Application of RT-PCR for the detection of avian reovirus contamination in avian viral vaccines

Avian reovirus: a furious and fast evolving pathogen

Avian reoviruses (ARVs) have a significant economic impact on the poultry industry, affecting commercial and backyard flocks. Spread feco-orally, or vertically, many do not cause morbidity, but pathogenic strains can contribute to several diseases, including tenosynovitis/arthritis, which is clinically the most significant. The last decade has seen a surge in cases in the US, and due to ongoing evolution, seven genotypic clusters have now been identified. Control efforts include strict biosecurity and vaccination with commercial and autogenous vaccines. Research priorities include improving understanding of pathogenesis and developing new vaccines guided by ongoing molecular and serologic surveillance.

Avian Reoviruses from Clinical Cases of Tenosynovitis: An Overview of Diagnostic Approaches and 10-Year Review of Isolations and Genetic Characterization

Reoviral-induced tenosynovitis/viral arthritis is an economically significant disease of poultry. Affected birds present with lameness, unilateral or bilateral swollen hock joints or shanks, and/or reluctance to move. In severe cases, rupture of the gastrocnemius or digital flexor tendons may occur, and significant culling may be necessary. Historically, vaccination with a combination of modified live and inactivated vaccines has successfully controlled disease. Proper vaccination reduced vertical transmission and provided maternal-derived antibodies to progeny to protect against disease, at an age when they were most susceptible. Starting in 2011-2012, an increased incidence of tenosynovitis/viral arthritis was observed in chickens and turkeys. In chickens, progeny from reovirus-vaccinated breeders were affected, suggesting commercial vaccines did not provide adequate protection against disease. In turkeys, clinical disease was primarily in males, although females can also be affected. The most significant signs were observed around 14-16 wks of age and include reluctance to move, lameness, and limping on one or both legs. The incidence of tenosynovitis/viral arthritis presently remains high. Reoviruses isolated from clinical cases are genetically and antigenically characterized as variants, meaning they are different from vaccine strains. Characterization of the field isolates reveals multiple new genotypes and serotypes that are significantly different from commercial vaccines and each other. In 2012, a single prevalent virus was isolated from a majority of the cases submitted to the Poultry Diagnostic and Research Center at the University of Georgia. Genetic characterization of the σC protein revealed the early isolates belonged to genetic cluster (GC) 5. Soon after the initial identification of the GC5 variant reovirus, many broiler companies incorporated these isolates from their farms into their autogenous vaccines and continue to do so today. The incidence of GC5 field isolates has decreased significantly, likely because of the widespread use of the isolates in autogenous vaccines. Unfortunately, variant reoviruses belonging to multiple GCs have emerged, despite inclusion of these isolates in autogenous vaccines. In this review, an overview of nomenclature, sample collection, and diagnostic testing will be covered, and a summary of variant reoviruses isolated from clinical cases of tenosynovitis/viral arthritis over the past 10 yrs will be provided.

Isolation and Molecular Characteristics of a Novel Recombinant Avian Orthoreovirus From Chickens in China

In recent years, the emergence of avian orthoreovirus (ARV) has caused significant losses to the poultry industry worldwide. In this study, a novel ARV isolate, designated as AHZJ19, was isolated and identified from domestic chicken with viral arthritis syndrome in China. AHZJ19 can cause typical syncytial cytopathic effect in the chicken hepatocellular carcinoma cell line, LMH. High-throughput sequencing using Illumina technology revealed that the genome size of AHZJ19 is about 23,230 bp, which codes 12 major proteins. Phylogenetic tree analysis found that AHZJ19 was possibly originated from a recombination among Hungarian strains, North American strains, and Chinese strains based on the sequences of the 12 proteins. Notably, the σC protein of AHZJ19 shared only about 50% homology with that of the vaccine strains S1133 and 1733, which also significantly differed from other reported Chinese ARV strains. The isolation and molecular characteristics of AHZJ19 provided novel insights into the molecular epidemiology of ARV and laid the foundation for developing efficient strategies for control of ARV in China.

