Establishment of an antigen-capture enzyme-linked immunosorbent assay for detecting avian reticuloendotheliosis virus.

In this study, an antigen-capturing enzyme-linked immunosorbent assay (AC-ELISA) was established for the detection of avian reticuloendotheliosis virus (REV) using monoclonal and polyclonal antibodies against gp90. New Zealand white rabbits were immunized with recombinant REV-gp90 protein, and polyclonal antibodies were obtained after purification and used as the capture antibody. Mice monoclonal antibody 1A12D against REV-gp90 protein previously prepared in our laboratory was used as the detection antibody. The specificity of the AC-ELISA was confirmed with REV, avian leukosis virus subgroup J, Marek's disease virus serotype Ⅰ, avian hepatitis E virus and Fowl adenovirus serotype 4. The results showed that the AC-ELISA had specific binding reaction with REV, and did not react with other viruses. The detection limit of this assay was 195 TCID50 units of REV. Furthermore, commercial vaccine artificially contaminated with REV was detected by three methods: AC-ELISA, the TaqMan probe fluorescence real-time quantitative RT-PCR (RT-qPCR) and indirect immunofluorescence assay (IFA). The results showed that the positive coincidence rate of RT-qPCR and AC-ELISA was 90.63 %, and the positive coincidence rate of RT-qPCR and IFA was 96.88%, indicating that the AC-ELISA established in this study was effective and feasible. This method simplified the detection process for REV contamination in poultry attenuated vaccines, and provide necessary technical tools for high-throughput detection of REV.

Genetic Sequencing of Attwater's Prairie Chicken Avian Poxvirus and Evaluation of Its Potential Role in Reticuloendotheliosis Virus Outbreaks.

Efforts to breed Attwater's prairie chickens (APC; Tympanuchus cupido attwateri) in captivity to supplement wild populations of this endangered bird have been negatively affected by infections with Avipoxvirus and reticuloendotheliosis virus (REV). Because REV can be integrated into the genome of fowlpox virus (FPV) and may be transmitted in that manner, identifying the source of avipox disease in APC is important to mitigate the impact of this virus. Tissue samples from APC were collected from breeding programs in Texas from 2016 to 2020. These samples consisted of 11 skin lesions and three internal organs from a total of 14 different birds that died of unknown causes or were euthanized. Avipoxvirus was detected by PCR and isolation in embryonating chicken eggs in all skin lesion samples but was not detected in internal organs. Using sequence analysis of FPV polymerase and 4b genes, we determined that 10 out of 11 Avipoxvirus detections resided within the fowlpox clade and a single sample resided within the canarypox clade. REV sequences were detected in all FPV positive samples and in all internal organ tissues but were not detected in the sample matching the canarypox clade. Analysis of REV sequences and PCR detection showed the REV infecting APC was consistent with REV-A and had little variability on analysis of the U3 region of the long terminal repeat. The results of this study indicate control of REV in APC breeding colonies may benefit by a vaccination program targeting FPV and REV. However, a commercially available vaccine for REV is not available at this time.

