Nonbursal lymphomas induced by nondefective reticuloendotheliosis virus

Cytological and immunocytological detection and differentiation of Marek's disease and lymphoid leucosis in poultry

Marek's disease (MD) and lymphoid leucosis (LL) are the major diseases causing lymphoid tumors in chickens accounting for high economical losses. Gross examination could not yield definite diagnosis owing to their similar presentation of lesions. Thus present work was aimed for diagnosis and differentiation of MD and LL by utilizing simple cytology and novel immunocytology techniques. Cytological examination was carried out on slides with tumor touch imprints stained by simple Giemsa staining. The diagnosis was mainly achieved based on morphology of cell population. In the present study, out of a total of 595 cases examined, 502 cases had pleomorphic lymphocytic cell population suggestive of MD and 53 cases had uniform lymphocytic/lymphoblast cell population suggestive of LL, while the rest 40 cases remained inconclusive. A definitive diagnosis was achieved after performing immunocytology using specific antibodies that revealed 518 cases had reactivity for Meq oncoprotein specific for MD and 77 cases showed immunoreactivity for IgM in transformed B-cells confirming LL. The technique of immunocytology which has been useful for detecting human viral pathogens and MD in poultry has been applied for the first time as a novel, simple, rapid and inexpensive technique that could be used as an alternate test to effectively detect and differentiate MD and LL in poultry.

An outbreak of lymphomas in a layer chicken flock previously infected with fowlpox virus containing integrated reticuloendotheliosis virus

Visceral lymphomas occurred in a 236-day-old layer flock previously diagnosed with reticuloendotheliosis virus (REV)-integrated fowlpox virus (FPV) infection at the age of 77 days. Common pathologic lesions were multiple neoplastic nodules of homogeneous lymphocytes in the livers and spleens of all submitted chickens. All neoplastic tissues were positive for the REV envelope (env) gene by PCR. In a retrospective molecular study of FPV-infected 77-day-old chickens from the same flock, we identified nearly full-length REV provirus integrated into the genome of FPV as well as the REV env gene in trachea samples, whereas only the REV LTR region was present in the FPV strain used to vaccinate this flock. The 622-bp REV env gene nucleotide sequence derived from the trachea and neoplastic tissues was identical. Commercial ELISA of serum samples revealed that all chickens aged between 17 and 263 days in this flock were positive for REV but not for avian leukosis virus. Taken together, the evidence suggests that the visceral lymphomas were caused by a REV-integrated FPV field strain. FPV infections of commercial chickens should be followed up by careful monitoring for manifestations of REV infection, including lymphomas and immune depression, considering the ease with which the REV provirus appears to be able to integrate into the FPV genome.

The extraordinary evolutionary history of the reticuloendotheliosis viruses

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

Insertion of reticuloendotheliosis virus long terminal repeat into a bacterial artificial chromosome clone of a very virulent Marek's disease virus alters its pathogenicity

Co-cultivation of the JM/102W strain of Marek's disease virus (MDV) with reticuloendotheliosis virus (REV) resulted in the generation of a recombinant MDV containing the REV long terminal repeat (LTR) named the RM1 strain of MDV, a strain that was highly attenuated for oncogenicity but induced severe bursal and thymic atrophy. We hypothesize that the phenotypic changes were solely due to the LTR insertion. Furthermore, we hypothesize that insertion of REV LTR into an analogous location in a different MDV would result in a similar phenotypic change. To test these hypotheses, we inserted the REV LTR into a bacterial artificial chromosome (BAC) clone of a very virulent strain of MDV, Md5, and designated the virus rMd5-RM1-LTR. The rMd5-RM1-LTR virus and the rMd5 virus were passaged in duck embryo fibroblast cells for up to 40 passages before pathogenicity studies. Susceptible chickens were inoculated intra-abdominally at hatch with the viruses rMd5-RM1-LTR, rMd5 BAC parental virus, wild-type strain Md5, or strain RM1 of MDV. The rMd5-RM1-LTR virus was attenuated at cell culture passage 40, whereas the rMd5 BAC without RM1 LTR retained its pathogenicity at cell culture passage 40. Using polymerase chain analysis, the RM1 LTR insert was detected in MDV isolated from buffy coat cells collected from chickens inoculated with rMd5-RM1-LTR, but only at 1 week post inoculation. The data suggest that the presence of the RM1 LTR insert within MDV genome for 1 week post inoculation with virus at hatch is sufficient to cause a reduction in pathogenicity of strain Md5 of MDV.