Partial Molecular Characterization and Pathogenicity Study of an Avian Reovirus Causing Tenosynovitis in Commercial Broilers

This study describes the molecular characterization of avian reoviruses (ARVs) isolated during an outbreak in commercial chickens between 2015 and 2016. In addition, a pathogenicity study of a selected ARV strain isolated from a field case of viral tenosynovitis in commercial broiler chickens was performed. On the basis of phylogenetic analysis of a 1088-bp fragment of the ARV S1 gene, the investigated sequences were differentiated into five distinct genotypic clusters (GCs), namely GC1, GC2, GC3, GC4, and GC6. Specific-pathogen-free (SPF) and commercial broiler chickens were challenged with the GC1 genetic type MK247011, at 14 days of age via the interdigital toe web. No significant effects in body weight gain and feed conversion were detected in both chicken types. The Δ interdigital web thickness was most severe at 4 days postchallenge (DPC) in both the SPF and broiler subgroups. The inflammation in SPF birds was slightly more severe compared with broilers. Neither mortality nor clinical signs occurred in the infected groups for the duration of the experiment, despite the presence of significant microscopic lesions in challenged birds. Microscopic changes of tenosynovitis became evident at 3 DPC, with the highest incidence and severity detected at 14 and 21 DPC, respectively. Seroconversion against ARV occurred 3 wk postchallenge, and the microscopic lesions detected in tendon and heart sections were highly compatible with those described in the field. Increased severity of tenosynovitis and epicarditis lesions were noted in the ARV-challenged groups compared with the control groups. Although SPF and broiler chickens showed comparable responses to the challenge with an ARV genetic variant, detected lesions were subclinical, denoting the limitations of our challenge approach. The age selected in this experiment possibly influenced the course of the infection. Data from this study highlight the genotypic diversity of isolates in California, and the outcome of the pathogenicity study can be used as a basis to improve protocols for pathogenicity studies to characterize ARV variants causing clinical disease in the field.

First report of seroprevalence and genetic characterization of avian orthoreovirus in Egypt

Recently, the Egyptian broiler industry has experienced an increased incidence of avian reovirus (ARV) infections. However, to date, no studies have been carried out to investigate the epidemiologic status of ARV infections as well as the genetic characteristics of the currently circulating ARV strains. The present study estimates the seroprevalence of ARV infections in Alexandria, El-Behera, Giza, Kafr El-Sheikh, and Gharbia governorates, Egypt, during the period 2017-2018. A total of 150 serum samples from 15 unvaccinated broiler flocks with suspicious ARV infection were screened using a commercial enzyme-linked immunosorbent assay kit. All the tested flocks were found to be positive for ARV-specific antibodies, and the overall seropositivity rate was 80.6%. Meanwhile, 5 (33.3%) flocks were confirmed for the presence of ARV through a reverse transcription-polymerase chain reaction (RT-PCR) assay based on the σA-encoding gene. Phylogenetic analysis based on the nucleotide sequences of the σA-encoding gene revealed that the obtained ARV isolate, designated EGY1, was grouped in the S1113-like cluster of ARV and displayed 100% and 98.7% nucleotide identity with the Chinese MSO1 isolate and the S1133 vaccine strain, respectively. In addition, amino acid alignments with the S1133 vaccine strain revealed that the σA protein of the EGY1 isolate carried the substitutions G81S and A118V. In conclusion, the present study provides the evidence for a ubiquitous distribution of ARV infection in Egypt as well as represents a starting point for genetic characterization of the currently circulating ARV strains.

Genotypic Characterization of Emerging Avian Reovirus Genetic Variants in California

This study focuses on virus isolation of avian reoviruses from a tenosynovitis outbreak between September 2015 and June 2018, the molecular characterization of selected isolates based on partial S1 gene sequences, and the full genome characterization of seven isolates. A total of 265 reoviruses were detected and isolated, 83.3% from tendons and joints, 12.3% from the heart and 3.7% from intestines. Eighty five out of the 150 (56.6%) selected viruses for sequencing and characterization were successfully detected, amplified and sequenced. The characterized reoviruses grouped in six distinct genotypic clusters (GC1 to GC6). The most represented clusters were GC1 (51.8%) and GC6 (24.7%), followed by GC2 (12.9%) and GC4 (7.2%), and less frequent GC5 (2.4%) and GC3 (1.2%). A shift on cluster representation throughout time occurred. A reduction of GC1 and an increase of GC6 classified strains was noticed. The highest homologies to S1133 reovirus strain were detected in GC1 (~77%) while GC2 to GC6 homologies ranged between 58.5 and 54.1%. Over time these homologies have been maintained. Seven selected isolates were full genome sequenced. Results indicated that the L3, S1 and M2 genes, coding for proteins located in the virus capsid accounted for most of the variability of these viruses. The information generated in the present study helps the understanding of the epidemiology of reoviruses in California. In addition, provides insights on how other genes that are not commonly studied add variability to the reovirus genome.

Molecular identification of Mycoplasma synoviae from breeder chicken flock showing arthritis in Egypt

Aim:

Arthritis is one of the most economic problems facing poultry industry worldwide. The study was done to detect possible causes of arthritis in breeder chicken flock with emphasis on molecular identification of Mycoplasma synoviae (MS).

