Use of the polymerase chain reaction for the diagnosis of natural infection of chickens and turkeys with Marek's disease virus and reticuloendotheliosis virus

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.

Experimental infection of domestic turkeys with lymphoproliferative disease virus of North American origin

Lymphoproliferative disease virus (LPDV) was first documented in wild turkeys in North America in 2009. LPDV infection is often subclinical but can manifest as lymphoid proliferation or round cell neoplasia. Despite high prevalence across many sampled areas corresponding to declining populations of wild turkeys, knowledge regarding LPDV pathogenesis, risk factors for disease development, and associated impacts on population dynamics are unknown. To understand transmission, viral shedding, and tissue tropism, we inoculated 21 domestic turkeys via the oral cavity, crop, nasal cavity, subcutis, or coelomic cavity. For 12 weeks, oropharyngeal swabs, cloacal swabs, and whole blood were collected weekly. At 1 week postinoculation, 3 turkeys (3/21; 14%) had detectable LPDV proviral DNA in blood by polymerase chain reaction, and 10 developed DNAemia (50%; 10/20) by 12 weeks. LPDV proviral DNA was intermittently detected in oropharyngeal and cloacal swabs. Splenomegaly was the most consistent gross finding in DNAemic birds (8/11; 73%). Lymphoid hyperplasia in the spleen was the most significant microscopic finding (9/11; 82%). Three turkeys (3/11; 27%) developed round cell neoplasia characterized by sheets of pleomorphic, round to polygonal cells in the adrenal gland, bone marrow, skin, small intestine, and/or spleen. LPDV was detected in the spleen and bone marrow from all turkeys with DNAemia and all neoplasms. Our study establishes that infection and disease with North American LPDV from wild turkeys can be experimentally reproduced in domestic turkeys, laying the groundwork for future investigations into LPDV pathogenesis, development of diagnostic techniques, and understanding the impacts of LPDV on wild turkey populations.

Lymphoproliferative Disease Virus and Reticuloendotheliosis Virus Detection and Disease in Wild Turkeys (Meleagris gallopavo)

Lymphoproliferative disease virus (LPDV) and reticuloendotheliosis virus (REV) are oncogenic retroviruses that can cause disease in wild and domestic fowl. Lymphoproliferative disease virus infections are common and widespread in Wild Turkeys (Meleagris gallopavo) in the US and east-central Canada, while REV has been detected worldwide in numerous avian host species. We tested tissues (spleen, liver, and/or bone marrow, plus neoplastic tissue, if present) from 172 Wild Turkeys that underwent necropsy from December 2018 through October 2021 for both viruses using PCR. We evaluated demographic, geographic, temporal, and seasonal data by chi-square test of independence and logistic regression for turkeys infected with LPDV and/or REV. At least one of these retroviruses was detected in 80.8% (139/172) of Wild Turkeys from 15 US states, with significantly more turkeys being positive for LPDV (72.1%, 124/172) versus REV (43.6%, 75/172; P<0.001). Both viruses (coinfections) were detected in 34.9% (60/172) of turkeys. Among LPDV-infected turkeys (including coinfections), bone marrow had the highest detection rate (38/58, 65.5%), significantly higher than spleen (30/58, 51.7%) and liver (20/58, 34.5%; P<0.001). In REV-infected turkeys, bone marrow had the highest detection rate (24/58, 41.4%). All three tissues (spleen, liver, bone marrow) concurrently tested positive in most (15/25, 60%) REV-infected turkeys. These results suggest LPDV tissue tropism for bone marrow, whereas REV may have broader tissue tropism. Histopathology consistent with lymphoid proliferation and/or neoplasia characteristic of lymphoproliferative disease was evident in 29/172 (16.9%) turkeys assessed, including two REV-only-infected turkeys. Season was significantly associated with LPDV prevalence (highest in winter); year and season were both significantly associated with REV prevalence (highest in 2020 and winter). These data contribute to optimizing diagnostic strategies that may aid in pathogen monitoring and improve detections to increase our understanding of the potential impacts of these viruses on Wild Turkey populations.

Isolation and characterization of avian leukosis virus subgroup J associated with hemangioma and myelocytoma in layer chickens in China

A strain of avian leukosis virus (ALV) belonging to a new envelope subgroup J (ALV-J) emerged in 1988 as a new subgroup of ALV and spread rapidly throughout the world. Due to the infection and spread of ALV-J, the global poultry industry experienced a significant loss. Although the disease had been prevented and controlled effectively by culling domestic chickens in the infected zone, a few field cases of ALV-J infection were reported in China in recent years. This study was conducted to characterize the genome and analyze the lesions and histopathology of the ALV-J strain named HB2020, which was isolated from layer chickens in Hubei Province, China. The full-length proviral genome sequence analysis of ALV-J HB2020 revealed that it was a recombinant strain of ev-1 and HPRS-103 in the gag gene in comparison to ALV-J prototype HPRS-103. In the 3′-untranslated region (3'UTR) of the nucleotide sequence, there were found 205-base pairs (bp) deletion, of which 175 were detected in the redundant transmembrane (rTM) region. Besides, the surface glycoprotein gene gp85 had five mutations in a conservative site, whereas the transmembrane protein gene gp37 was relatively conserved. The animal experiments conducted later on this strain have shown that HB2020 can cause various neoplastic lesions in chickens, including enlarged livers with hemangiomas and spleens with white nodules. Additionally, as the exposure time increased, the number of tumor cells that resembled myelocytes in the blood smears of infected chickens gradually increased. These results indicated that HB2020 on recombination with ALV subgroup E (ALV-E) and ALV-J could induce severe hemangiomas and myelocytomas. This inference might provide a molecular basis for further research about the pathogenicity of ALV and emphasize the need for control and prevention of avian leukosis.

