Priming with DNA vaccine and boosting with killed vaccine conferring protection of chickens against infectious bursal disease

The present study, including seven trials, was conducted to determine if priming with DNA carrying a large segment gene of the IBDV and boosting with killed IBD vaccine could adequately confer protection of specific pathogen free (SPF) chickens against IBD. One-day-old chickens were intramuscularly injected with DNA plasmid coding for the large segment gene of the IBDV strain variant E (VE) (P/VP243/E) followed by an intramuscular injection of killed IBD vaccine containing both standard and variant IBDV at 1 or 2 weeks of age. Chickens were orally challenged with IBDV strain VE or standard challenge strain (STC) at 3 weeks of age. Chickens primed with 50, 100, 200, or 400 μg of P/VP243/E at 1 day of age and boosted with 0.5 ml of killed IBD vaccine at 1 or 2 weeks of age had 80-100% protection against challenge by IBDV strain VE or 71-100% protection against challenge by IBDV strain STC. Protected chickens had higher (P < 0.05) B/B ratios and lower (P < 0.05) bursal lesion scores than chickens in the challenge control (CC) groups and groups primed with saline or vector plasmid and boosted with killed IBD vaccine. No IBDV antigen was detected by immunofluorescent antibody assay (IFA) in bursae of chickens protected by the DNA vaccine prime and killed vaccine boost vaccination. Prior to challenge, chickens (21 days of age) in the groups primed with P/VP243/E and boosted with killed IBD vaccine had higher (P < 0.05) ELISA and VN titers to IBDV and lymphoproliferation stimulation indices. These results indicate that a prime-boost approach by priming with DNA vaccine encoding the large segment gene of the IBDV and boosting with killed IBD vaccine can adequately protect SPF chickens against challenge by homologous or heterologous IBDV.