Detection of reticuloendotheliosis virus as a contaminant of fowl pox vaccines

Poultry Vaccine Technology Platforms

The different technology platforms used to make poultry vaccines are reviewed. Vaccines based on classical technologies are either live attenuated or inactivated vaccines. Genetic engineering is applied to design by deletion, mutation, insertion, or chimerization, genetically modified target microorganisms that are used either as live or inactivated vaccines. Other vaccine platforms are based on one or a few genes of the target pathogen agent coding for proteins that can induce a protective immune response ("protective genes"). These genes can be expressed in vitro to produce subunit vaccines. Alternatively, vectors carrying these genes in their genome or nucleic acid-based vaccines will induce protection by in vivo expression of these genes in the vaccinated host. Properties of these different types of vaccines, including advantages and limitations, are reviewed, focusing mainly on vaccines targeting viral diseases and on technologies that succeeded in market authorization.

Research Note: Simultaneous detection of infectious laryngotracheitis virus, fowlpox virus, and reticuloendotheliosis virus in chicken specimens

Infectious laryngotracheitis (ILT), fowlpox (FP), and reticuloendotheliosis are important poultry diseases caused by gallid herpesvirus 1 (ILTV), fowlpox virus (FWPV), and reticuloendotheliosis virus (REV), respectively. Coinfections with ILTV and FWPV occur naturally in chickens, and FP in its more virulent wet form is characterized by diphtheritic lesions and easily confused with ILT. Moreover, the insertion of only partial REV-LTR or a nearly full-length REV into the FWPV genome, located between the ORF 201 and ORF 203, has increased recently in wild-type field FWPV isolates. Therefore, it is critical to detect ILTV, FWPV, REV-integrated FWPV, and REV early and accurately. In this study, we successfully developed a multiplex PCR assay for the simultaneous detection of ILTV, FWPV, REV-integrated FWPV, and REV, and the detection limits was 1 × 5⁴ copies/tube. When used to test clinical samples, the results of the multiplex PCR were in 100% agreement with singleplex PCRs and sequencing. This new multiplex PCR is a simple, rapid, sensitive, specific, and cost-effective method for detection of 4 viruses in clinical specimens.

Molecular Detection of Reticuloendotheliosis Virus 5' Long Terminal Repeat Integration in the Genome of Avipoxvirus Field Strains from Different Avian Species in Egypt

Avipoxviruses (APVs) are among the most complex viruses that infect a wide range of birds’ species. The infection by APVs is often associated with breathing and swallowing difficulties, reduced growth, decreased egg production, and high mortalities in domestic poultry. In the present study, 200 cutaneous nodular samples were collected from different avian species (chicken, pigeon, turkey, and canary) suspected to be infected with APVs from Dakahlia Governorate, Egypt. Pooled samples (n = 40) were prepared and inoculated in embryonated chicken eggs (ECEs). APVs were then identified by polymerase chain reaction (PCR) and sequence analysis of the APV P4b gene. Furthermore, the forty strains of APVs were screened for the presence of reticuloendotheliosis virus (REV)-5′LTR in their genomes. Interestingly, the phylogenic tree of the APV P4b gene was separated into 2 clades: clade 1, in which our fowlpox virus (FWPV), turkeypox virus (TKPV), and canarypox virus (CNPV) isolates were grouped, along with reference FWPVs and TKPVs retrieved from GenBank, whereas, in clade2, the pigeonpox virus (PGPV) isolate was grouped with PGPVs retrieved from GenBank. Likewise, REV-5′LTR was amplified from 30 strains isolated from chicken, turkey, and canary, while PGPV strains were free from REV-5′LTR integration. To the best of our knowledge, this study involved the detection and characterization of REV-5′LTR insertions in the APVs field isolates in Egypt for the first time. Given the above information, further future research seems recommended to understand the impact of the resulting REV-5′LTR insertions on the pathogenesis, virulence, and inadequate vaccine protection against APVs.

An atypical clinicopathological manifestation of fowlpox virus associated with reticuloendotheliosis virus in commercial laying hen flocks in Brazil

Fowlpox (FP) is a common epitheliotropic disease in chickens that is usually controlled by live attenuated vaccines. However, there have been some reports of outbreaks of FP in recent years, even in vaccinated flocks, presenting as atypical lesions and feathering abnormalities in chickens. These findings can be associated with fowlpox virus (FPV) with the reticuloendotheliosis virus (REV) integrated into its genome. In the present study, outbreaks of atypical FP were explored in vaccinated commercial laying hen flocks to determine the nature of the causative agent by histopathologic and molecular approaches. FPV and REV were detected and classified into subclade A1 of the genus Avipoxvirus and subtype 3 of REV (REV3), respectively. Additionally, heterogeneous populations of FPV with partial (containing only a remnant long terminal repeat-LTR) or total (all functional genes) integration of REV were identified by heterologous PCRs and detected considering reference integration sites. These results indicate the mechanism of chimeric genome FPV-REV associated with outbreaks and atypical clinicopathological manifestations in commercial laying hens for the first time in Brazil and in South America. In addition, this study demonstrates the emergence of REV integrated in the FPV genome in Brazilian chicken flocks.

