An outbreak of Pasteurella multocida pneumonia in lambs during a field trial of a vaccine against Pasteurella haemolytica

A vaccine against pneumonic pasteurellosis was evaluated for efficacy at two dilutions in lambs transported by sea from New Zealand to Saudi Arabia. The experimental vaccine was a killed Pasteurella haemolytica serotype A1 and A2 preparation. There was no evidence of either dilution of the vaccine leading to a lower pneumonia death or lesion rate than for the control group. However, bacteriological examinations to establish the causality of the pneumonia cases showed Pasteurella multocida to be the dominant organism, while P. haemolytica types A1 and/or A2 occurred at only a very low incidence.