Partial characterization of an adenovirus-like virus isolated from broiler chickens with transmissible viral proventriculitis

A Retrospective Study of Transmissible Viral Proventriculitis in Broiler Chickens in California: 2000-18

Transmissible viral proventriculitis (TVP) is a disease of chickens, mostly in broilers of 2-8 wk of age. Chicken proventricular necrosis virus (CPNV), a birnavirus, is the etiologic agent. Characteristic gross lesions are enlargement, atony, and pallor of the proventriculus. Cases diagnosed in California between 2000 and 2018 (n = 477), originating from 93 different farms representing all major companies in the region, were analyzed. Frequency of cases varied widely between years, with no recognizable seasonality. The flocks were between 6 and 61 days of age; the average age was 34.0 days, and the median age was 35 days. In 166 cases, between 6.3% and 100% of the submitted birds had gross lesions in the proventriculus. The most common findings were enlarged or dilated proventriculi, thickened walls, and pale or mottled serosal appearance. Histopathologically, inflammation of the glands was the most frequent finding. Other lesions included necrosis, hyperplasia, or both conditions of the glandular epithelium; dilated glands; and occasionally fibrin deposition, fibrosis, and hemorrhages. Twenty-three proventriculi from six cases were tested by immunohistochemistry for the presence of CPNV antigen; 21 stained positive. In 209 cases, birds also had lesions in the bursa fabricii attributed to infectious bursal disease, but with no significant difference in the mean percentage of birds with gross lesions in the proventriculus between cases with or without lesions in the bursa fabricii. The results show that TVP is a common disease of broiler flocks in California and confirms that CPNV is the likely causative agent.

Retrospective and prospective studies of transmissible viral proventriculitis in broiler chickens in Brazil

We investigated the occurrence and pathologic findings of transmissible viral proventriculitis (TVP) associated with the chicken proventricular necrosis virus (CPNV) in commercial broiler chickens in southeastern Brazil. Seventy-three broilers, 25-36 d old, with a history of reduced growth, were referred to our veterinary pathology services from 2013 to 2017. Broilers were clinically examined, weighed, and euthanized for postmortem examination. Broilers of different ages with proventricular histologic lesions were positive for CPNV by RT-PCR; however, the intensity of histologic lesions was higher among 33-d-old animals, and viral RNA detection was more frequent among those that were 28 d old. In the proventriculi of 35 of 73 (48%) broilers, lesions were characterized by glandular epithelial necrosis, lymphoplasmacytic and histiocytic infiltrates, and metaplasia of glandular epithelium to ductal epithelium. In 24 of 73 (36%) broilers with histologic TVP-compatible lesions, CPNV was detected by RT-PCR for the viral protein 1 (VP1) gene. Broilers with histologic lesions were lighter than expected compared to the Cobb 500 standard weight. TVP has not been reported previously in broiler chickens in Brazil, to our knowledge.

Detection of transmissible viral proventriculitis and chicken proventricular necrosis virus in the UK

Increasing evidence suggests that a new birnavirus, named chicken proventricular necrosis virus (CPNV), is the aetiological agent of transmissible viral proventriculitis (TVP). The present work aimed to explore the possible presence of both TVP and CPNV in the UK. Forty-four chickens showing TVP-compatible gross lesions were classified into three groups based on the histological lesions: (i) TVP-affected chickens: lymphocytic infiltration and glandular necrosis (n = 15); (ii) lymphocytic proventriculitis (LP)-affected chickens: lymphocytic infiltration without necrosis (n = 18); and (iii) without proventriculitis (WP): no lymphocytic infiltration or necrosis (n = 11). Nine proventriculi (seven out of 15 corresponding to TVP, and two out of 11 corresponding to LP) were positive for CPNV by reverse transcriptase polymerase chain reaction (RT-PCR). These results support the previously suggested idea of CPNV as causative agent of TVP. Moreover, these data show that CPNV can also be detected in a number of cases with LP, which do not fulfil the histological TVP criteria. Phylogenetic analysis of partial sequences of gene VP1 showed that British CPNV sequences were closer to other European CPNV sequences and might constitute a different lineage from the American CPNV. TVP cases with negative CPNV PCR results may be due to chronic stages of the disease or to the reduced PCR sensitivity on formalin-fixed paraffin-embedded tissues. However, involvement of other agents in some of the cases cannot totally be ruled out. As far as the authors are aware, this is the first peer-reviewed report of TVP as well as of CPNV in the UK, and the first exploratory CPNV phylogenetic study.

