Avian leukosis virus subgroup A and B infection in wild birds of Northeast China

Current knowledge on the epidemiology and prevention of Avian leukosis virus in China

Avian leukosis virus (ALV) is an enveloped retrovirus with a single-stranded RNA genome, belonging to the genus Alpharetrovirus within the family Retroviridae. The disease (Avian leukosis, AL) caused by ALV is mainly characterized by tumor development and immunosuppression in chickens, which increases susceptibility to other pathogens and leads to significant economic losses in the Chinese poultry industry. The government and poultry industry have made lots of efforts to eradicate ALV, but the threat of which remains not vanished. This review provides a summary of the updated understanding of ALV in China, which mainly focuses on genetic and molecular biology, epidemiology, and diagnostic methods. Additionally, promising antiviral agents and ALV eradication strategies performed in China are also included.

Avian Leukosis: Will We Be Able to Get Rid of It?

Avian leukosis viruses (ALVs) have been virtually eradicated from commercial poultry. However, some niches remain as pockets from which this group of viruses may reemerge and induce economic losses. Such is the case of fancy, hobby, backyard chickens and indigenous or native breeds, which are not as strictly inspected as commercial poultry and which have been found to harbor ALVs. In addition, the genome of both poultry and of several gamebird species contain endogenous retroviral sequences. Circumstances that support keeping up surveillance include the detection of several ALV natural recombinants between exogenous and endogenous ALV-related sequences which, combined with the well-known ability of retroviruses to mutate, facilitate the emergence of escape mutants. The subgroup most prevalent nowadays, ALV-J, has emerged as a multi-recombinant which uses a different receptor from the previously known subgroups, greatly increasing its cell tropism and pathogenicity and making it more transmissible. In this review we describe the ALVs, their different subgroups and which receptor they use to infect the cell, their routes of transmission and their presence in different bird collectivities, and the immune response against them. We analyze the different systems to control them, from vaccination to the progress made editing the bird genome to generate mutated ALV receptors or selecting certain haplotypes.

Global Maps of Avian Leukosis Viruses: Research Trends and Themes Based on Networking

Avian leukosis virus (ALV) has a tremendous adverse impact on the poultry industry. Since its discovery, research on different aspects of ALV have been published. Due to the vast academic emphasis and economic importance of the ALV infection in poultry worldwide, this bibliometric analysis explored the scientific output associated with ALV utilizing the Web of Science (Core Collection) database. The relevant data were collected using the search query "AVIAN LEUKOSIS VIRUS", further refined by document types (article, book chapter, and proceedings paper). Finally, 1060 items with full records were imported in Plaintext and tab-delimited formats. The data analysis was carried out using MS Excel, VOS viewer, and R (Biblioshiny) software. Chinese and American research institutions produced the majority of papers during study time period. The Journal of Virology and Avian Diseases appeared as the favorite journal/source for publications. Apart from the avian leukosis virus and the ALV-J, the important keywords mentioned included avian leukosis virus subgroup j, chicken, and retrovirus. The analysis revealed substantial findings on ALV research, with a strong research response from the USA and China.

Enhanced pathogenicity by up-regulation of A20 after avian leukemia subgroup a virus infection

Avian leukemia virus subgroup A (ALV-A) infection slows chicken growth, immunosuppression, and tumor occurrence, causing economic loss to the poultry industry. According to previous findings, A20 has a dual role in promoting and inhibiting tumor formation but has rarely been studied in avians. In this study, A20 overexpression and shRNA interference recombinant adenoviruses were constructed and inoculated into chicken embryos, and ALV-A (rHB2015012) was inoculated into 1-day-old chicks. Analysis of body weight, organ index, detoxification, antibody production, organ toxin load, and Pathological observation revealed that A20 overexpression could enhance ALV-A pathogenicity. This study lays the foundation for subsequent exploration of the A20-mediated tumorigenic mechanism of ALV-A.

