Full-length genomic sequencing and characterization of Borna disease virus 1 isolates: Lessons in epidemiology

Borna disease virus 1 (BoDV-1) is a nonsegmented, negative-strand RNA virus that infects mammals including humans. BoDV-1 strains occur globally, dominate the species Mammalian 1 bornavirus, and display highly conserved genomes and persistent infection (brain, blood). Subclinical infections prevail but the rare fatal outcomes even in people need awareness and risk assessment. Although BoDV-1 strains were successfully isolated, only limited full genomic sequences are available. In this study, the entire genomes of two natural BoDV-1 isolates (Hu-H2, Equ-Cres) and one vaccine strain (DessVac) were sequenced. They were compared with 20 genomes and 20 single-gene sequences (N and P) of worldwide human strains from psychiatric and neurologic patients and animal strains from horses with Borna disease available at GenBank. Phylogenetic analyses confirmed a low divergence not exceeding 5.55%, 5.34%, and 4.94% at the genome, P-gene, and N-gene level, respectively, characteristic of BoDV-1. Human viruses tended to cluster at the country level but appeared to be independent of hosts' diseases and/or time of isolation. Notably, our data also indicated that human viruses provided individual genetic signatures but exhibited no distinct genotypes that separated them from animal strains. Sequence similarities thus occurred between different host species and distant geographic regions, supporting global BoDV-1 prevalence. Overall low genetic divergence among BoDV-1 viruses shown here also argued against zoonotic concepts, requiring further clarification beyond sequence similarities. Finally, unlike shared sequence conservation, phenotyping of natural and laboratory variants revealed that they manipulated host cells differently, underpinning the authenticity of the human BoDV-1 strains.

Proteomics computational analyses suggest that the bornavirus glycoprotein is a class III viral fusion protein (gamma penetrene)

BACKGROUND

Borna disease virus (BDV) is the type member of the Bornaviridae, a family of viruses that induce often fatal neurological diseases in horses, sheep and other animals, and have been proposed to have roles in certain psychiatric diseases of humans. The BDV glycoprotein (G) is an extensively glycosylated protein that migrates with an apparent molecular mass of 84,000 to 94,000 kilodaltons (kDa). BDV G is post-translationally cleaved by the cellular subtilisin-like protease furin into two subunits, a 41 kDa amino terminal protein GP1 and a 43 kDa carboxyl terminal protein GP2.

RESULTS

Class III viral fusion proteins (VFP) encoded by members of the Rhabdoviridae, Herpesviridae and Baculoviridae have an internal fusion domain comprised of beta sheets, other beta sheet domains, an extended alpha helical domain, a membrane proximal stem domain and a carboxyl terminal anchor. Proteomics computational analyses suggest that the structural/functional motifs that characterize class III VFP are located collinearly in BDV G. Structural models were established for BDV G based on the post-fusion structure of a prototypic class III VFP, vesicular stomatitis virus glycoprotein (VSV G).

CONCLUSION

These results suggest that G encoded by members of the Bornavirdae are class III VFPs (gamma-penetrenes).

[Study on molecular epidemiology of Borna disease virus in Zunyi regions of Guizhou province]

OBJECTIVE

In order to study the epidemiology of Borna disease virus (BDV) in Zunyi region and its surrounding regions in Guizhou province.

METHODS

p24 fragment of BDV fragments in peripheral blood mononuclear cells (PBMC) from 43 patients with viral encephalitis (VE), 9 cases with multiple sclerosis (MS), 7 cases with Guillain-Barre syndrome (GBS), 5 cases with Parkinson disease (PD), 98 healthy donors and 300 goats were examined by quantitative fluorescence nested reverse transcriptase polymerase chain reaction (PCR). Gene sequence and amino acid sequence were analyzed for positive products.

RESULTS

The positive rate of BDV p24 fragment in PBMC from VE (13.95%) and MS (22.22%) were significantly higher than in healthy donors (0%, P < 0.05). The positive rate of BDV p24 fragment in PBMC from goats was 0.67%, without statistical difference when compared with healthy donors (P > 0.05). Guillain-Barre syndrome and Parkinson disease (PD) were tested negative. The sequence of the BDV p24 fragment from the patients with VE was in conformity with that of the MS. Results presented that 3 situs consistency silent mutation when compared with strain V and its homogeneity was 96.51%. 2 situs consistency silent mutation compared with BDV/MDCK and its homogeneity was 97.67%. 2 situs consistency silent mutation when compared with C6BV and its homogeneity was 97.67%. Sequences of the BDV p24 fragment from the goats presented 3 situs consistency silent mutation when compared with strain V and its homogeneity was 96.51%. 3 situs consistency silent mutation when compared with BDV/MDCK and its homogeneity was 96.51%. 3 situs consistency silent mutation when compared with C6BV and its homogeneity was 96.51%. However, there were no changes of encoding amino acids in all BDV p24 fragments from neuropsychiatric disorders.

