Nucleotide and deduced amino acid sequences of the nucleocapsid protein of the virulent A75/17-CDV strain of canine distemper virus

Molecular and pathological screening of canine distemper virus in Asiatic lions, tigers, leopards, snow leopards, clouded leopards, leopard cats, jungle cats, civet cats, fishing cat, and jaguar of different states, India

The present investigation was conducted to rule out canine distemper (CD) diseases in Indian wild felids (Asiatic lions, tigers, leopards, snow leopards, clouded leopards, leopard cats, jungle cats, civet cats, fishing cat, and jaguar). The collected samples were screened for CD virus (CDV) by histopathology (HP), immunohistochemistry (IHC) and reverse transcriptase-polymerase chain reaction (RT-PCR) targeting H gene and N gene. The HP and IHC of suspected samples portrayed that 22 [11 leopards, 6 lions, 3 tigers, 1 snow leopard and 1 civet cat] out of 129 (17.05%) wild felids were positive for CD. The major pathological consequences were observed in spleen, lung, kidney and brain. The syncytia and intranuclear as well as intracytoplasmic eosinophilic inclusion bodies were seen in CDV infected cells. Although the histopathological lesions in spleen were more specific and consistent, however, the severe demyelinated leukoencephalitis (usually expected in CD infected dog) was not observed in the brain of any Indian wild felids. Conversely, the CDV antigen has been portrayed via IHC in pancreatic islets of Langerhans of tiger species for the first time in this study. Moreover, the concurrent CD and babesiosis has also been observed in a lioness without a usual coffee-coloured urine. The N gene and H gene of CDV isolates were amplified, sequenced and subsequently constructed the phylogenetic tree. The phylogenetic analysis of H gene revealed that the CDV isolates from Indian lion formed separate clade with CDV isolates from Indian dog and Indian palm civet cat. Furthermore, two CDV isolates from Indian tigers formed clade with Onderstepoort vaccine strain and CDV isolates from dogs of Uttar Pradesh, USA and UK. Evidently, CDV is circulating in Indian wild felids and causing diseases in them.

Comparison of Growth Characteristics and Genomics of Two Canine Distemper Virus Strains Isolated From Minks in China

Canine distemper (CD), caused by the CDV variant strain with H^I542N/Y549H, has become an epidemic in fur-bearing animals in China since 2012. To well understand the genomic and replicated characteristics of the CDV variants, we determined the viral growth kinetics and completed the genome sequences of two CDV strains, namely SDZC(17)M2 and LNDL(17)M4, isolated from CDV-infected minks from Shandong and Liaoning province in China, in 2017. SDZC(17)M2 showed higher viral titers and extensive syncytia in BHK-minkSLAM (BMS) cells than LNDL(17)M4. Although both two strains belong to the Asia-1 genotype and clustered an independent clade in the phylogenetic tree, SDZC(17)M2, harboring I542N/Y549H substitutions in the H protein, shared high identity (99.3–99.6% nt) with the other variant strains, whereas LNDL(17)M4, with the only Y549H substitution, shared a lower identity (97.7%–97.9% nt) with the other variant strains. Furthermore, a novel R223K substitution was identified in the conserved cleavage site (RRQRR → RRQKR) of the F protein in the SDZC(17)M2 strain. However, it which did not significantly affect the cell to cell fusion activity when combined with the CDV H/minkSLAM in BHK-21 cells. The key variations in the genome contributed to the virulence and the evolutionary trend need to be determined in the future.

Tropism and molecular pathogenesis of canine distemper virus

Background

Canine distemper virus (CDV), currently termed Canine morbillivirus, is an extremely contagious disease that affects dogs. It is identified as a multiple cell tropism pathogen, and its host range includes a vast array of species. As a member of Mononegavirales, CDV has a negative, single-stranded RNA genome, which encodes eight proteins.

Main body

Regarding the molecular pathogenesis, the hemagglutinin protein (H) plays a crucial role both in the antigenic recognition and the viral interaction with SLAM and nectin-4, the host cells’ receptors. These cellular receptors have been studied widely as CDV receptors in vitro in different cellular models. The SLAM receptor is located in lymphoid cells; therefore, the infection of these cells by CDV leads to immunosuppression, the severity of which can lead to variability in the clinical disease with the potential of secondary bacterial infection, up to and including the development of neurological signs in its later stage.

