EFFICACY OF SUBCUTANEOUS APPLICATION OF LIVE INFECTIOUS BURSAL DISEASE VACCINE IN YOUNG CHICKENS WITH MATERNALLY DERIVED ANTIBODY

The infectivity of neutralized IBDV by normal chicken serum (NCS) was detected in day-old and 3-week-old chicken spleen adherent (CSA) cells, and that of neutralized IBDV by maternal antibody (MN-Ab) was detected in 3-week-old CSA cells. Moreover, CSA cells from day-old chickens had complement receptor (CR), and CSA cells from 1-week-old had both CR and Fc receptor (FcR). However, the infectivity of neutralized IBDV by MN-Ab was confirmed on CSA cells which were blocked for FcR on CSA cells by heat-aggregated NCS (56 degrees C, 60 min). These results indicated that infection of neutralized IBDV by NCS on CSA cells occurred via CR, and neutralized IBDV by MN-Ab was infected via FcR. In day-old specific pathogen free (SPF) chickens, the antibody level in NCS treated and non-treated IBD live vaccine subcutaneously inoculated groups was higher than the levels in the MN-Ab-treated IBDV inoculated group, and detected until 28 days old. Moreover, subcutaneously inoculated chickens were protected against the challenge of wild IBDV at 21. days old, whereas subcutaneously inoculated chickens were infected with MN-Ab-treated IBD live vaccine. In commercial layers which had MN-Ab, antibody levels of subcutaneously vaccinated group were higher than both the non-vaccinated and orally vaccinated groups, and Virus isolation and viral antigen were positive with high detection rates on peripheral lymphocytes of each subcutaneously vaccinated group of SPF and commercial chickens. There were no distinct pathological changes, no decrease in complement activity measured via the alternative pathway, and no secondary antibody response of NCS-treated and/or non-treated IBDV subcutaneously vaccinated SPF chickens and commercial layers, after challenge. These results suggest that the subcutaneous application of live vaccine to day-old chickens has a more protective effect against a virulent IBDV exposure at 21 days old than the oral application.