First isolation and characterization of canine distemper virus in Vietnam with the immunohistochemical examination of the dog

Phylogenetic characterization of the canine distemper virus isolated from veterinary clinics in the Mekong Delta, Vietnam

Background and Aim

Canine distemper (CD) caused by the CD virus (CDV) has a high mortality rate that severely affects dog populations and other terrestrial carnivores worldwide. However, the genetics of CDV strains circulating in various regions in Vietnam, especially the Mekong Delta, remains unclear. This study aimed to characterize the molecular status of CDV strains circulating in the Mekong Delta, Vietnam.

Materials and Methods

Ocular/nasal swabs were collected from 550 dogs with clinically suspected CDV infection from veterinary clinics in three Vietnamese provinces. A reverse transcription-polymerase chain reaction on the part of the hemagglutinin gene was performed. A phylogenetic tree was constructed to analyze the relationship between the detected CDV and GenBank sequences.

Results

The molecular study demonstrated that 4.18% (23/550) of the dogs were positive for CDV. The clinical findings revealed that the positive dogs exhibited clinical signs of distemper. The phylogenetic analysis indicated that the identified CDV sequences were clustered in the same branch with the genotype Asia-1 and distantly related to the vaccine strains. Notably, the CDV sequences detected in this study were grouped with the sequences previously found in southeast Vietnam; however, they were distant from those found in the north.

Conclusion

The present study confirmed the presence of CDV and to the best of our knowledge, highlighted for the first time that the CDV strains circulating in the Mekong Delta of Vietnam belong to the genotype Asia-1.

Detection and genetic characterization of canine distemper virus isolated in civets in Vietnam

Canine distemper (CD), caused by the canine distemper virus (CDV), is a lethal systemic disease to a wide range of wild and domestic carnivorous hosts, including civets. In this study, a possible CD outbreak in a backyard farm with 32 diseased civets (Viverricula indica) in Hanoi, Vietnam, was investigated. The sick civets showed CD-like clinical signs such as anorexia, sedentary behavior, diarrhea, dermatitis, nasal, and footpad hyperkeratosis. Various tissue samples collected from the dead civets were utilized for molecular screening of CDV and histopathological examination. The genetic detection and characterization confirmed that samples collected from dead civets tested positive for CDV. The phylogenetic analysis based on the full-length H gene sequences indicated that all CDV strains isolated from civets belonged to the Asia-1 lineage and were closely related to the CDV strains previously reported from dogs in Thailand, China, and Vietnam. Histopathological examination showed severe interstitial pneumonia, hemorrhagic alveolar septa, necrotic alveolar epithelial cells, necrotic, degenerated, or lost Purkinje cells, eosinophilic intracytoplasmic inclusion bodies, edema, and perivascular cuff. This study confirmed the detection of CDV in civets for the first time in Vietnam.

Isolation and genetic characterization of canine distemper virus in domestic dogs from central and northern provinces in Vietnam

Canine distemper virus (CDV) is a pathogen causing fatal disease in a wide range of carnivores. Sequence analysis of CDV strains has been classified into several geographically-related lineages, and the evolution and emergence of these strains are not fully yet investigated. In this study, the complete H gene sequences of 15 CDV strains isolated on Vero DST cell culture from clinical samples of vaccinated domestic dogs in Vietnam were investigated. Fifteen CDV isolates belonging to Asia-1 CDV variants were predominant antigenic type circulated in Central and Northern Vietnam with notable differences regarding the region and some genetic variation, and the most closely related Asia-1 variants lineage reported in Vietnam, China, Taiwan, and Japan. All identified CDV isolates clustered into 2 novel clades Asia-1-C1 and Asia-1-C2. The major amino acid mutation variants of Vietnamese Asia-1 CDV strains were found at sites 51, 157, 159, 160, 171, 178, 186, 235, 245, 277, 288, 313, 324, 330, 337, 345, 358, 359, 365, 383, 446, 475, 517, 530, 584, 598 which include N-glycosylation sites and neutralizing epitope regions in H gene. The results of the virus neutralization titer (VNT) assay showed that the dogs vaccinated with commercial vaccines had significantly low VNT (4.89 and 12.8) against field CDV isolate strains (VNUA NA04, HN18, and NB05) isolated in northern and central Vietnam, respectively. These data may suggest the need for further research in CDV monitoring and development of preventative measures against CDV in Vietnam.

