Die neuropathische Drüsenmagendilatation der Psittaziden und das aviäre Bornavirus als potenzielle Ursache

Gegenstand: Die neuropathische Drüsenmagendilatation der Psittaziden (PDD) ist eine bedeutende Erkrankung von Papageien, die stets letal endet. Sie tritt bei zahlreichen Papageienspezies auf und bedroht ganze Zuchtbestände, kommt bei anderen Vogelfamilien dagegen sehr selten vor. Die Ursache dieser Erkrankung war bislang unklar, obwohl schon lange eine Virusätiologie vermutet wurde. Kürzlich gelang der Nachweis eines neuen Virus (aviäres Bornavirus [ABV]) aus an PDD erkrankten Papageien, das seitdem als wahrscheinlichste Ursache gilt. Obwohl auch klinisch gesunde Papageien eine ABV-Infektion aufweisen können, zeigen verschiedene Studien einen Zusammenhang zwischen der Virusinfektion und der klinischen Erkrankung der PDD auf. Neben dem direkten Virusnachweis eignen sich auch serologische Methoden zum Infektionsnachweis. Schlussfolgerungen: Das aviäre Bornavirus ist zurzeit der wahrscheinlichste Kandidat als Erreger der PDD. Zuchtbestände und Neuzugänge sollten daher molekularbiologisch und serologisch auf eine Infektion mit ABV überprüft werden. Der diagnostische Wert des ABV-Infektionsnachweises zur Absicherung der klinischen Diagnose PDD muss in weiteren Studien genauer abgeklärt werden.

Neuronal ceroid lipofuscinosis (NCL) is caused by the entire deletion of CLN8 in the Alpenländische Dachsbracke dog

Neuronal ceroid lipofuscinoses (NCLs) are inherited lysosomal storage diseases that have been described in a variety of dog breeds, where they are caused by different mutations in different genes. However, the causative gene defect in the breed Alpenländische Dachsbracke remained unknown so far. Here we present two confirmed cases of NCL in Alpenländische Dachsbracke dogs from different litters of the same sire with a different dam harboring the same underlying novel mutation in the CLN8 gene. Case 1, a 2-year-old male Alpenländische Dachsbracke was presented with neurological signs including disorientation, character changes including anxiety states and aggressiveness, sudden blindness and reduction of food intake. Magnetic resonance imaging (MRI) scans showed cerebral atrophy with dilation of all cerebral ventricles, thinning of the intermediate mass of the thalamus and widening of the cerebral sulci. Postmortem examination of the central nervous system (CNS) showed neuronal loss in the cerebral cortex, cerebellum and spinal cord with massive intracellular deposits of ceroid pigment. Additional ceroid-lipofuscin deposits were observed in the enteric nervous system and in macrophages within spleen, lymph nodes and lung. Ultrastructural analyses confirmed NCL with the presence of osmiophilic membrane bounded lamellar-like structures. Case 2, a 1,5-year old female Alpenländische Dachsbracke was presented with progressive generalized forebrain disease including mental changes such as fearful reactions to various kinds of external stimuli and disorientation. The dog also displayed seizures, absence of menace reactions and negative cotton-ball test with normal pupillary light reactions. The clinical and post mortem examination yielded similar results in the brain as in Case 1. Whole genome sequencing of Case 1 and PCR results of both cases revealed a homozygous deletion encompassing the entire CLN8 gene as the most likely causative mutation for the NCL form observed in both cases. The deletion follows recessive inheritance since the dam and a healthy male littermate of Case 1 were tested as heterozygous carriers. This is the first detailed description of CLN8 gene associated NCL in Alpenländische Dachsbracke dogs and thus provides a novel canine CLN8 model for this lysosomal storage disease. The presence of ceroid lipofuscin in extracerebral tissues may help to confirm the diagnosis of NCL in vivo, especially in new dog breeds where the underlying mutation is not known.

Metastasizing Esthesioneuroblastoma in a Dog

A 7-year-old Afghan hound presented with a history of disorientation, loss of vision, and seizures. Magnetic resonance imaging helped identify a mass at the level of the main olfactory bulb that compressed and displaced adjacent tissues in the cribriform plate into the nasal cavity and nasopharynx. Bony structures were osteolytic. After removing almost 80% of the mass, the tumor recurred a few months later. Due to severe respiratory distress and subsequent to an ultrasound diagnosis of a liver tumor, the dog was euthanized. In addition to the nasal mass, a single nodule in the liver and multiple nodules in the lung were present. All masses had similar cell morphology and were diagnosed as metastasizing esthesioneuroblastoma. The neoplastic cells expressed neuron-specific enolase and chromogranin A, and a few cells within the nasal mass were positive for cytokeratin. This is the first description of a canine esthesioneuroblastoma with distant metastases.

