Cloning and characterization of budgerigar fledgling disease virus, an avian polyomavirus

Molecular Characterization of a Novel Budgerigar Fledgling Disease Virus Strain From Budgerigars in China

Budgerigar fledgling disease virus (BFDV) is the causative polyomavirus of budgerigar fledgling disease, an important avian immunosuppressive disease in budgerigars (Melopsittacus undulatus). In the current study, we explored the etiological role and molecular characteristics of BFDV. We identified a novel BFDV strain, designated as SC-YB19, belonging to a unique cluster with three other domestic strains (WF-GM01, SD18, and APV-P) and closely related to Polish isolates based on complete sequences. Sequence analysis showed that SC-YB19 had an 18-nucleotide (nt) deletion in the enhancer region, corresponding to the sequence position 164–181 nt, which differed significantly from all other BFDV strains. Based on sequence alignment, three unique nucleotide substitutions were found in VP4 (position 821), VP1 (position 2,383), and T-antigen (position 3,517) of SC-YB19, compared with SD18, WF-GM01, QDJM01, HBYM02, APV7, and BFDV1. Phylogenetic analyses based on complete sequences suggested that SC-YB19, along with the domestic WF-GM01, SD18, and APV-P strains, formed a single branch and were closely related to Polish, Japanese, and American isolates. These results demonstrate that BFDV genotype variations are co-circulating in China, thus providing important insight into BFDV evolution.

JCPyV VP1 Mutations in Progressive MultifocalLeukoencephalopathy: Altering Tropismor Mediating Immune Evasion?

Polyomaviruses are ubiquitous human pathogens that cause lifelong, asymptomatic infections in healthy individuals. Although these viruses are restrained by an intact immune system, immunocompromised individuals are at risk for developing severe diseases driven by resurgent viral replication. In particular, loss of immune control over JC polyomavirus can lead to the development of the demyelinating brain disease progressive multifocal leukoencephalopathy (PML). Viral isolates from PML patients frequently carry point mutations in the major capsid protein, VP1, which mediates virion binding to cellular glycan receptors. Because polyomaviruses are non-enveloped, VP1 is also the target of the host's neutralizing antibody response. Thus, VP1 mutations could affect tropism and/or recognition by polyomavirus-specific antibodies. How these mutations predispose susceptible individuals to PML and other JCPyV-associated CNS diseases remains to be fully elucidated. Here, we review the current understanding of polyomavirus capsid mutations and their effects on viral tropism, immune evasion, and virulence.

Fifty Years of JC Polyomavirus: A Brief Overview and Remaining Questions

In the fifty years since the discovery of JC polyomavirus (JCPyV), the body of research representing our collective knowledge on this virus has grown substantially. As the causative agent of progressive multifocal leukoencephalopathy (PML), an often fatal central nervous system disease, JCPyV remains enigmatic in its ability to live a dual lifestyle. In most individuals, JCPyV reproduces benignly in renal tissues, but in a subset of immunocompromised individuals, JCPyV undergoes rearrangement and begins lytic infection of the central nervous system, subsequently becoming highly debilitating-and in many cases, deadly. Understanding the mechanisms allowing this process to occur is vital to the development of new and more effective diagnosis and treatment options for those at risk of developing PML. Here, we discuss the current state of affairs with regards to JCPyV and PML; first summarizing the history of PML as a disease and then discussing current treatment options and the viral biology of JCPyV as we understand it. We highlight the foundational research published in recent years on PML and JCPyV and attempt to outline which next steps are most necessary to reduce the disease burden of PML in populations at risk.