Measles vaccination: Threat from related veterinary viruses and need for continued vaccination post measles eradication

Measles virus (MV) is the only human virus within the morbillivirus genus of the Paramyxoviridae. The veterinary members are canine distemper virus (CDV), peste des petits ruminants virus (PPRV), Rinderpest Virus (RPV) as well as the marine morbilliviruses phocine distemper virus (PDV), dolphin morbillivirus (DMV) and porpoise morbillivirus (PMV). Morbilliviruses have a severe impact on humans and animal species. They confer diseases which have contributed to morbidity and mortality of the population on a global scale. There is substantial evidence from both natural and experimental infections that morbilliviruses can readily cross species barriers. Of most concern with regard to zoonosis is the more recently reported fatal infection of primates in Japan and China with strains of CDV which have adapted to this host. The close genetic relationship, shared cell entry receptors and similar pathogenesis between the morbilliviruses highlights the potential consequences of complete withdrawal of MV vaccination after eradication. Therefore, it would be prudent to continue the current MV vaccination. Ultimately development of novel, safe vaccines which have higher efficacy against the veterinary morbilliviruses is a priority. These would to protect the human population long term against the threat of zoonosis by these veterinary viruses.

Homologous recombination is a force in the evolution of canine distemper virus

Canine distemper virus (CDV) is the causative agent of canine distemper (CD) that is a highly contagious, lethal, multisystemic viral disease of receptive carnivores. The prevalence of CDV is a major concern in susceptible animals. Presently, it is unclear whether intragenic recombination can contribute to gene mutations and segment reassortment in the virus. In this study, 25 full-length CDV genome sequences were subjected to phylogenetic and recombinational analyses. The results of phylogenetic analysis, intragenic recombination, and nucleotide selection pressure indicated that mutation and recombination occurred in the six individual genes segment (H, F, P, N, L, M) of the CDV genome. The analysis also revealed pronounced genetic diversity in the CDV genome according to the geographically distinct lineages (genotypes), namely Asia-1, Asia-2, Asia-3, Europe, America-1, and America-2. The six recombination events were detected using SimPlot and RDP programs. The analysis of selection pressure demonstrated that a majority of the nucleotides in the CDV individual gene were under negative selection. Collectively, these data suggested that homologous recombination acts as a key force driving the genetic diversity and evolution of canine distemper virus.

Isolation and phylogenetic analysis of canine distemper virus among domestic dogs in Vietnam

Canine distemper virus (CDV) is one of the most serious pathogens found in many species of carnivores, including domestic dogs. In this study, hemagglutinin (H) genes were detected in five domestic Vietnamese dogs with diarrhea, and two CDVs were successfully isolated from dogs positive for H genes. The complete genome of one isolate, CDV/dog/HCM/33/140816, was determined. Phylogenetic analysis showed that all Vietnamese CDVs belonged to the Asia-1 genotype. In addition, the H proteins of Vietnamese CDV strains were the most homologous to those of Chinese CDVs (98.4% to 99.3% identity). These results indicated that the Asia-1 genotype of CDV was the predominant genotype circulating among the domestic dog population in Vietnam and that transboundary transmission of CDV has occurred between Vietnam and China.

The V protein of canine distemper virus is required for virus replication in human epithelial cells

Canine distemper virus (CDV) becomes able to use human receptors through a single amino acid substitution in the H protein. In addition, CDV strains possessing an intact C protein replicate well in human epithelial H358 cells. The present study showed that CDV strain 007Lm, which was isolated from lymph node tissue of a dog with distemper, failed to replicate in H358 cells, although it possessed an intact C protein. Sequence analyses suggested that a cysteine-to-tyrosine substitution at position 267 of the V protein caused this growth defect. Analyses using H358 cells constitutively expressing the CDV V protein showed that the V protein with a cysteine, but not that with a tyrosine, at this position effectively blocked the interferon-stimulated signal transduction pathway, and supported virus replication of 007Lm in H358 cells. Thus, the V protein as well as the C protein appears to be functional and essential for CDV replication in human epithelial cells.

