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

A novel linear B cell epitope of the canine coronavirus nucleocapsid protein identified by a monoclonal antibody

The infection of canine coronavirus (CCoV) causes a highly contagious disease in dogs with acute gastroenteritis. The efficient serological diagnostics is critical for controlling the disease caused by CCoV. Nucleocapsid (N) protein of CCoV is an important target for developing serological approaches. However, little is known about the antigenic sites in the N protein of CCoV. In this study, we generated a monoclonal antibody (mAb) against the N protein of CCoV, designated as 13E8, through the fusion of the sp2/0 cells with the spleen cells from a mouse immunized with the purified recombinant GST-N protein. Epitope mapping revealed that mAb 13E8 recognized a novel linear B cell epitope in N protein at 294-314aa (named as EP-13E8) by using a serial of truncated N protein through Western blot and ELISA. Sequence analysis showed that the sequence of EP-13E8 was highly conserved (100 %) among different CCoV strains analyzed, but exhibited a low similarity (31.8-63.6 %) with the responding sequence in other coronaviruses of the same genus such as FCoV, PEDV and HCoV except for TGEV (95.5 % identity). Structural assay suggested that the epitope of EP-13E8 were located in the close proximity on the surface of the N protein. Overall, the mAb 13E8 against N protein generated and its epitope EP-13E8 identified here paid the way for further developing epitope-based serological diagnostics for CCoV.

Novel high-coverage primers for detection of canine morbillivirus by end-point and real-time RT-PCR assays

Canine distemper virus (CDV) is a major threat to domestic dogs and wildlife worldwide. Molecular assays are the most sensitive and specific tests to diagnose the disease, however, the high CDV genetic variability may compromise laboratory diagnosis. Herein, we designed a high-coverage primer set for end-point (RT-PCR) and real-time (RT-qPCR) for CDV detection. Initially, we collected 194 complete/near-complete CDV genomes (GenBank) and analyzed them for highly conserved regions for primer design. We then assessed the in silico coverage, analytical sensitivity, specificity and diagnostic performance of RT-PCR/RT-qPCR reactions based on our primers. Furthermore, the coverage of our primers, as well as their analytical sensitivity and diagnostic performance, were compared to a commonly used primer set for CDV detection (named PP-I). Our forward (F) and reverse (R) primers fully matched 100 % (194/194) and 99 % (192/194) of the analyzed sequences, whereas the PP-I F and R primers fully matched 15 % (29/194) and 9 % (18/194) sequences, respectively. The detection limit of our RT-PCR and RT-qPCR was equivalent to that of PP-I primers (0.001 TCID50/mL). Out of 70 clinical samples tested, 38 were positive by our RT-PCR/RT-qPCR assays, whereas reactions with primers PP-I failed to detect 9/28 (32 %) positive samples selected for comparison purposes. In addition, our assays did not amplify other canine viruses associated with respiratory and neurological diseases: canine adenovirus 2, canine parainfluenza virus 2, canine herpesvirus 1 and rabies virus. Overall, we describe a high-coverage primer set for CDV detection, which represents an attractive tool for laboratory diagnosis of canine distemper.

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.

An appraisal of gene targets for phylogenetic classification of canine distemper virus: Is the hemagglutinin the best candidate?