Antibody profiles of avian leukosis virus subgroups A/B and J In layer flocks suspected to have Marek’s disease in Nigeria

Previous reports indicate high seroprevalence of avian leukosis virus (ALV) p72 antigen in layer flocks suspected to have Marek’s disease (MD) in Kaduna and Plateau States. However, the specific subgroups responsible for ALV infection in layers in the States are still unknown, hence the need for this study. Therefore, the objective of this study was to determine the antibody profiles of ALV subgroups A/B and J in layer flocks suspected to have MD in Kaduna and Plateau States. Sera from 7 and 16 layer flocks suspected to have MD in Kaduna and Plateau States respectively, were screened for the presence of antibodies to ALV subgroups A/B and J using IDEXX enzyme linked immunosorbent assay (ELISA) kits. Out of the seven layer flocks screened in Kaduna State, antibodies to ALV subgroup A/B was detected in six of the flocks (85.7%), while antibodies to ALV subgroup J was detected in only one flock (14.3%). Antibodies to both ALV subgroups A/B and J were detected in one flock (14.3%), which suggests co-infection of the two ALV subgroups. Out of the 16 flocks screened in Plateau State, antibodies to ALV subgroup A/B were detected in 15 flocks (93.8%), while antibodies to ALV subgroup J were detected in six flocks (37.5%). Antibodies to both ALV subgroups A/B and J were detected in five flocks (31.3%). The high detection of antibodies to ALV A/B suggests that ALV infection in layers is mostly due to ALV subgroup A or B in the study areas.

Rapid detection of avian leukosis virus subgroup J by cross-priming amplification

Avian leukosis virus subgroup J (ALV-J) causes oncogenic disease in chickens in China, resulting in great harm to poultry production, and remains widespread in China. Herein, we employed a cross-priming amplification (CPA) approach and a nucleic acid detection device to establish a visual rapid detection method for ALV-J. The sensitivity of CPA, polymerase chain reaction (PCR) and real-time PCR (RT-PCR) was compared, and the three methods were used to detect ALV-J in the cell cultures which inoculated with clinical plasma. The result showed when the amplification reaction was carried out at 60 °C for just 60 min, the sensitivity of CPA was 10 times higher than conventional PCR, with high specificity, which was comparable with RT-PCR, based on detection of 123 cell cultures which inoculated with clinical plasma, the coincidence rate with real-time PCR was 97.3% (71/73). CPA detection of ALV-J does not require an expensive PCR instrument; a simple water bath or incubator is sufficient for complete DNA amplification, and the closed nucleic acid detection device avoids aerosol pollution, making judgment of results more intuitive and objective. The CPA assay would be a promising simple, rapid and sensitive method for identification of ALV-J.

Regulatory effects of chicken TRIM25 on the replication of ALV-A and the MDA5-mediated type I interferon response

This study focuses on the immunoregulatory effects of chicken TRIM25 on the replication of subgroup A of avian leukosis virus (ALV-A) and the MDA5-mediated type I interferon response. The ALV-A-SDAU09C1 strain was inoculated into DF1 cells and 1-day-old SPF chickens, and the expression of TRIM25 was detected at different time points after inoculation. A recombinant overexpression plasmid containing the chicken TRIM25 gene (TRIM25-GFP) was constructed and transfected into DF1 cells to analyse the effects of the overexpression of chicken TRIM25 on the replication of ALV-A and the expression of MDA5, MAVS and IFN-β. A small interfering RNA targeting chicken TRIM25 (TRIM25-siRNA) was prepared and transfected into DF1 cells to assess the effects of the knockdown of chicken TRIM25 on the replication of ALV-A and the expression of MDA5, MAVS and IFN-β. The results showed that chicken TRIM25 was significantly upregulated at all time points both in ALV-A-infected cells and in ALV-A-infected chickens. Overexpression of chicken TRIM25 in DF1 cells dramatically decreased the antigenic titres of ALV-A in the cell supernatant and upregulated the relative expression of MDA5, MAVS and IFN-β induced by ALV-A or by poly(I:C); in contrast, knockdown of chicken TRIM25 significantly increased the antigenic titres of ALV-A and downregulated the relative expression of MDA5, MAVS and IFN-β. It can be concluded that chicken TRIM25 can inhibit the replication of ALV-A and upregulate the MDA5 receptor-mediated type I interferon response in chickens. This study can help improve the understanding of the antiviral activities of chicken TRIM25 and enrich the knowledge of antiviral responses in chickens.