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.

Isolation and Molecular Characteristics of a Novel Recombinant Avian Orthoreovirus From Chickens in China

In recent years, the emergence of avian orthoreovirus (ARV) has caused significant losses to the poultry industry worldwide. In this study, a novel ARV isolate, designated as AHZJ19, was isolated and identified from domestic chicken with viral arthritis syndrome in China. AHZJ19 can cause typical syncytial cytopathic effect in the chicken hepatocellular carcinoma cell line, LMH. High-throughput sequencing using Illumina technology revealed that the genome size of AHZJ19 is about 23,230 bp, which codes 12 major proteins. Phylogenetic tree analysis found that AHZJ19 was possibly originated from a recombination among Hungarian strains, North American strains, and Chinese strains based on the sequences of the 12 proteins. Notably, the σC protein of AHZJ19 shared only about 50% homology with that of the vaccine strains S1133 and 1733, which also significantly differed from other reported Chinese ARV strains. The isolation and molecular characteristics of AHZJ19 provided novel insights into the molecular epidemiology of ARV and laid the foundation for developing efficient strategies for control of ARV in China.

Characterization of Avian Pox in a Ruffed Grouse (Bonasa umbellus) from Pennsylvania

A free-ranging, adult male ruffed grouse (Bonasa umbellus) was harvested by a hunter during November 2019 in Forest County, PA. The bird was submitted for necropsy due to a skin mass on its left leg. Upon necropsy, two proliferative skin masses were grossly visible, one on the left leg and one on the cere. An additional mass was present on the oropharyngeal mucosa covering the hard palate. These masses were diagnosed as avian pox based on histopathologic and cytologic findings, including marked epithelial hypertrophy, hyperplasia, vacuolar degeneration with eosinophilic stippling, and intracytoplasmic inclusion bodies. An avipoxvirus was detected using PCR and was identified as fowlpox virus through sequencing of the 4b core gene segment. The avipoxvirus from this case showed genetic similarity to isolates from Eastern wild turkeys (Meleagris gallopavo silvestris).

Gallid Alphaherpesvirus 2 in the Egyptian Turkeys: Molecular Characterization and Establishment of a Universal System for Phylogenetic Classification

INTRODUCTION

Gallid alphaherpesvirus 2 (GaHV-2) is a highly contagious oncogenic virus that causes Marek's disease in chickens and occasionally in turkeys. Among 100 genes identified in GaHV-2 genome, the Meq gene appears to involve viral virulence, oncogenicity, and genetic diversity. Despite the use of Meq gene sequences in phylogenetic classification of GaHV-2 strains circulating in many countries worldwide, no integrated system exists yet.

METHODS

Turkeys from 2 commercial Egyptian farms were presented with signs of dullness, dehydration, and emaciation. Samples prepared from the internal organs were examined by histopathology and immunohistochemistry. Pools of the internal organs were analyzed by PCR for identification of GaHV-2, avian leucosis virus, and reticuloendotheliosis virus. The Meq gene of an Egyptian strain was sequenced and analyzed in comparison to 40 reference strains for generation of a universal system for phylogenetic classification of GaHV-2 strains.

RESULTS

Gross and histopathological examination revealed grayish-white soft masses in the internal organs characterized by diffuse infiltration of pleomorphic neoplastic cells. All lymphoma cells were identified as T-lymphocytes of CD3+ phenotype. Samples of both farms were only positive for GaHV-2 by PCR. Sequence analysis of the Meq gene has classified the current turkey strain as related to the Egyptian strains identified in chicken in 2012. A universal phylogenetic system for classification of GaHV-2 strains into 4 clusters was proposed. The vaccine strains were all grouped in cluster 2, and most of the classical American strains belonged to cluster 4. Cluster 1 was further divided into 3 subclusters (1.1-1.3).

CONCLUSION

GaHV-2 was identified in turkeys for the first time in Africa and the Middle East. Sequence analysis of the Meq gene of the Egyptian strain along with a wide array of the global strains has enabled the construction of a novel phylogenetic classification system.

Gut microbiota profiles of commercial laying hens infected with tumorigenic viruses

BACKGROUND

Studies have shown that some viral infections cause structural changes in the intestinal microflora, but little is known about the effects of tumorigenic viral infection on the intestinal microflora of chickens.

RESULTS

A 29-week commercial layer flock positive for avian leukosis virus-J (ALV-J), Marek's disease virus (MDV) and avian reticuloendotheliosis virus (REV) was selected, and fresh fecal samples were collected and examined for the composition of the gut microflora by Illumina sequencing of the V3-V4 region of the 16S rRNA gene. The operational taxonomic units (OTUs) of the fecal microbiota differentiated the chickens infected with only ALV-J and those coinfected with ALV-J and MDV or REV from infection-negative chickens. The enrichment and diversity of cloacal microflora in chickens infected with ALV-J alone were slightly different from those in the infection-negative chickens. However, the diversity of cloacal microflora was significantly increased in chickens coinfected with both ALV-J and MDV or REV.

CONCLUSIONS

The intestinal microbiota was more strongly disturbed in chickens after coinfection with ALV-J and MDV or REV than after infection with ALV-J alone, and there may be underlying mechanisms by which the capacity for the stabilization of the intestinal flora was impaired due to viral infection and tumorigenesis.