Secuenciación genética de un virus de la viruela aviar de un gallo grande de las praderas Attwater y evaluación de su papel potencial en los brotes del virus de la reticuloendoteliosis. Los esfuerzos para criar gallos de las praderas grandes de Attwater (APC; Tympanuchus cupido attwateri) en cautiverio para complementar las poblaciones silvestres de esta ave en peligro de extinción se han visto afectados negativamente por infecciones con Avipoxvirus y con el virus de la reticuloendoteliosis (REV). Debido a que el virus de la reticuloendoteliosis puede integrarse en el genoma del virus de la viruela del pollo (FPV) y puede transmitirse de esa manera, identificar la fuente del virus pox en gallos de las praderas grandes es importante para mitigar el impacto de este virus. Se recolectaron muestras de tejido de gallos de las praderas grandes de programas de reproducción en Texas entre los años 2016 a 2020. Estas muestras consistieron en 11 lesiones cutáneas y tres órganos internos de un total de 14 aves diferentes que murieron por causas desconocidas o fueron sacrificadas. El Avipoxvirus se detectó mediante PCR y por aislamiento en huevos embrionados de pollo en todas las muestras de lesiones cutáneas, pero no se detectó en los órganos internos. Utilizando el análisis de secuencia de la polimerasa del virus de la viruela del pollo y de los genes 4b, se determinó que diez de las once detecciones de Avipoxvirus residían dentro del clado de la viruela aviar del pollo y una sola muestra residía dentro del clado de la viruela del canario. Se detectaron secuencias del virus de la reticuloendoteliosis en todas las muestras positivas para virus de la viruela de pollo y en todos los tejidos de órganos internos, pero no se detectaron en la muestra que coincidía con el clado de la viruela del canario. El análisis de las secuencias del virus de la reticuloendoteliosis y la detección por PCR mostró que los virus de reticuloendoteliosis que infectan a gallos de las praderas grandes eran compatible con virus de la reticuloendoteliosis A y tenía poca variabilidad en el análisis de la región U3 de la región repetida terminal larga. Los resultados de este estudio indican que el control del virus de la reticuloendoteliosis en colonias reproductoras de gallos de las praderas grandes puede beneficiarse de un programa de vacunación dirigido los virus de la viruela del pollo y de la reticuloendoteliosis. Sin embargo, una vacuna disponible comercialmente contra el virus de la reticuloendoteliosis no está disponible en este momento.

Poly (I: C) inhibits reticuloendothelial virus replication in chicken macrophage-like cells through the activation of toll-like receptor-3 signaling.

Reticuloendothelial virus (REV) is widely found in many domestic poultry areas and results in severe immunosuppression of infected chickens. This increases the susceptibility to other pathogens, which causes economic losses to the poultry industry. The aim of our study was to determine whether polyinosinic-polycytidylic acid [Poly (I: C)] treatment could inhibit REV replication in chicken macrophage-like cell line, HD11. We found that Poly (I: C) treatment could markedly inhibit REV replication in HD11 from 24 to 48 h post infection (hpi). Additionally, Poly (I: C) treatment could switch HD11 from an inactive type into M1-like polarization from 24 to 48 hpi. Furthermore, Poly (I: C) treatment promoted interferon-ß secretion from HD11 post REV infection. Moreover, Toll-like receptor-3 (TLR-3) mRNA and protein levels in HD11 treated with Poly (I: C) were markedly increased compared to those of HD11 not treated with Poly (I: C). The above results suggested that Poly (I: C) treatment switches HD11 into M1-like polarization to secret more interferon-ß and activate TLR-3 signaling, which contributes to block REV replication. Our findings provide a theoretical reference for further studying the underlying pathogenic mechanism of REV and Poly (I: C) as a potential therapeutic intervention against REV infection.

An optimized secretory expression system and immunogenicity evaluation for glycosylated gp90 of avian reticuloendotheliosis virus.

Reticuloendotheliosis is an important immunosuppressive disease, associated with avian reticuloendotheliosis virus (REV) infection, and causes notable economic losses worldwide. Glycoprotein gp90 is an important structural protein of REV, and considered to be the most important immunogenic antigen, which can induce neutralizing antibodies against REV. In this study, an optimized suspension culture system was developed and applied to secretory express the immunogenic surface antigen gp90. To achieve an optimal glycosylation, the gp90 was designed to secretory expressed into the supernatant of the cell culture, which also occurs in the natural protein maturation procedure of REV. Serum-free culture medium was introduced to simplify the purification process and reduce the production costs. Based on the purified glycosylated gp90, an oil-emulsion subunit REV vaccine candidate was developed and evaluated in chickens. The subunit gp90-based vaccine induced fast immune responses, high levels of antibodies (REV-specific antibody, gp90-specific antibody, and neutralizing antibody against REV), and preferential T helper 2 (Th2) (interleukin-4 secretion) not Th1 (interferon-γ secretion) response. Furthermore, the viremia induced by REV infection was significantly reduced in chickens immunized with the glycosylated gp90. Overall, an optimized secretory expression system for glycosylated gp90 was developed, and the glycosylated gp90 obtained in this study retained good immunogenicity and could be an attractive vaccine candidate to protect chickens against REV horizonal infection.

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.

Isolation and pathogenicity testing of avian reticuloendotheliosis virus from layer chickens in China.

