embryos and weak, pale hatchlings indicate vertical transmission of the strains associated with white chick hatchery disease. Hatch levels are typically restored after two weeks when seroconversion of the hens to chicken astrovirus has occurred. Currently, there are no commercial vaccines available for the virus; therefore, the only means of protection is by good levels of biosecurity. This review aims to outline the current understanding regarding white chick hatchery disease in broiler chick flocks suffering from severe early mortality and increased embryo death in countries worldwide.

A Review of the Emerging White Chick Hatchery Disease

White chick hatchery disease is an emerging disease of broiler chicks with which the virus, chicken astrovirus, has been associated. Adult birds typically show no obvious clinical signs of infection, although some broiler breeder flocks have experienced slight egg drops. Substantial decreases in hatching are experienced over a two-week period, with an increase in mid-to-late embryo deaths, chicks too weak to hatch and pale, runted chicks with high mortality. Chicken astrovirus is an enteric virus, and strains are typically transmitted horizontally within flocks via the faecal–oral route; however, dead-in-shell embryos and weak, pale hatchlings indicate vertical transmission of the strains associated with white chick hatchery disease. Hatch levels are typically restored after two weeks when seroconversion of the hens to chicken astrovirus has occurred. Currently, there are no commercial vaccines available for the virus; therefore, the only means of protection is by good levels of biosecurity. This review aims to outline the current understanding regarding white chick hatchery disease in broiler chick flocks suffering from severe early mortality and increased embryo death in countries worldwide.

Norovirus GII and astrovirus in shellfish from a mangrove region in Cananéia, Brazil: molecular detection and characterization

In recent years, annual cases of gastroenteritis have been reported in the world at high rates, suggesting an association with the consumption of shellfish with enteric viruses in their tissues. Anthropic activities are considered a source of environmental pollution and the main responsible for contamination by pathogenic microorganisms in aquatic environments. The objective of this study was to evaluate, by RT-semi-nested PCR, the presence of astrovirus (AstV) and norovirus genogroup II (NoV GII) in mussels (Mytella falcata) and oysters (Crassostrea brasiliana) collected in two sites of the Lagunar Complex of Cananéia, State of São Paulo, Brazil. A total of 150 samples of mussels and oysters (75 samples each) were analyzed. AstV was not identified in any shellfish sample. NoV GII was detected in 21 samples (14%), 8 mussel samples (38%), and 13 oyster samples (62%). From the 21 positive samples, 16 were analyzed by nucleotide sequencing. The molecular characterization revealed that Brazilian samples were grouped into clades along with other sequences from Brazil, Japan, and Mexico. There was 93.8-100% amino acid sequence similarity among the samples in this study and > 94.9% when compared with the strains isolated from clinical cases in Brazil. The screening of shellfish for the presence of health-significant enteric viruses can help prevent outbreaks among consumers and contribute to the improvement of the estuarine environment.

Metagenomic sequencing determines complete infectious bronchitis virus (avian Gammacoronavirus) vaccine strain genomes and associated viromes in chicken clinical samples

Infectious bronchitis virus (IBV, genus Gammacoronavirus) causes an economically important and highly contagious disease in chicken. Random primed RNA sequencing was applied to two IBV positive clinical samples and one in ovo-passaged virus. The virome of a cloacal swab pool was dominated by IBV (82% of viral reads) allowing de novo assembly of a GI-13 lineage complete genome with 99.95% nucleotide identity to vaccine strain 793B. In addition, substantial read counts (16% of viral reads) allowed the assembly of a near-complete chicken astrovirus genome, while lower read counts identified the presence of chicken calicivirus and avian leucosis virus. Viral reads in a respiratory/intestinal tissue pool were distributed between IBV (22.53%), Sicinivirus (Picornaviridae, 24%), and avian leucosis virus (37.04%). A complete IBV genome with 99.95% nucleotide identity to vaccine strain H120 (lineage GI-1), as well as a near-complete avian leucosis virus genome and a partial Sicinivirus genome were assembled from the tissue sample data. Lower read counts identified chicken calicivirus, Avibirnavirus (infectious bursal disease virus, assembling to 98.85% of segment A and 69.66% of segment B closely related to D3976/1 from Germany, 2017) and avian orthoreovirus, while three avian orthoavulavirus 1 reads confirmed prior real-time RT-PCR result. IBV sequence variation analysis identified both fixed and minor frequency variations in the tissue sample compared to its in ovo-passaged virus. Metagenomic methods allow the determination of complete coronavirus genomes from clinical chicken samples while providing additional insights in RNA virus sequence diversity and coinfecting viruses potentially contributing to pathogenicity.