An atypical clinicopathological manifestation of fowlpox virus associated with reticuloendotheliosis virus in commercial laying hen flocks in Brazil

Fowlpox (FP) is a common epitheliotropic disease in chickens that is usually controlled by live attenuated vaccines. However, there have been some reports of outbreaks of FP in recent years, even in vaccinated flocks, presenting as atypical lesions and feathering abnormalities in chickens. These findings can be associated with fowlpox virus (FPV) with the reticuloendotheliosis virus (REV) integrated into its genome. In the present study, outbreaks of atypical FP were explored in vaccinated commercial laying hen flocks to determine the nature of the causative agent by histopathologic and molecular approaches. FPV and REV were detected and classified into subclade A1 of the genus Avipoxvirus and subtype 3 of REV (REV3), respectively. Additionally, heterogeneous populations of FPV with partial (containing only a remnant long terminal repeat-LTR) or total (all functional genes) integration of REV were identified by heterologous PCRs and detected considering reference integration sites. These results indicate the mechanism of chimeric genome FPV-REV associated with outbreaks and atypical clinicopathological manifestations in commercial laying hens for the first time in Brazil and in South America. In addition, this study demonstrates the emergence of REV integrated in the FPV genome in Brazilian chicken flocks.

Biotic concerns in generating molecular diagnosis matrixes for 4 avian viruses with emphasis on Marek's disease virus

The great advance in the field of diagnosis of avian viruses is reflecting the highly sophisticated molecular assays of the human and general virology in providing highly sensitive and fast methods of diagnosis. The present review will discuss the biotic factors and the complexities that became evident with the evolution of the novel molecular diagnostic assays with emphasis on 4 avian viruses, chicken anemia, infectious laryngotracheitis, turkey meningoencephalitis, but mainly on Marek's disease virus. To create a biologically meaningful diagnosis, attention should be dedicated to various biotic factors and not only of the diagnostic assay. Included among the important factors are, (a) the sample examined and the sampling strategy, (b) the outcomes of the pathogen amplification ex vivo, (c) the sampling time and its reflection on the disease diagnosis, (d) the impact of simultaneous multiple virus-infections regarding the ability to demonstrate all pathogens and inter- and intra-interactions between the pathogens. A concerted consideration of the relevant factors and the use of advanced molecular diagnostic assay would yield biologically significant diagnosis in real-time that would beneficiate the poultry industry.

Molecular characterization of a Marek's disease virus strain detected in tumour-bearing turkeys

Marek's disease (MD) is a lymphoproliferative disease caused by Gallid alphaherpesvirus 2 (GaHV-2), which primarily affects chickens. However, the virus is also able to induce tumours in turkeys, albeit less frequently than in chickens. This study reports the molecular characterization of a GaHV-2 strain detected in a flock of Italian meat-type turkeys exhibiting visceral lymphomas. Sequencing and phylogenetic analysis of the meq gene revealed that the turkey GaHV-2 has molecular features of high virulence and genetic similarity with GaHV-2 strains recently detected in Italian commercial and backyard chickens. GaHV-2 is ubiquitous among chickens despite vaccination, and chicken-to-turkey transmission is hypothesized due to the presence of broilers in neighbouring pens.RESEARCH HIGHLIGHTS A GaHV-2 strain from Italian turkeys was molecularly characterized.The turkey strain presented molecular characteristics of high virulence in its meq gene.The turkey strain was closely related to previously detected chicken strains.

Co-infection of vvMDV with multiple subgroups of avian leukosis viruses in indigenous chicken flocks in China

BACKGROUND

In China, although the ALV eradication program and the MD vaccination strategy greatly reduce the disease burdens caused by the infection of ALV and MDV, the frequent emergence of novel ALV-K or vvMDV in the vaccinated chicken flock challenges the current control strategies for both diseases.

RESULTS

In Guangdong Province, an indigenous chicken flock was infected with neoplastic disease. Hematoxylin-eosin staining of the tissues showed the typical characteristics of MDV and classical ALV infection. The PCR and sequencing data demonstrated that the identified MDV was clustered into a very virulent MDV strain endemic in domestic chickens in China. Moreover, subgroups ALV-A and ALV-K were efficiently recovered from two samples. The full genome sequence revealed that the ALV-K isolate was phylogenetically close to the ALV TW3593 isolate from Taiwan Province.

CONCLUSIONS

A co-infection of vvMDV with multiple ALV subgroups emerged in a chicken flock with neoplastic disease in Guangdong Province. The co-infection with different subgroups of ALV with vvMDV in one chicken flock poses the risk for the emergence of novel ALVs and heavily burdens the control strategy for MDV.

Marek's disease herpesvirus serotype 1 in broiler breeder and layer chickens in Malaysia

Aim:

This study aimed to investigate the occurrence of Marek’s disease (MD) in five poultry farms in Malaysia using postmortem examination, histopathology, and polymerase chain reaction (PCR).

Materials and Methods:

Tissue samples were collected from 24 broiler breeder chickens from four commercial broiler breeder farms and six layer chickens from one layer farm. Gross and histopathological examinations and PCR amplification of the gene encoding for avian MD herpesvirus (MDV-1) were conducted.

Results:

Gross pathological changes including hepatomegaly, splenomegaly, lymphomatous lesion at the mesentery, oviduct atrophy, and follicular atresia with lymphomatous were observed, whereas diffuse multifocal whitish infiltration of the spleen, neoplastic infiltration in the liver, intrafollicular lymphoid infiltration of the bursa of Fabricius, and lymphomatous tumor at the mesentery were seen on histopathological examinations. Confirmation by PCR showed that a total of 16 (53.33%) samples were positive for avian MDV-1. Although the outbreak involved a much larger number of birds in the respective farms, our investigation was limited based on resource and time frame allocated for the study.

Conclusion:

The findings from this study help in emphasizing the potential threats of MDV to the poultry industry globally, in general, and in Malaysia, in particular. As the scope of the current study is limited, future studies focusing on MDV pathogenesis, typing, and causes of vaccine failures are recommended.

