The Influence Of Bursa Of Fabricius On Infectious Bronchitis Vaccination In Commercial Broiler Chicks

Ganapathy K. & Wilkins M., Forrester A., Lemiere S. & Jones R.C. 


This paper evaluates the immune responses and protection against virulent infectious bronchitis viruses (IBV) in groups of broiler chicks that were having intact or regressed bursa of Fabricius. One of each HVT-IBDV vector or IBDVantibody complex vaccinated group was vaccinated with IBV H120 at day old and later with IBV CR88 at 13 days old. The other group from each of the IBDVvaccinated group remained as controls. At 7, 14, 21, 28, 35 and 42 days-old, blood collected for sera (for IBDV and IBV serology), 5 chicks from each group were sacrificed to determine bursa:body weight ratio (BBR). Also, tissues of trachea, lungs, kidneys, cæcal tonsil and rectum were collected for detection of IBV virus by RT-PCR and virus isolation (VI). At 35 days-old, 10 chicks from each group were challenged with virulent M41 or virulent IB QX strain KG3P. Five days later, 5 chicks were euthanized for ciliary score and another 5 for collection of various tissues. Group that received the HVT-IBDV vector vaccine had intact bursa similar to IBDV-unvaccinated control chicks. The other groups that were vaccinated with IBDV-antibody complex vaccine produced bursa that regressed significantly. Bursal lesion score of the IBDV-complex-vaccinated groups also deteriorated 3-4 weeks after the day-old vaccination. There were no differences in clinical protection against respective IBV challenge viruses (M41 or QX), post-vaccination IBDV or IBV humoral antibody titres. The main finding was a decreased detection of the vaccine viruses in chicks with intact compared to regressed bursa. This may reflect the importance of bursa in the clearance of the vaccine viruses hence avoiding or reducing respiratory diseases in chicks.