New pathogenetic characters of reticuloendotheliosis virus isolated from Chinese partridge in specific-pathogen-free chickens

Avian reticuloendotheliosis virus (REV) infection can induce a runting syndrome, immunosuppression, acute reticulum cell neoplasia and lymphomas in a variety of domestic and wild birds. To evaluate the pathogenicity and oncogenicity of REV-JX0927 that isolated from Chinese partridge, experimental inoculated day-old specific-pathogen-free (SPF) White Leghorn chickens were examined at regular intervals. The examination procedures included hematology, serology and histopathology; also including immunohistochemistry and apoptosis assay. Body weight, relative immune organs weight and apoptosis assay results revealed that the immunosuppression of infected birds is associated with apoptosis of lymphocytes in lymphoid tissues, especially in thymus induced by REV-JX0927. Hematology and apoptosis assay results showed that the 7th week of post-infection is a critical time point for lymphocytes to be transformed into tumor cells. Histopathology evidences demonstrated that REV-JX0927 induced reticuloendotheliosis at early stage (1 week), and lymphosarcomas at middle stage (after 7 weeks). In addition, squamous-cell carcinoma, adenocarcinoma and aneurysm were found in infected birds. Arteritis was associated with concentration of serum protein and fat. REV antigen expression was observed in infected birds through the experimental period. REV has high tropism for proventriculus, kidney, liver, lymphoid tissues, pancreas, lymphosarcoma cells and blood vessels. Data from this study showed that several new pathogenitic characters caused by REV-JX0927 were observed. It indicated that REV-JX0927 is a multipotential oncogenic retrovirus.

Enhancement of reticuloendotheliosis virus-induced bursal lymphomas by serotype 2 Marek's disease virus

The effect of serotype 2 and 3 Marek's disease virus (MDV) vaccines on the pathogenesis of reticuloendotheliosis virus (REV)-induced bursal and non-bursal lymphomas was examined in chickens of RPRL lines 15I(5) X 7(1) and 6(3) X 0, respectively. At hatch, chickens were vaccinated with strain 301B/1 of serotype 2 MDV or strain FC126 of turkey herpesvirus (HVT), a serotype 3 MDV and inoculated with spleen necrosis virus (SNV), a non-defective strain of REV. In another experiment, bursas from 14-week-old 15I(1) X 7(1) chickens coinfected with strain 301B of serotype 2 MDV and SNV strain of REV at hatch were examined microscopically for REV-induced transformed follicles by methyl green pyronin stain and for the presence of MDV by in situ hybridization. The incidence of REV-induced bursal lymphomas was significantly higher in 15I(5) X 7(1) chickens vaccinated with serotype 2 MDV than in unvaccinated chickens or chickens vaccinated with HVT. On the other hand, the incidence of REV induced nonbursal lymphoma in chickens of line 63 X 0 vaccinated with serotype 2 MDV was comparable to that in unvaccinated chickens or chickens vaccinated with HVT. The average number of hyperplastic follicles in bursas from REV-infected 15I(5) X 7(1) chickens was significantly higher in chickens vaccinated with serotype 2 MDV than that in unvaccinated chickens or chickens vaccinated with HVT, and the MDV was more frequently detected in REV-transformed than in untransformed bursal follicles. Data from this study suggest that serotype 2, but not serotype 3, of MDV may enhance the development of REV-induced bursal lymphomas, and that neither serotype 2 nor serotype 3 MDV influence the development of REV-induced nonbursal lymphomas. The data also suggest that the enhancement effects of serotype 2 MDV on REV bursal lymphomas may be at the stage of formation of hyperplastic or transformed bursal follicles.

An outbreak of lymphomas in commercial broiler breeder chickens vaccinated with a fowlpox vaccine contaminated with reticuloendotheliosis virus

Gross and microscopic examinations of affected tissues from chickens of two commercial broiler breeder flocks aged 27 and 31 weeks revealed lesions of visceral lymphomas with bursal involvement in some chickens. Reticuloendotheliosis virus (REV), but not avian leukosis virus (ALV), was isolated from blood of affected chickens. Furthermore, DNA extracted from tumours tested positive for REV, but not for ALV or Marek's disease virus by polymerase chain reaction (PCR) test. Attempts to determine the source of REV infection included testing a commercial fowlpox (FP) vaccine used to immunize flocks at 7 days of age. Chicken-embryo fibroblasts inoculated with the FP vaccine tested positive for REV by PCR and immunofluorescent tests. REV was also isolated from plasma of pathogen-free chickens experimentally inoculated with FP vaccine at hatch; two of eight (25%) inoculated chickens developed lymphomas by 34 weeks of age. Antigenic characterization of REV isolated from commercial broiler breeder chickens and from FP vaccine, using monoclonal antibodies, revealed that both isolates belong to subtype 3 of REV. The data represent the first report of an outbreak of REV-induced lymphomas in commercial chickens. The data also indicate that the source of REV infection is an REV-contaminated commercial FP vaccine.

