Nested polymerase chain reaction for detection of the avian leukosis virus causing so-called fowl glioma

Simultaneous Detection of Three Subgroups of Avian Leukosis Virus Using the Nanoparticle-Assisted PCR Assay

Nanoparticle-assisted polymerase chain reaction (nanoPCR) is a novel method for the rapid detection of pathogens. A sensitive and specific multiple nanoPCR assay was developed for simultaneous detection of avian leucosis virus (ALV) subgroups A, B and J. In this study, three pairs of primers were designed, based on the conserved region of the gp85 gene. An exploration of the optimal primer concentration and annealing temperature were carried out, for better performance of the nanoPCR assay. According to the results, the multiple nanoPCR assay amplified 336 pb, 625 bp and 167 bp fragments of ALV-A, -B and -J, respectively, and showed no cross-reactivity with irrelevant pathogens, suggesting the excellent specificity of the assay. The constructed standard DNA templates were used to estimate the limit of detection. As shown by the results, the detection limit of the nanoPCR assay was nearly 10 copies/μL. To further evaluate the detection ability of the assay, 186 clinical samples were detected using the nanoPCR assay, among which, 14 samples were confirmed as ALV positive; the results were further confirmed by sequencing. In conclusion, a highly specific and sensitive nanoPCR assay was successfully developed, which could be a useful tool for clinical diagnosis as well as for the discrimination of ALV-A, -B and -J.

Neuropathogenicity of newly isolated avian leukosis viruses from chickens with osteopetrosis and mesenchymal neoplasms

ABSTRACT The prototype fowl glioma-inducing virus (FGVp) causes fowl glioma and cerebellar hypoplasia in chickens. In this study, we investigated whether a strain of avian leukosis virus (ALV), associated with avian osteopetrosis and mesenchymal neoplasms, is able to induce fowl glioma. We encountered avian osteopetrosis and mesenchymal neoplasms, including myxosarcoma and rhabdomyosarcoma, in Japanese native chickens used for both egg-laying and meat production. These birds were also affected by non-suppurative encephalitis and glioma in their brains. Four ALV strains (GifN_001, GifN_002, GifN_004, GifN_005) were isolated, and a phylogenic analysis of envSU showed that these isolates were classified into different clusters from FGVp and the variants previously reported. Whereas the envSU shared a high identity (94.7%) with that of Rous sarcoma virus (strain Schmidt-Ruppin B) (RSV-SRB), the identity between envTM of GifN_001 and that of FGVp was high (94.5%), indicating that GifN_strains may emerge by recombination between FGVp and other exogenous ALVs. Specific-pathogen-free chickens inoculated in ovo with GifN_001 revealed fowl glioma and cerebellar hypoplasia. These results suggest that the newly isolated strains have acquired neuropathogenicity to chickens.

Identification of a novel linear B-cell epitope in the p27 of Avian leukosis virus

Avian leukosis virus (ALV) is an avian oncogenic retrovirus that can induce virus-associated neoplasia and causes great economic loss in poultry industry. It is known that the capsid antigen p27 is the group-specific antigen that is highly conserved among all ALV subgroups, and is the most abundant immunogenic viral protein. In the present study, five overlapping fragments (GST- p27-F1/2, GST- p27-F2-1/2/3) of ALV-p27 were subjected to Western blotting analysis using a monoclonal antibody (5D3) against ALV-p27 to identify the epitope. The result showed that the epitope recognized by 5D3 is located within 173-240 amino acid of the ALV-p27 protein. For precise mapping of this epitope, a set of overlapping peptides were synthesized. Indirect enzyme linked immunosorbent assay (ELISA) revealed that ¹⁹³CFRQKSQPDI²⁰² motif was the minimal fragment recognized by 5D3, so this motif represented a linear B-cell epitope of ALV-p27. Homology analysis indicated that 5D3 defined epitope is highly conserved among ALV strains. The identified epitope might be useful in clinical applications and as a tool for further study of the structure and function of ALV-p27.

