Hemorrhagic septicemia: naturally acquired antibodies against Pasteurella multocida types B and E in calves in the United States.

Antibodies against Pasteurella multocida capsular types B and E, which cause hemorrhagic septicemia, were demonstrated in a high percentage of sera from domestic feeder calves. Since the calves had not been vaccinated with any Pasteurella organisms, the antibodies were considered to be naturally acquired. The antibodies were demonstrated by passively immunizing mice and by indirect hemagglutination and agglutination tests. Sera from 81% (44 of 54) of the calves protected mice that were challenge exposed with a capsular type B organism, and sera from 91% (49 of 54) of the calves protected mice that were challenge exposed with a capsular type E organism. Indirect hemagglutination and agglutination tests demonstrated antibody in nearly all sera. Since capsular type E organisms have been isolated only in Africa and there is only 1 report of capsular type B isolation from cattle in the United States, these organisms were not considered likely sources of the antigenic stimulation that provoked production of these antibodies.