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Neurovirulence in mice of neural cell-adapted canine distemper virus.

Neurovirulence of the Onderstepoort strain of canine distemper virus (CDV) adapted to human neural cell lines was determined by the intracerebral inoculation of DDD mice at 3 and 5 weeks of age. Intensity of neurovirulence was estimated by histopathological changes in the central nervous system and clinical symptoms. The original virus propagated in Vero cells induced leptomeningoencephalitis, whereas neuroblastoma-adapted virus induced nerve cell degeneration and mild encephalitis with relatively low morbidity and fatality. In contrast, the viruses adapted to glioblastoma and oligodendroglioma caused high morbidity and fatality. The latter two viruses induced necrotizing encephalopathy including edema and hyperemia. In addition, the glioblastoma-adapted virus induced formation of giant cells. The oligodendroglioma-adapted virus caused demyelination and spongy state associated with degeneration of glial cells and axons. These observations are discussed in regard to a possible correlation between the neurovirulence of CDV in mice and its tropism for neural cells in vitro.

Aging↗

Characterization of canine distemper viruses adapted to human neural cells.

The biochemical characteristics of canine distemper virus (CDV) adapted to three human neural cells (glioblastoma, oligodendroglioma, and neuroblastoma cells) were compared with those of the unadapted original virus. The specific gravity of the virions and nucleocapsids of the original and the three adapted viruses were not different. The molecular weights of genomic RNA and messenger RNAs encoding H, F, P, and NP proteins of the adapted viruses as estimated by Northern blot hybridization were similar to those of the original virus. By T1-resistant oligonucleotide analysis of the genomic RNA, the glioblastoma- and the neuroblastoma-adapted viruses gave two more spots than the original virus; the oligodendroglioma-adapted virus had a pattern identical to that of the original virus. By two-dimensional gel electrophoresis of virion proteins, we found a difference in the isoelectric point of the viral envelope proteins H and F between the original and the adapted viruses. These results suggest that viral genomic changes occurred during adaptation, resulting in the alteration of viral envelope proteins.

Adaptation, Physiological↗

Reversion of neurovirulence and in vitro phenotype of neural cell-adapted canine distemper virus after passage in non-neural cells.

The stability of neurovirulence and in vitro phenotypes of canine distemper viruses adapted to neural cells was examined. Neurovirulence was estimated by the morbidity, mortality, and histopathological changes in the central nervous system of mice. After a single passage of the adapted viruses in Vero cells in which the unadapted virus had been passed, the neurovirulence of glioblastoma-adapted and oligodendroglioma-adapted viruses reverted completely to that of the unadapted virus. However, the neurovirulence of a neuroblastoma-adapted virus reverted partially. In vitro phenotypes such as the two-dimensional electrophoretic patterns of viral proteins and the cross-neutralization patterns also reverted to those of the unadapted virus. However, plaque sizes remained similar to those of the viruses adapted to neural cells.

Adaptation, Physiological↗

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.

Animals↗

In vivo and in vitro detection of canine distemper virus nucleoprotein gene with digoxigenin-labelled RNA, double-stranded DNA probes and oligonucleotides by in situ hybridization.

A single-stranded RNA, two double-stranded (ds) DNA probes and 10 oligonucleotides labelled with digoxigenin were comparatively evaluated for their usefulness to detect canine distemper virus (CDV) nucleoprotein RNA in in vitro infected Vero cells and in tissues of dogs with spontaneous CDV infection by in situ hybridization (ISH). In addition, results were compared to CDV nucleoprotein antigen distribution as demonstrated by immunohistochemistry. The RNA probe was derived from the virulent A75/17 strain, the DNA and oligonucleotide probes from the avirulent Onderstepoort strain of CDV. The two DNA probes were 287 and 126 base pairs long. For ISH, various factors including fixatives, proteolytic digestion, probe concentration, hybridization conditions and detection systems were compared. All probes were suitable for demonstration of CDV RNA in in vitro infected cells, regardless of the CDV strain employed. In vivo CDV nucleic acid was detected by RNA and the dsDNA probes. However, the probes varied substantially with respect to sensitivity and specificity. The CDV RNA probe was far superior in sensitivity when compared to the DNA probes. Furthermore, the shorter DNA probe displayed a higher sensitivity, indicating that length of the probe is an important parameter when selecting probes. Oligonucleotides displayed only rarely a positive signal and caused frequently hybridization signals in the nucleus, which where considered not specific for CDV. Summarized, the present study reveals that RNA probes are currently the most sensitive tool for detection of CDV RNA in tissues.

