Studies on the pathogenicity of enterovirus-like viruses in chickens

Molecular characterization of chicken astrovirus and pathogenicity of a novel isolate in China

As an enteric virus, chicken astrovirus has been related to various kinds of diseases in chickens, including white chick syndrome, runting-stunting syndrome, severe kidney disease, urate deposits and visceral gout, generating economic losses in the poultry industry globally. The complete ORF2 gene of 31 CAstV isolates in six provinces of China during 2020-2022 was characterized and analyzed with the purpose of better understanding the molecular epidemiology and genetic diversity of CAstV field isolates. Phylogenetic analysis which was based on the complete ORF2 (capsid) amino acid sequence of 31 CAstV isolates and 57 reference strains indicated that 2 isolates belonged to subgroup Ai, 10 isolates belonged to subgroup Bi, 3 isolates belonged to subgroup Bii, 5 isolates belonged to subgroup Biii, 7 isolates belonged to subgroup Biv, 3 isolates belonged to subgroup Bv, and one isolate (JS202103) belonged to a new B subgroup. In addition, the novel CAstV strain JS202103 was successfully isolated in vitro, and its whole genome shared 76.9-94.3% identity with the 29 CAstV reference strains. JS202103 caused hatchability reduction, dead embryos, kidney disease and visceral gout in chicken embryos. Moreover, this is the also the initial study focusing on diverse CAstV strains including subgroups Biii, Biv, and Bv circulate in China. The current work contributes to improving our understanding of CAstV isolates in China, and it will also provide references for developing efficient measures to control this virus.

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.

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.

Transcriptome Sequencing of the Spleen Reveals Antiviral Response Genes in Chickens Infected with CAstV

Astrovirus infections pose a significant problem in the poultry industry, leading to multiple adverse effects such as a decreased egg production, breeding disorders, poor weight gain, and even increased mortality. The commonly observed chicken astrovirus (CAstV) was recently reported to be responsible for the "white chicks syndrome" associated with an increased embryo/chick mortality. CAstV-mediated pathogenesis in chickens occurs due to complex interactions between the infectious pathogen and the immune system. Many aspects of CAstV-chicken interactions remain unclear, and there is no information available regarding possible changes in gene expression in the chicken spleen in response to CAstV infection. We aim to investigate changes in gene expression triggered by CAstV infection. Ten 21-day-old SPF White Leghorn chickens were divided into two groups of five birds each. One group was inoculated with CAstV, and the other used as the negative control. At 4 days post infection, spleen samples were collected and immediately frozen at -70 °C for RNA isolation. We analyzed the isolated RNA, using RNA-seq to generate transcriptional profiles of the chickens' spleens and identify differentially expressed genes (DEGs). The RNA-seq findings were verified by quantitative reverse-transcription PCR (qRT-PCR). A total of 31,959 genes was identified in response to CAstV infection. Eventually, 45 DEGs (p-value < 0.05; log2 fold change > 1) were recognized in the spleen after CAstV infection (26 upregulated DEGs and 19 downregulated DEGs). qRT-PCR performed on four genes (IFIT5, OASL, RASD1, and DDX60) confirmed the RNA-seq results. The most differentially expressed genes encode putative IFN-induced CAstV restriction factors. Most DEGs were associated with the RIG-I-like signaling pathway or more generally with an innate antiviral response (upregulated: BLEC3, CMPK2, IFIT5, OASL, DDX60, and IFI6; downregulated: SPIK5, SELENOP, HSPA2, TMEM158, RASD1, and YWHAB). The study provides a global analysis of host transcriptional changes that occur during CAstV infection in vivo and proves that, in the spleen, CAstV infection in chickens predominantly affects the cell cycle and immune signaling.

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.

Small but mighty: old and new parvoviruses of veterinary significance

In line with the Latin expression "sed parva forti" meaning "small but mighty," the family Parvoviridae contains many of the smallest known viruses, some of which result in fatal or debilitating infections. In recent years, advances in metagenomic viral discovery techniques have dramatically increased the identification of novel parvoviruses in both diseased and healthy individuals. While some of these discoveries have solved etiologic mysteries of well-described diseases in animals, many of the newly discovered parvoviruses appear to cause mild or no disease, or disease associations remain to be established. With the increased use of animal parvoviruses as vectors for gene therapy and oncolytic treatments in humans, it becomes all the more important to understand the diversity, pathogenic potential, and evolution of this diverse family of viruses. In this review, we discuss parvoviruses infecting vertebrate animals, with a special focus on pathogens of veterinary significance and viruses discovered within the last four years.

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.

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.

A metagenomic comparison of endemic viruses from broiler chickens with runting-stunting syndrome and from normal birds

Runting-stunting syndrome (RSS) in broiler chickens is an enteric disease that causes significant economic losses to poultry producers worldwide due to elevated feed conversion ratios, decreased body weight during growth, and excessive culling. Of specific interest are the viral agents associated with RSS which have been difficult to fully characterize to date. Past research into the aetiology of RSS has implicated a wide variety of RNA and DNA viruses however, to date, no individual virus has been identified as the main agent of RSS and the current opinion is that it may be caused by a community of viruses, collectively known as the virome. This paper attempts to characterize the viral pathogens associated with 2–3-week-old RSS-affected and unaffected broiler chickens using next-generation sequencing and comparative metagenomics. Analysis of the viromes identified a total of 20 DNA and RNA viral families, along with 2 unidentified categories, comprised of 31 distinct viral genera and 7 unclassified genera. The most abundant viral families identified in this study were the Astroviridae, Caliciviridae, Picornaviridae, Parvoviridae, Coronaviridae, Siphoviridae, and Myoviridae. This study has identified historically significant viruses associated with the disease such as chicken astrovirus, avian nephritis virus, chicken parvovirus, and chicken calicivirus along with relatively novel viruses such as chicken megrivirus and sicinivirus 1 and will help expand the knowledge related to enteric disease in broiler chickens, provide insights into the viral constituents of a healthy avian gut, and identify a variety of enteric viruses and viral communities appropriate for further study.