Visceral Marek's disease in white-peafowl (Pavo cristatus)

ABSTRACT Marek's disease (MD) is a lymphoproliferative disorder caused by Gallid herpesvirus 2 (MDV) that infects mainly domestic gallinaceous birds although wild birds may occasionally be affected. The current report describes the anatomopathological and molecular findings of a case of MD in a white-peafowl (Pavo cristatus). The signs included apathy, hyporexia, and diarrhea. Grossly, 0.5 to 1.5cm in diameter, yellow, soft nodules were observed in the skeletal muscle, lung, kidney, air sacs, small intestine, heart, ovary, ventriculus, and proventriculus. Microscopically, numerous atypical round neoplastic cells were noted. The molecular detection of MDV DNA was implemented to amplify part of the meq gene and products were sequenced for the phylogenetic analysis. Template DNA was obtained from tissues of the affected bird and from blood of all the gallinaceous birds of the Zoo. The expected amplicon for the partial amplification of MDV meq gene was obtained and the amplicons were sequenced. Sequences obtained enabled grouping the strain (accession no. KT768121) with MDV serotype 1 strains from the GenBank. Based on the anatomopathological and molecular findings, the diagnosis of MD in a white-peafowl was reached, and to the authors' knowledge, no previous report regarding MD was published in Pavo cristatus.

Identification of a linear B-cell epitope on the avian leukosis virus P27 protein using monoclonal antibodies

Avian leukosis virus (ALV) is an avian oncogenic retrovirus that can induce various clinical tumors. The capsid protein P27 is the group-specific antigen of ALV and has many viral antigen sites that are easy to detect. In this study, we produced a monoclonal antibody (mAb), 3A9, that is specific for the P27 protein. A series of partially overlapping peptides were screened to define (181)PPSAR(185) as the minimal linear epitope recognized by mAb 3A9. The identified epitope could be recognized by chicken anti-ALV and mouse anti-ALV P27 sera. The epitope was highly conserved among a number of ALV-A, ALV-B and ALV-J strains. MAb 3A9 might be a valuable tool for the development of new immunodiagnostic approaches for ALV, and the defined linear epitope might help further our understanding of the antigenic structure of the P27 protein.

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.

Identification of a novel B-cell epitope specific for avian leukosis virus subgroup J gp85 protein

Avian leukosis virus subgroup J (ALV-J) is an avian oncogenic retrovirus that has caused severe economic losses in China. Gp85 protein is the main envelope protein and the most variable structural protein of ALV-J. It is also involved in virus neutralization. In this study, a specific monoclonal antibody, 4A3, was produced against the ALV-J gp85 protein. Immunofluorescence assays showed that 4A3 could react with different strains of ALV-J, including the British prototype isolate HPRS103, the American strains, an early Chinese broiler isolate, and layer isolates. A linear epitope on the gp85 protein was identified using a series of partially overlapping fragments spanning the gp85-encoding gene and subjecting them to western blot analysis. The results indicated that (134)AEAELRDFI(142) was the minimal linear epitope that could be recognized by mAb 4A3. Enzyme-linked immunosorbent assay (ELISA) revealed that chicken anti-ALV-J sera and mouse anti-ALV-J gp85 sera could also recognize the minimal linear epitope. Alignment analysis of amino acid sequences indicated that the epitope was highly conserved among 34 ALV-J strains. Furthermore, the epitope was not conserved among subgroup A and B of avian leukosis virus (ALV). Taken together, the mAb and the identified epitope may provide valuable tools for the development of new diagnostic methods for ALV-J.

Astrocytic growth through the autocrine/paracrine production of IL-1β in the early infectious phase of fowl glioma-inducing virus

Fowl glioma is characterized morphologically by multiple nodular astrocytic growth with disseminated non-suppurative encephalitis. The disease is caused by fowl glioma-inducing virus (FGV) and its variants, belonging to subgroup A of avian leukosis virus (ALV-A). Fifty-seven FGV variants have so far been isolated from Japanese fowls and these variants have a variable degree of glioma inducibility. However, how these ALVs induce glioma with different degrees and frequencies has not been fully elucidated. In this study, we investigated the relationship between intracerebral viral replication and astrocytic growth in the early infectious phase. Replication abilities of two ALV strains, Sp-53 (a FGV variant) and ALV-based replication-competent vector RCAS(A) without glioma inducibility, were compared in the brains of C/O specific pathogen free chickens at 35 days of age. Sp-53 replicated faster than RCAS(A), and the histological score and the level of interleukin (IL)-1β in brains increased depending on the level of intracerebral viral RNA. Up-regulation of IL-1β was also demonstrated in primary cultured astrocytes. These results suggest that the astrocytic growth in this phase is enhanced through the autocrine/paracrine production of IL-1β in the FGV-infected astrocytes.