Development of a colorimetric loop-mediated isothermal amplification assay for rapid and specific detection of Aves polyomavirus 1 from psittacine birds

A colorimetric loop-mediated isothermal amplification (LAMP) assay was developed for the rapid and specific detection of the T gene of Aves polyomavirus 1 (APyV), a causative agent of budgerigar fledgling disease (BFD) in psittacine birds. The amplification can be completed in 40 min at 60 °C, and the results can be visually detected by the naked eye using hydroxyl naphthol blue as a colorimetric indicator. The assay specifically amplified APyV DNA but not other viral and bacterial nucleic acids. The limit of detection of the assay was 5 × 10² DNA copies/reaction, which was comparable to those of previously reported conventional polymerase chain reaction assays. In the clinical evaluation, the LAMP results showed 100% concordance with those of the previously reported PCR assays with regard to specificity, sensitivity, and percentage of overall agreement, with a kappa value of 1.0. These results indicate that the developed LAMP assay will be a valuable tool for the rapid, sensitive and specific detection of APyV from BFD-suspected psittacine bird samples even in resource-limited laboratories.

Survey of captive parrot populations around Port Phillip Bay, Victoria, Australia, for psittacine beak and feather disease virus, avian polyomavirus and psittacine adenovirus

OBJECTIVE

This study investigated the prevalence of psittacine beak and feather disease virus (BFDV), avian polyomavirus (APV) and psittacine adenovirus (PsAdV) in captive psittacine birds around Port Phillip Bay, Victoria, Australia.

METHODS

Samples of fresh droppings were collected from 118 psittacine birds (109 clinically normal and 9 with feather abnormalities) from 11 avaries in different locations and were used for detection of BFDV, APV and PsAdV using PCR.

RESULTS

BFDV, APV and PsAdV were detected in 31%, 13% and 4%, respectively, of the specimens tested. One budgerigar was found to be co-infected with BFDV and PsAdV. At least one sample tested positive for BFDV at each location.

CONCLUSION

This is the first report of the prevalence of BFDV, APV and PsAdV in Victoria and provides a foundation for future studies examining the influence of these viruses on the health of aviary birds in Victoria.

Epizootic occurrence of haemorrhagic nephritis enteritis virus infection of geese

Recent outbreaks of haemorrhagic nephritis enteritis in geese flocks of 3 to 10 weeks in age in Hungary were investigated. Mortality varied between 4% and 67%. Affected birds generally died suddenly. Occasional clinical signs included tremors of the head and neck, subcutaneous haemorrhages and excretion of faeces containing partly digested blood. At necropsy the most frequent findings were a turgid wall and reddish mucosa of the intestines and reddish discolouration of the swollen kidneys, but oedema and haemorrhages of the subcutaneous connective tissue, hydropericardium and ascites were also seen. In subacute cases, visceral gout was frequently observed. Histological examination revealed zonal necrosis of the tubular epithelial cells with haemorrhages in the kidney. Other histological findings were serous hepatitis with fatty infiltration, necrotizing haemorrhagic enteritis and haemorrhages in the different organs including the brain. Experimental geese infected parenterally with crude liver and spleen homogenates prepared from diseased birds died after 8 to 20 days without premonitory signs, and had typical gross and histological lesions. Attempts to isolate cytopathic virus on different tissue cultures failed. The presence of polyomavirus was proven by polymerase chain reaction. Five isolates were further investigated by analysing their complete VP1 gene sequence. All tested strains were very closely related to each other on the basis of the nucleotide sequence, and they were identical at the deduced amino acid level.

Avian polyomavirus mutants with deletions in the VP4-encoding region show deficiencies in capsid assembly and virus release, and have reduced infectivity in chicken

Avian polyomavirus (APV) is the causative agent of an acute fatal disease in psittacine and some non-psittacine birds. In contrast to mammalian polyomaviruses, the APV genome encodes the additional capsid protein VP4 and its variant VP4Delta, truncated by an internal deletion. Both proteins induce apoptosis. Mutation of their common initiation codon prevents virus replication. Here, the generation of replication competent deletion mutants expressing either VP4 or VP4Delta is reported. In contrast to infection with wild-type virus, chicken embryo cells showed no cytopathic changes after infection with the mutants, and induction of apoptosis as well as virus release from the infected cells were delayed. Electron microscopy revealed the presence of a high proportion of small particles and tubules in preparations of the VP4 deletion mutant, indicating a scaffolding function for VP4. Wild-type and mutant viruses elicited neutralizing antibodies against APV after intramuscular and intraperitoneal infection of chicken; however, VP4-specific antibodies were only detected after infection with wild-type virus. Using the oculonasal route of infection, seroconversion was only observed in chickens infected with the wild-type virus, indicating a strongly reduced infectivity of the mutants. Based on the biological properties of the deletion mutants, they could be considered as candidates for APV marker vaccines.

