Spread and distribution of viral antigen in nervous canine distemper

Caprine arthritis encephalitis virus-induced apoptosis associated with brain lesions in naturally infected kids

Acute demyelinating leucoencephalomyelitis was the most conspicuous microscopic change in the brain and spinal cord of kids infected with caprine arthritis encephalitis virus (CAEV). TUNEL positivity and labelling of anti-bax and anti-caspases-3, -8 and -9 were found in a distinct population of glial cells, mainly at the edges of the demyelinated plaques and perivascular areas and, to a lesser extent, in neurons. Double labelling revealed that most of these apoptotic cells in the demyelinated plaques were astrocytes and a few were oligodendroglia. In contrast, expression of bcl-2, an anti-apoptotic protein, was found mainly in neurons of the brainstem and cerebellum and motor neurons of the spinal cord, but was restricted in glial cells. These results suggest that apoptosis plays an important role in the pathogenesis of CAE demyelinating encephalitis.

Evaluation of the Efficacy and Safety of Silver Nanoparticles in the Treatment of Non-Neurological and Neurological Distemper in Dogs: A Randomized Clinical Trial

Canine distemper is caused by canine distemper virus (CDV), a multisystemic infectious disease with a high morbidity and mortality rate in dogs. Nanotechnology represents a development opportunity for new molecules with antiviral effects that may become effective treatments in veterinary medicine. This study evaluated the efficacy and safety of silver nanoparticles (AgNPs) in 207 CDV, naturally infected, mixed-breed dogs exhibiting clinical signs of the non-neurological and neurological phases of the disease. Group 1a included 52 dogs (experimental group) diagnosed with non-neurologic distemper treated with 3% oral and nasal AgNPs in addition to supportive therapy. Group 1b included 46 dogs (control group) diagnosed with non-neurological distemper treated with supportive therapy only. Group 2a included 58 dogs with clinical signs of neurological distemper treated with 3% oral and nasal AgNPs in addition to supportive therapy. Group 2b included 51 dogs (control group) diagnosed with clinical signs of neurological distemper treated with supportive therapy only. Efficacy was measured by the difference in survival rates: in Group 1a, the survival rate was 44/52 (84.6%), versus 7/46 in Group 1b (15.2%), while both showed clinical signs of non-neurological distemper. The survival rate of dogs with clinical signs of neurological distemper in Group 2a (38/58; 65.6%) was significantly higher than those in Control Group 2b (0/51; 0%). No adverse reactions were detected in experimental groups treated with AgNPs. AgNPs significantly improved survival in dogs with clinical signs of neurological and non-neurological distemper. The use of AgNPs in the treatment of neurological distemper led to a drastic increase in the proportion of dogs recovered without sequels compared to dogs treated without AgNPs. The evidence demonstrates that AgNP therapy can be considered as a targeted treatment in dogs severely affected by canine distemper virus.

Phenotypic and Transcriptional Changes of Pulmonary Immune Responses in Dogs Following Canine Distemper Virus Infection

Canine distemper virus (CDV), a morbillivirus within the family Paramyxoviridae, is a highly contagious infectious agent causing a multisystemic, devastating disease in a broad range of host species, characterized by severe immunosuppression, encephalitis and pneumonia. The present study aimed at investigating pulmonary immune responses of CDV-infected dogs in situ using immunohistochemistry and whole transcriptome analyses by bulk RNA sequencing. Spatiotemporal analysis of phenotypic changes revealed pulmonary immune responses primarily driven by MHC-II⁺, Iba-1⁺ and CD204⁺ innate immune cells during acute and subacute infection phases, which paralleled pathologic lesion development and coincided with high viral loads in CDV-infected lungs. CD20⁺ B cell numbers initially declined, followed by lymphoid repopulation in the advanced disease phase. Transcriptome analysis demonstrated an increased expression of transcripts related to innate immunity, antiviral defense mechanisms, type I interferon responses and regulation of cell death in the lung of CDV-infected dogs. Molecular analyses also revealed disturbed cytokine responses with a pro-inflammatory M1 macrophage polarization and impaired mucociliary defense in CDV-infected lungs. The exploratory study provides detailed data on CDV-related pulmonary immune responses, expanding the list of immunologic parameters potentially leading to viral elimination and virus-induced pulmonary immunopathology in canine distemper.

Neuropathologic and molecular aspects of a canine distemper epizootic in red foxes in Germany

In the last fifteen years, an epidemic of canine distemper virus (CDV) with marked neurotropism has occurred in Europe after a longer period of endemic transmission. Many wildlife species have been infected, with red foxes (Vulpes vulpes) being particularly affected. Given that this species is assumed to mediate cross-species CDV infections to domestic and wild animals, tissue samples from foxes with confirmed CDV infection in North-Western Germany were investigated to better understand the neurotropic aspects of the disease. This analysis included histopathology, virus distribution and cell tropism, phenotyping of inflammatory responses and determination of the genotype of the viruses based on the phylogeny of the hemagglutinin (H) gene. The predominant lesion type is gliosis in both gray and white matter areas associated with an accumulation of Iba1+ macrophages/microglia and upregulation of major histocompatibility complex class II molecules in the brain, while sequestration of CD3+ T and Pax5+ B cell in CDV-infected foxes is limited. Demyelination is found in few foxes, characterized by reduced myelin staining with loss of CNPase+ oligodendrocytes in the cerebellar white matter and brainstem. In addition, axonal damage, characterized by β-amyloid precursor protein expression, is found mainly in these brain regions. In situ hybridization reveals a primary infection of the cerebral and cerebellar gray matter and brain stem. Iba1+ cells and NeuN+ neurons represent the main CDV targets. Sequencing of the CDV H open reading frame from fox tissues reveals that the virus strains belongs to three different sub-lineages of the Europe-1/South America-1 genotype, suggesting independent transmission lines.

Canine distemper virus in wildlife in south-western Europe

Multi-host pathogens emerging and re-emerging at the wildlife-domestic animal interface affect wildlife management and conservation. This is the case of canine distemper virus (CDV), a paramyxovirus closely related to human measles virus and rinderpest virus of cattle. With an area of 10,603 km² , Asturias region in Atlantic Spain is a hotspot of carnivore diversity, which includes the largest Eurasian brown bear (Ursus arctos arctos) population and one of the largest wolf (Canis lupus) populations in south-western Europe. In 2020-2021, we recorded mortality due to distemper in four carnivore species including three mustelids (Eurasian badger Meles meles, European marten Martes martes and European polecat Mustela putorius) and one canid (red fox, Vulpes vulpes). Clinical signs and pathology were similar across species and consistent with the emergence of a highly pathogenic viral strain, with CDV antigen mainly located in the central nervous system, lungs, spleen and lymph nodes. A molecular study in eight wild carnivore species, also including the Iberian wolf, Eurasian brown bear, American mink (Neovison vison) and stone marten (Martes foina), revealed 19.51% (16/82) of positivity. Phylogenetic analysis demonstrated that CDV belonged to the previously described European lineage. A retrospective serosurvey (2008-2020) showed a high seroprevalence of CDV antibodies (43.4%) in 684 analyzed badgers, indicating a long-term though not stable viral circulation in this multi-host community. The possible triggers of the 2020-2021 outbreak and the implications for carnivore management and conservation are discussed.