Materials and Methods:

This study was carried on chicken from broiler breeder flock of 57 weeks’ age in Dakahlia, Egypt, suffered from arthritis with frequently 5-7% decrease in egg production, reduced fertility, and hatchability. Forty blood samples were randomly collected from individual birds in sterile tubes and used for serum separation. Serum samples were tested using serum plate agglutination (SPA) test against colored antigens for Mycoplasma gallisepticum (MG), MS, and Salmonella gallinarum-pullorum (SGP). On the other hand, 24 joint samples were collected. Of those 24 samples, 12 joint samples were subjected to bacteriological examination, while the other 12 were utilized for molecular diagnosis by polymerase chain reaction (PCR) for MS and avian reovirus (ARV).

Results:

SPA test results revealed the presence of antibodies against MG, MS, and SGP in tested sera in rates of 14/40 (35%), 35/40 (87.5%), and 9/40 (22.5%), respectively. Furthermore, 19 bacterial isolates were recognized from joint samples and identified as five Staphylococcus spp., nine Escherichia coli, three SGP, one Citrobacter, and one Proteus. The identified Staphylococcal isolates were three coagulase-positive staphylococci (two Staphylococcus aureus and one Staphylococcus hyicus) and two coagulase-negative staphylococci (one Staphylococcus epidermidis and one Staphylococcus lentus), while E. coli isolate serotypes were 1 O11, 2 O55, 3 O78, 1 O124, 1 O125, and 1 untyped. PCR proved that 12/12 (100%) samples were positive for MS variable lipoprotein hemagglutinin A (vlhA) gene, while ARV was not diagnosed in any of the examined samples. Four amplified vlhA gene of MS isolates (named MS-2018D1, MS-2018D2, MS-2018D3, and MS-2018D4) was successfully sequenced.

Analysis of phylogenetic tree revealed the presence of 100% identity between each two sequenced isolates(isolates MS-2018D1 and MS-2018D4 and also isolates 2018D2 and MS-2018D3). However, the nucleotide similarity between four isolates was 88.6%. On the other hand, our field isolates MS-2018D1, MS-2018D4, MS-2018D2, and MS-2018D3 showed nucleotide identity with vaccine strain MS-H 98.4%, 98.4%, 88.1%, and 88.1%, respectively. Furthermore, the nucleotide similarities with field strains from Argentina ranged between 87.8% and 98.6%.

Conclusion:

Four field isolates of MS were identified in examined broiler breeder flock. A phylogenetic study of these isolates revealed the variation between isolated MS strains and vaccine strain. Therefore, further studies are required for evaluating the vaccine efficacy against the present field isolates of MS. In addition, application of MS immunization of breeder flocks is necessary for proper control of the disease.

Serologic response to porcine circovirus type 1 (PCV1) in infants vaccinated with the human rotavirus vaccine, Rotarix™: A retrospective laboratory analysis

In 2010, porcine circovirus type 1 (PCV1) material was unexpectedly detected in the oral live-attenuated human rotavirus (RV) vaccine, Rotarix™ (GSK Vaccines, Belgium). An initial study (NCT01511133) found no immunologic response against PCV1 in 40 vaccinated infants. As a follow-up, the current study (NCT02153333), searched for evidence of post-vaccination serologic response to PCV1 in a larger number of archived serum samples. Unlike the previous study, serum anti-PCV1 antibodies were assessed with an adapted Immuno Peroxidase Monolayer Assay (IPMA) using a Vero-adapted PCV1 strain. Samples from 596 infants who participated in clinical trials of the human RV vaccine were randomly selected and analyzed. The observed anti-PCV1 antibody seropositivity rate 1–2 months post-dose 2 was approximately 1% [90% Confidence Interval (CI): 0.3–2.6] (3/299 samples) in infants who received the human RV vaccine and 0.3% [90% CI: 0.0–1.6] (1/297 samples) in those who received placebo; the difference between the groups was −0.66 [90% CI: −2.16–0.60]. One subject in the vaccinated group was also seropositive before vaccination. Notably, the seropositivity rate observed in vaccinated subjects was below that observed during assay qualification in samples from unvaccinated subjects outside of this study (2.5%; 5/200 samples). No serious adverse events had been reported in any of the 4 subjects providing anti-PCV1 positive samples during the 31-day post-vaccination follow-up period in the original studies. In conclusion, the presence of PCV1 in the human RV vaccine is considered to be a manufacturing quality issue and does not appear to pose a safety risk to vaccinated infants.

