Neurological diseases and viral dynamics in the brains of neonatally borna disease virus-infected gerbils

Age-dependent development and clinical characteristics of an experimental parrot bornavirus-4 (PaBV-4) infection in cockatiels (Nymphicus hollandicus)

Parrot bornavirus (PaBV) is a pathogen often found in psittacine populations. Infected, clinically healthy carrier birds are of major importance for epidemiology, but the underlying pathomechanism of this carrier status is poorly understood. The age, implying the maturation status of the immune system, at the time of infection might be significant for the clinical outcome. Therefore, two groups of 11 cockatiels of different ages (adult and newly hatched) were inoculated with a PaBV-4 isolate intravenously. The trial lasted for 233 days and all birds were observed for clinical signs, PaBV-RNA shedding and anti-PaBV antibody production. At the end of the trial, histopathology, immunohistochemistry, PCR and virus re-isolation were performed. All 22 birds seroconverted and shed PaBV-RNA during the investigation period; the juvenile group earlier and more homogeneously. Nine of 11 birds of the adult group developed clinical signs; five birds died or had to be euthanized before the end of the study. In the juvenile group none of the birds developed clinical signs and only one bird died due to bacterial septicaemia. Eight birds of the adult group, but none of the juvenile group, showed a dilatation of the proventriculus. PaBV-RNA detection and virus re-isolation were successful in all birds. Immunohistochemically, PaBV antigen was found in all birds. Histopathology revealed mononuclear infiltrations in organs in birds of both groups, but the juveniles were less severely affected in the brain.Thus, PaBV infection at an age with a more naïve immune system makes the production of carrier birds more likely.RESEARCH HIGHLIGHTS PaBV infection at a young age might favour the development of carrier birds.Cockatiels infected at a very young age showed inflammation but no clinical signs.The juvenile group started seroconversion and PaBV-RNA shedding earlier.Seroconversion and PaBV-RNA shedding occurred more homogeneously in the juveniles.

Distribution of Viral Antigen and Inflammatory Lesions in the Central Nervous System of Cockatiels ( Nymphicus hollandicus) Experimentally Infected with Parrot Bornavirus 2

Neurotropism is a striking characteristic of bornaviruses, including parrot bornavirus 2 (PaBV-2). Our study evaluated the distribution of inflammatory foci and viral nucleoprotein (N) antigen in the brain and spinal cord of 27 cockatiels ( Nymphicus hollandicus) following experimental infection with PaBV-2 by injection into the pectoral muscle. Tissue samples were taken at 12 timepoints between 5 and 114 days post-inoculation (dpi). Each experimental group had approximately 3 cockatiels per group and usually 1 negative control. Immunolabeling was first observed within the ventral horns of the thoracic spinal cord at 20 dpi and in the brain (thalamic nuclei and hindbrain) at 25 dpi. Both inflammation and viral antigen were restricted to the central core of the brain until 40 dpi. The virus then spread quickly at 60 dpi to both gray and white matter of all analyzed sections of the central nervous system (CNS). Encephalitis was most severe in the thalamus and hindbrain, while myelitis was most prominent in the gray matter and equally distributed in the cervical, thoracic, and lumbosacral spinal cord. Our results demonstrate a caudal to rostral spread of virus in the CNS following experimental inoculation of PABV-2 into the pectoral muscle, with the presence of viral antigen and inflammatory lesions first in the spinal cord and progressing to the brain.

Newly breeding an inbred strain of ischemia-prone Mongolian gerbils and its reproduction and genetic characteristics

The Mongolian gerbil has been a useful laboratory animal in many research fields, especially in ischemia studies. However, due to the variation of the circle of Willis (COW), the ischemic model is unstable and various. To solve this problem, we newly established an inbred strain of gerbils, restricting breeding and keeping to F₂₃. The data on the breeding and growth of the animals are described in the present study. The genetic characteristics of F₄ to F₂₀ detected by microsatellite DNA and biochemical markers are also shown here. The results demonstrated that the frequency of ischemic model by unilateral carotid occlusion and the frequency of incomplete COW increased, increasing from 50% and 75% in F₁ to 88.89% and 100% in F₂₀, respectively. The ratios of consistent patterns of COW in parents were positively related with the number of inbred generations. A reproductive performance analysis indicated that the average size of litters in the inbred gerbils was less than that of outbred gerbils and that adult body weight was also lower in inbred gerbils; also, the pups in the 2nd litter were the best ones chosen to reproduce. The genetic detection results indicated that 26 out of 28 microsatellite loci and all 26 biochemical markers were homozygous in F₂₀, showing comparably identical genetic composition in inbred gerbils. All the data demonstrated that an inbred strain of ischemia-prone gerbil has been established successfully. This strain can be used in stroke research and can largely reduce the number of animals needed in experiments.