Avian leukosis virus contamination in live vaccines: A retrospective investigation in China

Avian leukosis (AL) is one of the most pandemic immunosuppressive diseases and has been widely spread between 2006 and 2009 in China. The contamination of avian leukosis virus (ALV) in attenuated vaccine is considered as one of the possible transmission routes of this disease. Based on a retrospective survey of 918 batches of attenuated vaccine produced before 2010, three of them were identified as ALV-positive and corresponding ALV strains were successfully isolated from a live Fowlpox virus vaccine, a live Newcastle disease virus vaccine and a live Infectious Bursal Disease virus vaccine, respectively, and whole-genome sequencing showed that these three isolates shared the highest homology with ALV-A wild strains isolated in China (97.7%) over the same period, and the phylogenetic analysis based on their gp85 genes further confirmed that they belong to subgroup A. Meanwhile, although these three ALV-A strains isolated from contaminated vaccines shared a close genetic relationship, their U3 region of genome have a relatively low identity, suggesting that these three strains may have different sources. This study reminds us once again that the possibility of ALV infecting chickens through contaminated live vaccines, requiring us to carry out stricter exogenous virus monitoring in vaccines.

TRIM62 From Chicken as a Negative Regulator of Reticuloendotheliosis Virus Replication

Emerging evidence suggests that the tripartite motif containing 62 (TRIM62), a member of the TRIM family, plays an important role in antiviral processes. The objective of the study was to explore the role of TRIM62 in reticuloendotheliosis virus (REV) infection and its potential molecular mechanism. We first demonstrated that the REV infection affected the TRIM62 expression first upregulated and then downregulated in CEF cells. Next, we evaluated the effect of TRIM62 on viral replication. Overexpression of TRIM62 decreased REV replication. On the contrary, silencing of endogenously expressed TRIM62 increased viral replication. Then, to explore the necessity of domains in TRIM62's negative regulation on viral replication, we transfected CEF cells with TRIM62 domain deletion mutants. Deletion domain partially abolished TRIM62's antiviral activity. The effect of SPRY domain deletion was the highest and that of coiled-coil was the lowest. Further, we identified 18 proteins that coimmunoprecipitated and interacted with TRIM62 by immunocoprecipitation and mass spectrometry analysis. Strikingly, among which, both Ras-related protein Rab-5b (RAB5B) and Arp2/3 complex 34-kDa subunit (ARPC2) were involved in actin cytoskeletal pathway. Altogether, these results strongly suggest that chicken TRIM62 provides host defense against viral infection, and all domains are required for its action. RAB5B and ARPC2 may play important roles in its negative regulation processes.

First report on molecular characterization and phylogenetic analysis of Reticuloendotheliosis virus in Sudan

The reticuloendotheliosis virus (REV) group of retroviruses infects a wide range of avian species, including chickens, turkeys, ducks, geese, quail, and prairie chickens. The infection can result in immunosuppression, runting syndrome, high mortality, acute reticular cell neoplasia, or T- and/or B-cell lymphoma. One PCR positive chicken spleen sample obtained in a previous study in addition to one Marek's disease and three fowl pox (FP) vaccine samples were investigated in this study. A PCR assay was performed to detect the presence of REV provirus DNA in these samples. The results indicated the contamination of fowl pox virus and Marek's disease vaccines with REV. In addition, detection of integration of REV inside the genome of fowl pox vaccine was confirmed using primers corresponding to the FPV DNA regions flanking the REV integration site. Alignments of two sequences, one from the spleen tissue and the other from contaminated FP vaccine with REV, with other REV (env) gene sequences obtained from GenBank indicated their high similarity. Furthermore, phylogenetic analysis indicated that the partial part of (env) gene of our two isolates was closely related to variants from India, USA, Taiwan, and China. These results confirmed the contamination of commercial fowl pox and Marek's disease vaccines used in Sudan with REV. Phylogenetic analysis indicated that the partial part of (env) gene sequences from Sudan was closely related to variants from India, USA, Taiwan, and China.

