Molecular characterization of Marek's Disease virus reveals reticuloendotheliosis virus-long terminal repeat integration in the genome of the field isolates in Egypt.

The highly contagious, immunosuppressive, and cancer-causing Marek's disease virus (MDV) infects chickens. The financial costs of Marek's disease (MD) are significant for the chicken industry. In this study, a total of 180 samples from chicken farms suspected to be MDV-infected were collected. The chickens were sampled during the period between the months of October 2016 and February 2018 at Dakahlia and Damietta Governorates, Egypt. A total of 36 pooled samples were created. The prepared samples were inoculated into embryonated chicken eggs (ECEs). Indirect fluorescent antibody technique (IFAT) and ICP4 gene-based polymerase chain reaction (PCR) were used for MDV identification. For the genetic characterization of the identified virus, The ICP4 gene sequence was identified and compared with the sequences available from various regions of the world. Furthermore, the genomes of all detected MDVs were screened for the long terminal repeat (LTR) region of reticuloendotheliosis (REV) in their genomes. The results showed that 31 out of 36 pooled samples (86.1%) inoculated into ECEs displayed the characteristic pock lesions. By using IFAT and PCR to identify MDV in ECEs, positive results were found in 27 samples (75%). The Egyptian virus is thought to be genetically closely related to MDVs circulating in Ethiopia, China, and India. REV-LTR was amplified from 6 out of 27 field isolates genomes (22.2 %) while MDV vaccine strains were free from REV-LTR insertion. The integrated REV-LTRs depicted a close genetic relationship with those integrated in fowl poxvirus (FWPV) circulating in Egypt as well as those integrated in FWPVs and MDVs from China, USA, South Africa, and Australia. To the best of our knowledge, this investigation represents the first identification and characterization of REV-LTR insertions in Egyptian MDV field isolates. Given the findings above, additional research in the future seems crucial to determine how the REV-LTR insertions affect MDV pathogenesis, virulence, and insufficient vaccination protection.

Optimizing protocols for monitoring in vivo replication of a novel chimeric Marek's disease vaccine with an insertion of the long terminal repeat of reticuloendotheliosis virus in the CVI988 strain genome (CVI-LTR).

Monitoring Marek's disease (MD) vaccination is routinely done by evaluating the load of MD vaccine in the feather pulp (FP) between 7 and 10 days of age. However, attempts in our laboratory to detect a novel CVI-LTR vaccine in the FP samples from commercial flocks failed. The objective of this study was to evaluate the most suitable tissue and age to monitor CVI-LTR vaccination. We used two different commercial CVI988 vaccines as controls. One hundred and sixty 1-day-old commercial brown layers were vaccinated with either CVI-LTR, CVI988-A, CVI988-B or remained unvaccinated. Samples of the spleen, thymus, and bursa were collected at 3, 4, 5, and 6 days of age and samples of FP were collected at 7 and 21 days for DNA isolation. Our results showed that CVI-LTR replicated earlier than CVI988 vaccines in the lymphoid organs but was not detected in the FP at either 7 or at 21 days of age. We also confirmed that either the spleen or thymus collected at 4-6 days was a suitable sample to monitor CVI-LTR vaccination in commercial flocks. Finally, we evaluated the load of oncogenic MDV DNA in five commercial flocks that were vaccinated with either CVI-LTR + rHVT or CVI988-A + rHVT. The load of oncogenic MDV DNA was evaluated at 21 days in the FP in 20 chickens per group. Our results demonstrated that CVI-LTR was more successful in reducing oncogenic MDV DNA at 21 days of age than the CVI988-A strain.RESEARCH HIGHLIGHTSCVI-LTR replicates in the thymus and spleen earlier than CVI988.CVI-LTR replicates in lymphoid organs but it cannot be detected in feather pulp.CVI-LTR reduced the load of oncogenic MDV DNA more efficiently than CVI988.

miR-155 facilitates the synergistic replication between avian leukosis virus subgroup J and reticuloendotheliosis virus by targeting a dual pathway.