The pathogenesis of bornaviral diseases in mammals

Natural bornavirus infections and their resulting diseases are largely restricted to horses and sheep in Central Europe. The disease also occurs naturally in cats, and can be induced experimentally in laboratory rodents and numerous other mammals. Borna disease virus-1 (BoDV-1), the cause of most cases of mammalian Borna disease, is a negative-stranded RNA virus that replicates within the nucleus of target cells. It causes severe, often lethal, encephalitis in susceptible species. Recent events, especially the discovery of numerous new species of bornaviruses in birds and a report of an acute, lethal bornaviral encephalitis in humans, apparently acquired from squirrels, have revived interest in this remarkable family of viruses. The clinical manifestations of the bornaviral diseases are highly variable. Thus, in addition to acute lethal encephalitis, they can cause persistent neurologic disease associated with diverse behavioral changes. They also cause a severe retinitis resulting in blindness. In this review, we discuss both the pathological lesions observed in mammalian bornaviral disease and the complex pathogenesis of the neurologic disease. Thus infected neurons may be destroyed by T-cell-mediated cytotoxicity. They may die as a result of excessive inflammatory cytokine release from microglia. They may also die as a result of a ‘glutaminergic storm’ due to a failure of infected astrocytes to regulate brain glutamate levels.

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.

Intracerebral Borna disease virus infection of bank voles leading to peripheral spread and reverse transcription of viral RNA

Bornaviruses, which chronically infect many species, can cause severe neurological diseases in some animal species; their association with human neuropsychiatric disorders is, however, debatable. The epidemiology of Borna disease virus (BDV), as for other members of the family Bornaviridae, is largely unknown, although evidence exists for a reservoir in small mammals, for example bank voles (Myodes glareolus). In addition to the current exogenous infections and despite the fact that bornaviruses have an RNA genome, bornavirus sequences integrated into the genomes of several vertebrates millions of years ago. Our hypothesis is that the bank vole, a common wild rodent species in traditional BDV-endemic areas, can serve as a viral host; we therefore explored whether this species can be infected with BDV, and if so, how the virus spreads and whether viral RNA is transcribed into DNA in vivo.We infected neonate bank voles intracerebrally with BDV and euthanized them 2 to 8 weeks post-infection. Specific Ig antibodies were detectable in 41%. Histological evaluation revealed no significant pathological alterations, but BDV RNA and antigen were detectable in all infected brains. Immunohistology demonstrated centrifugal spread throughout the nervous tissue, because viral antigen was widespread in peripheral nerves and ganglia, including the mediastinum, esophagus, and urinary bladder. This was associated with viral shedding in feces, of which 54% were BDV RNA-positive, and urine at 17%. BDV nucleocapsid gene DNA occurred in 66% of the infected voles, and, surprisingly, occasionally also phosphoprotein DNA. Thus, intracerebral BDV infection of bank vole led to systemic infection of the nervous tissue and viral excretion, as well as frequent reverse transcription of the BDV genome, enabling genomic integration. This first experimental bornavirus infection in wild mammals confirms the recent findings regarding bornavirus DNA, and suggests that bank voles are capable of bornavirus transmission.

Borna disease virus antibody and RNA from peripheral blood mononuclear cells of race horses and jockeys in Korea

OBJECTIVE

During the last two decades, Borna disease virus (BDV) has received much attention as a possible zoonotic agent, particularly as a cause of psychiatric disease. Although several studies have shown that BDV is present in Asia, BDV has not been detected in Korea. This study was designed to further investigate the presence of BDV infection in Korea.

METHODS

Blood samples were taken from 39 race horses and 48 jockeys. Antibody to BDV was detected by indirect immunofluorescence antibody test and RNA of BDV by real time reverse transcriptase PCR (rRT-PCR).

