Studies on Pasteurella multocida. VI. Nature of systemic immunity and analysis of the correlation between levels of immunity induced by various fowl cholera vaccines and protection against challenge.

The nature of the systemic immunity induced by various vaccines against fowl cholera disease in turkeys was investigated. Used as vaccines were three avirulent strains (CU, M2283, and P1580) of Pasteurella multocida administered in the drinking water and a bacterin administered parenterally. A passive hemagglutination test was developed to measure levels of systemic humoral immunity. Systemic cell-mediated immune response was assayed by an in vitro immunostimulation microculture system utilizing peripheral blood lymphocytes. The bacterin induced high levels of systemic humoral and cell-mediated immune responses which respectively persisted for 8 and 6 weeks. The CU strain of live vaccine induced average levels of systemic immunity (humoral and cell-mediated) which respectively persisted for 4 and 6 weeks. The M2283 strain of live vaccine also induced average levels of systemic immunity (less than induced by the CU strain) which respectively persisted for 4 and 6 weeks. The P1580 strain of live vaccine induced low levels of systemic immunity which persisted for only 2 weeks. Results from data generated from an analysis of correlation between levels of immunity and protection indicate that systemic immunity (humoral and cell-mediated) played a significant role.