Unilateral cerebellar hypoplasia and mesencephalic malformation in a Hanoverian foal

Neurological cases, especially in foals, are rare in the daily practical work. The most common causes are traumata and infectious diseases of the central nervous system (CNS). This case report provides further insights into the wide spectrum of possible neuropathological lesions by detailing a complex malformation with unilateral neurological signs that occurred later post natum. Thus, clinicians should also be aware of malformations in case of respective neurological patients. A Hanoverian foal was presented with progressive ataxia. General and blood examination revealed no further alterations. By neurologic examination, a unilateral hypermetria was diagnosed and a cysternography of the head was performed. A cerebellar malformation was assumed and the foal was euthanized due to poor prognosis. At necropsy, a unilateral absence of a cerebellar hemisphere and vermis accompanied by contralateral malformation of the mesencephalon was diagnosed. The missing areas of the right cerebellar hemisphere were replaced by a cystic formation. The left part of the mesencephalic lamina quadrigemina was reduced in size and the corpus callosum was hypoplastic. Additional microscopical findings were most obvious near the cyst formation and included angiofibrosis in remaining cerebellar and mesencephalic parenchyma and leptomeninges, heterotopia of cerebellar neurons, sclerosis in cerebellar cortex, focal proliferation of meningeal cells and mild mononuclear perivascular infiltrates. Occassional irregular neuronal arrangement in the mesencephalon was also present. Infectious agents such as Borna disease virus, rabies virus, and equine herpesvirus were not detected. Therefore, the complex malformation in this foal might have been caused by a destructive, possibly ischemic event, or could represent a sequel of a primary retrocerebellar cyst with accompanying compression of adjacent parenchyma.

Unilateral cerebellar hypoplasia and mesencephalic malformation in a Hanoverian foal

Neurological cases, especially in foals, are rare in the daily practical work. The most common causes are traumata and infectious diseases of the central nervous system (CNS). This case report provides further insights into the wide spectrum of possible neuropathological lesions by detailing a complex malformation with unilateral neurological signs that occurred later post natum. Thus, clinicians should also be aware of malformations in case of respective neurological patients. A Hanoverian foal was presented with progressive ataxia. General and blood examination revealed no further alterations. By neurologic examination, a unilateral hypermetria was diagnosed and a cysternography of the head was performed. A cerebellar malformation was assumed and the foal was euthanized due to poor prognosis. At necropsy, a unilateral absence of a cerebellar hemisphere and vermis accompanied by contralateral malformation of the mesencephalon was diagnosed. The missing areas of the right cerebellar hemisphere were replaced by a cystic formation. The left part of the mesencephalic lamina quadrigemina was reduced in size and the corpus callosum was hypoplastic. Additional microscopical findings were most obvious near the cyst formation and included angiofibrosis in remaining cerebellar and mesencephalic parenchyma and leptomeninges, heterotopia of cerebellar neurons, sclerosis in cerebellar cortex, focal proliferation of meningeal cells and mild mononuclear perivascular infiltrates. Occassional irregular neuronal arrangement in the mesencephalon was also present. Infectious agents such as Borna disease virus, rabies virus, and equine herpesvirus were not detected. Therefore, the complex malformation in this foal might have been caused by a destructive, possibly ischemic event, or could represent a sequel of a primary retrocerebellar cyst with accompanying compression of adjacent parenchyma.

Aprosencephaly with otocephaly in a lamb (Ovis aries)

Aprosencephaly is a rare condition in veterinary and human medicine characterized by the complete absence of telencephalon and diencephalon. Some cases are accompanied by a facial dysmorphism designated as otocephaly. A stillborn lamb had splanchnocranial anomalies that were classified by computed tomography, magnetic resonance imaging, and pathologic examination as aprosencephaly and otocephaly. The brain included parts of the cerebellum and brainstem but no telencephalon, diencephalon, or mesencephalon. The cerebellum had a structurally normal cortex with expression of neuronal nuclear antigen in the inner and doublecortin in the outer granular cell layers, as well as an irregularly situated nucleus dentatus. Aprosencephaly with otocephaly has been described in mice with heterozygous mutations in the Otx2 gene; however, no causative polymorphisms were detected in the Otx2 gene region of this lamb.