Genomic sequence analysis and biological characteristics of a rescued clone of avian leukosis virus strain JS11C1, isolated from indigenous chickens

The strain JS11C1, a member of a putative new subgroup of avian leukosis virus (ALV) that is different from all six known subgroups from chickens based on Gp85 amino acid sequence comparison, was isolated from Chinese native chicken breeds in 2012. In order to further study the genome structure, biological characteristics, and the evolutionary relationship of the virus with others of known subgroups from infected chickens, we determined the complete genome sequence, constructed an infectious clone of ALV strain JS11C1, and performed comparative analysis using the whole genome sequence or elements with that of other ALVs available in GenBank. The results showed that the full-length sequence of the JS11C1 DNA provirus genome was 7707 bp, which is consistent with a genetic organization typical of a replication-competent type C retrovirus lacking viral oncogenes. The rescued infectious clone of JS11C1 showed similar growth rate and biological characteristics to its original virus. All the comparison analyses based on whole genomes support the opinion that the new isolates are relatively distantly related to any known subgroups of ALVs and might be classified as a new subgroup.

Congenital cerebellar dysplasia in White Leghorn chickens (Gallus gallus domesticus)

Congenital cerebellar anomalies have been rarely reported in birds. We examined cerebellums with disorganized folia from seven specific-pathogen-free White Leghorn chickens (Gallus gallus domesticus). Islands of heterotopic cortex were distributed from the deeper cortices to the medulla in the cerebellum. The characteristic lesions were composed of randomly admixed components of the cerebellar cortex, including Purkinje cells, a molecular layer and granular cells. Immunofluorescent analysis revealed Purkinje cells with haphazardly extended dendrites and a lack of Bergmann's glial fibres in the foci. Chicken parvovirus, Aino virus and avian retrovirus were not detected in the affected birds by polymerase chain reaction. This is the first report of cerebellar dysplasia in chickens possibly caused by a genetic abnormality.

Epidemiological study of fowl glioma-inducing virus in chickens in Asia and Germany

Fowl glioma-inducing virus (FGV), which belongs to avian leukosis virus (ALV) subgroup A, induces fowl glioma. This disease is characterized by multiple nodular gliomatous growths of astrocytes and has been previously reported in Europe, South Africa, Australia, the United States and Japan. FGV and FGV variants have spread to ornamental Japanese fowl, including Japanese bantams (Gallus gallus domesticus), in Japan. However, it is unclear how and where FGV emerged and whether FGV is related to the past fowl glioma in European countries. In this study, the prevalence of FGV in European, Asian and Japanese native chickens was examined. FGV could not be isolated from any chickens in Germany and Asian countries other than Japan. Eighty (26%) out of 307 chickens reared in Japan were positive by FGV-screening nested polymerase chain reaction and 11 FGV variants with an FGV-specific sequence in their 3' untranslated region were isolated. In addition, four other ALVs lacking the FGV-specific sequence were isolated from Japanese bantams with fowl glioma and/or cerebellar hypoplasia. These isolates were considered to be distinct recombinant viruses between FGV variants and endogenous/exogenous avian retroviruses. These results suggest that the variants as well as distinct recombinant ALVs are prevalent among Japanese native chickens in Japan and that FGV may have emerged by recombination among avian retroviruses in the chickens of this country.

Natural infection and transmission of a retrovirus closely related to myeloblastosis-associated virus type 1 in egg-type chickens

Myeloblastosis-associated virus type 1 (MAV-1) is an exogenous avian retrovirus with oncogenic potential. MAV-1 was detected in young chicks hatching from eggs produced by an experimental genetic line of egg-type chickens. Transmissibility of MAV-1 had not been documented previously. This investigation was intended to partially characterize the virus involved and to study its transmissibility and oncogenicity in naturally and contact-infected chickens. Commercially produced white and brown layer pullets free of exogenous avian leukosis viruses were commingled at hatch with naturally MAV-1-infected chickens. The original MAV-1-infected chickens were discarded after approximately 8 wk, and the contact-exposed chickens were maintained in isolation for 36 wk. Young specific-pathogen-free (SPF) single comb white leghorn chickens were added to the group to study possible horizontal transmission of MAV-1 in young chickens. Upon weekly virus isolation attempts, MAV-1 was readily isolated from the contact-exposed white layers but not from the brown layers between 36 and 53 wk of age (18 wk in total). Three-week-old SPF chickens were readily infected with MAV-1 by contact as early as 1 wk postexposure. Throughout 22 hatches derived from the white and brown MAV-1-contact-exposed layers (between 36 and 53 wk of age), MAV-1 was frequently detected in the white layer progeny, whereas the virus was seldom isolated from the progeny produced by the brown layers during the same 18-wk period. MAV-1 induced a persistent infection in some of the SPF chickens that were exposed by contact at 3 wk of age. Gross tumors were not detected in any of the originally infected experimental chickens at 8 wk of age, in the contact-exposed brown or white layers at the termination of the study at 53 wks of age, or in the contact-exposed SPF chickens at the end of the study at 12 wk of age. Exogenous avian leukosis-related viruses may still be detected in egg-type chickens, emphasizing the importance of thorough screening before incorporation of experimental genetic material into commercial genetic lines of egg-type chickens.