Apoptotic investigation of brain tissue cells in dogs naturally infected by canine distemper virus

Background

Canine distemper caused by canine distemper virus that belongs to the Morbillivirus genus of the Paramyxoviridae family is still a global epidemic significant infectious disease, especially in pet dogs in China and serious harm to the development of the dog industry. It has been known that apoptosis caused by the canine distemper virus can show in culture cells, lymphoid tissues, and the cerebellum. However, its occurrence in brain tissue cells remains unclear. To investigate the relationship among canine distemper infecting brain tissues, apoptosis in brain tissue cells, and demyelinating pathogenesis was investigated.

Methods

16 naturally infected dogs that exhibited clinical signs of CD and tested positive for the anti-CDV monoclonal antibody and six healthy dogs that served as the control, were used in the research. Brain specimens were divided into the cerebrum, brain stem, and cerebellum embedded in paraffin and made the sections respectively. Approximately 5 µm-thick sections were stained by hematoxylin–eosin, methyl green pyronin, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling technique, and immunohistochemistry. CDV nucleocapsid protein was detected by immune streptavidin-biotinylated peroxidase complex.

Results

Alterations in the brain tissues of CDV-infected dogs involved both various cells and nerve fibers. CDV had varying degrees of cytotropism to all brain tissue cells; apoptosis also occurred in all brain cells, especially in the endothelia of cerebral vessels, astrocytes, oligodendrocytes, and ependymal cells, the more serious infection, the more obvious apoptosis. Serious infections also involved the pyramidal and Purkinje cells. The nervous fibers exhibited demyelinating lesions (showed small multifocal vacuole), and some axonal neuron atrophy gradually disappeared (formed large vacuole).

Conclusions

Apoptosis in brain tissue cells was mainly related to the propagation path and cytotropism of CDV. The apoptosis of astrocytes, oligodendrocytes, and some neurons may play a significant role in the demyelinating pathogenesis in dogs with acute canine distemper. A lot of diverse nervous signs shown in the clinic may be related to different neuron apoptosis.

Neurotoxic potential of reactive astrocytes in canine distemper demyelinating leukoencephalitis

Canine distemper virus (CDV) causes a fatal demyelinating leukoencephalitis in young dogs resembling human multiple sclerosis. Astrocytes are the main cellular target of CDV and undergo reactive changes already in pre-demyelinating brain lesions. Based on their broad range of beneficial and detrimental effects in the injured brain reactive astrogliosis is in need of intensive investigation. The aim of the study was to characterize astrocyte plasticity during the course of CDV-induced demyelinating leukoencephalitis by the aid of immunohistochemistry, immunofluorescence and gene expression analysis. Immunohistochemistry revealed the presence of reactive glial fibrillary acidic protein (GFAP)+ astrocytes with increased survivin and reduced aquaporin 4, and glutamine synthetase protein levels, indicating disturbed blood brain barrier function, glutamate homeostasis and astrocyte maladaptation, respectively. Gene expression analysis revealed 81 differentially expressed astrocyte-related genes with a dominance of genes associated with neurotoxic A1-polarized astrocytes. Accordingly, acyl-coA synthetase long-chain family member 5+/GFAP+, and serglycin+/GFAP+ cells, characteristic of A1-astrocytes, were found in demyelinating lesions by immunofluorescence. In addition, gene expression revealed a dysregulation of astrocytic function including disturbed glutamate homeostasis and altered immune function. Observed findings indicate an astrocyte polarization towards a neurotoxic phenotype likely contributing to lesion initiation and progression in canine distemper leukoencephalitis.

Expression of canine distemper virus receptor nectin-4 in the central nervous system of dogs

Canine distemper virus (CDV) exhibits lymphotropic, epitheliotropic, and neurotropic nature, and causes a severe systemic infection in susceptible animals. Initially, signaling lymphocyte activation molecule (SLAM) expressed on immune cells has been identified as a crucial cellular receptor for CDV. Currently, nectin-4 expressed in epithelia has been shown to be another receptor for CDV. Our previous study demonstrated that neurons express nectin-4 and are infected with CDV. In this study, we investigated the distribution pattern of nectin-4 in various cell types in the canine central nervous system and showed its relation to CDV infection to further clarify the pathology of disease. Histopathological, immunohistochemical and immunofluorescent analyses were done using formalin-fixed paraffin-embedded tissues of CDV-infected dogs. Dual staining of nectin-4 and CDV antigen or nectin-4 and brain cell markers was performed. Nectin-4 was detected in ependymal cells, epithelia of choroid plexus, meningeal cells, neurons, granular cells, and Purkinje's cells. CDV antigens were detected in these nectin-4-positive cells, further suggesting contribution of nectin-4 for the CDV neurovirulence. On the other hand, astrocytes did not express nectin-4, although they were frequently infected with CDV. Since astrocytes are negative for SLAM expression, they must express an unidentified CDV receptor, which also contributes to CDV neurovirulence.

Accumulation of Extracellular Matrix in Advanced Lesions of Canine Distemper Demyelinating Encephalitis

In demyelinating diseases, changes in the quality and quantity of the extracellular matrix (ECM) may contribute to demyelination and failure of myelin repair and axonal sprouting, especially in chronic lesions. To characterize changes in the ECM in canine distemper demyelinating leukoencephalitis (DL), histochemical and immunohistochemical investigations of formalin-fixed paraffin-embedded cerebella using azan, picrosirius red and Gomori`s silver stain as well as antibodies directed against aggrecan, type I and IV collagen, fibronectin, laminin and phosphacan showed alterations of the ECM in CDV-infected dogs. A significantly increased amount of aggrecan was detected in early and late white matter lesions. In addition, the positive signal for collagens I and IV as well as fibronectin was significantly increased in late lesions. Conversely, the expression of phosphacan was significantly decreased in early and more pronounced in late lesions compared to controls. Furthermore, a set of genes involved in ECM was extracted from a publically available microarray data set and was analyzed for differential gene expression. Gene expression of ECM molecules, their biosynthesis pathways, and pro-fibrotic factors was mildly up-regulated whereas expression of matrix remodeling enzymes was up-regulated to a relatively higher extent. Summarized, the observed findings indicate that changes in the quality and content of ECM molecules represent important, mainly post-transcriptional features in advanced canine distemper lesions. Considering the insufficiency of morphological regeneration in chronic distemper lesions, the accumulated ECM seems to play a crucial role upon regenerative processes and may explain the relatively small regenerative potential in late stages of this disease.

