Studies on a new enterovirus‐like virus isolated from chickens

Genetic diversity and pathogenicity of novel chicken astrovirus in China

AbstractFive novel chicken astrovirus (CAstV) strains, designated ZDF, MHC, WSC, WSW and MHW, were successfully isolated from chickens with gout and were subjected to full genome sequencing characterization and tested for their pathogenic effects on Specific pathogen free (SPF) chicken embryos and chickens. The complete genomes of the 5 isolated strains were approximately 7436 nt to 7511 nt in length. Phylogenetic analysis revealed that strains ZDF and MHC were clustered in a clade with strains isolated in China and that the others were clustered with strains from other countries. Based on the amino acids of ORF2, strains MHW and WSW belonged to subgroup Ai, strain WSC belonged to Bii, and strains ZDF and MHC belonged to Bi. The pathogenicity of strains MHW, MHC and WSC belonging to different subgroups was studied. The results showed that the mortality of the chicken embryos was 100% when infected with any strain more than 10³ TCID₅₀, 35% in SPF chickens infected with strain WSC, 25% with MHC and 15% with MHW. The body weights of chickens infected and embryos infected with 0.2 mL 10 TCID₅₀ were significantly reduced after hatching. SPF chickens infected with any of the strains had similar lesions characterized by urate deposits on the epicardium and kidney and necrotic spots on the liver. This study identified the three kinds of genotypic CAstV prevalent in China, with high mortality in embryonated chicken eggs and leading to white chick syndrome, retarded growth and visceral gout in infected chicks.

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.

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.

Molecular characterisation and pathogenicity of novel Malaysian chicken astrovirus isolates

ABSTRACTChicken astrovirus (CAstV) has for over a decade been associated with runting stunting syndrome (RSS), severe kidney disease and visceral gout, and white chick syndrome (WCS). However, molecular characteristics and pathogenicity of the virus in day-old specific pathogen-free (SPF) chicks is scarce. This study focused on the characterisation of near-complete genome of three Malaysian CAstV isolates following virus propagation in specific-pathogen-free (SPF) embryonated chicken eggs (ECE) and pathogenicity in day-old SPF chicks. The three isolates demonstrated unique features including a point mutation in their intergenic regions and an additional stem-loop II-like motif (s2 m) in ORF-2. Pairwise sequence comparison and phylogenetic analysis of the ORF-2 amino acid of the three isolates revealed an identity share of 86 to 91% with group B CAstVs while forming a new subgroup in addition to the known four subgroups (Bi, Bii, Biii and Biv) that exhibit high identity of between 95 to 100% within the subgroups. In the pathogenicity study, birds in the infected and exposed sentinel groups exhibited lethargy and diarrhoea 3 days post-inoculation (dpi) that declined by 6 dpi and 20% growth retardation by 9 dpi. Mild lymphocytic aggregates in the duodenum, tubular degeneration and interstitial nephritis were observed in the intestines and kidneys, respectively, in both groups. In addition, the mean virus copy number of the cloacal swabs were log₁₀ 13.23 at 3 dpi and log₁₀ 9.04 at 6 dpi for the infected and exposed sentinels, respectively. The study suggests that the Malaysian isolates should be assigned to a new subgroup, Bv within group B CAstV.

A case of clubbed down syndrome in broilers

This study presents a case of clubbed down syndrome in conventional broilers. During the first week of life, severe growth retardation was observed in approximately 25% of the flock. The growth-retarded chicks weighed only 45 g and showed a typical feather disorder which was most apparent on their abdomen and was defined in literature as typical for clubbed down syndrome. Necropsies, histology, biochemical analysis of blood and liver samples, serology and different PCR tests were performed in broilers to assess the aetiology of the clinical signs that were present in the affected broiler farm. Because of the suspicion of a possible link with the broiler-breeder farms, different investigations including serology, PCR and feed analysis were also performed on these farms. The results suggest that an accidentally excessive amount of calcium and iron in the feed of broiler-breeders, 3 weeks prior to first clinical signs in broilers, led to the development of clubbed down in the offspring, because of a relative Zn-deficiency in broiler-breeders and an absolute Zn-deficiency in the hatching eggs that were produced during this period. This appeared to be a reversible process as no clinical signs were observed in younger offspring of these broiler-breeders after they had consumed more of the new batch of feed. A potential involvement of Astrovirus could not be completely ruled out. This study demonstrates the importance of correct mineral concentrations in broiler-breeder feed and the impact it can have on the development of the offspring.

