Pathological and phylogenetic features of prevalent canine distemper viruses in wild masked palm civets in Japan

Ten wild masked palm civets infected with canine distemper virus (CDV), captured in Japan from 2005 to 2007, were histopathologically and phylogenetically analyzed. Phylogenetic analysis based on the amino acid sequences of the H protein of two CDV isolates from masked palm civets revealed that the two isolates were classified into the clade of recent isolates in Japan. Histopathologically marked lesions of virus encephalitis were present in the brain, whereas gastrointestinal lesions were absent or at a mild degree. The distribution of the lesions resembles that of recent CDV cases in dogs. Therefore, recent CDV infections in masked palm civets could be caused by recently prevalent CDV in dogs. The possibility of the masked palm civet as a spreader of CDV among wildlife is also discussed.     

Genetic diversity of Hungarian canine distemper virus strains

To achieve proper diagnosis of dogs based on acute clinical symptoms and poorly preserved field samples taken from animals that died due to canine distemper (CD), a new differential diagnostic test has been developed based on polymerase chain reaction (PCR). In this study, more than 150 samples collected from dogs showing respiratory, gastrointestinal and neurological signs suggesting canine distemper virus (CDV) infection were examined. The samples consisted of urine, blood and nasal swabs collected from clinically ill patients, sent to our laboratory by clinicians from various veterinary clinics throughout Hungary. Various organs collected during the necropsy of dogs with pathological changes that suggested CDV infection were also included. Three distinct PCRs were designed. For diagnostic purposes, a primer pair specific to a 409 bases-long segment within the conservative part of the large polymerase region (L) of the CDV genome was designed. Using this test, out of the 150 analyzed samples, 46 (30.66%) proved to be positive for CDV, indicating that CDV still represents a high risk to the canine population in Hungary. For the phylogenetical analysis, a primer pair that completely encompasses the hemagglutinin (H) gene of the CDV genome was designed. The amplicons of this region were sequenced in both directions using the appropriate primers. Our results indicate that several different CDV genotypes are currently present in Hungary. Nine of the analyzed Hungarian strains turned out to belong to the so-called Arctic group of CDVs, and were most closely related to non-European strains from North America, China and Greenland, as well as to the phocine distemper virus 2 (PDV-2) isolated from Baikal seals (Phoca sibirica). One of the Hungarian strains showed high similarity to other European isolates from Denmark, Germany, Italy and Turkey, as well as to other isolates from geographically more distant regions, such as the USA. Three Hungarian strains seem to join a new cluster that is formed by only a couple of strains, one isolated from a mink in Denmark, and another from a dog in North America. Using a third set of primers, a restriction fragment length polymorphism (RFLP) assay has also been designed for the fast and reliable differentiation of the wild-type CDVs from the vaccine strains.     

Effect of vaccination with recombinant canine distemper virus vaccine immediately before exposure under shelter-like conditions

Vaccination with modified-live virus (MLV) canine distemper virus (CDV) vaccine has historically been recommended for animals in high-risk environments because of the rapid onset of immunity following vaccination. Recombinant CDV (rCDV) vaccine was deemed a suitable alternative to MLV-CDV vaccination in pet dogs, but insufficient data precluded its use where CDV was a serious threat to puppies, such as in shelters, kennels, and pet stores. In this study, dogs experimentally challenged hours after a single dose of rCDV or MLV vaccine became sick but recovered, whereas unvaccinated dogs became sick and died. Dogs vaccinated with a single dose of rCDV or MLV vaccine 1 week before being experimentally challenged remained healthy and showed no clinical signs. Dogs given one dose of rCDV vaccine hours before being placed in a CDV-contaminated environment did not become sick. These findings support the hypothesis that rCDV vaccine has a similar time-to-immunity as MLV-CDV vaccines and can likewise protect dogs in high-risk environments after one dose.     