Reticuloendotheliosis virus (REV) can cause runting, immunosuppression, acute reticulum cell neoplasia, and chronic lymphoid tumors in a variety of domestic and wild birds. We diagnosed a case of reticuloendotheliosis with obvious tumors in liver and kidney. We isolated and sequenced the virus and performed pathogenicity testing of the REV strain. Immunohistochemistry and PCR confirmed that the diseased layer chickens were infected with REV. The strain, named BJ1503, was successfully isolated from the case by inoculation of tissue homogenates onto chicken embryo fibroblasts. The length of the proviral REV genome is 8,293 nucleotides. The isolate had 99.7% identity with REV-HA9901 (AY842951.1), which was isolated from Jiangsu, China, in 1999. The chickens infected with REV-BJ1503 had depressed weight gain and lymphoid atrophy. Our findings suggest that REV isolate BJ1503 was phylogenetically close to the earlier strain found in China, with minor variations, and the virus was associated with severe production problems.

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 of Reticuloendotheliosis Virus in Muscovy Ducks, Wild Turkeys, and Chickens in Brazil.

Reticuloendotheliosis viruses (REVs) are known to cause immunosuppressive and oncogenic disease that affects numerous avian species. Reticuloendotheliosis viruses are present worldwide and recently have been reported in South America with cases of infected commercial flocks in Argentina. We surveyed for the presence of REV in birds from a state in the northern region of Brazil using real-time PCR. We report here the presence of REV in Brazil, detected in Muscovy Ducks (Cairina moschata), Wild Turkeys (Meleagris gallopavo), and chickens (Gallus gallus) at a relatively high prevalence (16.8%). Phylogenetic analysis indicated a close relationship of these strains to variants in the US. This study provides evidence of REV in the Amazon biome and provides a baseline for future surveillance of the virus in the region and throughout Brazil.

Serological and molecular identification of Reticuloendotheliosis virus (REV) in chickens in Sudan.

BACKGROUND: Reticuloendotheliosis virus (REV) is a gammaretrovirus that belongs to the family of Retroviridae. The infection can result in immunosuppression, runting syndrome, high mortality, acute reticular cell neoplasia or T- and/ or B-cell lymphoma, in a variety of domestic and wild birds. The disease is widespread around the world. No related data have been reported in Sudan about the disease. The present study was conducted to determine the prevalence of REV antibodies and DNA in local and commercial breeds of chickens older than 20 weeks from June 2014 to February, 2017. METHODS: A total of 460 sera samples and 150 (50 liver and 100 spleen) tissue samples were collected from local and commercial breeds of chickens older than 20 weeks and screened for anti-REV antibodies in four states of Sudan using a commercial REV antibody ELISA test kit (IDEXX). Polymerase chain reaction (PCR) was performed to detect REV DNA in tissue samples in Khartoum State. RESULTS: The results revealed that the overall seroprevalence of REV was 74.6% among local and commercial chicken breeds, but in commercial it was 79.5% (190/239) and 69.2% in local breeds (153/221). One hundred and fifty tissue samples of chickens (50 liver, 100 spleen) were tested using PCR for detection of REV using primer sets of the conserved region in envelope glycoprotein (env) gene with a band length of 850 bp. Five out of 50 (10%) liver samples were RE provirus DNA positive detected by PCR, whereas 15 out of 100 (15%) spleen samples were PCR positive. Univariate analysis revealed there was a difference (p ≤ 0.05) between locality and breed of chickens and seropositivity to REV. CONCLUSIONS: The prevalence of the disease was high in Sudan and more studies are needed to evaluate the epidemiology and pathogenesis of the virus.

Survey of Reticuloendotheliosis Virus in Wild Turkeys (Meleagris gallopavo) in Texas, USA.