A Review of Pathogen Transmission at the Backyard Chicken-Wild Bird Interface

Habitat conversion and the expansion of domesticated, invasive species into native habitats are increasingly recognized as drivers of pathogen emergence at the agricultural-wildlife interface. Poultry agriculture is one of the largest subsets of this interface, and pathogen spillover events between backyard chickens and wild birds are becoming more commonly reported. Native wild bird species are under numerous anthropogenic pressures, but the risks of pathogen spillover from domestic chickens have been historically underappreciated as a threat to wild birds. Now that the backyard chicken industry is one of the fastest growing industries in the world, it is imperative that the principles of biosecurity, specifically bioexclusion and biocontainment, are legislated and implemented. We reviewed the literature on spillover events of pathogens historically associated with poultry into wild birds. We also reviewed the reasons for biosecurity failures in backyard flocks that lead to those spillover events and provide recommendations for current and future backyard flock owners.

Roles of MOV10 in Animal RNA Virus Infection

Animal epidemic diseases caused by RNA viruses are the primary threat to the livestock industry, and understanding the mechanisms of RNA virus clearance from target cells is critical to establish an effective method to reduce economic losses. As an SF-1, ATP-dependent RNA helicase in the UPF1p family, MOV10 participates in the RNA degradation of multiple viruses mediated via miRNA pathways and therefore contributes to a decrease in the replication of RNA viruses. This review primarily focuses on the bioactivity of MOV10, the mechanism of RNA virus removal, and the potential roles of MOV10 in RNA virus clearance. In addition, clues are provided to reduce animal diseases caused by RNA viruses.

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.

A cell line resistant to avian leukosis virus subgroup B infection

The expression of env proteins that bind to viral cell receptors on avian leukosis virus (ALV)-susceptible cells can block ALV infection. In this study, we constructed a cell line (DF-1/B) by expressing the ALV-B env protein in DF-1 cells. PCR, immune fluorescence assay, Western blot, and immune electron microscopy results showed that the env gene can be stably expressed in DF-1cells and the env protein could be detected on the DF-1 cell membrane. An antiviral experiment concluded that the DF-1/B cell line could be resistant to 1 × 10⁴ TCID₅₀ ALV-B virus infection, but had no inhibitory effect on other subgroup ALV. This means that the DF-1/B cell line is specifically resistant to ALV-B and can be used as a tool for ALV-B diagnosis.

Geese not susceptible to virulent subgroup J avian leukosis virus isolated from chickens

To determine whether geese are susceptible to infection by avian leukosis virus (ALV), 702 serum samples from domestic and foreign goose breeds were screened for p27 antigen as well as being inoculated into DF-1 cell cultures to isolate ALV. Although 5.7% of samples were positive for p27 antigen, reactivity appeared to be non-specific because no ALV was detected in the corresponding DF-1 cultures. To further determine whether geese are susceptible to ALV-J isolated from chickens, ALV-J strain JS09GY7 was artificially inoculated into 10-day-old goose embryos, with one-day-old hatched goslings then screened for p27 antigen and the presence of ALV. In all cases, the results of both tests were negative. Liver tissues from the 1-day-old goslings were screened using a polymerase chain reaction-based assay, which failed to amplify ALV-J gene fragments from any of the samples. Further, no histopathological damage was observed in the liver tissues. ALV-J was further inoculated intraperitoneally into one-day-old goslings, with cloacal swabs samples and plasma samples then collected every 5 days for 30 days. All samples were again negative for the presence of p27 antigen and ALV, and liver tissues from the challenged geese showed no histopathological damage and were negative for the presence of ALV-J gene fragments. Furthermore, p27 antigen detection, PCR-based screening, and indirect immunofluorescence assays were all negative following the infection of goose embryo fibroblasts with ALV-J. Together, these results confirm that virulent chicken-derived ALV-J strains cannot infect geese, and that p27 antigen detection in goose serum is susceptible to non-specific interference.