Runting Stunting Syndrome Associated with Transmissible Viral Proventriculitis in Broiler Chickens

This report describes an outbreak of transmissible viral proventriculitis (TVP) associated with runting stunting syndrome (RSS) in 25- and 28-day-old broiler chickens, in which chicken proventricular necrosis virus (CNPV) was detected. Clinical signs included poor uniformity, very small birds for their age, increased mortality, and culling of smaller birds. Almost all birds necropsied exhibited moderate to severely enlarged proventriculi with diffusely pale serosa and thickened walls. Microscopically the proventriculi had lesions of degeneration and necrosis of the epithelium of the proventricular glands, accompanied by lymphocytic inflammation and glandular hyperplasia, with occasional formation of lymphoid nodules within the glandular parenchyma. Immunohistochemistry staining for CPNV was positive. Positive staining was generally found in the cytoplasm of glandular epithelial cells in the form of finely granular brown pigment. CPNV RNA was detected in the proventriculi by reverse transcriptase-PCR (RT-PCR). Other findings included mild enteritis in a few birds and small bursa of Fabricius. Direct electron microscopy performed on the intestinal samples was negative for viral particles. RT-PCR analysis of bursae was positive for infectious bursal disease virus (IBDV). In conclusion, this report associates TVP with RSS by describing an outbreak in which TVP attributable to CPNV was the most commonly found lesionin chickens with a clinical history compatible with RSS. Therefore, TVP should be considered as a possible differential diagnosis in cases compatible with RSS.

Identification of a picornavirus from chickens with transmissible viral proventriculitis using metagenomic analysis

Transmissible viral proventriculitis (TVP), an infectious disease in chickens, is responsible for economic losses in the commercial poultry industry. The major etiologic agent, however, is unknown. Using metagenomics, we compared the diversity of viruses present in proventriculus samples from flocks diagnosed with TVP to those of healthy flocks in South Korea between 2003 and 2012. Each sample had a mean of 21,538,726 sequence reads generated by high-throughput sequencing, with a mean length of 160 nt. Enrichment in viral sequences suggested that at least three viruses were present in each TVP sample. Although we could not determine a pathogen of TVP that matched the known morphology, picornavirus sequences were present in all five disease samples, suggesting an association with TVP. The five samples yielded 1,045-1,720 bp contigs with 81-84 % nt sequence identity to turkey hepatitis virus (accession number: HM751199). Whole-genome analysis indicated that the QIA01 strain of the novel picornavirus was similar to turkey hepatitis virus in the P2 and P3 regions (82.7 % nt and 95.5 % aa sequence identity), but different in the structural region and partial 2A peptides (56.2 % nt and 23.9 % aa sequence identity). In addition, the QIA01 virus was similar (87.0 % nt and 95.6 % aa sequence identity) to chicken megrivirus, recently detected in chickens with malabsorption syndrome in Hungary. Our results are useful for understanding the genetic diversity of avian picornaviruses and for classifying chicken megrivirus as a pathogen affecting the digestive tract of chickens.

Transmissible viral proventriculitis identified in broiler breeder and layer hens

Transmissible viral proventriculitis (TVP) is a recognized cause of production losses in broiler chickens, but previously it has not been reported in broiler breeder and commercial layer hens. In this study, TVP was identified in broiler breeder and commercial layer hens, 9-20 wk of age, based on histopathologic detection of characteristic microscopic lesions. Microscopic lesions in proventriculi of affected hens consisted of glandular epithelial necrosis, ductal epithelial hyperplasia, replacement of glandular epithelium with ductal epithelium, and diffuse interstitial lymphoid infiltration. Additionally, chicken proventricular necrosis virus (CPNV), a virus previously identified as the etiology of TVP in broiler chickens, was detected in proventriculi of TVP-affected hens using a reverse transcriptase-polymerase chain reaction procedure. The findings identify TVP as a potential cause of production losses in broiler breeder and commercial layer hens and provide additional evidence for etiologic involvement in TVP by CPNV.

Detection of chicken proventricular necrosis virus (R11/3 virus) in experimental and naturally occurring cases of transmissible viral proventriculitis with the use of a reverse transcriptase-PCR procedure

A reverse-transcriptase-polymerase-chain-reaction (RT-PCR) procedure was evaluated for detection of chicken proventricular necrosis virus (CPNV) in transmissible viral proventriculitis (TVP) -affected chickens. The RT-PCR procedure was compared with indirect immunofluorescence (IFA) and virus isolation for detection of CPNV in experimentally infected chickens. Microscopic lesions characteristic of TVP were detected on days 5-35 postexposure (PE) in CPNV-infected chickens; CPNV was detected by RT-PCR on days 3-14 PE in freshly collected proventriculi, and on days 1-14 PE in formalin-fixed paraffin-embedded (FFPE) proventriculi. CPNV was detected in proventriculi of experimentally infected chickens by IFA on days 3-10 PE, and by virus isolation on days 1-14 PE. With IFA used as a reference, sensitivity of the RT-PCR procedure with freshly collected and FFPE proventriculi was 88% and 100%, respectively; specificity was 83% and 86%, respectively. Proventriculi (FFPE) obtained from suspect TVP cases (n=19) were evaluated for presence of CPNV by RT-PCR and microscopic lesions consistentwith TVP. CPNV was detected by RT-PCR in proventriculi from 8/11 TVP (+) cases (24/36 tissue sections). TVP (+) cases were defined by microscopic lesions characteristic of TVP; CPNV was not detected in proventriculi (0/8 cases, 0/32 tissue sections) in the absence of these lesions. The association between presence of TVP-characteristic microscopic lesions and presence of CPNV was highly significant (P = 0.0014). These findings indicate the utility of the RT-PCR procedure for detection of CPNV and provide additional evidence for an etiologic role for this virus in TVP.