Detection of Avian Reoviruses in Wild Birds in Poland

Introduction

The purpose of this study was to determine the occurrence of avian reovirus (ARV) infections in wild birds in Poland and attempt to propagate the selected ARV strains in chicken embryo kidney (CEK) cells or chicken SPF embryos.

Material and Methods

The study included 192 wild birds representing 32 species, collected between 2014 and 2016. A part of the S4 segment encoding the σNS protein of avian reoviruses (ARVs) isolated from different species of wild birds from that period was amplified.

Results

The presence of ARV was demonstrated in 58 (30.2%) wild birds belonging to nine orders. The isolated strains were propagated in chicken embryos by yolk sac inoculation, and CPE was induced in the infected CEK monolayer. Agar gel precipitation showed that two ARV isolates from rock pigeon and mute swan shared a common group-specific antigen with chicken reovirus S1133. Specific products of predicted size were found in two ARV isolates from the chicken embryo passage and 13 ARVs isolated from CEK cells.

Conclusion

The study indicates the high prevalence of ARV among wild birds in Poland and its possible transmission to farmed birds.

A Coronavirus Associated with Runting Stunting Syndrome in Broiler Chickens

Runting stunting syndrome (RSS) is a disease condition that affects broilers and causes impaired growth and poor feed conversion because of enteritis characterized by pale and distended small intestines with watery contents. The etiology of the disease is multifactorial, and a large variety of viral agents have been implicated. Here we describe the detection and isolation of an infectious bronchitis virus (IBV) -like coronavirus from the intestines of a flock of 60,000 14-day-old brown/red broiler chicks. The birds showed typical clinical signs of RSS including stunting and uneven growth. At necropsy, the small intestines were pale and distended with watery contents. Histopathology of the intestines revealed increased cellularity of the lamina propria, blunting of villi, and cystic changes in the crypts. Negative stain electron microscopy of the intestinal contents revealed coronavirus particles. Transmission electron microscopy of the intestine confirmed coronavirus in the cytoplasm of enterocytes. Using immunohistochemistry (IHC), IBV antigen was detected in the intestinal epithelial cells as well as in the proventriculus and pancreas. There were no lesions in the respiratory system, and no IBV antigen was detected in trachea, lung, air sac, conjunctiva, and cecal tonsils. A coronavirus was isolated from the intestine of chicken embryos but not from the allantoic sac inoculated with the intestinal contents of the broiler chicks. Sequencing of the S1 gene showed nucleic acid sequence identities of 93.8% to the corresponding region of IBV California 99 and of 85.7% to IBV Arkansas. Nucleic acid sequence identities to other IBV genotypes were lower. The histopathologic lesions in the intestines were reproduced after experimental infection of specific-pathogen-free chickens inoculated in the conjunctiva and nares. Five days after infection, six of nine investigated birds showed enteritis associated with IBV antigen as detected by IHC. In contrast to the field infection, birds in the experimental group showed clear respiratory signs and lesions in the upper respiratory tract. The results suggest a broader tissue tropism of this isolate, which might be related to the mutations in the S1 gene.

Whole genome alignment based one-step real-time RT-PCR for universal detection of avian orthoreoviruses of chicken, pheasant and turkey origins

Newly emerging avian orthoreovirus (ARV) variants have been continuously detected in Pennsylvania poultry since 2011. In this paper, we report our recent diagnostic assay development of one-step real-time RT-PCR (rRT-PCR) for the rapid and universal detection of all ARVs or reference strains of chicken, pheasant and turkey origins and six σC genotypes of the newly emerging field ARV variants in Pennsylvania (PA) poultry. Primers and probes for the rRT-PCR were designed from the conserved region of the M1 genome segment 5' end based on the whole-genome alignment of various ARV strains, including six field variants or novel strains obtained in PA poultry. The detection limit of the newly developed rRT-PCR for ARV was as low as 10 copies/reaction of viral RNA, and 10(0.50)-10(0.88) tissue culture infectious dose (TCID50)/100 μL of viruses. This new rRT-PCR detected all six σC genotypes from the 66 ARV field variant strains and reference strains tested in this study. There were no cross-reactions with other avian viruses. Reproducibility of the assay was confirmed by intra- and inter-assay tests with variability from 0.12% to 2.19%. Sensitivity and specificity of this new rRT-PCR for ARV were achieved at 100% and 88%, respectively, in comparison with virus isolation as the "gold standard" in testing poultry tissue specimen.