Animals↗

Dogs, distemper, and multiple sclerosis in the United States.

Geographic distribution of multiple sclerosis (MS) was defined by case/control ratios for state of pre-illness residence for US white male veterans "service-connected" for MS. The Veterinary Medical Data Program of the National Cancer Institute receives diagnostic information from most of the university veterinary medical centers in the US (and Canada). The Center for Disease Control had carried out a 2-year surveillance program for human bites by animals. State distributions for MS were compared with those for the proportion of admissions for canine distemper (CD), the ratio of CD cases to the human population, and human bites by dogs per unit of population. There was no evidence that any of the CD risk indices was positively correlated with that for MS. These results suggest that CD, exposure to dogs, or dog bites are unlikely to be involved in the etiology of MS.

Animals↗

Simultaneous use of contrasting fluorochromes to separate measles and canine distemper viruses in a common system.

Measles and canine distemper viruses were grown together in a Vero monkey kidney cell line. Each virus could be identified and individually titrated by using the color contrast produced by the reddish tetra-methyl rhodamine isothiocyanate-tagged antimeasles conjugate and the green fluorescein isothiocyanate-tagged antidistemper conjugate. Both blue light and green light were used for the excitation of the fluorochromes. Incident light was transmitted to the specimen by a vertical illuminator of the Ploem type.

Animals↗

Seroprevalence of canine distemper virus in cats.

A seroepidemiological survey of canine distemper virus (CDV) infection in Asian felids revealed that the prevalence of antibodies varied depending on region and, in some cases, exposure to dogs. The serologic pattern in cats with antibodies indicated that they had likely been exposed to field strains rather than typical CDV vaccine strains.

Animals↗

Biological properties of a canine distemper virus isolate associated with demyelinating encephalomyelitis.

A canine distemper virus (CDV), DESIGNATED R252, originally recovered from a dog with demyelinating encephalomyelitis was shown to reproduce this disease in gnotobiotic dogs with a high incidence as compared to other CDV strains, which produced an acute fatal infection. In this investigation, R252 was propagated for the first time in Vero cells and compared to two known strains of CDV, Snyder-Hill (SH) and Onderstepoort (Ond). The results of this study revealed that intracellular R252 accumulated more slowly than either SH or Ond. There was extensive destruction of Vero monolayers infected with either R252 or SH. Each virus induced the formation of intracytoplasmic and intranuclear inclusions. Ond infection resulted in minimal cytopathic changes and intracytoplasmic inclusions. Immunofluorescence studies indicated that the spread of R252 infection within the monolayers was intermediate between the rapidly spreading SH and slowly spreading Ond. R252-infected cells developed characteristic immunofluorescent cytoplasmic inclusions. Initially, each stained homogeneously and later appeared as a non fluorescent body surrounded by a fluorescent ring. This characteristic pattern of fluorescence was observed only infrequently in thelate stage of SH infection and was absent in Ond-infected cultures. Reciprocal neutralization studies indicated that the three strains are of one serotype. These findings suggest that R252-CDV has biological properties which differ from two other strains of CDV and which may have bearing upon the in vivo capability of this virus to produce demyelinating encephalomyelitis.

Animals↗

Autorosette formation of erythrocytes on peripheral blood mononuclear cells in dogs vaccinated with canine distemper live-virus vaccine.