RESULTS

No evidence of BDV was detected in either the horses or the jockeys group.

CONCLUSION

Our results suggest that BDV infection may not be endemic in Korea. Further studies with novel diagnostic tools are required to clarify the prevalence of BDV infection in Korea.

Development of novel microsatellite DNA markers by cross-amplification and analysis of genetic variation in gerbils

The objectives of this study are to establish microsatellite loci for the Mongolian gerbil based on mouse microsatellite DNA sequences and to investigate genetic variation in the laboratory gerbil (Capital Medical University, CMU) and 2 wild gerbil populations (from Yin Chuan city [YIN] and the Hohehot Municipality [HOH]). In total, 536 mouse microsatellite markers were chosen to identify polymorphic dinucleotide repeat loci in the gerbil by cross-amplification. Of these markers, 313 (58.39%) have been discretely amplified from the CMU laboratory gerbil and been sequenced. Of the 313 sequenced markers, 130 were confirmed as simple sequence repeat (SSR) loci in the gerbil. In total, 6 of those newly identified loci plus 6 identified in previous reports were used to estimate the genetic polymorphism for 30 laboratory gerbils and 54 wild gerbils (27 each of the HOH and YIN groups). A total of 29 alleles were observed in the 3 populations, and 11 of 12 loci (91.67%) are polymorphic markers. Nei's standard genetic distances of 0.0592 (CMU vs. HOH) and 0.1033 (CMU vs. YIN) were observed. The averages of observed versus expected heterozygosity are 0.5231/0.4008, 0.5051/0.3882, and 0.4825/0.3665 for the YIN, HOH, and CMU populations, respectively. These results show that cross-amplification using mouse microsatellite primers is an efficient way to identify gerbil SSR loci. By using these 12 selected markers, we have demonstrated that genetic variation level within the CMU population is higher than that has been reported previously and are comparable with the levels found in 2 wild populations.

Localization of avian bornavirus RNA by in situ hybridization in tissues of psittacine birds with proventricular dilatation disease

Proventricular dilatation disease (PDD) of psittacine birds is caused by a number of different genotypes of a novel viral species, avian bornavirus (ABV). Here we present an in situ hybridization (ISH) procedure using digoxigenin-labeled RNA probes for localizing viral genomic and mRNA of ABV-2 and ABV-4 in tissues of affected birds. Out of eleven immunohistochemically positive birds ISH signals were only found in seven. Partial sequencing of the viral genome had shown that four of them were infected with ABV-2, two with ABV-4 and one had a mixed infection with ABV-2 and ABV-4. ISH signals were present in the brain, in the vegetative nerve system, glandular epithelia and smooth muscle cells of the intestinal tract and in cardiomyocytes. Hybridization signals for viral genome were more abundant than signals for mRNA. As the probes were not strictly genotype-specific, four of the birds had hybridization signals with both, the ABV-2 and ABV-4 probes. The signals achieved with the homologous probes were more intense and more abundant than those resulting from heterologous probes. Taken together, the results of this study show that ISH can be used as a tool for localizing ABV sequences in tissues of birds with PDD and confirm the causative role of ABVs by showing viral replication in affected tissues.

Failure to detect borna disease virus antibody and RNA from peripheral blood mononuclear cells of psychiatric patients

OBJECTIVE

Borna disease virus (BDV) is a highly neurotropic agent causing various neuropsychiatric symptoms in animals. Over the past two decades, it has been suggested that BDV might be associated with human psychiatric diseases. We aimed to investigate whether BDV is associated with psychiatric patients in Korea.

METHODS

We recruited 60 normal controls and 198 psychiatric patients (98 patients with depressive disorder, 60 with schizophrenia, and 40 with bipolar disorder). We used an indirect immunofluorescence antibody (IFA) test for the BDV antibody and a real-time reverse transcriptase polymerase chain reaction (rRT-PCR) assay for p24 and p40 RNA from peripheral blood mononuclear cells (PBMCs).

RESULTS

Neither the BDV antibody nor p24, p40 RNA was detected in controls and patients groups.

CONCLUSION

Our results suggest that BDV might not be associated with psychiatric patients in Korea.

