Studies On The Pathogenicity Of Duck Tembusu Virus To Sheldrake

A New disease which was named Duck Tembusu virus disease has been found inseveral provinces in china since April2010. It was a new viral disease characterizedby hemorrhagic ovaritis and egg-droping. That caused huge economic losses to theduck industry in china. But the transmission of the disease, the mainly target organs,carriers of the virus and detoxification, immune mechanisms, pathogenesis remainsunclear, which bring about many difficulties to the prevention and treatment of thedisease.Study on the mortality rate, clinical symptoms and pathological changes of duckswere infected by DTV at different days, detections of Immunity organ index, antibodylevels detected by indirect ELISA, Tissue distribution and Carriers of the virus anddetoxification detected by RT-PCR.Studies showed that the DTV was infected to ducks with low mortality rate.Severe ovarian follicles with hamorrhage and hyperemia and follicles ruptured andliquefaction were the most prominent gross morphologic changes. Histopathologicchanges included infiltration of heterophilic leukocytes in ovarian tissue, granulosacells separated from the basement membrane, followed by necrosis and disintegration,dissolution of egg yolk, vacuolar degeneration of hepatocytes, granular degenerationof myocardial cells and meningitis, other organs lesions do not obvious.Immunity organ index showed that there were significant difference in spleenand thymus compared with control groups, but there were no significant difference inthe index of bursa. Antibody levels detected by indirect ELISA indicated that theantibodies can be detected after21dpi and are maintained as long as12weeks.The distribution of the DTV in the duck showed that the virus is widespread invarious organs, including blood. The viral quantities in organs is highest on3dpi. Themajor target organs are not only ovarian,liver and brain but also heart.The challenged duck started to distribution the virus at1dpi and stop at25dpi,which may be the reason for duck morbidity and mortality and the exist of maternalantibodies in un-immunized ducklings ducks. The viral RNA was detected in the cotton swab of cloaca until the25dpi, but still detected in rectum until the27dpi,which indicated that the challenged duck stop to excretion the vius firstly, but remainssubclinical infection.So, DTV may be increased fastly when to invade the duck, and the organs withprominent changes are primarily ovarian, liver, brain, heart.Target organs are mainlyovarian,liver,brain,heart and spleen. Virus remains in the body at27dpi, but hasstopped to excretion the virus to the outside world at25dpi. immunity organ indexshowed that there were significant difference in spleen and thymus compared withcontrol groups, but there were no significant difference in the index of bursa and theantibodies can be detected after21dpi and are maintained as long as12weeks. Inaddition, the virus has little influece on the humoral immune response, but thecell-mediated immunity has immunosuppressed, which need further studies on it.