Detection and Molecular Characterization of a Natural Coinfection of Marek's Disease Virus and Reticuloendotheliosis Virus in Brazilian Backyard Chicken Flock

Marek’s disease virus (MDV) and the reticuloendotheliosis virus (REV) are two of the primary oncogenic viruses that significantly affect chickens. In Brazil, there have been no previous published reports on the presence of field REV alone or in coinfection. This retrospective study analyzes samples from a case of lymphoproliferative lesions from a backyard chicken flock. MDV and REV were detected by PCR and classified as MDV1 and REV3, respectively, through sequencing and phylogenetic analysis based on the glycoprotein B (gB) genes for MDV and the polymerase (pol) and envelope (env) genes for REV. Real-time PCR reactions were performed for MDV to rule out the presence of the Rispens vaccine strain. This is the first report of the presence of REV in coinfection with a MDV clinical case in Brazil and the first molecular characterization of REV in South America. This study highlights the importance of molecular diagnosis for REV and MDV in poultry. In addition, this study highlights the distribution of these two viruses worldwide and the latent risk of them solely or in coinfection to this part of the world.

A high frequency of Gallid herpesvirus-2 co-infection with Reticuloendotheliosis virusis associated with high tumor rates in Chinese chicken farms

The prevalence of Marek's disease (MD) caused by Gallid herpesvirus-2 (GaHV-2) has been increasing in chickens in China despite universal vaccination. Among the possible reasons for this trend, of Reticuloendotheliosis virus (REV) contamination in vaccines could lead to co-infection and reduce the vaccine efficacy. Here, we report the epidemiological findings of our continuous surveillance of MD, and an examination of the effects of REV and/or GaHV-2 co-infection. A total of 1230 samples were collected between 2011 and 2015 from 305 flocks covering many of the chicken-raising regions of China. Among these, 606 samples were determined to be GaHV-2-positive, 13.0% of which were found to be co-infected with REV from 18.8% of the flocks. One GaHV-2 strain (HS/1412), a REV strain (HS/1412R), and a GaHV-2 and REV-co-infected strain (HS/1412 GR) were isolated from different chickens of a GaHV-2 and REV co-infected flock. Pathogenicity tests showed that HS/1412 and HS/1412 GR caused disease in all chickens and that HS/1412R induced morbidity in 84.6% of the infected chickens. HS/1412 GR induced 100% mortality and 76.9% tumor formation, which were significantly higher frequencies than those observed with strain HS/1412 (38.5% and 15.4%, respectively) and HS/1412R (0% and 0%). These results indicate that co-infection with GaHV-2 and REV might explain the persistent, sporadic outbreaks of neoplastic disease in some commercial flocks, resulting in a significant economic burden to the poultry industry of China.

Changes in apoptosis, proliferation and T lymphocyte subtype on thymic cells of SPF chickens infected with reticuloendotheliosis virus

Reticuloendotheliosis virus (REV), an avian retrovirus is able to infect a variety of birds and can cause immunosuppression. The aim of this study was to investigate the relationship of thymic lymphocytes apoptosis, proliferation and T cell subtype with immunosuppression. In this study, a hundred and twenty one-day old SPF chickens were randomly divided into control groups (group C) and a REV infection groups (group I). The chickens of group I received intraperitoneal injections of REV with 10^4.62/0.1 ml TCID₅₀. On day 14, 21, 28 and 35 post-inoculation, the chickens of C group and I group were sacrificed by cardiac puncture blood collection, and the thymic lymphocytes was sterile collected. The proliferation ability of lymphocytes was tested by Cell Counting Kit-8. Flow cytometry was performed to detect apoptosis, cell cycle stage and the change in T cell subtype. The RNA genome copy numbers of REV virus were detected using real-time PCR. Real-time PCR and western blotting were performed to analyze the expression of CyclinD1 and Bcl-2. Our results showed that REV genome copy number steadily declined, the proliferation potential of thymic lymphocytes was inhibited, lymphocytes apoptosed, the ratio of CD4+/CD8+ decreased and the expression of CyclinD1 and Bcl-2 were firstly inhibited, then rapidly recovered. Thus, immunosuppression lead by REV is closely related to the change of T cell subtype, apoptosis, and proliferation of thymic lymphocytes.

Molecular detection of integrated reticuloendothelial virus genes in fowlpox virus field isolates and live vaccines of poultry

Two field isolates (FWPV-W1 and FWPV-W2) obtained from unvaccinated backyard poultry chickens and four commercial live vaccines (FWPV-G, FWPV-V, FWPV-B and FWPV-H) of fowlpox virus origin were isolated on chorio-allantoic membrane (CAM) of embryonated chicken eggs. The CAM tissues infected with FWPV-W1, FWPVW2, FWPV-G, FWPV-V, FWPV-B and FWPV-H individually were subjected to DNA isolation. The isolated DNA was tested for the presence of P4b gene by PCR to confirm FWPV. Then, each of the field isolates and commercial vaccines were screened for presence of reticuloendothelial virus envelope (REV-env) gene and long terminal repeat (LTR) region by PCR. FWPV-W1 isolate was positive for REV-env gene (807 bp) and REV-LTR region (370 bp), which confirmed presence of near full-length REV integration in its genome. Whereas, FWPV-W2 isolate was positive for LTR region and negative for REV-env gene. This suggested that full-length REV is not present in all FWPV field isolates. All the four commercial live vaccines, were negative for REV-env gene. This showed that full-length REV is absent in these commercial vaccines, ensuring safety of the usage of these vaccines in India. However, the commercial vaccines were positive for REV-LTR region, which does not affect the vaccine safety.