New aspects of the pathogenesis of canine distemper leukoencephalitis

Canine distemper virus (CDV) is a member of the genus morbillivirus, which is known to cause a variety of disorders in dogs including demyelinating leukoencephalitis (CDV-DL). In recent years, substantial progress in understanding the pathogenetic mechanisms of CDV-DL has been made. In vivo and in vitro investigations provided new insights into its pathogenesis with special emphasis on axon-myelin-glia interaction, potential endogenous mechanisms of regeneration, and astroglial plasticity. CDV-DL is characterized by lesions with a variable degree of demyelination and mononuclear inflammation accompanied by a dysregulated orchestration of cytokines as well as matrix metalloproteinases and their inhibitors. Despite decades of research, several new aspects of the neuropathogenesis of CDV-DL have been described only recently. Early axonal damage seems to represent an initial and progressive lesion in CDV-DL, which interestingly precedes demyelination. Axonopathy may, thus, function as a potential trigger for subsequent disturbed axon-myelin-glia interactions. In particular, the detection of early axonal damage suggests that demyelination is at least in part a secondary event in CDV-DL, thus challenging the dogma of CDV as a purely primary demyelinating disease. Another unexpected finding refers to the appearance of p75 neurotrophin (NTR)-positive bipolar cells during CDV-DL. As p75NTR is a prototype marker for immature Schwann cells, this finding suggests that Schwann cell remyelination might represent a so far underestimated endogenous mechanism of regeneration, though this hypothesis still remains to be proven. Although it is well known that astrocytes represent the major target of CDV infection in CDV-DL, the detection of infected vimentin-positive astrocytes in chronic lesions indicates a crucial role of this cell population in nervous distemper. While glial fibrillary acidic protein represents the characteristic intermediate filament of mature astrocytes, expression of vimentin is generally restricted to immature or reactive astrocytes. Thus, vimentin-positive astrocytes might constitute an important cell population for CDV persistence and spread, as well as lesion progression. In vitro models, such as dissociated glial cell cultures, as well as organotypic brain slice cultures have contributed to a better insight into mechanisms of infection and certain morphological and molecular aspects of CDV-DL. Summarized, recent in vivo and in vitro studies revealed remarkable new aspects of nervous distemper. These new perceptions substantially improved our understanding of the pathogenesis of CDV-DL and might represent new starting points to develop novel treatment strategies.

Transcriptional changes in canine distemper virus-induced demyelinating leukoencephalitis favor a biphasic mode of demyelination

Canine distemper virus (CDV)-induced demyelinating leukoencephalitis in dogs (Canis familiaris) is suggested to represent a naturally occurring translational model for subacute sclerosing panencephalitis and multiple sclerosis in humans. The aim of this study was a hypothesis-free microarray analysis of the transcriptional changes within cerebellar specimens of five cases of acute, six cases of subacute demyelinating, and three cases of chronic demyelinating and inflammatory CDV leukoencephalitis as compared to twelve non-infected control dogs. Frozen cerebellar specimens were used for analysis of histopathological changes including demyelination, transcriptional changes employing microarrays, and presence of CDV nucleoprotein RNA and protein using microarrays, RT-qPCR and immunohistochemistry. Microarray analysis revealed 780 differentially expressed probe sets. The dominating change was an up-regulation of genes related to the innate and the humoral immune response, and less distinct the cytotoxic T-cell-mediated immune response in all subtypes of CDV leukoencephalitis as compared to controls. Multiple myelin genes including myelin basic protein and proteolipid protein displayed a selective down-regulation in subacute CDV leukoencephalitis, suggestive of an oligodendrocyte dystrophy. In contrast, a marked up-regulation of multiple immunoglobulin-like expressed sequence tags and the delta polypeptide of the CD3 antigen was observed in chronic CDV leukoencephalitis, in agreement with the hypothesis of an immune-mediated demyelination in the late inflammatory phase of the disease. Analysis of pathways intimately linked to demyelination as determined by morphometry employing correlation-based Gene Set Enrichment Analysis highlighted the pathomechanistic importance of up-regulated genes comprised by the gene ontology terms “viral replication” and “humoral immune response” as well as down-regulated genes functionally related to “metabolite and energy generation”.

Immunopathogenic and neurological mechanisms of canine distemper virus

Canine distemper is a highly contagious viral disease caused by the canine distemper virus (CDV), which is a member of the Morbillivirus genus, Paramyxoviridae family. Animals that most commonly suffer from this disease belong to the Canidae family; however, the spectrum of natural hosts for CDV also includes several other families of the order Carnivora. The infectious disease presents worldwide distribution and maintains a high incidence and high levels of lethality, despite the availability of effective vaccines, and no specific treatment. CDV infection in dogs is characterized by the presentation of systemic and/or neurological courses, and viral persistence in some organs, including the central nervous system (CNS) and lymphoid tissues. An elucidation of the pathogenic mechanisms involved in canine distemper disease will lead to a better understanding of the injuries and clinical manifestations caused by CDV. Ultimately, further insight about this disease will enable the improvement of diagnostic methods as well as therapeutic studies.

Canine distemper virus infection in fennec fox (Vulpes zerda)

Fifteen 8-month-old fennec foxes imported from Sudan showed fever, mucopurulent ocular discharge, diarrhea, severe emaciation, seizures, and generalized ataxia, and died. Three of the 15 animals were presented for diagnostic investigation. Severe dehydration, brain congestion, and gastric ulcers were observed in all animals. In one animal, the lungs had failed to collapse and were multifocally dark red in appearance. Histopathologically, there were lymphohistiocytic meningoencephalitis with malacia, mild interstitial pneumonia, lymphoid depletion of lymphoid tissues and organs, and intestinal villous atrophy with intralesional coccidia. There were many intracytoplasmic and/or intranuclear inclusion bodies in the epithelial cells of the medullary velum, lungs, liver, kidneys, trachea, pancreas, stomach, gall bladder, urinary bladder, and ureters, and in macrophages of malacia foci and lymphocytes and macrophages of lymphoid organs. Additionally, intestinal coccidia were confirmed to be Isospora species by a fecal test. To our knowledge, this is the first report of canine distemper with intestinal coccidiosis in fennec fox.

Acute canine distemper encephalitis is associated with rapid neuronal loss and local immune activation

For most virus infections of the central nervous system (CNS), immune-mediated damage, the route of inoculation and death of infected cells all contribute to the pathology observed. To investigate the role of these factors in early canine distemper neuropathogenesis, we infected ferrets either intranasally or intraperitoneally with the neurovirulent canine distemper virus strain Snyder Hill. Regardless of the route of inoculation, the virus primarily targeted the olfactory bulb, brainstem, hippocampus and cerebellum, whereas only occasional foci were detected in the cortex. The infection led to widespread neuronal loss, which correlated with the clinical signs observed. Increased numbers of activated microglia, reactive gliosis and different pro-inflammatory cytokines were detected in the infected areas, suggesting that the presence and ultimate death of infected cells at early times after infection trigger strong local immune activation, despite the observed systemic immunosuppression.

