Response of Susceptible versus Immune Chicks to Killed, Live-Modified, and Wild Infectious Bursal Disease Virus Vaccines

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Abstract
Modified infectious bursal disease virus (IBDV) administered ocularly to susceptible or passively immune chicks did not induce protection against bursal atrophy by wild IBDV, while i.m. or intrabursal (i.b.) injection protected susceptible chickens. No protection was obtained in passively immune chickens vaccinated i.m. or i.b. Susceptible and passively immune chickens vaccinated with a single dose of killed-virus suspension (KVS) did not become resistant to wild IBDV challenge. A killed-virus multiple emulsion (KVME) induced partial protection (3/5) against challenge 28 days after s.c. vaccination of 3-day-old susceptible chickens. At 35 and 42 days old, all susceptible chickens were protected by KVME. Protection by passive antibodies [Ab] was observed in unvaccinated, KVS- and KVME-vaccinated chickens challenged at 10 and 17 days of age. Protection was only partial in passively immune chickens vaccinated with KVME after passive Ab were no longer protective to unvaccinated and KVS-vaccinated chicks. Modified IBDV was detected 2 days post i.b. inoculation only in the bursa of Fabricius of susceptible chickens and wild IBDV was found in the thymus, spleen and blood. No evidence of virus was found in immune chickens inoculated IB with modified IBDV. The growth of wild IBDV was limited to the bursa of Fabricius in immune chickens. Intensity of fluorescence and number of positive bursa cells was low when compared with fluorescence in the bursa of susceptible chickens infected with wild IBDV.