Histologic findings and viral antigen distribution in natural coinfection of layer hens with subgroup J avian leukosis virus, Marek's disease virus, and reticuloendotheliosis virus

We investigated the histologic findings and viral antigen distribution in 3 cases of natural coinfection of layer hens with subgroup J avian leukosis virus (ALV-J), Marek's disease virus (MDV), and reticuloendotheliosis virus (REV) in hens. At autopsy, diseased hens were found to have hepatosplenomegaly and thickened proventriculi, with white tumor nodules in the liver, spleen, lung, kidney, and ovary. Microscopically, most tissues had been infiltrated by neoplastic lymphocytes; the spleen, lung, proventriculus, heart, and liver had been infiltrated by both neoplastic lymphocytes and myeloblastic cells and/or primitive reticular cells. Fluorescence multiplex immunohistochemistry staining revealed ALV-J, MDV, and REV antigens co-expressed in the same tissue, even the same cell.

Comparison of Viremia, Cloacal Virus Shedding, Antibody Responses and Pathological Lesions in Adult Chickens, Quails, and Pigeons Infected with ALV-A

Subgroup A of the avian leukosis virus (ALV-A) can cause severe pathological lesions and death in infected chickens, and its reported hosts have increased recently. To assess the susceptibility of adult chickens, quails, and pigeons to ALV-A, three sets of 250-day-old birds were intraperitoneally inoculated with ALV-A. Viremia and cloacal virus shedding were dynamically detected using an immunofluorescence assay (IFA), ALV-P27 antigen ELISA or RT-PCR; pathological lesions were assessed using tissue sections; ALV-A in tissues was detected by IFA; and ALV-A antibody responses were detected using antibody ELISA kits and an immune diffusion test. The results indicated that persistent viremia occurred in 80% (8/10) of infected chickens, and transient viremia occurred in 17% (2/12) of infected quails, but no viremia occurred in infected pigeons. Cloacal virus shedding occurred intermittently in 80% (8/10) of infected chickens and in 8% (1/12) of infected quails but did not occur in infected pigeons. Severe inflammatory pathological lesions occurred in the visceral tissues of most infected chickens, and mild lesions occurred in a few of the infected quails, but no pathological lesions occurred in the infected pigeons. The ALV-A virus was detected in the visceral tissues of most infected chickens but not in the infected quails and pigeons. Obviously different ALV-A antibody responses occurred in the infected chickens, quails and pigeons. It can be concluded that adult chickens, quails and pigeons have dramatically different susceptibilities to ALV-A. This is the first report on artificial infection by ALV-A in different birds.

Fecal virome composition of migratory wild duck species

The fecal virome comprises a complex diversity of eukaryotic viruses, phages and viruses that infect the host. However, little is known about the intestinal community of viruses that is present in wild waterfowl, and the structure of this community in wild ducks has not yet been studied. The fecal virome compositions of six species of wild dabbling ducks and one species of wild diving duck were thus analyzed. Fecal samples were collected directly from the rectums of 60 ducks donated by hunters. DNA and RNA virus particles were purified and sequenced using the MiSeq Illumina platform. The reads obtained from the sequencing were analyzed and compared with sequences in the GenBank database. Viral-related sequences from the Herpesviridae, Alloherpesviridae, Adenoviridae, Retroviridae and Myoviridae viral families showed the highest overall abundances in the samples. The virome analysis identified viruses that had not been found in wild duck feces and revealed distinct virome profiles between different species and between samples of the same species. This study increases our understanding of viruses in wild ducks as possible viral reservoirs and provides a basis for further studying and monitoring the transmission of viruses from wild animals to humans and disease outbreaks in domestic animals.