Conserved leucine residue in the head region of morbillivirus fusion protein regulates the large conformational change during fusion activity

Paramyxovirus cell entry is controlled by the concerted action of two viral envelope glycoproteins, the fusion (F) and the receptor-binding (H) proteins, which together with a cell surface receptor mediate plasma membrane fusion activity. The paramyxovirus F protein belongs to class I viral fusion proteins which typically contain two heptad repeat regions (HR). Particular to paramyxovirus F proteins is a long intervening sequence (IS) located between both HR domains. To investigate the role of the IS domain in regulating fusogenicity, we mutated in the canine distemper virus (CDV) F protein IS domain a highly conserved leucine residue (L372) previously reported to cause a hyperfusogenic phenotype. Beside one F mutant, which elicited significant defects in processing, transport competence, and fusogenicity, all remaining mutants were characterized by enhanced fusion activity despite normal or slightly impaired processing and cell surface targeting. Using anti-CDV-F monoclonal antibodies, modified conformational F states were detected in F mutants compared to the parental protein. Despite these structural differences, coimmunoprecipitation assays did not reveal any drastic modulation in F/H avidity of interaction. However, we found that F mutants had significantly enhanced fusogenicity at low temperature only, suggesting that they folded into conformations requiring less energy to activate fusion. Together, these data provide strong biochemical and functional evidence that the conserved leucine 372 at the base of the HRA coiled-coil of F(wt) controls the stabilization of the prefusogenic state, restraining the conformational switch and thereby preventing extensive cell-cell fusion activity.

Neuropatologia da cinomose canina: 70 casos (2005-2008)

Este estudo teve como objetivo realizar uma investigação anátomo-patológica detalhada das lesões e sua distribuição no sistema nervoso central (SNC) de cães com cinomose. Foram avaliadas secções padronizadas do encéfalo e da medula espinhal de 70 cães. Os casos foram agrupados de acordo com a idade dos cães e classificados conforme a evolução das lesões. Os resultados permitem concluir que: (1) encefalomielite induzida pelo vírus da cinomose canina é mais prevalente em filhotes e adultos; (2) lesões macroscópicas no SNC ocorrem com baixa freqüência; (3) o encéfalo é mais acometido do que a medula espinhal; (4) as cinco regiões anatômicas mais afetadas do encéfalo são, em ordem decrescente de freqüência, o cerebelo, o diencéfalo, o lobo frontal, a ponte e o mesencéfalo; (5) a região anatômica mais afetada da medula espinhal é o segmento cervical cranial (C1-C5); (6) lesões subagudas e crônicas são mais comuns do que lesões agudas; (7) desmielinização é a lesão mais prevalente e ocorre principalmente no cerebelo, na ponte e no diencéfalo, quase sempre acompanhada de astrogliose e inflamação não-supurativa; (8) na maior parte dos casos em que há astrogliose, observam-se astrócitos gemistocíticos, freqüentemente com formação de sincícios; (9) leptomeningite não-supurativa, malacia e necrose cortical laminar são lesões relativamente freqüentes no encéfalo, mas não na medula espinhal; (10) corpúsculos de inclusão no encéfalo são muito comuns, ocorrem principalmente em astrócitos e com freqüência menor em neurônios; no entanto, independentemente da célula afetada, são vistos predominantemente no núcleo; (11) uma classificação da encefalite na cinomose com base em síndromes clínicas relacionadas com a idade do cão é imprecisa.

Pathogenesis and immunopathology of systemic and nervous canine distemper

Canine distemper is a worldwide occurring infectious disease of dogs, caused by a morbillivirus, closely related to measles and rinderpest virus. The natural host range comprises predominantly carnivores. Canine distemper virus (CDV), an enveloped, negative-sense RNA virus, infects different cell types, including epithelial, mesenchymal, neuroendocrine and hematopoietic cells of various organs and tissues. CDV infection of dogs is characterized by a systemic and/or nervous clinical course and viral persistence in selected organs including the central nervous system (CNS) and lymphoid tissue. Main manifestations include respiratory and gastrointestinal signs, immunosuppression and demyelinating leukoencephalomyelitis (DL). Impaired immune function, associated with depletion of lymphoid organs, consists of a viremia-associated loss of lymphocytes, especially of CD4+ T cells, due to lymphoid cell apoptosis in the early phase. After clearance of the virus from the peripheral blood an assumed diminished antigen presentation and altered lymphocyte maturation cause an ongoing immunosuppression despite repopulation of lymphoid organs. The early phase of DL is a sequel of a direct virus-mediated damage and infiltrating CD8+ cytotoxic T cells associated with an up-regulation of pro-inflammatory cytokines such as interleukin (IL)-6, IL-8, tumor necrosis factor (TNF)-alpha and IL-12 and a lacking response of immunomodulatory cytokines such as IL-10 and transforming growth factor (TGF)-beta. A CD4+-mediated delayed type hypersensitivity and cytotoxic CD8+ T cells contribute to myelin loss in the chronic phase. Additionally, up-regulation of interferon-gamma and IL-1 may occur in advanced lesions. Moreover, an altered balance between matrix metalloproteinases and their inhibitors seems to play a pivotal role for the pathogenesis of DL. Summarized, DL represents a biphasic disease process consisting of an initial direct virus-mediated process and immune-mediated plaque progression. Immunosuppression is due to early virus-mediated lymphocytolysis followed by still poorly understood mechanisms affecting antigen presentation and lymphocyte maturation.

Signal peptide and helical bundle domains of virulent canine distemper virus fusion protein restrict fusogenicity

Persistence in canine distemper virus (CDV) infection is correlated with very limited cell-cell fusion and lack of cytolysis induced by the neurovirulent A75/17-CDV compared to that of the cytolytic Onderstepoort vaccine strain. We have previously shown that this difference was at least in part due to the amino acid sequence of the fusion (F) protein (P. Plattet, J. P. Rivals, B. Zuber, J. M. Brunner, A. Zurbriggen, and R. Wittek, Virology 337:312-326, 2005). Here, we investigated the molecular mechanisms of the neurovirulent CDV F protein underlying limited membrane fusion activity. By exchanging the signal peptide between both F CDV strains or replacing it with an exogenous signal peptide, we demonstrated that this domain controlled intracellular and consequently cell surface protein expression, thus indirectly modulating fusogenicity. In addition, by serially passaging a poorly fusogenic virus and selecting a syncytium-forming variant, we identified the mutation L372W as being responsible for this change of phenotype. Intriguingly, residue L372 potentially is located in the helical bundle domain of the F(1) subunit. We showed that this mutation drastically increased fusion activity of F proteins of both CDV strains in a signal peptide-independent manner. Due to its unique structure even among morbilliviruses, our findings with respect to the signal peptide are likely to be specifically relevant to CDV, whereas the results related to the helical bundle add new insights to our growing understanding of this class of F proteins. We conclude that different mechanisms involving multiple domains of the neurovirulent A75/17-CDV F protein act in concert to limit fusion activity, preventing lysis of infected cells, which ultimately may favor viral persistence.

