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18 January 2019 Infectious Bronchitis Virus Vaccination at Day 1 of Age Further Limits Cross Protection
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Cross-protection and immune responses elicited by infectious bronchitis virus (IBV) vaccination on Day 1 of age or at later time points were examined. Specific-pathogen-free chickens were vaccinated with a Massachusetts-type vaccine and heterologous challenge was performed with an Arkansas (Ark) -type virulent strain. In Trial 1, chickens vaccinated on Day 1 or Day 10 of age were challenged 21 days after vaccination. Analysis of tracheal histopathology and viral load demonstrated less cross protection when vaccination was performed on Day 1 of age. In Trial 2, chickens were vaccinated on Day 1 or Day 14 of age. A somewhat stronger systemic antibody response to IBV was detected in chickens vaccinated at 14 days of age. In addition, avidity of antibodies to Ark-type S1 protein elicited by vaccination at 14 days of age was greater. Differences in immune-cell populations in the Harderian gland (HG) observed at the time of sampling (35 days following vaccination) between chickens vaccinated at 1 day or 14 days of age indicated greater, rather than reduced, immune activity in the chickens vaccinated at 1 day of age. These differences are, perhaps, a result of the higher levels of persisting vaccine virus observed in the younger chickens. Both nonvaccinated/challenged groups showed significantly higher (P < 0.05) proportions of B cells and CD8+ T cells 7 days after challenge than age-matched vaccinated/challenged groups or age-matched nonvaccinated/nonchallenged control groups. These results indicate infiltration and/or expansion of B cells and CD8+ cells in HGs following challenge of nonvaccinated chickens. A fortuitous finding was that the more immature immune system of chickens vaccinated at 1 day of age was less effective at clearing vaccine virus after vaccination. Collectively, the current results indicate that IBV vaccination at 1 day of age can decrease the potential for heterologous cross protection compared with vaccination at least 10 days after hatch. A lower level of antibody affinity maturation likely contributes to decreased cross protection.

R. A. Zegpi, S. L. Gulley, V. L. van Santen, K. S. Joiner, and H. Toro "Infectious Bronchitis Virus Vaccination at Day 1 of Age Further Limits Cross Protection," Avian Diseases 63(2), 302-309, (18 January 2019).
Received: 5 December 2018; Accepted: 9 January 2019; Published: 18 January 2019

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