Avian nephritis virus (ANV) on Brazilian chickens farms: circulating genotypes and intra-genotypic diversity

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

RESEARCH HIGHLIGHTS

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

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

BACKGROUND

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

RESULTS

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

CONCLUSIONS

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

Genome Sequences and Characterization of Chicken Astrovirus and Avian Nephritis Virus from Tanzanian Live Bird Markets

The enteric chicken astrovirus (CAstV) and avian nephritis virus (ANV) are the type species of the genus Avastrovirus (AAstV; Astroviridae family), capable of causing considerable production losses in poultry. Using next-generation sequencing of a cloacal swab from a backyard chicken in Tanzania, we assembled genome sequences of ANV and CAstV (6918 nt and 7318 nt in length, respectively, excluding poly(A) tails, which have a typical AAstV genome architecture (5'-UTR-ORF1a-ORF1b-ORF2-'3-UTR). They are most similar to strains ck/ANV/BR/RS/6R/15 (82.72%) and ck/CAstV/PL/G059/14 (82.23%), respectively. Phylogenetic and sequence analyses of the genomes and the three open reading frames (ORFs) grouped the Tanzanian ANV and CAstV strains with Eurasian ANV-5 and CAstV-Aii viruses, respectively. Compared to other AAstVs, the Tanzanian strains have numerous amino acid variations (substitutions, insertions and deletions) in the spike region of the capsid protein. Furthermore, CAstV-A has a 4018 nt recombinant fragment in the ORF1a/1b genomic region, predicted to be from Eurasian CAstV-Bi and Bvi parental strains. These data should inform future epidemiological studies and options for AAstV diagnostics and vaccines.

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

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

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.

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

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

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

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

Isolation of avian nephritis virus from chickens showing enteric disorders

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

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

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

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.

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

Aim:

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

Materials and Methods:

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

Results:

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

Conclusion:

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