Involvement of morbilliviruses in the pathogenesis of demyelinating disease

Two members of the morbillivirus genus of the family Paramyxoviridae, canine distemper virus (CDV) and measles virus (MV), are well-known for their ability to cause a chronic demyelinating disease of the CNS in their natural hosts, dogs and humans, respectively. Both viruses have been studied for their potential involvement in the neuropathogenesis of the human demyelinating disease multiple sclerosis (MS). Recently, three new members of the morbillivirus genus, phocine distemper virus (PDV), porpoise morbillivirus (PMV) and dolphin morbillivirus (DMV), have been discovered. These viruses have also been shown to induce multifocal demyelinating disease in infected animals. This review focuses on morbillivirus-induced neuropathologies with emphasis on aetiopathogenesis of CNS demyelination. The possible involvement of a morbillivirus in the pathogenesis of multiple sclerosis is discussed.

Canine distemper virus infection of primary hippocampal cells induces increase in extracellular glutamate and neurodegeneration

The canine distemper virus (CDV) belongs to the Morbillivirus genus which includes important human pathogens like the closely related measles virus. CDV infection can reach the nervous system where it causes serious malfunctions. Although this pathology is well described, the molecular events in brain infection are still poorly understood. Here we studied infection in vitro by CDV using a model of dissociated cell cultures from newborn rat hippocampus. We used a recombinant CDV closely related to the neurovirulent A75/17 which also expresses the enhanced green fluorescent protein. We found that infected neurons and astrocytes could be clearly detected, and that infection spreads only slowly to neighboring cells. Interestingly, this infection causes a massive cell death of neurons, which includes also non-infected neurons. Antagonists of NMDA-type or alpha-amino-3-hydroxy-5-methylisoxazole-4-propinate (AMPA)-type glutamate receptors could slow down this neuron loss, indicating an involvement of the glutamatergic system in the induction of cell death in infected and non-infected cells. Finally, we show that, following CDV infection, there is a steady increase in extracellular glutamate in infected cultures. These results indicate that CDV infection induces excitotoxic insults on neurons via glutamatergic signaling.

Canine distemper virus uses both the anterograde and the hematogenous pathway for neuroinvasion

Canine distemper virus (CDV), a member of the Morbillivirus genus that also includes measles virus, frequently causes neurologic complications, but the routes and timing of CDV invasion of the central nervous system (CNS) are poorly understood. To characterize these events, we cloned and sequenced the genome of a neurovirulent CDV (strain A75/17) and produced an infectious cDNA that expresses the green fluorescent protein. This virus fully retained its virulence in ferrets: the course and signs of disease were equivalent to those of the parental isolate. We observed CNS invasion through two distinct pathways: anterogradely via the olfactory nerve and hematogenously through the choroid plexus and cerebral blood vessels. CNS invasion only occurred after massive infection of the lymphatic system and spread to the epithelial cells throughout the body. While at early time points, mostly immune and endothelial cells were infected, the virus later spread to glial cells and neurons. Together, the results suggest similarities in the timing, target cells, and CNS invasion routes of CDV, members of the Morbillivirus genus, and even other neurovirulent paramyxoviruses like Nipah and mumps viruses.

Adaptation of canine distemper virus to canine footpad keratinocytes modifies polymerase activity and fusogenicity through amino acid substitutions in the P/V/C and H proteins

The wild-type canine distemper virus (CDV) strain A75/17 induces a non-cytocidal infection in cultures of canine footpad keratinocytes (CFKs) but produces very little progeny virus. After only three passages in CFKs, the virus produced 100-fold more progeny and induced a limited cytopathic effect. Sequence analysis of the CFK-adapted virus revealed only three amino acid differences, of which one was located in each the P/V/C, M and H proteins. In order to assess which amino acid changes were responsible for the increase of infectious virus production and altered phenotype of infection, we generated a series of recombinant viruses. Their analysis showed that the altered P/V/C proteins were responsible for the higher levels of virus progeny formation and that the amino acid change in the cytoplasmic tail of the H protein was the major determinant of cytopathogenicity.

Cerebellum progesterone concentration decreased in canine distemper virus infection

Progesterone has neuroprotective effects including augmentation of myelination in the central and peripheral nervous system. This study was designed to determine if demyelinating lesions in the cerebellum resulting from canine distemper virus (CDV) infection are associated with progesterone levels. Progesterone was measured using radioimmunoassay in samples of the cerebellum, corpus callosum, medulla oblongata, parietal, frontal, temporal, and occipital cortices as well as cerebrospinal fluid (CSF) and plasma collected from ten CDV infected and six non-infected dogs. The cerebellum progesterone level was significantly different between CDV infected (0.66+/-0.09 ng/g) and control dogs (1.14+/-0.09 ng/g) (p<0.001); however, no difference was observed for the other CNS regions, plasma and CSF (p>0.05). The cerebellum progesterone level was also significantly different between acute (0.71+/-0.0 5 ng/g) and chronic cases (0.61+/-0.09 ng/g) (p<0.05). The CDV infected cerebella were also categorized histopathologically according to the severity of demyelinating lesions as mild (n=5), moderate (n=2), or severe (n=3) among which the cerebellum progesterone level was significantly different (p<0.05). Progesterone concentration was 0.71+/-0.05 ng/g in mild, 0.65+/-0.10 ng/g in moderate, and 0.56+/-0.07 ng/g in severe cases. In conclusion, progesterone concentration decreases in the cerebellum in CDV infection and the severity of demyelinating lesions is the greatest in cerebella with the lowest progesterone concentrations. The results suggest that local impairment of progesterone metabolism may be associated with the initiation and progression of cerebellar lesions in CDV infection.

Immunohistochemical investigation of cerebellum in dogs infected with canine distemper virus

The cerebella of 21 dogs with canine distemper virus (CDV) infection and four normal dogs were examined histopathologically and immunohistochemically. Cerebella of CDV-infected dogs showed nonsuppurative demyelinating encephalomyelitis, classified as acute, subacute or chronic. Immunolocalisation of CDV antigen also confirmed the infection. Tissues were examined for co-localisation of the CDV antigen with either an astrocyte-specific marker, glial fibrillary acidic protein (GFAP), or an oligodendrocyte-specific marker, galactocerebroside (GalC). Immunoreactive cells were counted in demyelinating areas of the white matter. The number of astrocytes (GFAP positive) was significantly (p < 0.05) higher in CDV-infected dogs compared to controls. In contrast, the number of oligodendrocytes (GalC positive) was significantly (p < 0.001) lower in CDV-infected dogs and was much lower in chronic cases (p < 0.05). Approximately 41% of astrocytes and 17% of oligodendrocytes were immunoreactive for CDV. The ratio of CDV-infected oligodendrocytes and astrocytes remained almost constant during the progression of the disease (P > 0.05). In conclusion, CDV infects both astrocytes and oligodendrocytes. The gradual loss of oligodendrocytes is most likely responsible for the progressive demyelination in CDV infection. Astrocytosis in CDV infection should be further investigated if it occurs to stimulate oligodendrocytes for myelin production to compensate for the loss or to induce oligodendrocyte degeneration.