CONCLUSION

Our data indicated that the BDV infection was presented in patients with VE, MS and goats from Zunyi region and its surrounding regions of Guizhou province. BDV might play a potential role in the development of VE, MS as well as having correlations with animals.

Meta-analysis of putative human bornavirus sequences fails to provide evidence implicating Borna disease virus in mental illness

All Borna disease virus (BDV) sequences derived from human specimens published till date were thoroughly analysed and compared to sequences of BDV laboratory strains and to BDV sequences from animals which succumbed to classical Borna disease (BD). Despite high sequence conservation of the BDV genome, animal-derived BDV sequences clustered according to their geographic origin. However, in marked contrast, human-derived BDV sequences did not cluster according to their geographic origin but showed high sequence identities to BDV laboratory strains and animal-derived BDVs handled in the laboratories reporting the human strains. Japanese, US, Australian and French human-derived BDV sequences proved to be identical or very similar to animal-derived BDV sequences from Germany, although the human specimens were collected hundreds to thousands of miles away from the central European BD endemic regions. These findings suggest that previous studies linking BDV to human neuropsychiatric disease may have been compromised by inadvertent sample contamination.

Borna disease: current knowledge and virus detection in France

For over two centuries, Borna disease (BD) has been described as a sporadically occurring infectious meningoencephalomyelitis affecting horses and sheep in Central Europe. Over the last decade, the BD epidemiology has been discussed. Firstly, its geographical distribution seems larger than what was previously thought. Secondly, the disease can affect a large number of warm-blooded animal species, including humans. The aetiological agent is the Boma disease virus (BDV), an enveloped, nonsegmented negative-stranded RNA virus classified in the new virus family Bornaviridae (Mononegavirales order). It can induce severe clinical signs of encephalitis with striking behavioural disturbances and may cause death. BDV genome has recently been detected in France in the blood and brain of several animal species (horses, bovines, foxes).

Conservation of coding potential and terminal sequences in four different isolates of Borna disease virus

We determined the complete nucleotide sequences of two poorly characterized strains of Borna disease virus (BDV) and compared them to reference strains V and He/80. Strain H1766 was almost 98% and 95% identical to strains V and He/80, respectively, whereas strain No/98 was only about 81% identical to both reference strains. In contrast to earlier reports, we found an additional A residue at the extreme 3'-end of the single-stranded RNA genome in all four BDV strains. The exact numbers of nucleotides in the four BDV genomes could not be determined due to a micro-heterogeneity at the 5'-end. If our longest sequence is a correct copy of the viral RNA, the two ends of the BDV genome would show almost perfect complementarity. All three transcription start sites, all four termination sites, both splice donor sites and both major splice acceptor sites are highly conserved, whereas a minor alternative splice acceptor site is not. The L protein of No/98 differs at 7% of its amino acid positions from the polymerase in the other strains, with most differences mapping to the C-terminal moiety of the molecule. Re-evaluation of L protein sequences of strains V and He/80 revealed differences at several positions compared to published information, indicating that variant forms of the viral polymerase have previously been characterized. These results are important because correct structures of genome ends and of the polymerase gene are the most critical parameters for the future development of techniques that will permit the genetic manipulation of BDV.

Borna disease virus

Borna disease virus (BDV) is unique amongst animal RNA viruses in its molecular biology and capacity to cause persistent, noncytolytic CNS-infection in a wide variety of host species. Unlike other non-segmented negative-strand RNA animal viruses, BDV replicates in the nucleus of the host cell where splicing is employed for expression of a very compact genome. Epidemiological studies indicate a broad host range and geographical distribution, and some investigators have proposed that human infection may result in neuropsychiatric disorders. Experimental Borna disease in neonatal and adult rats provides an intriguing model for immune-mediated disturbances of brain development and function.

Isolation and characterization of a new subtype of Borna disease virus

Borna disease virus (BDV), the causative agent of severe meningoencephalitis in a wide variety of animal species, has been considered to be genetically invariable and to form a single type within the genus Bornavirus of the family Bornaviridae. BDV infections are of particular interest, because for the first time a virus infection appears to be linked to human psychiatric disorders. We now describe a new subtype of BDV isolated from a horse which was euthanatized due to severe, incurable neurological disease. The nucleotide sequence of this new strain, named No/98, differs from the reference strains by more than 15%, and the subtype is difficult to detect by standard reverse transcriptase PCR protocols. The nucleotide exchanges of the novel BDV isolate have surprisingly little effect on the primary structures of most viral proteins, with the notable exception of the X protein (p10), which is only 81% identical to its counterpart in reference strains. Our data indicate that the genome of BDV is far more variable than previously assumed and that naturally occurring subtypes may escape detection by currently used diagnostic assays.