A time course study of the peripheral blood leukocytes of dogs vaccinated with canine distemper live virus (a paramyxovirus) vaccines showed that autorosette-forming leukocytes appeared from day 3 to day 10 after vaccination. The number of these cells peaked at day 7 when as many as 35% of mononuclear cells formed rosettes with autologous erythrocytes. In contrast, in nonvaccinated dogs, only 0.6 +/- 0.3% (standard error of the mean) of mononuclear cells formed rosettes throughout the 2-week period.

Animals↗

Ultrastructural study of long-term canine distemper virus infection in tissue culture cells.

The morphogenesis of canine distemper virus was studied in Vero cell cultures for 43 days post-inoculation. Active replication of the virus was observed by electron microscopy and assay from 12 h after inoculation on, and peak production was observed on days 5, 14, and 22. From day 28 on, constant but smaller amounts of infectious virus were detected. Two ultrastructural types of intracytoplasmic nucleoprotein filaments were observed; although they first appeared at different times, their subsequent chronological patterns of development were similar. The cells apparently became free of virus by a mechanism of vacuolation. Intranuclear filaments were seen about day 11 and appeared to increase in number thereafter, whereas the infectious titer declined. Possible mechanisms of persistence are discussed in the light of these findings.

Animals↗

Macrophage Fc receptors control infectivity and neutralization of canine distemper virus-antibody complexes.

Dogs that are persistently infected or that become moribund after exposure to canine distemper virus (CDV) have antibody that neutralized CDV when tested in dog lung macrophage cultures but failed to neutralize CDV when tested in epithelial, fibroblastic, or lymphatic cells. The antibody attached to protein A and was found in the immunoglobulin G fraction. The antibody bound complement and lysed CDV-infected target cells. The neutralizing activity in macrophages could be abolished (i) by pepsin digestion and removal of Fc portions from the antibody, (ii) by blocking the Fc receptors of macrophages with heat-treated normal dog serum, and (iii) by binding of protein A to Fc portions of the antibody. It was concluded that attachment of the CDV-antibody complex to Fc receptors of macrophages was essential for virus neutralization. If this attachment was hindered, the CDV-antibody complex became infectious for macrophages. In contrast, serum from recovering dogs neutralized CDV when tested in epithelial, fibroblastic, or lymphatic cells as well as in macrophages.

Animals↗

Matrix genes of measles virus and canine distemper virus: cloning, nucleotide sequences, and deduced amino acid sequences.

The nucleotide sequences encoding the matrix (M) proteins of measles virus (MV) and canine distemper virus (CDV) were determined from cDNA clones containing these genes in their entirety. In both cases, single open reading frames specifying basic proteins of 335 amino acid residues were predicted from the nucleotide sequences. Both viral messages were composed of approximately 1,450 nucleotides and contained 400 nucleotides of presumptive noncoding sequences at their respective 3' ends. MV and CDV M-protein-coding regions were 67% homologous at the nucleotide level and 76% homologous at the amino acid level. Only chance homology was observed in the 400-nucleotide trailer sequences. Comparisons of the M protein sequences of MV and CDV with the sequence reported for Sendai virus (B. M. Blumberg, K. Rose, M. G. Simona, L. Roux, C. Giorgi, and D. Kolakofsky, J. Virol. 52:656-663; Y. Hidaka, T. Kanda, K. Iwasaki, A. Nomoto, T. Shioda, and H. Shibuta, Nucleic Acids Res. 12:7965-7973) indicated the greatest homology among these M proteins in the carboxyterminal third of the molecule. Secondary-structure analyses of this shared region indicated a structurally conserved, hydrophobic sequence which possibly interacted with the lipid bilayer.

Amino Acid Sequence↗

The hemagglutinin envelope protein of canine distemper virus (CDV) confers cell tropism as illustrated by CDV and measles virus complementation analysis.