Genotypic lineages and restriction fragment length polymorphism of canine distemper virus isolates in Thailand

Canine distemper virus (CDV) is known to cause multisystemic disease in all families of terrestrial carnivores. Attenuated live vaccines have been used to control CDV in a variety of species for many decades, yet a number of CDV infections in vaccinated dogs are still observed. The aims of this study were to investigate the genetic diversity of CDV lineages based on phosphoprotein (P), hemagglutinin (H) and fusion protein (F) genes and to develop the restriction fragment length polymorphism (RFLP) technique for effective differentiation among individual wild-type and vaccine lineages in Thailand. Four commercial vaccine products, thirteen conjunctival swabs and various tissues from 9 necropsied dogs suspected of having CDV infections were included. Virus isolation was performed using Vero cell expressing canine signaling lymphocyte activation molecules (Vero-DST cells). Reverse-transcription polymerase chain reaction (RT-PCR) on 3 gene regions from the dog derived specimens and the vaccines were carried out, then RFLP analysis upon F-gene amplified fragments was developed. Nucleotide sequence and phylogenetic analysis were compared with other CDV lineages in Genbank. Phylogenetic relationships revealed that CDV field isolates were separated from the vaccine lineage and could be divided into two clusters; one of which belonged to the Asia-1 lineage and another, not related to any previous recognized lineages was proposed as 'Asia-4'. RFLP patterns demonstrating concordance with phylogenetic trees of the distemper virus allowed for differentiation between the Asia-1, Asia-4 and vaccine lineages. Thus, RFLP technique is able to effectively distinguish individual wild-type canine distemper virus from vaccine lineages in Thailand.

Simultaneous detection of canine respiratory disease associated viruses by a multiplex reverse transcription-polymerase chain reaction assay

A multiplex reverse transcription polymerase chain reaction (mRT-PCR) assay was developed for the simultaneous detection of canine distemper virus (CDV), canine respiratory coronavirus (CRCoV) and canine influenza virus (CIV). These viral pathogens are all causative agents of canine infectious respiratory disease (CIRD). The sensitivity and specificity of the mRT-PCR were determined by comparing it to a rapid antigen test (RAT) or immuno-chromatography test kit and reverse transcription-polymerase chain reaction (RT-PCR) in the detection of CDV, CRCoV and CIV antigens present in 100 clinical samples (nasal swabs and whole blood samples) from 50 dogs with respiratory disease symptoms. This study revealed that mRT-PCR had almost exactly the same performance or results were almost 100% in agreement with that of RT-PCR and RAT both in terms of the assay sensitivity and specificity which was more highly evident in detecting CIV, CDV and CRCoV antigens present in canine nasal swab samples. Therefore, this assay could be a better alternative for the definitive and simultaneous ante-mortem detection of the three viral pathogens that cause CIRD by using nasal swabs.

Nectin4 is an epithelial cell receptor for canine distemper virus and involved in neurovirulence

Canine distemper virus (CDV) uses signaling lymphocyte activation molecule (SLAM), expressed on immune cells, as a receptor. However, epithelial and neural cells are also affected by CDV in vivo. Wild-type CDV strains showed efficient replication with syncytia in Vero cells expressing dog nectin4, and the infection was blocked by an anti-nectin4 antibody. In dogs with distemper, CDV antigen was preferentially detected in nectin4-positive neurons and epithelial cells, suggesting that nectin4 is an epithelial cell receptor for CDV and also involved in its neurovirulence.

Phylogenetic analysis of the haemagglutinin gene of canine distemper virus strains detected from breeding foxes, raccoon dogs and minks in China

Canine distemper virus (CDV) infects a variety of carnivores, including wild and domestic Canidae. Genetic/antigenic heterogeneity has been observed among the various CDV strains, notably in the haemagglutinin (H) gene, that appears as a good target to gather epidemiological information. Based on sequence analysis of the H gene, wild-type CDV strains cluster into distinct geographic lineages (genotypes), irrespective of the species of isolation. The sequence of the H gene of 28 CDV strains detected from both vaccinated and non-vaccinated breeding foxes, raccoon dogs and minks from different geographical areas of China during the years 2004-2008 was determined. All the CDV strains but two (strains HL and HLJ2) were characterized as Asia-1 genotype and were highly similar to each other (96.2-99.7% at the amino acid [aa] level) and to other Asia-1 strains (96.1-99.5% aa) previously detected in China. The CDV strains HL and HLJ2 were both collected from foxes in Heilongjiang province in 2005. Strain HL resembled CDVs of the Arctic genotype (GR88-like) and displayed high aa identity (98.0%) to the Chinese canine strain Liu. By converse, strain HLJ2 was barely related to CDVs of the Asia-2 genotype (88.7-90.3% aa identity), and could represent a novel CDV genotype, tentatively proposed as Asia-3. These results suggest that at least three different CDV genotypes, distantly related (81.8-91.6% aa identity) to the vaccine strains, Onderstepoort-like (America-1 genotype), are currently circulating in breeding foxes, raccoon dogs and minks in China, and that the genotype Asia-1 is predominant. Whether the diversity between wild-type CDVs and the vaccine strains may affect, to some extent, the efficacy of the vaccines deserves further investigations.