Genetic Variation of the VP1 Gene of the Virulent Duck Hepatitis A Virus Type 1(DHAV-1) Isolates in Shandong Province of China

To investigate the relationship of the variation of virulence and the external capsid proteins of the pandemic duck hepatitis A virus type 1(DHAV-1) isolates,the virulence,cross neutralization assays and the complete sequence of the virion protein 1(VP1) gene of nine virulent DHAV-1 strains,which were isolated from infected ducklings with clinical symptoms in Shandong province of China in 2007-2008,were tested.The fifth generation duck embryo allantoic liquids of the 9 isolates were tested on 12-day-old duck embryos and on 7-day-old ducklings for the median embryonal lethal doses(ELD 50 s) and the median lethal doses(LD 50 s),respectively.The results showed that the ELD 50 s of embryonic duck eggs of the 9 DHAV-1 isolates were between 1.9 × 10 6 /mL to 1.44 × 10 7 /mL,while the LD 50 s were 2.39 × 10 5 /mL to 6.15 × 10 6 /mL.Cross-neutralization tests revealed that the 9 DHAV-1 isolates were completely neutralized by the standard serum and the hyperimmune sera against the 9 DHAV-1 isolates,respectively.Compared with other virulent,moderate virulent,attenuated vaccine and mild strains,the VP1 genes of the 9 strains shared 89.8%-99.7% similarity at the nucleotide level and 92.4%-99.6% at amino acid level with other DHAV-1 strains.There were three hypervariable regions at the C-terminus(aa 158-160,180-193 and 205-219) and other variable points in VP1 protein,but which didn't cause virulence of DHAV-1 change.

Molecular Characterization and SYBR Green I-Based Quantitative PCR for Duck Hepatitis Virus Type 1

To determine the genomic sequence of a duck hepatitis virus type 1 （DHV-1） strain, real-time quantitative polymerase chain reaction （RTQ-PCR） assay based on SYBR Green I technology was developed to target 3D gene of DHV-1, Comparative sequence analysis showed that the genome has a typical picornarivus genetic organization, and strain DHV-1 R genetic organaiztion is 5＇ untranslated region （UTR）-VP0-VP3-VPI-2A1-2A2-2B-2C-3A-3B-3C-3D-3＇ UTR, DHV-1 R has close relationship with Parechovirus, and has 95.1-99.1% nucleotide sequence identity with other DHV-1 strains. Based on the DHV-1 sequences in GenBank, three pairs of specific primers were designed to amplify DHV-1 using real-time PCR. The results showed that real-time PCR Tm value is 85.6℃ and the real-time PCR provides a broad dynamic range, detecting from 102 to 109 copies of DHV-1 cDNA per reaction. No cross-reactions were found in specimens containing DPV, AIV and NDV. It is concluded that DHV-1 belongs to a new group of the family Picornaviridae that may form a separate genus most closely related to the genus Parechovirus. All results showed that the real-time PCR has high sensitivity and specificity to detect DHV-1 using SYBR Green I dissociation curve analysis, isolates can be distinguished by their melting temperature. These methods are rapid, sensitive, and reliable, and can be readily adapted for detection of DHV-1 from other clinical samples.