Assessment on reticuloendotheliosis virus infection in specific-pathogen-free chickens based on detection of yolk antibody

Reticuloendotheliosis virus (REV) is the most frequent exogenous virus that contaminates attenuated vaccines. Therefore, it is extremely important to select REV-free specific-pathogen-free (SPF) chicken embryos. Generally, REV infection is assessed by detecting REV antibodies in SPF chickens. This present study seeks to evaluate REV infection by replacing serum antibody detection with yolk antibody detection. A cohort of 40 nineteen-week-old SPF chickens were artificially inoculated with REV, with 32 SPF chickens raised in another isolation environment served as a blank control. Eggs and serum from 23-week-old chickens were sampled, and yolks were diluted separately to ratios of 1:150, 1:200, 1:300 and 1:400, which were detected together with serum. We found that the yolk antibody detection findings at a dilution of 1:300 had the highest coincidence rate compared with that based on serum antibody measurements. At a dilution ratio of 1:300 for yolk antibody, 72 chickens were continuously observed for 10 weeks from 25- to 34-weeks-old. Our findings were based on serum antibody or yolk antibody detection, and the evaluation results were completely consistent. Therefore, all serum antibody-positive chickens were yolk antibody-positive, and vice versa. Accordingly, vaccine producers can estimate REV cleanliness in a poultry farm by sampling yolk antibody titers.

Synergetic pathogenicity of Newcastle disease vaccines LaSota strain and contaminated chicken infectious anemia virus

Newcastle disease virus (NDV)-attenuated vaccine has been widely used to prevent ND in poultry flocks, while many reports also mentioned the exogenous virus contamination in attenuated vaccines, which might be the reason for the widespread of some contagious diseases. Recently, the chicken infectious anemia virus (CIAV) contamination in the NDV-attenuated vaccine was also found in China, though no systemic study has studied the pathogenicity or infection mechanism of this special transmission route. Accordingly, simulation experiments were launched using CIAV isolated from a contaminated NDV-attenuated vaccine. Results showed that using NDV-attenuated vaccine contaminated with CIAV could cause CIA in chickens with obvious symptoms, including anemia, hemorrhage, lymphoatrophy, and growth retardation, while the synergistic reaction of CIAV and LaSota prompted their multiplication in vivo and disturbed the production of antibodies against each other. And CIAV could significantly reduce the NDV antibody titers and decrease the protective effectiveness. This study showed the synergetic pathogenicity of CIAV and LaSota strain after using contaminated NDV-attenuated vaccine, helping us to understand how the CIAV causes infection and induces severe diseases with a relatively low dose through the mouth, as well as reminding us that the damage of an attenuated vaccine contaminated with CIAV even in extremely low dose is not insignificant.

Avian Reticuloendotheliosis in Chickens - An Update on Disease Occurrence and Clinical Course

Avian reticuloendotheliosis (RE) represents an important immunosuppressive disease of poultry. The occurrence of RE in both chickens and turkeys has an immunosuppressive effect and may lead to vaccination failures. Avian reticuloendotheliosis virus (REV) is widely distributed in different kinds of birds, causing subclinical infections. Another important issue adhering to this disease is contamination of vaccines against fowl pox (FP) and Marek’s disease (MD) with REV. The capability of REV to integrate into the genome of other larger DNA viruses complicates its diagnosis and prevention. There are no efficient vaccines against RE nor treatment, which also complicates how to limit its impact on poultry farming. This paper reviews the current state of knowledge of this important immunosuppressive agent of poultry emphasising the importance of this problem in terms of diagnosis of RE.

Avian leukosis virus subgroup - J as a contaminant in live commercially available poultry vaccines distributed in Nigeria

Globally, vaccines are used to prevent and control the menace of infectious diseases in livestock with some reported to be inadvertently contaminated with extraneous agents (EAs). With the aim of screening and characterizing for some selected EAs, 44 live viral poultry vaccines were randomly selected based on availability. The vaccines comprised 14 manufacturers in 10 different countries including Nigeria were screened by Polymerase Chain Reaction. In 9% (4/44) of the vaccines, contamination with only avian leukosis virus (ALV) subgroup J (ALV-J) was recorded. Other exogenous ALV subgroups, chicken infectious anemia and infectious laryngotracheitis viruses were absent. The EAs was found in infectious bursal disease (n = 1), Fowlpox (n = 2) and Mareks disease (n = 1) vaccines. Phylogenetic analysis of the ALV-J env gene showed clustering with contemporary group I and II. The result underscores the importance of screening vaccines to avoid the introduction and spread of EAs that could pose a threat to poultry production.