Neurogenesis in a Young Dog With Epileptic Seizures

Epileptic seizures can lead to various reactions in the brain, ranging from neuronal necrosis and glial cell activation to focal structural disorganization. Furthermore, increased hippocampal neurogenesis has been documented in rodent models of acute convulsions. This is a report of hippocampal neurogenesis in a dog with spontaneous epileptic seizures. A 16-week-old epileptic German Shepherd Dog had marked neuronal cell proliferation (up to 5 mitotic figures per high-power field and increased immunohistochemical expression of proliferative cell nuclear antigen) in the dentate gyrus accompanied by microglial and astroglial activation. Some granule cells expressed doublecortin, a marker of immature neurons; mitotically active cells expressed neuronal nuclear antigen. No mitotic figures were found in the brain of age-matched control dogs. Whether increased neurogenesis represents a general reaction pattern of young epileptic dogs should be investigated.

Malignant mesenchymoma in the nasal cavity of a bull

A 4-year-old bull was presented with facial distortion and abnormal respiratory noise. Endoscopically, a proliferative mass was found obliterating the left nasal cavity and a tumour was suspected. The head was examined after slaughter and there was a well-circumscribed solid structure (15×12×6 cm) extending into the paranasal sinus, the choanal region and the bones of the orbit, with focal penetration of the nasal septum. Microscopically, the mass consisted of well-differentiated trabeculae of woven and lamellar bone, areas of chondromyxomatous, immature and mature cartilaginous tissue, and regions with irregular whorled spindle cells. Tissue differentiation of the mass was variable. Centrally, there was osseous differentiation with an outermost fibromatous area resembling a zone of endochondral ossification. There was suppurative and ulcerative inflammation where the tumour extended through the hard palate and into the pharynx. A nasal malignant mesenchymoma was diagnosed on the basis of these features.

Anencephaly in a German Shepherd Dog

Anencephaly results from defects in neural tube closure early in gestation and, to the authors' knowledge, has not been reported in dogs. In this case, the canine fetus was stillborn at the 62nd day of gestation and had a hypoplastic calvarium, with flattened base of the skull and shallow orbits, causing protrusion of the eyes. Macroscopically, the brain was completely missing. Histologically, well-differentiated nerve fibers, fragments of cerebellar folia, and ganglia with large neurons and glial cells were detected in a loose stroma in sections through the cranial bone and adjacent soft tissue in the rudimentary cranial cavity. Immunohistochemically, single cells within the stroma expressed NeuN, consistent with mature neurons, whereas intracranial ganglion cells and nerves had mild expression of doublecortin. The presence of many immature, and only a few mature, neurons in the rudimentary nerve tissue in this case indicates a failure of physiological brain development and differentiation.

Proposing the term purkinjeoma: protein gene product 9.5 expression in 2 porcine cardiac rhabdomyomas indicates possible purkinje fiber cell origin

Rhabdomyomas, defined as rare benign tumors of striated muscle, predominantly occur in the myocardium. In veterinary medicine, cardiac rhabdomyomas have rarely been reported but most frequently in pigs as an incidental finding. In the present case report, multiple circumscribed nodules found in the myocardium of 2 pigs were composed of large, vacuolated, glycogen-loaded cells. They expressed vimentin and desmin, neuron-specific enolase, and atrial natriuretic peptide. In addition, these cells expressed protein gene product 9.5, a marker for neuronal tissue and Purkinje fiber cells, in contrast to adjacent myocytes. The present findings-especially, the protein gene product 9.5 immunoreactivity-provide further evidence for the Purkinje fiber cell origin of the porcine myocardial proliferation. Therefore, the term purkinjeoma or purkinjeomatosis is proposed for cardiac rhabdomyoma in pigs.

Borna disease in an adult alpaca stallion (Lama pacos)

Borna disease (BD) was diagnosed in a 2-year-old male alpaca with a history of chronic suppressed sexual desire and acute stretching convulsions. Microscopical examination of the central nervous system revealed non-purulent meningoencephalitis with mononuclear perivascular cuffing. The diagnosis was confirmed by immunohistochemistry, in-situ hybridization, polymerase chain reaction (PCR) and sequencing of PCR products and alignment with known Borna disease virus sequences. Serological screening of the herd was performed. This is the first detailed report of naturally occurring BD in alpacas.