Complete genome sequencing and characterization revealed a recombinant subgroup B isolate of avian leukosis virus with a subgroup J-like U3 region

One natural recombinant subgroup B avian leukosis virus (ALV) with a subgroup J-like U3 region was isolated from commercial native chickens that experienced disease in 2014 and named GX14FF03. GX14FF03 was isolated by DF-1 cell culture and then identified with ELISA detection of avian leukosis virus p27 group-specific antigen, the detection of subtype specific PCR, and indirect immunofluorescence assay with ALV-B-specific monoclonal antibody. Its complete proviral genome was sequenced and compared with the reference strains of ALVs and found that the gag and pol were relatively conservative. The gp85 of GX14FF03 showed 91.3-96.2% amino acid identity to the other ALV-B reference strains and 36.0-37.1% identity to the ALV-J reference strains, and its U3 region showed 49.4-89.3% nucleotide identity to ALV-A, B, C, D, E, K reference strains and 91.6-95.3% identity to ALV-J reference strains. Phylogenetic analysis of U3 region showed that GX14FF03 and ALV-J reference strains were in the same cluster. Moreover, an additional AIB REP1 retroviral transcription regulatory element was found in GX14FF04 U3 region which was only presenting in ALV-J strains. These results suggested that isolate GX14FF03 may be a recombinant ALV-B with the ALV-J-like U3 region.

A novel avian retrovirus associated with lymphocytoma isolated from a local Chinese flock induced significantly reduced growth and immune suppression in SPF chickens

Avian Leukosis Viruses (ALVs) are associated with neoplasias, immune suppression and reduced performance in chicken flocks. In the present study, a naturally occurring recombinant strain of ALV (FJ15HT0) was isolated from an infected flock of Chinese "Hetian" chickens, and was subsequently identified as an exogenous ALV by immuno-fluorescence assay (IFA), PCR and following entire proviral DNA nucleotide sequencing. This isolate is revealed as a novel recombinant virus, lacking viral oncogenes, with the gp85 (93.4%) of subgroup B, the U3 (92.1%) and R (95.2%) region of subgroup J, the U5 (93.8%) region and 5'UTR (95.7%) of subgroup C, as well as the gp37 (90.6%) and 3' (92.2%) of ALV-E. The simulative congenital infection with this isolate in SPF chickens resulted in significant weight loss (P<0.05) and a significant reduction in the humoral immune response to the live NDV vaccine (P<0.05), but not to the inactive AIV-H₅ vaccine (P>0.05). Foci of lymphocytomas were observed in tissues of congenitally infected chickens at 11 weeks post-hatch, demonstrating the acute oncogenicity of the isolate.

Immunity to Avian Leukosis Virus: Where Are We Now and What Should We Do?

Avian leukosis virus (ALV) is an avian oncogenic retrovirus causing enormous economic losses in the global poultry industry. Although ALV-related research has lasted for more than a century, there are no vaccines to protect chickens from ALV infection. The interaction between chickens and ALV remains not fully understood especially with regard to the host immunity. The current review provides an overview of our current knowledge of innate and adaptive immunity induced by ALV infection. More importantly, we have pointed out the unknown area involved in ALV-related studies, which is worthy of our serious exploring in future.

Inhibition of ERK/MAPK suppresses avian leukosis virus subgroup A and B replication

We have previously shown that the extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) pathway contributes to subgroup J avian leukosis virus (ALV-J) replication and tumorigenicity. However, a role for ERK/MAPK signaling in ALV-A and ALV-B replication is unknown. In this study we successfully constructed and recovered a recombinant form of ALV-A strain GD13-1 which showed similarities in growth to the parental wild type virus in vitro. ALV subgroups J, A or B all triggered ERK2 activation in primary CEF cells. ERK/MAPK inhibition markedly suppressed ALV-A and ALV-B replication as shown by extremely low levels of viral transcription and virus protein production. This finding provides evidence that ERK/MAPK signaling responses play important roles in ALV replication and may represent novel drug targets for therapeutic intervention strategies.

