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Vaccination of puppies with a lipid-formulated plasmid vaccine protects against a severe canine distemper virus challenge.

We assessed whether the formulation of a DNA vaccine expressing the canine distemper virus (CDV) hemagglutinin (HA) and fusion (F) immunogens with the cationic lipid DMRIE-DOPE could induce serological responses and protection against a severe CDV challenge in the dog. Although clear protection was observed in dogs vaccinated with formulated plasmids only limited CDV specific antibody titers were observed in protected dogs before challenge, suggesting that protection could be explained by cell-mediated immunity and/or by a strong antibody-based memory response (priming) triggered by the infectious challenge. The high level of protection achieved in this study, demonstrated that formulated DNA CDV vaccines can generate in dogs a level a protection comparable to conventional CDV vaccines.

Adjuvants, Immunologic↗

Epizootiological investigations of canine distemper virus in free-ranging carnivores from Germany.

Canine distemper virus (CDV) infects a broad range of carnivores. To assess whether wild carnivores may play a role in the epidemiology of CDV in domestic dogs in Germany, the seroprevalence of CDV was determined. In sera from red foxes (30 of 591 (5%)) and stone martens (2 of 10 (20%)) antiviral antibodies were detected using a neutralization assay, whereas sera of raccoons, two mink, one pine marten and one raccoon dog were negative. In foxes, there was a significantly higher prevalence in urban and suburban compared to rural regions. When testing lung and spleen tissue samples (fox, badger, stone marten, polecat, raccoon dog) 13 of 253 (5.1%) foxes, 2 of 13 (15.4%) stone martens and 2 of 6 (33%) badgers were virus positive using RT-PCR. Phylogenetic analysis based on partial sequences of the F gene revealed a distinct relatedness to canine CDV isolates. Together, the data support the concept of transmission of CDV between domestic dogs and wild carnivores.

Amino Acid Sequence↗

Contact rates between wild and domestic canids: no evidence of parvovirus or canine distemper virus in crab-eating foxes.

Evaluating the risk of disease spill-over from domestic dogs to wildlife depends on knowledge of inter-specific contact rates and/or exposure to aetiological agents in dog environments. Here, contact rates of crab-eating foxes (Cerdocyon thous) with sympatric domestic dog populations were measured over 25months in Amazon Brazil. Foxes and dogs were serologically and clinically monitored for exposure to canine parvovirus (CPV-2) and canine distemper virus (CDV), pathogens known to have caused wildlife population declines elsewhere. Twenty-two of 24 (92%) tagged foxes visited one or more houses in a median 2 (range 1-3) villages per night where dog densities ranged from 7.2 to 15.4 per km(2) (mean 9.5 per km(2)). Foxes spent an average 6.4% (0-40.3%) of their 10h nocturnal activity period in villages, the equivalent of 38m (range 0-242) per night. The rate of potential exposure to disease agents was thus high, though varied by 3 orders of magnitude for individual foxes. Overall, 46% of the fox population was responsible for 80% of all contacts. None of the 37 monitored foxes however showed serological or clinical evidence of infection with CPV-2 or CDV. Seroprevalences for CPV-2 and CDV antibodies in the local domestic dog population were 13% (3/23) and 9% (2/23), respectively, and 89% of 97 monitored pups born during the study presented clinical signs consistent with active CPV-2 infection (haemorrhagic diarrhoea, vomiting, rapid morbidity and emaciation). Although there was no evidence for infection with either virus in foxes, the high level of contact of foxes with peridomestic habitats suggests that the probability of potential spill-over infections from dogs to foxes is high.

Age Factors↗

Canine distemper of vaccine origin in European mink, Mustela lutreola--a case report.

Cases of canine distemper (CD) related to vaccination of exotic carnivores extend over three decades and have been described in at least nine different species. Our report describes a case of acute CD in a European mink, Mustela lutreola, vaccinated with live attenuated CD vaccine licensed for use in fur-farmed mink. The male mink died of an acute grey matter disease with an unusually long incubation period. A female vaccinated at the same time showed no obvious signs of illness. The diagnosis was confirmed by reverse transcriptase-polymerase chain reaction (RT-PCR) and by subsequent sequencing of the PCR products. The sequenced products of the virus isolated from the mink and of the vaccine batch showed 100% identity. This is the first report in which molecular methods were used to confirm that the disease was caused by the vaccine strain. Based on our findings, it is clearly evident that current CD vaccines cannot be safely used in exotic species.

