Relationship between HI Antibody Titer and Newcastle Disease Virus Shedding in Chickens Infected with the Prevalent Strain

To elucidate the infection and epidemic of virulent Newcastle disease virus (NDV) in the vaccinated chicken flocks,the relationship between hemagglutination inhibition (HI) antibody titers of serum and virus shedding post-infection was evaluated in this study. Thirty chickens were randomly and averagely divided into 3 groups. The chickens in group 1 and 2 were injected by 0.02 mL and 0.4 mL La Sota-based oil-emulsion vaccine respectively,while the chickens in group 3 were injected by 0.4 mL PBS as the negative control. Sera samples were taken on day 7,14 and 21 post-immunization (pi) and subjected to HI assays. Three weeks pi,the chickens were challenged by 105 ELD50 of genotype Ⅶ NDV strain JS5/05 and were monitored daily for overt clinical signs post-challenge (pc). Oropharyngeal and cloacal swabs were collected on day 3,5 and 7 pc for virus isolation. The results showed that the mean HI antibody titer of chickens in group 1 and 2 was 5.4 log2 and 8.2 log2 at day 21 pi,respectively. The positive isolation of the virus from swabs in group 1 was higher than that group 2,and the virus shedding period in group 1 was longer than that group 2,which displayed the negative relationship between HI antibody titers and virus shedding.