Development and evaluation of a droplet digital PCR assay for the detection of fowl adenovirus serotypes 4 and 10 in attenuated vaccines

In recent years, there has been an increase in reported cases of fowl adenovirus serotype 4 (FAdV-4) in chickens in China. The use of live attenuated vaccines contaminated with FAdV-4 has been proved to be one of the important causes of massive outbreaks of hydropericardium syndrome. To detect the contamination with FAdV-4 in attenuated vaccines more promptly and accurately, a droplet digital PCR (ddPCR) assay was developed for the rapid detection of FAdV-4 and FAdV-10. The ability of this assay to detect FAdV-4 contamination in attenuated Newcastle disease virus vaccines was assessed in comparison to a quantitative real-time PCR (qPCR) and a conventional PCR assay. The findings indicated that the ddPCR assay could detect FAdV-4 contamination at 0.1 EID₅₀/1,000 feathers, while the qPCR could detect FAdV-4 contamination at 1 EID₅₀/1,000 feathers with identical genomic targets, which was 1,000-fold more sensitive than conventional PCR detection with a sensitivity of 10² EID₅₀/1,000 feathers. The ddPCR assay also showed high specificity for FAdV-4/10 and no positive signals were detected for other FAdVs. Consequently, the intuitive and rapid results were especially suitable for the detection of FAdV-4 contamination in vaccines. In this study, a ddPCR assay was developed to effectively detect and quantify low-dose FAdV-4 contamination, providing a new method for rapid detection of FAdV-4 contamination in various samples, especially vaccines.

Newcastle disease virus-attenuated vaccine LaSota played a key role in the pathogenicity of contaminated exogenous virus

Newcastle disease virus (NDV)-attenuated vaccine has been widely used since the 1950s and made great progress in preventing and controlling Newcastle disease. However, many reports mention exogenous virus contamination in attenuated vaccines, while co-contamination with fowl adenovirus (FAdV) and chicken infectious anaemia virus (CIAV) in the NDV-attenuated vaccine also emerged in China recently, which proved to be an important reason for the outbreaks of inclusion body hepatitis–hydropericardium syndrome in some flocks. It is amazing that exogenous virus contamination at extremely low doses still infected chickens and induced severe disease; thus, we speculated that there must be some interaction between the NDV-attenuated vaccine and the contaminated exogenous viruses within. Accordingly, simulation experiments were launched using FAdV and CIAV isolated from the abovementioned vaccine. The results showed that the pathogenicity of FAdV and CIAV co-infection through the contaminated vaccine was significantly higher than that of direct oral infection, while the synergistic reaction of these viruses and LaSota prompted their multiplication in vivo and disturbed the production of antibodies against each other. This study showed the interactions of FAdV, CIAV and LaSota after using contaminated NDV-attenuated vaccine, helping us to understand how the contaminated exogenous viruses cause infection and induce severe disease at a relatively low dose through the oral route.

Newcastle disease virus-attenuated vaccine co-contaminated with fowl adenovirus and chicken infectious anemia virus results in inclusion body hepatitis-hydropericardium syndrome in poultry

Inclusion body hepatitis-hydropericardium syndrome (IBH-HPS) induced by fowl adenovirus type 4 (FAdV-4) has caused huge economic losses to the poultry industry of China, but the source of infection for different flocks, especially flocks with high biological safety conditions, has remained unclear. This study tested the pathogenicity of Newcastle disease virus (NDV)-attenuated vaccine from a large-scale poultry farm in China where IBH-HPS had appeared with high mortality. Analysis revealed that the NDV-attenuated vaccine in use from the abovementioned poultry farm was simultaneously contaminated with FAdV-4 and chicken infectious anemia virus (CIAV). The FAdV and CIAV isolated from the vaccine were purified for the artificial preparation of an NDV-attenuated vaccine singly contaminated with FAdV or CIAV, or simultaneously contaminated with both of them. Seven-day-old specific pathogen-free chicks were inoculated with the artificially prepared contaminated vaccines and tested for corresponding indices. The experiments showed that no hydropericardium syndrome (HPS) and corresponding death occurred after administering the NDV-attenuated vaccine singly contaminated with FAdV or CIAV, but a mortality of 75% with IBH-HPS was commonly found in birds after administering the NDV-attenuated vaccine co-contaminated with FAdV and CIAV. In conclusion, this study found the co-contamination of FAdV-4 and CIAV in the same attenuated vaccine and confirmed that such a contaminated attenuated vaccine was a significant source of infection for outbreaks of IBH-HPS in some flocks.