Isolation, identification, and complete genome sequence of an avian reticuloendotheliosis virus isolated from geese

Naturally occurring lymphoreticular tumors in geese have been found from time to time in Taiwan, but their etiology has not been determined except through morphological descriptions. This study observed a reticuloendotheliosis virus (REV) infection occurring in a white Roman goose (Anser anser) farm in Yunlin, Taiwan in 2006. These geese showed growth-retarded and nodular lymphoma-like tumors in the liver, lung, kidney, and pancreas. Thirty blood samples were taken for REV detection and 21 (70%) of them contained REV genetic sequences using polymerase chain reaction (PCR). Virus isolation was attempted from 11 blood samples by inoculating the buffy coat onto DF1 cells. Nine (81%) REVs were isolated after three blind passages. The complete proviral sequence from one isolate was determined for phylogenetic analysis by direct sequencing using overlapping PCR products. The length of the provial genome is 8284 nucleotides. By comparing with other published REV complete sequences, the nucleotide percent identity ranged from 93.5% to 99.8% with most LTR varieties, ranging from 74.9% to 99.8%. The present isolated goose REV is most close to REV APC-566, a REV isolated from Attwater's Prairie chickens.

Isolation of a reticuloendotheliosis-like virus from naturally occurring lymphoreticular tumours of domestic goose

Naturally occurring lymphoreticular tumours were found in an adult goose flock. Diffuse and/or nodular lymphoma-like tumours occurred in the spleen, liver, pancreas, intestines and rarely in other internal organs. Osteopetrosis-like lesions and signs of other diseases such as amidostomosis, enteritis, arthritis and air sacculitis were also observed. The tumourous lesions consisted of proliferations of undifferentiated lymphoblasts and slightly differentiated plasmablasts of the bursal system of lymphocytes. Tumour cell proliferation was usually associated with parenchymal atrophy and occasionally with amyloid depositions along the walls of capillaries of the spleen and the liver. In tissue cultures, chloroform sensitive, typical C-type virus particles of about 100 nm were isolated. The isolate incorporated 3H-uridine, banded at about 1.19 to 1.20 g/cm(3) in sucrose gradient ultracentrifugation and was shown to be antigenically related to the reticuloendotheliosis group of avian retroviruses. In transmission experiments with chickens and geese, one of the four tested reticuloendotheliosis virus-positive cellular field materials caused a highly lethal neoplastic disease similar in cytology to that seen in the natural disease outbreak within four weeks after infection. The other three cellular field materials and the tissue-culture-propagated virus isolates induced either a runting disease syndrome or a similar chronic neoplasia to that found in the naturally diseased geese during an experimental period of 30 weeks. Reticuloendotheliosis virus was reisolated from the experimentally inoculated birds, and antibodies to the T strain of reticuloendotheliosis virus were also demonstrated in sera of surviving chickens. Neither Marek's disease virus nor avian leukosis-sarcoma viruses could be demonstrated in tissue cultures or in chickens of transmission experiments. The reported transmissible lymphoreticular tumours of domestic goose seem to be associated with infection of a new isolate of the reticuloendotheliosis group of viruses designated as Reticuloendotheliosis Virus Hungary-2 (REV-H-2).

Pathogenicity and Transmission of Reticuloendotheliosis Virus Isolated from Endangered Prairie Chickens

The pathogenicity and transmission of a field isolate of reticuloendotheliosis virus (REV) was studied using an experimental model in Japanese quail. Oncogenicity was also evaluated after inoculations in chickens and turkeys. The original REV (designated APC-566) was isolated from Attwater's prairie chickens (Tympanuchus cupido attwateri), an endangered wild avian species of the southern United States. The transmissibility of the REV isolate was studied in young naive Japanese quail in contact with experimentally infected quail. Vertical transmission was not detected by virus isolation and indirect immunofluorescence. Seroconversion was detected in few contact quails, suggesting horizontal transmission. The APC-566 isolate induced tumors beginning at 6 wk of age in quails infected as embryos. Most of the tumors detected in Japanese quail were lymphosarcomas, and 81% of these neoplasias contained CD3+ cells by immunoperoxidase. REV APC-566 was also oncogenic in chickens and turkeys infected at 1 day of age, with tumors appearing as early as 58 days after infection in chickens and at 13 wk of age in turkeys. This study was conducted in part as an attempt to understand the potential for pathogenicity and transmission of REV isolated from endangered avian species.