Apoptosis in the cerebellum of dogs with distemper

Canine distemper virus (CDV) may induce multifocal demyelination in the central nervous system of infected dogs. The pathogenesis of this process is not clear. The present work identifies the presence of apoptotic cells in white and grey matter of dogs'cerebellum, naturally infected with CDV. Fifteen dogs with clinical signs of canine distemper that tested positive for CDV nucleoprotein were used. Brain specimens were processed and embedded in paraffin. Sections 5 microm thick were stained with hematoxylin-eosin and Shorr. Other sections were submitted to TUNEL reaction and to immunohistochemistry for CDV nucleoprotein detection. Acute and chronic demyelinated plaques were observed in the white matter, while apoptosis occurred particularly in the granular layer of grey matter. Apoptosis seems to play an important role in the pathogenesis of canine distemper demyelination.

Canine distemper, a re-emerging morbillivirus with complex neuropathogenic mechanisms

Paramyxoviruses are responsible for a wide variety of diseases both in humans and in animals. Common to many paramyxoviruses is the fact that they can cause neurological symptoms in their final host. Newly discovered paramyxoviruses, such as the Hendra and Nipah viruses, show the same pattern of pathogenesis as that of the paramyxoviruses already known. Canine distemper virus (CDV) is a well-studied member of the genus Morbillivirus. Study of the neuropathogenesis of CDV might give insight into disease mechanisms and suggest approaches for the prevention of other recently discovered paramyxovirus infections.

Distribution of 3beta-hydroxysteroid dehydrogenase in the cerebellum in canine distemper virus infection

The cerebella of eight dogs naturally infected with canine distemper virus (CDV) and two normal dogs were examined immunohistochemically for glial fibrillary acidic protein (GFAP) and 3beta-hydroxysteroid dehydrogenase (3beta-HSD). The clinical diagnosis of canine distemper was confirmed histopathologically and by the immunohistochemical demonstration of CDV antigen. In all dogs (healthy and infected), the Purkinje cells of the cerebellum were immunolabelled for 3beta-HSD activity. In infected dogs, 3beta-HSD labelling was prominent in astrocytes (particularly in areas of astrocytosis) whereas in healthy dogs such immunolabelling was weak. Double immunolabelling demonstrated that all GFAP-positive cells (especially in demyelinating areas) were also positive for 3beta-HSD. The results suggest that 3beta-HSD expression by astrocytes is associated with demyelination in CDV infection.

Measles virus-induced disruption of the glial-fibrillary-acidic protein cytoskeleton in an astrocytoma cell line (U-251)

A recombinant measles virus which expresses enhanced green fluorescent protein (MVeGFP) has been used to infect two astrocytoma cell lines (GCCM and U-251) to study the effect of virus infection on the cytoskeleton. Indirect immunocytochemistry was used to demonstrate the cellular localization of the cytoskeletal components. Enhanced green fluorescent protein autofluorescence was used to identify measles virus-infected cells. No alteration of the actin, tubulin, or vimentin components of the cytoskeleton was observed in either cell type, whereas a disruption of the glial-fibrillary-acidic protein filament (GFAP) network was noted in MVeGFP-infected U-251 cells. The relative amounts of GFAP present in infected and uninfected U-251 cells were quantified by image analysis of data sets obtained by confocal microscopy by using vimentin, another intermediate filament on which MVeGFP has no effect, as a control.

Sequence analysis and expression of the attachment and fusion proteins of canine distemper virus wild-type strain A75/17

The biological properties of wild-type A75/17 and cell culture-adapted Onderstepoort canine distemper virus differ markedly. To learn more about the molecular basis for these differences, we have isolated and sequenced the protein-coding regions of the attachment and fusion proteins of wild-type canine distemper virus strain A75/17. In the attachment protein, a total of 57 amino acid differences were observed between the Onderstepoort strain and strain A75/17, and these were distributed evenly over the entire protein. Interestingly, the attachment protein of strain A75/17 contained an extension of three amino acids at the C terminus. Expression studies showed that the attachment protein of strain A75/17 had a higher apparent molecular mass than the attachment protein of the Onderstepoort strain, in both the presence and absence of tunicamycin. In the fusion protein, 60 amino acid differences were observed between the two strains, of which 44 were clustered in the much smaller F2 portion of the molecule. Significantly, the AUG that has been proposed as a translation initiation codon in the Onderstepoort strain is an AUA codon in strain A75/17. Detailed mutation analyses showed that both the first and second AUGs of strain A75/17 are the major translation initiation sites of the fusion protein. Similar analyses demonstrated that, also in the Onderstepoort strain, the first two AUGs are the translation initiation codons which contribute most to the generation of precursor molecules yielding the mature form of the fusion protein.

Clinical and electroencephalographic findings of inflammatory and infectious diseases of the central nervous system in dogs: a retrospective study

In the present study medical records of 97 dogs with inflammatory/infectious diseases of the central nervous system (CNS), including 26 dogs with a history of seizures, were retrospectively examined. The aims of the study were to analyse the incidence rate of seizures, to search for criteria to recognize specific inflammatory diseases and to determine how far electroencephalography may be useful in the early confirmation of encephalitis and encephalitis-associated seizures. The incidence rate of seizures in this dog population was 26.8%, and dogs with protozoal encephalitis had the highest rate. Signalment, history, extraneural and neurological signs including localization contributed only a little to a specific diagnosis. Surprisingly focal clinical signs were observed in two-thirds of the dogs. Either focal or multifocal clinical signs were related mainly to the forebrain in dogs with a history of seizures and to the brainstem in dogs without seizures. Cerebrospinal fluid (CSF) analyses were useful to separate encephalitis from other CNS diseases and to distinguish certain conditions from others in approximately half the cases. Electroencephalography (EEG) revealed two distinct patterns in 25 examined dogs with histopathologically confirmed disease entities, which were characterized by high voltage, slow activity (HVSA) with superimposed low voltage, fast activity (LVFA). These changes were consistent and no significant differences (P > 0.05) between dogs with and without seizures, nor between different disease entities, were noted. However, all the dogs with seizures had in addition a uniform paroxysmal EEG activity with a high voltage (mean = 106.3 microV), fast activity (mean = 8.5 Hz) pattern. Moreover in several dogs from the present study this pattern had a focal distribution despite the fact that clinically seizures appear generalized. Therefore it was concluded that EEG may be a very helpful diagnostic tool to confirm an early diagnosis of encephalitis and to separate potential seizure cases from those without seizures.

Distemper: not a new disease in lions and tigers

In light of recent canine distemper virus (CDV) epidemics, we set out to determine the historical significance of CDV infection in captive lions and tigers in Switzerland. The retrospective case material consisted of 42 lion and tiger necropsy cases from 1972 to 1992. Necropsy reports for all lions and tigers were reviewed. All existing paraffin tissues were immunohistochemically examined with a polyclonal antibody raised against CDV. The results for 19 of the 42 lions and tigers were classified as positive by immunohistochemistry; 23 results were negative or questionable. The results for four animals (three positive and one negative ) were further tested by in situ hybridization, and the results concurred with the immunohistochemistry findings. CDV infection of large cats is older and more widespread than previously thought. All large cats in captivity should be immunized even if canine distemper is not believed to be a problem for large cats in the area.

