Study On Pathogenic Character And Sequencing And Analysis Of Complete Genome Of Duck Hepatitis Virus Type Ⅰ SG Strain

Duck viral hepatitis (DVH) is a highly mortal disease and spreads rapidly in six-week-old ducklings. It is caused by duck hepatitis virus typeⅠ(DHV-Ⅰ).The virus mainly infects the ducklings between two-day-old and three-week-old.But the adults have some resistance to the disease. Three different viruses,duck hepatitis virus type 1, 2and3 have been found to be associated with these symptoms. DHV-1 and DHV-3 were classified as a picornavirus. However, DHV-2 was classified as an astrovirus.Duck virus hepatitis type l is very popular in China and have become one of the biggest trouble maker of the development of the poultry industry.This study included as following:1. One virus was obtained through uscovy duck embryo allantoic sacinoculation from duckling liver samples collected from Shouguang district Shandong province in China in 2007. Meanwhile, the virus was identified by neutralization test, duck embryo and ducklings pathogenicity test, recurrence test, RT-PCR detection and determine the ELD50 and LD50 of the virus .The result showed that the isolate had no hemagglutination.12-day-old duck embryo and ducklings appeared typical symptoms of DHV after being infected the isolate. The virus could be neutralized by DHV-Ⅰstandard anti-serum, RT-PCR detection and sequence determination showed it was a traditional virus. Above all, we had successfully identified a tradditioanal isolate in Shouguang district Shandong province and named SG strain.2. According to the study of pathogenicity of SG strain, we knew the ELD50 of the SG strain detected by duck embryos was 10^–5.58/ 0.2ml and the LD50 detected by ducklings was 3.9226×10^-3. So we found the DHV-1 SG strain had higher pathogenicity.3. Based on the DHV-1 sequences in GenBank, nine pairs of specific primers were designed to amplify DHV-Ⅰusing RT-PCR. The complete genomic sequence of duck hepatitis virus 1(DHV-Ⅰ). In this study, we reported and analyzed the complete nucleotide sequence and demonstrated clearly that SG strain belonged to DHV-Ⅰwhich was a member of the family Picornaviridae. GenBank accession number was FJ971623. SG isolate was sequenced and determined to be 7690 base pair (bp) in length (not including the poly (A)tail). One large open reading flame (ORF) was found within the genome coding for a polypeptide of 2249 amino acids. The genome structure is 5'UTR-VP0-VP3-VP1-2A1-2A2-2B-2C-3A-3B-3C-3D-3'UTR.31 DHV-Ⅰstrains from different area were analyzed in phylogeny and the SG strain can be grouped into traditionanl isolates. Phylogenetic analysis to do sequence homology based on the complete sequence, Polyprotein sequences, P1 nucleotide sequences and 3D protein sequences showed that the SG isolate was at the same branch with other 30 traditional isolates and different from variants, which was identical to the result of part 1.