Comparison of the Immunogenicity and Pathogenicity of a Genetically Engineered Infectious Bursal Disease Virus Vaccine and Two Commercial Live Vaccines in Chickens with Maternal Antibodies

The objective of this study was to determine the immunogenicity and pathogenicity of an experimental infectious bursal disease virus (IBDV) live vaccine, BD3-tc, derived by genetic engineering from a Bangladeshi very virulent IBDV strain. Two commercial live IBDV vaccines, D-78 and 228E, were included for comparison. Two-hundred 1-day-old commercial layer chickens were raised in relative isolation and at 14 days of age the chickens were divided into 4 groups in 4 separate houses. Three groups were vaccinated intraocularly with the BD3-tc or D-78 or 228E at 14 and 21 days of age and the fourth group served as an unvaccinated control. At 21, 28, and 35 days of age, chickens were individually weighed, bled, and necropsied. The bursa of Fabricius (BF) from each chicken was collected, weighed, formalin fixed, and examined histologically. The immunogenicity was evaluated by serum antibody titer to IBDV as measured by an enzyme linked immunosorbent assay. The pathogenicity was analyzed by bursa/body-weight (B/Bw) ratio and gross and histopathological lesions in BF. The chickens were found to have high maternal antibody (mAb) titers (mean titer = 7324 on day 3). Following primary vaccination, no significant level of acquired antibody was observed in any of the vaccine groups. However, on day 35, two weeks after booster, the 228E group had nearly unchanged and the BD3-tc group had a slight increase of antibody titer. In contrast, antibody level in the D-78 group continued to decline. No significant changes in B/Bw ratios and bursal lesion scores were observed in any of the vaccine groups. Together, these findings show that high mAb titers in chicks can interfere with the take of IBDV vaccines, however, the 228E and BD3-tc vaccines are capable of breaking through the mAb at a relatively higher level as compared to the D-78.