Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: May 1, 1996
Publication Date: N/A
Technical Abstract: Haemorrhagic septicaemia (HS) is caused by Pasteurella multocida of groups B or E. Classical HS strains are serotype B:2. However, unusual serotypes (B:1, B:3, B:3,4 and B:4) can be isolated from cattle, bison, elk, deer, antelope and moose in North America. Naturally acquired immunity to HS can occur, and P. multocida can be isolated from upper respiratory tracts of apparently healthy cattle, buffalo, and elk; this indicates carrier animal may be reservoirs of infection. The P. multocida capsule is a virulence factor; it inhibits phagocytosis. A protein toxin has not been found in group B or E strains. The B:2 and E:2 strains are avirulent for poultry, whereas other B serotypes vary in virulence. Serotype B:2 strains are unique because they alone produce hyaluronidase. Immune cross-protection occurs amongst P. multocida serotypes that cause HS. Three major antigens (alpha, beta, and gamma) are recognized. The gamma antigen is a structural lcomponent of the bacterial cell wall identical with lipopolysaccharide (LPS). LPS is not a good immunogen. However, in vaccinated ruminants or ruminants with naturally acquired immunity, serum antibodies to LPS are sometimes found. The alpha and beta antigens are associated with the capsule. Both antigens are suspected to be responsible for immune protection. The beta antigens of group B are antigenically distinct from those of group E. Antibodies to alpha and beta antigens can occur in sera of animals vaccinated with group B strains, as well as animals with naturally acquired immunity to HS. In addition to alpha, beta, and gamma antigens, porin proteins of different antigenicities can be found. The role of porin proteins as immunogens for protecting animals against HS has not been studied.