Chicken Astrovirus (CAstV) Molecular Studies Reveal Evidence of Multiple Past Recombination Events in Sequences Originated from Clinical Samples of White Chick Syndrome (WCS) in Western Canada

In this study, we aimed to molecularly characterize 14 whole genome sequences of chicken astrovirus (CAstV) isolated from samples obtained from white chick syndrome (WCS) outbreaks in Western Canada during the period of 2014–2019. Genome sequence comparisons showed all these sequences correspond to the novel Biv group from which no confirmed representatives were published in GenBank. Molecular recombination analyses using recombination detection software (i.e., RDP5 and SimPlot) and phylogenetic analyses suggest multiple past recombination events in open reading frame (ORF)1a, ORF1b, and ORF2. Our findings suggest that recombination events and the accumulation of point mutations may have contributed to the substantial genetic variation observed in CAstV and evidenced by the current seven antigenic sub-clusters hitherto described. This is the first paper that describes recombination events in CAstV following analysis of complete CAstV sequences originated in Canada.

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.

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.

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.

Development of an indirect enzyme-linked immunosorbent assay test for detecting antibodies to chicken astrovirus in chicken sera

The development of an indirect enzyme-linked immunosorbent assay (ELISA) for the serological diagnosis of Group B chicken astrovirus (CAstV) infections is described. The test was based on the use of an affinity-purified capsid antigen, specific to CAstV isolate 11672, produced as a glutathione-S-transferase N-terminal fusion protein by a recombinant baculovirus. Strongly positive ELISA signals were elicited against experimentally produced antisera raised to CAstVs from Group B (subgroups i and ii) but were negative for antisera raised to a Group A CAstV. Using a panel of 240 selected serum samples, 99% agreement was observed when the results obtained by ELISA were compared to those from an indirect immunofluorescence test for CAstV 11672. The ELISA test was applied to 68 serum sets comprising 1864 samples, which were obtained from parent and grandparent flocks originating mainly in the UK. Of the 52 sets containing ELISA-positive samples, 24 sets had >75% samples positive and nine sets had <25% samples positive and were regarded as having high and low seropositivities, respectively. Of the 1864 serum samples tested 1090 (58.5%) were ELISA positive and of these, 234 sera (21.5%) produced strongly positive signals, whereas moderately positive and weakly positive signals were produced by 562 (51.5%) and 294 (27%) sera. When used for flock screening purposes, this ELISA test can be used to (i) investigate the occurrence of first-time CAstV infections of parent flocks during lay and the possible adverse effects caused by vertically transmitted CAstV infections on broiler hatchability and performance and (ii) diagnose Group B CAstV infections within specific pathogen free flocks.

Chicken astrovirus capsid proteins produced by recombinant baculoviruses: potential use for diagnosis and vaccination

Chicken astroviruses (CAstVs) have been characterized recently. Due to their relatively poor growth in cell culture, virus-specific antigens are not readily available for the development of diagnostic reagents and vaccines. For this purpose two capsid protein antigens, specified by the 11672 isolate of CAstV, were produced in insect cells following infection with recombinant baculoviruses. The GST-11672 capsid protein, a fusion protein comprising the capsid protein and glutathione-S-transferase (GST) as an N-terminal affinity tag, and the 11672 capsid protein alone were detected by western blotting as proteins of ~100 and 70 kDa, respectively. Immunization with the affinity-purified GST-11672 capsid protein produced a polyclonal rabbit antiserum, which reacted by indirect immunofluorescence with Group B CAstVs but which showed no reactivity with the Group A CAstV isolate, 612. When used as part of an immunoperoxidase-based immunohistochemical procedure, this rabbit antiserum facilitated the detection of CAstV antigen in formalin-fixed, paraffin-embedded kidney tissue at the sites of histopathology characteristic of nephritis. Although further evaluation with sera from commercial chickens is required, a prototype indirect antibody-detecting enzyme-linked immunosorbent assay (ELISA) based on affinity-purified GST-11672 capsid protein as coating antigen demonstrated considerable potential with low ELISA absorbance values being generated with sera from specific pathogen free (SPF) chickens, and high absorbance values being generated with serum samples from experimentally infected chickens. Immunization experiments of SPF chickens showed that, when administered as mixtures with oil adjuvant, crude cell lysates containing the GST-11672 capsid protein or the 11672 capsid protein elicited virus-specific antibody responses that were detectable by indirect immunofluorescence and by virus neutralization assays.

