Immunity Following Aerosol Exposure to High-Embryo-Passage Avian Infectious Bronchitis Virus

Live virus vaccines are used extensively in the control of avian infectious bronchitis. The virus used in today's vaccines is an embryo-propagated strain that has been passaged serially at least 25-30 times in embryonating chicken eggs. At this passage level the virus retains its immunogenicity while its pathogenicity for chickens is somewhat reduced. Correctly applied, these vaccines induce a good immunity. However, have been reported following bronchitis immunization (7). Since there are several serological types of infectious bronchitis virus (IBV), it is surprising that more breaks do not occur following vaccination. It was observed in cross-immunity studies (5) that some degree of immunity to challenge could be demonstrated between serological types of IBV even though the serum antibody level was low or negligible. The experiments reported here were made to study the response of the tracheal mucosa to virus challenge over 6-8 months following initial aerosol exposure of chicks to a high-embryo-passage bronchitis virus.