[Proventricular dilatation disease and Avian Bornavirus as a possible cause]

OBJECTIVE

Proventricular Dilatation Disease (PDD) is a very important letal disease in parrots. It affects several psittacine species and is a high risk factor for the health of breeding collections, but is rarely observed in other avian families. To date, the etiology of the disease remained unclear, though a virus infection was always assumed. Recently, a novel virus (Avian Bornavirus [ABV]) was discovered in parrots suffering from PDD so that ABV is now considered as the most likely cause. Despite the fact that clinically healthy birds may be infected with ABV, several studies demonstrate a correlation between ABV-infection and clinically present PDD. Apart from direct virus detection, serological methods allow the demonstration of an infection.

CONCLUSIONS

Currently, Avian Bornavirus is the leading candidate as the aetiologic agent of PDD. Breeding collections and birds planned to be introduced into collections should therefore be investigated by molecular biological and serological methods for the presence of an ABV-infection. The diagnostic value of the demonstration of an ABV-infection for the diagnosis of a clinically present PDD has to be investigated further.

Expression of activity-dependent neuroprotective protein in the brain of adult rats

Activity-dependent neuroprotective protein (ADNP) is a VIP-regulated gene, which is essential for brain development. A synthetic peptide (NAP) derived from the ADNP sequence is highly neuroprotective, therefore it has been hypothesised that ADNP has a similar role. ADNP contains classical transcription factor motifs and nuclear localisation domains, but it has also been reported to be secreted and to co-localise with microtubules, indicating that ADNP may have multiple functions. We investigated the pattern of ADNP expression by immunohistology in normal rat brain, in order to generate a framework for future studies examining changes in ADNP expression in response to noxious stimuli or in models of disease. We found widespread ADNP-like immunoreactivity in neurons throughout the rat brain, with the highest expression in the cerebellum, and strong expression in the thalamus, mesencephalon, pons and medulla oblongata. ADNP-like immunoreactivity was mainly observed in the cytoplasm of neurons, and fibre tracts were often strongly positive as well. In addition, positive neuronal nuclei were occasionally observed. ADNP-like immunoreactivity was lost in degenerating "dark" neurons, whereas it appeared to locate to the nucleus in some of the morphologically unaltered adjacent cells. Occasional astrocyte and microglial cells were also positive. We suggest that the widespread expression of ADNP may correlate with the wide-ranging protective effects of NAP, and that the cytoplasmic and axonal localisation of ADNP-like immunoreactivity suggests additional, non-transcriptional functions of ADNP.

Unusual type of reactive astrocytes in the feline central nervous system

An unusual type of hypertrophic astrocytes termed plump polygonal astrocytes (PPA) has been observed in the feline central nervous system which was characterized in a first preliminary study of 17 cats. These cells presented an oval to polygonal shape, measured about 20 microm in diameter, and displayed short, barely detectable processes. The condensed, hyperchromatic, eccentric nucleus was surrounded by an abundant, homogenous, eosinophilic cytoplasm. These GFAP-and S-100-positive and vimentin-negative cells were predominantly found in brains showing status spongiosus and less frequently in association with inflammation and in brains lacking histological lesions. They were mainly detected in white matter areas of the hindbrain. In addition, these cells were also observed in the dentate hilar region adjacent to degenerated neurons and a small amount of PPA were positive for caspase-3. It remains to be determined if PPA represent a specific type of reactive astrocytes and whether they are characteristic for a specific cause or response in the feline brain.

Non-suppurative meningoencephalitis of unknown origin in cats and dogs: an immunohistochemical study

Non-suppurative meningoencephalitis of unknown cause is a frequent finding in dogs and cats. Fifty-three dogs and 33 cats with non-suppurative meningoencephalitis of unknown aetiology were examined immunohistochemically for 18 different infectious agents, including viruses, bacteria and prion protein^Sc. In 14 (26%) of the dogs and 13 (39%) of the cats a causative agent was identified in the central nervous system (CNS), two dogs and one cat giving positive results for two infectious agents simultaneously. The study revealed infections with known causative agents (porcine herpes virus 1, feline infectious peritonitis virus, Escherichia coli) and a new disease pattern of parvovirus infection in the CNS of dogs and cats. Infection of the CNS with feline leukaemia virus was found in a cat. Five dogs and four cats gave positive results for West Nile virus (WNV) antigen. In one dog, canine parainfluenza virus antigen was detected in the brain. Four dogs and four cats gave positive results for encephalomyocarditis virus (EMCV). The significance of the detection of WNV and EMCV antigen requires further study. The aetiology remained undetermined in 39 dogs (74%) and 20 cats (61%). Although it is possible that non-infectious causes play a more important role than previously thought, infections with hitherto unrecognized agents cannot be ruled out.