Reticuloendotheliosis virus (REV) is an immunosuppressive and sometimes oncogenic avian retrovirus that establishes lifelong infection in a wide range of avian species. REV-infected wild birds roaming near at-risk captive flocks, such as is the case for the highly endangered Attwater's Prairie Chicken (APC; Tympanuchus cupido attwateri), could act as a reservoir for viral transmission. In wild birds, prevalence rates of REV are low and appearance of associated disease is uncommon. During 2016-17, nearly half of all captive adult APC mortality at Fossil Rim Wildlife Center captive breeding facility in Glen Rose, Texas, US was attributed to REV infection. The unusually high REV prevalence rate prompted us to survey for this virus in wild galliforms throughout the region. From 2016-17, 393 blood samples collected from two subspecies of Wild Turkeys (Meleagris gallopavo) were tested for REV proviral DNA through amplification of the viral 3' long terminal repeat and segments of the viral pol gene. In REV-affected counties, 5% (5/98) of native Rio Grande Wild Turkeys (Meleagris gallopavo intermedia) were identified as REV-positive. In addition, we detected REV in one of 62 Eastern Wild Turkeys (Meleagris gallopavo silvestris) that had been imported during conservation efforts. To better determine protective measures, continued surveillance, including collection and genetic analysis of REV-infected samples, is necessary to identify sources of REV outbreaks in captive APC flocks.

DETECTION OF LYMPHOPROLIFERATIVE DISEASE VIRUS IN CANADA IN A SURVEY FOR VIRUSES IN ONTARIO WILD TURKEYS ( MELEAGRIS GALLOPAVO).

The successful reintroduction of Wild Turkeys ( Meleagris gallopavo) to Ontario, Canada, has led to established populations in southern portions of the province and currently allows for biannual hunting seasons. These populations geographically overlap Domestic Turkey farms, an important sector of the provincial agri-food industry. Potential pathogen transmission between Wild Turkeys and Domestic Turkeys ( Meleagris gallopavo) is a concern, because they are susceptible to infection with many of the same pathogens and have direct and indirect contact in outdoor or open farm settings and contaminated environmental substrates. However, data concerning potential poultry pathogens in Wild Turkeys in Canada are scarce. Thus, we assessed the prevalence and geographic distribution of geographically relevant viruses in Ontario Wild Turkeys. Oropharyngeal and cloacal swabs were tested for avian influenza viruses (AIV) by real-time reverse transcriptase (RT)-PCR ( n=207), pooled tissues for lymphoproliferative disease virus (LPDV; n=183) and reticuloendotheliosis virus ( n=119) by PCR, and gross skin lesions by real-time RT-PCR for avian poxvirus ( n=8). We sequenced a fragment of the gag polyprotein (p31) gene of LPDV on a subset ( n=10) of LPDV-positive samples for phylogenetic analysis and tested additional upland game bird species ( n=39) and domestic fowl for LPDV ( n=17). To the best of our knowledge, we document the first detection of LPDV in Wild Turkeys in Canada, with a prevalence of 65% (119/183). Phylogenetic analysis revealed that LPDV sequences from Ontario were genetically similar to other North American strains and did not group into separate clades. Reticuloendotheliosis virus was detected in 4% (5/119) of LPDV-positive Wild Turkeys. Grossly evident skin lesions from five Wild Turkeys tested positive for poxvirus, and all turkeys tested negative for AIV. This study provides evidence of LPDV circulation in Canada and provides a baseline for comparison with future Wild Turkey pathogen surveillance and monitoring in Ontario and elsewhere.

A multiplex xTAG assay for the simultaneous detection of five chicken immunosuppressive viruses.

BACKGROUND: Chicken anemia virus (CAV), avian reovirus (ARV), infectious bursal disease virus (IBDV), Marek's disease virus (MDV) and reticuloendotheliosis virus (REV) all cause immunosuppressive disease in birds through vertical or horizontal transmission. Mixed infections with these immunosuppressive pathogens lead to atypical clinical signs and obstruct accurate diagnoses and epidemiological investigations. Therefore, it is essential to develop a high-throughput assay for the simultaneous detection of these immunosuppressive viruses with high specificity and sensitivity. The aim of this study was to establish a novel method using a RT-PCR assay combined with fluorescence labeled polystyrene bead microarray (multiplex xTAG assay) to detect single or mixed viral infections. RESULTS: The results showed that the established xTAG assay had no nonspecific reactions with avian influenza virus (AIV), infectious bronchitis virus (IBV), newcastle disease virus (NDV), infectious laryngotracheitis virus (ILTV), Mycoplasma gallisepticum (MG) and Mycoplasma synoviae (MS). The limit of detection was 1.0 × 103 copies/µL for IBDV and 1.0 × 102copies/µL for the other four viruses. Ninety field samples were tested and the results were confirmed using conventional RT-PCR methods. The detection results of these two methods were 100% consistent. The established multiplex xTAG assay allows a high throughput and simultaneous detection of five chicken immunosuppressive viruses. CONCLUSION: The multiplex xTAG assay has been showed to be an additional tool for molecular epidemiology studies of five chicken immunosuppressive viruses in the poultry industry.