Experimental Infection of Attwater's/Greater Prairie Chicken Hybrids with the Reticuloendotheliosis Virus

Reticuloendotheliosis virus (REV), a common pathogen of poultry, has been associated with runting and neoplasia in an endangered subspecies of grouse, the Attwater's prairie chicken. The pathogenesis of REV infection was examined in experimentally infected prairie chickens. Three groups of four Attwater's/greater prairie chicken hybrids were infected intravenously with varying doses (tissue culture infective dose [TCID50], 200, 1000, and 5000) of a prairie chicken-isolated REV. A fourth group of four birds was not infected. Blood was collected prior to infection, and at various times up to 37 wk following infection. Peripheral blood mononuclear cells were examined for integrated proviral DNA by a single-amplification polymerase chain reaction (PCR) and nested PCR of a region within the pol gene. The nested PCR identified REV proviral DNA in all REV-inoculated birds by 2 wk postinfection and confirmed chronic infection throughout the study. With the exception of a bird that died from bacterial pneumonia 8 wk postinfection, neoplasia, resembling that seen in naturally occurring infections, was observed in all birds, even those receiving as little as 200 TCID50 of virus.

Serological and Virological Surveys of Reticuloendotheliosis in Chickens in Taiwan

Reticuloendotheliosis virus (REV) is widespread in the world. No related data has been reported in Taiwan. To determine the REV infection status, antibody determination and virus isolation were performed on chickens in Taiwan. The results revealed that serological flock prevalence for the REV antibody reached 92.8% (39/42) amongst breeders (> 16 weeks old). Two different REV isolates were identified by reverse transcriptase-polymerase chain reaction, electron microscopic, immunofluorescent, and western blot assays after isolation. One of these viruses was isolated from a broiler breeder farm and the other was isolated from a Taiwan Country Chicken farm. Despite their different origins, the percent identity of the nucleotide sequences of the env gene of these two isolates was 99.7%. These two strains were similar to the FPV-UI-REV strain, featuring 99.7% and 99.8% percent identity. Indeed, REV infection would appear to be quite common amongst chickens.

Novel criteria for the diagnosis of Marek's disease virus-induced lymphomas

Several novel criteria have been tested to assist in the differential diagnosis of tumours induced by Marek's disease virus (MDV) from those induced by avian leukosis virus (ALV) and reticuloendotheliosis virus (REV). A collection of tumours induced by inoculation of specific strains of MDV, ALV and REV, alone or in combination, were tested for quantification of MDV DNA by real-time polymerase chain reaction, expression of the MDV oncogene Meq, expression of several cell markers associated with transformation (CD30, Marek's disease-associated surface antigen, and p53), and level of DNA methylation in the tumour cells. In addition, tissues latently infected with MDV and non-infected tissues were tested as controls. Tumours induced by MDV had about 10(2)-fold more copies of MDV DNA than either tissues latently infected by MDV or tumours induced by retrovirus in MDV-vaccinated chickens. Moreover, the MDV antigen Meq was consistently expressed in all MDV tumours but it could not be detected in tissues latently infected with MDV or in tumours induced by retrovirus in MDV-vaccinated chickens. Other markers studied were not specific for MDV and therefore had limited value for diagnosis. Nonetheless, some of these markers might have potential value in research as they will help to identify transformed cells.

Characterization of T-cell lymphomas associated with an outbreak of reticuloendotheliosis in turkeys

Increased mortality and decreased egg production associated with disseminated lymphoma were observed in a turkey breeding flock for more than 20 weeks. A few unrelated meat turkey flocks, from the same integrator, experienced increased condemnation due to neoplasia in a few organs. Lymphoma was characterized by a uniform population of large lymphocytes with large vesicular nuclei containing one or two nucleoli and with little, faintly staining, basophilic cytoplasm. Neoplastic cells replaced normal tissue and were consistent with lesions seen with reticuloendotheliosis virus (REV) infection. Immunoperoxidase and fluorescent antibody staining characterized the neoplastic cells as CD3+, CD4+ and CD8- lymphocytes. Infection with REV was confirmed by virus isolation, polymerase chain reaction, serology and indirect fluorescent antibody. Poults hatched from these breeders tested positive for REV antibodies at hatch, but the performance of these flocks was normal and lymphoma was not observed. The origin of REV infection in this outbreak could not be determined. This is the first documented report of T-cell lymphomas associated with REV in commercial flocks. Furthermore, this is the first time that lymphomas have been characterized as T helper cells (CD3+ CD4+ and CD8-) in an outbreak of REV in turkeys.