A Serosurvey of Greater Sage-Grouse ( Centrocercus urophasianus ) in Nevada, USA

To better understand the potential avian diseases in Greater Sage-grouse ( Centrocercus urophasianus ) in the Great Basin in Nevada, US, we collected 31 blood samples March-April 2014 and tested for antibodies to eight viruses and two bacteria. Specifically, sera were tested for antibodies to avian leukosis virus type A, B, and J (ALV-A, ALV-B, and ALV-J, respectively), infectious bursal disease virus, infectious bronchitis virus, reticuloendothelial virus, avian influenza virus (AIV), West Nile virus, Pasteurella multocida (PM), and Salmonella enterica serovar Pullorum. Serum antibodies against ALV-A and -B (1/31, 3%), ALV-J (5/31, 16%), PM (1/31, 3%), and AIV (2/31, 6%) were detected by enzyme-linked immunosorbent assay (ELISA). While ELISA tests used have only been validated in domestic poultry, the serologic data should be used as a potential indicator of the range of bacterial and viral infectious agents that can infect the Greater Sage-grouse.

Rapid detection of the common avian leukosis virus subgroups by real-time loop-mediated isothermal amplification

Background

Subgroups A, B, E and J are the major subgroups of avian leukosis virus (ALV) infecting chickens. ALV infection has become endemic in China and has a significant negative effect on the poultry industry. Consequently, there is an urgent need for a specific, sensitive and rapid method for diagnosis and eradication of ALV. Therefore, we developed a simple and rapid real-time loop-mediated isothermal amplification (LAMP) reaction for the timely detection of the common ALV subgroups, whereby the amplification can be obtained in 35 min under isothermal conditions at 63 °C, ability to specific, sensitive and rapid detect all the common ALV subgroups.

Methods

A set of four specific primers was designed to target the sequences of the pol gene of ALV, and the loop-mediated isothermal amplification (LAMP) assay were developed and compared with PCR and virus isolation methods.

Results

The results from specificity of the LAMP assay showed that only target ALVs DNA was amplified. The LAMP assay demonstrated a sensitivity of 20 copies/reaction of ALV DNA, which was 10 times higher than the conventional PCR measurement. To further evaluate the reliability of the method, the assay was evaluated with ALV DNA from a panel of 81 clinical samples suspected of ALV infection. The results verify that the LAMP method was more sensitive than the conventional PCR and virus isolation method.

Conclusion

In conclusion, the developed LAMP assay was a simple, inexpensive, sensitive method for the rapid detection of the most common subgroups of ALV, and it provided a useful and practical tool in the eradication program for ALV in the poultry industry.

Development and application of SYBR Green I real-time PCR assay for the separate detection of subgroup J Avian leukosis virus and multiplex detection of avian leukosis virus subgroups A and B

Background

Subgroup A, B, and J ALVs are the most prevalent avian leukosis virus (ALV). Our study attempted to develop two SYBR Green I-based real-time PCR (RT-PCR) assays for specific detection of ALV subgroup J (ALV-J) and multiplex detection of ALV subgroups A and B (ALV-A/B), respectively.

Results

The two assays showed high specificity for ALV-J and ALV-A/B and the sensitivity of the two assays was at least 100 times higher than that of the routine PCR assay. The minimum virus detection limit of virus culture, routine PCR and real-time PCR for detection of ALV-A strain was 10³ TCID₅₀ units, 10² TCID₅₀ units and fewer than 10 TCID₅₀ units, respectively. In addition, the coefficients of variation for intra- and inter-assay were both less than 5%. Forty clinical plasma samples were evaluated by real-time PCR, routine PCR, and virus culture with positive rates of 80% (32/40), 72.5% (29/40) and 62.5% (25/40), respectively. When the assay for detection of ALV-J was used to quantify the viral load of various organ tissues in chicken inoculated by ALV-J strains CHN06 and NX0101, the results exhibited that ALV-J genes could be detected in all organ tissues examined and the highest copies of ALV-J were mainly in heart and kidney samples at 30 weeks post-infection. Except in lung, the virus copies of CHN06 group were higher than that of NX0101 group in various organ tissues.