Differential amplification of Marek's disease CVI988 vaccine and of wild-type isolates from organs of commercial chickens using single or duplexed probes in real-time PCR

The differentiation of Marek's disease virus (MDV)-infected and vaccinated animal (DIVA) test, based on the MDV pp38 gene was described by Baigent et al. [(2016). Real-time PCR for differential quantification of CVI988 vaccine and virulent MDV strains. Journal of Virological Methods, 233, 23-36], using similar primers and alternate probes for virulent MDV-1 and the vaccine CVI988 virus. We explored the assay's applicability for commercial vaccines and commercial chickens, as the above-mentioned study employed tissue-cultured MDV strains and tissues from experimental trials. DNA of visceral organs and feathers of vaccinated or naturally infected chickens was used. Further, the applicability of the DIVA assay was evaluated using single or duplexed probes for the two viruses in the same amplification tube. Due to the high viral content in the commercial vaccines and in the clinical cases of MDV-1 infected commercial chickens, their examination by the MDV-1 DIVA real-time PCR was performed in one step. However, for the feather DNAs of commercially vaccinated birds, a step of pre-amplification was required. The MDV-1 DIVA real-time PCR performed as single probe in separate tubes using the Vir3 probe was very sensitive for virulent MDV-1 strains, but not very specific, as it also gave a clear signal with CVI988 vaccine virus. In contrast, the CVI vaccine probe was specific for CVI988, and did not recognize the MDV-1 strains. When both probes were present in one tube, the CVI probe showed a greater sensitivity for CV1988, while the Vir3 probe showed a much better specificity for virulent MDV-1.

Magnetowetting of Ferrofluidic Thin Liquid Films

An extended meniscus of a ferrofluid solution on a silicon surface is subjected to axisymmetric, non-uniform magnetic field resulting in significant forward movement of the thin liquid film. Image analyzing interferometry is used for accurate measurement of the film thickness profile, which in turn, is used to determine the instantaneous slope and the curvature of the moving film. The recorded video, depicting the motion of the film in the Lagrangian frame of reference, is analyzed frame by frame, eliciting accurate information about the velocity and acceleration of the film at any instant of time. The application of the magnetic field has resulted in unique changes of the film profile in terms of significant non-uniform increase in the local film curvature. This was further analyzed by developing a model, taking into account the effect of changes in the magnetic and shape-dependent interfacial force fields.

Protective efficacy of a recombinant bacterial artificial chromosome clone of a very virulent Marek's disease virus containing a reticuloendotheliosis virus long terminal repeat

Marek's disease virus (MDV), an alphaherpesvirus, causes Marek's disease (MD), a lymphoproliferative disease in poultry characterized by T-cell lymphomas, nerve lesions, and mortality. Vaccination is used worldwide to control MD, but increasingly virulent field strains can overcome this protection, driving a need to create new vaccines. Previous studies revealed that insertion of reticuloendotheliosis virus (REV) long terminal repeat (LTR) into a bacterial artificial chromosome (BAC) clone of a very virulent strain of MDV, Md5, rendered the resultant recombinant virus, rMd5 REV-LTR BAC, fully attenuated in maternal antibody positive (Mab+) chickens at passage 40. In the current study, the protective efficacy of rMd5 REV-LTR BAC was evaluated. First, passage 70 was identified as being fully attenuated in maternal antibody negative chickens and chosen as the optimal passage level for use in protective efficacy studies. Second, three protective efficacy trials were conducted comparing the rMd5 REV-LTR p70 BAC to the CVI988/Rispens vaccine. Groups of Mab+ and Mab- 15I₅ × 7₁ chickens were vaccinated in ovo at 18 days of embryonation or intra-abdominally at day of hatch, and challenged at 5 days post-hatch with the vv+MDV strain 686. Vaccination at day of hatch and in ovo with rMd5 REV-LTR p70 BAC protected chickens against MDV-induced bursa and thymic atrophy, but did not provide the same level of protection against MD tumours as that afforded by the commercial vaccine, CVI988/Rispens.

Outbreak of Marek's disease in a vaccinated broiler breeding flock during its peak egg-laying period in China

Background

Outbreaks of Marek’s disease (MD), caused by Marek’s disease virus (MDV), primarily occur in 10–12-week-old hens.

Case presentation

We report a case of MD in a breeding flock of 24–30-week-old vaccinated broilers in China. The clinical signs in the affected chickens appeared at 24 weeks, and the incidence of tumours peaked at 30 weeks. The morbidity and mortality of the hens were 5 % and 80 %, respectively. Hematoxylin–eosin staining of the tissues showed the typical characteristics of MD. MDV infection was confirmed in the hens with an agar gel diffusion precipitation assay for the MD antigen in the feather follicle epithelium. An MDV strain, designated AH1410, was isolated from the blood lymphocytes. Sequence analyses of the pp38, meq, and gB genes revealed that strain AH1410 had molecular features consistent with a virulent, previously identified MDV.

Conclusion

Our data provide evidence that not only is MDV becoming more virulent, but that the period of its onset in chickens is expanding. These findings provide the basis the molecular surveillance and further study of virulent MDV mutants and control strategies for MD in China.