Ribavirin inhibits Borna disease virus proliferation and fatal neurological diseases in neonatally infected gerbils

By using neonatal gerbils, we assessed the effect of ribavirin on the proliferation of Borna disease virus (BDV) in the brain. The intracranial inoculation of ribavirin reduced viral propagation in the acutely infected brain, resulting in protection from fatal neurological disorders. We found that the treatment with ribavirin markedly reduces the numbers of OX-42-positive microglial cells, but does not activate expression of Th1 cytokines, in BDV-infected gerbil brains. Our results suggested that ribavirin directly inhibits BDV replication and might be a potential tool for the treatment of BDV infection.

Development of a real-time RT-PCR assay for improved detection of Borna disease virus

Borna disease virus (BDV) is a non-segmented, negative-stranded RNA virus, which infects cells of the central nervous system (CNS) in many different species. BDV is the causative agent of the neurological disorders in horses and sheep termed classical Borna disease (BD), as well as staggering disease in cats. At present, the diagnosis staggering disease or feline BD is made by histopathology or immunohistochemistry of the CNS. In order to obtain a better clinical diagnostic tool, a duplex real-time RT-PCR assay (rRT-PCR) was developed. TaqMan probes and primers specific for the BDV P and BDV L genes were designed by aligning the sequences of known BDV strains. After optimisation, the sensitivity and specificity of the rRT-PCR were established. The detection limit was set to 10-100 viral genomic copies per reaction and the assay detects the BDV strains V and He/80, as well as the most divergent BDV strain known so far, No/98. Furthermore, the system detected feline BDV variants in five naturally infected cats and a feline isolate used in experimental infection of cats. This rRT-PCR assay will be a powerful tool in further studies of BDV, including epidemiological screening and diagnosis.

Downregulation of an astrocyte-derived inflammatory protein, S100B, reduces vascular inflammatory responses in brains persistently infected with Borna disease virus

Borna disease virus (BDV) is a neurotropic virus that causes a persistent infection in the central nervous system (CNS) of many vertebrate species. Although a severe reactive gliosis is observed in experimentally BDV-infected rat brains, little is known about the glial reactions contributing to the viral persistence and immune modulation in the CNS. In this regard, we examined the expression of an astrocyte-derived factor, S100B, in the brains of Lewis rats persistently infected with BDV. S100B is a Ca(2+)-binding protein produced mainly by astrocytes. A prominent role of this protein appears to be the promotion of vascular inflammatory responses through interaction with the receptor for advanced glycation end products (RAGE). Here we show that the expression of S100B is significantly reduced in BDV-infected brains despite severe astrocytosis with increased glial fibrillary acidic protein immunoreactivity. Interestingly, no upregulation of the expression of S100B, or RAGE, was observed in the persistently infected brains even when incited with several inflammatory stimuli, including lipopolysaccharide. In addition, expression of the vascular cell adhesion molecule 1 (VCAM-1), as well as the infiltration of encephalitogenic T cells, was significantly reduced in persistently infected brains in which an experimental autoimmune encephalomyelitis was induced by immunization with myelin-basic protein. Furthermore, we demonstrated that the continuous activation of S100B in the brain may be necessary for the progression of vascular immune responses in neonatally infected rat brains. Our results suggested that BDV infection may impair astrocyte functions via a downregulation of S100B expression, leading to the maintenance of a persistent infection.

Reverse transcription real-time PCR assays for detection and quantification of Borna disease virus in diseased hosts

Borna disease is a severe, immunopathological disorder of the central nervous system caused by the infection with the Borna disease virus (BDV). The detection of BDV in diseased animals, mainly sheep and horses, is achieved by histological, immunohistochemical and serological approaches and/or PCR-based technologies. In the present study, reverse transcription, real-time PCR assays were established for the detection of BDV in the brain tissue from sheep and horses, using loci for the p40 (nucleoprotein) and the p24 (phosphoprotein) genes. The PCRs were equally specific and sensitive, detecting 10 target molecules per reaction and one BDV-infected cell among 10(6) non-infected cells. In tissues from BDV-diseased sheep and horses, the p24 target was detected at higher abundance than for p40. Therefore, the p24 test is suggested to be of higher value in the diagnostic laboratory. However, both assays should be useful for addressing questions in pathogenesis and for detecting BDV reservoirs in endemic areas.

