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Abstract
The present study was dedicated to investigate duck viral hepatitis outbreaks in ducklings. For this purpose a total of 25 duckling flocks (1-3 weeks old) in different localities in El-Behira province suffering from sudden death and high mortalities were investigated during the years of 2006 and 2007 .
Besides virological examination for viral infections , sampled diseased ducklings were examined microbiological to exclude other infections .
The results revealed the following findings:
1- Clinically all the affected flocks had sudden onset of high mortalities occurred within 3-4 days in 4-19 days old ducklings and ranged (20- 90%) .The affected ducklings were lethargic , unable to stand , lag behind the flock , separated in one corner with partially closed eyes , shaking of head and neck and fell on their sides with spasmodic paddling of legs and died rapidly in an opisthotonus position .
2- The recorded gross lesions were multiple petechial , echymotic hemorrhage and larger streaks of congestion on the enlarged liver surface , distended gall bladder , enlarged and mottled spleen , swollen and congested kidneys Some times necrotic foci on liver surface were recorded.
3- Isolation of suspected DVH-1 isolates in embryonated chicken eggs through allantoic sac inoculation at 10-days-old CE was successful and most embryo died 2-3 days post inoculation .
4- Identification of the inoculated suspected isolates was achieved by agar gel immnodiffusion test which proved to be valuable and achieved positive results for (23) isolates (92%) .
5- Identification of two unidentified isolates no. (1 and 21) which produced mortalities and lesions in embryonated chicken egg by IUDR in chicken embryo fibroblast tissue culture indicated that both isolates were RNA and produced cytopathic effect with 10 ,50 and 100 ug IUDR /ml of tissue culture medium . Further identification by immunoperoxidase revealed positive granular brown staining indicating that both isolates were DVH-1.
6- Titration of 4 suspected isolate after being inoculated in embryonated chicken egg indicated that the titer ranged from 106 ELD50/ ml to 107 ELD50/ml.
7- Histopathological findings were vacuolar degeneration of hepatic cell with heterophilic cell infiltration , aggregation of lymphocyte around hepatic blood vessels , hyperplasia of bile duct , lymphocytic depletion of spleen .
8- The immunoperoxidase test proved to be sensitive for confirmation of DVH-1 in paraffinized tissue section of liver and spleen .
9- Experimental infection with 4 isolates no. (1, 9, 15 and 21) for estimation of their pathogenicity in 9-day-old susceptible Pekin ducklings achieved mortalities ranged from 70-90% .
10- Vaccination using freeze dried modified live vaccine (SVRI) of 2 days-old ducklings achieved protection ranged from 60%to 80% after challenge with the 4 isolates at 9 days-old.