Relationship between anti-Pasteurella multocida antibody titers after CU vaccination and survival after challenge

The relationship between serum anti-Pasteurella multocida antibodies and survival rates after challenge was determined in turkeys vaccinated one or more times with the live avirulent Clemson University (CU) vaccine and then challenged with a virulent isolate (9481) of P. multocida in the drinking water. A microtiter agglutination test for assaying anti-P. multocida serum antibodies demonstrated a highly significant (P less than 0.001) correlation between the serum antibody titer 1 week after the initial or single vaccination and the survival rate after challenge, and a significant (P less than 0.01) correlation between the antibody titer immediately before challenge and the survival rate after challenge. A highly significant (P less than 0.0001) correlation was also observed between the antibody titer before vaccination and the survival rate after challenge. This relationship was considered the result of an anamnestic response by the CU vaccine to a previous sensitization by antigens of other microbial organisms, probably in the intestine and similar antigenically to P. multocida. In contrast, a significant (P less than 0.05) but negative correlation was seen between the antibody titer 1 week after challenge and the survival rate. This relationship was thought to be the result of a marked stimulation of the antibody titer by the systemic infection of P. multocida that subsequently killed the turkeys.