Isolation And Identification Of Duck Hepatitis Virus BD-â…  Strain In Hebei Province And Cultivation Of Attenuated Virus Strain Of BD-â… 

Duck viral hepatitis is an acute, highly contagious , viral disease of young ducklings by Duck Hepatitis Virus . It is characterized by high mortality and short incubation period. It is one of the main serious diseases in duck, it exist in many places of our country.Many viruses and bacteria co-infect with the DHV-I, which causes great loss . Clinical signs include anorexia,sudden death,opisthotonos and enlarged liver with haemorrhagic lesions. Three distinct types of duck hepatitis virus have been isolated from diseased ducklings. DHV- I is present in all duck-raising areas of the world , DHV- II and DHV-III are rest ricted to the United Kingdoms and United States of America respectively. Three kinds of serotype strains have no immunological cross-reactions except for different physiochemi-al and molecular characteristics. Recently distinct serologic variants of DHV-I have been described and complete genome sequence of DHV-I has been finished. Subsequence appearance of diagnosis method by RT-PCR is important to prevention and treatment of duck viral hepatitis.A strain of virus ,which was suspected to be duck hepatitis virus (DHV), was isolated from duckling liver samples through chicken embryo by allantoic sac inoculation . The sample was collected from ducklings diagnosed clinically dying from duck virus hepatitis on the duck farm in Baoding County of Hebei Province.The strain was named DHV BD-I strain. It was confirmed by pathological examination , physical-chemical characterization tests, neutralization test and animal relapsing test that the virus strain was DHV serotype I and had resulted in plenty of ducks to be pathogenetic and dead on the farm.A RT- PCR method for detecting the duck hepatitis virus I type was established with a pair of primers designed and synthesized based on the gene of GenBank.The primer was designed with help of Primer Premier 5.0 design software .A specific 506 bp fragment was amplified from RNA templates of DHV- I virulence AV2111 strain.And the sensitivity,specificity tests were carried out. The RT- PCR method could detect 128 folds dilution of the liver samples of duck hepatitis virus I .But it couldn' t detect Newcastle disease virus (NDV) ,infectious bursal disease virus(IBDV),duck plague virus(DPV) , Muscovy parvovirus(MPV), duck swollenhead hemorrhagic disease virus(DSHDV),and Goose paramyxoviridae(GPV). The rates were 76.92%(10/13) when liver samples of clinical cases from Hebei province of China stored at -80°C were detected by the RT-PCR.The results showed that the sensitivity and specificity was very high. So the method can be applied for the fastly diagnosis of Duck hepatitis virus I type.The strain of DHV was attenuated by passage in chicken embryos and designated BD-I strain. Diluted allantotic fluid virus was used to immunize 1-day-old ducklings and the immunized ducklings were challenged with virulent serotype I 14 days after immunization .The result indicated that the protection rate of 500ELD₅₀ of BD-I -40 could reach up to 100 percent. The sera of the immunized ducklings were collected and the antibody liters were measured by virus neutralization test. The antibody level reached peak in 14 days post vaccination and then decreased.The results showed that BD-I strain could provide protection against the infection with serotype I DHV and maybe used as the candidate vaccine strain.