| Duck hepatitis virus (DHV) is the causative agent of duck viral hepatitis, which is an acute and fatal infectious disease of ducklings. Three distinct serotypes of DHV (DHV-1, DHV-2 and DHV-3) had been described by ICTV before 2000. Compared with the other two serotypes, DHV-1 is more wildly distributed and higher pathogenic. Today, it is proved that both DHV-2 and DHV-3 belong to avian astrovirus. Recently, outbreaks of new serotypes of DHV were reported in China, Korea, and elsewhere. In order to prevent the distribution of DHV, it is significant to identify the antigenicity of DHV strains isolated in China.Nine DHV strains isolated at different time and in different areas of China were cultured and passaged on duck embryos and duck embryo liver cells. During the passage, the adapted viruses had the relatively stable titers and caused the death of the embryos with the specific pathological changes and obvious CPE on the cells. Serum cross neutralization test and passive protection test of 8-day-old ducklings were employed to make identification on antigenicity of viruses. Referring on the classification standard on serotype and sero-subtype of Foot and mouth disease virus belonging to Picornaviridae, the judgment on the correlation of antigenicity was carried out by calculating the related value (R) between the different strains. The results showed that, compared to the type strain of DHV-1, the R value of strain GD was less than 0.47%, however the value of strain YN29 was 100%. It is suggested that the strain GD was N-DHV and strain YN29 was DHV-1. According to the cross-neutralization test among the seven strains isolated in China with the antisera of standard DHV-1 and N-DHV, Strains PLK and YB3 were all DHV-1, while Strains YB1, YB2, YB5, HY2 and HY3 were N-DHV. Meanwhile, the VP1 genes of about strains were amplified and sequenced. By analyzing the nucleic acid sequence and induced amino acid sequence, the homology of amino acid sequence among the DVH-1 strains was about 95%, while the homology of amino acid sequence among the N-DVH strains was about 98%. The homology of amino acid sequence between the DVH-1 and N-DVH strains was 72-77%. Referring on the serotyping criteria of human enterovirus belonging to Picornaviridae, the serotypes of the strains were classified by the homology of the VP1 genes. The results of serotyping by the homology of the VP1 genes were correspondent with that of serotyping by the identification of antigenicity. VP1 gene mutations among the strains belonging to the same serotypes were limited and it was proved that the antigenicity of the same serotype strains was stable. The small mutations in VP1 gene of the different strains with the same serotypes could lead to the different pathogenicity and infection. The results indicated that two serotypes of DHV were prevalent in China, but no mutations of sero-subtype were found.The complete genomes of three strains of N-DHV isolated in China were sequenced and analyzed. The analysis on the genetic evolution of DHV was carried out with the reference on complete genome of DHV-1 and other strains of N-DHV from Genbank. The homogeneity of nucleic acid sequence of the VP1 gene between the N-DHV strains isolated in China and Korea was 94-95% and these strains belonged to the same genotype. The identities of the N-DHV strains isolated in China and Korea aligned with DHV-1 and the N-DHV strains in Taiwan were 72-77% and 80%, respectively, and they belonged to the different genotypes. Drawing a phylogenetic tree based on 3D (RNA-dependent RNA polymerase) conserved nucleic acid sequence, identical conclusion could be drawn that N-DHV in China and Korea belonging to same genetic group. Analyzing on the genome structures of three strains of N-DHV, typical features of genome structures of Picornaviruses and other special features were shown.
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