Live attenuated duck hepatitis virus vaccine in breeder ducks: Protective efficacy and kinetics of maternally derived antibodies

摘要

Duck viral hepatitis type I is a rapidly spreading infection lethal in young ducklings, caused by the duck hepatitis A virus (DHAV). Vaccination of breeder ducks is a common practice to control DHAV. However, maintaining proper maternal antibody levels in large flocks is difficult. Therefore, a simple vaccination strategy that can induces stable high antibody levels through mass vaccination is desirable. We evaluated a DHAV vaccination strategy for breeder ducks involving oral administration under field conditions, and examined the kinetics of antibody response in the ducks and their progeny. The strategy included a primary intramuscular vaccination, followed by secondary and tertiary oral vaccinations. Five weeks after the primary vaccination, virus-neutralizing antibody titers increased by 8.4 +/- 1.3 log(2). The titers remained stable at around 9.0 +/- 1.1 log(2) for up to 36 weeks. None of the progeny died when challenged with virulent DHAV at 1, 7 or 14 days of age. The transfer percentage of antibodies from the breeder ducks to their progeny was 12.8 +/- 3.0%. When antibody levels of the progeny were measured from the day of hatching to 20 days of age, the levels steadily declined, reaching a mean titer of 0 log(2) at 20 days. The half-life of the maternally derived antibodies against DHAV was 3.4 +/- 1.1 days. Our vaccination strategy might be effective in breeder ducks because it can be easily applied and induced strong immunity. Moreover, our results might provide a foundation for the mechanistic study of maternally derived antibodies in passive protection.