Infectious bursal disease (IBD) remains a potential worldwide threat to the poultry industry
despite several vaccination approaches. Because maternally derived antibodies (MDA)
constitute a critical problem for IBD vaccination, we examined the efficiency of the
intracloacal vaccination approach in breaking through MDA. Experiment 1 determined the
ability of the vaccinal strain to multiply in the bursa of Fabricius (BF) in chicks with a high
level of MDA. Using real-time polymerase chain reaction, we quantified the strain in the
bursae of vaccinated and non-vaccinated chicks. Experiment 2 was performed on three
groups of chicks with high levels of MDA: group 1, non-vaccinated non-challenged; group 2,
non-vaccinated challenged; and group 3, vaccinated challenged. Seroconversion to IBDV was
measured using enzyme-linked immunosorbent assay. Groups 2 and 3 were challenged by
vvIBDV at 25 days of age. Experiment 3 studied the effect of early IBD vaccinal strain
multiplication on the immune response of vaccinated and non-vaccinated chicks to other
vaccines. In experiment 1, the vaccinal strain showed progressive multiplication and reached
the detectable titre in BF at 12 h post-vaccination despite high MDA titre. Experiment 2
showed that chicks in group 3 had significant seroconversion against IBDV. After challenge,
group 3 showed significant improvements in several measured parameters compared with
group 2. Moreover, results of experiment 3 proved that early multiplication of the vaccinal
strain in the BF has no significant effect on the immune system or immune response to
other vaccines. These results proved the promising success of this IBD vaccination approach. |