Expression of allograft inflammatory factor-1 and haeme oxygenase-1 in brains of rats infected with the neurotropic Borna disease virus

Experimental infection of Lewis rats with Borna disease virus (BDV) causes an immune-mediated nonpurulent meningoencephalitis. Viral persistence in the central nervous system is accompanied by mononuclear infiltrates, activated monocytic/microglial cells and reactive astrocytes. The immune-mediated process was further characterized by expression analysis of allograft inflammatory factor-1 (AIF-1), a novel marker of monocyte/microglial activation and of glial fibrillary acid protein (GFAP) between day 3 and day 50 post infection (p.i.). Potential neuroprotective effects of these cells were studied by the induction of haeme oxygenase-1 (HO-1), a defensive molecule against oxidative stress in various brain insults. In BDV-infected rat brains, mononuclear infiltrates and AIF-1 expression increased up to day 28 p.i. During early time points p.i., AIF-1 expression was mainly found in inflammatory lesions and adjacent brain parenchyma. Already 24 days p.i., a widespread upregulation of AIF-1 was observed which declined only moderately beyond day 28 p.i. HO-1 induction was maximal between days 18 and 28 p.i. Increased amounts of GFAP-positive astrocytes were present beyond 24 days p.i. Viral antigen expression increased simultaneously to the inflammatory reaction and persisted up to 50 days p.i. Widespread upregulation of AIF-1 indicates an early, long-lasting microglial activation, which might be involved in the immunesurveillance of the immune-mediated inflammatory events. The early peak of HO-1 most likely represents a neuroprotective, anti-inflammatory response by invading monocytes, microglial cells and astrocytes during the formation of encephalitic lesions and acute viral replication.

Unusual manifestation of hepatic encephalopathy in two Irish wolfhound siblings

In hepatic encephalopathy the brain lesions are usually characterised by polymicrocavitation, preferentially in the white matter, and the occurrence of Alzheimer type II cells. This paper describes an unusual manifestation of hepatic encephalopathy in two Irish wolfhound siblings in which the white matter was not involved predominantly. Both puppies had developed progressive neurological disturbances and signs of blindness. Histologically, there were widespread spongiform changes in the neuropil and fibre bundles interspersed within the grey matter, and there were some neuronal vacuoles. In both animals, the regions of the brain mainly affected were the nucleus caudatus, amygdala, cerebellar nuclei, mesencephalon, thalamus, hypothalamus and medulla oblongata. An astrogliosis characterised by Alzheimer type II-like cells was also observed. Electron microscopy revealed a splitting of the myelin sheath. No infectious agents such as rabies virus, canine distemper virus or prion proteins were detected. The main findings in the portal regions of the liver consisted of a dilatation of the lymphatic vessels and increased numbers of small arteries, indicating that a portosystemic shunt was the probable cause of the spongiform brain lesions.

[Canine distemper virus--an agent looking for new hosts]

Canine distemper is caused by the canine distemper virus (CDV), a RNA virus belonging to the genus Morbillivirus of the family Paramyxoviridae. The genus Morbillivirus includes measles virus, Rinderpest virus and peste-des-petits-ruminants virus. The host spectrum of CDV, which includes numerous families of Carnivores, has been changed in the last years and distemper-like diseases have been observed in numerous other species. These include epidemics in large felids, marine mammals and javelinas. Different viruses have been isolated from pinnipeds including a seal-specific isolate, termed phocine distemper virus 1, PDV-1, and a CDV strain, named PDV-2. Retrospective analysis of previous epidemics among marine mammals in various regions of the world provide evidence for the occurrence of so far unrecognized morbillivirus epidemics. In some including the mass mortalities of Baikal and Caspian seals and of large felids in the Serengeti, terrestrial carnivores including dogs and wolves have been suspected as a vector for the infectious agent. However, in other epidemics among marine mammals the source of infection remains unknown including both seal epidemics in northwestern Europe in 1988 and 2002. It remains to be determined whether a morbillivirus from other marine mammals or terrestrial carnivores caused the infection in this unprotected seal populations.

Temporal development of photorefractive solitons up to telecommunication wavelengths in strontium-barium niobate waveguides

We experimentally investigate the temporal development of photorefractive solitons in strontium-barium niobate waveguides at visible and infrared wavelengths. The development times in the infrared are shown to be comparable with those in the visible. The results are compared with predictions of a previously published model.