Chronological analysis of gross and histological lesions induced by field strains of fowl adenovirus serotypes 1, 8b and 11 in one-day-old chickens

Fowl adenoviruses (FAdVs) cause diseases in domestic chickens, including inclusion body hepatitis (IBH), with immunosuppression believed to play a role in their pathogenesis. To gain a better understanding of the pathogenesis and chronology of disease caused by FAdVs, the gross pathology, histopathology and dissemination of virus were examined at several different time points, after inoculation of one-day-old specific pathogen-free chickens with FAdV-1, FAdV-8b or FAdV-11 via the ocular route. FAdV-8b had a slightly greater virulence than FAdV-11, but both were primary pathogens. The presence and severity of hepatic lesions were used to define the three stages of the disease: incubation (1-3 days post-inoculation, PI), degeneration (4-7 days PI) and convalescence (14 days PI). Both viruses were detected in the liver, kidney, bursa, thymus and gizzard of most birds during the degenerative stage, and persisted in the gizzard into convalescence. The FAdV-1 isolate was found to be apathogenic, but virus was detected in the bursa and/or gizzard of several birds between 2 and 7 days PI. This is the first study examining the chronology of gross and microscopic lesions of pathogenic and apathogenic FAdVs in association with viral presence in multiple tissues. It was concluded that both FAdV-8b and FAdV-11 are primary pathogens, and that these strains may play a role in immunosuppression.

Genotyping and Classification of Tunisian Strains of Avian Reovirus using RT-PCR and RFLP Analysis

Since 1998, avian reovirus (ARV) infection has been detected in broiler and breeding chicken flocks in Tunisia. The genotype of avian reoviruses was established using simple and rapid approaches. Reverse transcription PCR (RT-PCR) on both sigma C (σC) and sigma B (σB)-encoding genes followed by restriction fragment length polymorphism (RFLP) analyses were used to better characterize Tunisian isolated strains. The RT-PCR amplified fragments of 738 and 540 bp for σC- and σB-encoding genes, respectively, of 15 ARV Tunisian strains. DNA fragments amplified from S 1133 vaccine and isolated strains were digested with different restrictions enzymes. RFLP on the σC gene indicated that the field isolates and the S 1133 vaccine strain have identical profiles when separately digested with TaqI, PstI, DdeI, and HincII. Considering the σB gene, RFLP profiles were identical with RsaI, BclI, DpnII, and NciI restriction enzymes for all the strains. However, using MseI and AciI enzymes, it was shown that all tested isolates could be clearly distinguished from the vaccine strain. ARV strains could be classified in groups with strong relatedness. Strain-typing based on cleavage site results are in agreement with ARV clustering based on nucleotide sequences of both the σC and σB genes. RT-PCR-RFLP provides a simple and a rapid approach for genotyping ARV isolates, especially when a large number of isolates are being studied. Additionally, this approach may also determine whether a new variant strain has been introduced into a flock or if a given virus strain is being spread from one flock to another.

One-step real-time reverse transcription-PCR for the detection of turkey reoviruses

During late 2010 and early 2011, an unusual problem of lameness and swollen hock joints in commercial turkeys was reported in the upper Midwest, which continues to this day. The disease caused substantial economic losses to turkey producers. Reovirus was isolated from tendons and joint fluids of lame turkeys submitted to the Minnesota Veterinary Diagnostic Laboratory. This study was undertaken to develop a TaqMan real-time reverse transcription-PCR (rRT-PCR) assay for the early detection of turkey reoviruses (both enteric and lameness strains). A primer probe set was designed from the conserved region of the S4 segment of the turkey reovirus genome. The newly developed rRT-PCR was specific for the detection of turkey reoviruses. The detection limit of this assay was 10 genome copies per reaction. For the TARV-MN4 strain of turkey arthritis reovirus, one 50% tissue culture infectious dose was equivalent to 11.6 +/- 0.2 genome copies. The highest coefficient of variation for intraexperimental and interexperimental variability was 0.08 and 0.06, respectively, indicating the reproducibility of the assay. This new test should be useful for the detection of turkey enteric and arthritis reoviruses.

The development and evaluation of cross-priming amplification for the detection of avian reovirus

AIMS

The aim of this study was to develop and evaluate cross-priming amplification (CPA) for the detection of avian reovirus (ARV).

