EFFICACY OF A NOVEL INFECTIOUS BURSAL DISEASE VIRUS IMMUNE-COMPLEX VACCINE IN BROILER-CHICKENS

Two experiments were conducted to test the efficacy of a novel infecti ous bursal disease virus (IBDV) vaccine in broiler chickens with mater nal IBDV immunity. The IBDV vaccine was formulated by mixing IBDV stra in 2512 with bursal disease antibodies (BDA) to produce the IBDV-BDA c omplex vaccine. In Expt. I, 1-day-old Cobb x Cobb broiler chickens wer e vaccinated subcutaneously with either IBDV-BDA or commercial live in termediate IBDV vaccine (vaccine A) or were left unvaccinated. In Expt . 2, the vaccine A group was not included; instead, IBDV strain 2512 w as included. Chickens were maintained in isolation houses. On day 28 ( Expt. 1) and day 32 (Expt. 2) of age, chickens from each group were ch allenged with a standard USDA IBDV (STC strain) challenge. Challenged and unchallenged chickens were evaluated for their bursa/body weight r atios and antibody titers 3 days post-challenge. Bursae collected from Expt. 2 were examined histologically to evaluate bursal lesions and c onfirm gross examination. None of the unvaccinated chickens was protec ted against the challenge virus as evidenced by the presence of acute bursal lesions (edema/hemorrhage). All chickens receiving the IBDV-BDA complex or the IBDV strain 2512 (Expt. 2) were protected from the cha llenge virus as evidenced by no acute bursal lesions. Additionally, ch ickens receiving the IBDV-BDA complex vaccine or the IBDV strain 2512 had antibody titers to IBDV, indicating the presence of an active immu ne response. In Expt. 1, chickens vaccinated with vaccine A and challe nged had bursal lesions similar to those observed in the unvaccinated, challenged chickens. These chickens also showed no indication of acti ve immunity against the virus. These results suggest that the 1-day-of -age-administered IBDV-BDA complex vaccine can induce active immunity and protection against a standard IBDV challenge in the face of variab le levels of maternal IBDV immunity.