Isolation and characterization of a novel chicken astrovirus in China

Chicken astrovirus (CAstV) is associated with kidney disease and visceral gout, runting and stunting syndrome, and white chick hatchery disease, causing economic losses to the poultry industry worldwide. In this study, 55.6% of 36 clinical samples from Guangdong province in China were positive for CAstV, but negative for other common enteric viruses, including avian nephritis virus, infectious bronchitis virus, fowl adenovirus Group I, Newcastle disease virus, chicken parvovirus, reovirus, and rotavirus by PCRs and RT-PCRs. A CAstV strain, named GD202013, was isolated from Guangdong province in south China, and was identified by CAstV RT-PCR. A whole genome sequence analysis demonstrated that GD202013 shares 76.0 to 88.1% identity with 24 reference strains in GenBank. Phylogenetic analysis, based on whole genome and capsid protein, showed that GD202013 is more closely related to 2 US strains (GA2011/US/2011 and 4175/US/2011) belonging to subgroup Bii. Recombination analysis indicated that GD202013 is a recombinant strain formed by 3 strains: a major parent strain CkP5/US/2016, and 2 minor parent strains (GA2011/US/2011 and G059/PL/2014). In addition, the chicken embryo infection experiment demonstrated that GD202013 causes hatchability reduction, growth depression, and death of embryos. Macroscopic and microscopic lesions in the liver, kidney and small intestine were observed in the dead-in-shell embryos. This is the first report of the novel CAstV infection in China.

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.

Detection and characterization of chicken astrovirus associated with hatchery disease in commercial day-old turkeys in southwestern Nigeria

Infectious diseases are a major obstacle to profitable poultry production in Nigeria due to the mortality and severe economic losses they cause. In particular, they are a potent threat to attainment of the food security goals of government and national self-sufficiency in food production. Thus, there is a need for continuous monitoring of the nation’s poultry population for these diseases. As part of an ongoing investigation of enteric viruses associated with poor performance or hatchery diseases in commercial poultry in southwestern Nigeria, intestinal contents from 97 condemned or runted day-old commercial turkey poults were examined for turkey astroviruses, infectious bronchitis virus, chicken astrovirus (CAstV), avian nephritis virus, avian rotavirus, avian reovirus, fowl adenovirus, and chicken parvovirus by virus isolation, electron microscopy (EM), polymerase chain reaction (PCR), and reverse transcription PCR. The samples were collected from five commercial hatcheries and five farms located in southwestern Nigeria. While all samples tested negative for other viruses, CAstV was detected in the majority (83.5%) of the birds, although some pleomorphic virus-like particles with surface projections that appeared fringed or fimbriated were observed in five of the cell culture samples by EM. Phylogenetic analysis revealed these CAstV strains belonged to the Bi clade. These findings not only implicate CAstV as the major cause of hatchery condemnations in commercial turkeys in southwestern Nigeria but also highlight the need for experimental studies to further establish its role in this disease condition.

Serodetection of astroviruses in runted commercial broilers and turkeys in southwest Nigeria

Infections with divergent strains of astroviruses appear to be endemic in commercial poultry. In order to investigate enteric viruses associated with hatchery condemnations in Nigerian poultry, an indirect immunofluorescence test with CAstV-612- (Group A), CAstV-11672- (Group B) and ANV-1-infected cells was used to screen sera obtained from commercial broilers (n = 164) and turkeys (n = 97) in farms and hatcheries in southwest Nigeria. Of the 261 sera tested, 16 (6.1%) were positive for CAstV antibodies after immunofluorescent staining with CAstV-11672-infected cells. Thirteen (81.3%) of the positive sera were from broilers with three (18.7%) being from turkeys. Conversely, all tested sera were negative for CAstV-612 and ANV-1 antibodies. Since CAstV-11672, a group B CAstV is known to be antigenically and genetically distinct from CAstV-612 that belongs to group A, these findings reveal that the circulating serotype of CAstV in commercial broilers and turkeys in southwest Nigeria belongs to group B of CAstV. Education of veterinary personnel and poultry farmers about this emerging virus and its impact on commercial poultry in Nigeria, as well as continuous monitoring of chicken and turkey flocks for infections caused by it are therefore imperative in order to facilitate the implementation of effective prevention and control measures.