The roles of viruses in brain tumor initiation and oncomodulation

While some avian retroviruses have been shown to induce gliomas in animal models, human herpesviruses, specifically, the most extensively studied cytomegalovirus, and the much less studied roseolovirus HHV-6, and Herpes simplex viruses 1 and 2, currently attract more and more attention as possible contributing or initiating factors in the development of human brain tumors. The aim of this review is to summarize and highlight the most provoking findings indicating a potential causative link between brain tumors, specifically malignant gliomas, and viruses in the context of the concepts of viral oncomodulation and the tumor stem cell origin.

Pathogenicity of avian leukosis viruses related to fowl glioma-inducing virus

Fowl glioma-inducing virus (FGV), which belongs to avian leukosis virus subgroup A, causes the so-called fowl glioma and cerebellar hypoplasia in chickens. In the present study, the complete nucleotide sequences of four isolates (Tym-43, U-1, Sp-40 and Sp-53) related to the FGV prototype were determined and their pathogenicity was investigated. Phylogenetic analysis showed that the 3'-long terminal repeat of all isolates grouped together in a cluster, while sequences of the surface (SU) proteins encoded by the env gene of these viruses had 85 to 96% identity with the corresponding region of FGV. The SU regions of Tym-43, U-1 and FGV grouped together in a cluster, but those of Sp-40 and Sp-53 formed a completely separate cluster. Next, C/O specific-pathogen-free chickens were inoculated in ovo with these isolates as well as the chimeric virus RCAS(A)-(FGVenvSU), constructed by substituting the SU region of FGV into the retroviral vector RCAS(A). The four variants induced fowl glioma and cerebellar hypoplasia and the birds inoculated with Sp-53 had the most severe lesions. In contrast, RCAS(A)-(FGVenvSU) provoked only mild non-suppurative inflammation. These results suggest that the ability to induce brain lesions similar to those of the FGV prototype is still preserved in these FGV variants.

Detection of avian leukosis virus subgroups in albumen of commercial and native fowl eggs using RT-PCR in Iran

Avian leukosis viruses (ALVs) belong to Alpharetrovirus genus of the family Retroviridae that are widespread in nature. Different subgroups of ALV commonly infect egg-laying hens. They are responsible for economic losses due to both mortality and depressed performance in chickens. To investigate the presence of these viruses in chickens in Iran, 560 egg albumens were selected from different farms of Fars province, Iran. These eggs were obtained from flocks of two research centers of native fowl production (60 eggs), a broiler grandparent farm (100 eggs), three broiler breeder farms (300 eggs), and a commercial layer flock (100 eggs). Firstly, for primary screening a degenerative primer set (PU1 and PU2) were used in reverse transcriptase-polymerase chain reaction (RT-PCR). Positive cases were detected in 47 of 300 (15.7%) samples from three broiler breeders, 40 of 100 (40%) samples from commercial layer, 53 of 60 (88.3%) samples from flocks of two research centers of native fowl production, and none from the samples of broiler grandparent. Then RT-PCR was undertaken with primers PA1 and PA2 on the positive samples. RT-PCR analysis detected ALVs in two of 47 (4.3%) samples from three broiler breeders, 13 of 40 (32.5%) samples from commercial layer, and 19 of 53 (35.8%) samples from flocks of two research centers of native fowl production. The sequencing results showed that subgroup E of ALV was the most detected virus among chicken eggs and subgroup B was more prevalent in the eggs of native fowls. This is the first report of the ALV subgroup B and E in egg albumen in Iran.