Detection and sequence analysis of avian polyomavirus and psittacine beak and feather disease virus from psittacine birds in Taiwan

Avian polyomavirus (APV) and psittacine beak and feather disease virus (PBFDV) are the most common viral diseases of psittacine birds. In Taiwan, however, the existence of these viruses in psittacine birds has not been established. Polymerase chain reaction (PCR) methodology was therefore employed to ascertain whether APV and PBFDV genomes were present in isolates from psittacine birds of Taiwan. A total of 165 psittacine birds belonging to 22 genera were examined between 2002 and 2005. Findings revealed an APV-positive rate of 15.2%, a PBFDV-positive rate of 41.2%, and an APV/PBFDV dual infection rate of 10.3%. After cloning and sequencing, sequences of the PCR products were compared with sequences obtained from GenBank. For APV, the nucleotide identity among VP1 and t/T antigen coding regions ranged from 97.5% to 100% and 97.6% to 100%, respectively. For PBFDV, the nucleotide identity of ORF V1 and ORF C1 sequences ranged from 92.2% to 100% and 83.3% to 100%, respectively. The derived amino acid sequence alignment for PBFDV ORF V1 fragments revealed the conservation of two replication motifs and of the nucleotide binding site motif. In PBFDV, six of 42 deduced positions in the ORF C1 amino acid sequence were considered hypervariable. The established phylogenetic trees based on the four genome fragments examined in this study did not allow the assignment of particular APV or PBFDV nucleotide sequences to distinct avian species.

Duplex shuttle PCR for differential diagnosis of budgerigar fledgling disease and psittacine beak and feather disease

Two common viral diseases in psittacine birds including budgerigar fledgling disease (BFD), generally called avian polyomavirus (APV) infection, and psittacine beak and feather disease (PBFD) have similar clinical manifestations characterized by feather disorders. A duplex shuttle PCR was developed for detection of APV and PBFD virus (PBFDV). Two pairs of oligonucleotide primers were designed to amplify a 298-bp fragment of the t/T antigen region of APV genome and a 495-bp fragment of the capsid protein region encoded by open reading frame (ORF) C1 of PBFDV genome, respectively. In the present study, APV and PBFDV were detected simultaneously in one tube by duplex shuttle PCR using these two pairs of primers. The detection limits were 2 viral copies of APV and 3 viral copies of PBFDV. In the clinical application, we detected 16 APV-positive, 15 PBFDV-positive, and 3 mixed infected samples in 39 samples examined. Sequences of the amplified products were read. The t/T antigen region was conserved in the APV-positive samples as expected. ORF C1 of PBFDV genome showed diversity. Phylogenic analysis indicated that PBFDV ORF C1 consisted of 6 clusters which were related to subfamilies of psittacine birds. Our duplex shuttle PCR could be a useful method for differential diagnosis and molecular epidemiology of BFD and PBFD.

Detection of beak and feather disease virus (BFDV) and avian polyomavirus (APV) DNA in psittacine birds in Italy

Beak and feather disease (psittacine circovirus) and Budgerigar fledgling disease (avian polyomavirus) are viral diseases that can frequently affect captive psittacine birds. We designed the first survey to investigate the presence of beak and feather disease virus (BFDV) and Avian polyomavirus (APV) inside the population of captive psittacine birds in Italy. Samples were collected in 18 Italian psittacine breeding centres and four trade centres over a 4-year period. A total of 1516 birds were tested for BFDV and 877 birds were tested for APV by means of a polymerase-chain-reaction (PCR) assay. BFDV was found in 122 (8.05%) and APV in 7 (0.79%) birds. No significant difference in infection rate was found between imported and locally raised parrots. We report the first BFDV DNA isolation in wild birds imported to Italy from Papua New Guinea.