Development and application of a multiplex PCR method for rapid differential detection of subgroup A, B, and J avian leukosis viruses

Avian leukosis virus (ALV) subgroups A, B, and J are very common in poultry flocks and have caused serious economic losses in recent years. A multiplex PCR (mPCR) method for the detection of these three subgroups was developed and optimized in this study. We first designed a common forward primer, PF, and three downstream primers, AR, BR, and JR, which can amplify 715 bp for subgroup A, 515 bp for subgroup B, and 422 bp for subgroup J simultaneously in one reaction. The mPCR method produced neither cross-reactions with other subgroups of ALVs nor nonspecific reactions with other common avian viruses. The detection limit of the mPCR was as low as 1 × 10(3) viral DNA copies of each of the three subgroups. In animal experiments, the mPCR detected ALVs 2 to 4 days earlier than did virus isolation from whole-blood samples and cloaca swabs. Furthermore, a total of 346 clinical samples (including 127 tissue samples, 86 cloaca swabs, 59 albumen samples, and 74 whole-blood samples) from poultry flocks with suspected ALV infection were examined by mPCR, routine PCR, and virus isolation. The positive sample/total sample ratios for ALV-A, ALV-B, and ALV-J were 48% (166/346) as detected by mPCR and 48% (166/346) as detected by routine PCR. However, the positive sample/total sample ratio detected by virus isolation was 40% (138/346). The results of the mPCR and routine PCR were confirmed by sequencing the specific fragments. These results indicate that the mPCR method is rapid, specific, sensitive, and convenient for use in epidemiological studies of ALV, clinical detection of ALV, and ALV eradication programs.

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

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

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.

The use of serotype 1- and serotype 3-specific polymerase chain reaction for the detection of Marek's disease virus in chickens

A serotype 1- and serotype 3-specific detection of Marek's disease virus (MDV) by polymerase chain reaction (PCR) was developed. The sensitivity of the method when applied to cell culture grown virus was comparable with that of cultivation. The method was applied to various tissue samples from chickens experimentally inoculated with serotype 1 or serotype 3 MDV.The serotype 1 strains CVI988 and RB-1B could be detected in feather follicle epithelium up to 56 and 84 days post-inoculation (p.i.), respectively, while the MDV-3 serotype was detected until 42 days p.i. The purpose of this study was to develop and evaluate a reliable and easy-to-handle method for surveillance of the occurrence of MDV in chicken flocks. We emphasize the development of a method, which can be applied to types of samples conveniently collected in the field, e.g. feather tips and blood samples. In addition, the PCR was applied to samples collected from four commercial table egg layer flocks of young stock or pullets vaccinated with either serotype 1 (CVI988) or serotype 3 (HVT) vaccine. These flocks had various clinical signs of Marek's disease. MDV-1 was detected in buffy-coat cells, spleen, liver, skin, feather tips and ovaries. The detection of MDV in feather tips appeared to be as sensitive as co-cultivation of buffy-coat cells, although an inhibiting factor was observed in extracts from feather tips of non-white chickens. This inhibition could be overcome in most extracts by applying a bovine serum albumen pretreatment. The PCR proved to be a convenient tool for the monitoring of MDV in the poultry population, and feather tips were the most convenient and sensitive samples.

Differential diagnosis of two paralytic conditions affecting young chickens with emphasis on PCR findings

Two paralytic conditions affecting flocks of young commercial chickens that were indistinguishable histopathologically from lesions caused by Marek's disease virus (MDV) were investigated. The first, transient paralysis, was observed only in broilers while the second condition, a spastic paralysis, was seen in replacement White Leghorn pullets aged between 6 and 16 weeks. PCR examination of DNA extracted from the blood, brain and spleens of affected birds using primers specific for MDV serotype 1 confirmed the diagnosis of MD for transient paralysis only. None of the Leghorn DNA samples was positive by PCR. Some evidence for a genetic predisposition is offered for the neuritis affecting the pullets based on epidemiological considerations.

Field isolates of fowlpox virus contaminated with reticuloendotheliosis virus

The polymerase chain reaction (PCR) method was used to examine samples from field cases of fowlpox for the presence of reticuloendotheliosis virus (REV). The S-strain fowlpox vaccine, known to be contaminated with REV, served as a positive control. Fowlpox virus was grown from field samples and vaccines by inoculation of embryonated hen eggs by the chorioallantoic membrane (CAM) route. DNA was extracted from the CAM lesions and examined for REV proviral sequences using primers specific for the long terminal repeats of REV. Amplicons of the expected length were detected in all the 45 field samples from poultry and in the S strain vaccine. Two other vaccines and two isolates from wild birds contained no detectable REV sequences. The PCR products from the vaccine and one field isolate were sequenced and were identical. These products showed 81 to 87.5% homology with the published sequences for the long terminal repeats of REV. It was not determined whether the REV proviral DNA was integrated with cellular DNA, fowlpox DNA or both. Inoculation of day-old chickens with the S-strain vaccine resulted not only in the production of fowlpox lesions but also feathering defects and proventriculitis. This suggests that the REV present in the vaccine is replication competent. Problems being encountered with protection from fowlpox following vaccination in Australia might be attributed to simultaneous challenge with fowlpox virus and REV.

A duplex real-time polymerase chain reaction assay for the simultaneous detection of long terminal repeat regions and envelope protein gene sequences of Reticuloendotheliosis virus in avian blood samples

The Reticuloendotheliosis virus (REV) group of retroviruses infects a wide range of avian species, including chickens, turkeys, ducks, geese, quail, and prairie chickens. The objective of the present study was to develop a highly sensitive and specific diagnostic test for the detection of REV in whole blood samples. In order to increase the diagnostic sensitivity, a duplex real-time polymerase chain reaction (PCR) that detects both the envelope protein gene ( env) and the long terminal repeat (LTR) region of REV was designed. This assay demonstrated greater analytical and diagnostic sensitivity than the gel-based PCR assay when using DNA extracted from whole blood by both phenol-chloroform and magnetic bead methods. In general, threshold cycle values in the duplex real-time PCR assay were lower from DNA extracted using the magnetic bead system compared to DNA extracted by the phenol-chloroform method. Data presented herein show the successful development of a rapid and accurate test procedure, with high-throughput capability, for the diagnosis of REV infection using avian blood samples.

