Complete Genome Sequence Analysis Of Canine Distemper Virus SD(14)7 Strain Originated From Fox And Pathogenic Research

Canine distemper(CD) caused by Canine distemper virus(CDV), is an acute and highly contacting transmitted diseases. Although effective vaccine prevention, CD tends to be highly infection and mortality rate worldwide, that brings huge harm to the rare and fur animals. Consequently, it is extremely important to research the variation and pathogenicity of the current epidemic strain.In order to survey the prevalence and genetic variation situation of CDV in fur animals culture zones, suspected samples infected by CDV were collected from Shandong, Hebei, Liaoning provinces from 2012 to 2014. After detected by canine distemper antigen detection strip and RT-PCR, the positive ones were used to be cloned and sequenced for 15 Fsp genes, 10 H genes and 12 F genes sequences. Phylogenetic tree analysis of Fsp gene showed that all of the strains of CDV belonged to the Asia-1 genotype. Amino acid sequence similarity analysis of H, Fsp、F2、F1 indicated that the H and Fsp protein showed highly variation while the F1, F2 showed lower. Phylogenetic tree analysis of F and H showed that the sequenced strains belonged to the Asia-1 genotype, which was far away from vaccine strain. Amino acid sequence similarity analysis of H and F showed that H amino acid of most strains had mutations of I542 N and Y549 H, which leaded the number of potential N-glycosylation sites to be ten and Fsp protein had higher variation. The occurrence of CDV in China probably may be caused by the variation of Y549 H in H protein, the increased numbers of N-glycosylation site, and the variation of Fsp protein, while it was not caused by the enhanced atavistic virulence of vaccine strains.A CDV strain was isolated from lung samples of fox that was possible infected by CDV from animal farms in Rongcheng city of Shandong province. After identification of RT-PCR, virus morphology observation, indirect immunofluorescence test, and animal regression, the isolate was proved to be a CDV wild strain, named by SD(14)7. The whole genome was segmented amplificated by RT-PCR. Cloning and sequencing, the segments were spliced into SD(14)7 whole genome sequence. Analysis of whole genome and H gene showed that the length of the whole genome sequence was 15690 nt, which had a highly similarity with LN(10)1 strain(98.8%), 91.9%—92.2% similarity with the vaccine strains. Phylogenetic tree analysis of the whole genome of SD(14)7 strain and H gene showed that SD(14)7 strain belonged to Asia-1 genotype and it was a wild strain in prevalence circling. Analysis of deduced amino acid sequence of H genes showed that there were mutations of I542 N and Y549 H. A increased locus of potential N-glycosylation site occurrencing in 542—544, and the total number of N-glycosylation sites was ten.In order to reveal the pathogenicity of SD(14)7 strain, animal models were valuated. The results indicated that the fox showed highest sensitive to this strain; mink appeared obvious symptoms after infection, but tolerance for a long time; the raccoon dog showed neurologic symptoms. From the symptoms and the histopathological changes, conjunctivitis and increased eye secretions, tissue lesions of bleeding or lymph node enlarged, with necrosis of spleen, lung inflammation, bleeding and so on. The results showed that the main infection was in lymphatic tissues and organs. Biopsy and immunohistochemical results showed tissue lesion of raccoon dog was most serious, followed by mink, fox was lighter. Inclusions were found in the cerebrum of raccoon dog and CDV was detected in the cerebrum of the animal, suggesting SD(14)7 strain can infect the nervous system Temperature change had no obvious characteristics of “dual phase heat”. CDV can be detected in feces and eye and nasal secretions from 3~7 d and 6~9 d post infection respectively. The lymph nodes had the highest levels of virus. This study revealed that the strain caused serious infection in the lymph nodes and lymphoid tissue and leaded the host to be infected by external environment and death.