Animals↗

Molecular analysis of the nucleocapsid protein of recent isolates of canine distemper virus in Japan.

We analyzed the molecular properties of the nucleocapsid protein (NP) of canine distemper viruses (CDV), isolated between 1992 and 1995 in Japan. Four CDV field isolates (Yanaka, Ueno, Hamamatsu, and Adachi strains) obtained were antigenically identical. Sequence analysis of entire region of the NP gene of a field isolate, the Yanaka strain, revealed that the NP gene contained 1683 nucleotides and was 93.2% homologous with a laboratory strain, the Onderstepoort strain. The deduced amino acid sequence contained 523 amino acids and was 95.2 and 99% homologous with those of the Onderstepoort and a virulent strain, A75/17 strain, respectively. Since most of the diversities in amino acid sequence occurred in two domains, at the N'- and the C'- termini, we further sequenced 3'-terminal regions of the remaining three field isolates. Based on the sequences, the new CDV isolates had one cluster that distinguished them from the laboratory strain.

Amino Acid Sequence↗

Epitopes and nuclear localization analyses of canine distemper virus nucleocapsid protein by expression of its deletion mutants.

A series of nucleocapsid protein (NP)-deleted genes of the Onderstepoort strain was constructed in order to locate antigenic regions of the NP of canine distemper virus. The expression of proteins from 5'-deleted NP genes was examined in COS-7 cells by indirect immunofluorescence assay using three monoclonal antibodies (MAbs), c-5, f-5 and h-6, and a rabbit serum against NP. These MAbs reacted with two regions of NP. Amino acid residues from 1 to 80, and 337-358, were necessary and sufficient for formation of the epitopes identified by MAbs f-5 and h-6, and c-5, respectively. The proteins translated from intact or 3'-deleted genes were found to be localized in the nuclei of COS-7 cells, whereas the proteins from the 5'-deleted genes were mainly detected in the cytoplasm. These results suggested that 80 amino acid residues at the N-terminus are required for transportation of NP into the nucleus.

Animals↗

Antigenic differences in the H proteins of canine distemper viruses.

Antigenic properties between new Japanese field isolates and vaccine strains of canine distemper virus (CDV) have been compared using four monoclonal antibodies (MAbs) (JD-5, JD-7, JD-11 and d-7) against the hemagglutinin (H) proteins of CDV. JD-5, JD-7 and JD-11 are newly established antibodies. Three MAbs, namely d-7, JD-5 and JD-11, reacted similarly to all the CDV strains examined. However, JD-7 reacted much more strongly with the vaccine strains and an old field isolate than the recent field isolates in immunofluorescence, radio immunoprecipitation and virus neutralization assays. These results indicate that an antigenic region in the H protein, concerned with neutralization and recognized by JD-7, has been altered in the recent field isolates.

Animals↗

Serological and demographic evidence for domestic dogs as a source of canine distemper virus infection for Serengeti wildlife.

Following an epidemic of canine distemper virus (CDV) in Serengeti lions in 1994, the role of domestic dogs in the epidemiology of the disease was investigated by serological and demographic analyses. From 1992 to 1994, data were collected from two domestic dog populations bordering the Serengeti National Park. Several lines of evidence indicated that patterns of CDV infection differed significantly between higher-density dog populations of Serengeti District to the west of the park and lower-density populations of Ngorongoro District to the south-east: (a) CDV age-seroprevalence patterns differed significantly between years in Ngorongoro District populations but not in Serengeti District populations; (b) CDV seropositive pups (<12 months of age) were detected in Ngorongoro District only in 1994, whereas a proportion of pups in Serengeti District were seropositive in each year of the study; (c) in Ngorongoro District, the proportion of deaths attributed to disease was significantly higher in 1994 than in 1993, whereas in Serengeti District, there was no significant difference in disease-related mortality between years; (d) in Ngorongoro District, significantly more CDV seronegative dogs than seropositive dogs died in 1994, whereas there was no difference in survival of CDV seropositives and seronegatives between years in Serengeti District. We concluded that, between 1992 and 1994, CDV persisted in higher-density dog populations of Serengeti District, but occurred only sporadically in lower-density Ngorongoro District populations. Data from Ngorongoro District are consistent with exposure of dogs to CDV in 1991 and 1994, but not in 1992 and 1993. These findings suggest that higher-density domestic dog populations to the west of the Serengeti National Park were a more likely source of CDV infection for wildlife during 1994 than lower-density pastoralist dogs to the south and east of the park.

Age Factors↗

Canine distemper virus--a morbillivirus in search of new hosts?