Molecular Characterization and Determination of Relative Cytokine Expression in Naturally Infected Day-Old Chicks with Chicken Astrovirus Associated to White Chick Syndrome

White chick syndrome (WCS) is an emergent disease that affects hatchability and hatched chicks, resulting in high mortality and economic losses, and is related to chicken astrovirus (CAstV). This syndrome has been reported in several countries worldwide, and groups A iii and B vi of CAstV have been determined; however, in Brazil, the virus has not been genotyped. The innate immunity of chicks affected by WCS or any CAstV is poorly understood and studied, and it is important to determine whether relative cytokine expression occurs during the early stages of the life of chicks. The aim of the present investigation is to detect and molecularly characterize CAstV associated with WCS, examine the macroscopic and microscopic lesions in the jejunum and spleen, and determine cytokine expression in the jejunum, liver, spleen and thymus of chicks naturally infected with WCS. To do so, we applied a pathological and molecular approach for CAstV detection and characterization, as well as the quantification of the relative mRNA expression of several cytokine genes. The phylogenetic analyses of the sequences obtained herein classified CAstV as uniquely belonging to group B iv, showing a high similarity of nucleotides (NT) (75.7-80.6%) and amino acids (AA) (84.2-89.9%) with the members of group B and a low similarity of NT (46.7-47.9%) and AA (37.8-38.9%) with the virus belonging in group A. CAstV was also detected and quantified in the serum, spleen, thymus and jejunum, the latter being the organ where CAstV had the highest viral concentration. However, this organ did not present any microscopical alterations. In contrast, we observed necrotic hepatitis in the liver of the affected subjects. On the other hand, we observed the activation of several T helper 1 (Th1)- and T helper 2 (Th2)-cytokines (IFN-γ, IL-2, IL-8, IL-12p40, IL-15, TGF-β4, TNF-SF-15 and t-BET), without being able to control the viral replication due to the high concentration of viral particles in some organs, principally in the gut. One possible role of these cytokines is contributing to the control of inflammation and cell protection of intestinal cells, principally during the early activation of immune responses. However, the fact that these responses are not mature enough to control the viral infection means that more studies need to be carried out to elucidate this topic.

A Cross Sectional Survey of Chicken Astroviruses Antibody in Broiler and Sonali (Cross-Bred) Chickens in Selected Areas in Bangladesh

Chicken astroviruses (CAstV) are enteric viruses of poultry causing gastroenteritis, malabsorption, gout and white chick disease commonly known as runting-stunting syndrome (RSS). It can affect the wide range of poultry birds, especially chicken, turkey and duck worldwide. To our best knowledge there is no published report on presence of antibodies against CAstV in Bangladesh. Therefore, the study aimed to detect the presence of CAstV antibodies in broilers and sonali chickens (a cross-bread) in Bangladesh through a cross-sectional survey. A total of 454 blood samples from 66 flocks of broiler (n=343) and sonali chickens (n=111) of different ages were obtained during 2017 from four districts. The birds were healthy but were not vaccinated against CAstV. The samples were tested for specific antibodies against CAstV Group B by using commercially available ELISA kit. Overall, 16.74% (76/454) samples and 34.84% (23/66) flocks were positive for CAstV antibodies. The seroprevalence of CAstV was significantly (p=0.001) higher in sonali chickens (36.96%) than broiler (10.20%), while it was significantly higher (p=0.001) in birds of Bogura district (36.94%) than the other three districts. Regarding the age groups, seroprevalence was insignificantly (p=0.192) higher in sonali chicken before laying age (45%) than during laying age (27.45%). Regarding the seasons, CAstV infection was prevalent significantly (p=0.001) higher in winter season. Thus, the present study indicated the presence of CAstV in poultry in Bangladesh, so further studies are required to find out the magnitude of the problem in the country.

White Chick Syndrome Associated with Chicken Astrovirus in Ontario, Canada

Sixty-four cases of white chick syndrome (WCS) in broiler breeders producing affected progeny were reported from seven hatcheries in Ontario, Canada, between 2009 and 2016, with 43 of those originating from two hatcheries owned by a single company. WCS cases were identified by the presence of typical chicks in the hatchery that were generally weak with pale to white down, enlarged abdomens, and occasionally brown wiry fluff on the dorsum of the neck. Affected embryos and chicks had characteristic gross and histologic liver lesions, and livers were positive for chicken astrovirus (CAstV) RNA by real-time reverse transcriptase PCR. Affected broiler breeder flocks experienced egg production drops of 0% to 21% and hatchability drops of 0% to 68.4%. The amino acid sequence of the region encoding the capsid gene of WCS viruses demonstrated all Ontario CAstV to be in Group B, Subgroup Bii.