Measles virus (MV) and canine distemper virus (CDV) are morbilliviruses that cause acute illnesses and several persistent central nervous system infections in humans and in dogs, respectively. Characteristically, the cytopathic effect of these viruses is the formation of syncytia in permissive cells. In this study, a vaccinia virus expression system was used to express MV and CDV hemagglutinin (HA) and fusion (F) envelope proteins. We found that cotransfecting F and HA genes of MV or F and HA genes of CDV resulted in extensive syncytium formation in permissive cells while transfecting either F or HA alone did not. Similar experiments with heterologous pairs of proteins, CDV-F with MV-HA or MV-F with CDV-HA, caused significant cell fusion in both cases. These results indicate that in this expression system, cell fusion requires both F and HA; however, the functions of these proteins are interchangeable between the two types of morbilliviruses. Human-mouse somatic hybrids were used to determine the human chromosome conferring susceptibility to either MV and CDV. Of the 12 hybrids screened, none were sensitive to MV. Two of the hybrids containing human chromosome 19 formed syncytia following CDV infection. In addition, these two hybrids underwent cell fusion when cotransfected with CDV-F and CDV-HA (but not MV-F and MV-HA) glycoproteins by using the vaccinia virus expression system. To discover the viral component responsible for cell specificity, complementation experiments coexpressing CDV-HA with MV-F or CDV-F with MV-HA in the CDV-sensitive hybrids were performed. We found that syncytia were formed only in the presence of CDV-HA. These results support the idea that the HA protein is responsible for cell tropism. Furthermore, while the F protein is necessary for the fusion process, it is interchangeable with the F protein from other morbilliviruses.

Animals↗

Canine distemper virus persistence in the nervous system is associated with noncytolytic selective virus spread.

Canine distemper virus (CDV), a negative-strand RNA morbillivirus, causes a progressive demyelinating disease in which virus persistence plays an essential role. The antiviral immune response leads to virus clearance in the inflammatory lesions. However, CDV can replicate and persist outside these inflammatory lesions within the brain. How CDV is capable of persisting in the presence of an effective antiviral immune response is poorly understood. In the present investigation, we studied several aspects of virus replication in primary dog brain cell cultures (DBCC), comparing an attenuated CDV strain and a virulent CDV strain. Confluent DBCC were infected with either virulent A75/17-CDV or attenuated Onderstepoort-CDV and monitored for 60 days. Persistence was not associated with defective virus production, because all mRNAs and corresponding proteins were continuously expressed in the noncytolytic infection. Quantitative measurements did not detect a difference between the two types of infection in the rate of virus transcription and protein synthesis at the level of the single cell. However, electron microscopy and virus titration experiments showed that in the persistent CDV infection virus budding is strongly limited compared with that of the attenuated virus. Morphometry and immunocytochemistry showed profound differences in the way the two viruses spread in the culture. The attenuated CDV spread randomly to immediately adjacent cells, whereas persistent CDV spread selectively to more-distant cells by way of cell processes. In conclusion, the present study supports a mechanism of CDV persistence through selective spread by way of cell processes, enabling virulent CDV to invade the central nervous system without the need of releasing much virus into the extracellular space.

Animals↗

Downregulation of endothelin receptor mRNA synthesis in C6 rat astrocytoma cells by persistent measles virus and canine distemper virus infections.

Persistent infections of C6 rat astrocytoma cells with measles (subacute sclerosing panencephalitis [SSPE]) virus (C6/SSPE cells) or canine distemper virus (C6/CDV cells) cause a loss of endothelin-1 (ET-1) binding to its specific receptors (ETRA type) and subsequent ET-1-induced Ca2+ signaling. It was the aim of this study to investigate the underlying mechanism of this phenomenon in more detail. By using an RNase protection assay, it was found that ETRA mRNA disappears, whereas other cellular mRNA species, e.g., beta-actin mRNA, were not influenced. The data show that the loss of the ET-1 signaling pathway in C6/SSPE and C6/CDV cells is due to a receptor downregulation at the transcriptional level.

Animals↗

CD9, a tetraspan transmembrane protein, renders cells susceptible to canine distemper virus.