IMPORTANCE: The synergy of two oncogenic retroviruses is an essential phenomenon in nature. The synergistic replication of ALV-J and REV in poultry flocks increases immunosuppression and pathogenicity, extends the tumor spectrum, and accelerates viral evolution, causing substantial economic losses to the poultry industry. However, the mechanism of synergistic replication between ALV-J and REV is still incompletely elusive. We observed that microRNA-155 targets a dual pathway, PRKCI-MAPK8 and TIMP3-MMP2, interacting with the U3 region of ALV-J and REV, enabling synergistic replication. This work gives us new targets to modulate ALV-J and REV's synergistic replication, guiding future research on the mechanism.

RIOK3-Mediated Akt phosphorylation facilitates synergistic replication of Marek's disease and reticuloendotheliosis viruses.

Co-infection of Marek's disease virus (MDV) and reticuloendotheliosis virus (REV) synergistically drives disease progression, yet little is known about the mechanism of the synergism. Here, we found that co-infection of REV and MDV increased their replication via the RIOK3-Akt pathway. Initially, we noticed that the viral titres of MDV and REV significantly increased in REV and MDV co-infected cells compared with single-infected cells. Furthermore, tandem mass tag peptide labelling coupled with LC/MS analysis showed that Akt was upregulated in REV and MDV co-infected cells. Overexpression of Akt promoted synergistic replication of MDV and REV. Conversely, inhibition of Akt suppressed synergistic replication of MDV and REV. However, PI3K inhibition did not affect synergistic replication of MDV and REV, suggesting that the PI3K/Akt pathway is not involved in the synergism of MDV and REV. In addition, we revealed that RIOK3 was recruited to regulate Akt in REV and MDV co-infected cells. Moreover, wild-type RIOK3, but not kinase-dead RIOK3, mediated Akt phosphorylation and promoted synergistic replication of MDV and REV. Our results illustrate that MDV and REV activated a novel RIOK3-Akt signalling pathway to facilitate their synergistic replication.

TMT-based proteomic analysis reveals integrins involved in the synergistic infection of reticuloendotheliosis virus and avian leukosis virus subgroup J.

BACKGROUND: Co-infection with the avian leukosis virus subgroup J (ALV-J) and the reticuloendotheliosis virus (REV) increases mutual viral replication, causing a more serious pathogenic effect by accelerating the progression of neoplasia and extending the tumor spectrum. However, the molecular mechanism underlying the synergistic replication of ALV-J and REV remains unclear. RESULTS: Here, we performed this study to compare the differentially expressed proteins among CEF cells infected with ALV-J, REV or both at the optimal synergistic infection time using TMT-based quantitative proteomics. We identified a total of 719 (292 upregulated and 427 downregulated) and 64 (35 upregulated and 29 downregulated) proteins by comparing co-infecting both viruses with monoinfecting ALV-J and REV, respectively. GO annotation and KEGG pathway analysis showed the differentially expressed proteins participated in virus-vector interaction, biological adhesion and immune response pathways in the synergistic actions of ALV-J and REV at the protein levels. Among the differentially expressed proteins, a large number of integrins were inhibited or increased in the co-infection group. Further, eight integrins, including ITGα1, ITGα3, ITGα5, ITGα6, ITGα8, ITGα9, ITGα11 and ITGß3, were validated in CEF cells by qRT-PCR or western blot. CONCLUSIONS: These findings proved that integrins may be key regulators in the mechanism of synergistic infection of REV and ALV-J, which will provide more insight into the pathogenesis of synergism of REV and ALV-J at protein level.

Complete Genome Characterization of Reticuloendotheliosis Virus Detected in Chickens with Multiple Viral Coinfections.