Conclusion

Improving the understanding of the CDV molecules implicated in the determination of infection, especially the H protein, can help to enhance the biochemical comprehension of the difference between a wide range of CDV variants, their tropism, and different steps in viral infection. The regions of interaction between the viral proteins and the identified host cell receptors have been elucidated to facilitate this understanding. Hence, this review describes the significant molecular and cellular characteristics of CDV that contribute to viral pathogenesis.

Electronic supplementary material

The online version of this article (10.1186/s12985-019-1136-6) contains supplementary material, which is available to authorized users.

Development of CDV-specific monoclonal antibodies for differentiation of variable epitopes of nucleocapsid protein

The highly contagious canine distemper viruses (CDVs) are still a major threat to a wide range of natural susceptible hosts. The nucleocapsid (N) protein plays various roles in the virus-induced immune response. But precise mapping of epitopes and antigenic variations in N protein of CDV are still scant. In this study, two monoclonal antibodies (MAbs), designated as F8N and G3N, against the N protein of CDV were generated and characterized. The epitopes recognized by the two MAbs were mapped by truncated N protein fragments expressed in E.coli based on western blotting. The 470ESRYDTQ476 and 385GITKEEAQL393 were identified as the minimal linear epitopes recognized by F8N and G3N, respectively. The amino acid residues of the epitope (385-393aa) were highly conserved in a variety of CDV strains from the databases as well as five CDV strains in this study, indicating that MAb G3N can detect various CDV strains. However, MAb F8N was found not to react with an older CDV 851 strain of the five CDV strains due to both of two amino substitution (S471P and Y473H) in the epitope, whereas either single mutant S471P or Y473H did not eliminate the binding of F8N. Further, the variable epitopes existed in the N protein of six CDV strains resembling CDV3 in phylogenic tree by alignment with sequences from the databases. This is the first record of a precise epitope affecting antigenity of N protein of CDV. These results may facilitate future investigations into the function of NP of CDV and diagnostic methods for CDV infection.

Identification of a novel linear B-cell epitope using a monoclonal antibody against the carboxy terminus of the canine distemper virus nucleoprotein and sequence analysis of the identified epitope in different CDV isolates

BACKGROUND

The Nucleoprotein (NP) is the most abundant and highly immunogenic protein in canine distemper virus (CDV), playing an important role in CDV viral replication and assembly.

RESULTS

In this study, a specific monoclonal antibody, named C8, was produced against the NP protein C terminal (amino acids 401-523). A linear N protein epitope was identified by subjecting a series of partially overlapping synthesized peptides to enzyme-linked immunosorbent assay (ELISA) analysis.The results indicated that ⁴⁴⁴GDKYPIHFNDER⁴⁵⁵ was the minimal linear epitope that could be recognized by mAb C8. Sequence alignments demonstrated that this linear epitope is less conserved among three CDV genotypes. We next analyzed the level of conservation of the defined epitope in19 Chinese CDV clinical isolates, and it has one site variation in amino acid among these CDV isolations. 2 isolates have the amino acid mutations F451L, while one has P448Ssubstitution.Phylogenetic analysis showed the two isolates with F451Lsubstitution had a closer relationship in a virulent strain ZJ-7, so the epitope may be a significant tag associated with virus virulence.

CONCLUSION

This collection of mAb along with defined linear epitope may provide useful reagents for investigations of NP protein function and the development of CDV specific diagnostics.

Development of recombinant nucleocapsid protein based IgM-ELISA for the early detection of distemper infection in dogs

An IgM-ELISA based on a 16-kDa recombinant protein produced for the conserved and functional middle region of nucleocapsid protein of Canine distemper virus was developed. Out of 70 serum samples from distemper-suspected and vaccinated dogs analyzed, 34 serum samples (49%) were positive. The specificity of this ELISA was confirmed by blocking and adsorption experiments. The IgM-ELISA based on the recombinant nucleocapsid protein showed a strong correlation (r=0.857, p<0.0001 at 95% CI) and good agreement (kappa=0.714) with the conventional Vero cell culture distemper antigen based IgM-ELISA. The percent positivity was more in dogs with systemic signs (62%) by recombinant nucleocapsid protein IgM-ELISA. Out of 70 clinical serum samples, 69 samples were used along with 4 control sera used in the IgM-ELISA for the detection of viral RNA by Slot blot hybridization and 26 of them (36%) were positive. Fifty-one percent agreement was observed between the recombinant nucleocapsid protein IgM-ELISA and Slot blot hybridization. The analysis of clinical history of the dogs with systemic signs supported the application of IgM-ELISA over Slot blot hybridization in the early detection of distemper infection.