METHODS AND RESULTS

Five specific primers were designed, on the basis of the σNS sequence of the S1133 ARV strain. Incubation temperature and primer concentrations were determined. The optimal incubation conditions in a water bath were 61.3°C for 45 min. No reverse transcription stage was required. The results were recorded under UV light illumination as a bright, greenish fluorescence in positive samples, and through the lack of this in negative controls and samples. Additionally, the gel electrophoresis performed during analysis showed the presence of ladder-like patterns, formed by hairpin-like CPA products. The developed CPA method was compared to reverse-transcription polymerase chain reaction (RT-PCR) and real-time RT-PCR. Sensitivity of CPA was estimated using seven dilutions of standard S1133 strain and reached 0.05 log10 TCID50 ml(-1). RT-PCR sensitivity reached 2.5 log10 TCID50 ml(-1) and was 1000 times lower than for CPA, whereas real-time RT-PCR sensitivity reached 1.5 log10 TCID50 ml(-1). Analysis of 32 RNAs extracted from field specimens showed the presence of an ARVσNS fragment in 4 (12.5%) samples. Interestingly, the positive samples originated from flocks affected by Marek's disease (MD) or fowl adenovirus (FadV). RT-PCR was unable to detect ARV, due to its lower sensitivity. However, the real-time RT-PCR that was conducted confirmed the CPA study.

CONCLUSIONS

CPA is a very sensitive and rapid method, which allows ARV detection using simple laboratory equipment.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report on the application of the CPA method for detection of ARV, using simple laboratory equipment.

An unusual case of concomitant infection with chicken astrovirus and group A avian rotavirus in broilers with a history of severe clinical signs

A molecular study of intestinal samples from 21 broiler flocks with a history of enteritis revealed that 23.8% and 14.3% were positive for chicken astrovirus (CAstV) and avian rotavirus (ARV), respectively. CAstV and group A ARV were simultaneously detected in only one broiler flock. Birds in this group developed the significant intestinal lesions characterized by frothy contents, paleness, and thin intestinal walls. In this report we present an unusual case of runting stunting syndrome (RSS) with a history of high mortality and growth retardation in broiler chickens. We also make the first identification of CAstV and group A ARV in broiler chickens in Korea.

An Optimized Polymerase Chain Reaction Assay to Identify Avian Virus Vaccine Contamination with Chicken Anemia Virus

The use of embryonating chicken eggs in preparation of avian virus vaccines is the principle cause for contamination with Chicken anemia virus (CAV). Identification of CAV in contaminated vaccines relies on the expensive, tedious, and time-consuming practice of virus isolation in lymphoblastoid cell lines. The experience of the last 2 decades indicates that polymerase chain reaction is extending to replace most of the classic methods for detection of infectious agents. In the present report, a simple, rapid, and accurate polymerase chain reaction method for detection of CAV in poultry vaccines is described. Oligonucleotide primers homologous to highly conserved sequences of the VP1 gene were used to amplify a fragment of 676 bp. The developed assay was specific for detecting CAV from different sources, with no cross reactivity with many avian viruses. No inter- and intra-assay variations were observed. The analytical sensitivity of the test was high enough to detect 5 TCID50 (50% tissue culture infective dose) of the virus per reaction; however, different factors related to the vaccine matrix showed considerable effects on the detection limit. In conclusion, this method may represent a suitable alternative to virus isolation for identification of CAV contamination of poultry virus vaccines.

Infection with a pathogenic turkey coronavirus isolate negatively affects growth performance and intestinal morphology of young turkey poults in Canada

Turkey coronavirus (TCoV) is an important viral pathogen causing diarrhoea of young turkey poults that is associated with sizeable economic losses for the turkey industry. Using a field isolate that was found to be free from turkey astrovirus and avian reovirus we were able to reproduce the clinical disease associated with TCoV. Clinical signs and weight gain of poults during experimental infections were compared with age-matched, uninfected controls. Poults infected at 2 days of age had 100% morbidity and 10% mortality, and birds infected at 28 days of age showed 75% morbidity and no mortality. Diarrhoea was consistently seen in infected poults at 2 to 3 days post infection (d.p.i.) with a duration of about 3 to 5 days. Mean body weights of birds infected at 2 or 28 days of age were significantly reduced compared with uninfected birds by 7 d.p.i. and remained significantly lower for the duration of the study. At 44 days of age, poults infected at 2 or 28 days of age weighed only 68.1% or 77.7%, respectively, compared with uninfected turkeys of the same age on the same diet, a mean difference in body weights of 683 or 477g, respectively. Infected birds had profound villus atrophy with some compensatory crypt hyperplasia at 5 to 7 d.p.i. Villus heights in the duodenum were significantly reduced at 7 d.p.i. We were able to reproduce enteric disease using only a pathogenic field isolate (MG10) of TCoV that negatively affected growth performance and intestinal morphology of young turkey poults.