Comparative analysis of oncogenic genes revealed unique evolutionary features of field Marek's disease virus prevalent in recent years in China

BACKGROUND

Marek's disease (MD) is an economically important viral disease of chickens caused by Marek's disease virus (MDV), an oncogenic herpesvirus. This disease was well controlled since the widespread use of commercial vaccines, but field MDVs have shown continuous increasing in virulence and acquired the ability to overcome the immune response induced by vaccines. Nowadays, MD continues to be a serious threat to poultry industry, isolation and characterization of MDVs are essential for monitoring changes of viruses and evaluating the effectiveness of existing vaccines.

RESULTS

Between 2008 and 2010, 18 field MDV strains were isolated from vaccinated chicken flocks in Sichuan province, China. Three oncogenic genes including Meq, pp38 and vIL-8 genes of the 18 isolates were amplified and sequenced. Homology analysis showed that the deduced amino acid sequences of these three genes exhibit 95.0-98.8%, 99.3-100% and 97.0-98.5% homology respectively with these of other reference strains published in GenBank. Alignment analysis of the nucleotide and deduced amino acid sequences showed that four amino acid mutations in Meq gene and two amino acid mutations in vIL-8 gene displayed perfect regularity in MDVs circulating in China, which could be considered as features of field MDVs prevalent in recent years in China. In addition, one amino acid mutation in pp38 gene can be considered as a feature of virulent MDVs from USA, and three amino acid mutations in Meq gene were identified and unique in very virulent plus (vv+) MDVs. Phylogenetic analysis based on Meq and vIL-8 protein sequences revealed that field MDVs in China evolved independently. Virulence studies showed that CVI988 could provide efficient protection against the field MDVs epidemic recently in China.

CONCLUSIONS

This study and other published data in the GenBank have demonstrated the features of Meq, pp38 and vIL-8 genes of MDVs circulating in recent years in Sichuan, China. Mutations, deletions or insertions were observed in these three genes, and some mutations could be considered as the unique marks of the MDVs circulating presently in China. The paper supplies some valuable information concerning the evolution of MDV which is useful for the vaccine development and control of MD in China.

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.

Detection and differentiation of re-emerging fowlpox virus (FWPV) strains carrying integrated reticuloendotheliosis virus (FWPV-REV) by real-time PCR

Current strains of fowlpox virus (FWPV) carrying circulating reticuloendotheliosis virus (FWPV-REV) sequence are becoming more pathogenic to poultry. This is evidenced by the fact that vaccination with current available FWPV vaccines provides limited protection against them. To characterize REV insertions in a collection of both older and more recent field isolates, we developed three different types of adjacent oligoprobes and primer sets from specific genomic locations of FWPV and REV: REV-ENV (accession no. K02537, 1382-2260), FWPV-REV integration site (accession no. AF006064, 86-1328), FWPV (accession no. AF198100, 232461-232670), and REV-LTR (accession no. V01204, 305-496). The data indicated that the primers from the REV-ENV region and the TaqMan probes specifically targeted REV-ENV sequences of FWPV-REV strains. Furthermore, the strains were differentiated based on quantitative melting temperature (T(m)) of their amplified products using FRET-based probes. The amplified products were further characterized by sequencing and multiple sequence alignment analysis. The results suggest that integrated REV-ENV sequences are both common and mostly conserved in field isolates. However, the minor variations found within the short-targeted ENV sequence from FWPV-REV strains suggest that these strains could have either undergone periodic point mutational changes or integration with different REV-ENV subtypes.

The contribution of feathers in the spread of chicken anemia virus

Chicken anemia virus (CAV) spreads vertically and horizontally, however, the process is mostly still obscure. To further clarify the horizontal CAV spread, we examined the contribution of feathers. We demonstrated that CAV could be amplified from DNA purified from feather shafts of experimentally infected chicks, and the process efficacy was evaluated by comparing the amplification of DNA purified from feather shafts and lymphoid organs of CAV-experimentally infected chicks. DNA from feathers was found as an efficient source for CAV detection. Further, to substantiate whether CAV reaches the feather shafts passively via the blood, or intrinsically, causing histopathological changes, the feather follicle tissues were examined for CAV-induced lesions. Specific histological changes were found, however, immunohistochemistry failed to detect viral proteins. To determine whether the feather shafts are a source of infective virus, they were homogenized and used to infect 1-day-old chicks via the mucosal entries (eyes, nose and oropharynx). That infection mode simulates the natural route of horizontal infection in commercial poultry houses. We demonstrated the CAV-infection by serology, virology and pathology, showing that feather shafts carry infectious CAV either on their surface or within their feather pulp, and concluded that feathers contribute to the horizontal CAV dissemination.

Relationship between Marek's disease virus load in peripheral blood lymphocytes at various stages of infection and clinical Marek's disease in broiler chickens

Vaccination with herpesvirus of turkey (HVT) vaccine provides protection against clinical Marek's disease (MD) but does not preclude infection with wild-type MD virus (MDV). The quantity of MDV detected in circulating lymphocytes during the early period after infection may be a useful predictor of subsequent clinical MD later in the life. A study was designed to quantify MDV and HVT copy number in peripheral blood lymphocytes (PBL) using real-time polymerase chain reaction between days 5 and 35 post-challenge and to relate this to subsequent development of gross MD lesions. Female commercial broiler chickens were vaccinated with HVT or were sham-vaccinated at hatch, then challenged with MDV strain MPF-57 at day 2 post-vaccination and reared in positive-pressure isolators up to 56 days post-challenge, when all survivors were euthanized. All dead and euthanized chickens were examined post mortem for gross MD lesions. Birds were scored for MD lesions and mortality. MDV and HVT genome copy numbers were determined for each PBL sample. There was an increase in HVT load in PBL between days 7 and 37 post-vaccination, with marked increases between days 7 and 16 and again between days 30 and 37. There was a steady increase in MDV load to 35 days post-challenge. The mean MDV copy number (log(10)) was greater in chickens subsequently exhibiting gross MD lesions (5.05 +/- 0.21) than in those that did not (2.88 +/- 0.223), with the largest difference at 14 and 21 days post-challenge (P < 0.001). Quantification of MDV during early infection is therefore a potential tool for monitoring MD in broiler flocks.

