Studies on the Isolation,Identification and Pathogenic Characteristic of Duck Hepatitis Virus

[Objective] To determine the pathogen of duck viral hepatitis which is prevalent recently and to analyze the reasons for difficult control.[Method] Viruses were isolated from livers and spleens of ducks in farms of Linyi,Weifang and Binzhou of Shandong Province which displayed typical clinical symptoms of duck viral hepatitis.Their pathogenic characteristics were studied by chicken or duck embryo inoculation,RT-PCR,serological test,and duck regression.[Result] Four duck hepatitis virus(DHV) strains were isolated,and the 5th passage allantoic fluid contained 103.41-105.20 ELD50 /ml.They had serum cross protection rates of 20%-80% against DHV type I.The mortality of 4-day-old healthy ducks challenged by these four stains was 50%-100%.All challenged ducks had typical lesions of duck viral hepatitis,and a peak appeared after 24-48 h post challenge.[Conclusion] The virulence of DHV isolates has regional difference.