Neuron-glia interactions in the rat retina infected by Borna disease virus

Neuron-glia interactions in the Borna disease virus (BDV)-infected rat retina were investigated with emphasis on the ultrastructural characterization of degenerative alterations in the ganglion cell and photoreceptor layer. Immuno- and cytochemical techniques were applied to label microglia, macrophages and Müller (macroglial) cells. Four weeks after intracerebral infection of adult rats, the total thickness of the retina was considerably diminished, primarily due to the loss of photoreceptor segments and ganglion cells. A gradual reduction of both plexiform layers was also observed. There was a remarkable increase in the number of microglial cells, predominantly in the ganglion cell and the inner plexiform layers. Ultrastructural analysis confirmed that microglia, but also macrophages, were involved in phagocytosis accompanying severe neuronal degeneration in the ganglion cell and the photoreceptor layer. In contrast, Müller cells showed moderate morphological and cytochemical alterations, indicating that Müller cells play only a minor role in early stages of BDV-induced retinitis. Monitoring neuron-glia interactions in BDV-induced retinopathy, combined with the application of different protocols of immunosuppression effecting the BDV virus and/or the microglia, might help to establish specific strategies to suppress BDV-induced neuronal degeneration.

Distribution of Borna disease virus in the brain of rats infected with an obesity-inducing virus strain

Experimental infection of Lewis rats with Borna disease virus (BDV), a nonsegmented, single-stranded RNA virus, usually causes an immune-mediated biphasic neurobehavioral disorder. Such animals develop a persistent infection of the CNS with viral antigen expression in all brain regions and a disseminated nonpurulent meningoencephalitis. Interestingly, intracerebral infection of Lewis rats with a BDV-variant (BDV-ob) causes a rapid increase of body weight with the development of an obesity syndrome without obvious neurological signs. The obese phenotype is correlated with a characteristic distribution of inflammatory lesions and BDV-antigen in the rat brain. Infiltration with mononuclear immune cells and viral antigen expression are restricted to the septum, hippocampus, amygdala and ventromedian tuberal hypothalamus. Therefore, infection with the obesity-inducing BDV-ob results most likely in neuroendocrine dysregulations leading to the development of an obesity syndrome. This might be due to the restriction of viral antigen expression and inflammatory lesions to brain areas which are involved in the regulation of body weight and food intake. The BDV-induced obesity syndrome represents a model for the study of immune-mediated neuroendocrine disorders caused by viral infections of the CNS.

Processing of the Borna disease virus glycoprotein gp94 by the subtilisin-like endoprotease furin

Open reading frame IV (ORF-IV) of Borna disease virus (BDV) encodes a protein with a calculated molecular mass of ca. 57 kDa (p57), which increases after N glycosylation to 94 kDa (gp94). The unglycosylated and glycosylated proteins are proteolytically cleaved by the subtilisin-like protease furin. Furin most likely recognizes one of three potential cleavage sites, namely, an arginine at position 249 of the ORF-IV gene product. The furin inhibitor decRVKRcmk decreases the production of infectious BDV significantly, indicating that proteolytic cleavage of the gp94 precursor molecule is necessary for the full biological activity of the BDV glycoprotein.

Detection of a novel Borna disease virus-encoded 10 kDa protein in infected cells and tissues

Borna disease (BD) is a transmissible, progressive polioencephalomyelitis primarily of horses and sheep. The genomes of two cell-adapted strains of Borna disease virus (BDV), the aetiological agent of BD, have been cloned and sequenced. According to the structural characterization achieved so far, BDV contains a non-segmented negative-sense 8.9 kb single-stranded RNA genome. In this paper we report the expression, purification and intracellular tracing of a novel non-glycosylated BDV-specific protein with a molecular mass of approximately 10 kDa (BDV p10 protein). The successful isolation of the corresponding mRNA from infected cells, amplification of the genetic region by RT-PCR and its efficient expression as a glutathione S-transferase (GST) fusion protein demonstrated that antibodies specific for the BDV p10 protein are induced in infected animals. In addition, we have produced monospecific antisera against the GST-p10 fusion protein in rabbits. This monospecific antiserum recognized the BDV p10 protein in brain cells of naturally and experimentally infected animals as well as in persistently BDV-infected cells. Antibody-mediated affinity-chromatography using the anti-p10 serum could successfully be applied to purify a ca. 10 kDa antigen from infected animal cells to such an extent that glycosylation of this component could be ruled out.