DNA-mediated vaccination conferring protection against infectious bursal disease in broiler chickens in the presence of maternal antibody

Abstract

The objective of the present study was to determine if a DNA vaccine carrying large segment gene of infectious bursal disease virus (IBDV) could confer protection against infectious bursal disease (IBD) in broiler chickens in the presence of maternal antibody. Broiler chickens with maternal antibody titers to IBDV were intramuscularly injected with a DNA plasmid coding for VP2, VP3, and VP4 genes of IBDV strain variant E (VE) (P/VP243/E) at 1-day, 1-week, and/or 2 weeks old. The dose of P/VP243/E used ranging from 400microg to 10mg. Broiler chickens at 3 weeks old were orally challenged with IBDV strain (VE) and observed for 10 days. Only broiler chickens vaccinated with 7.5 or 10mg of P/VP243/E 3 times had 90 or 100% protection against challenge by IBDV strain VE and protected broiler chickens had significantly higher (P<0.05) bursa weight/body weight (B/B) ratios, significantly lower (P<0.05) bursal lesion scores, and the absence of IBDV antigens in bursae determined by immunofluorescent antibody assay (IFA). Antibody titers to IBDV as determined by enzyme-linked immunosorbent assay (ELISA) or virus neutralization (VN) assay in chickens of each group in each trial were gradually decreased prior to challenge. There was no significant difference (P>0.05) in ELISA or VN titers to IBDV among all groups of broiler chickens or among the groups of broiler chickens vaccinated with various dose of P/VP243/E before challenge. Broiler chickens in the groups receiving 7.5 or 10mg of P/VP243/E had significantly lower (P<0.05) ELISA or VN titers to IBDV than those in the challenge control (CC) groups or the other groups vaccinated with various dose of P/VP243/E after challenge. Broiler chickens in the groups vaccinated with 10mg of P/VP243/E 3 times had significantly higher (P<0.05) stimulation indices for IBDV-stimulated lymphocyte proliferation response than those in the vector control (VC) or CC group at 14, 21, 24, or 31 days after first DNA vaccination. The results indicated that DNA vaccination with DNA encoding large segment gene of IBDV confers protection against challenge by IBDV in broiler chickens with maternal antibody to IBDV.