Allicin Alleviates Reticuloendotheliosis Virus-Induced Immunosuppression via ERK/Mitogen-Activated Protein Kinase Pathway in Specific Pathogen-Free Chickens

Reticuloendotheliosis virus (REV), a gammaretrovirus in the Retroviridae family, causes an immunosuppressive, oncogenic, and runting-stunting syndrome in multiple avian hosts. Allicin, the main effective component of garlic, has a broad spectrum of pharmacological properties. The hypothesis that allicin could relieve REV-induced immune dysfunction was investigated in vivo and in vitro in the present study. The results showed that dietary allicin supplementation ameliorated REV-induced dysplasia and immune dysfunction in REV-infected chickens. Compared with the control groups, REV infection promoted the expression of inflammatory cytokines including interleukin (IL)-1β, IL-6, IL-10, interferon (IFN)-γ, and tumor necrosis factor-α (TNF-α), whereas, allicin reversed these changes induced by REV infection. The decreased levels of IFN-α, IFN-β, and IL-2 were observed in REV-infected chickens, which were significantly improved by allicin. Allicin suppressed the REV-induced high expression of toll-like receptors (TLRs) as well as melanoma differentiation-associated gene 5 (MDA5) and the activation of mitogen-activated protein kinase (MAPK) and the nuclear factor kappa B p65. REV stimulated the phosphorylation of JNK, ERK, and p38, the downstream key signaling molecules of MAPK pathway, while allicin retarded the augmented phosphorylation level induced by REV infection. The decreased phosphorylation level of ERK was associated with REV replication, suggesting that ERK signaling is involved in REV replication, and allicin can alleviate the REV-induced immune dysfunction by inhibiting the activation of ERK. In addition, REV infection induced oxidative damage in thymus and spleen, whereas allicin treatment significantly decreased the oxidative stress induced by REV infection, suggesting that the antioxidant effect of allicin should be at least partially responsible for the harmful effect of REV infection. In conclusion, the findings suggest that allicin alleviates the inflammation and oxidative damage caused by REV infection and exerts the potential anti-REV effect by blocking the ERK/MAPK pathway.

Molecular characterization and phylogenetic analysis of a virulent Marek's disease virus field strain in broiler chickens in Japan

Marek's disease is a lymphoproliferative disease causing a serious threat in poultry production. Field strains of Marek's disease virus (MDVs) are continuously re-emerging, causing great economical losses to the poultry industry worldwide in spite of the intensive vaccination and restrictive management policy used. Histopathological and molecular characterizations of MDVs are essential for monitoring the changes of viruses and evaluating the effectiveness of existing vaccines. During 2016, 190 visceral tumour tissues representing 30 vaccinated chicken flocks from the Gifu prefecture, Japan, were analysed. A pathological examination revealed the presence of lymphoproliferative lesions in the visceral organs. Polymerase chain reaction screening of tissue specimens using specific primers for avian leucosis virus, reticuloendotheliosis virus, and MDV was positive only for MDV. The polymerase chain reaction products of meq, pp38, virus-induced IL-8 homology, and glycoprotein MDV genes were sequenced and used for homology, phylogenetic, and similarity level analysis with the published reference of MDVs in the database. The results revealed high similarity between the field isolates, vv and vv+ strains of MDV from the USA and China. Several point mutations in the nucleotide sequence of the field isolates and their deduced amino acid sequences were detected in those genes. The present molecular analyses indicated that nucleotide and amino acid changes could be valuable criteria for differentiation and determination of the pathogenicity and oncogenicity of MDVs according to the Avian Disease and Oncology Laboratory pathotyping in vivo studies. Furthermore, the results suggest that development of a new vaccine must be considered to overcome this devastating avian oncogenic viral disease.

Genome analysis and pathogenicity of reticuloendotheliosis virus isolated from a contaminated vaccine seed against infectious bursal disease virus: first report in China

Specific-pathogen-free (SPF) chickens were inoculated with the virus seed of an infectious bursal disease virus (IBDV)-attenuated vaccine, and positive reticuloendotheliosis virus (REV) antibody levels were subsequently detected in the chicken sera, indicating potential REV contamination of the vaccine. After neutralization with IBDV-positive blood serum, the vaccine was inoculated into DF-1 cells for REV isolation and identification. An REV strain, designated IBD-C1605, was identified using an immunofluorescence assay test. Three pairs of primers were employed for the amplification, cloning and sequencing of three overlapping fragments of the IBD-C1605 genome, and the whole-genome sequence of this isolate was obtained after gene assembly. The genome was 8362 base pairs (nt) in length and its homology with the nucleotide sequences of different reference strains varied between 94.2 and 99.2 %. Isolate IBD-C1605 was inoculated into 1-day-old SPF chickens to observe its pathogenicity. Infection with this organism slowed down the weight gain of SPF chickens and caused atrophy of their immune organs, such as the bursa of Fabricius and thymus gland. Furthermore, the chicken antibody levels decreased significantly after Newcastle disease virus and avian influenza virus subtype H9 vaccine immunization. This is the first report on the isolation and identification of REV from attenuated vaccine virus seeds in China, and is also the first study on the pathogenicity of REV from a contaminated vaccine in China. Our findings contribute towards a better understanding of the detrimental effects of vaccine contamination with exogenous viruses such as REV.