Role of chicken astrovirus as a causative agent of gout in commercial broilers in India

Several outbreaks of gout were reported in commercial broilers in India during 2011 and 2012, causing up to 40% mortality in the birds. Gross and histopathological observations confirmed gout. Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) analysis from kidney samples of gout-affected birds indicated the presence of chicken astrovirus (CAstV) in 41.7% of cases and a mixed infection of CAstV and avian nephritis virus (ANV) in 36.4% of cases. CAstV isolated from gout-affected kidneys by inoculating embryonated specific pathogen free (SPF) eggs showed dwarfing in embryos and a cytopathic effect in chicken embryo kidney cells. Inoculation of 1-day-old SPF and broiler chicks with CAstVs caused gout and mortality between 4 and 10 days post inoculation. Virus isolation and qRT-PCR analysis showed the presence of only CAstV in inoculated chicks. Sequence analysis of capsid genes indicated a major group of Indian CAstVs that displayed 92.0 to 99.2% intergroup amino acid identity and 83.9 to 90.4% identity with subgroup Bi CAstVs of UK origin. We designated this group Indian Bi. Analysis of the partial polymerase amino acid sequences of our isolates indicated two groups of CAstVs (Indian 1 and 2) that displayed 90.2 to 95.5% amino acid identity between them. We thus report for the first time that, in addition to infectious bronchitis virus and ANV, CAstVs are a causative agent of gout.

Capsid protein sequence diversity of chicken astrovirus

The complete capsid gene sequences of 24 chicken astroviruses (CAstVs), collected in the UK, Germany, the Netherlands and South Africa from the 1980s to 2008, were determined and compared with that of a US CAstV (UGA-2006). Pairwise comparisons and phylogenetic analysis demonstrated the existence of two major capsid groups, designated A and B, which shared 38 to 40% amino acid identity. CAstVs from groups A and B shared capsid protein identities ranging from 26 to 38% with other avian astroviruses. The group A CAstVs comprised three subgroups, which displayed inter-subgroup identities ranging from 77 to 82%, while group B comprised two clearly separated subgroups, Bi and Bii, which displayed intra-subgroup identities of 97 to 99% and 94 to 99%, respectively, and shared inter-subgroup identities of 84 to 85%. Phylogenetic analyses performed with contiguous open reading frame 1b (polymerase) and open reading frame 2 (capsid) CAstV sequences showed that CAstVs from capsid subgroup Bi had polymerase genes that differed from those possessed by CAstVs belonging to group A and subgroup Bii. The N-terminal capsid regions (residues 1 to 415) were more conserved than the C-terminal regions, with the C-terminal regions of the subgroup Bi and Bii CAstVs sharing 76 to 78% amino acid identity, while the C-terminal regions of the A subgroups displayed identities less than 75%. CAstVs representative of both capsid groups and more than one subgroup were detected within the same broiler flock. The high level of capsid sequence diversity observed in this study has important implications for both the control and diagnosis of CAstV infections.

Astrovirus infections in humans and animals - molecular biology, genetic diversity, and interspecies transmissions

Astroviruses are small, non-enveloped, positive sense, single-stranded RNA viruses first identified in 1975 in children suffering from diarrhea and then described in a wide variety of animals. To date, the list of animal species susceptible to astrovirus infection has expanded to 22 animal species or families, including domestic, synantropic and wild animals, avian, and mammalian species in the terrestrial and aquatic environments. Astrovirus infections are considered among the most common cause of gastroenteritis in children, second only to rotavirus infections, but in animals their association with enteric diseases is not well documented, with the exception of turkey and mink astrovirus infection. Genetic variability has been described in almost all astrovirus species sufficiently examined infecting mammals and birds; however, antigenic variability has been demonstrated for human astroviruses but is far less investigated in animal viruses. Interestingly, there is an increasing evidence of recombination events occurring in astroviruses, which contributes to increase the genetic variability of this group of viruses. A wide variety of species infected, the evident virus genetic diversity and the occurrence of recombination events indicate or imply either cross-species transmission and subsequent virus adaptation to new hosts or the co-infection of the same host with different astroviruses. This can also favor the emergence of novel astroviruses infecting animals or with a zoonotic potential. After more than 30 years from their first description in humans, there are many exciting streams of research to be explored and intriguing questions that remain to be answered about the relatively under-studied Astroviridae family. In the present work, we will review the existing knowledge concerning astrovirus infections in humans and animals, with particular focus on the molecular biology, interspecies transmission and zoonotic potential of this group of viruses.