Three-year rabies duration of immunity in dogs following vaccination with a core combination vaccine against canine distemper virus, canine adenovirus type-1, canine parvovirus, and rabies virus

Thirty-two seronegative pups were vaccinated at 8 weeks of age with modified-live canine distemper virus (CDV), canine adenovirus type-2 (CAV-2), and canine parvovirus (CPV) vaccine and at 12 weeks with a modified-live CDV, CAV-2, CPV, and killed rabies virus vaccine. An additional 31 seronegative pups served as age-matched, nonvaccinated controls. All test dogs were strictly isolated for 3 years after receiving the second vaccination and then were challenged with virulent rabies virus. Clinical signs of rabies were prevented in 28 (88%) of the 32 vaccinated dogs. In contrast, 97% (30 of 31) of the control dogs died of rabies infection. These study results indicated that no immunogenic interference occurred between the modified-live vaccine components and the killed rabies virus component. Furthermore, these results indicated that the rabies component in the test vaccine provided protection against virulent rabies challenge in dogs 12 weeks of age or older for a minimum of 3 years following vaccination.     

Three-year duration of immunity in dogs following vaccination against canine adenovirus type-1, canine parvovirus, and canine distemper virus

A challenge-of-immunity study was conducted to demonstrate immunity in dogs 3 years after their second vaccination with a new multivalent, modified-live vaccine containing canine adenovirus type 2 (CAV-2), canine parvovirus (CPV), and canine distemper virus (CDV). Twenty-three seronegative pups were vaccinated at 7 and 11 weeks of age. Eighteen seronegative pups, randomized into groups of six dogs, served as challenge controls. Dogs were kept in strict isolation for 3 years following the vaccination and then challenged sequentially with virulent canine adenovirus type 1 (CAV-1), CPV, and CDV. For each viral challenge, a separate group of six control dogs was also challenged. Clinical signs of CAV-1, CPV, and CDV infections were prevented in 100% of vaccinated dogs, demonstrating that the multivalent, modified-live test vaccine provided protection against virulent CAV-1, CPV, and CDV challenge in dogs 7 weeks of age or older for a minimum of 3 years following second vaccination.     

Anosmia associated with canine distemper

The sense of smell in dogs infected with canine distemper virus (CDV) was examined by use of EEG olfactometry, behavioral olfactometry, and electro-olfactography. Infection with CDV was confirmed by a direct immunofluorescence technique in 8 active cases and was suggested by clinical history compatible with canine distemper 10 to 26 weeks earlier in 6 cases. Pathologic alterations of the olfactory mucosa in 3 clinically affected dogs was examined by light microscopy. Infection with CDV was found to be associated with anosmia and lack of recorded responses on electro-olfactogram in 8 of 8 dogs with clinical signs of acute distemper from naturally acquired infections. Anosmia was found in 5 of 6 dogs that had recovered from acute distemper 10 to 26 weeks earlier. The sixth dog had hyposmia, with abnormalities on the electro-olfactogram. Histologic examination was not performed on the 6 dogs that had recovered. Histologic lesions observed at necropsy in 3 dogs that had had clinical signs of acute distemper were those of subacute purulent rhinitis and atrophy of the olfactory epithelium. Altered olfactory function could be explained by mucopurulent exudate blocking odors from olfactory receptors in the acutely affected dogs, but alteration of olfactory function in the dogs that had recovered without clinical evidence of rhinitis could not be explained.     

Immunohistochemical demonstration of canine distemper virus antigen as an aid in the diagnosis of canine distemper encephalomyelitis

Brain tissue from 33 dogs with non-suppurative encephalitis was examined for evidence of canine distemper virus (CDV) encephalitis. Sections were examined for lesions, inclusion bodies, syncytial cells and CDV antigen using a double bridge unlabelled antibody enzyme technique. Histopathological lesions considered to be typical of granulomatous meningoencephalomyelitis were found in seven dogs. They all lacked inclusion bodies, syncytial cells and CDV antigen. The remaining 26 dogs all had histopathological lesions typical of CDV encephalitis. Inclusion bodies were found in 24 dogs, four of which also had syncytial cells and CDV antigen was detected immunocytochemically in 25. One dog had no inclusion bodies or syncytial cells and was immunohistochemically negative. Syncytial cells have been found to be of limited diagnostic value for the diagnosis of CDV encephalitis. While inclusion bodies proved to be a good diagnostic criterion for the confirmation of CDV infection, the immunohistochemical demonstration of CDV antigen proved to be superior. CDV antigen was more prevalent than inclusion bodies in tissue sections and much more easily detectable.     

