Isolation And Identification Of Duck Tambusu Virus And Preliminary Study On The Immune Effect Of Oil-emulsion Inactivated Vaccine

The incidence of Tambusu virus disease which was one of the main viral diseases in ducks can reach 100%.Without secondary infection,the mortality rate is not high,just less than 10%.It mainly leads to slow growth and development,decline in laying eggs,or even stop production.It was harmful to breeding ducks,causing serious economic losses to farmers,and greatly restricting the healthy and sustainable development of duck industry.In this study,the prevalence of Tambusu virus in duck farms was investigated by extensive epidemiological investigation in Guangling District of Yangzhou.A strain of virus was isolated and identified as Tambusu virus by RT-PCR,named YZDTV-18.The biological characteristics,pathogenicity and cell infection of the strain were further studied.The results showed that the homology ratio between the isolate and Duck Tambusu virus was the highest,ranging from 97.5%to 99.6%.It was far from the genetic evolution of dengue virus and West Nile virus,the other representatives of Flaviviridae.The 7-day-old ducklings which inoculated with the strain could cause death and obvious clinical symptoms and pathological changes.EID50 of the strain was 10-4.15,indicating that the strain was highly pathogenic.The physicochemical characteristics of the strain showed that it was sensitive to chloroform,high temperature,acidity and trypsin,and had no hemagglutination activity.YZDTV-18 strain could induce apoptotic abscission after inoculation with duck embryonic fibroblasts,which further proved that the strain had strong pathogenicity.Immunization was one of the key measures to prevent and control the disease.Effective and targeted vaccine was essential for the prevention of the disease.In this study,YZDTV-18 strain was used as antigen to prepare Oil-emulsion Inactivated Vaccine after formaldehyde inactivation.The parents of 45 weeks Gaoyou ducks were immunized.The effects of the vaccine on laying rate,feed intake and protection rate of ducks were analyzed.The results showed that the highest serum neutralization titer of immunized ducks was 1:19.There was no significant difference in feed intake and egg laying rate between immunized ducks and healthy control groups,while the feed intake and egg laying rate of non-immunized ducks decreased significantly.Vaccine could effectively resist viral infection.No clinical symptoms and pathological changes were found in ducks immunized with the vaccine.The clinical symptoms in the control group were manifested as mental depression,pulling green feces,and death cases.The follicular hemorrhage and splenic necrosis were observed at the dissection.Liver steatosis and necrosis and splenic lymphocyte infiltration were observed in pathological sections.In conclusion,a highly pathogenic strain of Tambusu virus was obtained from duck farms in Guangling District.The immune protection of Gaoyou duck breeds was evaluated using the strain as inactivated antigen.The results of the study provide important reference for the prevention and control of duck Tambusu virus infection and vaccine research.