A survey to detect subclinical polyomavirus infections of captive psittacine birds in Germany

Infections of avian polyomavirus (APV) are known to cause fatal disease in a wide range of psittacine and non-psittacine birds. Here, we present a survey to investigate the existence of subpopulation of persistent or subclinically infected parrots inside the population of captive psittacine birds in Germany. DNA was isolated from feathers of 85 symptom-free birds from 20 different genera (all psittaciformes) taken from 30 different breeders from all over Germany. The presence of APV was analysed by performing polymerase chain reaction assays (PCR). APV was detected in none of the samples, indicating that the existence of a subpopulation of captive psittacine birds having a persistent APV infection in Germany seems to be relatively low.

Sertoli cell tumor associated with polyomavirus infection in a Gouldian finch (Erythrura gouldiae)

A 3-yr-old male Gouldian finch (Erythrura gouldiae) died after 2 wk of lethargy, emaciation, feather loss, and abdominal distension. The bird was housed in an aviary for breeding, but it had shown loss of fertility in the previous breeding season. Necropsy revealed a gross, firm, and yellow mass involving the left testis. Histologically, the mass was a mixed form, intratubular and diffuse, Sertoli cell tumor. Some neoplastic cells had intranuclear inclusion bodies that immunoelectron microscopy proved to be polyomavirus particle aggregates. There were no viral inclusions in other tissues. The possible role of infection in the pathogenesis of the tumor is discussed.

Avian polyomavirus agnoprotein 1a is incorporated into the virus particle as a fourth structural protein, VP4

Agnoproteins, encoded by the 5'-region of the late bicistronic mRNA of some polyomaviruses, are small proteins with largely unknown functions. In avian polyomavirus (APV)-infected cells, mRNAs of seven putative agnoproteins have been observed. Recently, it has been shown that agnoprotein 1a and its truncated variant agnoprotein 1b, encoded by the predominant mRNA species, are essential for APV replication. Here, the presence of agnoprotein 1a is demonstrated in the nucleus of APV-infected cells and in purified APV particles. Interaction between agnoprotein 1a and the major structural protein, VP1, was demonstrated by co-immunoprecipitation experiments using lysates of recombinant baculovirus-infected insect cells. With proteins expressed in E. coli, binding to double-stranded DNA in a sequence-unspecific manner was shown for agnoprotein 1a, whereas agnoprotein 1b failed to bind. A leucine zipper-like motif present in agnoprotein 1a is considered to be involved in DNA binding. Due to the absence of any structural or functional homologies between APV agnoprotein 1a and the agnoproteins of mammalian polyomaviruses, it is suggested that this protein should be renamed VP4, indicating its function as a fourth structural protein of APV.

Development of a blocking enzyme-linked immunosorbent assay for the detection of avian polyomavirus-specific antibodies

Avian polyomavirus, described originally as budgerigar fledgling disease virus, has been associated with devastating contagious disease outbreaks in budgerigar aviaries. At present, this virus affects a wide range of psittacine and non-psittacine birds worldwide, and the serum neutralisation test is used for the serodiagnosis of avian polyomavirus infections. A blocking enzyme-linked immunosorbent assay was developed for the screening of large numbers of sera collected from various avian species. The assay employs a monoclonal antibody directed against the major structural protein VP1 as a blocking antibody in a sandwich blocking procedure. Either purified avian polyomavirus particles or avian polyomavirus VP1 expressed in recombinant baculovirus-infected Sf9 cells were used as antigen. The specificity of the blocking enzyme-linked immunosorbent assay was evaluated by testing sera directed against mammalian polyomaviruses. Using sera obtained from chicken infected experimentally with avian polyomavirus and a collection of psittacine field-origin sera, a good correlation was observed between the results of the blocking enzyme-linked immunosorbent assay and the serum neutralisation test. However, the blocking enzyme-linked immunosorbent assay is more rapid and more economic. Both, avian polyomavirus particles and VP1 produced by recombinant DNA technology proved to be suitable antigens.