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)-α and IL-12 and a lacking response of immunomodulatory cytokines such as IL-10 and transforming growth factor (TGF)-β. A CD4+-mediated delayed type hypersensitivity and cytotoxic CD8+ T cells contribute to myelin loss in the chronic phase. Additionally, up-regulation of interferon-γ 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.     

An outbreak of canine distemper virus in tigers (Panthera tigris): possible transmission from wild animals to zoo animals

Canine distemper virus (CDV), a morbillivirus that causes one of the most contagious and lethal viral diseases known in canids, has an expanding host range, including wild animals. Since December 2009, several dead or dying wild raccoon dogs (Nyctereutes procyonoides) were found in and around one safari-style zoo in Japan, and CDV was isolated from four of these animals. In the subsequent months (January to February 2010), 12 tigers (Panthera tigris) in the zoo developed respiratory and gastrointestinal diseases, and CDV RNA was detected in fecal samples of the examined tigers. In March 2010, one of the tigers developed a neurological disorder and died; CDV was isolated from the lung of this animal. Sequence analysis of the complete hemagglutinin (H) gene and the signal peptide region of the fusion (F) gene showed high homology among these isolates (99.8-100%), indicating that CDV might have been transmitted from raccoon dog to tiger. In addition, these isolates belonged to genotype Asia-1 and had lower homology (<90%) to the vaccine strain (Onderstepoort). Seropositivity of lions (Panthera leo) in the zoo and wild bears (Ursus thibetanus) captured around this area supported the theory that a CDV epidemic had occurred in many mammal species in and around the zoo. These results indicate a risk of CDV transmission among many animal species, including large felids and endangered species.     

犬瘟热的诊断及其预防免疫的研究进展

本文对犬瘟热（CD）的诊断、预防免疫和免疫失败的影响因素及犬瘟热病毒（CDV）的宿主范围进行了综述。CDV不仅感染陆生食肉动物，而且也感染水生食肉动物，并且其宿主范围还在不断扩大。CDV感染主要采用病毒分离、特异性病毒抗原或特异性核酸检测等方法确诊。疫苗包括灭活的CDV疫苗、麻疹病毒（MV）异源苗及CDV弱毒活苗。疫苗接种犬的免疫反应主要取决于毒株特性及犬的应答能力，只有弱毒活苗能诱导产生持久而坚强的保护力。尽管多年来CDV弱毒活苗的使用控制了CD的发生，但最近免疫过的犬发生CD的病例并不少见。分析免疫失败的原因，主要是母源抗体干扰、疫苗质量差、其它病毒的免疫抑制以及CDV流行株可能发生了变异等因素的影响。     

The identification of frequent variations in the fusion protein of canine distemper virus

Canine distemper (CD) is a highly contagious disease with a worldwide distribution. Genetic diversity in genes encoding the haemagglutinin (H) and fusion (F) virus envelope proteins have been implicated in the increasing incidence of CD. Unlike the H gene, little is known about the genetic variability of the F gene in this virus. In the present study sequence analysis of the complete coding region of the F protein from CD virus isolates from Taiwan were carried out. Phylogenetic analysis demonstrated that the majority of isolates were similar to those found in neighbouring China and Japan, but were genetically distinct from vaccine strains. Remarkable variations were found scattered throughout the pre-peptide region (residues 1–135). The sequence identity of this region between locally sourced strains and between these strains and vaccine strains was 89% and 64 to 67%, respectively. Analysis suggested a novel strain of distant genetic lineage was present in dogs in the geographically isolated city of Hualien.     