Detection and characterization of a new astrovirus in chicken and turkeys with enteric and locomotion disorders

In the present paper, we report the unexpected discovery of a new virus in samples from chicken and turkey flocks with clinical disorders such as tenosynovitis, enteric problems, or runting and/or stunting-like conditions. Since 1987, several virus isolation attempts on samples from these flocks resulted in the same macroscopic characteristic lesions in embryonated specific pathogen free eggs, being mortality with bright-red discolouration of legs and wing-tips, a swollen dark-red liver and oedema. Initial work suggested the presence of an agent with characteristics of a non-enveloped RNA virus. Further work, which is described in this paper, showed that the isolated strains formed a new group of avian nephritis viruses, which is genetically and antigenically distinct from known avian astroviruses. Inoculation of a representative strain (isolate 19) of this new group of avian nephritis viruses, provisionally named avian nephritis virus-3, in specific pathogen free layer chicks resulted in diarrhoea, runting and stunting, and even mortality.

Development and evaluation of real-time TaqMan® RT-PCR assays for the detection of avian nephritis virus and chicken astrovirus in chickens

The development and preliminary evaluations of two TaqMan®-based, real-time reverse transcriptase-polymerase chain reaction (rRT-PCR) assays for the quantitative detection of avian nephritis virus (ANV) and chicken astrovirus (CAstV) RNAs are described. The assays used amplicons generated from the 3' untranslated region of the ANV genome and a conserved region of CAstV open reading frame 1b including its junction with open reading frame 2. High virus RNA levels (>10(5.99) viral copies) were detected for ANV and CAstV in 81% and 67% gut content samples from growth-retarded broiler flocks. Results from longitudinal surveys of two broiler flocks showed that ANV and CAstV RNAs were detected in most gut content and kidney samples collected at all time points from day 0 to day 35, with RNA levels of both astroviruses being higher in the gut contents than in the kidneys, and with the ANV RNA levels being greater than those of CAstV especially at early (days 7 and 14) time points. When the results obtained for the days 4/5 time-point samples from four broiler flocks with varying growth performances were compared, the two better-performing flocks had 100-fold to 1000-fold less ANV viral copies than the flocks that performed least well. Application of the rRT-PCR tests to samples collected from broiler chicks, which were experimentally infected with a crude gut content inoculum, demonstrated that ANV RNA could be detected in gut content and kidney samples at levels similar to those found at corresponding time points in longitudinal survey samples, whereas CAstV RNA was detected at lower levels than in the longitudinal survey samples, especially in kidney samples.

Detection of chicken astrovirus by reverse transcriptase-polymerase chain reaction

The development of a reverse transcriptase-polymerase chain reaction (RT-PCR) test for detecting chicken astroviruses (CAstV) is described. Primers, which amplified a fragment of 510 base pairs, were located in conserved regions within the ORF 1b (RNA polymerase) gene. The limit of detection of the test was estimated to be approximately 60 viral copies using a 10-fold dilution series of in vitro transcribed RNA. Positive signals were produced with representative CAstV samples, some of which were not detected by a previously described RT-PCR test for detecting CAstV, but other avian astroviruses including avian nephritis virus and duck hepatitis virus types 2 and 3 tested negative. When applied to gut content samples and swabs from UK and German broiler flocks with growth problems, CAstVs were detected by RT-PCR in 50/52 (96%) samples. CAstVs were detected in between 30% and 72.5% pooled gut content samples from longitudinal surveys of four broiler flocks displaying below-average performances. Whereas all day 0 samples were CAstV-negative, high detection rates were observed when the surveyed birds were aged 4, 5 and 7 days. Based on partial ORF 1b sequences, a phylogenetic analysis of 20 CAstVs indicated the existence of two groups. One group comprised four CAstV isolates, including FP3 and 11672, and two field CAstVs, which shared >94% nucleotide identity. The remaining 14 CAstVs, comprising the first characterized CAstV and 612 isolates and 12 field CAstVs, shared 85% to 99% nucleotide identity and displayed 76% to 79% nucleotide identity with the 11672-like and FP3-like CAstVs.