Reticuloendotheliosis virus (REV) is a retroviral pathogen capable of infecting several avian hosts and is associated with immunosuppression, anemia, proventriculitis, neoplasia, and runting-stunting syndrome. Its genome contains the three major genes, gag, pol, and env, and two flanking long terminal repeat (LTR) regions. Complete genome sequences of REV are limited in terms of geographical origin. The aim of this study was to characterize the complete genome of REV detected in Brazilian chickens with multiple viral coinfections and analyze the polymorphisms in the deduced amino acids sequences corresponding to its encoded proteins. We tested the presence and completeness of REV as well as other viral pathogens in samples from Brazilian poultry farms by qPCR. The complete genomes of two REV strains were sequenced by overlapping fragments through the dideoxy method. Phylogenetic analysis, pairwise identity matrix, polymorphism identification and protein modeling were performed along the entire genome. We detected REV in 65% (26/40) of the tested samples. Concomitant viral infections were detected in 82.5% (33/40) of the samples and in 90% (9/10) of the farms. Multiple infections included up to seven viruses. Phylogenetic analysis classified both Brazilian strains into REV subtype 3, and the pairwise comparison indicated that strains from the USA and fowlpox virus (FWPV)-related strains were the most identical. The subdomain p18 in gag, the reverse transcriptase/ribonuclease H in pol, and the surface (SU) in the env protein were the most polymorphic in genomic comparisons. The relevant motifs for each protein were highly conserved, with fewer polymorphisms in the fusion peptide, immunosuppression domain, and disulfide bonds on the surface (SU) and transmembrane (TM) of env. This is the first study to include complete genomes of REV in Brazil and South America detected in farms with multiple viral coinfections. Our findings suggest an involvement of REV as an immunosuppressor and active agent in the emergence and progression of multiple infectious diseases. We also found a possible etiological relationship between Brazilian strains and the USA and FWPV recombinant strains. This information highlights the need for epidemiological vigilance regarding REV in association with another pathogens.

Epidemic of cutaneous fowlpox in a naïve population of chickens and turkeys in Austria: Detailed phylogenetic analysis indicates co-evolution of fowlpox virus with reticuloendotheliosis virus.

Cutaneous fowlpox is a disease of chickens and turkeys caused by the fowlpox virus (FWPV), characterized by the development of proliferative lesions and scabs on unfeathered areas. FWPVs regularly carry an integrated, active copy of the reticuloendotheliosis virus (REV), and it has been hypothesized that such FWPVs are more problematic in the field. Extensive outbreaks are usually observed in tropical and sub-tropical climates, where biting insects are more difficult to control. Here, we report an epidemic of 65 cutaneous fowlpox cases in Austria in layer chickens (91% of the cases) and broiler breeders and turkeys, all of them unvaccinated against the disease, from October 2018 to February 2020. The field data revealed appearance in flocks of different sizes ranging from less than 5000 birds up to more than 20,000 animals, with the majority raised indoors in a barn system. The clinical presentation was characterized by typical epithelial lesions on the head of the affected birds, with an average decrease of 6% in egg production and an average weekly mortality of 1.2% being observed in the flocks. A real-time multiplex polymerase chain reaction (PCR) confirmed the presence of FWPV-REV DNA, not only in the lesions but also in the environmental dust from the poultry houses. The integration of the REV provirus into the FWPV genome was confirmed by PCR, and revealed different FWPV genome populations carrying either the REV long terminal repeats (LTRs) or the full-length REV genome, reiterating the instability of the inserted REV. Two selected samples were fully sequenced by next generation sequencing (NGS), and the whole genome phylogenetic analysis revealed a regional clustering of the FWPV genomes. The extensive nature of these outbreaks in host populations naïve for the virus is a remarkable feature of the present report, highlighting new challenges associated with FWPV infections that need to be considered.

Reemergence of reticuloendotheliosis virus and Marek's disease virus co-infection in Yellow-Chickens in Southern China.