Molecular analysis of the N gene of canine distemper virus in dogs in Brazil

Eleven central-nervous-system samples collected from stray dogs between 2000 and 2004 were found positive by RT-PCR, which amplified a 480bp fragment of the N gene of canine distemper virus (CDV). Phylogenetic analysis based on partial N-gene sequences showed four major clusters. All dog strains segregated into cluster I, with a mean nucleotide identity of 95.8% and 95.6% with the Onderstepoort and Lederle vaccine strains, respectively. Cluster II contained all the raccoon-related strains, cluster III Orient strains and Cluster IV the Onderstepoort and Lederle vaccine strains, with a mean nucleotide identity of 99.7% between them. This is the first report of phylogenetic analysis of CDV strains in Brazil.

Evaluation of ELISA based on the conserved and functional middle region of nucleocapsid protein to detect distemper infection in dogs

A 287bp fragment from the middle region of the nucleocapsid protein of canine distemper virus (CDV) was amplified from the conjunctival samples of distemper-infected dogs and was cloned into pRSET B vector. The recombinant protein was expressed as a 16-kDa-fusion protein with histidine tag in E. coli. Sera of distemper-infected and vaccinated dogs contained IgG antibodies against the purified recombinant protein as observed by enzyme linked immunosorbent assays (ELISA) and showed a strong correlation (r=0.882, p<0.0001 at 95% CI) and good agreement (kappa=0.718) with the conventional tissue culture viral antigen based ELISA. Further, the results of recombinant protein based ELISA and Western blotting with the sera from the infected and vaccinated dogs correlated well (kappa=0.8226). These findings recommend the use of the recombinant protein in the serodiagnosis of canine distemper virus infection in dogs.

Phylogenetic characterization of canine distemper viruses detected in naturally infected dogs in North America

In 2004, six puppies and one adult dog from a total of four premises were subjected to necropsy evaluation. For five of the seven dogs, disease caused by canine distemper virus (CDV) infection was suspected based on clinical signs. In all of the dogs, a diagnosis of CDV infection was established by the presence of compatible gross and histologic lesions, immunohistochemical labeling for CDV antigen, and detection of CDV RNA by reverse transcription-PCR. To further characterize the CDV strains detected in the four cases, complete gene sequences were determined for the hemagglutinin (H) and fusion (F) protein genes, while partial gene sequencing was performed for the phosphoprotein gene. A total of 4,508 bases were sequenced for the CDV strains detected from each of the four cases. Two cases were found to have identical sequences except for 2 bases in the intergenic region of the F and H genes. Phylogenetic analysis strongly suggested an evolutionary relationship between sequences detected in these two cases and those of phocine distemper virus 2 and two other strains of CDV not previously detected in the continental United States. Clear phylogenetic relationships were not established for viruses detected in the two additional cases; however, one strain showed similarity to CDV strains detected in a panda from China. Importantly, the three CDV strains detected were demonstrated to be genetically distinct from known vaccine strains and strains previously reported in the continental United States.

Nucleotide sequence analysis of nucleocapsid protein gene of canine distemper virus isolates in Thailand

The C-terminal part of the nucleocapsid protein gene of 13 canine distemper virus (CDV) isolates from Thailand, were analyzed. The nucleotide sequences were assigned to two clusters; cluster A exhibited a high degree of homology with the vaccine strain Onderstepoort, 99.10 and 97.61%, respectively, in the two isolates examined. Cluster B appeared closely related to virulent strains registered in the GeneBank database and to the virulent reference strain (A75/17); a total of 11 samples were analyzed, with 94.63-99.10% homology at the same position. The deduced amino acid sequences correlated with the two-nucleotide sequence clusters. However, there was no association among the CDV groups with histories of vaccination, sex, ages, clinical findings and evidence of viral antigen in tissues.