Diagnosis of inflammatory and infectious diseases of the central nervous system in dogs: a retrospective study

The medical records of 220 dogs with inflammatory/infectious diseases of the central nervous system (CNS) were retrospectively examined. The aims of the study were to determine if clinical and clinicopathologic data (not including biopsy or necropsy examination) could distinguish inflammatory CNS diseases from diseases of other types, and to search for criteria allowing differentiation of specific inflammatory diseases. The signalment, historical findings, extraneural and neurological signs, and the lesion site contributed marginally to a specific diagnosis. Multifocal signs were only noticed in one third of the dogs with inflammatory/infectious diseases. Particular neurological abnormalities were more frequent in certain diseases than in others (eg, myoclonus was frequent in dogs with distemper, but it was also found in those with other meningoencephalomyelitides). Hematologic findings contributed to the diagnosis in certain conditions (eg, canine distemper encephalitis, protozoal encephalomyelitis, steroid-responsive meningitis-arteritis). Cerebrospinal fluid examinations, including immunoglobulin G index and cytology were useful to separate meningoencephalomyelitides from the other CNS diseases and to distinguish certain conditions from others. In most cases a specific diagnosis depended on a combination of clinical signs and ancillary diagnostic aids. Still, a specific diagnosis remained very difficult, if not impossible, in at least one third of the dogs.

Studies on canine distemper virus persistence in the central nervous system

Chronic progressive demyelination in canine distemper virus (CDV) infection is associated with persistence of the virus in the nervous system. We studied persistence by examining expression of CDV mRNA corresponding to all genes of the virus as well as genomic CDV RNA in brain sections of dogs with acute and chronic demyelinating disease. All virus mRNAs were expressed in acute demyelinating lesions in a way similar to that seen in lymphoid tissues, the primary replication site of CDV. Their distribution corresponded very well with immunohistochemical detection of virus protein. In contrast, much more CDV mRNA than virus protein was found in gray matter areas suggesting that translation of CDV can be impaired in nervous distemper. Virus protein and RNA were cleared from chronic inflammatory demyelinating lesions. mRNA corresponding to the distal genes (F; H; L) of CDV disappeared first in inflammatory lesions for technical reasons associated with the particular mode of transcription of morbilliviruses. CDV RNA and protein persisted in chronically ill dogs in other areas of the CNS in which inflammation had not occurred. Our results suggest that persistence of CDV is favored by non-cytolytic spread of the virus and restricted infection of certain cells with reduced viral protein expression. Both tend to delay immune recognition of the virus.

The neurobiology of canine distemper virus infection

Canine distemper virus (CDV) invades the nervous system and replicates in neurons and glial cell of the white matter during a period of severe viral induced immunosuppression. Demyelination occurs in infected white matter areas in the absence of inflammation. The mechanism of demyelination is not apparent because there is no ultrastructural evidence of viral replication in the oligodendrocytes, the myelin producing cells. However, brain tissue culture studies have shown that oligodendrocytes support transcription of all CDV genes and later on degenerate, although no viral proteins can be found in these cells. It remains to be shown how such a restricted infection leads to demyelination. Concomitant with immunologic recovery during the further course of the disease, inflammation occurs in the demyelinating lesions with progression of the lesions in some animals. A series of experiments in vitro suggested that chronic demyelination is due to a bystander mechanism associated with the virus-induced immune response in which antibody dependent cell-mediated reactions play an important role. The progressive, or even relapsing, course of the disease is associated with viral persistence in the nervous system. Persistence of CDV in the brain appears to be due to non-cytolytic selective spread of the virus with very limited budding. In this way CDV escaped immune surveillance.

Pathogenesis of virus-induced demyelination

Demyelination is a component of several viral diseases of humans. The best known of these are subacute sclerosing panencephalitis (SSPE) and progressive multifocal leukoencephalopathy (PML). There are a number of naturally occurring virus infections of animals that involve demyelination and many of these serve as instructive models for human demyelinating diseases. In addition to the naturally occurring diseases, many viruses have been shown to be capable of producing demyelination in experimental situations. In discussing virus-associated demyelinating disease, the chapter reviews the architecture and functional organization of the CNS and considers what is known of the interaction of viruses with CNS cells. It also discusses the immunology of the CNS that differs in several important aspects from that of the rest of the body. Experimental models of viral-induced demyelination have also been considered. Viruses capable of producing demyelinating disease have no common taxonomic features; they include both DNA and RNA viruses, enveloped and nonenveloped viruses. The chapter attempts to summarize the important factors influencing viral demyelination, their common features, and possible mechanisms.

Canine distemper virus increases procoagulant activity of macrophages

Inflammatory demyelination in canine distemper has been proposed to be due to a "bystander" mechanism, in which macrophages play an important role. In the present work we studied whether infection of macrophages by canine distemper virus (CDV) results in changes of macrophage functions, including Fc receptor-dependent and -independent phagocytosis, release of reactive oxygen species (ROS), and procoagulant activity (PCA). As a source of macrophages, dog bone marrow cells were seeded in teflon bags and grown for 1-2 weeks, at which time a marked enrichment of macrophages was noted. These cells were infected with the A75/17 strain of CDV. We could not detect any significant difference between uninfected and CDV-infected macrophages with respect to Fc receptor-dependent or -independent phagocytosis or with respect to the release of ROS. However, from Day 4 p.i. to the end of our observation period (10 days p.i.), PCA was up to 10-fold higher in CDV-infected unstimulated macrophage cultures than in uninfected unstimulated cultures of the same age. Increase in PCA was not due to the inoculation procedure by itself nor to components of the inoculum other than CDV; in particular, PCA was not due to contaminating endotoxin. Thus, several important macrophage functions do not appear to be impaired by CDV infection. The marked increase of macrophage PCA expression suggests that certain macrophage functions may even be enhanced as a result of infection. Such macrophage activation might contribute to the pathogenesis of the disease.

Canine distemper virus-immune complexes induce bystander degeneration of oligodendrocytes

Demyelination in chronic canine distemper encephalitis may be the result of a bystander effect in which the antiviral immune response is involved. In the present report we demonstrate that canine distemper virus-antiviral antibody immune complexes induce oligodendroglial degeneration in mixed brain cell cultures, particularly at the level of the cell processes. The involvement of macrophages as effector cells in this process was confirmed by depletion of these cells from the cultures which prevented the immune complex-mediated oligodendroglial degeneration. Canine distemper virus-immune complex-induced oligodendroglial pathology is thought to be mediated by toxic factors released from stimulated macrophages, this bystander effect demonstrated here in vitro may be relevant to the mechanisms of demyelination in vivo, in which virus persistence plays an important role.