Prevalence of Borna disease virus antibodies in healthy Japanese black cattle in Kyushu

Epidemiological studies have demonstrated that asymptomatic infection of Borna disease virus (BDV) is found in various species of animals in Japan. Recent reports have also revealed that neurological diseases caused by this virus could exist in horses, cattle, a dog, and cats in this country. In this study, we investigated seroprevalence of BDV antibodies in Japanese black cows reared in Kyushu, the southernmost main island of Japan, using ELISA and Western-immunoblotting. Of 101 serum samples, 11 (10.9%) and 21(20.7%) sera were identified as having antibodies to the BDV N and P antigens, respectively. Among the positive sera, three cows (2.9%) were seropositive for both of the antigens. Furthermore, interestingly, only female cows showed antibodies to P, whereas N antibodies were detected in male and female cows with a comparative ratio. Together with previous studies, our results indicate that BDV might be widely spread in cattle raised in Japan. Furthermore, this is the first report to show that beef cattle, Japanese black cattle, have antibodies against a possible zoonotic pathogen, BDV.

A methionine-rich domain mediates CRM1-dependent nuclear export activity of Borna disease virus phosphoprotein

Borna disease virus (BDV) is a nonsegmented, negative-strand RNA virus that replicates and transcribes in the nucleus of infected cells. Recently, we have demonstrated that BDV phosphoprotein (P) can modulate its subcellular localization through binding to the protein X, which is encoded in the overlapping open reading frame (T. Kobayashi et al., J. Virol. 77:8099-8107, 2003). This observation suggested a unique strategy of intracellular trafficking of a viral protein that is essential for the formation of a functional BDV ribonucleoprotein (RNP). However, neither the mechanism nor the consequences of the cytoplasmic retention or nuclear export of BDV X-P complex have been elucidated. In this study, we show that BDV P contains a bona fide nuclear export signal (NES) and can actively shuttle between the nucleus and cytoplasm. A transient transfection analysis of cDNA clones that mimic the BDV bicistronic X/P mRNA revealed that the methionine-rich (MetR) domain of P is responsible for the X-dependent cytoplasmic localization of the protein complex. Mutational and functional analysis revealed that the methionine residues within the MetR domain are critical for the activity of the NES of P. Furthermore, leptomycin B or small interfering RNA for inhibition of CRM1 strongly suggested that a CRM1-dependent pathway mediates nuclear export of P. Fluorescence loss in photobleaching analysis confirmed the nucleocytoplasmic shuttling of P. Moreover, we revealed that the nuclear export of P is not involved in the inhibition of the polymerase activity by X in the BDV minireplicon system. Our results may provide a unique strategy for the nucleocytoplasmic transport of viral RNP, which could be critical for the formation of not only infectious virions in the cytoplasm but also a persistent viral state in the nucleus.

Borna disease virus interference with neuronal plasticity

Viruses able to infect the central nervous system (CNS) are increasingly being recognized as important factors that can cause mental diseases by interfering with neuronal plasticity. The mechanisms whereby such infections disturb brain functions are beginning to emerge. Borna disease virus (BDV), which causes a persistent infection of neurons without direct cytolysis in several mammalian hosts, has recently gained interest as a unique model to study the mechanisms of viral interference with neuronal plasticity. This review will summarize several hypotheses that have been put forward to explain possible levels of BDV interference with brain function.

Patterned Purkinje cell death in the cerebellum

The object of this review is to assemble much of the literature concerning Purkinje cell death in cerebellar pathology and to relate this to what is now known about the complex topography of the cerebellar cortex. A brief introduction to Purkinje cells, and their regionalization is provided, and then the data on Purkinje cell death in mouse models and, where appropriate, their human counterparts, have been arranged according to several broad categories--naturally-occurring and targeted mutations leading to Purkinje cell death, Purkinje cell death due to toxins, Purkinje cell death in ischemia, Purkinje cell death in infection and in inherited disorders, etc. The data reveal that cerebellar Purkinje cell death is much more topographically complex than is usually appreciated.