Evaluation of the sensitivity of PCR methods for the detection of extraneous agents and comparison with in vivo testing

In this study the sensitivity of polymerase chain reaction (PCR) methods for the detection of Newcastle disease virus (NDV), avian reovirus (ARV), avian influenza virus (AIV) and avian infectious bronchitis virus (IBV) was compared to the sensitivity of the corresponding serological tests described in the European Pharmacopoeia (Ph. Eur.). For this purpose, serial 10-fold dilutions of the respective inactivated vaccines were prepared and groups of SPF chickens were vaccinated with a double dose of the vaccine dilutions. After a period of 21 days, the animals were revaccinated with a single dose. Two weeks later, serum samples from each animal were tested for antibodies using an Idexx enzyme linked immunosorbent assay (ELISA). In parallel, samples of the diluted vaccines were tested by PCR. It was found that the sensitivity of the four PCR tests is comparable to or even slightly better than that of the corresponding serological tests. Thus these PCR tests fulfil the sensitivity requirements of the Ph. Eur. and could be used as alternative tests for the detection of extraneous agents in final batches of inactivated vaccines.

Virus shedding and serum antibody responses during experimental turkey coronavirus infections in young turkey poults

The course of turkey coronavirus (TCoV) infection in young turkey poults was examined using a field isolate (TCoV-MG10) from a diarrhoeal disease outbreak on a commercial turkey farm in Ontario, Canada. Two-day-old and 28-day-old poults were inoculated orally with TCoV-MG10 to examine the effect of age on viral shedding and serum antibody responses to the virus. The presence of coronavirus particles measuring 105.8+/-21.8 nm in the cloacal contents was confirmed using transmission electron microscopy. The pattern of cloacal TCoV shedding was examined by reverse-transcription polymerase chain reaction amplification of the nucleocapsid gene fragment. TCoV serum antibody responses were assessed with two recently developed TCoV enzyme-linked immunosorbent assays that used TCoV nucleocapsid and S1 polypeptides as coating antigens. Poults were found equally susceptible to TCoV infection at 2 days of age and at 4 weeks of age, and turkeys of either age shed virus in their faeces starting as early as 1 day post-inoculation and up to 17 days post-inoculation. Poults infected at 2 days of age were immunologically protected against subsequent challenge at 20 days post-inoculation. The protection was associated with measurable serum antibody responses to both the nucleocapsid and S1 structural proteins of TCoV that were detectable as early as 1 week post-infection.

Seroprevalence of avian reovirus in egg-laying chicken flocks in China

In the present study, the epidemiologic status of avian reovirus (ARV) infections was investigated from egg-laying chicken flocks in China with an enzyme-linked immunosorbent assay (ELISA) kit. Because the chickens were not vaccinated against ARV, antibodies were attributed to the infection. Antibodies specific to ARV were found in more than 92% (542/587) of the average positivity and ranged from 30% to 100% in different chicken population. A virus, designated HB06, was isolated from flocks with suspicious ARV infections. Sequence analysis of the S1 gene revealed that strain HB06 was closely related with the most ARVs with less than 2% nucleotide divergence, and the homology was highest with the vaccine strain S1133, with a 98.97% nucleotide identity. The potential significance of vaccination against ARV in egg-laying chicken flocks in China is also discussed.

Development of a reliable assay protocol for identification of diseases (RAPID)-bioactive amplification with probing for detection of avian reovirus

Avian reovirus (ARV) causes several disease syndromes in poultry including arthritis, malabsorption syndrome and chronic respiratory disease that result in major economic losses. Early detection is very important for the control of the ARV-induced infections. This study was therefore aimed at developing a reliable assay protocol for identification of diseases (RAPID)-bioactive amplification with probing (BAP) assay for detection of ARV. This assay combines nested polymerase chain reaction (PCR) and magnetic bead-based DNA probing systems greatly increasing its sensitivity and specificity. Alignment of ARV S2 gene from different ARV genotypes and serotypes was done to find the highly conserved regions for primer and probe design. Two reverse transcription (RT)-PCR primer pairs, six nested PCR primer pairs, and one magnetic probe were tested to find the most specific ones for ARV detection. The optimal conditions for RT-PCR, nested PCR, and hybridization of magnetic probe were established. The optimal annealing temperatures for RT-PCR and nested PCR were 62.1 and 54.8 degrees C, respectively. The optimal hybridization temperature was 51.2 degrees C using hybridization buffer (5x SSC and 0.5% SDS). The sensitivity of the kit was 5 copies/microl of ARV genomic RNA. The kit was very specific as all negative controls failed to show any positive reactions. The kit shows good reproducibility with intra- and inter-assay coefficient of variation (CV) of 1.3 and 1.7%, respectively. In addition, different serotypes and genotypes of ARV were tested by RAPID-BAP assay to estimate the practicability of the kit in clinical samples. All of ARV serotypes and genotypes tested could be detected by this kit proving that the kit is suitable for clinical application.