Borna disease virus infection in racing horses with behavioral and movement disorders

Borna disease virus (BDV) is a neurotropic agent with capacity to infect and cause neurological disease in a broad range of warmblooded hosts including horses, sheep, cattle, cats, and possibly also humans. The epidemiology of BDV is largely unknown. However, it is likely that subclinically infected animals may represent potential virus reservoirs. In two groups of Swedish racing horses, one clinically healthy and one consisting of horses with diffuse neurological signs, the BDV seroprevalence was 24.5% and 57.7%, respectively. BDV RNA was detected in peripheral blood mononuclear cells in 8 out of 28 (28.6%) investigated horses, the majority of the BDV RNA-positive horses belonging to the group with neurological signs. There was a close relationship between the Swedish equine BDV isolates and previously reported equine BDVs in Europe. Our results point to an association of BDV infection with atypical disease patterns in horses such as diffuse mental and gait disturbances. These findings may be of importance for the understanding of the epidemiology of BDV infections in animals and man.

Borna disease in a dog with lethal meningoencephalitis

A dog was euthanatized because of progressive neurological signs. Histologically, a nonsuppurative meningoencephalitis was found. By immunohistochemistry, in situ hybridization, and nested PCR procedures, Borna disease virus (BDV) antigen and BDV-specific RNA were demonstrated in brain tissues of the dog. The nucleotide sequence of the PCR product showed 94 to 98% homology to published BDV sequences. This is the first description of Borna disease in a dog.

Clinical similarities and close genetic relationship of human and animal Borna disease virus

Borna disease virus (BDV) is the prototype genus of a new family, Bornaviridae, within the order Mononegavirales. BDV naturally infects animals and man. The symptomatology in animals ranges from subclinical infection to rare cases of encephalitis. Asymptomatic infection seemed more frequent than expected, based on antibody data from 100 healthy horses derived from different stables with a history of diseased cases (30-40% carriers). Likewise, phasic episodes of a neurobehavioral syndrome followed by recovery were much more common than fatal neurologic disease. They were paralleled by expression of BDV antigens (N-protein p40, P-protein p24) and RNA transcripts in peripheral blood mononuclear cells, indicating viral activation. Representative longitudinal studies showed that episodes of depressive illness in humans as well as apathetic phases in infected horses were accompanied by antigen expression and followed a similar clinical course. After recovery, BDV antigen disappeared. This temporal congruence, together with the recent isolation of infectious BDV from such patients, points to a contributory role of this virus in human affective disorders. Successful amelioration of BDV-induced neurobehavioral disease in horses with antidepressants applied in psychiatry, supported a common viral pathomechanism, involving reversible disturbances of the neurotransmitter network in the limbic system. Sequences of genetic material amplified from infected animal tissue and human PBMCs revealed a close interspecies relationship and high sequence conservation of the BDV genome. In human BDV isolates, however, single unique mutations were prominent in four genes. This finding supports the hypothesis that despite of high genomic conservation, species-specific genotypes may be definable, provided the sequences are derived from RNA of infectious virus.

Borna disease virus: implications for human neuropsychiatric illness

The cause of Borna disease, a neurological syndrome affecting mammals and birds, has recently been shown to be infection with an RNA virus. Molecular genetic analysis suggests that Borna disease virus represents a new viral taxon. It has a wide host range and is tropic for specific circuits in the central nervous system. There is indirect evidence that links it to diseases of the human central nervous system.

Sequence and genome organization of Borna disease virus

We have previously demonstrated that Borna disease virus (BDV) has a negative nonsegmented single-stranded (NNS) RNA genome that replicates in the nucleus of infected cells. Here we report for the first time the cloning and complete sequence of the BDV genome. Our results revealed that BDV has a genomic organization similar to that of other members of the Mononegavirales order. We have identified five main open reading frames (ORFs). The largest ORF, V, is located closest to the 5' end in the BDV genome and, on the basis of strong homology with other NNS-RNA virus polymerases, is a member of the L-protein family. The intercistronic regions vary in length and nucleotide composition and contain putative transcriptional start and stop signals. BDV untranslated 3' and 5' RNA sequences resemble those of other NNS-RNA viruses. Using a set of overlapping probes across the BDV genome, we identified nine in vivo synthesized species of polyadenylated subgenomic RNAs complementary to the negative-strand RNA genome, including monocistronic transcripts corresponding to ORFs I, II, and IV, as well as six polycistronic polyadenylated BDV RNAs. Interestingly, although ORFs III and V were detected within polycistronic transcripts, their corresponding monocistronic transcripts were not detected. Our data indicate that BDV is a member of the Mononegavirales, specially related to the family Rhabdoviridae. However, in contrast to the rest of the NNS-RNA animal viruses, BDV replication and transcription occur in the nucleus of infected cells. These findings suggest a possible relationship between BDV and the plant rhabdoviruses, which also replicate and transcribe in the nucleus.