Conclusions

The SYBR Green I-based real-time RT-PCR assay provides a powerful tool for the detection of ALV and study of virus replication and infection.

The MET gene is a common integration target in avian leukosis virus subgroup J-induced chicken hemangiomas

Avian leukosis virus subgroup J (ALV-J) is a simple retrovirus that can cause hemangiomas and myeloid tumors in chickens and is currently a major economic problem in Asia. Here we characterize ALV-J strain PDRC-59831, a newly studied U.S. isolate of ALV-J. Five-day-old chicken embryos were infected with this virus, and the chickens developed myeloid leukosis and hemangiomas within 2 months after hatching. To investigate the mechanism of pathogenesis, we employed high-throughput sequencing to analyze proviral integration sites in these tumors. We found expanded clones with integrations in the MET gene in two of the five hemangiomas studied. This integration locus was not seen in previous work characterizing ALV-J-induced myeloid leukosis. MET is a known proto-oncogene that acts through a diverse set of signaling pathways and is involved in many neoplasms. We show that tumors harboring MET integrations exhibit strong overexpression of MET mRNA.

IMPORTANCE

These data suggest that ALV-J induces oncogenesis by insertional mutagenesis, and integrations in the MET oncogene can drive the overexpression of MET and contribute to the development of hemangiomas.

Antibody responses induced by recombinant ALV-A gp85 protein vaccine combining with CpG-ODN adjuvant in breeder hens and the protection for their offspring against early infection

To observe the antibody responses induced by recombinant A subgroup avian leukosis virus (ALV-A) gp85 protein vaccine plus CpG-ODN adjuvant and the protection of maternal antibodies (MAbs) for the hatched chickens against early infection, the gp85 gene was amplified from the proviral cDNA of ALV-A-SDAU09C1 strain using PCR and the recombinant plasmid containing target gene was constructed and expressed in EscherichiaColi. The expressed product was confirmed using SDS-PAGE and western blot that it is about 46KD of recombinant protein. The purified recombinant proteins combining with CpG-ODN adjuvant or Freund's adjuvant were inoculated into the breeder hens, the ALV-A antibodies in serum and in egg-yolk were detected; the fertilized eggs from the vaccinated hens with different titers of egg-yolk antibody were hatched and then challenged with 10(4.2)/0.1mL TCID50 of ALV-A-SDAU09C1 strain, all the hatched chickens were weekly detected for the viremias and the cloacal swab P27 antigen and pathological lesions; the neutralizing test of antisera in vitro was conducted. The results showed that the recombinant gp85 proteins combining with CpG-ODN adjuvant could induce the breeder hens to produce better antibody responses than gp85 protein with Freund's adjuvant or without adjuvant; the MAbs with higher titers induced by CpG-ODN+gp85 proteins could obviously decrease the ratios of viremias (13% vs 33%), cloacal detoxification (20% vs 67%) and death (0% vs 22%) caused by ALV-A infection than those by gp85 protein without adjuvant. The results of the neutralizing test indicated that the antisera from the hatched chickens could neutralize the ALV-A-SDAU09C1 strain in vitro, but which depends on the antibody titers. The results of IFA confirmed that the serum antibody could combine with the ALV in DF1 cells. It can be concluded that the prepared ALV-A gp85 subunit vaccine combining with CpG-ODN adjuvant could induce the breeder hens to produce better neutralizing antibody responses and protect 80% of their offspring chickens against early infection.