Canine distemper morbillivirus (CDV) induces a multisystemic, often fatal disease in a wide and seemingly expanding host range among the Carnivora. Several genotypes of an otherwise monotypic virus species co-circulate in a geographically restricted pattern. Interspecies transmissions frequently occur, often leading to devastating epizootics in highly susceptible or immunologically naive populations.

Animals↗

Establishment of a persistent mutant of canine distemper virus.

We produced a B95a lymphoid cell line persistently infected with canine distemper virus (CDV), in which virus-specific antigens were present in nearly 100% of cells without causing cytopathic effect. The virus recovered from this cell line was able to infect fresh B95a cells persistently, indicating that a persistent CDV was established.

Amino Acid Sequence↗

A canine distemper virus epidemic in Serengeti lions (Panthera leo).

Canine distemper virus (CDV) is thought to have caused several fatal epidemics in canids within the Serengeti-Mara ecosystem of East Africa, affecting silver-backed jackals (Canis mesomelas) and bat-eared foxes (Otocyon megalotis) in 1978 (ref. 1), and African wild dogs (Lycaon pictus) in 1991 (refs 2, 3). The large, closely monitored Serengeti lion population was not affected in these epidemics. However, an epidemic caused by a morbillivirus closely related to CDV emerged abruptly in the lion population of the Serengeti National Park, Tanzania, in early 1994, resulting in fatal neurological disease characterized by grand mal seizures and myoclonus; the lions that died had encephalitis and pneumonia. Here we report the identification of CDV from these lions, and the close phylogenetic relationship between CDV isolates from lions and domestic dogs. By August 1994, 85% of the Serengeti lion population had anti-CDV antibodies, and the epidemic spread north to lions in the Maasai Mara National reserve, Kenya, and uncounted hyaenas, bat-eared foxes, and leopards were also affected.

Amino Acid Sequence↗

Detection of IgM antibodies against a recombinant nucleocapsid protein of canine distemper virus in dog sera using a dot-blot assay.

A dot-blot assay for the detection of IgM antibodies (ABs) against canine distemper virus (CDV) in canine serum is described. The diagnostic potential of this technique was evaluated by analysing sera from three test groups: (i) specific pathogen-free (SPF) beagle dogs experimentally infected with virulent CDV; (ii) SPF dogs immunized with a combined vaccine containing CDV, and (iii) SPF dogs immunized with a CDV-free vaccine. As antigen for the dot-blot assay we used the recombinant nucleocapsid protein (N protein) of the virulent A75/17 CDV strain. All 12 dogs of group 1, infected with virulent CDV, showed detectable CDV-specific IgM levels in their serum. All dogs of group 2 were also positive for anti-CDV IgM after the first immunization with the CDV-containing vaccine. The four dogs immunized with a CDV-free vaccine (group iii) remained negative throughout the course of the experiment. From these results, we conclude that the IgM detection test, which requires only a single serum sample, is a useful method for diagnosing current or recent CDV infection in CDV-infected or CDV-immunized dogs under experimental conditions.

Animals↗

Canine distemper virus causes apoptosis of Vero cells.

Apoptosis of Vero cells infected with two canine distemper virus (CDV) vaccine strains was detected using TdT (terminal deoxynucleotidyl transferase)-mediated dUTP nick end-labelling (TUNEL), flow cytometric analysis, agarose gel electrophoresis and electron microscopy (EM). By TUNEL, apoptotic cells were found in CDV-Onderstepoort (CDV-Ond)-infected cells. DNA fragments isolated from infected cells were separated by agarose gel electrophoresis and a 'ladder' pattern appeared. EM observations demonstrated that the cells undergoing cytopathic effect (CPE) possessed morphological characteristics of apoptotic cells. Flow cytometric analysis indicated that CDV could induce apoptosis of Vero cells, but the percentages of the apoptotic cells were correlated with the CPE types. The strain showing the cell-rounding type of CPE produced a much higher percentage of apoptotic cells than CDV-Ond with the syncytium type of CPE (P < 0.01). It was concluded that CDV vaccine strains could induce apoptosis of Vero cells and the apoptosis was virus strain-dependent and cell-dependent. The mechanism remains to be studied.

Animals↗

Relation of clinical signs to pathological changes in 19 cases of canine distemper encephalomyelitis.

