Use of an infectious bronchitis virus and Escherichia coli model infection to assess the ability to vaccinate successfully against infectious bronchitis in the presence of maternally-derived immunity.
Using as challenge, a mixed infectious bronchitis virus (IBV) and Escherichia coli infection, specified pathogen-free (SPF) chicks and chicks with maternally-derived immunity (MDI) could be protected by a single intra-nasal vaccination with a live-attenuated IB vaccine given at 1 day of age against intranasal challenge with either a homologous or a heterologous IBV strain for at least 7 weeks. However, protection was incomplete if challenge occurred within approximately 14 days of vaccination. Vaccination at 7 or 14 days of age was also equally effective in protecting both SPF and MDI chicks for at least 4 weeks. The value of using in challenge studies a mixed IBV and E. coli infection, which takes account of the response of the intact chicken to challenge, is discussed.
Cook
J K
JK
AFRC Institute for Animal Health, Houghton Laboratory, Houghton, Huntingdon, Cambridgeshire, England.
Huggins
M B
MB
Ellis
M M
MM