Co-Infection with Marek's Disease Virus and Reticuloendotheliosis Virus Increases Illness Severity and Reduces Marek's Disease Vaccine Efficacy.

Marek's disease virus (MDV) and reticuloendotheliosis virus (REV) cause Marek's disease (MD) and reticuloendotheliosis (RE), respectively. Co-infection with MDV and REV is common in chickens, causing serious losses to the poultry industry. However, experimental studies of such co-infection are lacking. In this study, Chinese field strains of MDV (ZW/15) and REV (JLR1501) were used as challenge viruses to evaluate the pathogenicity of co-infection and the influence of MD vaccination in chickens. Compared to the MDV-challenged group, the mortality and tumor rates increased significantly by 20.0% (76.7 to 96.7%) and 26.7% (53.3 to 80.0%), in the co-challenged group, respectively. The protective index of the MD vaccines CVI988 and 814 decreased by 33.3 (80.0 to 47.7) and 13.3 (90.0 to 76.7), respectively. These results indicated that MDV and REV co-infection significantly increased disease severity and reduced the vaccine efficacy. The MDV genome load showed no difference in the feather pulps and spleen, and pathogenicity-related MDV gene expression (meq, pp38, vIL-8, and ICP4) in the spleen significantly increased at some time points in the co-challenged group. Clearly, synergistic pathogenicity occurred between MDV and REV, and the protective efficacy of existing MD vaccines was attenuated by co-infection with Chinese field MDV and REV strains.

Serologic survey of wild turkeys (Meleagris gallopavo) and evidence of exposure to avian encephalomyelitis virus in Georgia and Florida, USA.

Wild Turkeys (Meleagris gallopavo) are susceptible to many of the same diseases as domestic turkeys. Before 2005, most Wild Turkeys in southern Georgia, US, had little or no exposure to commercial poultry operations. As part of a pathogen survey examining the effects of commercial poultry on Wild Turkeys, samples were collected from Wild Turkeys from March 2005 through May 2008. The turkeys were collected from 13 counties in southern Georgia and Madison County, Florida, and tested for antibodies to various pathogens of poultry. Three (13%) of the turkeys were positive for antibodies to Salmonella. Thirteen turkeys (54%) were positive for Newcastle disease virus antibodies, and 15 turkeys (63%) were positive for antibodies to reticuloendotheliosis virus. One turkey (4%) from Madison County was positive for avian encephalomyelitis virus antibodies.

Synergistic pathogenic effects of co-infection of subgroup J avian leukosis virus and reticuloendotheliosis virus in broiler chickens.

To study interactions between avian leukosis virus subgroup J (ALV-J) and reticuloendotheliosis virus (REV) and the effects of co-infection on pathogenicity of these viruses, 1-day-old broiler chicks were infected with ALV-J, REV or both ALV-J and REV. The results indicated that co-infection of ALV-J and REV induced more growth retardation and higher mortality rate than ALV-J or REV single infection (P < 0.05). Chickens co-infected with ALV-J and REV also showed more severe immunosuppression than those with a single infection. This was manifested by significantly lower bursa of Fabricius and thymus to body weight ratios and lower antibody responses to Newcastle disease virus and H9-avian influenza virus (P < 0.05). Perihepatitis and pericarditis related to severe infection with Escherichia coli were found in many of the dead birds. E. coli was isolated from each case of perihepatitis and pericarditis. The mortality associated with E. coli infection in the co-infection groups was significantly higher than in the other groups (P < 0.05). Among 516 tested E. coli isolates from 58 dead birds, 12 serotypes of the O-antigen were identified in two experiments. Different serotypes of E. coli strains were even isolated from the same organ of the same bird. Diversification of O-serotypes suggested that perihepatitis and pericarditis associated with E. coli infection was the most frequent secondary infection following the immunosuppression induced by ALV-J and REV co-infection. These results suggested that the co-infection of ALV-J and REV caused more serious synergistic pathogenic effects, growth retardation, immunosuppression, and secondary E. coli infection in broiler chickens.