Absolute quantitation of Marek's disease virus and Herpesvirus of turkeys in chicken lymphocyte, feather tip and dust samples using real-time PCR

The further development of Taqman quantitative real-time PCR (qPCR) assays for the absolute quantitation of Marek's disease virus serotype 1 (MDV1) and Herpesvirus of turkeys (HVT) viruses is described and the sensitivity and reproducibility of each assay reported. Using plasmid DNA copies, the lower limit of detection was determined to be 5 copies for the MDV1 assay and 75 copies for the HVT assay. Both assays were found to be highly reproducible for Ct values and calculated copy numbers with mean intra- and inter-assay coefficients of variation being less than 5% for Ct and 20% for calculated copy number. The genome copy number of MDV1 and HVT viruses was quantified in PBL and feather tips from experimentally infected chickens, and field poultry dust samples. Parallelism was demonstrated between the plasmid-based standard curves, and standard curves derived from infected spleen material containing both viral and host DNA, allowing the latter to be used for absolute quantification. These methods should prove useful for the reliable differentiation and absolute quantitation of MDV1 and HVT viruses in a wide range of samples.

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.

Insect contribution to horizontal transmission of Reticuloendotheliosis virus

The involvement of insects in Reticuloendotheliosis virus (REV) transmission was examined by testing insects trapped at commercial farms and by controlled feeding experiments using mosquitoes, Culex pipiens L. and house flies, Musca domestica L. We established sensitive methods of REV detection, including reverse transcription-polymerase chain reaction (PCR) for REV-LTR and REV-gag genes, REV antigenemia measurements by enzyme-linked immunosorbent assay, and virus isolation in tissue cultures. A variety of blood-sucking species of insects were trapped at farms with infected poultry and tested, but none were positive. To rule out the possibility of PCR inhibition by insect RNA, spiking experiments were conducted and no interference was observed. Because Cx. pipiens mosquitoes were trapped frequently at farms, we performed feeding experiments with mosquito females fed on a REV-containing tissue culture medium and chicken blood mixture. Virus was detected in the mosquitoes up to 5 h postfeeding, compared with 96 h in the feeding mixture, indicating that Cx. pipiens can only harbor REV for a short period. House flies were suspected to be involved in the virus transmission because they frequently were trapped on positive farms. In contrast to mosquitoes, REV was harbored within the house fly digestive tract for up to 72 h and could infect chickens, as demonstrated by seroconversion and by detection of viral gag-sequence in the cloaca. The current study is supportive for the role of house flies as a mechanical vector of REV among poultry.

Chicken Infectious Anemia Virus Infection in Israeli Commercial Flocks: Virus Amplification, Clinical Signs, Performance, and Antibody Status

The impact of chicken infectious anemia virus (CIAV) infection on commercial chicken flocks in Israel was examined by analyzing flocks with or without typical CIAV signs, signs of other diseases, or apparently healthy flocks. In 23 flocks (broilers and layers) of ages up to 8 wk, typical signs of CIAV infection (stunting, gangrenous dermatitis, and secondary bacterial infections) were recorded. When permitted by flock owners, in several cases among these 23 flocks the morbidity, mortality, and performance parameters were recorded; the presence of CIAV was detected by polymerase chain reaction (PCR); and the antibody status of parents and broilers was measured. In addition, total mortality, number of birds sold, total kilograms of meat sold, density (kg/m2), mean age at slaughter, daily growth rate in grams, total kilogram of food consumed, food conversion rate, and the European Index were calculated. We also surveyed flocks affected by other diseases, such as tumors, respiratory diseases, or coccidiosis, and flocks with no apparent clinical signs. The latter flocks were negative by CIAV-PCR, indicating that typical CIAV clinical signs are associated with one-step PCR-CIAV amplification. However, a small amount of CIAV might still be present in these flocks, acting to induce the subclinical effects of CIAV infection. These data indicate a link between the presence of virus sequences and typical CIAV signs and strengthen the concept that CIAV infection has a negative economic impact on the chicken industry.

Novel applications of feather tip extracts from MDV-infected chickens; diagnosis of commercial broilers, whole genome separation by PFGE and synchronic mucosal infection

Marek's disease virus (MDV) productive replication occurs in the feather follicle epithelium and the feather tips are valuable both for research and disease diagnosis. Three novel applications of feather tip extracts are described now: (A). As a source of DNA for amplifying either MDV and/or ALV-J. In two clinical situations a marked advantage was obtained compared to blood and organs; in broiler breeder flocks with a mixed MDV and ALV-J infection, and in young broilers with neurological Marek's disease (MD). (B). Separation of the large ( approximately 200 kbp) MDV genome directly from the infected chickens. Using pulsed field gel electrophoresis, the DNA extracted from tumors or feather tips was separated and hybridized to a 132 bp tandem repeat MDV probe. Compared to 2/55 polymerase chain reaction (PCR) positive tumor samples, 15/61 feather tip extracts contained whole MDV genomes. (C). Experimental MDV infection was induced by the mucosal route by dripping feather tip extract to the eye and mouth of the bird. That attempted to reproduce the native infection process, however the use of extracts, instead of dry feather dust was a compromise, aimed to synchronize the infection. In one trial, tumors were induced 6 weeks after dripping day-old broilers, while in another, feather tips were PCR positive 16 days after dripping of 2-month-old layers.