Genomic Analysis of the Chicken Infectious Anemia Virus in a Specific Pathogen-Free Chicken Population in China

The antibody to chicken infectious anemia virus (CIAV) was positive in a specific pathogen-free (SPF) chicken population by ELISA test in our previous inspection, indicating a possible infection with CIAV. In this study, blood samples collected from the SPF chickens were used to isolate CIAV by inoculating into MSB1 cells and PCR amplification. A CIAV strain (SD1403) was isolated and successfully identified. Three overlapping genomic fragments were obtained by PCR amplification and sequencing. The full genome sequence of the SD1403 strain was obtained by aligning the sequences. The genome of the SD1403 strain was 2293 bp with a nucleotide identity of 94.8% to 98.5% when compared with 30 referred CIAV strains. The viral proteins VP2 and VP3 were highly conserved, but VP1 was not relatively conserved. Both amino acids 139 and 144 of VP1 were glutamine, which was in accord with the low pathogenic characteristics. In this study, we first reported that CIAV exists in Chinese SPF chicken populations and may be an important reason why attenuated vaccine can be contaminated with CIAV.

Common occurrence of Gallid herpesvirus-2 with reticuloendotheliosis virus in chickens caused by possible contamination of vaccine stocks

AIMS

The aim of this study was to investigate the common occurrence of reticuloendotheliosis virus (REV) among Gallid herpesvirus 2 (GaHV-2) infected chickens. The possible cause of this co-occurrence may be linked to contaminated vaccine stocks, which were also examined.

METHODS AND RESULTS

The study was conducted on 25 field isolates of GaHV-2 collected between 2007 and 2013 from vaccinated chickens. Additionally, 10 commercial Marek's Disease vaccine stocks manufactured between 1993 and 2013, comprising of FC126 HVT, CVI988/Rispens and bivalent HVT + Rispens vaccines were examined. Chicken isolates were collected from the liver. Due to difficulties in differentiation between GaHV-2 and REV, by observation of clinical signs or lesions presented in liver or spleen, loop-mediated isothermal amplification (LAMP and RT-LAMP) as well as PCR-based methods were applied.

CONCLUSIONS

The co-occurrence of GaHV-2 and REV genetic material was shown in 24 (96%) of 25 examined isolates. A marginal REV contamination was detected in three out 10 (30%) commercial vaccine stocks, mainly in bivalent HVT + Rispens vaccines produced between 2009 and 2012.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our results indicated the common occurrence of GaHV-2 and REV in Polish chicken flocks, which is probably linked to contaminated HVT + Rispens vaccine stocks. Reasons for the detection of a marginal REV contamination need to be further elucidated.

Avian Immunosuppressive Diseases and Immunoevasion

Subclinical immunosuppression in chickens is an important but often underestimated factor in the subsequent development of clinical disease. Immunosuppression can be caused by pathogens such as chicken infectious anemia virus, infectious bursal disease virus, reovirus, and some retroviruses (e.g., reticuloendotheliosis virus). Mycotoxins and stress, often caused by poor management practices, can also cause immunosuppression. The effects on the innate and acquired immune responses and the mechanisms by which mycotoxins, stress and infectious agents cause immunosuppression are discussed. Immunoevasion is a common ploy by which viruses neutralize or evade immune responses. DNA viruses such as herpesvirus and poxvirus have multiple genes, some of them host-derived, which interfere with effective innate or acquired immune responses. RNA viruses may escape acquired humoral and cellular immune responses by mutations in protective antigenic epitopes (e.g., avian influenza viruses), while accessory non-structural proteins or multi-functional structural proteins interfere with the interferon system (e.g., Newcastle disease virus).

Complete Genome Sequence of Reticuloendotheliosis Virus Strain MD-2, Isolated from a Contaminated Turkey Herpesvirus Vaccine

Here, we present the complete genomic sequence of a reticuloendotheliosis virus (REV) isolated from a contaminated turkey herpesvirus (HVT) vaccine. This report will be helpful for epidemiological studies on REV infection in avian flocks.