Sequence analysis of the canine distemper virus (CDV) hemagglutinin (H) gene may provide important insights on virus-host interactions and has also been frequently used for CDV phylogenetic classification. Herein, we performed an in silico analysis of CDV complete genomes (CGs) available in GenBank in order to investigate the suitability of H for CDV classification into lineages/genotypes. In addition, we analyzed the other viral genes for their potential use in CDV classification. Initially, we collected 116 CDV CGs from GenBank and compared their phylogenetic classification with that of their respective H nucleotide (nt) and amino acid (aa) sequences. Subsequently, we calculated the geodesic distance between the CG and H phylogenetic trees. These analyses were later performed with other CDV genes. All CDV CGs were also evaluated for possible recombination events. Nucleotide and aa analyses of H misclassified some Vaccine/America 1/Asia 3 lineage sequences compared to CG analysis, finding supported by both Maximum Likelihood (ML) and Bayesian Markov Chain Monte Carlo (B-MCMC) methods. Moreover, aa-based H analysis showed additional disagreements with the classification obtained by CG. The geodesic distance between the H and CG trees was 0.0680. Strong recombination signals were identified in the H gene, including Vaccine/America 1/Asia 3 lineage sequences. In contrast, C and P were the only genes that fully reproduced the CG classification (by ML and/or B-MCMC) and that did not show strong recombination signals. Furthermore, the P phylogenetic tree showed the lowest geodesic distance from the CG tree (0.0369). These findings suggest C and P as potential targets for CDV phylogenetic classification, especially when full genome sequencing is not possible. Finally, since our results were obtained considering the CDV CGs available to date, future analyses performed as more CDV sequences become available will be useful to assess probable issues of H-based phylogeny and to consolidate the suitability of the C and P genes for CDV classification.

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.

Phylogenetic analysis of canine distemper viruses isolated from vaccinated dogs in Wuhan

Canine distemper virus (CDV) is an infectious agent that can cause canine distemper (CD), a lethal disease. Immunization is an effective method to control the infection; however, some cases of failed immunization are observed in animal hospitals every year. Therefore, in this study, we conducted phylogenetic analysis of the H gene of isolated CDVs. We first constructed a modified MDCK cell line, which constitutively expressed signaling lymphocyte activation molecule (SLAM), a specific receptor for CDV. The modified cell line was more suitable for propagation of CDV than the original MDCK cell line. Next, 9 CDVs were successfully isolated from 20 dogs with suspected CD-associated diseases. Of these CDV isolates, three were from vaccinated dogs. The analysis indicated that the H gene sequences of these 9 viruses were highly similar. The present study further supported the finding that the majority of CDV in China belonged to the genotype Asia-1, which was different from vaccine strains (America-1 and America-2). Although the clinical application of the vaccine suggested that it is effective against CDV infection, it remains an open question whether a novel vaccine based on the genotype of the Asia-1 strain would be more suitable for protection of dogs against Asia-1 CDVs infection.

Characterization of canine coronavirus spread among domestic dogs in Vietnam

Canine coronavirus (CCoV) is an important pathogen that causes enteritis in dogs, but there is no information on CCoV infection in Vietnam. To examine the prevalence of CCoV infection among Vietnamese dogs, 201 serum samples were analyzed by virus-neutralization (VN) test. The results showed that antibody against CCoV-II was present in 87 dogs (43.3%). To detect genes of CCoV, fecal samples collected from 30 diarrheic and 50 healthy dogs were examinated by RT-PCR, confirming that 2 diarrheic dogs and 5 healthy dogs were positive for CCoV. Nucleotide sequences of N-terminal region of spike (S) gene indicated that CCoV strains were divided into two subgenotypes, CCoV-IIa and -IIb, respectively. Furthemore, we succeeded in isolating CCoV/dog/HCM47/2015, the isolate was plaque-purified three times, and 3’-terminal one-third of the genome was analyzed. Interestingly, the plaque-purified virus had a large deletion in ORF3abc and E genes (1,165 nt), and a short deletion in ORF7b gene (60 nt), suggesting that these regions are not necessary for in vitro replication of CCoV. Next, the antigenicity between the isolated CCoV-IIb and the other CCoV-IIa was compared by VN test, revealing that antigenicty of the isolated CCoV is equal or higher than that of the other CCoV. In summary, two subgenotypes of CCoV-II are spreading among Vietnamese dogs. The isolated virus with a large deletion after in vitro passage may be useful for the development of vaccine, owing to its antigenicity and efficient viral growth in vitro.