Immunophenotypical characterization of monocytes in canine distemper virus infection

Canine distemper virus (CDV) infection induces multifocal demyelination in the central nervous system (CNS). It is thought that the resident macrophages of the CNS, the microglia, as well as invading monocytes associated with the inflammatory reaction may play a central role in the demyelinating process. To evaluate changes in peripheral monocytes in CDV infection their immunophenotype was characterized by flow cytometry during the course of an experimental CDV infection in dogs. The highest number of CDV-infected monocytes was found in dogs developing demyelinating lesions. In CD18, CD45, CD44, and CD14 neither up- nor down-regulation was observed. Marked up-regulation occurred in a number of surface molecules including CD1c, B7-1 and B7-2, MHC I, and CD11b. Peak expression was found at 4-5 weeks post-infection (PI), regardless of clinical outcome. All these molecules play an important role in the host's immune response, notably antigen presentation and cell adhesion. These results demonstrate that CDV infection in vivo may enhance several macrophage functions. This could lead to more effective clearance of the virus but may also increase demyelination through a bystander effect in animals that accumulated significant amounts of CDV in the CNS.     

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.     

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.     

Serologic response of domestic ferrets (Mustela putorius furo) to canine distemper and rabies virus vaccines

Nine unrelated 12-week-old naive domestic ferrets (Mustela putorius furo) were used to evaluate the serologic responses to commercial canine distemper virus (CDV) and rabies virus (RV) vaccines. Five of the ferrets (group 1) were inoculated 3 times at 2-week intervals with a multivalent modified-live virus vaccine of canine cell-line origin, containing CDV and an inactivated RV vaccine. Four of the ferrets (group 2) were inoculated once with the multivalent modified-live virus vaccine containing CDV and were not inoculated with the RV vaccine. Both group-1 and group-2 ferrets seroconverted to the CDV component of the vaccine. Group-1 ferrets also seroconverted after RV vaccination and maintained serum antibody titers to both CDV and RV for at least 7 months. Domestic ferret sera were found to have IgG epitopes similar to sera of domestic dogs and cats. Domestic ferret sera did not contain antibodies to feline coronavirus or FeLV antigens.     

A canine distemper virus seroprevalence study of dogs on three islands in the Torres Strait region,Australia

Canine distemper virus (CDV) can cause mortality in domestic dogs, which is easily prevented by the consistent application of vaccination protocols. The aim of this study was to determine if the dog populations of three strategically located islands in the Torres Strait of Australia, adjacent to Papua New Guinea, are infected by CDV. Eighty-four serum samples were collected from 70 dogs resident on Saibai, Dauan and Boigu Islands during 2017–2018. Sera were tested for CDV antibodies by a virus neutralization test (VNT). Overall, 7 (8.3%) sera from 6 (8.6%) dogs resident on all three islands were test positive. VNT titres ranged from 20 to >1280. Male adult dogs were more commonly seropositive than female and juvenile dogs. Considering the origin and age of test positive dogs, and veterinary visits to these islands, it was concluded that there is evidence of exposure to a field strain of CDV – rather than previous vaccination – in 4 of the 70 dogs (5.7%) tested in this study. Given the strategic location of these islands in a zone of high biosecurity risk, ongoing surveillance of pathogens such as CDV could inform on potential disease spread pathways in this region. In addition, the presence of high serological titres in the apparent absence of clinical disease requires further investigation.     

Sequence analysis of the genes encoding the phosphoprotein of recent isolates of canine distemper virus in Japan

The nucleotide sequences of the phosphoprotein (P) of canine distemper virus (CDV) strains isolated between 1992 and 1996 in Japan were determined. This is the first report of the complete sequences of the P genes of recently prevalent CDV strains. The deduced amino acid sequences of the P, C and V proteins showed that in the new Japanese isolates, these proteins have approximately 93%, 90-91% and 92% identities with those of the Onderstepoort vaccine strain, respectively. The predicted functional regions were conserved. RNA editing resulting in a shift to the open reading frame (ORF) of the V protein was shown to occur with the same efficiency in both the field isolates and vaccine strain.