First finding of subgroup-E avian leukosis virus from wild ducks in China

To analyze the status of avian leukosis virus subgroup E (ALV-E) in wild ducks in China, we collected 276 wild ducks, including 12 species, from four provinces of China. The PCR detection for ALV-E identified four samples as positive samples and the detection rate was 1.45%. The env sequences of ALV-E were cloned and sequenced. In gp85, genes of the four ALV-E strains showed a high homology (98.1-99.5%) with ev-1, ev-3, and SD0501 and more than 90% homology with other subgroup-A and subgroup-B avian leukosis viruses. However, they showed a slightly lower identity with subgroup-J (NX0101 and HPRS103), from 47.5 to 48.1%. Simultaneously, a further comparison with ALV-E representative isolates indicated that the amino acid substitutions of the four wild duck strains were distributed throughout the gp85. In total, these results suggested that the subgroup-E avian leukosis virus has been found in wild ducks in China.

Molecular characteristics of the complete genome of a J-subgroup avian leukosis virus strain isolated from Eurasian teal in China

The J-subgroup avian leukosis virus (ALV-J) strain WB11098J was isolated from a wild Eurasian teal, and its proviral genomic sequences were determined. The complete proviral sequence of WB11098J was 7868 nt long. WB11098J was 95.3.9 % identical to the prototype strain HPRS-103, 94.2 % identical to the American strain ADOL-7501, 94.5-94.7 % identical to Chinese broiler isolates, 94.8-97.5 % identical to layer chicken isolates, and 94.4-95.0 % identical to Chinese local chicken isolates at the nucleotide level. Phylogenetic analysis showed that the WB11098J isolate shared the greatest homology with the layer strain SD09DP03 and was included in the same cluster. Interestingly, two 19-bp insertions in the U3 regions of the 5'LTR and 5'UTR that were most likely derived from other retroviruses were found in the WB11098J isolate. These insertions separately introduced one E2BP-binding site in the U3 region of the 5'LTR and a RNA polymerase II transcription factor IIB and core promoter motif of ten elements in the 5'UTR. A 5-bp deletion was identified in the U3 region of the 5'LTR. No nucleotides were deleted in the rTM or DR-1 regions in the 3'UTR. A 1-bp deletion was detected in the E element and introduced a specific and distinct binding site for c-Ets-1. Our study is the first to report the molecular characteristics of the complete genome of an ALV-J that was isolated from a wild bird and will provide necessary information for further understanding of the evolution of ALV-J.

Detection and molecular characterization of J subgroup avian leukosis virus in wild ducks in China

To assess the status of avian leukosis virus subgroup J (ALV-J) in wild ducks in China, we examined samples from 528 wild ducks, representing 17 species, which were collected in China over the past 3 years. Virus isolation and PCR showed that 7 ALV-J strains were isolated from wild ducks. The env genes and the 3′UTRs from these isolates were cloned and sequenced. The env genes of all 7 wild duck isolates were significantly different from those in the prototype strain HPRS-103, American strains, broiler ALV-J isolates and Chinese local chicken isolates, but showed close homology with those found in some layer chicken ALV-J isolates and belonged to the same group. The 3′UTRs of 7 ALV-J wild ducks isolates showed close homology with the prototype strain HPRS-103 and no obvious deletion was found in the 3′UTR except for a 1 bp deletion in the E element that introduced a binding site for c-Ets-1. Our study demonstrated the presence of ALV-J in wild ducks and investigated the molecular characterization of ALV-J in wild ducks isolates.

Avian retroviral replication

Avian retroviruses were originally identified as cancer-inducting filterable agents in chicken neoplasms at the beginning of the 20th century. Since their discovery, the study of these simple retroviruses has contributed greatly to our understanding of viral replication and cancer. Avian retroviruses continue to evolve and have great economic importance in the poultry industry worldwide. The aim of this review is to provide a broad overview of the genome, pathology, and replication of avian retroviruses. Notable gaps in our current knowledge are highlighted, and areas where avian retroviruses differ from other retroviruses are emphasized.