Agnoprotein 1a and agnoprotein 1b of avian polyomavirus are apoptotic inducers

Avian polyomavirus (APV) causes an acute fatal disease in a variety of avian species. DNA laddering indicating apoptosis was demonstrated in APV-infected chicken embryo (CE) cells. DNA laddering, however, was not observed in Vero cells infected with mammalian polyomavirus simian virus 40. Expression of APV agnoprotein 1a and agnoprotein 1b induced apoptosis in insect cells and CE cells. An APV full-length plasmid transfected in CE cells induced apoptosis, and infectious virus was produced. After transfection of CE cells with a plasmid containing a mutated initiation codon for agnoprotein 1a and agnoprotein 1b, however, a considerably lower number of apoptotic cells was observed, and no infectious progeny was produced.

Agnoprotein-1a of avian polyomavirus budgerigar fledgling disease virus: identification of phosphorylation sites and functional importance in the virus life-cycle

The avian polyomavirus budgerigar fledgling disease virus (BFDV) encodes an unusual set of four agnoproteins in its late upstream region. Of the two pairs of these proteins, which overlap each other in two different reading frames, the p(L1)-promoted agnoprotein-1a (agno-1a) is the dominant species and is able to support virus propagation in the absence of the other three polypeptides. Viral BFDV agno-1a, and also agno-1a expressed via an influenza virus vector, consists of a complex series of electrophoretically separable subspecies that can be reduced by phosphatase action down to a primary unphosphorylated protein with an apparent molecular mass of 31 kDa. Through peptide mass spectrometry and site-directed mutagenesis, the positions of four serine and three threonine residues have been determined as phosphate-accepting groups, which are partially modified by the combined action of three different cellular kinases. Since extensively phosphorylated agno-1a is required for its intracellular function, control over VP protein expression, and unphosphorylated agno-1a is observed as an additional component in the BFDV virion, both extreme subspecies appear to be drawn from that complex mixture, which also includes the intermediate stages of phosphorylation.

Recombinant expression of late genes agno-2a and agno-2b of avian polyomavirus BFDV

Budgerigar fledgling disease virus (BFDV) genome contains two times two (two pairs) open reading frames (agnogenes) at the 5' end of the late coding region. Recombinant influenza A viruses were constructed to express the second pair of BFDV agnoproteins, agno-2a and agno-2b, with a fusion of a histidine-tag at their carboxy-termini, respectively. Specific proteins were detected in Western blot analysis using anti histidine-tag monoclonal antibody. By indirect immunofluorescence experiments agno-2a and agno-2b were shown to be located on the surface and in the perinuclear and cytoplasmic areas of infected cells. Comparisons of the expression patterns of BFDV agno-2a and agno-2b with that of simian virus 40 agnoprotein reveal high similarity, suggesting that they might have the same function(s) in polyomavirus infectious cycle.

Avian polyomavirus major capsid protein VP1 interacts with the minor capsid proteins and is transported into the cell nucleus but does not assemble into capsid-like particles when expressed in the baculovirus system