Molecular characterization of reticuloendotheliosis virus insertions in the genome of field and vaccine strains of fowl poxvirus

Evidence of the widespread occurrence of reticuloendotheliosis virus (REV) sequence insertions in fowl poxvirus (FPV) genome of field isolates and vaccine strains has increased in recent years. However, only those strains carrying a near intact REV provirus are more likely to cause problems in the field. Detection of the intact provirus or REV protein expression from FPV stocks has proven to be technically difficult. The objective of the present study was to evaluate current and newly developed REV and FPV polymerase chain reaction (PCR) assays to detect the presence of REV provirus in FPV samples. The second objective was to characterize REV insertions among recent "variant" FPV field isolates and vaccine strains. With REV, FPV, and heterologous REV-FPV primers, five FPV field isolates and four commercial vaccines were analyzed by PCR and nucleotide sequence analysis. Intact and truncated REV 5' long terminal repeat (LTR) sequences were detected in all FPV field isolates and vaccine strains, indicating heterogeneous REV genome populations. However only truncated 3' LTR and envelope sequences were detected among field isolates and in one vaccine strain. Amplifications of the REV envelope and 3' LTR provided strong evidence to indicate that these isolates carry a near intact REV genome. Three of the four FPV vaccine strains analyzed carried a solo complete or truncated 5' LTR sequence, indicating that intact REV provirus was not present. Comparison of PCR assays indicated that assays amplifying REV envelope and REV 3' LTR sequences provided a more accurate assessment of REV provirus than PCR assays that amplify the REV 5' LTR region. Therefore, to differentiate FPV strains that carry intact REV provirus from those that carry solo 5' LTR sequences, positive PCR results with primers that amplify the 5' LTR should be confirmed with more specific PCR assays, such as the envelope, or the REV 3' LTR PCR.

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.

The feather tips of commercial chickens are a favorable source of DNA for the amplification of Marek's disease virus and avian leukosis virus, subgroup J

Marek's disease virus (MDV), a herpesvirus, and avian leukosis virus, subgroup J (ALV-J), a retrovirus, are oncogenic viruses of poultry. The present report describes a case-report study aimed at examining the efficacy of amplifying MDV and/or ALV-J from feather-tip DNA as compared with DNA purified from liver and spleen. We show that the polymerase chain reaction for MDV and ALV-J env using DNA from feather tips was more effective for diagnosis of naturally infected commercial chickens than using the liver and spleen.

Marek's disease in turkeys. I. A seven-year survey of commercial flocks and experimental infection using two field isolates

Marek's disease virus (MDV) causes immunosuppression and tumors in chickens, but the turkey is an unusual host for the virus, and tumors caused by MDV in turkeys are unique. We describe the prevalence of turkey tumors in Israel between 1993 and 2000, their molecular diagnosis by polymerase chain reaction (PCR), and the natural distribution of herpesvirus of turkeys (HVT). Most clinical cases with tumors in commercial turkeys were diagnosed as MDV. The reproduction of Marek's disease (MD) in turkeys by two turkey MDV strains, Ar and La, was analyzed, and it was shown that these strains can induce tumors in experimental trials. The severity of experimental disease differed from those features of the original outbreak, since a less severe disease was recorded.

Marek's disease in turkeys. II. Characterization of the viral glycoprotein B gene and antigen of a turkey strain of Marek's disease virus

Marek's disease virus (MDV) causes immunosuppression and tumors in chickens. As sporadic cases of Marek's disease (MD) were recorded in turkeys, the antigenic and genomic characteristics of the MDV glycoprotein B (gB) gene and antigen of turkeys were compared to the chicken MDV gB. The whole chicken and turkey gB genes were sequenced and found identical. By immunoblotting of infected-cell culture lysates using chicken convalescent and gB monoclonal antibodies, the antigenic epitopes of the chicken and turkey viruses were found to differ. The turkey MDV had a unique epitope, compared to the chicken MDV and compared with our previous findings. While the chicken MDV had two epitope types, heat-labile but dithiothreitol (DTT)-stable and heat-stable but DTT-labile, the turkey MDV gB epitope is both heat and DTT-labile.

Molecular identification of the Marek's disease virus vaccine strain CVI988 in vaccinated chickens

The study describes three polymerase chain reaction (PCR) systems for the CVI988 vaccine virus: the meq gene, the MDV BamHI-D/H 132 bp tandem repeat fragment and the MDV-gB gene. Whereas the PCR product of virulent MDV strains and of the CVI988 virus strain with the meq and the 132 bp primer sets differed for the two templates, the MDV-gB PCR products were similar. The sensitivity of the three PCRs was determined for the two templates: the CVI988 DNA was detected up to 2.48 plaque forming units, and a MDV-1 DNA, was amplified with the 132 bp primers up to the 10(-3) DNA dilution, and up to the 10(-2) with the MDV-gB and meq gene primers. As conventional detection for the CVI988 vaccine virus is by tissue culture, the aim was to analyse the feasibility of the molecular detection of the vaccine virus in the vaccinated chick. In two experimental trials employing specific pathogen free and commercial Lohmann chicks, respectively, the vaccine virus replicated to a limited extent; it was detected only in the spleen of up to 60% chicks at 2-4 weeks and in one chick at 3 weeks, respectively. The survey of three commercial Lohmann flocks, kept in biosecurity conditions, revealed the vaccine virus only in the spleen of 40% of 30-day-old chicks. The present study shows that CV1988 DNA is present in vaccinated chicks in a low quantity and it is difficult to detect directly from the chick, probably because vaccine viruses are latent in vivo. For an efficient detection it is pertinent to cultivate the vaccine virus on chicken embryo fibroblasts (CEF), as then the virus escapes the latent state, enters into the productive mode of replication, and a high viral copy number is produced.