Age- and host-dependent control of Borna disease virus spread in the developing brains of gerbils and rats

Borna disease virus (BDV) is a non-cytolytic, neurotropic RNA virus that has a broad host range in warm-blooded animals, probably including humans. Recently, we have demonstrated that the neonatal gerbil is a unique model for analyzing BDV-induced acute neurological disease. In this report, to understand the effects of the brain development of gerbils in BDV-induced neuropathogenesis, as well as to investigate the host-dependent differences in BDV propagation and pathogenesis in the brains, we performed experimental infection of BDV using two different infant rodent models, gerbils and rats. We demonstrated here that most of the gerbils infected with BDV on postnatal days (PD) 14, but not on PD1 and PD7, could survive neurological disorders during the observation period of PD85. Interestingly, the levels of BDV RNA and antigen in surviving PD14 inoculated gerbil brains were extremely low, whereas diseased gerbils and both PD7 and PD14 inoculated rats contained significant amounts of BDV antigen in the central nervous system, suggesting that PD14 gerbils successfully controlled BDV spread in the brain. Furthermore, the viral distribution, as well as the expression levels of cytokine and CD8 mRNAs, in the brains was markedly different between the rodent models and between diseased and non-diseased statuses of the gerbils. These results demonstrated that developmentally regulated and host-specific factors could contribute to the prevention of BDV spread in developing animal brains. Studies using different animal systems would provide novel insights into the mechanisms of host defense responses to neurotropic virus infections.

Glial expression of Borna disease virus phosphoprotein induces behavioral and neurological abnormalities in transgenic mice

One hypothesis for the etiology of behavioral disorders is that infection by a virus induces neuronal cell dysfunctions resulting in a wide range of behavioral abnormalities. However, a direct linkage between viral infections and neurobehavioral disturbances associated with human psychiatric disorders has not been identified. Here, we show that transgenic mice expressing the phosphoprotein (P) of Borna disease virus (BDV) in glial cells develop behavioral abnormalities, such as enhanced intermale aggressiveness, hyperactivity, and spatial reference memory deficit. We demonstrate that the transgenic brains exhibit a significant reduction in brain-derived neurotrophic factor and serotonin receptor expression, as well as a marked decrease in synaptic density. These results demonstrate that glial expression of BDV P leads to behavioral and neurobiological disturbances resembling those in BDV-infected animals. Furthermore, the lack of reactive astrocytosis and neuronal degeneration in the brains indicates that P can directly induce glial cell dysfunction and also suggests that the transgenic mice may exhibit neuropathological and neurophysiological abnormalities resembling those of psychiatric patients. Our results provide a new insight to explore the relationship between viral infections and neurobehavioral disorders.

Borna disease virus induces acute fatal neurological disorders in neonatal gerbils without virus- and immune-mediated cell destructions

Borna disease virus (BDV) is a noncytolytic, neurotropic RNA virus that is known to cause neurological disturbances in various animal species. Our previous experiment demonstrated that neonate gerbils develop an acute fatal neurological disease following infection with BDV, Virology 282, 65-76). The study suggested that BDV directly causes functional damage of neuronal cells resulting in the lethal disorder in neonatal gerbils. To extend this finding, we examined whether BDV can induce neurological diseases in the absence of virus- and immune-mediated cell destruction, by using cyclosporine A (CsA)-treated neonatal gerbils. Although CsA completely suppressed specific antibody production and brain inflammation in the infected gerbil brains, the fatal neurological disorder was not inhibited by the treatment. Furthermore, we demonstrated that CsA treatment significantly decreased brain levels of cytokines, except interleukin (IL)-1 beta, in the infected gerbils. These results suggested that BDV replication, as well as brain cytokines, at least IL-1 beta, rapidly induces fatal disturbances in gerbil brain. We demonstrate here that BDV exhibits a unique neuropathogenesis in neonatal gerbil that may be pathologically and immunologically different from those in two other established rodent models, rats and mice. With this novel rodent model of virus infection it should be possible not only to examine acute neurological disturbances without severe neuroanatomical and immunopathological alterations but also to analyze molecular and cellular damage by virus replication in the central nervous system.