Early DNA vaccination of puppies against canine distemper in the presence of maternally derived immunity

Canine distemper (CD) is a disease in carnivores caused by CD virus (CDV), a member of the morbillivirus genus. It still is a threat to the carnivore and ferret population. The currently used modified attenuated live vaccines have several drawbacks of which lack of appropriate protection from severe infection is the most outstanding one. In addition, puppies up to the age of 6-8 weeks cannot be immunized efficiently due to the presence of maternal antibodies. In this study, a DNA prime modified live vaccine boost strategy was investigated in puppies in order to determine if vaccinated neonatal dogs induce a neutralizing immune response which is supposed to protect animals from a CDV challenge. Furthermore, a single DNA vaccination of puppies, 14 days after birth and in the presence of high titers of CDV neutralizing maternal antibodies, induced a clear and significant priming effect observed as early as 3 days after the subsequent booster with a conventional CDV vaccine. It was shown that the priming effect develops faster and to higher titers in puppies preimmunized with DNA 14 days after birth than in those vaccinated 28 days after birth. Our results demonstrate that despite the presence of maternal antibodies puppies can be vaccinated using the CDV DNA vaccine, and that this vaccination has a clear priming effect leading to a solid immune response after a booster with a conventional CDV vaccine.

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.

A canine distemper outbreak in Alaska: diagnosis and strain characterization using sequence analysis

Vaccination with modified-live vaccines has been very effective in reducing the incidence of canine distemper, a disease that can be devastating in unvaccinated populations. A diagnostic submission to the Animal Health Diagnostic Laboratory at Michigan State University, East Lansing, Michigan, involved a case in which several hundred dogs in an Alaskan town died in a suspected canine distemper outbreak. Cytoplasmic and intranuclear eosinophilic inclusion bodies, consistent with canine distemper virus (CDV) infection, were found in urinary bladder, spleen, lung, and salivary gland. Direct fluorescent antibody test gave results that could be considered positive for canine distemper. Because of the condition of the tissues received, the histopathology and fluorescent antibody-staining results were suggestive but not conclusive of CDV. In this study, immunohistochemistry, reverse transcriptase-polymerase chain reaction (RT-PCR), and DNA sequencing were used to confirm the presence of canine distemper virus in these tissues and to perform molecular characterization of the virus. Immunohistochemistry showed the presence of the virus in spleen, lung, and salivary gland. Viral RNA was detected by RT-PCR in brain, spleen, liver, lung, and kidney, both with nucleoprotein and phosphoprotein (P)-gene-specific primers. Sequence alignment and phylogenetic analysis of a 540-bp P-gene fragment of the Alaskan strain with corresponding sequences of 2 vaccine and 7 wild-type CDV strains showed that the virus responsible for the outbreak was closely related to a virulent strain of distemper virus from Siberia.

Detection and genetic characterization of canine distemper virus (CDV) from free-ranging red foxes in Italy

Fragments of the genes encoding the haemoagglutinin (H) and the nucleocapsid protein (N) of a canine distemper (CDV)-like virus affecting a red fox (Vulpes vulpes) were sequenced and analysed. The CDV-like virus detected in the fox was found to be not dissimilar, in both the H and N gene, from other CDVs spreading in Italy, as well as all over the world, and phylogenetic analysis on the H protein-encoding gene allowed to include all the Italian CDVs in the H European genotype.

DNA vaccine encoding nucleocapsid and surface proteins of wild type canine distemper virus protects its natural host against distemper

Canine distemper virus (CDV), a member of the genus Morbillivirus induces a highly infectious, frequently lethal disease in dogs and other carnivores. Current vaccines against canine distemper consisting of attenuated viruses have been in use for many years and have greatly reduced the incidence of distemper in the dog population. However, certain strains may not guarantee adequate protection and others can induce post vaccinal encephalitis. We tested a DNA vaccine for its ability to protect dogs, the natural host of CDV, against distemper. We constructed plasmids containing the nucleocapsid, the fusion, and the attachment protein genes of a virulent canine distemper virus strain. Mice inoculated with these plasmids developed humoral and cellular immune responses against CDV antigens. Dogs immunized with the expression plasmids developed virus-neutralizing antibodies. Significantly, vaccinated dogs were protected against challenge with virulent CDV, whereas unvaccinated animals succumbed to distemper.