The baculovirus system was used to construct and isolate AcMNPV-VP1, AcMNPV-VP2 and AcMNPV-VP3 recombinant viruses which express the respective avian polyomavirus (APV) structural proteins in Sf9 insect cells. These recombinant AcMNPVs containing APV structural protein genes were utilized to investigate protein-protein interactions between the structural proteins. Immunofluorescence studies utilizing Sf9 cells infected with the AcMNPV-VP1 revealed that the VP1 protein was expressed and localized in the cytoplasm and not transported into the nucleus. When the cells were co-infected with the VP1 and either VP2 or VP3 recombinant viruses, immunofluorescence of the VP1 protein was localized in the nucleus, indicating that the VP1 protein was transported to the nucleus by both the VP2 and VP3 minor proteins. This observation was suggestive of a protein-protein interaction between the expressed proteins. This protein-protein interaction was substantiated by laser scanning confocal microscopy of Sf9 cells that were co-infected with VP1, VP2 and VP3 recombinant viruses. However, the minor proteins could not be co-isolated with VP1 protein by immunoaffinity chromatography using a monoclonal anti-VP1 serum. In addition, capsid-like particles could not be purified either by CsC1 density gradient centrifugation or by immunoaffinity chromatography. VP1 capsomeres were isolated by immunoaffinity chromatography from Sf9 cells infected with AcMNPV-VP1, with or without the minor protein(s), and these capsomeres could assemble in vitro into capsid-like particles. Electron microscopic observation of thin-sectioned Sf9 cells, which were co-infected with VP1, VP2 and VP3 recombinant viruses, demonstrated capsomere-like structures in the nucleus, but capsid-like particles were not observed.

Characterization of a calcium binding domain in the VP1 protein of the avian polyomavirus, budgerigar fledgling disease virus

Calcium ions appear to play a major role in maintaining the structural integrity and assembly of papovavirus virions and are likely involved in the process of viral uncoating. Recently it was reported that the purified recombinant VP1 protein of budgerigar fledgling disease virus (BFDV) was capable of assembling into capsid-like particles in the presence of calcium. It is now reported that the major capsid protein VP1 of BFDV binds calcium ions in an in vitro calcium binding assay. Two deletions were made in the VP1 protein to identify a calcium binding domain and to further characterize the role of calcium ions in the capsid assembly process. Recombinant VP1 lacking a putative calcium binding domain (Asp-237-Asp-248) failed to bind radioactive 45Ca2+ yet associated into capsomeres. These capsomeres were similar in shape to the wild-type VP1 but were unable to assemble into capsid-like particles. Likewise, recombinant VP1 lacking ten carboxyl terminal amino acids (Glu-334-Arg-343) also formed capsomeres that were unable to assemble into capsid-like particles. In contrast to the VP1 protein with the internal deletion, the protein with the truncated carboxyl terminus bound 45Ca2+ in the in vitro assay. These results have identified a calcium binding domain (Asp-237-Asp-248) for the BFDV VP1 protein and a crucial role for the VP1 carboxyl terminal amino acids (Glu-334-Arg-343) in capsid assembly.

Purification of recombinant budgerigar fledgling disease virus VP1 capsid protein and its ability for in vitro capsid assembly

A recombinant system for the major capsid VP1 protein of budgerigar fledgling disease virus has been established. The VP1 gene was inserted into a truncated form of the pFlag-1 vector and expressed in Escherichia coli. The budgerigar fledgling disease virus VP1 protein was purified to near homogeneity by immunoaffinity chromatography. Fractions containing highly purified VP1 were pooled and found to constitute 3.3% of the original E. coli-expressed VP1 protein. Electron microscopy revealed that the VP1 protein was isolated as pentameric capsomeres. Electron microscopy also revealed that capsid-like particles were formed in vitro from purified VP1 capsomeres with the addition of Ca2+ ions and the removal of chelating and reducing agents.

Phosphorylation of the budgerigar fledgling disease virus major capsid protein VP1

The structural proteins of the budgerigar fledgling disease virus, the first known nonmammalian polyomavirus, were analyzed by isoelectric focusing and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The major capsid protein VP1 was found to be composed of at least five distinct species having isoelectric points ranging from pH 6.45 to 5.85. By analogy with the murine polyomavirus, these species apparently result from different modifications of an initial translation product. Primary chicken embryo cells were infected in the presence of 32Pi to determine whether the virus structural proteins were modified by phosphorylation. SDS-PAGE of the purified virus structural proteins demonstrated that VP1 (along with both minor capsid proteins) was phosphorylated. Two-dimensional analysis of the radiolabeled virus showed phosphorylation of only the two most acidic isoelectric species of VP1, indicating that this posttranslational modification contributes to VP1 species heterogeneity. Phosphoamino acid analysis of 32P-labeled VP1 revealed that phosphoserine is the only phosphoamino acid present in the VP1 protein.