The reticuloendotheliosis virus (REV) and the Marek's disease virus (MDV) cause reticuloendotheliosis (RE) and Marek's disease (MD) in poultry, respectively. According to epidemiological results obtained in our laboratory from 2010 to 2017, the positive rates of REV and MDV co-infection remained at low levels. In the present study, during the period of October 2018 to July 2020, 4 clinical cases with high morbidity (5%-20%) and mortality (2%-10%), caused by the co-infection of REV and vv+ MDV-like strains, were diagnosed and analyzed by histopathological observation, cell cultures and detection with ELISA and IFA, and the PCR and by sequencing of the isolates' genes. Sequencing and the sequence analysis on the complete genomes of the REV strains and the meq genes of the MDV strains were performed. The results, based on the complete genome, LTR, gag, pol, and env genes' nucleotide sequences of the REV strains, showed that the REV isolates and 68.0 % (17/25) of the reference strains were in a same branch, and all had a high sequence similarity (>99.0%). The similarities between the four isolates and a vv+MDV strain GX18NNM4 were very high, up to 99.3-99.8%. Also, the amino acid residuals at locations 71, 77, 80, 115, 139, 176, and 217 were all the same as A, E, Y, A, A, R, and A, respectively, in the meq gene of the four MDV isolates. In addition, the substitutes at P176R and P217A interrupted the stretches of the proline-rich repeat PPPP, indicating that these strains belonged to the vv+ MDV-like category. Our findings indicated that the more recent and frequent reemergence of REV and the subsequent co-infection with vv+ MDV-like strain has become one of the causes of the clinical outbreaks of tumors and is undoubtedly a threat to the poultry industry in southern China.

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.

An outbreak in three-yellow chickens with clinical tumors of high mortality caused by the coinfection of reticuloendotheliosis virus and Marek's disease virus: a speculated reticuloendotheliosis virus contamination plays an important role in the case.

Both reticuloendotheliosis and Marek's disease are neoplastic diseases of chickens caused by reticuloendotheliosis virus (REV) and Marek's disease virus (MDV), respectively. The infection of REV or MDV may lead to clinical tumors and also result in immunosuppression and easily allow secondary infection by other pathogens. Here, we investigated a breeder flock of three-yellow chickens in southern China that had been vaccinated with CVI988/Rispens at hatching and had experienced depression, weakness, reduction in weight gain, and an increased death rate after 120 d of age. The morbidity and mortality were 20% and 10%, respectively, at 140 d of age when this infection was diagnosed. The necropsy of the birds revealed significant tumor-like lesions in the heart, liver, spleen, and ceca. Peripheral blood lymphocytes and tumor-like tissues were sampled for PCR detection and for histopathological observation, for virus isolation and the subsequent immunofluorescent assay on the cell cultures and for gene sequencing of the isolated viruses. A REV isolate GX18NNR1 and a MDV isolate GX18NNM5 were both recovered from the sampled bird. Further phylogenetic analysis based on the env gene of REV and the meq gene of MDV demonstrated that GX18NNR1 was closely related to the reference REV strain MD-2, which was isolated from a contaminated commercial turkey herpesvirus vaccine. In addition, the GX18NNM5 was found to belong to the Chinese very virulent MDV strains' cluster. The coinfection of REV and MDV may contribute to tumor outbreaks with high morbidity and mortality in three-yellow chicken flocks.

Emergence of spontaneously occurring neoplastic disease caused by reticuloendotheliosis virus in breeding Muscovy ducks in China, 2019.

Reticuloendotheliosis virus (REV) has a wide range of avian hosts leading to reticuloendotheliosis, and its characteristic of vertical transmission makes it to be one of the most important diseases in breeder avian populations. Up to date, reports on neoplastic disease caused by REV in breeding ducks are few. Here, spontaneously occurring neoplastic disease caused by REV in breeding Muscovy ducks was reported in Guangdong province, China. The most significant gross lesions of sick ducks were tumour-bearing liver and enlarged spleen. Histopathological examination found proliferation of malignant lymphoreticular cells in the liver and reticuloendothelial cells in the spleen. REV strain, CH-GD2019, was successfully isolated using DF-1 cells, and the presence of REV was confirmed by PCR detection and transmission electron microscopy. The length of complete proviral genome is 8,238 nucleotides. Genetic and phylogenetic analyses revealed that CH-GD2019 was closely related to chicken-origin REV strains circulating in China. The results will provide a basic data for better understanding of REV in breeding ducks and suggest that REV from chickens may be a threat to ducks.

Proteome analysis of reticuloendotheliosis-virus-infected chicken embryo fibroblast cells through iTRAQ-based quantitative proteomics.