Canine distemper virus (CDV), a lymphotropic and neurotropic negative-stranded RNA virus of the Morbillivirus genus, causes a life-threatening disease in several carnivores, including domestic dogs. To identify the cellular receptor(s) involved in the uptake of CDV by susceptible cells, we isolated a monoclonal antibody (MAb K41) which binds to the cell surface and inhibits the CDV infection of several cell lines from various species. Pretreatment of cells with MAb K41 reduces the number of infectious centers and the size of the syncytia. Using affinity chromatography with MAb K41, we purified from HeLa and Vero cell extracts a 26-kDa protein which contained the amino acid sequence TKDEPQRETLK of human CD9, a member of the tetraspan transmembrane or transmembrane 4 superfamily of cell surface proteins. Transfection of NIH 3T3 or MDBK cells with a CD9 expression plasmid rendered these cells permissive for viral infection and raised virus production by a factor of 10 to 100. The mechanism involved is still unclear, since we were unable to detect direct binding of CDV to CD9 by using immunoprecipitation and a virus overlay protein binding assay. These findings indicate that human CD9 and its homologs in other species are necessary factors for the uptake of CDV by target cells, the formation of syncytia, and the production of progeny virus.

3T3 Cells↗

Vaccination against canine distemper virus infection in infant ferrets with and without maternal antibody protection, using recombinant attenuated poxvirus vaccines.

Canine distemper virus (CDV) infection of ferrets is clinically and immunologically similar to measles, making this a useful model for the human disease. The model was used to determine if parenteral or mucosal immunization of infant ferrets at 3 and 6 weeks of age with attenuated vaccinia virus (NYVAC) or canarypox virus (ALVAC) vaccine strains expressing the CDV hemagglutinin (H) and fusion (F) protein genes (NYVAC-HF and ALVAC-HF) would induce serum neutralizing antibody and protect against challenge infection at 12 weeks of age. Ferrets without maternal antibody that were vaccinated parenterally with NYVAC-HF (n = 5) or ALVAC-HF (n = 4) developed significant neutralizing titers (log(10) inverse mean titer +/- standard deviation of 2.30 +/- 0.12 and 2.20 +/- 0.34, respectively) by the day of challenge, and all survived with no clinical or virologic evidence of infection. Ferrets without maternal antibody that were vaccinated intranasally (i.n.) developed lower neutralizing titers, with NYVAC-HF producing higher titers at challenge (1.11 +/- 0.57 versus 0.40 +/- 0.37, P = 0.02) and a better survival rate (6/7 versus 0/5, P = 0.008) than ALVAC-HF. Ferrets with maternal antibody that were vaccinated parenterally with NYVAC-HF (n = 7) and ALVAC-HF (n = 7) developed significantly higher antibody titers (1.64 +/- 0. 54 and 1.28 +/- 0.40, respectively) than did ferrets immunized with an attenuated CDV vaccine (0.46 +/- 0.59; n = 7) or the recombinant vectors expressing rabies glycoprotein (RG) (0.19 +/- 0.32; n = 8, P = 7 x 10(-6)). The NYVAC vaccine also protected against weight loss, and both the NYVAC and attenuated CDV vaccines protected against the development of some clinical signs of infection, although survival in each of the three vaccine groups was low (one of seven) and not significantly different from the RG controls (none of eight). Combined i.n.-parenteral immunization of ferrets with maternal antibody using NYVAC-HF (n = 9) produced higher titers (1.63 +/- 0. 25) than did i.n. immunization with NYVAC-HF (0.88 +/- 0.36; n = 9) and ALVAC-HF (0.61 +/- 0.43; n = 9, P = 3 x 10(-7)), and survival was also significantly better in the i.n.-parenteral group (3 of 9) than in the other HF-vaccinated animals (none of 18) or in controls immunized with RG (none of 5) (P = 0.0374). Multiple routes were not tested with the ALVAC vaccine. The results suggest that infant ferrets are less responsive to i.n. vaccination than are older ferrets and raises questions about the appropriateness of this route of immunization in infant ferrets or infants of other species.

Administration, Intranasal↗