In an attempt to associate the clinical neurological syndromes with the neuropathological features of canine distemper (CD), 19 spontaneous cases with neurological involvement were examined, before and after euthanasia. Seventeen dogs were less than one year of age and all except two (89.4%) were unvaccinated against CD. Various extraneural signs associated with CD encephalomyelitis (CDE) were seen in 15 dogs. Generalized or localized myoclonus was the most common sign observed (13/19). Seventeen of the dogs presented with signs suggestive of one neuroanatomical location of lesions. Of these animals, seven had signs of cerebral, two of cerebellar, four of cervical, one of cervicothoracic, two of thoracolumbar and two of lumbosacral syndrome. The diagnosis of CD was confirmed immunohistochemically (detection of CD viral antigen), serologically (neutralizing serum antibody titre > or = 16) and histopathologically (CDV inclusion bodies, type of central nervous system lesions). An association of the neuroanatomical lesion location and the histopathological findings was noted in 14 out of 17 dogs (82.3%). Myoclonus could be attributed to lower motor neuron damage in eight out of 13 dogs (61.5%).

Animals↗

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.

Animals↗

Cell type-dependent cytokine expression after canine distemper virus infection.

Canine cells of different histogenesis were infected with the Onderstepoort strain of distemper virus (CDV) to study the effect of viral infection on cytokine production. Included were primary brain cells, dermal fibroblasts, and two cell lines, DH 82 cells (macrophage-like) and epithelial Madin-Darby canine kidney (MDCK) cells. All cultures produced infective virus. MDCK cells had the lowest percentage of CDV-antigen positive cells, and infection did not cause a significant increase of cell death. After infection, mRNA steady state levels of interleukin (IL)-1, IL-6, IL-8, IL-12, tumor necrosis factor-alpha (TNF), and transforming growth factor-beta (TGF) were analyzed using RT-PCR. IL-6 and TNF protein were assessed immunohistochemically. In general, CDV infection resulted in induction of pro-inflammatory cytokines. In primary brain and DH 82 cells, IL-1, IL-6, and TNF were induced, and IL-1 and TNF but not IL-6 were upregulated in dermal fibroblasts. In contrast, in MDCK cells IL-1 and TNF expression was similar in infected and noninfected cells, whereas IL-6 was not produced in either condition. In addition, cytokine induction correlated to the degree of level of CDV production, and therefore cytopathic effects are presumed to be due to a direct virus-mediated or cytokine-mediated process. These findings suggest that pro-inflammatory cytokines, namely IL-1, IL-6, and TNF, which might play an important role in CDV pathogenesis, are induced in a cell-specific manner.

Animals↗

A canine distemper model of virus-induced anergy.

For development of an animal model of virus-induced anergy, the effect of canine distemper virus (CDV) upon cell-mediated immunity in dogs was investigated. First, canine cutaneous reactions and in vitro lymphocyte responses to soluble protein antigens were characterized. Dogs immunized with picryl guinea pig albumin and with keyhole limpet hemocyanin (both in complete Freund's adjuvant) responded reproducibly to intracutaneous challenge with these antigens. Reactivity peaked in 20-40 days (maximal induration, 6-50 mm). Lymphocytes from these animals responded in vitro to stimulation with keyhole limpet hemocyanin or purified protein derivative. This stimulation was antigen-specific and was maximal on day 6 of culture. Infection with CDV depressed cutaneous reactivity and lymphocyte response in vitro to antigens and mitogens. This effect was transient in animals previously vaccinated with attenuated CDV; however, gnotobiotic puppies (susceptible to CDV) had prolonged depression of cell-mediated immunity and lymphopenia. Some of these animals developed neurologic symptoms and died. The findings indicate that CDV infection is a potentially useful model for study of virus-induced depression of T (thymus)-cell responses and support the hypothesis that there is more than one mechanism responsible for this phenomenon.

Animals↗

Age-related susceptibility to infection with canine distemper virus in gnotobiotic dogs.

The influence of age on the susceptibility of gnotobiotic dogs to infection with virulent canine distemper virus (R252-CDV) was studied. Of the dogs infected at less than one week of age, 85% died of acute encephalitis two to five weeks after infection. In contrast, only 28.5% of infected weanling and 33.3% of infected adult dogs died after receiving inoculations of R252-CDV. Furthermore, about one-half of the fatally infected weanling dogs developed chronic encephalitis characterized by infiltration of lymphocytes and plasma cells in areas where demyelination of the central nervous system had occurred. Age-related susceptibility correlated with in vitro responses of peripheral blood lymphocytes to phytomitogens. The results of this study suggest that physiological immaturity of the immune system of neonatal dogs may account for their increased susceptibility to infection with CDV.

Acute Disease↗