Reticuloendotheliosis virus (REV) is an important representative avian retrovirus. To improve our understanding of the host cellular responses to virus infection and the pathogenesis of REV infection, we applied isobaric tags for relative and absolute quantification (iTRAQ) labeling coupled with multidimensional liquid chromatography-tandem mass spectrometry to detect changes in protein levels in chicken embryo fibroblast cells (CEFs) that were infected with REV or mock infected. In total, 605 cellular proteins were differentially expressed, among which 196, 345, and 286 were differentially expressed in REV-infected CEFs at 1, 3, and 5 days postinfection, respectively. Gene Ontology analysis indicated that the biological processes of the differentially expressed proteins were primarily related to cellular processes, metabolic processes, biological regulation, response to stimulus, and immune system processes and that the molecular functions in which the differentially expressed proteins were mainly involved were binding, catalytic activity, and enzyme regulator activity. Pathway analysis showed that a total of 143, 167, and 179 pathways, including protein digestion and absorption, focal adhesion, ECM-receptor interaction, cytokine-cytokine receptor interaction, Toll-like receptors, and JAK-STAT signaling, were enriched in REV-infected CEFs at 1, 3, and 5 days postinfection, respectively. In conclusion, this study is the first to analyze the protein profile of REV-infected CEFs using an iTRAQ approach. The results of this study provide valuable information for better understanding the host response to REV infection.

Genetic characterization of reticuloendotheliosis virus in chickens in Thailand.

Reticuloendotheliosis virus (REV) causes an immunosuppressive, runting, and oncogenic disease in poultry, posing a significant threat to the poultry industry. In Thailand, an unidentified disease associated with runting-stunting syndrome and neoplasia, resembling REV infection, has been continuously observed in several chicken farms. However, REV infection in Thailand has never been reported. In this study, we investigated the occurrence and genetic characteristics of REVs in chickens in Thailand from 2013 to 2016. Of the 130 clinical samples obtained from 29 chicken farms from 9 provinces located in the major chicken-raising regions of Thailand, including the central, eastern, northern, and northeastern parts of Thailand, 51 samples (39.23%) and 21 farms (72.41%) were REV-positive. REV-positive samples were detected in all 9 provinces tested. Our results demonstrated that REV was extensively distributed in the major chicken-raising regions of Thailand. Phylogenetic analysis of the whole genome sequence showed that Thai REV was most closely related to Chinese, Taiwanese, and the US REV strains isolated from different avian species and clustered into REV subtype III. This finding indicates that REV subtype III was predominantly circulated in Thai chicken flocks. This study is the first report on REV infection in chickens in Thailand. Our findings raise the awareness of REV as another causative agent of runting and oncogenic disease in chickens in Thailand and highlight the wide distribution of REV infection among chickens worldwide.

Detection of Fowlpox virus carrying distinct genome segments of Reticuloendotheliosis virus.

Fowlpox virus (FWPV), the type species of the genus Avipoxvirus family Poxviridae, is a large double-stranded DNA virus that causes fowlpox in chickens and turkeys. Notably, sequences of the avian retrovirus reticuloendotheliosis virus (REV) are frequently found integrated into the genome of FWPV. While some FWPV strains carry remnants of the REV long terminal repeats (LTRs), other strains have been shown to contain insertions of nearly the full-length REV provirus in their genome. In the present study we detected heterogeneous FWPV populations carrying the REV LTR or the near full-length REV provirus genome in a Merriam's wild turkey (Meleagris gallopavo merriami). The bird presented papules distributed throughout the non-feathered areas of the head. Avipoxvirus-like virions were observed in the lesions by transmission electron microscopy and the presence of FWPV was confirmed by DNA sequencing. Metagenomic sequencing performed on nucleic acid extracted from the skin lesions revealed two FWPV genome populations carrying either a 197-nt remnant of the REV LTR or a 7939-nt long fragment corresponding to the full-length REV provirus. Notably, PCR amplification using primers targeting FWPV sequences flanking the REV insertion site, confirmed the natural occurrence of the heterogeneous FWPV genome populations in one additional clinical sample from another turkey affected by fowlpox. Additionally, sequencing of a historical FWPV isolate obtained from chickens in the US in 2000 also revealed the presence of the two FWPV-REV genome populations. Results here demonstrate distinct FWPV populations containing variable segments of REV genome integrated into their genome. These distinct genome populations are likely a result of homologous recombination events that take place during FWPV replication.

