Submitted to: Avian Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2004
Publication Date: 10/31/2004
Citation: Bacon, L.D., Hunter, D.B., Zhang, H.M., Brand, K., Etches, R. 2004. Retrospective evidence that the MHC (B haplotype) of chickens influences genetic resistance to attenuated infectious bronchitis vaccine strains in chickens. Avian Pathology. 33(6):605-609. Interpretive Summary: Infectious bronchitis is a respiratory disease of chickens that is caused by a virus termed the infectious bronchitis virus (IBV). Virtually all broiler and layer breeder flocks are vaccinated against IBV, but there is variability in protection against infectious bronchitis. We mistakenly vaccinated day old chicks of four different lines from two hatches with a live vaccine intended for older chickens previously vaccinated with a mild vaccine. This resulted in infectious bronchitis in over 50% of the chicks in three lines, whereas chicks of the other line were resistant. This mortality did not occur in chicks of any of the lines from two other hatches that were appropriately vaccinated with a mild vaccine. The chickens of the resistant line had a specific group of genes not present in the other lines, and this may help chicken breeders identify genes leading to better responses to IBV vaccines. These chicken genes may also assist vaccine producers in identifying the segments of IBV that induce good immunity following vaccination.
Technical Abstract: Infectious bronchitis is a respiratory disease of chickens that is caused by a Corona Infectious Bronchitis virus (IBV). Virtually all broiler and layer breeder flocks are routinely vaccinated against IBV. Two hatches of day-old chicks from four lines were mistakenly vaccinated for IB using a moderately-attenuated vaccine designed for chicks of an older age. The vaccination resulted in high mortality, and chicks from three of four lines died with signs typical of IB. The mortality that occurred using this less-attenuated vaccine was significantly influenced by the genetic line, and the MHC haplotype in chickens of three MHC-congenic lines. Chicks from two further hatches of the four lines were vaccinated appropriately with a more attenuated IBV vaccine, and only limited chick mortality was seen. These retrospective data from two repeated hatches confirm earlier data indicating chicken genes influence resistance to IBV, and indicate for the first time that MHC genes are relevant in the resistance to IBV. Factors that may enhance definition of the role of the MHC in immune response to IBV, and the desirability for further analysis of the MHC influence on immunity to IBV are discussed.