A seroprevalence investigation of chicken astrovirus infections

Two genetically different isolates of chicken astrovirus (CAstV), named CAstV612 and CAstV11672, which share low levels of antigenic relatedness in cross-indirect immunofluorescence (IIF) tests, have been identified recently. In the present study, separate IIF tests for detecting antibodies to the CAstV612 and CAstV11672 isolates have been used to determine the seroprevalences of CAstV infections in four generations of flocks involved in broiler chicken production. CAstV antibodies were detected in 78% (73% CAstV612; 46% CAstV11672) of serum samples from UK broiler flocks and in all 10 flocks tested, indicating that infections were very common. Twenty-three (96%) out of 24 and 26 (93%) out of 28 broiler parent flocks, aged 23 to 26 weeks from three UK organizations, were positive for antibody to CAstV612 and CAstV11672, respectively. Of 718 samples tested from these parent flocks, 415 (53%) were positive for either CAstV612 or CAstV11672 antibody. CAstV infections were also widespread in parent flocks, with screening of pooled serum samples showing that antibodies to both CAstVs were detected in flocks from seven other UK poultry organizations and in flocks from eight other European countries. The seropositivities for CAstVs were substantially less in grandparent (28%) and great grandparent (21%) flocks. Overall, higher seropositivities were observed for CAstV612 than for CAstV11672 in broiler, parent, grandparent and great-grandparent flocks. A limited study of 99 sera from 10 turkey breeder flocks showed low-level seropositivities for CAstV612 (9%) and CAstV11672 (2%), indicating that turkeys were infected with CAstVs or antigenically related viruses.

Studies on the pathogenicity of enterovirus-like viruses in chickens

FP3 and 612 viruses are enterovirus-like viruses. Antibody to these viruses is widespread in chicken flocks, but nothing is known about their pathogenicity. Seven experiments were carried out to investigate the tissue tropism and associated pathology of these novel fowl enterovirus-like viruses and to compare these with the effects of the previously studied enterovirus-like viruses, ELV-1 and avian nephritis (ANV). ANV is now classified as an astrovirus. Preliminary experiments were carried out with FP3 virus, 612 virus and ELV-1 to determine the distribution of viral antigen. Each preliminary experiment was followed by a larger experiment that included more birds and in which a greater range of tissues was studied. It was shown that all four viruses studied replicated in the intestine and had differing abilities to spread to other tissues. Histological changes were present in most antigen-positive tissues but they were usually relatively mild. ELV-1 was associated with the most severe intestinal lesions, followed by FP3 virus. FP3 virus produced lesions in the kidney that were marginally more severe than those caused by the G-4260 strain of ANV. FP3 virus also caused pancreatic lesions. The 612 virus was found to be only mildly pathogenic in specific pathogen free chickens.

Molecular characterization and typing of chicken and turkey astroviruses circulating in the United States: implications for diagnostics

Avian astroviruses were detected by reverse transcriptase and polymerase chain reaction in intestinal contents collected from commercial chickens and turkeys from throughout the United States from 2003 through 2005. Astroviruses were detected in birds from both healthy and poorly performing flocks with or without enteric disease. Phylogenetic analysis was performed with sequence data from the polymerase (ORF-1b) genes of 41 turkey-origin astroviruses and 23 chicken-origin astroviruses. All currently available avian astrovirus sequence data and selected mammalian astrovirus sequence data were included in the analysis. Four groups of avian astroviruses were observed by phylogenetic analysis: turkey astrovirus type 1 (TAstV-1)-like viruses, turkey astrovirus type 2 (TAstV-2)-like viruses, both detected in turkeys; avian nephritis virus (ANV)-like viruses, detected in both chickens and turkeys; and a novel group of chicken-origin astroviruses (CAstV). Among these four groups, amino acid identity was between 50.1% and 73.8%, and was a maximum of 49.4% for all avian isolates when compared with the mammalian astroviruses. There were multiple phylogenetic subgroups within the TAstV-2, ANV, and CAstV groups based on 9% nucleotide sequence divergence. Phylogenetic analysis revealed no clear assortment by geographic region or isolation date. Furthermore, no correlation was observed between the detection of a particular astrovirus and the presence of enteric disease or poor performance. Based on these data, a revision of the present taxonomic classification for avian astroviruses within the genus Avastrovirus is warranted.