Analysis of alternative splicing in chicken embryo fibroblasts in response to reticuloendotheliosis virus infection.

Alternative splicing (AS) plays a significant role in regulation of genomic expression at the transcriptional level and is involved in many important biological functions of cells, thus a gene can be spliced into distinct transcript variants then translated to many different kinds of protein. Reticuloendotheliosis virus (REV) is a kind of retrovirus that can infect multiple avian species, leading to runting syndrome, immunosuppression and oncogenesis. In this present study, we analyzed AS in REV-infected chicken embryo fibroblasts (CEFs) which were inoculated with the second generation of REV (group VB) and compared with normal CEFs (group C) by high-throughput RNA sequencing technology. A total of 6,939 genes which were alternatively spliced were detected, among them, skipped exon (SE) was the most common pattern. Moreover, 5,607 AS genes were detected as differentially expressed; compared with group C, group VB has 2,825 genes upregulated significantly and 2,782 genes downregulated significantly. These 5,607 differentially expressed AS genes are involved in many important biological processes. Many of them are involved in apoptosis and tumourigenesis. We also proved, by agarose gel electrophoresis, that AS events predicted by our study are authentic and AS is closely related with apoptosis and tumourigenesis in REV-infected CEFs. Our study provides the best analysis to date of the potential link between AS and CEFs in response to REV infection. Research highlights Transcriptomics analysis of REV-infected CEFs using high-throughput sequencing. Potential link between alternative splicing and CEFs in response to REV infection. Skipped exon is the most common spliced pattern in REV-infected CEFs. Differentially expressed genes mainly involved in apoptosis and tumourigenesis.

Inhibition of v-rel-Induced Oncogenesis through microRNA Targeting.

Several studies have shown that microRNA-targeting is an effective strategy for the selective control of tissue-tropism and pathogenesis of both DNA and RNA viruses. However, the exploitation of microRNA-targeting for the inhibition of transformation by oncogenic viruses has not been studied. The v-rel oncoprotein encoded by reticuloendotheliosis virus T strain (Rev-T) is a member of the rel/NF-κB family of transcription factors capable of transforming primary chicken spleen and bone marrow cells. Here, by engineering the target sequence of endogenous microRNA miR-142 downstream of the v-rel gene in a Replication-Competent ALV (avian leukosis virus) long terminal repeat (LTR) with a splice acceptor (RCAS) vector and using a v-rel-induced transformation model of chicken embryonic splenocyte cultures, we show that hematopoietic-specific miR-142 can inhibit the v-rel-induced transformation, and that this inhibition effect is due to the silencing of v-rel expression. The data supports the idea that microRNA-targeting can be used to inhibit viral oncogene-induced oncogenesis.

Development of reliable techniques for the differential diagnosis of avian tumour viruses by immunohistochemistry and polymerase chain reaction from formalin-fixed paraffin-embedded tissue sections.

A variety of techniques have been developed as diagnostic tools for the differential diagnosis of tumours produced by Marek's disease virus from those induced by avian leukosis virus and reticuloendotheliosis virus. However, most current techniques are unreliable when used in formalin-fixed paraffin-embedded (FFPE) tissues, which often is the only sample type available for definitive diagnosis. A collection of tumours was generated by the inoculation of different strains of Marek's disease virus, reticuloendotheliosis virus or avian leukosis virus singularly or in combination. FFPE tissue sections from tumour and non-tumour tissues were analysed by optimized immunohistochemistry (IHC) techniques and traditional as well as quantitative polymerase chain reaction (PCR) with newly designed primers ideal for DNA fragmented by fixation. IHC and PCR results were highly sensitive and specific in tissues from single-infected birds. Virus quantity was higher in tumours compared to non-tumour spleens from Marek's disease (MD) virus-infected birds. Thus, using FFPE sections alone may be sufficient for the diagnosis of MD by demonstration of high quantities of viral antigens or genome in tumour cells, along with the absence of other tumour viruses by traditional PCR, and if standard criteria are met based on clinical history and histology. IHC furthermore allowed detection of the specific cells that were infected with different viruses in tumours from birds that had been inoculated simultaneously with multiple viruses. Following validation with field samples, these new protocols can be applied for both diagnostic and research purposes to help accurately identify avian tumour viruses in routine FFPE tissue sections.

