Immunologic Response of Turkeys to an Avirulent Pasteurella multocida Vaccine in the Drinking Water

Turkeys were given either (1) commercial oil-base Pasteurella multocida bacterin (containing P-1059, P-1662, and X-73 strains), (2) avirulent P. multocida vaccine (P-1059 strain), or (3) bacterin plus the avirulent vaccine. Other turkeys were non-vaccinated. The bacterin was injected at 8 weeks of age and the avirulent vaccine was administered in the drinking water at 12 weeks of age. To evaluate the immunologic response, there were 3 separate trials using a challenge with either a virulent P-1059 strain, a P-1662 strain, or an X-73 strain, at 14 weeks of age. Under the conditions of the 3 experiments conducted, the total number infected was 12.5%–45.0% in the turkeys that had received the bacterin, 5.0–10.0% in the turkeys that had received the avirulent vaccine, and 2.5% in the turkeys that had received the bacterin prior to receiving the vaccine. The total number infected was 75–100% in the turkeys that had not received either bacterin or avirulent vaccine. The attenuated vaccine (a P-1059 strain) induced a high degree of immunity to challenge with a virulent homologous strain and to virulent heterologous strains (P-1662 and X-73) as well, confirming data reported by Heddleston et al. (1970). The results of these experiments suggest (1) that the avirulent vaccine prevented considerable, but not all infection, (2) the use of an oil-base bacterin prior to the use of the avirulent vaccine reduced the total number infected still further, and (3) that oil-base bacterin alone was effective in reducing the total number infected, but was not as good as the avirulent vaccine. An undesirable effect of the avirulent vaccine was a 2.5% infection that it induced in 120 turkeys that had previously received an oil-base bacterin and a 4.2% infection in 120 turkeys that had not received the bacterin. The results of these experiments further suggest that there is no valid foundation for the views that immunizing agents against fowl cholera are of questionable value because of the variety of serotypes.