Viral expression in experimental canine distemper demyelinating encephalitis

We have characterized the relationship between the expression of canine distemper virus (CDV) and demyelinating lesions in the white matter of the cerebellum of experimentally infected dogs. In animals which had demyelinating lesions, CDV proteins (N, P, F and H) were expressed and infectious virus could be recovered from brain tissue. Viral proteins (N, P, F and H) were detected by monoclonal antibodies and immunocytochemistry within demyelinating lesions as well as in scattered glial cells in areas of the white matter which lacked detectable lesions. Many cell types, including astrocytes, neurons, ependymal cells, choroid plexus cells, meningeal cells and perivascular inflammatory cells were labelled for viral antigen. We conclude from our results that the mechanism of demyelination in canine distemper virus-induced encephalitis involves expression of viral gene products at the lesion site.

Ultrastructural and biochemical findings in brain cell cultures infected with canine distemper virus

To study the pathomechanism of demyelination in canine distemper (CD), dog brain cell cultures were infected with virulent A75/17-CD virus (CDV) and examined ultrastructurally. Special attention was paid to the oligodendrocytes, which were specifically immunolabelled. In addition, cerebroside sulfotransferase (CST), an enzyme specific for oligodendrocyte activity was assayed during the course of the infection. Infection and maturation as well as CDV-induced changes were found in astrocytes and brain macrophages. Infection of oligodendrocytes was rarely seen, although CST activity of the culture markedly decreased and vacuolar degeneration of these cells occurred, resulting in their complete disappearance. We concluded that the degeneration of oligodendrocytes and demyelination is not due to direct virus-oligodendrocyte interaction, but due to CDV-induced events in other glial cells.

Production of antibodies to canine distemper virus in chicken eggs for immunohistochemistry

The present study describes the application of egg yolk antibodies in immunohistochemistry. In order to obtain specific antibodies against canine distemper virus (CDV), chickens were immunized with attenuated virus. Distinct antibody titres in serum and yolk could be detected by means of a modified plaque/focus immunoassay (ELISA) two weeks after a second immunization. The lower concentrations in corresponding yolk globulin preparations are attributed to the loss of antibodies caused by the isolation procedure (dextran and ammonium sulfate precipitation). After verification of the antibody specificity by indirect immunofluorescence technique high titred globulin fractions were employed in immunohistochemistry using the Avidin-Biotin-Complex method. A specific and distinct immunostaining in formalin fixed and paraffin embedded brain sections of CDV-infected dogs was obtained. The advantages of egg yolk antibodies for immunological purposes are discussed in detail.

Antibody-induced generation of reactive oxygen radicals by brain macrophages in canine distemper encephalitis: a mechanism for bystander demyelination

The mechanism of inflammatory demyelination in canine distemper encephalitis (CDE) is uncertain but macrophages are thought to play an important effector role in this lesion. Serum and cerebrospinal fluid (CSF), containing anti-canine distemper virus and anti-myelin antibodies from dogs with CDE were tested for their ability to generate reactive oxygen species (ROS) in macrophages in primary dog brain cell cultures using a chemiluminescence (CL) assay. The majority of serum samples and several CSF samples from animals with inflammatory demyelination elicited a CL signal in infected dog brain cell cultures. In contrast, none of these samples induced a positive response in uninfected cultures which contained large numbers of myelin antigen-presenting cells, although defined anti-myelin antibodies lead to a marked secretion of ROS in this system. It was concluded that antiviral antibody-induced secretion of ROS, known to be highly toxic for brain tissue, may play an important role in white matter damage in inflammatory lesions supporting a previous hypothesis of bystander demyelination in CDE. No evidence was found for a similar antibody-dependent cellular cytotoxicity-like mechanism mediated by anti-myelin antibodies in CDE, which does not support the concept of autoimmunity in this disease.

Antiviral antibodies stimulate production of reactive oxygen species in cultured canine brain cells infected with canine distemper virus

Canine distemper is characterized mainly by respiratory, enteric, and nervous symptoms. Infection of the central nervous system results in demyelination, to which inflammation has been shown to contribute significantly. It has been proposed that macrophages play a major role as effector cells in this process. We report that cultured dog brain cells contain a population of macrophages capable of producing reactive oxygen species as measured by luminol-dependent chemiluminescence. In cultures infected with canine distemper virus, a burst of reactive oxygen is triggered by antiviral antibody. This response depends on the presence of viral antigens on the surfaces of infected cells and is mediated by the interaction of antigen-bound antibody with Fc receptors on the macrophages. Since there is no evidence in vitro or in vivo that oligodendrocytes, the cells forming myelin, are infected, our observation supports the hypothesis that "innocent bystander killing" is important in demyelination caused by canine distemper virus. Reactive oxygen species released from macrophages may contribute to destruction of myelin.

Histopathologic and immunocytochemical studies of distemper in seals

Thousands of harbor seals (Phoca vitulina) died in European seas during 1988. Respiratory distress and oculonasal discharge were common clinical signs. We necropsied 76 affected seals. The main necropsy finding was severe pneumonia. Microscopic lung changes were characterized by proliferation of type II pneumocytes, filling of alveolar lumina with serofibrinous exudate, leukocytes, and macrophages, and necrosis of bronchial and bronchiolar epithelium. Intracytoplasmic and intranuclear acidophilic inclusion bodies characteristic of morbillivirus infection were seen in bronchial and bronchiolar epithelial cells. Microscopic lesions of non-suppurative demyelinating encephalitis were seen in the brain. There was degeneration and necrosis of neurons, focal gliosis, perivascular cuffing, and patchy demyelination. Many neurons and astrocytes contained intracytoplasmic and intranuclear inclusions. Using an immunoperoxidase technique, we detected morbillivirus antigen in many tissues including lung, brain, spleen, and urinary bladder. The origin of the seal morbillivirus is unknown.

Naturally occurring canine distemper virus encephalitis: distribution and expression of viral polypeptides in nervous tissues

Formalin-fixed brain tissues from 16 dogs with naturally occurring canine distemper virus (CDV) infection were investigated immunohistochemically by a panel of eight monoclonal antibodies (mAb) directed against four structural CDV proteins. Three mAb recognizing different epitopes of the polymerase (P-1, P-2, P-3) protein, two clones identifying different epitopes on each, the nucleocapsid (NP-1, NP-2) and fusion (F-2, F-3) protein, and one mAb directed against the hemagglutinin (H-2) protein were used. The immunoreactivity of the clones was tested on formalin-fixed, paraffin-embedded Vero cells, which were lytically infected with the neurotropic R252 (R252-CDV) or the Onderstepoort (CDV/Ond) strain of CDV. Clones directed against the H-2 and F-3 epitope recognized CDV/Ond but not R252-CDV. The remaining six clones showed positive immunoreaction with both CDV strains. In vivo expression and distribution of the individual proteins and their epitopes varied substantially between animals and within lesions from the same animal. The NP-2 epitope showed positive immunostaining in all 16 cases. The P-2 epitope was demonstrated in 13, the NP-1 epitope in 12, the P-3 epitope in 9, and the P-1 epitope in 3 brains, but staining was severely reduced compared with the NP-2 epitope and restricted to areas with strong NP-2 expression. Immunostaining was prominent in early and subacute and reduced in chronic demyelinating lesions. mAb directed against the H and F protein showed no immunoreaction in diseased brains.