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.

Neuropathological and aetiological studies of sporadic non-suppurative meningoencephalomyelitis of cattle

Sporadically occurring non-suppurative encephalitis appears to be a frequent condition of Swiss cattle. Fifty-one such cases diagnosed over a period of 10 years were examined retrospectively to investigate whether they constituted one or more distinct diseases, and to search for aetiological agents. Three cases were characterised by periventricular granulomatous encephalitis, and most probably represented a different disease, but the remaining 48 cases had disseminated non-suppurative encephalitis with widespread neuronal changes. Neuronal degeneration was very marked in the hippocampus of 10 cases and in the cerebellar Purkinje cells of 11. It was thought that the latter cases represented morphological variations of the same disease rather than a different disease because of their overlapping morphological features. The 48 cases had the following features in common: the disease had primarily neurological signs affecting mostly adult cattle, it was a sporadic condition, and there was a clear tendency for it to have a subacute to chronic course. Polymerase chain reaction (PCR) amplification for chlamydial DNA was negative except in one of 32 specimens, and immunohistochemistry did not demonstrate the presence of chlamydial antigens either in the one PCR-positive case or in the other cases examined. Immunohistochemistry for rabies virus, Borna disease virus, and central European tickborne encephalitis virus was negative. In four cases, immunolabelled cells were found in the lesions with antibodies against paramyxovirus antigens.

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.

Determinants of persistence in canine distemper viruses

Viral persistence in the central nervous system is the driving force behind the chronic progressive disease caused by natural canine distemper virus (CDV) infection in dogs. Persistence of CDV is associated with non-cytolytic spread and impaired viral budding. Since budding is to a large extend dependent on the nucleocapsid-(N) and matrixproteins (M) of the virus, we analyzed the nucleotide- and deduced amino acid sequences of the corresponding genes of a spectrum of CDV strains, that differ with respect to virulence and persistence in vivo and in vitro. The wild type CDV (A75/17), which is capable of causing a persistent infection in vivo was compared to two tissue culture adapted CDV strains (passaged A75/17-CDV and Rockborn-CDV), which CDV strains, that differ with respect to virulence and persistence in vivo and in vitro. The wild type CDV (A75/17), which is capable of causing a persistent infection in vivo was compared to two tissue culture adapted CDV strains (passaged A75/17-CDV and Rockborn-CDV), which retain a residual virulence and the capacity to spontaneously persist in vitro. A modified distemper virus (Snyder Hill-CDV), which is neurovirulent but not capable of causing a persistent infection in vivo, and an avianized virus (Onderstepoort-CDV) which is completely apathogenic and spreads by budding in cell cultures were also examined. Differences were found in the C-terminal of the nucleocapsid protein, which--comparing the two extremes of the spectrum (wild A75/17-CDV and OP-CDV)--lead to changes of the predicted protein structure. Such changes could affect the budding process and thus play a role in persistence. Marked changes in the M-gene were found in its non-coding region: the nucleotide sequences of the SH-CDV and OP-CDV differed considerably from the other three strains. Moreover, an additional second open reading frame was detected in the 'non-coding' region of the M gene in the wild A75-CDV, the two tissue culture adapted CDV strains and SH-CDV, but not in OP-CDV. The presence of this additional open reading frame correlated with the ability to cause a spontaneous persistent infection in vitro. Our findings support the notion that both N- and M-genes of CDV harbor determinants of viral persistence.

Detection of animal pathogens by using the polymerase chain reaction (PCR)

The polymerase chain reaction (PCR) is a nucleic acid-based technique that enables the rapid and sensitive detection of specific micro-organisms. Although this technique is widely used in veterinary research, it has not yet found applications in routine microbiological analysis of veterinary clinical samples. However, advances in sample preparation together with the increasing availability of specific gene sequences will probably lead to the more widespread diagnostic use of PCR in the future. PCR is likely to have a strong impact in the epidemiology, treatment and prevention of animal infectious diseases.