Enhanced neurovirulence of borna disease virus variants associated with nucleotide changes in the glycoprotein and L polymerase genes

Borna disease virus (BDV) infection produces a variety of clinical diseases, from behavioral illnesses to classical fatal encephalitis (i.e., Borna disease [BD]). Since the genomes of most BDV isolates differ by less than 5%, host factors are believed responsible for much of the reported variability in disease expression. The contribution of BDV genomic differences to variation in BD expression is largely unexplored. Here we compared the clinical outcomes of rats infected with one of two related BDV variants, CRP3 or CRNP5. Compared to rats inoculated with CRP3, adult and newborn Lewis rats inoculated with CRNP5 had more severe and rapidly fatal neurological disease, with increased damage to the hippocampal pyramidal neurons and rapid infection of brain stem neurons. To identify possible virus-specific contributions to the observed variability in disease outcome, the genomes of CRP3 and CRNP5 were sequenced. Compared to CRP3, there were four nucleotide changes in the CRNP5 variant, two each in the G protein and in the L polymerase, resulting in four amino acid changes. These results suggest that small numbers of genomic differences between BDV variants in the G protein and/or L polymerase can contribute to the variability in BD outcomes.

Molecular Techniques in the Diagnosis of Central Nervous System Infections

Development of polymerase chain reaction (PCR)-based molecular techniques has initiated a revolution in the field of diagnostic microbiology. These techniques have not only provided rapid, noninvasive detection of microorganisms that cause central nervous system (CNS) infections, but have also demonstrated that several neurologic disorders are linked to infectious agents. While PCR-based techniques are predicted to be widely used in diagnosing and monitoring CNS infections, the limitations, as well as strengths, of these techniques must be clearly understood by both clinicians and laboratory personnel to ensure proper utilization.

Varied persistent life cycles of Borna disease virus in a human oligodendroglioma cell line

Borna disease virus (BDV) establishes a persistent infection in the central nervous system of vertebrate animal species as well as in tissue cultures. In an attempt to characterize the life cycle of BDV in persistently infected cultured cells, we developed 30 clones by single-cell cloning from a human oligodendroglioma (OL) cell line after infection with BDV. According to the percentage of cells expressing the BDV major proteins, p40 (nucleoprotein) and p24 (phosphoprotein), the clones were classified into two types: type I (>20%) and type II (<20%). mRNAs corresponding to both proteins were detected by in situ hybridization (ISH) in a percentage of cells consistent with that for the protein expression in the two types. Surprisingly, ISH for the detection of the genomic RNA, mainly in type II, revealed a significantly larger cell population harboring the genomic RNA than that with the protein as well as the mRNA expression. By recloning from type II primary cell clones, the same phenotype was confirmed in the secondary cell clones obtained: i.e., low percentage of protein-positive cells and higher percentage of cells harboring the genomic RNA. After nerve growth factor treatment, the two types of clones showed increases in the percentage of cells expressing BDV-specific proteins that reached 80% in type II clones, in addition to increased expression levels per cell. Such enhancement might have been mediated by the activation of the mitogen-activated protein kinase in the clones as revealed by the detection of activated ERK1/2. Thus, our findings show that BDV may have established a persistent infection at low levels of viral expression in OL cells with the possibility of a latent infection.

Molecular and cellular biology of Borna disease virus infection

Borna disease virus (BDV) is a noncytolytic, neurotropic RNA virus that causes neurobehavioral disorders in a wide variety of warm-blooded animals. Recent evidence has revealed that BDV uses a unique strategy in its transcription and replication and directly affects cellular functions of infected central nervous systems. BDV research will provide new insights not only into the biology of neurotropic RNA virus but also into neuropsychiatry.

Real-time PCR in virology

The use of the polymerase chain reaction (PCR) in molecular diagnostics has increased to the point where it is now accepted as the gold standard for detecting nucleic acids from a number of origins and it has become an essential tool in the research laboratory. Real-time PCR has engendered wider acceptance of the PCR due to its improved rapidity, sensitivity, reproducibility and the reduced risk of carry-over contamination. There are currently five main chemistries used for the detection of PCR product during real-time PCR. These are the DNA binding fluorophores, the 5' endonuclease, adjacent linear and hairpin oligoprobes and the self-fluorescing amplicons, which are described in detail. We also discuss factors that have restricted the development of multiplex real-time PCR as well as the role of real-time PCR in quantitating nucleic acids. Both amplification hardware and the fluorogenic detection chemistries have evolved rapidly as the understanding of real-time PCR has developed and this review aims to update the scientist on the current state of the art. We describe the background, advantages and limitations of real-time PCR and we review the literature as it applies to virus detection in the routine and research laboratory in order to focus on one of the many areas in which the application of real-time PCR has provided significant methodological benefits and improved patient outcomes. However, the technology discussed has been applied to other areas of microbiology as well as studies of gene expression and genetic disease.