Genetic relationship of Borna disease virus isolates

Genetic stability of the open reading frame 2 (ORF2) of borna disease virus 1 (BoDV-1) distributed in cattle in Hokkaido

Borna disease virus (BoDV) is a neurotropic virus that causes several infections in humans and neurological diseases in a wide range of animals worldwide. BoDV-1 has been molecularly and serologically detected in many domestic and wild animals in Japan; however, the genetic diversity of this virus and the origin of its infection are not fully understood. In this study, we investigated BoDV-1 infection and genetic diversity in samples collected from animals in Hokkaido between 2006 and 2020. The analysis was performed by focusing on the P region of BoDV-1 for virus detection. The presence of BoDV-1 RNA was observed in samples of brain tissue and various organs derived from persistently infected cattle. Moreover, after inoculation, BoDV-positive brains were isolated from neonatal rats. The gene sequences of the P region of BoDV obtained from the rat brain were in the same cluster as the P region of the virus isolated from the original bovine. Thus, genetic variation in BoDV-1 was extremely low. The phylogenetic analysis revealed that BoDV-1 isolates obtained in this study were part of the same cluster, which suggested that BoDV-1 of the same cluster was widespread among animals in Hokkaido.

Epidemiology and host spectrum of Borna disease virus infections

Borna disease virus (BDV) has gained lot of interest because of its zoonotic potential, ability to introduce cDNA of its RNA transcripts into host genomes, and ability to cause severe neurobehavioural diseases. Classical Borna disease is a progressive meningoencephalomyelitis in horses and sheep, known in central Europe for centuries. According to current knowledge, BDV or a close relative also infects several other species, including humans at least occasionally, in central Europe and elsewhere, but the existence of potential 'human Borna disease' with its suspected neuropsychiatric symptoms is highly controversial. The recent detection of endogenized BDV-like genes in primate and various other vertebrate genomes confirms that at least ancient bornaviruses did infect our ancestors. The epidemiology of BDV is largely unknown, but accumulating evidence indicates vectors and reservoirs among small wild mammals. The aim of this review is to bring together the current knowledge on epidemiology of BDV infections. Specifically, geographical and host distribution are addressed and assessed in the critical light of the detection methods used. We also review some salient clinical aspects.

Role of Borna disease virus in neuropsychiatric illnesses: are we inching closer?

The biological cause of psychiatric illnesses continues to be under intense scrutiny. Among the various neurotropic viruses, Borna disease virus (BDV) is another virus that preferentially targets the neurons of the limbic system and has been shown to be associated with behavioural abnormalities. Presence of various BDV markers, including viral RNA, in patients with affective and mood disorders have triggered ongoing debate worldwide regarding its aetiopathogenic relationship. This article analyses its current state of knowledge and recent advances in diagnosis in order to prove or refute the association of BDV in causation of human neuropsychiatric disorders. This emerging viral causative association of behavioural disorders, which seems to be inching closer, has implication not only for a paradigm shift in the treatment and management of neuropsychiatric illnesses but also has an important impact on the public health systems.

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.

Epidemiological pattern of classical Borna disease and regional genetic clustering of Borna disease viruses point towards the existence of to-date unknown endemic reservoir host populations

Classical Borna disease (cBD), a non-purulent encephalitis of solipeds and sheep, is endemic in certain areas of central Europe. The etiologic agent is Borna disease virus (BDV), thus far the only member of the family Bornaviridae. Based on epidemiological patterns of cBD and recent phylogenetic findings this review hypothesizes the possible existence of yet unknown BDV reservoir host populations, and analyzes critically BDVs from outside endemic regions.

Constitutive activation of the transcription factor NF-kappaB results in impaired borna disease virus replication

The inducible transcription factor NF-kappaB is commonly activated upon RNA virus infection and is a key player in the induction and regulation of the innate immune response. Borna disease virus (BDV) is a neurotropic negative-strand RNA virus, which replicates in the nucleus of the infected cell and causes a persistent infection that can lead to severe neurological disorders. To investigate the activation and function of NF-kappaB in BDV-infected cells, we stably transfected the highly susceptible neuronal guinea pig cell line CRL with a constitutively active (IKK EE) or dominant-negative (IKK KD) regulator of the IKK/NF-kappaB signaling pathway. While BDV titers were not affected in cells with impaired NF-kappaB signaling, the expression of an activated mutant of IkappaB kinase (IKK) resulted in a strong reduction in the intracellular viral titer in CRL cells. Electrophoretic mobility shift assays and luciferase reporter gene assays revealed that neither NF-kappaB nor interferon regulatory factors (IRFs) were activated upon acute BDV infection of wild-type or vector-transfected CRL cells. However, when IKK EE-transfected cells were used as target cells for BDV infection, DNA binding to an IRF3/7-responsive DNA element was detectable. Since IRF3/7 is a key player in the antiviral interferon response, our data indicate that enhanced NF-kappaB activity in the presence of BDV leads to the induction of antiviral pathways resulting in reduced virus titers. Consistent with this observation, the anti-BDV activity of NF-kappaB preferentially spread to areas of the brains of infected rats where activated NF-kappaB was not detectable.

