Oral immunization of ducklings with attenuated duck hepatitis virus

Duck hepatitis, a highly fatal disease of ducklings, must be controlled in successful commercial duck enterprises. Several procedures which have been effective in controlling the disease are 1) vaccination of adult breeders with passive transfer of antibodies through the yolk to the duckling, 2) administration of antisera to ducklings at the onset of signs of disease, and 3) parenteral vaccination of ducklings with attenuated DH virus after the loss of passive immunity. However, in each of these procedures, some losses usually occur and the administration of antiserum or vaccine to 2- to 3-week-old ducklings is costly and involves physical stress. Experimental studies of oral immunization in ducklings from immunized and nonimmunized parents were conducted to determine the feasibility of a convenient control program with little stress to the ducklings. Ducklings immunized with attenuated live duck hepatitis virus by intramuscular method, oral instillation, and through the drinking water were challenged with virulent duck hepatitis virus either intramuscularly or orally. Intramuscular, oral instillation, and drinking water application all provided adequate protection on challenge with virulent virus. Rise in neutralizing antibody was detected following immunization especially in sera of ducklings from nonimmunized parents. On the basis of successful experimental results, over 350,000 ducklings from immunized parents on a commercial farm have been sucessfully vaccinated by the drinking water method.