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.

Enteric Virus Diversity Examined by Molecular Methods in Brazilian Poultry Flocks

Enteric viruses play an important role in the Brazilian poultry industry due to the economic impact of resulting low yields of broilers, layers, and breeders. The most common enteric viruses affecting commercial flocks in Brazil include Fowl Adenovirus of group I (FAdV-I), Chicken Parvovirus (ChPV), Chicken Astrovirus (CAstV), Avian Nephritis Virus (ANV), Infectious Bronchitis Virus (IBV), Avian Reovirus (AReo), and Avian Rotavirus (ARtV). The aim of this study was to identify single and multiple infections using data obtained from 270 samples from eleven Brazilian states, corresponding to the period between 2010 and 2017. This was accompanied by an analysis of the relationship between the age of birds, clinical signs, and geographical distribution, using Polymerase Chain Reaction (PCR) and Reverse Transcription-PCR (RT-PCR) techniques. Twenty-five profiles of virus combinations were detected. Single infections were encountered in 86.3% of samples, and multiple infections were present in the remaining 13.7%. Both single and multiple infections affected all kinds of commercial chickens with digestive problems, stunting syndrome, decreases in egg and meat production, increased mortality, and respiratory signs. FAdV-I, ChPV, CAstV, ANV, and ARtV were mostly detected in young broilers, in contrast with IBV, which was detected in hens from one to greater than 51 weeks of age. These results exhibit the complexity of enteric diseases and the still poorly understood role of each pathogen as a unique etiological agent.

Economic Impacts of White Chick Syndrome in Ontario, Canada

A cluster of 12 cases of White Chick Syndrome (WCS) in broiler breeder flocks producing affected progeny occurred from June to November 2015 in two broiler chicken hatcheries owned by a single company in Ontario, Canada. Cases were identified by the presence of typical chicks in the hatchery characterized by pale to white down, enlarged abdomens, and occasionally brown wiry fluff on the dorsum of the neck that were generally weak. Affected broiler breeder flocks experienced egg production drops of 0% to 15% and hatchability drops of 1.8% to 49.1%. Some flocks experienced increased feed clean-up duration and/or reduced hatching egg weight. The financial impacts of WCS to affected hatching egg producers averaged $5,912 CAD (US$4,417) per 10 000 hens and were as great as $16,788 CAD (US$12,544) per 10 000 hens. The financial impacts of WCS to the affected hatcheries averaged $1,723 CAD (US$1,287) per 10 000 broiler breeder hens and were as great as $4,096 (US$3,060) per 10 000 hens.

Propagation of Astrovirus VA1, a Neurotropic Human Astrovirus, in Cell Culture

Astrovirus VA1/HMO-C (VA1; mamastrovirus 9) is a recently discovered astrovirus genotype that is divergent from the classic human astroviruses (mamastrovirus 1). The gastrointestinal tract is presumed to be the primary site of infection and pathogenicity for astroviruses. However, VA1 has been independently detected in brain tissue of five cases of human encephalitis. Studies of the pathogenicity of VA1 are currently impossible because there are no reported cell culture systems or in vivo models that support VA1 infection. Here, we describe successful propagation of VA1 in multiple human cell lines. The initial inoculum, a filtered clinical stool sample from the index gastroenteritis case cluster that led to the discovery of VA1, was first passaged in Vero cells. Serial blind passage in Caco-2 cells yielded increasing copies of VA1 RNA, and multistep growth curves demonstrated a >100-fold increase in VA1 RNA 72 h after inoculation. The full-length genomic and subgenomic RNA strands were detected by Northern blotting, and crystalline lattices of viral particles of ∼26-nm diameter were observed by electron microscopy in infected Caco-2 cells. Unlike other human astrovirus cell culture systems, which require addition of exogenous trypsin for continued propagation, VA1 could be propagated equally well with or without the addition of trypsin. Furthermore, VA1 was sensitive to the type I interferon (IFN-I) response, as VA1 RNA levels were reduced by pretreatment of Caco-2 cells with IFN-β1a. The ability to propagate VA1 in cell culture will facilitate studies of the neurotropism and neuropathogenesis of VA1.IMPORTANCE Astroviruses are an emerging cause of central nervous system infections in mammals, and astrovirus VA1/HMO-C is the most prevalent astrovirus in cases of human encephalitis. This virus has not been previously propagated, preventing elucidation of the biology of this virus. We describe the first cell culture system for VA1, a key step necessary for the study of its ability to cause disease.

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.

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.