Genetic clustering of Borna disease virus natural animal isolates, laboratory and vaccine strains strongly reflects their regional geographical origin

The aim of this study was to gain more detailed insights into the genetic evolution and variability of Borna disease virus (BDV). Phylogenetic analyses were performed on field viruses originating from naturally infected animals, the BDV vaccine strain 'Dessau', four widely used laboratory strains and the novel BDV subtype No/98. Four regions of the BDV genome were analysed: the complete p40, p10 and p24 genes and the 5'-untranslated region of the X/P transcript. BDV isolates from the same geographical area exhibited a clearly higher degree of identity to each other than to BDV isolates from other regions, independent of host species and year of isolation. Five different clusters could be established within endemic areas, corresponding to the geographical regions from which the viruses originated: (i) a Swiss, Austrian and Liechtenstein Rhine valley group, related closely to the geographically bordering Baden-Wurttemberg and Bavaria II group (ii) in the western part of Germany; (iii) a third group, called Bavaria I group, limited in occurrence to Bavaria; (iv) a southern Saxony-Anhalt and bordering northern Saxony group, bound to the territories of these federal states in the eastern part of Germany; and (v) a mixed group, consisting of samples from different areas of Germany; however, these were mainly from the federal states of Thuringia and Lower Saxony. The laboratory strains and the vaccine strain clustered within these groups according to their geographical origins. All field and laboratory strains, as well as the vaccine strain, clearly segregated from the recently described and highly divergent BDV strain No/98, which originated from an area in Austria where Borna disease is not endemic.

Prevention of virus persistence and protection against immunopathology after Borna disease virus infection of the brain by a novel Orf virus recombinant

The Parapoxvirus Orf virus represents a promising candidate for novel vector vaccines due to its immune modulating properties even in nonpermissive hosts such as mouse or rat. The highly attenuated Orf virus strain D1701 was used to generate a recombinant virus (D1701-VrVp40) expressing nucleoprotein p40 of Borna disease virus, which represents a major antigen for the induction of a Borna disease virus-specific humoral and cellular immune response. Infection with Borna disease virus leads to distinct neurological symptoms mediated by the invasion of activated specific CD8+ T cells into the infected brain. Usually, Borna disease virus is not cleared from the brain but rather persists in neural cells. In the present study we show for the first time that intramuscular application of the D1701-VrVp40 recombinant protected rats against Borna disease, and importantly, virus clearance from the infected brain was demonstrated in immunized animals. Even 4 and 8 months after the last immunization, all immunized animals were still protected against the disease. Initial characterization of the immune cells attracted to the infected brain areas suggested that D1701-VrVp40 mediated induction of B cells and antibody-producing plasma cells as well as T cells. These findings suggest the induction of various defense mechanisms against Borna disease virus. First studies on the role of antiviral cytokines indicated that D1701-VrVp40 immunization did not lead to an enhanced early response of gamma or alpha interferon or tumor necrosis factor alpha. Collectively, this study describes the potential of the Orf virus vector system in mediating long-lasting, protective antiviral immunity and eliminating this persistent virus infection without provoking massive neuronal damage.

Immunization with dendritic cells can break immunological ignorance toward a persisting virus in the central nervous system and induce partial protection against intracerebral viral challenge

Dendritic cells (DCs) have been used successfully to induce CD8 T cells that control virus infections and growth of tumours. The efficacy of DC-mediated immunization for the control of neurotropic Borna disease virus (BDV) in mice was evaluated. Certain strains of mice only rarely develop spontaneous neurological disease, despite massive BDV replication in the brain. Resistance to disease is due to immunological ignorance toward BDV antigen in the central nervous system. Ignorance in mice can be broken by immunization with DCs coated with TELEISSI, a peptide derived from the N protein of BDV, which represents the immunodominant cytotoxic T lymphocyte epitope in H-2(k) mice. Immunization with TELEISSI-coated DCs further induced solid protective immunity against intravenous challenge with a recombinant vaccinia virus expressing BDV-N. Interestingly, however, this immunization scheme induced only moderate protection against intracerebral challenge with BDV, suggesting that immune memory raised against a shared antigen may be sufficient to control a peripherally replicating virus, but not a highly neurotropic virus that is able to avoid activation of T cells. This difference might be due to the lack of BDV-specific CD4 T cells and/or inefficient reactivation of DC-primed, BDV-specific CD8 T cells by the locally restricted BDV infection. Thus, a successful vaccine against persistent viruses with strong neurotropism should probably induce antiviral CD8 (as well as CD4) T-cell responses and should favour the accumulation of virus-specific memory T cells in cervical lymph nodes.

Borna disease virus infection, a human mental-health risk

This article focuses on human Borna disease virus (BDV) infections, most notably on the development of valid diagnostic systems, which have arisen as a major research issue in the past decade. The significance of a novel modular triple enzyme-linked immunosorbent assay that is capable of specifically measuring anti-BDV antibodies as well as major structural proteins N (p40) and P (p24) in the blood, either as free antigens in the plasma or as antibody-bound circulating immune complexes (CICs), is explained. The impact of CICs and plasma antigen, which indicate periods of antigenemia in the course of BDV infection, along with other infection markers that are still in use is discussed. The review further provides new insight into possible links of BDV to human diseases, summarizing cross-sectional and longitudinal data which correlate acute depression with the presence and amount of antigen and CICs. Moreover, BDV prevalence in healthy people is reevaluated, suggesting that this was previously underestimated. Antiviral efficacy of amantadine, in vivo and in vitro, is outlined as well, with emphasis on wild-type (human and equine) versus laboratory strains. Finally, the pros and cons of the association of BDV with human disease, as detailed in the literature, are critically discussed and related to our data and concepts. This article supports existing correlative evidence for a pathogenic role of BDV infection in particular human mental disorders, in analogy to what has been proven for a variety of animal species.