Molecular detection of chicken parvovirus in broilers with enteric disorders presenting curving of duodenal loop, pancreatic atrophy, and mesenteritis

Enteric disorders are an important cause of economic losses in broiler chickens worldwide. Several agents have been associated with enteric problems, such as viruses, bacteria, and parasites. In this study, broiler chickens showing signs of enteric disorders were subjected to molecular diagnosis for several viral agents and also for pathological examination for elucidating this problem. Thus, the chickens were screened for avian nephritis virus (ANV), chicken astrovirus (CAstV), avian rotavirus (ArtV), avian reovirus (AReoV), infectious bronchitis virus (IBV), fowl adenovirus group I (FAdV-1), and chicken parvovirus (ChPV). Postmortem examinations revealed a curving of the duodenal loop (J-like appearance) and intestines filled with liquid and gaseous content. Histopathological analysis of the duodenal loop showed pancreatic atrophy, acute mesenteritis, and enteritis. PCR results showed that ChPV was the sole viral agent detected in samples with lesions such as the curved duodenal loop and pancreatic atrophy. Molecular characterization of the nucleotide and deduced amino acid sequences revealed a high similarity with other strains of ChPV from Brazil, Canada, United States, Europe, and Asia. These findings suggest an association between ChPV and the development of enteritis, pancreatitis, and pancreatic atrophy, which may lead to curling of the duodenal loop. Together, these alterations may disrupt the normal functioning of the digestive system, diminishing digestion and the absorption of dietary nutrients and consequently leading to reduced weight gain, flock impairment, dwarfism, and an elevated feed conversion rate.

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.

Circulation and phylogenetic relationship of chicken and turkey-origin astroviruses detected in domestic ducks (Anas platyrhynchos domesticus)

The natural occurrence of chicken and turkey-origin astroviruses in domestic ducks (Anas platyrhynchos domesticus) is described. Twenty-two duck flocks were covered by this research. The liver, spleen, kidney and intestines were sampled and tested by reverse-transcription polymerase chain reaction for the presence of avian nephritis virus (ANV), chicken astrovirus (CAstV), turkey astrovirus (TAstV)-1, TAstV-2 and duck astrovirus. The astrovirus infection was confirmed in multiple organ samples from 59.1% of tested flocks. CAstV was detected in one flock, TAstV-2 in three flocks and ANV in 10 flocks. The molecular and phylogenetic analysis of the small open reading frame (ORF) 1b fragment (130 nucleotides) of all chicken and turkey-origin astroviruses detected in ducks showed that ANV-sequence group was more distant from CastV, TAstV-1 and TAstV-2 sequences, which formed a separate, more related group. ANV sequences were divided into three subgroups, suggesting that several types of ANV were circulating in Croatian duck flocks. The comparison of the partial ORF 1b (254 nucleotides) duck ANV sequences with 21 ANVs detected in various avian species (chickens, turkeys, geese, guinea fowl and pigeons) revealed they shared the higher nucleotide (95.6 to 97.2%) and amino acid (98.8 to 100%) identity with two ANV-2-like sequences from chickens (GA-SEP-A451-05 and GA-CK-SEP ANV-364-2005). Phylogenetic neighbour-joining tree analysis based on the same nucleotide alignment, and performed using the Jukes-Cantor method, clustered the compared sequences into three groups. All analysed duck ANV sequences showed a close phylogenetic relationship with chicken-origin ANVs. Additional work is required to determine the significance and pathogenicity of chicken and turkey-origin astroviruses in domestic ducks.

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.

Avian Astroviruses

Avian astroviruses comprise a diverse group of viruses affecting many avian species and causing enteritis, hepatitis, and nephritis. To date, six different astroviruses have been identified in avian species based on the species of origin and viral genome characteristics: two turkey-origin astroviruses [Turkey Astrovirus type 1 (TAstV-1) and type 2 (TAstV-2)]; two chicken-origin astroviruses [Avian Nephritis Virus (ANV) and Chicken Astrovirus (CAstV)]; and two duck-origin astrovirus [Duck Astrovirus type 1 (DAstV-1) and type 2 (DAstV-2)]. ANV has also been detected in turkeys, ducklings, pigeons, and guinea fowl; and TAstrovirus-2-like viruses have also been found in guinea fowl. Astroviruses are commonly associated with enteric disease syndromes in poultry including runting-stunting syndrome of broilers (RSS), poult enteritis complex or syndrome (PEC or PES), poult enteritis mortality syndrome (PEMS), and enteritis in guinea fowl. The molecular characterization of the different avian astroviruses shows great genetic variability among each type, and this variability influences the ability to detect these viruses by molecular and serological techniques. In this chapter, we review the different aspects related to avian astroviruses, including molecular biology, pathogenesis, diagnosis, and control.

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.