Causes of mortality and culling in adult pheasants

The causes of the deaths or culling of 155 adult pheasants in breeding pens on one site between 1995 and 1997 were investigated. Approximately half the deaths were the result of problems associated with the reproductive tract or trauma, including injuries acquired during fighting or mating. Sinusitis was the commonest infectious cause of mortality or culling, despite medication of the flocks for mycoplasmosis. Marble spleen disease and pheasant coronavirus-associated nephritis, two viral conditions capable of causing high mortality, were diagnosed in a few birds in 1996 and 1997. Histomoniasis (blackhead) contributed to the mortality in 1996. A lymphomatous condition of uncertain aetiology was detected in a small number of birds.

Avian retroviruses

Avian leukosis virus (ALV) and reticuloendotheliosis virus (REV) are the most common naturally occurring avian retroviruses associated with neoplastic disease conditions in domesticated poultry. Avian leukosis virus infects primarily chickens, whereas REV infects chickens, turkeys, and other avian species. In addition to causing tumors, both ALV and REV can reduce productivity and induce immunosuppression and other production problems in affected flocks.

Retrovirus insertion into herpesviruses

Recent studies have indicated that retroviruses can integrate into and mutate the genomes of herpesviruses during co-infection. This interaction has the potential to change the host range and pathogenicity of both viruses and result in novel infectious agents and diseases. This phenomenon also allows genetic material to be exchanged between these viruses and their hosts.

Antibody response elicited against empty reticuloendotheliosis virus particles in two inbred lines of chicken

Immunisation of Houghton White Leghorn line 15I and 6(1) chickens with empty reticuloendotheliosis virus particles elicited a primary antibody response which is probably directed against the viral envelope glycoproteins gp73/71 and gp22. Antibodies in line 15I birds were shown to be non-neutralising and did not protect against the tumourigenic effects of reticuloendotheliosis virus, strain T. However, immunised line 6(1) chicks did not exhibit the runting syndrome associated with reticuloendotheliosis virus infection, suggesting that antibody against viral coat proteins may play a role in modulating pathogenesis in certain lines of chicken.

Reticuloendotheliosis virus long terminal repeat elements are efficient promoters in cells of various species and tissue origin, including human lymphoid cells

Promiscuous transcriptional activity of the reticuloendotheliosis virus (REV) long terminal repeat (LTR) was detected in transient expression assays using LTR-chloramphenicol acetyltransferase-encoding gene chimeras, and cells of diverse species and tissue type; levels of expression from two different REV LTRs correlate with reports of pathogenicity of the respective viruses in vivo. REVs do not encode a transactivator targeted to the viral LTR, and cells infected with Marek's disease virus, a herpesvirus with an overlapping host range, do not express factors that preferentially enhance expression from REV or avian sarcoma/leukemia virus LTRs. REV LTRs work efficiently in human lymphoid cells, and are viable alternatives to promoters commonly used for expression of cloned genes. They may also prove useful in the identification of new, ubiquitous cellular transcription factors.

Rapid induction of B-cell lymphomas: insertional activation of c-myb by avian leukosis virus

EU-8 is a recombinant avian leukosis virus (ALV) constructed in vitro, which carries long terminal repeats and gag and pol genes from ring-necked pheasant virus and the env gene from UR2AV. Unlike either parent virus, when injected into 10-day-old chicken embryos, EU-8 induces a high incidence of clonally arising B-cell lymphomas within an unusually short latent period, often causing death within 5 to 7 weeks after infection. These tumors differ from the classic lymphoid leukosis induced by ALV in several respects, both biologically and at the molecular level. Most notably, in all of the EU-8-induced tumors examined, the provirus was integrated in the c-myb locus, and in no tumors were c-myc integrations found. Most of the proviral integrations were downstream of the initiation codon of c-myb and thus presumably resulted in some truncation of the c-myb gene product, although not to the same extent as has been found in other cases of c-myb activation. In addition, several of the proviruses were integrated well upstream of the c-myb coding region. This is the first report of ALV interaction with the c-myb proto-oncogene and the first report of c-myb activation resulting in tumors of lymphoid rather than myeloid origin, suggesting that the target cell specificity of transformation by the myb gene is not as restricted as previously believed.