Existence of variant strains Fowlpox virus integrated with Reticuloendotheliosis virus in its genome in field isolates in Tanzania.

Fowlpox virus (FPV) is one example of poultry viruses which undergoes recombination with Reticuloendotheliosis virus (REV). Trepidation had been raised, and it was well established on augmented pathogenicity of the FPV upon integration of the full intact REV. In this study, we therefore intended at assessing the integration of REV into FPV genome of the field isolates obtained in samples collected from different regions of Tanzania. DNA extraction of 85 samples (scabs) was performed, and FPV-specific PCR was done by the amplification of the highly conserved P4b gene. Evaluation of FPV-REV recombination was done to FPV-specific PCR positively identified samples by amplifying the env gene and REV long terminal repeats (5' LTR). A 578-bp PCR product was amplified from 43 samples. We are reporting for the first time in Tanzania the existence of variant stains of FPV integrated with REV in its genome as 65 % of FPV identified isolates were having full intact REV integration, 21 % had partial FPV-REV env gene integration and 5 % had partial 5' LTR integration. Despite of the fact that FPV-REV integrated stains prevailed, FPV-REV-free isolates (9 %) also existed. In view of the fact that full intact REV integration is connected with increased pathogenicity of FPV, its existence in the FPV genome of most field isolates could have played a role in increased endemic, sporadic and recurring outbreaks in selected areas in Tanzania.

Insertion of reticuloendotheliosis virus long terminal repeat into the genome of CVI988 strain of Marek's disease virus results in enhanced growth and protection.

Marek's disease (MD) is a lymphoproliferative disease of chickens caused by serotype 1 MD virus (MDV). Vaccination of commercial poultry has drastically reduced losses from MD, and the poultry industry cannot be sustained without the use of vaccines. Retrovirus insertion into herpesvirus genomes is an efficient process that alters the biological properties of herpesviruses. RM1, a virus derived from the virulent JM strain of MDV, by insertion of the reticuloendotheliosis (REV) long terminal repeat (LTR), was attenuated for oncogenicity but retains properties of the parental virus, such as lymphoid organ atrophy. Here we show that insertion of the REV LTR into the genome of vaccine strain CVI988 resulted in a virus (CVRM) that replicated to higher levels than parental CVI988 in cell culture and that remained apathogenic for chickens. In addition, CVRM showed protection indices similar or superior to those afforded by CVI988 virus in laboratory and field protection trials, indicating that it could be developed as a safe and efficacious vaccine to protect against very virulent plus MDV.

A DNA vaccine expressing ENV and GAG offers partial protection against reticuloendotheliosis virus in the prairie chicken (Tympanicus cupido).

Recurring infection of reticuloendotheliosis virus (REV), an avian oncogenic gammaretrovirus, has been a major obstacle in attempts to breed and release the endangered Attwater's prairie chicken (Tympanicus cupido attwateri). The aim of this study was to develop a DNA vaccine that protects the birds against REV infection. A plasmid was constructed expressing fusion proteins of REV envelope (env) and VP22 of Gallid herpesvirus 2 or REV gag and VP22. Birds vaccinated with these recombinant plasmids developed neutralizing antibodies; showed delayed replication of virus; and had significantly less infection of lymphocytes, specifically CD4+ lymphocytes. Although the vaccine did not prevent infection, it offered partial protection. Birds in field conditions and breeding facilities could potentially benefit from increased immunity when vaccinated.

Complete genomic sequence of a Muscovy duck-origin reticuloendotheliosis virus from China.

The complete proviral sequence of a Muscovy duck-origin reticuloendotheliosis virus (REV) associated with spontaneously occurring neoplastic disease in 2011 in Zhejiang province, China, was determined. Comparative sequence analyses indicate that the present REV is most closely related to the chicken-origin REV isolate HLJR0901 and the goose-origin isolate Goose/3410/06. These findings suggest that chickens or geese may transmit the REV to Muscovy ducks.