Development of an attenuated duck hepatitis A virus serotype 3 strain and evaluation of its antigenicity.

In 2002,a new serotype of duck hepatitis virus(DHAV-3) was first reported in China.Then the infection has been found in many duck-growing areas and caused great economic losses due to the high mortality.To develop a live vaccine against DHAV-3 infection,an isolate was attenuated by serial passage in duck embryos.After 53 passages,the virus did not cause any clinical signs and microscopic lesion in tissues for high dose inoculation,and no virulence reversion was found after repeated passage in 3-day-old ducklings.Ducklings vaccinated with the 54th virus(5×105.9 ELD50) on 1 or 3-day-old of age were well protected.The protection index was 81.4% and 100% on day 4 and 6 respectively against the challenge with virulent strain.The virus neutralizing antibody reached 10-3.29 at day 7 after vaccination of 1-day-old ducklings and peaked at 4th week.The level of immunity was sufficient to protect ducklings through the susceptible period.These results demonstrate that the attenuated virus is a promising vaccine candidate for the prevention of DHAV-3 infection.