Physical and genomic characteristics identify chicken proventricular necrosis virus (R11/3 virus) as a novel birnavirus

Chicken proventricular necrosis virus (CPNV), isolate R11/3, previously was isolated from transmissible viral proventriculitis-affected chickens and was determined to be the likely etiology of this disease. CPNV was identified as a birnavirus on the basis of virion size and morphology (icosahedral, approximately 75 nm in diameter, nonenveloped); buoyant density in cesium chloride (1.32 g/ml); a genome comprising bisegmented, double-stranded RNA (approximately 3.8 and 3.4 kilobase pairs); and nucleotide sequence analyses. Nucleotide sequencing of CPNV RNA, segment B, identified a single large open reading frame that encodes a 903-amino acid protein. The 903-amino acid protein was identified as the putative VP1, the viral RNA-dependent RNA polymerase (RdRp), on the basis of sequence homologies with other birnavirus VP1 proteins. The CPNV VP1 possessed the unique permuted RdRp sequence motif arrangement characteristic of birnaviruses; however, phylogenetic analyses based on VP1 demonstrated that CPNV is deeply divergent from other birnaviruses.

Genotyping of Canadian isolates of fowl adenoviruses

Five hundred and seventy-three clinical submissions with fowl adenovirus (FAdV) involvement were examined to investigate the association of different types of FAdV with clinical problems related to FAdV infection. Samples were received from 2000 to 2006 and originated from seven Canadian provinces. Four hundred and eighty-seven submissions were inclusion body hepatitis (IBH) related, while 86 were not IBH related. Viruses isolated from 287 samples were further analysed by hexon gene loop 1 sequencing. Twenty-seven genotyped FAdVs were from Alberta, 20 from British Columbia, 16 from Manitoba, one from Nova Scotia, 82 from Ontario, 64 from Quebec and 77 from Saskatchewan. Two hundred and forty-six analysed FAdVs were from IBH cases, confirmed by liver histopathology, by FAdV isolation from the liver, or both. Based on hexon gene loop 1 sequencing analysis, FAdVs associated with IBH outbreaks were genetically related to FAdV02 (nine isolates, 99.4%), FAdV08a (100 isolates, 99.4% to 100%) and FAdV11 (98 isolates, 99.4% to 100%). Thirty-nine viruses were 93.7% to 94.3% identical to FAdV07 strain x11a, but the genetic and immunogenic properties of this strain require further investigation. In IBH cases, the co-infection rates for infectious bursal disease virus, infectious bronchitis virus, reoviruses and Newcastle disease virus were 3.47%, 1.04%, 6.25% and 0.69%, respectively. Forty-one genotyped FAdVs were from "non-IBH" cases. Viruses isolated from non-IBH cases consisted of 22 FAdV01, 15 FAdV11, two FAdV08a and one each of FAdV02 and FAdV04 viruses. Co-infection rates in non-IBH submissions were 50.00% for infectious bursal disease virus, 40.70% for infectious bronchitis virus, 27.91% for reoviruses and 1.16% for Newcastle disease virus.

Experimental reproduction of transmissible viral proventriculitis by infection of chickens with a novel adenovirus-like virus (isolate R11/3)

Transmissible viral proventriculitis (TVP) was experimentally reproduced in 2-wk-old specific-pathogen-free chickens and commercial broiler chickens by eyedrop inoculation of adenovirus-like virus (AdLV), isolate R1 1/3. No clinical signs and no weight gain depression were observed in chickens inoculated with AdLV (R11/3); however, gross and microscopic lesions characteristic of TVP were present in proventriculi of inoculated chickens. Proventriculi of AdLV (R11/3)-inoculated chickens were markedly enlarged, compared with sham-inoculated controls, by day 7 postinoculation (PI). Microscopic lesions in proventriculi of inoculated chickens were detected beginning on day 3 PI and consisted of degeneration and necrosis of glandular epithelium, ductal epithelial hyperplasia, replacement of glandular epithelium with ductal epithelium, and diffuse interstitial lymphoid infiltration; no microscopic lesions were observed in other tissues. AdLV (R11/3) antigens were detected in proventriculi by immunohistochemistry on days 3-10 PI in inoculated SPF chickens and days 3-21 PI in inoculated commercial broiler chickens; no viral antigens were detected in other tissues. AdLV (R11/3) was reisolated from proventriculi of inoculated SPF and commercial broiler chickens on days 5 and 7 PI. No virus, viral antigens, or lesions were detected in proventriculi collected from sham-inoculated chickens. These findings indicate an etiologic role for AdLV (R11/3) in TVP.