Polymerase chain reaction assay for avian polyomavirus

A polymerase chain reaction assay was developed for detection of budgerigar fledgling disease virus (BFDV). The assay used a single set of primers complementary to sequences located in the putative coding region for the BFDV VP1 gene. The observed amplification product had the expected size of 550 bp and was confirmed to derive from BFDV DNA by its restriction digestion pattern. This assay was specific for BFDV and highly sensitive, being able to detect as few as 20 copies of the virus. By using the polymerase chain reaction, BFDV was detected in adult, nestling, and embryo budgerigar (Melopsitticus undulatus) tissue DNAs and in sera from adult and nestling budgerigars. These results suggest the possibility of persistent infections in adult birds and lend further support to previously described evidence of possible in ovo transmission. BFDV was also detected in chicken embryo fibroblast cell cultures and chicken eggs inoculated with the virus. A 550-bp product with identical restriction enzyme sites was amplified from a suspected polyomavirus isolated from a peach-faced lovebird (Agapornis pesonata) and from tissue DNA from a Hahn's macaw (Ara nobilis) and a sun conure (Aratinga solstitialis) with histological lesions suggestive of polyomavirus infection. These fragments also hybridized with a BFDV-derived probe, proving that they were derived from a polyomavirus very similar, if not identical, to BFDV.

Polyomavirus infection in budgerigars (Melopsittacus undulatus): clinical and aetiological studies

In order to get insight into the aetiology of French Moult (FM) and Budgerigar Fledgling Disease (BFD), and to determine relationships between the two diseases, 298 budgerigars from 49 different breeding flocks were examined. From all birds with BFD and from several birds with FM, viruses were isolated which produced characteristic cytopathic changes in chicken embryo fibroblasts. They were insensitive to chloroform treatment, and their replication was inhibited in the presence of 5-iododeoxyuridine. One of these isolates, from a bird exhibiting clinical signs of BFD, was determined by biochemical and biophysical methods to be a polyomavirus (BFDV). Nestling budgerigars 3 to 10 days of age, were inoculated with this BFDV isolate. They developed an acute systemic disease with high mortality rates, similar to naturally occurring infections. In this regard, BFDV differs markedly from all the other polyomaviruses known until now which only cause clinically asymptomatic, persistent infections in their natural hosts. Most of the birds examined with clinical signs of BFD or FM exhibited low titers of antibodies neutralizing the BFDV isolate, whereas in clinically healthy birds from flocks that never had any problems with FM or BFD, no antibodies against BFDV could be detected. On account of the results of our experiments described here we suspect that FM might be a milder, more protracted form of a BFDV infection.

Myristoylation of budgerigar fledgling disease virus capsid protein VP2

We present evidence that the structural protein VP2 of budgerigar fledgling disease virus, an avian polyomavirus, is specifically modified by covalent attachment of myristic acid. The fatty acid linkage is insensitive to hydroxylamine treatment and thus represents the amide type of fatty acylation of proteins.

The genome of budgerigar fledgling disease virus, an avian polyomavirus

Budgerigar fledgling disease virus (BFDV) represents the first avian member of the Polyomavirus family. In contrast to mammalian polyomaviruses BFDV exhibits unique biological properties, in particular it is able to cause an acute disease with distinct organ manifestations in affected birds. Here we present the complete nucleotide sequence of the BFDV genome, consisting of 4980 bp. When compared to published nucleotide sequences of other polyomaviruses, the BFDV genome exposes a number of very similar structural features, and undoubtedly qualifies as a member of that family of viruses. The most important differences include a large T antigen remarkably reduced in size, and an origin of replication region with fundamental deviations from the origin structure of all other polyomaviruses. The specific characteristics of the BFDV genome may be used to place this virus into a distinct subgroup within the Polyomavirus family and may give a clue to the elucidation of its extraordinary biological properties.