The experimental transmission of reticuloendotheliosis virus by cock semen.

Following artificial insemination, the egg-laying rate of a large-scale breeder chicken flock declined by10-15 %. Real-time quantitative polymerase chain reaction (qPCR) analysis detected the presence of reticuloendotheliosis virus (REV) in semen from the breeder cocks used. Six REV strains were successfully isolated from semen randomly extracted from those cocks. Additionally, the whole sequence of SDAUR-S1 was sequenced and analysed. Cock models with continuous production of REV-positive semen were established by intravenous injection with SDAUR-S1. Eggs were then collected from hens after artificial insemination with REV-positive semen, for virus detection. The positive REV antibody rate for egg albumen was 58.3 % and the REV-positive rate for hatched embryos was 8.3 %, which suggested not only that REV can infect cock semen, but can also infect the offspring. In conclusion, the present study is the first to report on the isolation, genome analysis and transmission of REV in cock semen.

Characterization of a Gallid herpesvirus 2 strain with novel reticuloendotheliosis virus long terminal repeat inserts.

A bacterial artificial chromosome clone, designated LCY, was constructed from a Gallid herpesvirus 2 (GaHV-2) isolate from a GaHV-2 and reticuloendotheliosis virus co-infected clinical sample. The LCY GaHV-2 insert was sequenced and found to consist of 175,319 nucleotides. LCY GaHV-2 open reading frames (ORFs) had a high sequence identity to those of reference strains. The major difference was that two REV long terminal repeats (LTRs), in the same direction, were inserted at the internal repeat short (IRs)/unique short (Us) and Us/terminal repeat short (TRs) junctions. In addition, the a-like sequence and UL36 were different from other strains. Phylogenetic analysis revealed that LCY was closely related to pandemic strains in China. A pathogenicity study and a vaccination-challenge test were performed on LCY and the reference strain, GA. The results showed that LCY induced gross Marek's disease (MD) lesions and mortality in 71.4 and 7.1% of chickens, respectively, which are lower rates than those observed for the reference strain GA (85.7 and 35.7%). The commercially available CVI988 vaccine provided complete protection against LCY and GA (100%). These results showed that the isolate exhibited lower pathogenicity in SPF chickens. This study revealed that a novel pattern of LTR inserts was found in the strain LCY and that the strain was of low virulence. The present work expands the available genetic information for GaHV-2 and will be useful for the control of MD in China.

Analysis of the spleen proteome of chickens infected with reticuloendotheliosis virus.

Infection with reticuloendotheliosis virus (REV), a gammaretrovirus in the family Retroviridae, can result in immunosuppression and subsequent increased susceptibility to secondary infections. In the present study, we identified differentially expressed proteins in the spleens of chickens infected with the REV-A HLJ07I strain, using two-dimensional gel electrophoresis on samples from time points coinciding with different phases of the REV life cycle. Differentially expressed proteins were identified using one-dimensional liquid chromatography electrospray ionization tandem mass spectrometry (1D LC ESI MS/MS). Comparative analysis of multiple gels revealed that the majority of changes occurred at early stages of infection. In total, 60 protein spots representing 28 host proteins were detected as either quantitatively (false discovery rate [FDR] ≤0.05 and fold change ≥2) or qualitatively differentially expressed at least once during different sampling points. The differentially expressed proteins identified in this study included antioxidants, molecular chaperones, cellular metabolism, formation of the cytoskeleton, signal transduction, cell proliferation and cellar aging. The present findings provide a basis for further studies to elucidate the role of these proteins in REV-host interactions. This could lead to a better understanding of REV infection mechanisms that cause immune suppression.