The extraordinary evolutionary history of the reticuloendotheliosis viruses

The reticuloendotheliosis viruses (REVs) comprise several closely related amphotropic retroviruses isolated from birds. These viruses exhibit several highly unusual characteristics that have not so far been adequately explained, including their extremely close relationship to mammalian retroviruses, and their presence as endogenous sequences within the genomes of certain large DNA viruses. We present evidence for an iatrogenic origin of REVs that accounts for these phenomena. Firstly, we identify endogenous retroviral fossils in mammalian genomes that share a unique recombinant structure with REVs-unequivocally demonstrating that REVs derive directly from mammalian retroviruses. Secondly, through sequencing of archived REV isolates, we confirm that contaminated Plasmodium lophurae stocks have been the source of multiple REV outbreaks in experimentally infected birds. Finally, we show that both phylogenetic and historical evidence support a scenario wherein REVs originated as mammalian retroviruses that were accidentally introduced into avian hosts in the late 1930s, during experimental studies of P. lophurae, and subsequently integrated into the fowlpox virus (FWPV) and gallid herpesvirus type 2 (GHV-2) genomes, generating recombinant DNA viruses that now circulate in wild birds and poultry. Our findings provide a novel perspective on the origin and evolution of REV, and indicate that horizontal gene transfer between virus families can expand the impact of iatrogenic transmission events.

Molecular characterization and phylogenetic analysis of the reticuloendotheliosis virus isolated from wild birds in Northeast China

To analyze the status of reticuloendotheliosis (RE) infection of wild birds in China, 585 samples from wild birds collected in Liaoning, Jilin and Heilongjiang provinces China were investigated and analyzed. The sampled birds represent 3 orders and more than 40 species. Virus isolation and PCR amplification showed that some of the wild birds were infected with REV, and 10 REV strains were isolated. The gp90 gene from each of the 10 REV strains was amplified, cloned, and sequenced. Sequence analysis indicated that the gp90 genes of the 10 REV strains isolated in this study were more similar at the nucleotide level with the northeast Chinese strains HLJR0901 and HLJR0801 and some REV strains found in the US and Taiwan than with the early Chinese REV isolate HA9901. Furthermore, phylogenetic analysis indicated that the gp90 genes of the 10 REV strains were more similar to the REV subtype III-representing strain (CSV) than to strains 170A (subtype I) or SNV (subtype II). This is the first study to investigate the status of wild birds infected with REV. The results of this paper will not only provide necessary information for further understanding the evolution of REV, but they also identify the potential role of wild birds in REV transmission and furthers our understanding of the ecology of REV in wild bird species.

Isolation and analysis of a very virulent Marek's disease virus strain in China

Background

A severe MD was broken out at a farm in Shandong, China, despite FC126 vaccination of the chickens at 1-day-old. The mortality of the flocks reached up to 38.3%. The infected chickens were found to have MD pathological changes, including enlargement of spleens, livers and kidneys, and tumors occured on organs later. Samples were collected from the chickens for diagnosis.

Methods

The collected samples were inoculated into primary duck embryo fibroblast (DEF) cells, and the MDV strain named SD2012-1 was isolated. In order to identify the isolate, amplification by PCR and sequencing of oncogenic Meq and vIL-8 gene were processed, the obtained sequences were compared with the sequences of reference strains, and SD2012-1 was used to challenge immunized SPF chickens.

Results

A very virulent MDV isolate strain, SD2012-1, was isolated from a chicken flock in Shandong Province, China, the isolate had the characteristics of very virulent MDV-1, nucleotide and deduced amino acid sequence comparisons of Meq and vIL-8 gene of SD2012-1 with those of reference strains showed SD2012-1 had high homology with MDV strains isolated from China, SD2012-1 could break through the protection provided by HVT vaccine and HVT + SB-1 vaccine immunization and caused the mortality of SPF chickens over 60%. The immune failure occured at the farm could be due to the improper selection of vaccines. SD2012-1 produced death later and the gross postmortem lesions of chickens died early and later were different.

Conclusions

MDV strain SD2012-1 isolated from Shandong Province, China was found to have the characteristics of very virulent MDV-1, which could break through the protection provided by HVT vaccine and HVT + SB-1 vaccine, the virus seemed to have a long latent period, and cause different gross postmortem lesions of chickens between chickens died early and later. A better immunization way should be chosen to prevent infection of this MDV strain in field.

Probable congenital transmission of reticuloendotheliosis virus caused by vaccination with contaminated vaccines

Contaminated vaccine is one unexpected and potential origin of virus infection. In order to investigate the most likely cause of disease in a broiler breeder company of Shandong Province, all 17 batches of live-virus vaccines used in the affected flocks and 478 tissue samples were tested by dot-blot hybridization, nested PCR, and IFA. The results suggested the outbreak of disease was most probably due to the vaccination of REV-contaminated MD-CVI988/Rispens vaccines and ND-LaSota+IB-H120 vaccines. Furthermore, the REV was probably transmitted to the commercial chickens through congenital transmission.