Development of a loop-mediated isothermal amplification assay for rapid detection of subgroup J avian leukosis virus

Infection of breeder flocks in China with subgroup J avian leukosis virus (ALV-J) has increased recently. In this study, we have developed a loop-mediated isothermal amplification (LAMP) assay for rapid detection of ALV-J from culture isolates and clinical samples. The ALV-J-specific LAMP assay efficiently amplified the target gene within 45 min at 63 degrees C using only a simple laboratory water bath. To determine the specificity of the LAMP assay, various subgroup ALVs and other related viruses were detected. A ladder pattern on gel electrophoresis was observed for ALV-J isolates but not for other viruses. To evaluate the sensitivities of the LAMP assay and conventional PCR, the NX0101 isolate plasmid DNA was amplified by them. The detection limit of the LAMP assay was 5 target gene copies/reaction, which was up to 20 times higher than that of conventional PCR. To evaluate the application of the LAMP assay for detection of ALV-J in clinical samples, 49 samples suspected of ALV infection from breeder flocks were tested by the LAMP assay and PCR. Moreover, virus isolation from these samples was also performed using cell culture. The positive-sample ratios were 21/49 (43%) by conventional PCR, 26/49 (53%) by the LAMP assay, and 19/46 (41%) by virus isolation. Additionally, a positive LAMP reaction can be visually ascertained by the observation of turbidity or a color change after addition of SYBR green I dye. Consequently, the LAMP assay is a simple, rapid, and sensitive diagnostic method and can potentially be developed for rapid detection of ALV-J infection in the field.

Detection of Avian Leukosis Virus Genome by a Nested Polymerase Chain Reaction using DNA and RNA from Dried Feather Shafts

The nested polymerase chain reaction (nPCR) using frozen feather pulp is useful for detecting fowl glioma-inducing virus (FGV), which belongs to the Avian leukosis virus family, and it has recently been suggested that FGV has spread to ornamental chickens kept in Japanese zoological gardens. In the current study, the practicality of using DNA and RNA from dried feather shafts as PCR samples was examined to establish a simple method for tissue preservation. Feather shafts were collected from 7 FGV-positive chickens and stored at room temperature for 30 days. DNA and RNA were extracted from these dried materials. All DNA and complementary DNA (cDNA) prepared from the RNA showed positive results for chicken β-actin and FGV, respectively. Screening for FGV was performed on Japanese fowls kept in zoological garden N. Of the feather shafts collected from 57 birds, 1 sample tested positive for FGV according to PCR of DNA and cDNA samples from the dried feather shafts. This positive bird originated from zoological garden A and had brain lesions suggestive of fowl glioma. The results suggest that DNA and RNA from dried feather shafts can be used in nPCR to detect the FGV genome.

Prevalence of fowl glioma-inducing virus in chickens of zoological gardens in Japan and nucleotide variation in the env gene

Fowl glioma-inducing virus (FGV), which belongs to subgroup A of avian leukosis virus (ALV), is tumorigenic in the nervous system. In a zoological garden in Japan, approximately 40% of chickens, including Japanese fowls, were infected with FGV. Because this zoological garden plays a role as a major supplier of Japanese fowl for other zoological gardens, FGV infection is suspected to have spread among ornamental chickens. In this study, the prevalence of the disease was examined in a total of 129 chickens in three other zoological gardens by nested polymerase chain reaction (PCR), reverse transcription nested PCR and enzyme-linked immunosorbent assay. Twenty-six to 56 percent of the fowls in each of the examined gardens were positive by nested PCR. The phylogenetic analysis revealed that the 3' untranslated region, including the specific sequence of FGV, of the 14 isolated ALVs showed high sequence identity and a close relationship with FGV. In addition, the env gene of the isolates frequently showed mutations and deletions of nucleotides. These results suggest that FGV is prevalent among ornamental chickens kept in zoological gardens in Japan.

Naturally Occurring Multiple Perineuriomas in a Chicken (Gallus domesticus)

A 2-year-old, male Japanese native fowl ( Gallus gallus domesticus) was presented with an inability to feed and torticollis. At a necropsy, there were cylindrical enlargements and yellow discoloration of multiple peripheral nerves, including nerves of the lumbosacral plexus, brachial plexus, and spinal ganglia. On histologic examination, these lesions consisted of diffuse proliferations of spindle cells with characteristic onion bulb-like structures around residual axons. The spindle cells were immunohistochemically positive for glucose transporter 1 (GLUT1) and negative for S-100 α/β proteins. On the basis of microscopic, histologic, and immunohistochemical findings, the tumors were diagnosed as multiple perineuriomas.