Characterization of the σB-encoding genes of muscovy duck reovirus: σC–σB-ELISA for antibodies against duck reovirus in ducks

The sigmaB/sigmaC-encoding genes of muscovy duck reovirus (DRV) S12 strain were cloned, sequenced, and expressed in Escherichia coli. The sigmaC-encoding gene of DRV showed only 21-22% identity to that of avian reovirus (ARV) at both nucleotide and amino acid level. The sigmaB-encoding gene of DRV comprised 1163bp with one open reading frame (ORF). The ORF comprised 1104bp and encoded 367 amino acids with a predicted molecular mass of 40.44 kDa. A zinc-binding motif and a basic amino acid motif were found within the predicted amino acid sequence of sigmaB. The identities between the S12 and ARV were 59.3-64.0% and 60.9-62.5%, respectively, at the nucleotide and deduced amino acid levels. Phylogenetic analysis of the sigmaB-encoding gene sequence indicated that S12 separated as a distinct virus relative to other avian strains. The expressed sigmaB/sigmaC fusion proteins in E. coli could be detected, approximately 45 and 50kDa, respectively, by duck anti-reovirus polyclonal serum. In addition, an ELISA (sigmaB-sigmaC-ELISA) using the expressed sigmaB-sigmaC proteins as coating antigen for detection of antibodies to DRV in ducks was developed. In comparison with the virus neutralization test and agar gel immuno-diffusion test (AGID), the sigmaB-sigmaC-ELISA showed perfect specificity and sensitivity. The sigmaB-sigmaC-ELISA did not react with the antisera to other duck pathogens, implying that these two proteins were specific in recognition of DRV antibodies. Taken together, the results demonstrated that sigmaB-sigmaC-ELISA was a sensitive and accurate method for detecting antibodies to DRV.

Detection and identification of avian, duck, and goose reoviruses by RT-PCR: goose and duck reoviruses are part of the same genogroup in the genus Orthoreovirus

A reverse transcription-polymerase chain reaction (RT-PCR) procedure for the detection of avian, duck, and goose reovirus (ARV, DRV, and GRV) RNA from cell culture supernatant and clinical samples was established. Based on multiple sequence alignment, a pair of degenerate primers was selected and synthesized. The amplified, cloned, and sequenced 598-base-pair products from the sigmaA-encoding gene fragment from 16 isolates (ranging over 30 years) indicated that the primer regions were well conserved. The sensitivity of this method was determined to be 10(-2) PFU. The specificity of the RT-PCR method was determined by testing specimens containing avian influenza A viruses, Newcastle disease virus, and infectious bronchitis virus, all of which yielded negative results with no discernible background. The efficiency of the system for detection of ARV, DRV, and GRV directly in 71/83 clinical samples was confirmed. The nucleotide sequence analysis indicated that DRV and GRV isolated from China in different locales and years were closely related, showing 97.4-100% homology to each other, but with only 86.7-88.5% identity to DRV 89026. The nucleotide and amino acid sequence identities in the amplified sigmaA-encoding gene were 74.2-78.4% and 86.9-92.0%, respectively, between duck/goose and chicken species. Phylogenetic analysis indicated that GRV and DRV aggregated into the same specified genogroup within subgroup II of the genus Orthoreovirus and are more closely related to ARV than to Nelson Bay virus. Overall, this study developed a sensitive and specific technique for the identification ARV, DRV, and GRV, and sequencing analysis has enhanced our understanding of the evolutionary relationship between ARV, DRV, and GRV.

Development of a quantitative Light Cycler real-time RT-PCR for detection of avian reovirus

A robust, ultrasensitive, and accurate quantitative assay was developed for avian reovirus (ARV) with the Light Cycler SYBR Green-based real-time reverse transcription-PCR (real-time LC RT-PCR). The assay exhibited high specificity as all negative controls and other avian pathogens, such as Newcastle disease virus (NDV), infectious bronchitis virus (IBV), infectious bursal disease virus (IBDV), avian influenza virus (AIV), and mycoplasma synovia (MS), failed to show any positive detection. A minimum of 39 copies/microl of ARV genomic RNA could be detected by the assay. By dilution analysis, the real-time LC RT-PCR developed in this study was 3-log more sensitive than the conventional RT-PCR for the detection of ARV. The vaccine and field isolates of ARV were detected by the real-time LC RT-PCR. As a result of the high sensitivity and specificity of the assay with a relatively rapid and simple procedure, the real-time LC RT-PCR will be useful as a routine assay for the clinical diagnosis of ARV infection.